





Network Working Group                                          J. Lennox
Request for Comments: 3880                                         X. Wu
Category: Standards Track                                 H. Schulzrinne
                                                     Columbia University
                                                            October 2004


                    Call Processing Language (CPL):
       A Language for User Control of Internet Telephony Services

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).

Abstract

   This document defines the Call Processing Language (CPL), a language
   to describe and control Internet telephony services.  It is designed
   to be implementable on either network servers or user agents.  It is
   meant to be simple, extensible, easily edited by graphical clients,
   and independent of operating system or signalling protocol.  It is
   suitable for running on a server where users may not be allowed to
   execute arbitrary programs, as it has no variables, loops, or ability
   to run external programs.



















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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
       1.1.   Conventions of This Document. . . . . . . . . . . . . .  4
   2.  Structure of CPL Scripts . . . . . . . . . . . . . . . . . . .  4
       2.1.   High-level Structure. . . . . . . . . . . . . . . . . .  4
       2.2.   Abstract Structure of a Call Processing Action. . . . .  5
       2.3.   Location Model. . . . . . . . . . . . . . . . . . . . .  6
       2.4.   XML Structure . . . . . . . . . . . . . . . . . . . . .  6
   3.  Script Structure: Overview . . . . . . . . . . . . . . . . . .  7
   4.  Switches . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
       4.1.   Address Switches. . . . . . . . . . . . . . . . . . . .  9
              4.1.1.  Usage of "address-switch" with SIP. . . . . . . 11
       4.2.   String Switches . . . . . . . . . . . . . . . . . . . . 12
              4.2.1.  Usage of "string-switch" with SIP . . . . . . . 13
       4.3.   Language Switches . . . . . . . . . . . . . . . . . . . 14
              4.3.1.  Usage of "language-switch" with SIP . . . . . . 14
       4.4.   Time Switches . . . . . . . . . . . . . . . . . . . . . 15
              4.4.1.  iCalendar differences and implementation
                      issues. . . . . . . . . . . . . . . . . . . . . 20
       4.5.   Priority Switches . . . . . . . . . . . . . . . . . . . 21
              4.5.1.  Usage of "priority-switch" with SIP . . . . . . 22
   5.  Location Modifiers . . . . . . . . . . . . . . . . . . . . . . 22
       5.1.   Explicit Location . . . . . . . . . . . . . . . . . . . 23
              5.1.1.  Usage of "location" with SIP. . . . . . . . . . 23
       5.2.   Location Lookup . . . . . . . . . . . . . . . . . . . . 24
              5.2.1.  Usage of "lookup" with SIP. . . . . . . . . . . 25
       5.3.   Location Removal. . . . . . . . . . . . . . . . . . . . 25
              5.3.1.  Usage of "remove-location" with SIP . . . . . . 26
   6.  Signalling Operations. . . . . . . . . . . . . . . . . . . . . 26
       6.1.   Proxy . . . . . . . . . . . . . . . . . . . . . . . . . 26
              6.1.1.  Usage of "proxy" with SIP . . . . . . . . . . . 29
       6.2.   Redirect. . . . . . . . . . . . . . . . . . . . . . . . 29
              6.2.1.  Usage of "redirect" with SIP. . . . . . . . . . 30
       6.3.   Reject. . . . . . . . . . . . . . . . . . . . . . . . . 30
              6.3.1.  Usage of "reject" with SIP. . . . . . . . . . . 30
   7.  Non-signalling Operations. . . . . . . . . . . . . . . . . . . 31
       7.1.   Mail. . . . . . . . . . . . . . . . . . . . . . . . . . 31
              7.1.1.  Suggested Content of Mailed Information . . . . 32
       7.2.   Log . . . . . . . . . . . . . . . . . . . . . . . . . . 32
   8.  Subactions . . . . . . . . . . . . . . . . . . . . . . . . . . 33
   9.  Ancillary Information. . . . . . . . . . . . . . . . . . . . . 34
   10. Default Behavior . . . . . . . . . . . . . . . . . . . . . . . 35
   11. CPL Extensions . . . . . . . . . . . . . . . . . . . . . . . . 35
   12. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
       12.1.  Example: Call Redirect Unconditional. . . . . . . . . . 37
       12.2.  Example: Call Forward Busy/No Answer. . . . . . . . . . 38
       12.3.  Example: Call Forward: Redirect and Default . . . . . . 39



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       12.4.  Example: Call Screening . . . . . . . . . . . . . . . . 40
       12.5.  Example: Priority and Language Routing. . . . . . . . . 41
       12.6.  Example: Outgoing Call Screening. . . . . . . . . . . . 42
       12.7.  Example: Time-of-day Routing. . . . . . . . . . . . . . 43
       12.8.  Example: Location Filtering . . . . . . . . . . . . . . 44
       12.9.  Example: Non-signalling Operations. . . . . . . . . . . 45
       12.10. Example: Hypothetical Extensions. . . . . . . . . . . . 46
       12.11. Example: A Complex Example. . . . . . . . . . . . . . . 48
   13. Security Considerations. . . . . . . . . . . . . . . . . . . . 49
   14. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 49
       14.1.  URN Sub-Namespace Registration for
              urn:ietf:params:xml:ns:cpl. . . . . . . . . . . . . . . 49
       14.2.  Schema registration . . . . . . . . . . . . . . . . . . 50
       14.3.  MIME Registration . . . . . . . . . . . . . . . . . . . 50
   15. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 51
   A.  An Algorithm for Resolving Time Switches . . . . . . . . . . . 52
   B.  Suggested Usage of CPL with H.323. . . . . . . . . . . . . . . 53
       B.1.   Usage of "address-switch" with H.323. . . . . . . . . . 53
       B.2.   Usage of "string-switch" with H.323 . . . . . . . . . . 55
       B.3.   Usage of "language-switch" with H.323 . . . . . . . . . 55
       B.4.   Usage of "priority-switch" with H.323 . . . . . . . . . 55
       B.5.   Usage of "location" with H.323. . . . . . . . . . . . . 56
       B.6.   Usage of "lookup" with H.323. . . . . . . . . . . . . . 56
       B.7.   Usage of "remove-location" with H.323 . . . . . . . . . 56
   C.  The XML Schema for CPL . . . . . . . . . . . . . . . . . . . . 56
   Normative References . . . . . . . . . . . . . . . . . . . . . . . 70
   Informative References . . . . . . . . . . . . . . . . . . . . . . 71
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 73
   Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 74

1.  Introduction

   The Call Processing Language (CPL) is a language that can be used to
   describe and control Internet telephony services.  It is not tied to
   any particular signalling architecture or protocol; it is anticipated
   that it will be used with both the Session Initiation Protocol (SIP)
   [1] and H.323 [16].

   CPL is powerful enough to describe a large number of services and
   features, but it is limited in power so that it can run safely in
   Internet telephony servers.  The intention is to make it impossible
   for users to do anything more complex (and dangerous) than describe
   Internet telephony services.  The language is not Turing-complete,
   and provides no way to write loops or recursion.

   CPL is also designed to be easily created and edited by graphical
   tools.  It is based on the Extensible Markup Language (XML) [2], so
   parsing it is easy and many parsers for it are publicly available.



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   The structure of the language maps closely to its behavior, so an
   editor can understand any valid script, even ones written by hand.
   The language is also designed so that a server can easily confirm the
   validity of a script when the server receives it, rather than
   discovering problems while a call is being processed.

   Implementations of CPL are expected to take place both in Internet
   telephony servers and in advanced clients; both can usefully process
   and direct users' calls.  This document primarily addresses the usage
   in servers.  A mechanism will be needed to transport scripts between
   clients and servers; this document does not describe such a
   mechanism, but related documents will.

   The framework and requirements for the CPL architecture are described
   in RFC 2824, "Call Processing Language Framework and Requirements"
   [17].

1.1.  Conventions of This Document

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119
   [3] and indicate requirement levels for compliant CPL
   implementations.

      Some paragraphs are indented, like this; they give motivations of
      design choices, advice to implementors, or thoughts on future
      development of or extensions to CPL.  They are not essential to
      the specification of the language, and are non-normative.

2.  Structure of CPL Scripts

2.1.  High-level Structure

   A CPL script consists of two types of information: ancillary
   information about the script, and call processing actions.

   A call processing action is a structured tree that describes the
   operations and decisions a telephony signalling server performs on a
   call set-up event.  There are two types of call processing actions:
   top-level actions and subactions.  Top-level actions are actions that
   are triggered by signalling events that arrive at the server.  Two
   top-level actions are defined: "incoming", the action performed when
   a call arrives whose destination is the owner of the script, and
   "outgoing", the action performed when a call arrives whose originator
   is the owner of the script.





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   Subactions are actions which can be called from other actions.  CPL
   forbids subactions from being called recursively: see Section 8.

   Ancillary information is information which is necessary for a server
   to correctly process a script, but which does not directly describe
   any operations or decisions.  Currently, no ancillary information is
   defined, but the section is reserved for use by extensions.

2.2.  Abstract Structure of a Call Processing Action

   Abstractly, a call processing action is described by a collection of
   nodes that describe operations that can be performed or decisions
   that can be made.  A node may have several parameters, which specify
   the precise behavior of the node; they usually also have outputs,
   which depend on the result of the decision or action.

   For a graphical representation of a CPL action, see Figure 1.  Nodes
   and outputs can be thought of informally as boxes and arrows; CPL is
   designed so that actions can be conveniently edited graphically using
   this representation.  Nodes are arranged in a tree, starting at a
   single root node; outputs of nodes are connected to additional nodes.
   When an action is run, the action or decision described by the
   action's top-level node is performed; based on the result of that
   node, the server follows one of the node's outputs, and the
   subsequent node it points to is performed; this process continues
   until a node with no specified outputs is reached.  Because the graph
   is acyclic, this will occur after a bounded and predictable number of
   nodes are visited.

   If an output to a node does not point to another node, it indicates
   that the CPL server should perform a node- or protocol-specific
   action.  Some nodes have specific default behavior associated with
   them; for others, the default behavior is implicit in the underlying
   signalling protocol, or can be configured by the administrator of the
   server.  For further details on this, see Section 10.
















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        _________________      ___________________    ________  busy
       | Address-switch  |    | location          |  | proxy  |--------\
Call-->|  field: origin  |  ->|   url: sip:jones@ |->|timeout:| timeout|
       |  subfield: host | /  |     example.com   |  |  10s   |--------|
       |-----------------|/   |___________________|  |        | failure|
       | subdomain-of:   |                           |________|--------|
       |   example.com   |                                             |
       |-----------------|  ___________________________________________/
       | otherwise       | /........................................
       |                 |\|. Voicemail                            .
       |_________________| \.  ____________________                .
                            ->| location           |   __________  .
                            . |   url: sip:jones@  |  | redirect | .
                            . |        voicemail.  |->|          | .
                            . |        example.com |  |__________| .
                            . |____________________|               .
                            ........................................

   Figure 1: Sample CPL Action: Graphical Version

2.3.  Location Model

   For flexibility, one piece of information necessary for CPL is not
   given as node parameters: the set of locations to which a call is to
   be directed.  Instead, this set of locations is stored as an implicit
   global variable throughout the execution of a processing action (and
   its subactions).  This allows locations to be retrieved from external
   sources, filtered, and so forth, without requiring general language
   support for such operations (which could harm the simplicity and
   tractability of understanding the language).  The specific operations
   which add, retrieve, or filter location sets are given in Section 5.

   For the incoming top-level call processing action, the location set
   is initialized to the empty set.  For the outgoing action, it is
   initialized to the destination address of the call.

2.4.  XML Structure

   Syntactically, CPL scripts are represented by XML documents.  XML is
   thoroughly specified by the XML specification [2], and implementors
   of this specification should be familiar with that document.
   However, as a brief overview, XML consists of a hierarchical
   structure of tags; each tag can have a number of attributes.  It is
   visually and structurally very similar to HTML [18], as both
   languages are simplifications of the earlier and larger standard SGML
   [19].





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   See Figure 2 for the XML document corresponding to the graphical
   representation of the CPL script in Figure 1.  Both nodes and outputs
   in CPL are represented by XML tags; parameters are represented by XML
   tag attributes.  Typically, node tags contain output tags, and vice-
   versa (with a few exceptions: see Sections 5.1, 5.3, 7.1, and 7.2).

   The connection between the output of a node and another node is
   represented by enclosing the tag representing the pointed-to node
   inside the tag for the outer node's output.  Convergence (several
   outputs pointing to a single node) is represented by subactions,
   discussed further in Section 8.

   The higher-level structure of a CPL script is represented by tags
   corresponding to each piece of ancillary information, subactions, and
   top-level actions, in order.  This higher-level information is all
   enclosed in a special tag "cpl", the outermost tag of the XML
   document.

   A complete XML Schema for CPL is provided in Appendix C.  The
   remainder of the main sections of this document describe the
   semantics of CPL, while giving its syntax informally.  For the formal
   syntax, please see the appendix.

3.  Script Structure: Overview

   As mentioned, a CPL script consists of ancillary information,
   subactions, and top-level actions.  The full syntax of the "cpl" node
   is given in Figure 3.

   <?xml version="1.0" encoding="UTF-8"?>
   <cpl xmlns="urn:ietf:params:xml:ns:cpl"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">
     <subaction id="voicemail">
       <location url="sip:jones@voicemail.example.com">
         <redirect />
       </location>
     </subaction>
     <incoming>
       <address-switch field="origin" subfield="host">
         <address subdomain-of="example.com">
           <location url="sip:jones@example.com">
             <proxy timeout="10">
               <busy> <sub ref="voicemail" /> </busy>
               <noanswer> <sub ref="voicemail" /> </noanswer>
               <failure> <sub ref="voicemail" /> </failure>
             </proxy>
           </location>



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         </address>
         <otherwise>
           <sub ref="voicemail" />
         </otherwise>
       </address-switch>
     </incoming>
   </cpl>

   Figure 2: Sample CPL Script: XML Version

           Tag:  "cpl"
    Parameters:  None
      Sub-tags:  "ancillary"  See Section 9
                 "subaction"  See Section 8
                 "outgoing"   Top-level actions to take on this user's
                              outgoing calls
                 "incoming"   Top-level actions to take on this user's
                              incoming calls

   Figure 3: Syntax of the top-level "cpl" tag

   Call processing actions, both top-level actions and subactions,
   consist of a tree of nodes and outputs.  Nodes and outputs are both
   described by XML tags.  There are four categories of CPL nodes:
   switches, which represent choices a CPL script can make, location
   modifiers, which add or remove locations from the location set,
   signalling operations, which cause signalling events in the
   underlying protocol, and non-signalling operations, which trigger
   behavior which does not effect the underlying protocol.

4.  Switches

   Switches represent choices a CPL script can make, based on either
   attributes of the original call request or items independent of the
   call.

   All switches are arranged as a list of conditions that can match a
   variable.  Each condition corresponds to a node output; the output
   points to the next node that should be executed if the condition is
   true.  The conditions are tried in the order they are presented in
   the script; the output corresponding to the first node to match is
   taken.

   There are two special switch outputs that apply to every switch type.
   The output "not-present", which MAY occur anywhere in the list of
   outputs, is true if the variable the switch was to match was not
   present in the original call setup request.  (In this document, this
   is sometimes described by saying that the information is "absent".)



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   The output "otherwise", which MUST be the last output specified if it
   is present, matches if no other condition matched.

   If no condition matches and no "otherwise" output was present in the
   script, the default script behavior is taken.  See Section 10 for
   more information on this.

   Switches MAY contain no outputs.  They MAY only contain an
   "otherwise" output.

      Such switches are not particularly useful, but might be created by
      tools which automatically generate CPL scripts.

4.1.  Address Switches

   Address switches allow a CPL script to make decisions based on one of
   the addresses present in the original call request.  They are
   summarized in Figure 4.

          Node:  "address-switch"
       Outputs:  "address"         Specific addresses to match
    Parameters:  "field"           "origin", "destination",
                                   or "original-destination"
                 "subfield"        "address-type", "user", "host",
                                   "port", "tel", or "display"
                                   (also: "password" and "alias-type")

        Output:  "address"
    Parameters:  "is"              Exact match
                 "contains"        Substring match (for "display" only)
                 "subdomain-of"    Sub-domain match (for "host", "tel")

   Figure 4: Syntax of the "address-switch" node

   Address switches have two node parameters: "field" and "subfield".
   The mandatory "field" parameter allows the script to specify which
   address is to be considered for the switch: either the call's origin
   address (field "origin"), its current destination address (field
   "destination"), or its original destination (field "original-
   destination"), the destination the call had before any earlier
   forwarding was invoked.  Servers MAY define additional field values.

   The optional "subfield" specifies which part of the address is to be
   considered.  The possible subfield values are: "address-type",
   "user", "host", "port", "tel", and "display".  Additional subfield
   values MAY be defined for protocol-specific values.  (The subfield
   "password" is defined for SIP in Section 4.1.1; the subfield "alias-
   type" is defined for H.323 in Appendix B.1.)  If no subfield is



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   specified, the "entire" address is matched; the precise meaning of
   this is defined for each underlying signalling protocol.  Servers MAY
   define additional subfield values.

   The subfields are defined as follows:

      address-type: This indicates the type of the underlying address,
            i.e., the URI scheme, if the address can be represented by a
            URI.  The types specifically discussed by this document are
            "sip", "tel", and "h323".  The address type is not case-
            sensitive.  It has a value for all defined address types.

      user: This subfield of the address indicates, for e-mail style
            addresses, the user part of the address.  For a telephone
            number style address, it includes the subscriber number.
            This subfield is case-sensitive; it may be absent.

      host: This subfield of the address indicates the Internet host
            name or IP address corresponding to the address, in host
            name, IPv4, or IPv6 [4] textual representation format.  Host
            names are compared as strings.  IP addresses are compared
            numerically.  (In particular, the presence or location of an
            IPv6 :: omitted-zero-bits block is not significant for
            matching purposes.)  Host names are never equal to IP
            addresses -- no DNS resolution is performed.  IPv4 addresses
            are never equal to IPv6 addresses, even if the IPv6 address
            is a v4-in-v6 embedding.  This subfield is not case
            sensitive, and may be absent.

            For host names only, subdomain matching is supported with
            the "subdomain-of" match operator.  The "subdomain-of"
            operator ignores leading dots in the hostname or match
            pattern, if any.

      port: This subfield indicates the TCP or UDP port number of the
            address, numerically, in decimal format.  It is not case
            sensitive, as it MUST only contain decimal digits.  Leading
            zeros are ignored.

      tel:  This subfield indicates a telephone subscriber number, if
            the address contains such a number.  It is not case
            sensitive (telephone numbers may contain the symbols 'A',
            'B', 'C', or 'D'), and may be absent.  It may be matched
            using the "subdomain-of" match operator.  Punctuation and
            separator characters in telephone numbers are discarded.






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      display: This subfield indicates a "display name" or user-visible
            name corresponding to an address.  It is a Unicode string,
            and is matched using the case-insensitive algorithm
            described in Section 4.2.  The "contains" operator may be
            applied to it.  It may be absent.

   For any completely unknown subfield, the server MAY reject the script
   at the time it is submitted with an indication of the problem; if a
   script with an unknown subfield is executed, the server MUST consider
   the "not-present" output to be the valid one.

   The "address" output tag may take exactly one of three possible
   parameters, indicating the kind of matching allowed.

      is:   An output with this match operator is followed if the
            subfield being matched in the "address-switch" exactly
            matches the argument of the operator.  It may be used for
            any subfield, or for the entire address if no subfield was
            specified.

      subdomain-of: This match operator applies only for the subfields
            "host" and "tel".  In the former case, it matches if the
            hostname being matched is a subdomain of the domain given in
            the argument of the match operator; thus, subdomain-
            of="example.com" would match the hostnames "example.com",
            "research.example.com", and
            "zaphod.sales.internal.example.com".  IP addresses may be
            given as arguments to this operator; however, they only
            match exactly.  In the case of the "tel" subfield, the
            output matches if the telephone number being matched has a
            prefix that matches the argument of the match operator;
            subdomain-of="1212555" would match the telephone number "1
            212 555 1212."

      contains: This match operator applies only for the subfield
            "display".  The output matches if the display name being
            matched contains the argument of the match as a substring.

4.1.1.  Usage of "address-switch" with SIP

   For SIP, the "origin" address corresponds to the address in the
   "From" header, "destination" corresponds to the "Request-URI", and
   "original-destination" corresponds to the "To" header.

   The "display" subfield of an address is the display-name part of the
   address, if it is present.  Because of SIP's syntax, the
   "destination" address field will never have a "display" subfield.




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   The "address-type" subfield of an address is the URI scheme of that
   address.  Other address fields depend on that "address-type".

   For SIP URIs, the "user", "host", and "port" subfields correspond to
   the "user," "host," and "port" elements of the URI syntax.  (Note
   that, following the definitions of RFC 3261 [1], a SIP URI which does
   not specify a port is not the same as an explicit port 5060; the
   former is indicated by an absent port subfield.)  The "tel" subfield
   is defined to be the "user" part of the URI, with visual separators
   stripped, if the "user=phone" parameter is given to the URI, or if
   the server is otherwise configured to recognize the user part as a
   telephone number.  An additional subfield, "password", is defined to
   correspond to the "password" element of the SIP URI, and is case-
   sensitive.  However, use of this field is NOT RECOMMENDED for general
   security reasons.

   For tel URLs, the "tel" and "user" subfields are the subscriber name;
   in the former case, visual separators are stripped.  The "host" and
   "port" subfields are both not present.

   For h323 URLs, subfields MAY be set according to the scheme described
   in Appendix B.

   For other URI schemes, only the "address-type" subfield is defined by
   this specification; servers MAY set other pre-defined subfields, or
   MAY support additional subfields.

   If no subfield is specified for addresses in SIP messages, the string
   matched is the URI part of the address.  For "is" matches, standard
   SIP URI matching rules are used; for "contains" matches, the URI is
   used verbatim.

4.2.  String Switches

   String switches allow a CPL script to make decisions based on free-
   form strings present in a call request.  They are summarized in
   Figure 5.

               Node:  "string-switch"
            Outputs:  "string"         Specific string to match
         Parameters:  "field"          "subject", "organization",
                                       "user-agent", or "display"

             Output:  "string"
         Parameters:  "is"             Exact match
                      "contains"       Substring match

   Figure 5: Syntax of the "string-switch" node



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   String switches have one node parameter: "field".  The mandatory
   "field" parameter specifies which string is to be matched.

   String switches are dependent on the call signalling protocol being
   used.

   Four fields are defined and listed below.  The value of each of these
   fields is a free-form Unicode string with no other structure defined.

      subject: The subject of the call.

      organization: The organization of the originator of the call.

      user-agent: The name of the program or device with which the call
            request was made.

      display: Free-form text associated with the call, intended to be
            displayed to the recipient, with no other semantics defined
            by the signalling protocol.

   Strings are matched as case-insensitive Unicode strings, in the
   following manner.  First, strings are canonicalized to the
   "Compatibility Composition" (KC) form, as specified in Unicode
   Standard Annex #15 [5].  Then, strings are compared using locale-
   insensitive caseless mapping, as specified in Unicode Standard Annex
   #21 [6].

      Code to perform the first step, in Java and Perl, is available;
      see the links from Annex 5 of UAX 15 [5].  The case-insensitive
      string comparison in the Java standard class libraries already
      performs the second step; other Unicode-aware libraries should be
      similar.

   The output tag of string matching is named "string", and has a
   mandatory argument, one of "is" or "contains", indicating whole-
   string match or substring match, respectively.

4.2.1.  Usage of "string-switch" with SIP

   For SIP, the fields "subject", "organization", and "user-agent"
   correspond to the SIP header fields with the same name.  These are
   used verbatim as they appear in the message.

   The field "display" is not used, and is never present.







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4.3.  Language Switches

   Language switches allow a CPL script to make decisions based on the
   languages in which the originator of the call wishes to communicate.
   They are summarized in Figure 6.

            Node:  "language-switch"
         Outputs:  "language"         Specific string to match
      Parameters:  None

          Output:  "language"
      Parameters:  "matches"          Match if the given language
                                      matches a language-range of the
                                      call.

      Figure 6: Syntax of the "language-switch" node

   Language switches take no parameters.

   The "language" output takes one parameter, "matches".  The value of
   the parameter is a language-tag, as defined in RFC 3066 [7].  The
   caller may have specified a set of language-ranges, also as defined
   in RFC 3066.  The CPL server checks each language-tag specified by
   the script against the language-ranges specified in the request.

   See RFC 3066 for the details of how language-ranges match language-
   tags.  Briefly, a language-range matches a language-tag if it exactly
   equals the tag, or if it exactly equals a prefix of the tag such that
   the first character following the prefix is "-".

   If the caller specified the special language-range "*", it is ignored
   for the purpose of matching.  Languages with a "q" value of 0 are
   also ignored.

   This switch MAY be not-present.

4.3.1.  Usage of "language-switch" with SIP

   The language-ranges for the "language-switch" switch are obtained
   from the SIP "Accept-Language" header field.  The switch is not-
   present if the initial SIP request did not contain this header field.

      Note that because of CPL's first-match semantics in switches, "q"
      values other than 0 of the "Accept-Language" header fields are
      ignored.






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4.4.  Time Switches

   Time switches allow a CPL script to make decisions based on the time
   and/or date the script is being executed.  They are summarized in
   Figure 7.

   Time switches are independent of the underlying signalling protocol.

         Node:  "time-switch"
      Outputs:  "time"         Specific time to match
   Parameters:  "tzid"         RFC 2445 Time Zone Identifier
                "tzurl"        RFC 2445 Time Zone URL

       Output:  "time"
   Parameters:  "dtstart"      Start of interval (RFC 2445 DATE-TIME)
                "dtend"        End of interval (RFC 2445 DATE-TIME)
                "duration"     Length of interval (RFC 2445 DURATION)
                "freq"         Frequency of recurrence ("secondly",
                               "minutely", "hourly", "daily",
                               "weekly", "monthly", or "yearly")
                "interval"     How often the recurrence repeats
                "until"        Bound of recurrence (RFC 2445 DATE-TIME)
                "count"        Number of occurrences of recurrence
                "bysecond"     List of seconds within a minute
                "byminute"     List of minutes within an hour
                "byhour"       List of hours of the day
                "byday"        List of days of the week
                "bymonthday"   List of days of the month
                "byyearday"    List of days of the year
                "byweekno"     List of weeks of the year
                "bymonth"      List of months of the year
                "wkst"         First day of the work week
                "bysetpos"     List of values within
                               set of events specified

   Figure 7: Syntax of the "time-switch" node

   Time switches are based closely on the specification of recurring
   intervals of time in the Internet Calendaring and Scheduling Core
   Object Specification (iCalendar COS), RFC 2445 [8].

      This allows CPL scripts to be generated automatically from
      calendar books.  It also allows us to re-use the extensive
      existing work specifying time intervals.

   If future standards-track documents are published that update or
   obsolete RFC 2445, any changes or clarifications those documents make
   to recurrence handling apply to CPL time-switches as well.



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   An algorithm to determine whether an instant falls within a given
   recurrence is given in Appendix A.

   The "time-switch" tag takes two optional parameters, "tzid" and
   "tzurl", both of which are defined in RFC 2445 (Sections 4.8.3.1 and
   4.8.3.5 respectively).  The "tzid" is the identifying label by which
   a time zone definition is referenced.  If it begins with a forward
   slash (solidus), it references a to-be-defined global time zone
   registry; otherwise it is locally-defined at the server.  The "tzurl"
   gives a network location from which an up-to-date VTIMEZONE
   definition for the timezone can be retrieved.

   While "tzid" labels that do not begin with a forward slash are
   locally defined, it is RECOMMENDED that servers support at least the
   naming scheme used by the Olson Time Zone database [9].  Examples of
   timezone databases that use the Olson scheme are the zoneinfo files
   on most Unix-like systems, and the standard Java TimeZone class.

   Servers SHOULD resolve "tzid" and "tzurl" references to time zone
   definitions at the time the script is uploaded.  They MAY
   periodically refresh these resolutions to obtain the most up-to-date
   definition of a time zone.  If a "tzurl" becomes invalid, servers
   SHOULD remember the most recent valid data retrieved from the URL.

   If a script is uploaded with a "tzid" and "tzurl" which the CPL
   server does not recognize or cannot resolve, it SHOULD diagnose and
   reject this at script upload time.  If neither "tzid" nor "tzurl" are
   present, all non-UTC times within this time switch should be
   interpreted as being "floating" times, i.e., that they are specified
   in the local timezone of the CPL server.

      Because of daylight-savings-time changes over the course of a
      year, it is necessary to specify time switches in a given
      timezone.  UTC offsets are not sufficient, or a time-of-day
      routing rule which held between 9 am and 5 pm in the eastern
      United States would start holding between 8 am and 4 pm at the end
      of October.

   Authors of CPL servers should be careful to handle correctly the
   intervals when local time is discontinuous, at the beginning or end
   of daylight-savings time.  Note especially that some times may occur
   more than once when clocks are set back.  The algorithm in Appendix A
   is believed to handle this correctly.

   Time nodes specify a list of periods during which their output should
   be taken.  They have two required parameters: "dtstart", which
   specifies the beginning of the first period of the list, and exactly
   one of "dtend" or "duration", which specify the ending time or the



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   duration of the period, respectively.  The "dtstart" and "dtend"
   parameters are formatted as iCalendar COS DATE-TIME values, as
   specified in Section 4.3.5 of RFC 2445 [8].  Because time zones are
   specified in the top-level "time-switch" tag, only forms 1 or 2
   (floating or UTC times) can be used.  The "duration" parameter is
   given as an iCalendar COS DURATION parameter, as specified in section
   4.3.6 of RFC 2445.  Both the DATE-TIME and the DURATION syntaxes are
   subsets of the corresponding syntaxes from ISO 8601 [20].

   For a recurring interval, the "duration" parameter MUST be small
   enough such that subsequent intervals do not overlap.  For non-
   recurring intervals, durations of any positive length are permitted.
   Zero-length and negative-length durations are not allowed.

   If no other parameters are specified, a time node indicates only a
   single period of time.  More complicated sets of period intervals are
   constructed as recurrences.  A recurrence is specified by including
   the "freq" parameter, which indicates the type of recurrence rule.
   Parameters other than "dtstart", "dtend", and "duration" SHOULD NOT
   be specified unless "freq" is present, though CPL servers SHOULD
   accept scripts with such parameters present, and ignore the other
   parameters.

   The "freq" parameter takes one of the following values: "secondly",
   to specify repeating periods based on an interval of a second or
   more, "minutely", to specify repeating periods based on an interval
   of a minute or more, "hourly", to specify repeating periods based on
   an interval of an hour or more, "daily", to specify repeating periods
   based on an interval of a day or more, "weekly", to specify repeating
   periods based on an interval of a week or more, "monthly", to specify
   repeating periods based on an interval of a month or more, and
   "yearly", to specify repeating periods based on an interval of a year
   or more.  These values are not case-sensitive.

   The "interval" parameter contains a positive integer representing how
   often the recurrence rule repeats.  The default value is "1", meaning
   every second for a "secondly" rule, every minute for a "minutely"
   rule, every hour for an "hourly" rule, every day for a "daily" rule,
   every week for a "weekly" rule, every month for a "monthly" rule, and
   every year for a "yearly" rule.

   The "until" parameter defines an iCalendar COS DATE or DATE-TIME
   value which bounds the recurrence rule in an inclusive manner.  If
   the value specified by "until" is synchronized with the specified
   recurrence, this date or date-time becomes the last instance of the
   recurrence.  If specified as a date-time value, then it MUST be





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   specified in UTC time format.  If not present, and the "count"
   parameter is not also present, the recurrence is considered to repeat
   forever.

   The "count" parameter defines the number of occurrences at which to
   range-bound the recurrence.  The "dtstart" parameter counts as the
   first occurrence.  The "until" and "count" parameters MUST NOT occur
   in the same "time" output.

   The "bysecond" parameter specifies a comma-separated list of seconds
   within a minute.  Valid values are 0 to 59.  The "byminute" parameter
   specifies a comma-separated list of minutes within an hour.  Valid
   values are 0 to 59.  The "byhour" parameter specifies a comma-
   separated list of hours of the day.  Valid values are 0 to 23.

   The "byday" parameter specifies a comma-separated list of days of the
   week.  "MO" indicates Monday, "TU" indicates Tuesday, "WE" indicates
   Wednesday, "TH" indicates Thursday, "FR" indicates Friday, "SA"
   indicates Saturday, and "SU" indicates Sunday.  These values are not
   case-sensitive.

   Each "byday" value can also be preceded by a positive (+n) or
   negative (-n) integer.  If present, this indicates the nth occurrence
   of the specific day within the "monthly" or "yearly" recurrence.  For
   example, within a "monthly" rule, +1MO (or simply 1MO) represents the
   first Monday within the month, whereas -1MO represents the last
   Monday of the month.  If an integer modifier is not present, it means
   all days of this type within the specified frequency.  For example,
   within a "monthly" rule, MO represents all Mondays within the month.

   The "bymonthday" parameter specifies a comma-separated list of days
   of the month.  Valid values are 1 to 31 or -31 to -1.  For example,
   -10 represents the tenth to the last day of the month.

   The "byyearday" parameter specifies a comma-separated list of days of
   the year.  Valid values are 1 to 366 or -366 to -1.  For example, -1
   represents the last day of the year (December 31st) and -306
   represents the 306th to the last day of the year (March 1st).

   The "byweekno" parameter specifies a comma-separated list of ordinals
   specifying weeks of the year.  Valid values are 1 to 53 or -53 to -1.
   This corresponds to weeks according to week numbering as defined in
   ISO 8601 [20].  A week is defined as a seven day period, starting on
   the day of the week defined to be the week start (see "wkst").  Week
   number one of the calendar year is the first week which contains at
   least four (4) days in that calendar year.  This parameter is only
   valid for "yearly" rules.  For example, 3 represents the third week
   of the year.



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      Note: Assuming a Monday week start, week 53 can only occur when
      January 1 is a Thursday or, for leap years, if January 1 is a
      Wednesday.

   The "bymonth" parameter specifies a comma-separated list of months of
   the year.  Valid values are 1 to 12.

   The "wkst" parameter specifies the day on which the work week starts.
   Valid values are "MO", "TU", "WE", "TH", "FR", "SA" and "SU".  This
   is significant when a "weekly" recurrence has an interval greater
   than 1, and a "byday" parameter is specified.  This is also
   significant in a "yearly" recurrence when a "byweekno" parameter is
   specified.  The default value is "MO", following ISO 8601 [20].

   The "bysetpos" parameter specifies a comma-separated list of values
   which corresponds to the nth occurrence within the set of events
   specified by the rule.  Valid values are 1 to 366 or -366 to -1.  It
   MUST only be used in conjunction with another byxxx parameter.  For
   example, "the last work day of the month" could be represented as:

      <time -timerange- freq="monthly" byday="MO,TU,WE,TH,FR"
            bysetpos="-1">

   Each "bysetpos" value can include a positive (+n) or negative (-n)
   integer.  If present, this indicates the nth occurrence of the
   specific occurrence within the set of events specified by the rule.

   If byxxx parameter values are found which are beyond the available
   scope (i.e., bymonthday="30" in February), they are simply ignored.

   Byxxx parameters modify the recurrence in some manner.  Byxxx rule
   parts for a period of time which is the same or greater than the
   frequency generally reduce or limit the number of occurrences of the
   recurrence generated.  For example, freq="daily" bymonth="1" reduces
   the number of recurrence instances from all days (if the "bymonth"
   parameter is not present) to all days in January.  Byxxx parameters
   for a period of time less than the frequency generally increase or
   expand the number of occurrences of the recurrence.  For example,
   freq="yearly" bymonth="1,2" increases the number of days within the
   yearly recurrence set from 1 (if "bymonth" parameter is not present)
   to 2.

   If multiple Byxxx parameters are specified, then after evaluating the
   specified "freq" and "interval" parameters, the Byxxx parameters are
   applied to the current set of evaluated occurrences in the following
   order: "bymonth", "byweekno", "byyearday", "bymonthday", "byday",
   "byhour", "byminute", "bysecond", and "bysetpos"; then "count" and
   "until" are evaluated.



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   Here is an example of evaluating multiple Byxxx parameters.

      <time dtstart="19970105T083000" duration="10M"
            freq="yearly" interval="2" bymonth="1" byday="SU"
            byhour="8,9" byminute="30">

   First, the interval="2" would be applied to freq="yearly" to arrive
   at "every other year."  Then, bymonth="1" would be applied to arrive
   at "every January, every other year."  Then, byday="SU" would be
   applied to arrive at "every Sunday in January, every other year."
   Then, byhour="8,9" would be applied to arrive at "every Sunday in
   January at 8 AM and 9 AM, every other year."  Then, byminute="30"
   would be applied to arrive at "every Sunday in January at 8:30 AM and
   9:30 AM, every other year."  Then the second is derived from
   "dtstart" to end up in "every Sunday in January from 8:30:00 AM to
   8:40:00 AM, and from and 9:30:00 AM to 9:40:00 AM, every other year."
   Similarly, if the "byminute", "byhour", "byday", "bymonthday", or
   "bymonth" parameter were missing, the appropriate minute, hour, day,
      or month would have been retrieved from the "dtstart" parameter.

   The iCalendar COS RDATE, EXRULE, and EXDATE recurrence rules are not
   specifically mapped to components of the time-switch node.
   Equivalent functionality to the exception rules can be attained by
   using the ordering of switch rules to exclude times using earlier
   rules; equivalent functionality to the additional-date RDATE rules
   can be attained by using "sub" nodes (see Section 8) to link multiple
   outputs to the same subsequent node.

   The "not-present" output is never true for a time switch.  However,
   it MAY be included to allow switch processing to be more regular.

4.4.1.  iCalendar Differences and Implementation Issues

   (This sub-sub-section is non-normative.)

   The specification of recurring events in this section is identical
   (except for syntax and formatting issues) to that of RFC 2445 [8],
   with only one additional restriction.  That one restriction is that
   consecutive instances of recurrence intervals may not overlap.

   It was a matter of some debate, during the design of CPL, whether the
   entire iCalendar COS recurrence specification should be included in
   CPL, or whether only a subset should be included.  It was eventually
   decided that compatibility between the two protocols was of primary
   importance.  This imposes some additional implementation issues on
   implementors of CPL servers.





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   It does not appear to be possible to determine, in constant time,
   whether a given instant of time falls within one of the intervals
   defined by a full iCalendar COS recurrence.  The primary concerns are
   as follows:

      o  The "count" parameter cannot be checked in constant running
         time, since it requires that the server enumerate all
         recurrences from "dtstart" to the present time, in order to
         determine whether the current recurrence satisfies the
         parameter.  However, a server can expand a "count" parameter
         once, off-line, to determine the date of the last recurrence.
         This date can then be treated as a virtual "until" parameter
         for the server's internal processing.

      o  Similarly, the "bysetpos" parameter requires that the server
         enumerate all instances of the occurrence from the start of the
         current recurrence set until the present time.  This requires
         somewhat more complex pre-processing, but generally, a single
         recurrence with a "bysetpos" parameter can be split up into
         several recurrences without them.

      o  Finally, constant running time of time switches also requires
         that a candidate starting time for a recurrence can be
         established quickly and uniquely, to check whether it satisfies
         the other restrictions.  This requires that a recurrence's
         duration not be longer than its repetition interval, so that a
         given instant cannot fall within several consecutive potential
         repetitions of the recurrence.  The restriction that
         consecutive intervals not overlap partially satisfies this
         condition, but does not fully ensure it.  Again, to some extent
         pre-processing can help resolve this.

   The algorithm given in Appendix A runs in constant time after these
   pre-processing steps.

   Servers ought to check that recurrence rules do not create any absurd
   run-time or memory requirements, and reject those that do, just as
   they ought to check that CPL scripts in general are not absurdly
   large.

4.5.  Priority Switches

   Priority switches allow a CPL script to make decisions based on the
   priority specified for the original call.  They are summarized in
   Figure 8.  They are dependent on the underlying signalling protocol.






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             Node:  "priority-switch"
          Outputs:  "priority"         Specific priority to match
       Parameters:  None

           Output:  "priority"
       Parameters:  "less"             Match if priority is less
                                       than that specified
                    "greater"          Match if priority is greater
                                       than that specified
                    "equal"            Match if priority is equal
                                       to that specified

   Figure 8: Syntax of the "priority-switch" node

   Priority switches take no parameters.

   The "priority" tag takes one of the three parameters "greater",
   "less", or "equal".  The values of these parameters are one of the
   following priorities: in decreasing order, "emergency", "urgent",
   "normal", and "non-urgent".  These values are matched in a case-
   insensitive manner.  Outputs with the "less" parameter are taken if
   the priority of the call is less than the priority given in the
   argument, and so forth.

   If no priority is specified in a message, the priority is considered
   to be "normal".  If an unknown priority is specified in the call, it
   is considered to be equivalent to "normal" for the purposes of
   "greater" and "less" comparisons, but it is compared literally for
   "equal" comparisons.

   Since every message has a priority, the "not-present" output is never
   true for a priority switch.  However, it MAY be included, to allow
   switch processing to be more regular.

4.5.1.  Usage of "priority-switch" with SIP

   The priority of a SIP message corresponds to the "Priority" header in
   the initial "INVITE" message.

5.  Location Modifiers

   The abstract location model of CPL is described in Section 2.3.  The
   behavior of several of the signalling operations (defined in Section
   6) is dependent on the current location set specified.  Location
   nodes add or remove locations from the location set.






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   There are three types of location nodes defined.  Explicit locations
   add literally-specified locations to the current location set,
   location lookups obtain locations from some outside source, and
   location filters remove locations from the set, based on some
   specified criteria.

5.1.  Explicit Location

   Explicit location nodes specify a location literally.  Their syntax
   is described in Figure 9.

   Explicit location nodes are dependent on the underlying signalling
   protocol.

          Node:  "location"
       Outputs:  None        (Next node follows directly)
     Next node:  Any node
    Parameters:  "url"       URL of address to add to location set
                 "priority"  Priority of this location (0.0-1.0)
                 "clear"     Whether to clear the location set before
                             adding the new value

   Figure 9: Syntax of the "location" node

   Explicit location nodes have three node parameters.  The mandatory
   "url" parameter's value is the URL of the address to add to the
   location set.  Only one address may be specified per location node;
   multiple locations may be specified by cascading these nodes.

   The optional "priority" parameter specifies a priority for the
   location.  Its value is a floating-point number between 0.0 and 1.0.
   If it is not specified, the server SHOULD assume a default priority
   of 1.0.  The optional "clear" parameter specifies whether the
   location set should be cleared before adding the new location to it.
   Its value can be "yes" or "no", with "no" as the default.

   Basic location nodes have only one possible result, since there is no
   way that they can fail.  (If a basic location node specifies a
   location which isn't supported by the underlying signalling protocol,
   the script server SHOULD detect this and report it to the user at the
   time the script is submitted.)  Therefore, their XML representations
   do not have explicit output tags; the <location> tag directly
   contains another node.

5.1.1.  Usage of "location" with SIP

   All SIP locations are represented as URLs, so the locations specified
   in "location" tags are interpreted directly.



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5.2.  Location Lookup

   Locations can also be specified up through external means, through
   the use of location lookups.  The syntax of these tags is given in
   Figure 10.

   Location lookup is dependent on the underlying signalling protocol.

          Node:  "lookup"
       Outputs:  "success"   Next node if lookup was successful
                 "notfound"  Next node if lookup found no addresses
                 "failure"   Next node if lookup failed
    Parameters:  "source"    Source of the lookup
                 "timeout"   Time to try before giving up on the lookup
                 "clear"     Whether to clear the location set before
                             adding the new values

        Output:  "success"
    Parameters:  none

        Output:  "notfound"
    Parameters:  none

        Output:  "failure"
    Parameters:  none

   Figure 10: Syntax of the "lookup" node

   Location lookup nodes have one mandatory parameter and two optional
   parameters.  The mandatory parameter is "source", the source of the
   lookup.  This can either be a URI, or a non-URI value.  If the value
   of "source" is a URI, it indicates a location which the CPL server
   can query to obtain an object with the text/uri-list media type (see
   the IANA registration of this type, which also appears in RFC 2483
   [10]).  The query is performed verbatim, with no additional
   information (such as URI parameters) added.  The server adds the
   locations contained in this object to the location set.

   CPL servers MAY refuse to allow URI-based sources for location
   queries for some or all URI schemes.  In this case, they SHOULD
   reject the script at script upload time.

      There has been discussion of having CPL servers add URI parameters
      to the location request, so that (for instance) CGI scripts could
      be used to resolve them.  However, the consensus was that this
      should be a CPL extension, not a part of the base specification.





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   Non-URL sources indicate a source not specified by a URL which the
   server can query for addresses to add to the location set.  The only
   non-URL source currently defined is "registration", which specifies
   all the locations currently registered with the server.

   The "lookup" node also has two optional parameters.  The "timeout"
   parameter specifies the time, as a positive integer number of
   seconds, the script is willing to wait for the lookup to be
   performed.  If this is not specified, its default value is 30.  The
   "clear" parameter specifies whether the location set should be
   cleared before the new locations are added.

   Lookup has three outputs: "success", "notfound", and "failure".
   Notfound is taken if the lookup process succeeded but did not find
   any locations; failure is taken if the lookup failed for some reason,
   including that the specified timeout was exceeded.  If a given output
   is not present, script execution terminates and the default behavior
   is performed.

5.2.1.  Usage of "lookup" with SIP

   For SIP, the "registration" lookup source corresponds to the
   locations registered with the server using "REGISTER" messages.

5.3.  Location Removal

   A CPL script can also remove locations from the location set, through
   the use of the "remove-location" node.  The syntax of this node is
   defined in Figure 11.

   The meaning of this node is dependent on the underlying signalling
   Protocol.

             Node:  "remove-location"
          Outputs:  None               (Next node follows directly)
        Next node:  Any node
       Parameters:  "location"         Location to remove

   Figure 11: Syntax of the "remove-location" node

   A "remove-location" node removes locations from the location set.  It
   is primarily useful following a "lookup" node.  An example of this is
   given in Section 12.8.

   The "remove-location" node has one optional parameter.  The parameter
   "location" gives the URI of a location to be removed from the set, in
   a signalling-protocol-dependent manner.  If this parameter is not
   given, all locations are removed from the set.



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   The "remove-location" node has no explicit output tags.  In the XML
   syntax, the XML "remove-location" tag directly encloses the next
   node's tag.

5.3.1.  Usage of "remove-location" with SIP

   The location specified in the "location" parameter of the "remove-
   location" node is matched against the location set using the standard
   rules for SIP URI matching (as are used, e.g., to match Contact
   addresses when refreshing registrations).

6.  Signalling Operations

   Signalling operation nodes cause signalling events in the underlying
   signalling protocol.  Three signalling operations are defined:
   "proxy," "redirect," and "reject."

6.1.  Proxy

   Proxy causes the triggering call to be forwarded on to the currently
   specified set of locations.  The syntax of the proxy node is given in
   Figure 12.

   The specific signalling events invoked by the "proxy" node are
   signalling-protocol-dependent, though the general concept should
   apply to any signalling protocol.

























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         Node:  "proxy"
      Outputs:  "busy"         Next node if call attempt returned "busy"
                "noanswer"     Next node if call attempt was not
                               answered before timeout
                "redirection"  Next node if call attempt was redirected
                "failure"      Next node if call attempt failed
                "default"      Default next node for unspecified outputs
   Parameters:  "timeout"      Time to try before giving up on the
                               call attempt
                "recurse"      Whether to recursively look up
                               redirections
                "ordering"     What order to try the location set in.

       Output:  "busy"
   Parameters:  none

       Output:  "noanswer"
   Parameters:  none

       Output:  "redirection"
   Parameters:  none

       Output:  "failure"
   Parameters:  none

       Output:  "default"
   Parameters:  none

   Figure 12: Syntax of the "proxy" node

   After a proxy operation has completed, the CPL server chooses the
   "best" response to the call attempt, as defined by the signalling
   protocol or the server's administrative configuration rules.

   If the call attempt was successful, CPL execution terminates and the
   server proceeds to its default behavior (normally, to allow the call
   to be set up).  Otherwise, the next node corresponding to one of the
   "proxy" node's outputs is taken.  The "busy" output is followed if
   the call was busy, "noanswer" is followed if the call was not
   answered before the "timeout" parameter expired, "redirection" is
   followed if the call was redirected, and "failure" is followed if the
   call setup failed for any other reason.

   If one of the conditions above is true, but the corresponding output
   was not specified, the "default" output of the "proxy" node is
   followed instead.  If there is also no "default" node specified, CPL
   execution terminates and the server returns to its default behavior
   (normally, to forward the best response upstream to the originator).



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      Note: CPL extensions to allow in-call or end-of-call operations
      will require an additional output, such as "success", to be added.

   If no locations were present in the set, or if the only locations in
   the set were locations to which the server cannot proxy a call (for
   example, "http" URLs), the "failure" output is taken.

   Proxy has three optional parameters.  The "timeout" parameter
   specifies the time, as a positive integer number of seconds, to wait
   for the call to be completed or rejected; after this time has
   elapsed, the call attempt is terminated and the "noanswer" branch is
   taken.  If this parameter is not specified, the default value is 20
   seconds if the "proxy" node has a "noanswer" or "default" output
   specified; otherwise the server SHOULD allow the call to ring for a
   reasonably long period of time (to the maximum extent that server
   policy allows).

   The second optional parameter is "recurse", which can take two
   values, "yes" or "no".  This specifies whether the server should
   automatically attempt to place further call attempts to telephony
   addresses in redirection responses that were returned from the
   initial server.  Note that if the value of "recurse" is "yes", the
   "redirection" output to the script is never taken.  In this case this
   output SHOULD NOT be present.  The default value of this parameter is
   "yes".

   The third optional parameter is "ordering".  This can have three
   possible values: "parallel", "sequential", and "first-only".  This
   parameter specifies in what order the locations of the location set
   should be tried.  Parallel asks that they all be tried
   simultaneously; sequential asks that the one with the highest
   priority be tried first, the one with the next-highest priority
   second, and so forth, until one succeeds or the set is exhausted.
   First-only instructs the server to try only the highest-priority
   address in the set, and then follow one of the outputs.  The priority
   of locations in a set is determined by server policy, though CPL
   servers SHOULD honor the "priority" parameter of the "location" tag.
   The default value of this parameter is "parallel".

   Once a proxy operation completes, if control is passed on to other
   nodes, all locations which have been used are cleared from the
   location set.  That is, the location set is emptied of proxyable
   locations if the "ordering" was "parallel" or "sequential"; the
   highest-priority item in the set is removed from the set if
   "ordering" was "first-only".  (In all cases, non-proxyable locations
   such as "http" URIs remain.)  In the case of a "redirection" output,
   the new addresses to which the call was redirected are then added to
   the location set.



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6.1.1.  Usage of "proxy" with SIP

   For SIP, the best response to a "proxy" node is determined by the
   algorithm of the SIP specification.  The node's outputs correspond to
   the following events:

      busy: A 486 or 600 response was the best response received for the
            call request.

      redirection: A 3xx response was the best response received for the
            call request.

      failure: Any other 4xx, 5xx, or 6xx response was the best response
            received for the call request.

      no-answer: No final response was received for the call request
            before the timeout expired.

   SIP servers SHOULD honor the "q" parameter of SIP registrations when
   determining location priority.

6.2.  Redirect

   Redirect causes the server to direct the calling party to attempt to
   place its call to the currently specified set of locations.  The
   syntax of this node is specified in Figure 13.

   The specific behavior the redirect node invokes is dependent on the
   underlying signalling protocol involved, though its semantics are
   generally applicable.

             Node:  "redirect"
          Outputs:  None         (No node may follow)
        Next node:  None
       Parameters:  "permanent"  Whether the redirection should be
                                 considered permanent

   Figure 13: Syntax of the "redirect" node

   Redirect immediately terminates execution of the CPL script, so this
   node has no outputs and no next node.  It has one parameter,
   "permanent", which specifies whether the result returned should
   indicate that this is a permanent redirection.  The value of this
   parameter is either "yes" or "no" and its default value is "no."







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6.2.1.  Usage of "redirect" with SIP

   The SIP server SHOULD send a 3xx class response to a call request
   upon executing a "redirect" tag.  If "permanent" was "yes", the
   server SHOULD send the response "301" (Moved permanently), otherwise
   it SHOULD send "302" (Moved temporarily).

6.3.  Reject

   Reject nodes cause the server to reject the call attempt.  Their
   syntax is given in Figure 14.  The specific behavior they invoke is
   dependent on the underlying signalling protocol involved, though
   their semantics are generally applicable.

                    Node:  "reject"
                 Outputs:  None      (No node may follow)
               Next node:  None
              Parameters:  "status"  Status code to return
                           "reason"  Reason phrase to return

   Figure 14: Syntax of the "reject" node

   A reject node immediately terminates the execution of a CPL script,
   so this node has no outputs and no next node.

   This node has two arguments: "status" and "reason".  The "status"
   argument is required, and can take one of the values "busy",
   "notfound", "reject", "error", or a signalling-protocol-defined
   status.

   The "reason" argument optionally allows the script to specify a
   reason for the rejection.

6.3.1.  Usage of "reject" with SIP

   Servers which implement SIP SHOULD also allow the "status" field to
   be a numeric argument corresponding to a SIP status in the 4xx, 5xx,
   or 6xx range.

   They SHOULD send the "reason" parameter in the SIP reason phrase.

   A suggested mapping of the named statuses is as follows.  Servers MAY
   use a different mapping, though similar semantics SHOULD be
   preserved.

      "busy": 486 Busy Here

      "notfound": 404 Not Found



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      "reject": 603 Decline

      "error": 500 Internal Server Error

7.  Non-signalling Operations

   In addition to the signalling operations, CPL defines several
   operations which do not affect and are not dependent on the telephony
   signalling protocol.

7.1.  Mail

   The mail node causes the server to notify a user of the status of the
   CPL script through electronic mail.  Its syntax is given in Figure
   15.

          Node:  "mail"
       Outputs:  None      (Next node follows directly)
     Next node:  Any node
    Parameters:  "url"     Mailto url to which the mail should be sent

   Figure 15: Syntax of the "mail" node

   The "mail" node takes one argument: a "mailto" URL giving the
   address, and any additional desired parameters, of the mail to be
   sent.  The server sends the message containing the content to the
   given url; it SHOULD also include other status information about the
   original call request and the CPL script at the time of the
   notification.

      Using a full "mailto" URL rather than just an e-mail address
      allows additional e-mail headers to be specified, such as
      <mail url="mailto:jones@example.com?subject=Lookup%20failed" />.

   A mail node has only one possible result, since failure of e-mail
   delivery cannot reliably be known in real time.  Therefore, its XML
   representation does not have output tags: the <mail> tag directly
   contains another node tag.

   Note that the syntax of XML requires that ampersand characters, "&",
   which are used as parameter separators in "mailto" URLs, be quoted as
   "&amp;" inside parameter values (see Section C.12 of the XML
   specification [2]).








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7.1.1.  Suggested Content of Mailed Information

   This section presents suggested guidelines for the mail sent as a
   result of the "mail" node, for requests triggered by SIP.  The
   message mailed (triggered by any protocol) SHOULD contain all this
   information, but servers MAY elect to use a different format.

      1. If the "mailto" URI did not specify a subject header, the
         subject of the e-mail is "[CPL]", followed by the subject
         header of the SIP request.  If the URI specified a subject
         header, it is used instead.

      2. The "From" field of the e-mail is set to a CPL server
         configured address, overriding any "From" field in the "mailto"
         URI.

      3. Any "Reply-To" header in the URI is honored.  If none is given,
         then an e-mail-ized version of the origin field of the request
         is used, if possible (e.g., a SIP "From" header with a sip: URI
         would be converted to an e-mail address by stripping the URI
         scheme).

      4. If the "mailto" URI specifies a body, it is used.  If none was
         specified, the body SHOULD contain at least the identity of the
         caller (both the caller's display name and address), the date
         and time of day, the call subject, and if available, the call
         priority.

   The server SHOULD honor the user's requested languages, and send the
   mail notification using an appropriate language and character set.

7.2.  Log

   The Log node causes the server to log information about the call to
   non-volatile storage.  Its syntax is specified in Figure 16.

               Node:  "log"
            Outputs:  None       (Next node follows directly)
          Next node:  Any node
         Parameters:  "name"     Name of the log file to use
                      "comment"  Comment to be placed in log file

   Figure 16: Syntax of the "log" node

   Log takes two arguments, both optional: "name", which specifies the
   name of the log, and "comment", which gives a comment about the
   information being logged.  Servers SHOULD also include other
   information in the log, such as the time of the logged event,



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   information that triggered the call to be logged, and so forth.  Logs
   are specific to the owner of the script which logged the event.  If
   the "name" parameter is not given, the event is logged to a standard,
   server-defined log file for the script owner.  This specification
   does not define how users may retrieve their logs from the server.

   The name of a log is a logical name only, and does not necessarily
   correspond to any physical file on the server.  The interpretation of
   the log file name is server defined, as is a mechanism to access
   these logs.  The CPL server SHOULD NOT directly map log names
   uninterpreted onto local file names, for security reasons, lest a
   security-critical file be overwritten.

   A correctly operating CPL server SHOULD NOT ever allow the "log"
   event to fail.  As such, log nodes can have only one possible result,
   and their XML representation does not have explicit output tags.  A
   CPL <log> tag directly contains another node tag.

8.  Subactions

   XML syntax defines a tree.  To allow more general call flow diagrams,
   and to allow script re-use and modularity, we define subactions.

   Two tags are defined for subactions: subaction definitions and
   subaction references.  Their syntax is given in Figure 17.

               Tag:  "subaction"
           Subtags:  Any node
        Parameters:  "id"              Name of this subaction

       Pseudo-node:  "sub"
           Outputs:  None in XML tree
        Parameters:  "ref"             Name of subaction to execute

   Figure 17: Syntax of subactions and "sub" pseudo-nodes

   Subactions are defined through "subaction" tags.  These tags are
   placed in the CPL script after any ancillary information (see Section
   9), but before any top-level tags.  They take one argument: "id", a
   token indicating a script-chosen name for the subaction.  The "id"
   value for every "subaction" tag in a script MUST be unique within
   that script.

   Subactions are called from "sub" tags.  The "sub" tag is a "pseudo-
   node", and can be used anyplace in a CPL action that a true node
   could be used.  It takes one parameter, "ref", the name of the
   subaction to be called.  The "sub" tag contains no outputs of its
   own, instead control passes to the subaction.



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   References to subactions MUST refer to subactions defined before the
   current action.  A "sub" tag MUST NOT refer to the action it appears
   in, or to any action defined later in the CPL script.  Top-level
   actions cannot be called from "sub" tags, or through any other means.
   Script servers MUST verify at the time the script is submitted that
   no "sub" node refers to any subaction that is not its proper
   predecessor.

      Allowing only back-references of subs forbids any sort of
      recursion.  Recursion would introduce the possibility of non-
      terminating or non-decidable CPL scripts, a possibility our
      requirements specifically excluded.

   Every sub MUST refer to a subaction ID defined within the same CPL
   script.  No external links are permitted.

   Subaction IDs are case sensitive.

      If any subsequent version or extension defines external linkages,
      it should probably use a different tag, perhaps XLink [21].
      Ensuring termination in the presence of external links is a
      difficult problem.

9.  Ancillary Information

   No ancillary information is defined in the base CPL specification.
   If ancillary information, not part of any operation, is found to be
   necessary for a CPL extension, it SHOULD be placed within this tag.

   The (trivial) definition of the ancillary information tag is given in
   Figure 18.

      It may be useful to include timezone definitions inside CPL
      scripts directly, rather than referencing them externally with
      "tzid" and "tzurl" parameters.  If it is, an extension could be
      defined to include them here.

                            Tag:  "ancillary"
                     Parameters:  None
                        Subtags:  None

   Figure 18: Syntax of the "ancillary" tag









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10.  Default Behavior

   When a CPL node reaches an unspecified output, either because the
   output tag is not present, or because the tag is present but does not
   contain a node, the CPL server's behavior is dependent on the current
   state of script execution.  This section gives the operations that
   should be taken in each case.

      no location modifications or signalling operations performed,
           location set empty: Look up the user's location through
           whatever mechanism the server would use if no CPL script were
           in effect.  Proxy, redirect, or send a rejection message,
           using whatever policy the server would use in the absence of
           a CPL script.

      no location modifications or signalling operations performed,
           location set non-empty: (This can only happen for outgoing
           calls.)  Proxy the call to the addresses in the location set.

      location modifications performed, no signalling operations:  Proxy
           or redirect the call, whichever is the server's standard
           policy, to the addresses in the current location set.  If the
           location set is empty, return a "notfound" rejection.

      noanswer output of proxy, no timeout given: (This is a special
           case.)  If the "noanswer" output of a proxy node is
           unspecified, and no timeout parameter was given to the proxy
           node, the call should be allowed to ring for the maximum
           length of time allowed by the server (or the request, if the
           request specified a timeout).

      proxy operation previously taken: Return whatever the "best"
           response is of all accumulated responses to the call to this
           point, according to the rules of the underlying signalling
           protocol.

11.  CPL Extensions

   Servers MAY support additional CPL features beyond those listed in
   this document.  Some of the extensions which have been suggested are
   a means of querying how a call has been authenticated, richer control
   over H.323 addressing, end-system or administrator-specific features,
   regular-expression matching for strings and addresses, and mid-call
   or end-of-call controls.

   CPL extensions are indicated by XML namespaces [11].  Every extension
   MUST have an appropriate XML namespace assigned to it.  The XML
   namespace of the extension MUST be different from the XML namespace



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   defined in Section 14.  The extension MUST NOT change the syntax or
   semantics of the CPL schema defined in this document.  All XML tags
   and attributes that are part of the extension MUST be appropriately
   qualified so as to place them within that namespace.

   Tags or attributes in a CPL script which are in the global namespace
   (i.e., not associated with any namespace) are equivalent to tags and
   attributes in the CPL namespace "urn:ietf:params:xml:ns:cpl".

   A CPL script SHOULD NOT specify any namespaces it does not use.  For
   compatibility with non-namespace-aware parsers, a CPL script MAY omit
   the base CPL namespace for a script which does not use any
   extensions.

   A CPL server MUST reject any script containing a reference to a
   namespace it does not understand.  It MUST reject any script
   containing an extension tag or attribute that is not qualified to be
   in an appropriate namespace.

      A syntax such as

      <extension-switch>
        <extension has="http://www.example.com/foo">
           [extended things]
        </extension>
        <otherwise>
           [non-extended things]
        </otherwise>
      </extension-switch>

      was suggested as an alternate way of handling extensions.  This
      would allow scripts to be uploaded to a server without requiring a
      script author to somehow determine which extensions a server
      supports.  However, experience developing other languages, notably
      Sieve [22], was that this added excessive complexity to languages.
      The "extension-switch" tag could, of course, itself be defined in
      a CPL extension.

   In the XML schema of CPL, we introduce three abstract elements,
   namely 'toplevelaction', 'switch', and 'action', which accordingly
   have the abstract type 'TopLevelActionType', 'SwitchType', and
   'ActionType'.  Any top-level action in a CPL extension MUST be
   defined as the substitutionGroup of the abstract 'toplevelaction'
   element, and have the type extended from the 'TopLevelActionType'.
   Any switch in a CPL extension MUST be defined as the
   substitutionGroup of the abstract 'switch' element, and have the type





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   extended from the 'SwitchType'.  Any action in a CPL extension MUST
   be defined as the substitutionGroup of the abstract 'action' element,
   and have the type extended from the 'ActionType'.

12.  Examples

12.1.  Example: Call Redirect Unconditional

   The script in Figure 19 is a simple script that redirects all calls
   to a single fixed location.

      <?xml version="1.0" encoding="UTF-8"?>
      <cpl xmlns="urn:ietf:params:xml:ns:cpl"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">
        <incoming>
          <location url="sip:smith@phone.example.com">
            <redirect/>
          </location>
        </incoming>
      </cpl>

   Figure 19: Example Script: Call Redirect Unconditional




























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12.2.  Example: Call Forward Busy/No Answer

   The script in Figure 20 illustrates some more complex behavior.  We
   see an initial proxy attempt to one address, with further operations
   if that fails.  We also see how several outputs take the same action
   subtree, through the use of subactions.

   <?xml version="1.0" encoding="UTF-8"?>
   <cpl xmlns="urn:ietf:params:xml:ns:cpl"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">
     <subaction id="voicemail">
       <location url="sip:jones@voicemail.example.com">
         <proxy/>
       </location>
     </subaction>
     <incoming>
       <location url="sip:jones@jonespc.example.com">
         <proxy timeout="8">
           <busy>
             <sub ref="voicemail"/>
           </busy>
           <noanswer>
             <sub ref="voicemail"/>
           </noanswer>
         </proxy>
       </location>
     </incoming>
   </cpl>

   Figure 20: Example Script: Call Forward Busy/No Answer




















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12.3.  Example: Call Forward: Redirect and Default

   The script in Figure 21 illustrates further proxy behavior.  The
   server initially tries to proxy to a single address.  If this attempt
   is redirected, a new redirection is generated using the locations
   returned.  In all other failure cases for the proxy node, a default
   operation -- forwarding to voicemail -- is performed.

   <?xml version="1.0" encoding="UTF-8"?>
   <cpl xmlns="urn:ietf:params:xml:ns:cpl"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">
     <incoming>
       <location url="sip:jones@jonespc.example.com">
         <proxy>
           <redirection>
             <redirect/>
           </redirection>
           <default>
             <location url="sip:jones@voicemail.example.com">
               <proxy/>
             </location>
           </default>
         </proxy>
       </location>
     </incoming>
   </cpl>

   Figure 21: Example Script: Call Forward: Redirect and Default






















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12.4.  Example: Call Screening

   The script in Figure 22 illustrates address switches and call
   rejection, in the form of a call screening script.  Note also that
   because the address-switch lacks an "otherwise" clause, if the
   initial pattern does not match, the script does not define any
   operations.  The server therefore proceeds with its default behavior,
   which would presumably be to contact the user.

   <?xml version="1.0" encoding="UTF-8"?>
   <cpl xmlns="urn:ietf:params:xml:ns:cpl"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">
     <incoming>
       <address-switch field="origin" subfield="user">
         <address is="anonymous">
           <reject status="reject" reason="I reject anonymous calls"/>
         </address>
       </address-switch>
     </incoming>
   </cpl>

   Figure 22: Example Script: Call Screening




























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12.5.  Example: Priority and Language Routing

   The script in Figure 23 illustrates service selection based on a
   call's priority value and language settings.  If the call request had
   a priority of "urgent" or higher, the default script behavior is
   performed.  Otherwise, the language field is checked for the language
   "es" (Spanish).  If it is present, the call is proxied to a Spanish-
   speaking operator; other calls are proxied to an English-speaking
   operator.

   <?xml version="1.0" encoding="UTF-8"?>
   <cpl xmlns="urn:ietf:params:xml:ns:cpl"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">
     <incoming>
       <priority-switch>
         <priority greater="urgent"/>
         <otherwise>
           <language-switch>
             <language matches="es">
               <location url="sip:spanish@operator.example.com">
                 <proxy/>
               </location>
             </language>
             <otherwise>
               <location url="sip:english@operator.example.com">
                 <proxy/>
               </location>
             </otherwise>
           </language-switch>
         </otherwise>
       </priority-switch>
     </incoming>
   </cpl>

   Figure 23: Example Script: Priority and Language Routing















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12.6.  Example: Outgoing Call Screening

   The script in Figure 24 illustrates a script filtering outgoing
   calls, in the form of a script which prevent 1-900 (premium) calls
   from being placed.  This script also illustrates subdomain matching.

   <?xml version="1.0" encoding="UTF-8"?>
   <cpl xmlns="urn:ietf:params:xml:ns:cpl"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">
     <outgoing>
       <address-switch field="original-destination" subfield="tel">
         <address subdomain-of="1900">
           <reject status="reject"
               reason="Not allowed to make 1-900 calls."/>
         </address>
       </address-switch>
     </outgoing>
   </cpl>

   Figure 24: Example Script: Outgoing Call Screening






























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12.7.  Example: Time-of-day Routing

   Figure 25 illustrates time-based conditions and timezones.

   <?xml version="1.0" encoding="UTF-8"?>
   <cpl xmlns="urn:ietf:params:xml:ns:cpl"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">
     <incoming>
       <time-switch tzid="America/New_York"
           tzurl="http://zones.example.com/tz/America/New_York">
         <time dtstart="20000703T090000" duration="PT8H" freq="weekly"
             byday="MO,TU,WE,TH,FR">
           <lookup source="registration">
             <success>
               <proxy/>
             </success>
           </lookup>
         </time>
         <otherwise>
           <location url="sip:jones@voicemail.example.com">
             <proxy/>
           </location>
         </otherwise>
       </time-switch>
     </incoming>
   </cpl>

   Figure 25: Example Script: Time-of-day Routing






















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12.8.  Example: Location Filtering

   Figure 26 illustrates filtering operations on the location set.  In
   this example, we assume that version 0.9beta2 of the "Inadequate
   Software SIP User Agent" mis-implements some features, and so we must
   work around its problems.  We know that it cannot talk successfully
   to one particular mobile device we may have registered, so we remove
   that location from the location set.  Once this operation has been
   completed, call setup is allowed to proceed normally.

   <?xml version="1.0" encoding="UTF-8"?>
   <cpl xmlns="urn:ietf:params:xml:ns:cpl"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">
     <incoming>
       <string-switch field="user-agent">
         <string is="Inadequate Software SIP User Agent/0.9beta2">
           <lookup source="registration">
             <success>
               <remove-location location="sip:me@mobile.provider.net">
                 <proxy/>
               </remove-location>
             </success>
           </lookup>
         </string>
       </string-switch>
     </incoming>
   </cpl>

   Figure 26: Example Script: Location Filtering





















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12.9.  Example: Non-signalling Operations

   Figure 27 illustrates non-signalling operations; in particular,
   alerting a user by electronic mail if the lookup server failed.  The
   primary motivation for having the "mail" node is to allow this sort
   of out-of-band notification of error conditions, as the user might
   otherwise be unaware of any problem.

   <?xml version="1.0" encoding="UTF-8"?>
   <cpl xmlns="urn:ietf:params:xml:ns:cpl"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">
     <incoming>
       <lookup
           source="http://www.example.com/cgi-bin/locate.cgi?user=mary"
           timeout="8">
         <success>
           <proxy/>
         </success>
         <failure>
           <mail url="mailto:mary@example.com?subject=Lookup%20failed"/>
         </failure>
       </lookup>
     </incoming>
   </cpl>

   Figure 27: Example Script: Non-signalling Operations
























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12.10.  Example: Hypothetical Extensions

   The example in Figure 28 shows a hypothetical extension that
   implements distinctive ringing.  The XML namespace
   "http://www.example.com/distinctive-ring" specifies a new node named
   "ring".

   <?xml version="1.0" encoding="UTF-8"?>
   <xs:schema targetNamespace="http://www.example.com/distinctive-ring"
     xmlns="http://www.example.com/distinctive-ring"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns:xs="http://www.w3.org/2001/XMLSchema"
     xmlns:CPL="urn:ietf:params:xml:ns:cpl"
     elementFormDefault="qualified"
     attributeFormDefault="unqualified">
     <xs:import namespace="urn:ietf:params:xml:ns:cpl"
         schemaLocation="cpl.xsd"/>
     <xs:complexType name="DRingAction">
       <xs:complexContent>
         <xs:extension base="CPL:ActionType">
           <xs:attribute name="ringstyle" type="xs:string"
               use="optional"/>
         </xs:extension>
       </xs:complexContent>
     </xs:complexType>
     <xs:element name="ring" type="DRingAction"
         substitutionGroup="CPL:action"/>
   </xs:schema>

   <?xml version="1.0" encoding="UTF-8"?>
   <cpl xmlns="urn:ietf:params:xml:ns:cpl"
     xmlns:dr="http://www.example.com/distinctive-ring"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd
         http://www.example.com/distinctive-ring distinctive-ring.xsd">
     <incoming>
       <address-switch field="origin">
         <address is="sip:boss@example.com">
           <dr:ring ringstyle="warble"/>
         </address>
       </address-switch>
     </incoming>
   </cpl>

   Figure 28: Example Schema and Script: Hypothetical
              Distinctive-Ringing Extension





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   The example in Figure 29 implements a hypothetical new attribute for
   address switches, to allow regular-expression matches.  It defines a
   new attribute "regex" for the standard "address" node.

   <?xml version="1.0" encoding="UTF-8"?>
   <cpl xmlns="urn:ietf:params:xml:ns:cpl"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">
     <incoming>
       <address-switch field="origin" subfield="user"
           xmlns:re="http://www.example.com/regex">
         <address re:regex="(.*.smith|.*.jones)">
           <reject status="reject"
               reason="I don't want to talk to Smiths or Joneses"/>
         </address>
       </address-switch>
     </incoming>
   </cpl>

   Figure 29: Example Script: Hypothetical Regular-Expression Extension































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12.11.  Example: A Complex Example

   Finally, Figure 30 is a complex example which shows the sort of
   sophisticated behavior that can be achieved by combining CPL nodes.
   In this case, the user attempts to have his calls reach his desk; if
   he does not answer within a small amount of time, calls from his boss
   are forwarded to his mobile phone, and all other calls are directed
   to voicemail.  If the call setup failed, no operation is specified,
   so the server's default behavior is performed.

   <?xml version="1.0" encoding="UTF-8"?>
   <cpl xmlns="urn:ietf:params:xml:ns:cpl"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">
     <subaction id="voicemail">
       <location url="sip:jones@voicemail.example.com">
         <redirect />
       </location>
     </subaction>
     <incoming>
       <location url="sip:jones@phone.example.com">
         <proxy timeout="8">
           <busy>
             <sub ref="voicemail" />
           </busy>
           <noanswer>
             <address-switch field="origin">
               <address is="sip:boss@example.com">
                 <location url="tel:+19175551212">
                   <proxy />
                 </location>
               </address>
               <otherwise>
                 <sub ref="voicemail" />
               </otherwise>
             </address-switch>
           </noanswer>
         </proxy>
       </location>
     </incoming>
   </cpl>

   Figure 30: Example Script: A Complex Example








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13.  Security Considerations

   CPL is designed to allow services to be specified in a manner which
   prevents potentially hostile or mis-configured scripts from launching
   security attacks, including denial-of-service attacks.  Because
   script runtime is strictly bounded by acyclicity, and because the
   number of possible script operations are strictly limited, scripts
   should not be able to inflict damage upon a CPL server.

   Because scripts can direct users' telephone calls, the method by
   which scripts are transmitted from a client to a server MUST be
   strongly authenticated.  Such a method is not specified in this
   document.

   Script servers SHOULD allow server administrators to control the
   details of what CPL operations are permitted.

14.  IANA Considerations

   This document registers a new MIME type, application/cpl+xml, and a
   new URN per RFC 2141 [12], RFC 2648 [13], and RFC 3688 [14].

   The XML namespace urn:ietf:params:xml:ns:cpl will only refer to the
   version of CPL in this document and will not change.  Any CPL
   enhancements MUST be made by extensions and MUST have different
   namespaces.

14.1.  URN Sub-Namespace Registration for urn:ietf:params:xml:ns:cpl

     URI: urn:ietf:params:xml:ns:cpl

     Registrant Contact: Jonathan Lennox <lennox@cs.columbia.edu>
          Xiaotao Wu <xiaotaow@cs.columbia.edu>
          Henning Schulzrinne <hgs@cs.columbia.edu>

     XML:

           BEGIN
           <?xml version="1.0"?>
           <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
               "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
           <html xmlns="http://www.w3.org/1999/xhtml">
           <head>
             <meta http-equiv="content-type"
                content="text/html;charset=iso-8859-1"/>
             <title>Call Processing Language Namespace</title>
           </head>
           <body>



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             <h1>Namespace for Call Processing Language</h1>
             <h2>urn:ietf:params:xml:ns:cpl</h2>
             <p><a href="ftp://ftp.rfc-editor.org/in-notes/rfc3880.txt">
                   RFC3880</a>.</p>
           </body>
           </html>
           END

14.2.  Schema registration

   This specification registers XML Schema for CPL, as per the
   guidelines in [14].

      URI: urn:ietf:params:xml:schema:cpl

      Registrant contact:
           Jonathan Lennox <lennox@cs.columbia.edu>
           Xiaotao Wu <xiaotaow@cs.columbia.edu>
           Henning Schulzrinne <hgs@cs.columbia.edu>

      XML: The XML can be found in Appendix C.

14.3.  MIME Registration

   As an XML type, CPL's MIME registration conforms with "XML Media
   Types," RFC 3023 [15].

      MIME media type name: application

      MIME subtype name: cpl+xml

      Mandatory parameters: none

      Optional parameters: charset
           As for application/xml in RFC 3023.

      Encoding considerations: As for application/xml in RFC 3023.

      Security considerations: See Section 13, and Section 10 of RFC
           3023.

      Interoperability considerations: Different CPL servers may use
           incompatible address types.  However, all potential
           interoperability issues should be resolvable at the time a
           script is uploaded; there should be no interoperability
           issues which cannot be detected until runtime.

      Published specification: This document.



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      Applications which use this media type: SIP proxy servers and
           other telephony servers, and client software to control
           their behavior.

      Additional information:

           Magic number: None

           File extension: .cpl or .xml

           Macintosh file type code: "TEXT"

      Person and e-mail address for further information:
           Jonathan Lennox <lennox@cs.columbia.edu>
           Xiaotao Wu <xiaotaow@cs.columbia.edu>
           Henning Schulzrinne <hgs@cs.columbia.edu>

      Intended usage: COMMON

      Author/Change Controller: The IETF.

15.  Acknowledgments

   This document was reviewed and commented upon by the IETF IP
   Telephony Working Group.  We specifically acknowledge the following
   people for their help:

   The outgoing call screening script was written by Kenny Hom.

   Paul E. Jones contributed greatly to the mappings of H.323 addresses.

   The text of the time-switch section was taken (lightly modified) from
   RFC 2445 [8], by Frank Dawson and Derik Stenerson.

   We drew a good deal of inspiration, notably the language's lack of
   Turing-completeness and the syntax of string matching, from the
   specification of Sieve [22], a language for user filtering of
   electronic mail messages.

   Thomas F. La Porta and Jonathan Rosenberg had many useful
   discussions, contributions, and suggestions.

   Richard Gumpertz performed a very useful last-minute technical and
   editorial review of the specification.







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A.  An Algorithm for Resolving Time Switches

   The following algorithm determines whether a given instant falls
   within a repetition of a "time-switch" recurrence.  If the pre-
   processing described in Section 4.4.1 has been done, it operates in
   constant time.  Open-source Java code implementing this algorithm is
   available at http://www.cs.columbia.edu/~lennox/Cal-Code/ on the
   world wide web.

   This algorithm is believed to be correct, but this section is non-
   normative.  Section 4.4, and RFC 2445 [8], are the definitive
   definitions of recurrences.

      1. Compute the time of the call, in the timezone of the time
         switch.

      2. If the call time is earlier than "dtstart", fail NOMATCH.

      3. If the call time is less than "duration" after dtstart, succeed
         MATCH.

      4. Determine the smallest unit specified in a "byxxx" rule or by
         the "freq."  Call this the Minimum Unit.  Determine the
         previous instant (before or equal to the call time) when all
         the time units smaller than the minimum unit are the same as
         those of "dtstart."  If the minimum unit is a second, this time
         is the same as the instant.  If the minimum unit is a minute or
         an hour, the minutes or the minutes and hours, respectively,
         must be the same as "dtstart".  For all other minimum units,
         the time-of-day must be the same as "dtstart."  If the minimum
         unit is a week, the day-of-the-week must be the same as
         "dtstart."  If the minimum unit is a month, the day-of-the-
         month must be the same as "dtstart."  If the minimum unit is a
         year, the month and day-of-month must both be the same as
         "dtstart."  (Note that this means it may be necessary to roll
         back more than one minimum unit -- if the minimum unit is a
         month, then some months do not have a 31st (or 30th or 29th)
         day; if the minimum unit is a year, then some years do not have
         a February 29th.  In the Gregorian calendar, it is never
         necessary to roll back more than two months if the minimum unit
         is a month, or eight years if the minimum unit is a year.
         Between 1904 and 2096, it is never necessary to roll back more
         than four years -- the eight-year rollback can only occur when
         the Gregorian calendar "skips" a leap year.

         Call this instant the Candidate Start Time.





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      5. If the time between the candidate start time and the call time
         is more than the duration, fail NOMATCH.

      6. If the candidate start time is later than the "until" parameter
         of the recurrence (or the virtual "until" computed off-line
         from "count"), fail NOMATCH.

      7. Call the unit of the "freq" parameter of the recurrence the
         Frequency Unit.  Determine the frequency unit enclosing the
         Candidate Start Time, and that enclosing "dtstart".  Calculate
         the number of frequency units that have passed between these
         two times.  If this is not a multiple of the "interval"
         parameter, fail NOMATCH.

      8. For every "byxxx" rule, confirm that the candidate start time
         matches one of the options specified by that "byxxx" rule.  If
         so, succeed MATCH.

      9. Calculate a previous candidate start time.  Repeat until the
         difference between the candidate start time and the call time
         is more than the duration.  If no candidate start time has been
         validated, fail NOMATCH.

B.  Suggested Usage of CPL with H.323

   This appendix gives a suggested usage of CPL with H.323 [16].   Study
   Group 16 of the ITU, which developed H.323, is proposing to work on
   official CPL mappings for that protocol.  This section is therefore
   not normative.

B.1.  Usage of "address-switch" with H.323

   Address switches are specified in Section 4.1.  This section
   specifies the mapping between H.323 messages and the fields and
   subfields of address-switches.

   For H.323, the "origin" address corresponds to the alias addresses in
   the "sourceAddress" field of the "Setup-UUIE" user-user information
   element, and to the Q.931 [23] information element "Calling party
   number."  If both fields are present, or if multiple alias addresses
   for "sourceAddress" are present, which one has priority is a matter
   of local server policy; the server SHOULD use the same resolution as
   it would use for routing decisions in this case.  Similarly, the
   "destination" address corresponds to the alias addresses of the
   "destinationAddress" field, and to the Q.931 information element
   "Called party number."





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   The "original-destination" address corresponds to the "Redirecting
   number" Q.931 information element, if it is present; otherwise it is
   the same as the "destination" address.

   The mapping of H.323 addresses into subfields depends on the type of
   the alias address.  An additional subfield type, "alias-type", is
   defined for H.323 servers, corresponding to the type of the address.
   Possible values are "dialedDigits", "h323-ID", "url-ID",
   "transportID", "email-ID", "partyNumber", "mobileUIM", and "Q.931IE".
   If future versions of the H.323 specification define additional types
   of alias addresses, those names MAY also be used.

   In versions of H.323 prior to version 4, "dialedDigits" was known as
   "e164".  The two names SHOULD be treated as synonyms.

   The value of the "address-type" subfield for H.323 messages is "h323"
   unless the alias type is "url-ID" and the URL scheme is something
   other than h323; in this case the address-type is the URL scheme, as
   specified in Section 4.1.1 for SIP.

   An H.323-aware CPL server SHOULD map the address subfields from the
   primary alias used for routing.  It MAY also map subfields from other
   aliases, if subfields in the primary address are not present.

   The following mappings are used for H.323 alias types:

      dialedDigits, partyNumber, mobileUIM, and Q.931IE: the "tel" and
           "user" subfields are the string of digits, as is the
           "entire-address" form.  The "host" and "port" subfields are
           not present.

      url-ID: the same mappings are used as for SIP, in Section 4.1.1.

      h323-ID: the "user" field is the string of characters, as is the
           "entire-address" form.  All other subfields are not present.

      email-ID: the "user" and "host" subfields are set to the
           corresponding parts of the e-mail address.  The "port" and
           "tel" subfields are not present.  The "entire-address" form
           corresponds to the entire e-mail address.

      transportID: if the TransportAddress is of type "ipAddress,"
           "ipSourceRoute," or "ip6Address," the "host" subfield is set
           to the "ip" element of the sequence, translated into the
           standard IPv4 or IPv6 textual representation, and the "port"
           subfield is set to the "port" element of the sequence
           represented in decimal.  The "tel" and "user" fields are not
           present.  The "entire-address" form is not defined.  The



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           representation and mapping of transport addresses is not
           defined for non-IP addresses.

   H.323 [16] defines an "h323" URI scheme.  This appendix defines a
   mapping for these URIs onto the CPL "address-switch" subfields, as
   given in Section 4.1.  This definition is also available as RFC 3508
   [24], which is an excerpt from the H.323 specification.

   For h323 URIs, the "user", "host", and "port" subfields are set to
   the corresponding parts of the H.323 URL.  The "tel" subfield is not
   present.  The "entire-address" form corresponds to the entire URI.

   This mapping MAY be used both for h323 URIs in an h323 "url-ID"
   address alias, and for h323 URIs in SIP messages.

B.2.  Usage of "string-switch" with H.323

   For H.323, the "string-switch" node (see Section 4.2) is used as
   follows.  The field "display" corresponds to the Q.931 information
   element of the same name, copied verbatim.  The fields "subject",
   "organization", and "user-agent" are not used and are never present.

      The "display" IE is conventionally used for Caller-ID purposes, so
      arguably it should be mapped to the "display" subfield of an
      "address-match" with the field "originator".  However, since a) it
      is a message-level information element, not an address-level one,
      and b) the Q.931 specification [23] says only that "[t]he purpose
      of the Display information element is to supply display
      information that may be displayed by the user," it seems to be
      more appropriate to allow it to be matched in a "string-switch"
      instead.

B.3.  Usage of "language-switch" with H.323

   The language-ranges for the "language-switch" switch are obtained
   from the H.323 UUIE "language".  The switch is not-present if the
   initial message did not contain this UUIE.

B.4.  Usage of "priority-switch" with H.323

   All H.323 messages are considered to have priority "normal" for the
   purpose of a priority switch (see Section 4.5).









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B.5.  Usage of "location" with H.323

   Locations in explicit location nodes (Section 5.1) are specified as
   URLs.  Therefore, all locations added in this manner are interpreted
   as being of alias type "url-ID" in H.323.

   Specifications of other H.323 address alias types will require a CPL
   extension (see Section 11).

B.6.  Usage of "lookup" with H.323

   For location lookup nodes (Section 5.2), the "registration" lookup
   source corresponds to the locations registered with the server using
   "RAS" messages.

B.7.  Usage of "remove-location" with H.323

   Location removal nodes (Section 5.3) remove addresses with the alias
   type "url-ID" using verbatim string matching on the URLs.  If a "tel"
   URL is specified as the location, matching addresses (ignoring visual
   separators) with the alias types "dialedDigits" ("e164"),
   "partyNumber", "mobileUIM", or "Q.931IE" are also removed.  No
   mechanism is provided to remove other alias types.

C.  The XML Schema for CPL

   This section includes a full XML Schema describing the XML syntax of
   CPL.   Every script submitted to a CPL server SHOULD comply with this
   XML Schema.   When parsing scripts comply with the CPL DTD in earlier
   documents, the DOCTYPE lines in the scripts should be ignored.  Note
   that compliance with this schema is not a sufficient condition for
   correctness of a CPL script, as many of the conditions described in
   this specification are not expressible in schema syntax.  Figure 31
   shows the structure of the schema.  'incoming' and 'outgoing' are
   defined as the substitutionGroup of the 'toplevelaction'.  All the
   switches are defined as the substitutionGroup of the 'switch'
   element.  All the actions are defined as the substitutionGroup of the
   'action' element.













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         +---------+    +------+                    +--address
       +-+ancillary|    |switch|** +--------------+ | +-not-present
       | +---------+    +---+--+ **|address-switch+-+-+-address
       |                    |    * +--------------+ +--otherwise
       | +---------+ +----+ |    *                   +--language
       +-+subaction+-+Node| |    * +---------------+ | +-not-present
       | +---------+ +----+ |    **|language-switch|-+-+-language
       |                    |    * +---------------+ +--otherwise
       |                    |    *                   +--priority
       |                    |    * +---------------+ | +-not-present
       |                    |    **|priority-switch|-+-+-priority
       |                    |    * +---------------+ +--otherwise
       |                    |    *                 +--string
   cpl-+                    |    * +-------------+ | +-not-present
       |                    |    **|string-switch|-+ +-string
       |                    |    * +-------------+ +--otherwise
       |                    |    *               +--time
       | +--------------+ +-+--+ * +-----------+ | +-not-present
       +-+toplevelaction+-+Node|  *|time-switch|-+-+-time
         +-----*--------+ +-+--+   +-----------+ +--otherwise
              *             |              +--------+ +----+
             *              |            **|location+-|Node|
             *              | +--------+ * +--------+ +----+
             * +--------+   |-+modifier|** +------+ +-success-Node
             **|incoming|   | +--------+ *-|lookup+-+-notfound-Node
             * +--------+   |            * +------+ +-failure-Node
             *              | +---+      * +---------------+ +----+
             * +--------+   +-+Sub+-sub  **|remove-location+-+Node|
              *|outgoing|   | +---+        +---------------+ +----+
               +--------+   |            +---+
                            |          **|log+-Node
                            |          * +---+
                            |          * +----+
                            | +------+ **|mail+-Node
                            +-+action|** +----+     +-busy-Node
        ----  contains        +------+ * +-----+    |
                                       **|proxy+----+-noanswer-Node
        ****  substitutes              * +-----+    |
                                       * +--------+ +-failure-Node
                                       **|redirect| |
                                       * +--------+ +-redirection-Node
                                       * +------+   |
                                        *|reject|   +-default-Node
                                         +------+

   Figure 31: The structure of the XML schema for CPL





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   BEGIN
   <?xml version="1.0" encoding="UTF-8"?>
   <xs:schema targetNamespace="urn:ietf:params:xml:ns:cpl"
     xmlns="urn:ietf:params:xml:ns:cpl"
     xmlns:xs="http://www.w3.org/2001/XMLSchema"
     elementFormDefault="qualified"
     attributeFormDefault="unqualified">
     <xs:complexType name="TopLevelActionType" abstract="true">
       <xs:group ref="Node"/>
     </xs:complexType>
     <xs:element name="toplevelaction" type="TopLevelActionType"/>
     <xs:complexType name="ActionType" abstract="true"/>
     <xs:element name="action" type="ActionType"/>
     <xs:complexType name="SwitchType" abstract="true"/>
     <xs:element name="switch" type="SwitchType"/>
     <xs:complexType name="ModifierType" abstract="true"/>
     <xs:element name="modifier" type="ModifierType"/>
     <xs:element name="location" type="LocationType"
         substitutionGroup="modifier"/>
     <xs:element name="lookup" type="LookupType"
         substitutionGroup="modifier"/>
     <xs:element name="remove-location" type="RemoveLocationType"
         substitutionGroup="modifier"/>
     <xs:element name="sub" type="SubAction"/>
     <xs:group name="Node">
       <xs:choice>
         <xs:element ref="switch" minOccurs="0" maxOccurs="1"/>
         <xs:element ref="modifier" minOccurs="0" maxOccurs="1"/>
         <xs:element ref="sub" minOccurs="0" maxOccurs="1"/>
         <xs:element ref="action" minOccurs="0" maxOccurs="1"/>
       </xs:choice>
     </xs:group>
     <xs:complexType name="OtherwiseAction">
       <xs:group ref="Node"/>
     </xs:complexType>
     <xs:complexType name="NotPresentAction">
       <xs:group ref="Node"/>
     </xs:complexType>
     <xs:simpleType name="YesNoType">
       <xs:restriction base="xs:NMTOKEN">
         <xs:enumeration value="yes"/>
         <xs:enumeration value="no"/>
       </xs:restriction>
     </xs:simpleType>
     <xs:simpleType name="StatusType">
       <xs:union>
         <xs:simpleType>
           <xs:restriction base="xs:NMTOKEN">



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             <xs:enumeration value="busy"/>
             <xs:enumeration value="notfound"/>
             <xs:enumeration value="reject"/>
             <xs:enumeration value="error"/>
           </xs:restriction>
         </xs:simpleType>
         <xs:simpleType>
           <xs:restriction base="xs:string"/>
         </xs:simpleType>
       </xs:union>
     </xs:simpleType>
     <xs:simpleType name="OrderingType">
       <xs:restriction base="xs:NMTOKEN">
         <xs:enumeration value="parallel"/>
         <xs:enumeration value="sequential"/>
         <xs:enumeration value="first-only"/>
       </xs:restriction>
     </xs:simpleType>
     <xs:simpleType name="AddressFieldType">
       <xs:union>
         <xs:simpleType>
           <xs:restriction base="xs:NMTOKEN">
             <xs:enumeration value="origin"/>
             <xs:enumeration value="destination"/>
             <xs:enumeration value="original-destination"/>
           </xs:restriction>
         </xs:simpleType>
         <xs:simpleType>
           <xs:restriction base="xs:string"/>
         </xs:simpleType>
       </xs:union>
     </xs:simpleType>
     <xs:simpleType name="AddressSubfieldType">
       <xs:union>
         <xs:simpleType>
           <xs:restriction base="xs:NMTOKEN">
             <xs:enumeration value="address-type"/>
             <xs:enumeration value="user"/>
             <xs:enumeration value="host"/>
             <xs:enumeration value="port"/>
             <xs:enumeration value="tel"/>
             <xs:enumeration value="display"/>
             <xs:enumeration value="password"/>
             <xs:enumeration value="alias-type"/>
           </xs:restriction>
         </xs:simpleType>





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         <xs:simpleType>
           <xs:restriction base="xs:string"/>
         </xs:simpleType>
       </xs:union>
     </xs:simpleType>
     <xs:complexType name="AddressType">
       <xs:annotation>
         <xs:documentation>Exactly one of the three attributes must
             appear</xs:documentation>
       </xs:annotation>
       <xs:group ref="Node"/>
       <xs:attribute name="is" type="xs:string" use="optional"/>
       <xs:attribute name="contains" type="xs:string" use="optional">
         <xs:annotation>
           <xs:documentation>for "display" only</xs:documentation>
         </xs:annotation>
       </xs:attribute>
       <xs:attribute name="subdomain-of" type="xs:string"
           use="optional">
         <xs:annotation>
           <xs:documentation>for "host", "tel" only</xs:documentation>
         </xs:annotation>
       </xs:attribute>
       <xs:anyAttribute namespace="##any" processContents="lax"/>
     </xs:complexType>
     <xs:complexType name="AddressSwitchType">
       <xs:complexContent>
         <xs:extension base="SwitchType">
           <xs:sequence>
             <xs:element name="address" type="AddressType" minOccurs="0"
                 maxOccurs="unbounded"/>
             <xs:sequence minOccurs="0">
               <xs:element name="not-present" type="NotPresentAction"/>
               <xs:element name="address" type="AddressType"
                   minOccurs="0" maxOccurs="unbounded"/>
             </xs:sequence>
             <xs:element name="otherwise" type="OtherwiseAction"
                 minOccurs="0"/>
           </xs:sequence>
           <xs:attribute name="field" type="AddressFieldType"
               use="required"/>
           <xs:attribute name="subfield" type="AddressSubfieldType"
               use="optional"/>
         </xs:extension>
       </xs:complexContent>
     </xs:complexType>
     <xs:element name="address-switch" type="AddressSwitchType"
         substitutionGroup="switch"/>



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     <xs:simpleType name="StringFieldType">
       <xs:restriction base="xs:NMTOKEN">
         <xs:enumeration value="subject"/>
         <xs:enumeration value="organization"/>
         <xs:enumeration value="user-agent"/>
         <xs:enumeration value="display"/>
       </xs:restriction>
     </xs:simpleType>
     <xs:complexType name="StringType">
       <xs:group ref="Node"/>
       <xs:attribute name="is" type="xs:string" use="optional"/>
       <xs:attribute name="contains" type="xs:string" use="optional"/>
       <xs:anyAttribute namespace="##any" processContents="lax"/>
     </xs:complexType>
     <xs:complexType name="StringSwitchType">
       <xs:complexContent>
         <xs:extension base="SwitchType">
           <xs:sequence>
             <xs:element name="string" type="StringType" minOccurs="0"
                 maxOccurs="unbounded"/>
             <xs:sequence minOccurs="0">
               <xs:element name="not-present" type="NotPresentAction"/>
               <xs:element name="string" type="StringType" minOccurs="0"
                   maxOccurs="unbounded"/>
             </xs:sequence>
             <xs:element name="otherwise" type="OtherwiseAction"
                 minOccurs="0"/>
           </xs:sequence>
           <xs:attribute name="field" type="StringFieldType"
               use="required">
             <xs:annotation>
               <xs:documentation>Strings are matched as case-insensitive
                   Unicode strings.</xs:documentation>
             </xs:annotation>
           </xs:attribute>
         </xs:extension>
       </xs:complexContent>
     </xs:complexType>
     <xs:element name="string-switch" type="StringSwitchType"
         substitutionGroup="switch"/>
     <xs:complexType name="LanguageType">
       <xs:group ref="Node"/>
       <xs:attribute name="matches" type="xs:string" use="required">
         <xs:annotation>
           <xs:documentation>The value of one of these parameters is a
               language-tag, as defined in RFC
               3066.</xs:documentation>
         </xs:annotation>



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       </xs:attribute>
       <xs:anyAttribute namespace="##any" processContents="lax"/>
     </xs:complexType>
     <xs:complexType name="LanguageSwitchType">
       <xs:complexContent>
         <xs:extension base="SwitchType">
           <xs:sequence>
             <xs:element name="language" type="LanguageType"
                 minOccurs="0" maxOccurs="unbounded"/>
             <xs:sequence minOccurs="0">
               <xs:element name="not-present" type="NotPresentAction"/>
               <xs:element name="language" type="LanguageType"
                   minOccurs="0" maxOccurs="unbounded"/>
             </xs:sequence>
             <xs:element name="otherwise" type="OtherwiseAction"
                 minOccurs="0"/>
           </xs:sequence>
         </xs:extension>
       </xs:complexContent>
     </xs:complexType>
     <xs:element name="language-switch" type="LanguageSwitchType"
         substitutionGroup="switch"/>
     <xs:simpleType name="FreqType">
       <xs:restriction base="xs:NMTOKEN">
         <xs:pattern value="[s|S][e|E][c|C][o|O][n|N][d|D][l|L][y|Y]"/>
         <xs:pattern value="[m|M][i|I][n|N][u|U][t|T][e|E][l|L][y|Y]"/>
         <xs:pattern value="[h|H][o|O][u|U][r|R][l|L][y|Y]"/>
         <xs:pattern value="[d|D][a|A][i|I][l|L][y|Y]"/>
         <xs:pattern value="[w|W][e|E][e|E][k|K][l|L][y|Y]"/>
         <xs:pattern value="[m|M][o|N][n|N][t|T][h|H][l|L][y|Y]"/>
         <xs:pattern value="[y|Y][e|E][a|A][r|R][l|L][y|Y]"/>
       </xs:restriction>
     </xs:simpleType>
     <xs:simpleType name="YearDayType">
       <xs:union>
         <xs:simpleType>
           <xs:restriction base="xs:integer">
             <xs:minInclusive value="-366"/>
             <xs:maxInclusive value="-1"/>
           </xs:restriction>
         </xs:simpleType>
         <xs:simpleType>
           <xs:restriction base="xs:integer">
             <xs:minInclusive value="1"/>
             <xs:maxExclusive value="366"/>
           </xs:restriction>
         </xs:simpleType>
       </xs:union>



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     </xs:simpleType>
     <xs:simpleType name="DayType">
       <xs:restriction base="xs:NMTOKEN">
         <xs:pattern value="[m|M][o|O]"/>
         <xs:pattern value="[t|T][u|U]"/>
         <xs:pattern value="[w|W][e|E]"/>
         <xs:pattern value="[t|T][h|H]"/>
         <xs:pattern value="[f|F][r|R]"/>
         <xs:pattern value="[s|S][a|A]"/>
         <xs:pattern value="[s|S][u|U]"/>
       </xs:restriction>
     </xs:simpleType>
     <xs:complexType name="TimeType">
       <xs:annotation>
         <xs:documentation>Exactly one of the two attributes "dtend" and
             "duration" must occur.  None of the attributes following
             freq are meaningful unless freq appears.
             </xs:documentation>
       </xs:annotation>
       <xs:group ref="Node"/>
       <xs:attribute name="dtstart" type="xs:string" use="required">
         <xs:annotation>
           <xs:documentation>RFC 2445 DATE-TIME</xs:documentation>
         </xs:annotation>
       </xs:attribute>
       <xs:attribute name="dtend" type="xs:string" use="optional">
         <xs:annotation>
           <xs:documentation>RFC 2445 DATE-TIME</xs:documentation>
         </xs:annotation>
       </xs:attribute>
       <xs:attribute name="duration" type="xs:string" use="optional">
         <xs:annotation>
           <xs:documentation>RFC 2445 DURATION</xs:documentation>
         </xs:annotation>
       </xs:attribute>
       <xs:attribute name="freq" type="FreqType" use="optional"/>
       <xs:attribute name="interval" type="xs:positiveInteger"
           default="1"/>
       <xs:attribute name="until" type="xs:string" use="optional">
         <xs:annotation>
           <xs:documentation>RFC 2445 DATE-TIME</xs:documentation>
         </xs:annotation>
       </xs:attribute>
       <xs:attribute name="count" type="xs:positiveInteger"
           use="optional"/>
       <xs:attribute name="bysecond" type="xs:string" use="optional">
         <xs:annotation>
           <xs:documentation>Comma-separated list of seconds within a



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               minute.  Valid values are 0 to 59.</xs:documentation>
         </xs:annotation>
       </xs:attribute>
       <xs:attribute name="byminute" type="xs:string" use="optional">
         <xs:annotation>
           <xs:documentation>Comma-separated list of minutes within an
               hour.  Valid values are 0 to 59.</xs:documentation>
         </xs:annotation>
       </xs:attribute>
       <xs:attribute name="byhour" type="xs:string" use="optional">
         <xs:annotation>
           <xs:documentation>Comma-separated list of hours of the day.
               Valid values are 0 to 23.</xs:documentation>
         </xs:annotation>
       </xs:attribute>
       <xs:attribute name="byday" type="xs:string" use="optional">
         <xs:annotation>
           <xs:documentation>Comma-separated list of days of the week.
               Valid values are "MO", "TU", "WE", "TH", "FR", "SA" and
               "SU".  These values are not case-sensitive.  Each can be
               preceded by a positive (+n) or negative (-n)
               integer.</xs:documentation>
         </xs:annotation>
       </xs:attribute>
       <xs:attribute name="bymonthday" type="xs:string" use="optional">
         <xs:annotation>
           <xs:documentation>Comma-separated list of days of the month.
               Valid values are 1 to 31 or -31 to
               -1.</xs:documentation>
         </xs:annotation>
       </xs:attribute>
       <xs:attribute name="byyearday" type="xs:string" use="optional">
         <xs:annotation>
           <xs:documentation>Comma-separated list of days of the year.
               Valid values are 1 to 366 or -366 to
               -1.</xs:documentation>
         </xs:annotation>
       </xs:attribute>
       <xs:attribute name="byweekno" type="xs:string" use="optional">
         <xs:annotation>
           <xs:documentation>Comma-separated list of ordinals specifying
               weeks of the year.  Valid values are 1 to 53 or -53 to
               -1.</xs:documentation>
         </xs:annotation>
       </xs:attribute>
       <xs:attribute name="bymonth" type="xs:string" use="optional">
         <xs:annotation>
           <xs:documentation>Comma-separated list of months of the year.



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               Valid values are 1 to 12.</xs:documentation>
         </xs:annotation>
       </xs:attribute>
       <xs:attribute name="wkst" type="DayType" default="MO"/>
       <xs:attribute name="bysetpos" type="YearDayType"/>
       <xs:anyAttribute namespace="##any" processContents="lax"/>
     </xs:complexType>
     <xs:simpleType name="TZIDType">
       <xs:restriction base="xs:string"/>
     </xs:simpleType>
     <xs:simpleType name="TZURLType">
       <xs:restriction base="xs:anyURI"/>
     </xs:simpleType>
     <xs:complexType name="TimeSwitchType">
       <xs:complexContent>
         <xs:extension base="SwitchType">
           <xs:sequence>
             <xs:element name="time" type="TimeType" minOccurs="0"
                 maxOccurs="unbounded"/>
             <xs:sequence minOccurs="0">
               <xs:element name="not-present" type="NotPresentAction"/>
               <xs:element name="time" type="TimeType" minOccurs="0"
                   maxOccurs="unbounded"/>
             </xs:sequence>
             <xs:element name="otherwise" type="OtherwiseAction"
                 minOccurs="0"/>
           </xs:sequence>
           <xs:attribute name="tzid" type="TZIDType"/>
           <xs:attribute name="tzurl" type="TZURLType"/>
         </xs:extension>
       </xs:complexContent>
     </xs:complexType>
     <xs:element name="time-switch" type="TimeSwitchType"
         substitutionGroup="switch"/>
     <xs:simpleType name="PriorityValues">
       <xs:restriction base="xs:NMTOKEN">
         <xs:pattern
             value="[e|E][m|M][e|E][r|R][g|G][e|E][n|N][c|C][y|Y]"/>
         <xs:pattern value="[u|U][r|R][g|G][e|E][n|N][t|T]"/>
         <xs:pattern value="[n|N][o|O][r|R][m|M][a|A][l|L]"/>
         <xs:pattern
             value="[n|N][o|O][n|N]-[u|U][r|R][g|G][e|E][n|N][t|T]"/>
       </xs:restriction>
     </xs:simpleType>
     <xs:complexType name="PriorityType">
       <xs:annotation>
         <xs:documentation>Exactly one of the three attributes must
             appear </xs:documentation>



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       </xs:annotation>
       <xs:group ref="Node"/>
       <xs:attribute name="less" type="PriorityValues"/>
       <xs:attribute name="greater" type="PriorityValues"/>
       <xs:attribute name="equal" type="xs:string">
         <xs:annotation>
           <xs:documentation>case-insensitive</xs:documentation>
         </xs:annotation>
       </xs:attribute>
       <xs:anyAttribute namespace="##any" processContents="lax"/>
     </xs:complexType>
     <xs:complexType name="PrioritySwitchType">
       <xs:complexContent>
         <xs:extension base="SwitchType">
           <xs:sequence>
             <xs:element name="priority" type="PriorityType"
                 minOccurs="0" maxOccurs="unbounded"/>
             <xs:sequence minOccurs="0">
               <xs:element name="not-present" type="NotPresentAction"/>
               <xs:element name="priority" type="PriorityType"
                   minOccurs="0" maxOccurs="unbounded"/>
             </xs:sequence>
             <xs:element name="otherwise" type="OtherwiseAction"
                 minOccurs="0"/>
           </xs:sequence>
         </xs:extension>
       </xs:complexContent>
     </xs:complexType>
     <xs:element name="priority-switch" type="PrioritySwitchType"
         substitutionGroup="switch"/>
     <xs:simpleType name="LocationPriorityType">
       <xs:restriction base="xs:float">
         <xs:minInclusive value="0.0"/>
         <xs:maxInclusive value="1.0"/>
       </xs:restriction>
     </xs:simpleType>
     <xs:complexType name="LocationType">
       <xs:complexContent>
         <xs:extension base="ModifierType">
           <xs:group ref="Node"/>
           <xs:attribute name="url" type="xs:anyURI" use="required"/>
           <xs:attribute name="priority" type="LocationPriorityType"
               use="optional" default="1.0"/>
           <xs:attribute name="clear" type="YesNoType" default="no"/>
         </xs:extension>
       </xs:complexContent>
     </xs:complexType>
     <xs:complexType name="LookupType">



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       <xs:complexContent>
         <xs:extension base="ModifierType">
           <xs:all>
             <xs:element name="success" minOccurs="0">
               <xs:complexType>
                 <xs:group ref="Node"/>
               </xs:complexType>
             </xs:element>
             <xs:element name="notfound" minOccurs="0">
               <xs:complexType>
                 <xs:group ref="Node"/>
               </xs:complexType>
             </xs:element>
             <xs:element name="failure" minOccurs="0">
               <xs:complexType>
                 <xs:group ref="Node"/>
               </xs:complexType>
             </xs:element>
           </xs:all>
           <xs:attribute name="source" type="xs:string"
               use="required"/>
           <xs:attribute name="timeout" type="xs:positiveInteger"
               default="30"/>
           <xs:attribute name="clear" type="YesNoType" default="no"/>
         </xs:extension>
       </xs:complexContent>
     </xs:complexType>
     <xs:complexType name="RemoveLocationType">
       <xs:complexContent>
         <xs:extension base="ModifierType">
           <xs:group ref="Node"/>
           <xs:attribute name="location" type="xs:string"
               use="optional"/>
         </xs:extension>
       </xs:complexContent>
     </xs:complexType>
     <xs:complexType name="LogAction">
       <xs:complexContent>
         <xs:extension base="ActionType">
           <xs:group ref="Node"/>
           <xs:attribute name="name" type="xs:string" use="optional"/>
           <xs:attribute name="comment" type="xs:string"
               use="optional"/>
         </xs:extension>
       </xs:complexContent>
     </xs:complexType>
     <xs:element name="log" type="LogAction"
         substitutionGroup="action"/>



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     <xs:complexType name="IncomingType">
       <xs:complexContent>
         <xs:extension base="TopLevelActionType"/>
       </xs:complexContent>
     </xs:complexType>
     <xs:element name="incoming" type="IncomingType"
         substitutionGroup="toplevelaction"/>
     <xs:complexType name="OutgoingType">
       <xs:complexContent>
         <xs:extension base="TopLevelActionType"/>
       </xs:complexContent>
     </xs:complexType>
     <xs:element name="outgoing" type="OutgoingType"
         substitutionGroup="toplevelaction"/>
     <xs:complexType name="ProxyAction">
       <xs:complexContent>
         <xs:extension base="ActionType">
           <xs:all>
             <xs:element name="busy" minOccurs="0">
               <xs:complexType>
                 <xs:group ref="Node"/>
               </xs:complexType>
             </xs:element>
             <xs:element name="noanswer" minOccurs="0">
               <xs:complexType>
                 <xs:group ref="Node"/>
               </xs:complexType>
             </xs:element>
             <xs:element name="failure" minOccurs="0">
               <xs:complexType>
                 <xs:group ref="Node"/>
               </xs:complexType>
             </xs:element>
             <xs:element name="redirection" minOccurs="0">
               <xs:complexType>
                 <xs:group ref="Node"/>
               </xs:complexType>
             </xs:element>
             <xs:element name="default" minOccurs="0">
               <xs:complexType>
                 <xs:group ref="Node"/>
               </xs:complexType>
             </xs:element>
           </xs:all>
           <xs:attribute name="timeout" type="xs:positiveInteger"
               use="optional" default="20"/>
           <xs:attribute name="recurse" type="YesNoType"
               use="optional" default="yes"/>



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           <xs:attribute name="ordering" type="OrderingType"
               use="optional" default="parallel"/>
         </xs:extension>
       </xs:complexContent>
     </xs:complexType>
     <xs:element name="proxy" type="ProxyAction"
         substitutionGroup="action"/>
     <xs:complexType name="RedirectAction">
       <xs:complexContent>
         <xs:extension base="ActionType">
           <xs:attribute name="permanent" type="YesNoType"
               default="no"/>
         </xs:extension>
       </xs:complexContent>
     </xs:complexType>
     <xs:element name="redirect" type="RedirectAction"
         substitutionGroup="action"/>
     <xs:complexType name="RejectAction">
       <xs:complexContent>
         <xs:extension base="ActionType">
           <xs:attribute name="status" type="StatusType"
               use="required"/>
           <xs:attribute name="reason" type="xs:string"
               use="optional"/>
         </xs:extension>
       </xs:complexContent>
     </xs:complexType>
     <xs:element name="reject" type="RejectAction"
         substitutionGroup="action"/>
     <xs:complexType name="MailAction">
       <xs:complexContent>
         <xs:extension base="ActionType">
           <xs:group ref="Node"/>
           <xs:attribute name="url" type="xs:anyURI" use="required"/>
         </xs:extension>
       </xs:complexContent>
     </xs:complexType>
     <xs:element name="mail" type="MailAction"
         substitutionGroup="action"/>
     <xs:complexType name="SubAction">
       <xs:attribute name="ref" type="xs:string" use="required"/>
     </xs:complexType>
     <xs:complexType name="AncillaryType"/>
     <xs:complexType name="SubactionType">
       <xs:group ref="Node"/>
       <xs:attribute name="id" use="required"/>
     </xs:complexType>
     <xs:complexType name="CPLType">



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       <xs:sequence>
         <xs:element name="ancillary" type="AncillaryType" minOccurs="0"
             maxOccurs="1"/>
         <xs:element name="subaction" type="SubactionType" minOccurs="0"
             maxOccurs="unbounded"/>
         <xs:element ref="toplevelaction" minOccurs="0"
             maxOccurs="unbounded">
           <xs:annotation>
             <xs:documentation>Any toplevel action MUST NOT appear more
                 than once.</xs:documentation>
           </xs:annotation>
         </xs:element>
       </xs:sequence>
     </xs:complexType>
     <xs:element name="cpl" type="CPLType"/>
   </xs:schema>
   END

Normative References

   [1]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
        Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
        Session Initiation Protocol", RFC 3261, June 2002.

   [2]  Bray, T., Paoli, J., Sperberg-McQueen, C. M., Maler, E., and F.
        Yergeau, "Extensible Markup Language (XML) 1.0 (Third Edition)",
        W3C Recommendation REC-xml-20040204, World Wide Web Consortium
        (W3C), February 2004.  Available at http://www.w3.org/XML/.

   [3]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [4]  Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6)
        Addressing Architecture", RFC 3513, April 2003.

   [5]  Davis, M. F. and M. Duerst, "Unicode Normalization Forms",
        Unicode Standard Annex #15, Unicode Consortium, April 2003.
        Revision 23; part of Unicode 4.0.0. Available at
        http://www.unicode.org/unicode/reports/tr15/.

   [6]  Davis, M. F., "Case Mappings", Unicode Standard Annex #21,
        Unicode Consortium, March 2001.  Revision 5; part of Unicode
        3.2.0.  Available at
        http://www.unicode.org/unicode/reports/tr21/.

   [7]  Alvestrand, H., "Tags for the Identification of Languages", BCP
        47, RFC 3066, January 2001.




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   [8]  Dawson, F. and D. Stenerson, "Internet Calendaring and
        Scheduling Core Object Specification (iCalendar)", RFC 2445,
        November 1998.

   [9]  Eggert, P., "Sources for Time Zone and Daylight Saving Time
        Data".  Available at http://www.twinsun.com/tz/tz-link.htm.

   [10] Mealling, M. and R. Daniel, "URI Resolution Services Necessary
        for URN Resolution", RFC 2483, January 1999.

   [11] Bray, T., Hollander, D., and A. Layman, "Namespaces in XML", W3C
        Recommendation REC-xml-names-19990114, World Wide Web Consortium
        (W3C), January 1999.  Available at http://www.w3.org/TR/REC-
        xml-names/.

   [12] Moats, R., "URN Syntax", RFC 2141, May 1997.

   [13] Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
        August 1999.

   [14] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January
        2004.

   [15] Murata, M., St.Laurent, S., and D. Kohn, "XML Media Types", RFC
        3023, January 2001.

Informative References

   [16] International Telecommunication Union, "Packet-based multimedia
        communication systems", Recommendation H.323, Telecommunication
        Standardization Sector of ITU, Geneva, Switzerland, July 2003.

   [17] Lennox, J. and H. Schulzrinne, "Call Processing Language
        Framework and Requirements", RFC 2824, May 2000.

   [18] Raggett, D., Le Hors, A., and I. Jacobs, "HTML 4.01
        Specification", W3C Recommendation REC-html401-19991224, World
        Wide Web Consortium (W3C), December 1999.  Available at
        http://www.w3.org/TR/html4/.

   [19] ISO (International Organization for Standardization),
        "Information processing -- Text and office systems -- Standard
        Generalized Markup Language (SGML)", ISO Standard ISO
        8879:1986(E), International Organization for Standardization,
        Geneva, Switzerland, October 1986.






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   [20] ISO (International Organization for Standardization), "Data
        elements and interchange formats -- Information interchange --
        Representation of dates and times", ISO Standard ISO
        8601:2000(E), International Organization for Standardization,
        Geneva, Switzerland, December 2000.

   [21] DeRose, S., Maler, E., Orchard, D., and B. Trafford, "XML
        Linking Language (XLink) Version 1.0", W3C Recommendation REC-
        xlink-20010627, World Wide Web Consortium (W3C), June 2001.
        Available at http://www.w3.org/TR/xlink/.

   [22] Showalter, T., "Sieve: A Mail Filtering Language", RFC 3028,
        January 2001.

   [23] International Telecommunication Union, "Digital Subscriber
        Signalling System No. 1 (DSS 1) - ISDN user-network interface
        layer 3 specification for basic call control", Recommendation
        Q.931, International Telecommunication Union, Geneva,
        Switzerland, March 1993.

   [24] Levin, O., "H.323 Uniform Resource Locator (URL) Scheme
        Registration", RFC 3508, April 2003.





























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Authors' Addresses

   Jonathan Lennox
   Dept. of Computer Science
   Columbia University
   1214 Amsterdam Avenue, MC 0401
   New York, NY 10027
   USA

   EMail: lennox@cs.columbia.edu


   Xiaotao Wu
   Dept. of Computer Science
   Columbia University
   1214 Amsterdam Avenue, MC 0401
   New York, NY 10027
   USA

   EMail: xiaotaow@cs.columbia.edu


   Henning Schulzrinne
   Dept. of Computer Science
   Columbia University
   1214 Amsterdam Avenue, MC 0401
   New York, NY 10027
   USA

   EMail: schulzrinne@cs.columbia.edu





















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Full Copyright Statement

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