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Versions: 00 01 02 03 04 05 06 07 08 09 RFC 3880

Internet Engineering Task Force                                 IPTEL WG
Internet Draft                                        Lennox/Schulzrinne
draft-ietf-iptel-cpl-06.txt                          Columbia University
January 15, 2002
Expires: July, 2002


    CPL: A Language for User Control of Internet Telephony Services

STATUS OF THIS MEMO

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress".

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   To view the list Internet-Draft Shadow Directories, see
   http://www.ietf.org/shadow.html.


Abstract

   The Call Processing Language (CPL) is a language that can be used to
   describe and control Internet telephony services. It is designed to
   be implementable on either network servers or user agent servers. 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.

   This document is a product of the IP Telephony (IPTEL) working group
   of the Internet Engineering Task Force. Comments are solicited and
   should be addressed to the working group's mailing list at
   iptel@lists.research.bell-labs.com and/or the authors.





Lennox/Schulzrinne                                            [Page 1]

                           Table of Contents



   1          Introduction ........................................    4
   1.1        Conventions of This Document ........................    4
   2          Structure of CPL Scripts ............................    4
   2.1        High-level Structure ................................    5
   2.2        Abstract Structure of a Call Processing Action ......    5
   2.3        Location Model ......................................    6
   2.4        XML Structure .......................................    6
   3          Document Information ................................    7
   3.1        CPL Document Identifiers for XML ....................    7
   3.2        MIME Registration ...................................    8
   4          Script Structure: Overview ..........................    9
   5          Switches ............................................   10
   5.1        Address Switches ....................................   11
   5.1.1      Usage of "address-switch" with SIP ..................   13
   5.2        String Switches .....................................   14
   5.2.1      Usage of "string-switch" with SIP ...................   15
   5.3        Language Switches ...................................   15
   5.3.1      Usage of "language-switch" with SIP .................   16
   5.4        Time Switches .......................................   16
   5.4.1      iCalendar differences and implementation issues .....   22
   5.5        Priority Switches ...................................   23
   5.5.1      Usage of "priority-switch" with SIP .................   24
   6          Location Modifiers ..................................   24
   6.1        Explicit Location ...................................   25
   6.1.1      Usage of "location" with SIP ........................   26
   6.2        Location Lookup .....................................   26
   6.2.1      Usage of "lookup" with SIP ..........................   28
   6.3        Location Removal ....................................   28
   6.3.1      Usage of "remove-location" with SIP .................   29
   7          Signalling Operations ...............................   29
   7.1        Proxy ...............................................   29
   7.1.1      Usage of "proxy" with SIP ...........................   32
   7.2        Redirect ............................................   32
   7.2.1      Usage of "redirect" with SIP ........................   32
   7.3        Reject ..............................................   33
   7.3.1      Usage of "reject" with SIP ..........................   33
   8          Non-signalling Operations ...........................   34
   8.1        Mail ................................................   34
   8.1.1      Suggested Content of Mailed Information .............   35
   8.2        Log .................................................   35
   9          Subactions ..........................................   36



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   10         Ancillary Information ...............................   37
   11         Default Behavior ....................................   38
   12         CPL Extensions ......................................   39
   13         Examples ............................................   40
   13.1       Example: Call Redirect Unconditional ................   40
   13.2       Example: Call Forward Busy/No Answer ................   40
   13.3       Example: Call Forward: Redirect and Default .........   40
   13.4       Example: Call Screening .............................   42
   13.5       Example: Priority and Language Routing ..............   42
   13.6       Example: Outgoing Call Screening ....................   42
   13.7       Example: Time-of-day Routing ........................   43
   13.8       Example: Location Filtering .........................   44
   13.9       Example: Non-signalling Operations ..................   44
   13.10      Example: Hypothetical Extensions ....................   45
   13.11      Example: A Complex Example ..........................   45
   14         Security Considerations .............................   48
   15         IANA Considerations .................................   49
   16         Acknowledgments .....................................   49
   A          An Algorithm for Resolving Time Switches ............   49
   B          Suggested Usage of CPL with H.323 ...................   51
   B.1        Usage of "address-switch" with H.323 ................   51
   B.2        Usage of "string-switch" with H.323 .................   53
   B.3        Usage of "language-switch" with H.323 ...............   53
   B.4        Usage of "priority-switch" with H.323 ...............   53
   B.5        Usage of "location" with H.323 ......................   53
   B.6        Usage of "lookup" with H.323 ........................   53
   B.7        Usage of "remove-location" with H.323 ...............   54
   C          The XML DTD for CPL .................................   54
   D          Changes from Earlier Versions .......................   60
   D.1        Changes from Draft -05 ..............................   60
   D.2        Changes from Draft -04 ..............................   61
   D.3        Changes from Draft -03 ..............................   62
   D.4        Changes from Draft -02 ..............................   62
   D.5        Changes from Draft -01 ..............................   63
   D.6        Changes from Draft -00 ..............................   65
   E          Authors' Addresses ..................................   66
   F          Bibliography ........................................   66














Lennox/Schulzrinne                                            [Page 3]

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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 SIP [1] and H.323 [2].

   The 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 describing
   Internet telephony services. The language is not Turing-complete, and
   provides no way to write loops or recursion.

   The CPL is also designed to be easily created and edited by graphical
   tools.  It is based on XML [3], so parsing it is easy and many
   parsers for it are publicly available. 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 scripts' validity at the time they
   are delivered to it, rather that discovering them while a call is
   being processed.

   Implementations of the 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"
   [4].

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 RFC 2119 [5] and
   indicate requirement levels for compliant CPL implementations.


        Some paragraphs are indented, like this; they give
        motivations of design choices, or questions for future
        discussion in the development of the CPL, and are not
        essential to the specification of the language.

2 Structure of CPL Scripts



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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 action names 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. Subactions are actions which can be
   called from other actions. The CPL forbids subactions from being
   called recursively:  see Section 9.

   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, which describe operations that can be performed or decisions
   which 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; the 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



Lennox/Schulzrinne                                            [Page 5]

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   server. For further details on this, see Section 11.




          _________________      ___________________      ________  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 the function
   of a 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 6.

   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



Lennox/Schulzrinne                                            [Page 6]

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   Syntactically, CPL scripts are represented by XML documents. XML is
   thoroughly specified by [3], and implementors of this specification
   should be familiar with that document, but 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 [6], as both languages are simplifications of the earlier and
   larger standard SGML [7].

   See Figure 2 for the XML document corresponding to the graphical
   representation of the CPL script in Figure 1. Both nodes and outputs
   in the 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 6.1, 6.3, 8.1, and
   8.2).

   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 9.

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


3 Document Information

   This section gives information describing how CPL scripts are
   identified.

3.1 CPL Document Identifiers for XML

   A CPL script list which appears as a top-level XML document is
   identified with the formal public identifier "-//IETF//DTD RFCxxxx
   CPL 1.0//EN".

   A CPL embedded as a fragment within another XML document is
   identified with the XML namespace identifier "http://www.rfc-
   editor.org/rfc/rfcxxxx.txt".




Lennox/Schulzrinne                                            [Page 7]

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   <?xml version="1.0" ?>
   <!DOCTYPE cpl PUBLIC "-//IETF//DTD RFCxxxx CPL 1.0//EN" "cpl.dtd">

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


   Figure 2: Sample CPL Script: XML Version


        [Note to RFC editor: please replace "xxxx" above with the
        number of this RFC.]


        Note that the URIs specifying XML namespaces are only
        globally unique names; they do not have to reference any
        particular actual object.  The URI of a canonical source of
        this specification meets the requirement of being globally
        unique, and is also useful to document the format.

3.2 MIME Registration

   As an XML type, CPL's MIME registration conforms with "XML Media
   Types," RFC 3023 [8].




Lennox/Schulzrinne                                            [Page 8]

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        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 14, 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.

        Applications which use this media type: None publicly released
             at this time, as far as the authors are aware.

        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>
             Henning Schulzrinne <hgs@cs.columbia.edu>

        Intended usage: COMMON

        Author/Change Controller: The IETF.

4 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.





Lennox/Schulzrinne                                            [Page 9]

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           Tag:  "cpl"
    Parameters:  None
      Sub-tags:  "ancillary"  See Section 10
                 "subaction"  See Section 9
                 "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 sub-actions,
   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.

5 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 to execute if the condition was 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".)
   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 11 for more
   information on this.

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



Lennox/Schulzrinne                                           [Page 10]

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   output.


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

5.1 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" only)


   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 what 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 5.1.1; the subfield "alias-type" is
   defined for H.323 in Appendix B.1.)  If no subfield is specified, the
   "entire" address is matched; the precise meaning of this is defined
   for each underlying signalling protocol. Servers MAY define
   additional subfield values.



Lennox/Schulzrinne                                           [Page 11]

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   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 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 [9] 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.

             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. This subfield is not case sensitive, and
             may be absent.

        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. This subfield may be absent; however,
             for address types with default ports, an absent port
             matches the default port number.

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

        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



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             described in Section 5.2. 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.

5.1.1 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.

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




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   For sip URLs, the "user", "host", and "port" subfields correspond to
   the "user," "host," and "port" elements of the URI syntax. The "tel"
   subfield is defined to be the "user" part of the URI, with visual
   separators stripped, if and only if the "user=phone" parameter is
   given to the URI. 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.

5.2 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



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



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

   Five fields are defined, listed below. The value of each of these
   fields, except as specified, 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
   Technical Report 15 [10]. Then, strings are compared using locale-
   insensitive caseless mapping, as specified in Unicode Technical
   Report 21 [11].


        Code to perform the first step, in Java and Perl, is
        available; see the links from Annex E of UTR 15 [10]. 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 tags of string matching are named "string", and have a
   mandatory argument, one of "is" or "contains", indicating whole-
   string match or substring match, respectively.

5.2.1 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.

5.3 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.



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   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" outputs take one parameter, "matches". The value of
   one of these parameters is a language-tag, as defined in RFC 3066
   [12]. 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.

5.3.1 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.

5.4 Time Switches



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   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 (one of "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 [13].


        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



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   obsolete RFC 2445, any changes or clarifications those documents make
   to recurrence handling apply to CPL time-switches as well.

   An algorithm to 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 Olson Time Zone database [14]. 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.




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   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
   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 [13]. 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 [15].

   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 periods intervals are
   constructed as recurrences. A recurrence is specified by including
   the "freq" parameter, which indicates the type of recurrence rule. No
   parameters other than "dtstart", "dtend", and "duration" SHOULD 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 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 an 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; "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 [15]. 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 Thursday is January 1 or if it is a leap year and
        Wednesday is January 1.

   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 [15].

   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 (ie, 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



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   order:  "bymonth", "byweekno", "byyearday", "bymonthday", "byday",
   "byhour", "byminute", "bysecond" and "bysetpos"; then "count" and
   "until" are evaluated.

   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 9) 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.

5.4.1 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 [13],
   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 the CPL, whether



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   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.

   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.

5.5 Priority Switches




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   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.


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

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


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



   Priority switches take no parameters.

   The "priority" tags take one of the three parameters "greater",
   "less", and "equal". The values of these tags 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 header 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.

5.5.1 Usage of "priority-switch" with SIP

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

6 Location Modifiers

   The abstract location model of the CPL is described in Section 2.3.
   The behavior of several of the signalling operations (defined in



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   Section 7) is dependent on the current location set specified.
   Location nodes add or remove locations from the location set.

   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.

6.1 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



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   do not have explicit output tags; the <location> tag directly
   contains another node.

6.1.1 Usage of "location" with SIP

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

6.2 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
                "use"       Caller preferences fields to use
                "ignore"    Caller preferences fields to ignore
                "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 four 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 [16]).



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   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.

   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 four 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.

   The other two optional parameters affect the interworking of the CPL
   script with caller preferences and caller capabilities.  By default,
   a CPL server SHOULD invoke the appropriate caller preferences
   filtering of the underlying signalling protocol, if the corresponding
   information is available. The two parameters "use" and "ignore" allow
   the script to modify how the script applies caller preferences
   filtering. The specific meaning of the values of these parameters is
   signalling-protocol dependent; see Section 6.2.1 for SIP and Appendix
   B.6 for H.323.

   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 specified timeout was exceeded. If a given output is
   not present, script execution terminates and the default behavior is
   performed.

   Clients SHOULD specify the three outputs "success", "notfound", and
   "failure" in that order, so their script complies with the DTD given
   in Appendix C, but servers MAY accept them in any order.




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6.2.1 Usage of "lookup" with SIP

   Caller preferences for SIP are defined in "SIP Caller Preferences and
   Callee Capabilities" [17]. By default, a CPL server SHOULD honor any
   "Accept-Contact" and "Reject-Contact" headers of the original call
   request, as specified in that document. The two parameters "use" and
   "ignore" allow the script to modify the data input to the caller
   preferences algorithm. These parameters both take as their arguments
   comma-separated lists of caller preferences parameters. If "use" is
   given, the server applies the caller preferences resolution algorithm
   only to those preference parameters given in the "use" parameter, and
   ignores all others; if the "ignore" parameter is given, the server
   ignores the specified parameters, and uses all the others. Only one
   of "use" and "ignore" can be specified.

   The addr-spec part of the caller preferences is always applied, and
   the script cannot modify it.

   If a SIP server does not support caller preferences and callee
   capabilities, if the call request does not contain any preferences,
   or if the callee's registrations do not contain any capabilities, the
   "use" and "ignore" parameters are ignored.

6.3 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
                "param"            Caller preference parameters to apply
                "value"            Value of caller preference parameters


   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 13.8.



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   The "remove-location" node has three optional parameters. The
   parameter "location" gives the URL (or a signalling-protocol-
   dependent URL pattern) of location or locations to be removed from
   the set. If this parameter is not given, all locations, subject to
   the constraints of the other parameters, are removed from the set.

   If param and value are present, their values are comma-separated
   lists of caller preferences parameters and corresponding values,
   respectively. The nth entry in the param list matches the nth entry
   in the value list. There MUST be the same number of parameters as
   values specified.  The meaning of these parameters is signalling-
   protocol dependent.

   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.

6.3.1 Usage of "remove-location" with SIP

   For SIP-based CPL servers, the "remove-location" node has the same
   effect on the location set as a "Reject-Contact" header in caller
   preferences [17]. The value of the "location" parameter is treated as
   though it were the addr-spec field of a Reject-Contact header; thus,
   an absent header is equivalent to an addr-spec of "*" in that
   specification. The "param" and "value" parameters are treated as
   though they appeared in the params field of a Reject-Location header,
   as "; param=value" for each one.

   If the CPL server does not support caller preferences and callee
   capabilities, or if the callee did not supply any preferences, the
   "param" and "value" parameters are ignored.

7 Signalling Operations

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

7.1 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



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   execution terminates and the server returns to its default behavior
   (normally, to forward the best response upstream to the originator).


        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



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   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.

7.1.1 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 to
             the call request.

        "redirection" A 3xx response was the best response received to
             the call request.

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

        "no-answer" No final response was received to the call request
             before the timeout expired.

   SIP servers SHOULD honor the "q" parameter of SIP registrations and
   the output of the caller preferences lookup algorithm when
   determining location priority.

7.2 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.


   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."

7.2.1 Usage of "redirect" with SIP

   The SIP server SHOULD send a 3xx class response to a call request



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             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


   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".

7.3 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



   This immediately terminates execution of the 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", and "error", or a signalling-protocol-defined
   status.

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

7.3.1 Usage of "reject" with SIP

   Servers which implement SIP SHOULD also allow the "status" field to



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   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

        "reject": 603 Decline

        "error": 500 Internal Server Error

8 Non-signalling Operations

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

8.1 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



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        <mail
        url="mailto:jones@example.com?subject=lookup%20failed" />.

   Mail nodes have 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 [3]).

8.1.1 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.

8.2 Log

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




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               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,
   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.

9 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.


   Subactions are defined through "subaction" tags. These tags are
   placed in the CPL after any ancillary information (see Section 10)
   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.



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               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 called from "sub" tags. The "sub" tag is a "pseudo-
   node": it 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; control
   instead passes to the subaction.

   References to subactions MUST refer to subactions defined before the
   current action. A "sub" tag MUST NOT refer to the action which 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 which 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 [18]. Ensuring termination in the presence of
        external links is a difficult problem.

10 Ancillary Information

   No ancillary information is defined in the base CPL specification. If
   ancillary information, not part of any operation, is found to be



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   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



11 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 "notfound"
             rejection.




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        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.

12 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; mid-call or
   end-of-call controls; and the parts of iCalendar COS recurrence rules
   omitted from time switches.

   CPL extensions are indicated by XML namespaces [19]. Every extension
   MUST have an appropriate XML namespace assigned to it. 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 "http://www.rfc-
   editor.org/rfc/rfcxxxx.txt".

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

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


        A syntax such as







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        <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 [20], was that
        this added excessive complexity to languages. The
        "extension-switch" tag could, of course, itself be defined
        in a CPL extension.


        It is unfortunately true that XML DTDs, such as the CPL DTD
        given in Appendix C, are not powerful enough to encompass
        namespaces, since the base XML specification (which defines
        DTDs) predates the XML namespace specification. XML schemas
        [21] are a work in progress to define a namespace-aware
        method for validating XML documents, as well as improving
        upon DTDs' expressive power in many other ways.

13 Examples

13.1 Example: Call Redirect Unconditional

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


13.2 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.


13.3 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



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   <?xml version="1.0" ?>
   <!DOCTYPE cpl PUBLIC "-//IETF//DTD RFCxxxx CPL 1.0//EN" "cpl.dtd">

   <cpl>
     <incoming>
       <location url="sip:smith@phone.example.com">
        <redirect />
       </location>
     </incoming>
   </cpl>


   Figure 19: Example Script: Call Redirect Unconditional



   <?xml version="1.0" ?>
   <!DOCTYPE cpl PUBLIC "-//IETF//DTD RFCxxxx CPL 1.0//EN" "cpl.dtd">

   <cpl>
     <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


   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.



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   <?xml version="1.0" ?>
   <!DOCTYPE cpl PUBLIC "-//IETF//DTD RFCxxxx CPL 1.0//EN" "cpl.dtd">

   <cpl>
     <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



13.4 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 did 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.


13.5 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.


13.6 Example: Outgoing Call Screening



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   <?xml version="1.0" ?>
   <!DOCTYPE cpl PUBLIC "-//IETF//DTD RFCxxxx CPL 1.0//EN" "cpl.dtd">

   <cpl>
     <incoming>
       <address-switch field="origin" subfield="user">
         <address is="anonymous">
            <reject status="reject"
                    reason="I don't accept anonymous calls" />
         </address>
       </address-switch>
     </incoming>
   </cpl>


   Figure 22: Example Script: 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" ?>
   <!DOCTYPE cpl PUBLIC "-//IETF//DTD RFCxxxx CPL 1.0//EN" "cpl.dtd">

   <cpl>
     <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



13.7 Example: Time-of-day Routing

   Figure 25 illustrates time-based conditions and timezones.





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   <?xml version="1.0" ?>
   <!DOCTYPE cpl PUBLIC "-//IETF//DTD RFCxxxx CPL 1.0//EN" "cpl.dtd">

   <cpl>
     <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


13.8 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 assume, first, that the value of its
   "feature" parameter in caller preferences is known to be unreliable,
   so we ignore it; we also 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 these two operations have been
   completed, call setup is allowed to proceed normally.


13.9 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



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   <?xml version="1.0" ?>
   <!DOCTYPE cpl PUBLIC "-//IETF//DTD RFCxxxx CPL 1.0//EN" "cpl.dtd">

   <cpl>
     <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


   of out-of-band notification of error conditions, as the user might
   otherwise be unaware of any problem.


13.10 Example: Hypothetical Extensions

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


   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. In this
   example, the global namespace is not specified.


13.11 Example: A Complex Example



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   <?xml version="1.0" ?>
   <!DOCTYPE cpl PUBLIC "-//IETF//DTD RFCxxxx CPL 1.0//EN" "cpl.dtd">

   <cpl>
     <incoming>
       <string-switch field="user-agent">
         <string is="Inadequate Software SIP User Agent/0.9beta2">
           <lookup source="registration" ignore="feature">
              <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



   <?xml version="1.0" ?>
   <!DOCTYPE cpl PUBLIC "-//IETF//DTD RFCxxxx CPL 1.0//EN" "cpl.dtd">

   <cpl>
     <incoming>
       <lookup
          source="http://www.example.com/cgi-bin/locate.cgi?user=jones"
          timeout="8">
         <success>
           <proxy />
         </success>
         <failure>
           <mail url="mailto:jones@example.com?subject=lookup%20failed" />
         </failure>
       </lookup>
     </incoming>
   </cpl>


   Figure 27: Example Script: Non-signalling Operations






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   <?xml version="1.0" ?>
   <!DOCTYPE cpl PUBLIC "-//IETF//DTD RFCxxxx CPL 1.0//EN" "cpl.dtd">

   <cpl xmlns="http://www.rfc-editor.org/rfc/rfcXXXX.txt"
        xmlns:dr="http://www.example.com/distinctive-ring">
     <incoming>
       <address-switch field="origin">
         <address is="sip:boss@example.com">
            <dr:ring ringstyle="warble" />
         </address>
       </address-switch>
     </incoming>
   </cpl>


   Figure 28: Example Script: Hypothetical Distinctive-Ringing Extension



   <?xml version="1.0" ?>
   <!DOCTYPE cpl PUBLIC "-//IETF//DTD RFCxxxx CPL 1.0//EN" "cpl.dtd">

   <cpl>
     <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


   Finally, Figure 30 is a complex example which shows the sort of
   sophisticated behavior which 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.





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   <?xml version="1.0" ?>
   <!DOCTYPE cpl PUBLIC "-//IETF//DTD RFCxxxx CPL 1.0//EN" "cpl.dtd">

   <cpl>
     <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


14 Security Considerations

   The 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



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   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.

15 IANA Considerations

   This document registers the MIME type application/cpl+xml. See
   Section 3.2.

16 Acknowledgments

   This document was reviewed and commented upon by 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 [13], 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 [20], 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.

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 5.4.1 has been done, it operates in
   constant time. Open-source Java code implementing this algorithm is
   available on the world wide web at
   <http://www.cs.columbia.edu/~lennox/Cal-Code/>

   This algorithm is believed to be correct, but this section is non-
   normative. Section 5.4, and RFC 2445 [13], are the definitive
   definitions of recurrences.



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        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.

        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.



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        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 [2].  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 5.1. 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 [22] information element "Calling party
   number." If both fields are present, or if multiple aliases 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."

   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.




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   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 5.1.1 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 5.1.1.

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

   H.323 version 4 [2] defines an "h323" URI scheme.  This appendix
   defines a mapping for these URIs onto the CPL "address-switch"
   subfields, as given in Section 5.1.  This definition is also
   available as RFC YYYY [23], which is an excerpt from the H.323
   specification. [Note to RFC Editor: "RFC YYYY" indicates the
   publication as an RFC of draft-levin-iptel-h323-url-scheme-04, which
   is currently in the RFC Editor's Queue.]

   For h323 URIs, the 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.




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   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 5.2) 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 [22] 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 5.5).

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

   Locations in explicit location nodes (Section 6.1) 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 12).

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

   For location lookup nodes (Section 6.2), the "registration" lookup
   source corresponds to the locations registered with the server using
   "RAS" messages.




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   As H.323 currently has no counterpart of SIP caller preferences and
   callee capabilities, the "use" and "ignore" parameters of the
   "lookup" node are ignored.

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

   For location removal nodes (Section 6.3), only literal URLs can be
   removed. No URL patterns are defined.

   As H.323 currently has no counterpart of SIP caller preferences and
   callee capabilities, the "param" and "value" parameters of the
   "remove-location" node are ignored.

C The XML DTD for CPL

   This section includes a full DTD describing the XML syntax of the
   CPL.  Every script submitted to a CPL server SHOULD comply with this
   DTD.  However, CPL servers MAY allow minor variations from it,
   particularly in the ordering of the outputs of nodes. Note that
   compliance with this DTD is not a sufficient condition for
   correctness of a CPL script, as many of the conditions described in
   this specification are not expressible in DTD syntax.





























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   <?xml version="1.0" encoding="US-ASCII" ?>

   <!-- Nodes. -->
   <!-- Switch nodes -->
   <!ENTITY % Switch 'address-switch|string-switch|language-switch|
                      time-switch|priority-switch' >

   <!-- Location nodes -->
   <!ENTITY % Location 'location|lookup|remove-location' >

   <!-- Signalling action nodes -->
   <!ENTITY % SignallingAction 'proxy|redirect|reject' >

   <!-- Other actions -->
   <!ENTITY % OtherAction 'mail|log' >

   <!-- Links to subactions -->
   <!ENTITY % Sub 'sub' >

   <!-- Nodes are one of the above four categories, or a subaction.
        This entity (macro) describes the contents of an output.
        Note that a node can be empty, implying default action. -->
   <!ENTITY % Node     '(%Location;|%Switch;|%SignallingAction;|
                        %OtherAction;|%Sub;)?' >


   <!-- Switches: choices a CPL script can make. -->

   <!-- All switches can have an 'otherwise' output. -->
   <!ELEMENT otherwise ( %Node; ) >

   <!-- All switches can have a 'not-present' output. -->
   <!ELEMENT not-present ( %Node; ) >

   <!-- Address-switch makes choices based on addresses. -->
   <!ELEMENT address-switch ( address*, (not-present, address*)?,
                              otherwise? ) >
   <!-- <not-present> must appear at most once -->
   <!ATTLIST address-switch
      field         CDATA    #REQUIRED
      subfield      CDATA    #IMPLIED
   >

   <!ELEMENT address ( %Node; ) >

   <!ATTLIST address
      is            CDATA    #IMPLIED



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      contains      CDATA    #IMPLIED
      subdomain-of  CDATA    #IMPLIED
   > <!-- Exactly one of these three attributes must appear -->


   <!-- String-switch makes choices based on strings. -->

   <!ELEMENT string-switch ( string*, (not-present, string*)?,
                             otherwise? ) >
   <!-- <not-present> must appear at most once -->
   <!ATTLIST string-switch
      field         CDATA    #REQUIRED
   >

   <!ELEMENT string ( %Node; ) >
   <!ATTLIST string
      is            CDATA    #IMPLIED
      contains      CDATA    #IMPLIED
   >  <!-- Exactly one of these two attributes must appear -->


   <!-- Language-switch makes choices based on the originator's preferred
        languages. -->

   <!ELEMENT language-switch ( language*, (not-present, language*)?,
                               otherwise? ) >
   <!-- <not-present> must appear at most once -->

   <!ELEMENT language ( %Node; ) >
   <!ATTLIST language
      matches      CDATA     #REQUIRED
   >


   <!-- Time-switch makes choices based on the current time. -->

   <!ELEMENT time-switch ( time*, (not-present, time*)?, otherwise? ) >
   <!ATTLIST time-switch
      tzid          CDATA    #IMPLIED
      tzurl         CDATA    #IMPLIED
   >

   <!ELEMENT time ( %Node; ) >

   <!-- Exactly one of the two attributes "dtend" and "duration"
        must occur. -->
   <!-- The value of "freq" is (daily|weekly|monthly|yearly).  It is
           case-insensitive, so it is not given as a DTD switch. -->



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   <!-- None of the attributes following freq are meaningful unless freq
            appears. -->
   <!-- The value of "wkst" is (MO|TU|WE|TH|FR|SA|SU).  It is
           case-insensitive, so it is not given as a DTD switch. -->
   <!ATTLIST time
      dtstart       CDATA  #REQUIRED
      dtend         CDATA  #IMPLIED
      duration      CDATA  #IMPLIED
      freq          CDATA  #IMPLIED
      until         CDATA  #IMPLIED
      count         CDATA  #IMPLIED
      interval      CDATA  "1"
      bysecond      CDATA  #IMPLIED
      byminute      CDATA  #IMPLIED
      byhour        CDATA  #IMPLIED
      byday         CDATA  #IMPLIED
      bymonthday    CDATA  #IMPLIED
      byyearday     CDATA  #IMPLIED
      byweekno      CDATA  #IMPLIED
      bymonth       CDATA  #IMPLIED
      wkst          CDATA  "MO"
      bysetpos      CDATA  #IMPLIED
   >


   <!-- Priority-switch makes choices based on message priority. -->

   <!ELEMENT priority-switch ( priority*, (not-present, priority*)?,
                               otherwise? ) >
   <!-- <not-present> must appear at most once -->

   <!ENTITY % PriorityVal '(emergency|urgent|normal|non-urgent)' >

   <!ELEMENT priority ( %Node; ) >

   <!-- Exactly one of these three attributes must appear -->
   <!ATTLIST priority
      less          %PriorityVal;  #IMPLIED
      greater       %PriorityVal;  #IMPLIED
      equal         CDATA          #IMPLIED
   >


   <!-- Locations: ways to specify the location a subsequent action
        (proxy, redirect) will attempt to contact. -->

   <!ENTITY % Clear  'clear (yes|no) "no"' >




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   <!ELEMENT location ( %Node; ) >
   <!ATTLIST location
      url           CDATA    #REQUIRED
      priority      CDATA    #IMPLIED
      %Clear;
   >
   <!-- priority is in the range  0.0 - 1.0.  Its default value SHOULD
         be 1.0 -->

   <!ELEMENT lookup ( success?,notfound?,failure? ) >
   <!ATTLIST lookup
     source         CDATA     #REQUIRED
     timeout        CDATA     "30"
     use            CDATA     #IMPLIED
     ignore         CDATA     #IMPLIED
     %Clear;
   >

   <!ELEMENT success  ( %Node; ) >
   <!ELEMENT notfound ( %Node; ) >
   <!ELEMENT failure ( %Node; ) >

   <!ELEMENT remove-location ( %Node; ) >
   <!ATTLIST remove-location
      param         CDATA    #IMPLIED
      value         CDATA    #IMPLIED
      location      CDATA    #IMPLIED
   >


   <!-- Signalling Actions: call-signalling actions the script can
        take. -->

   <!ELEMENT proxy ( busy?,noanswer?,redirection?,failure?,default? ) >

   <!-- The default value of timeout is "20" if the <noanswer> output
        exists. -->
   <!ATTLIST proxy
      timeout       CDATA    #IMPLIED
      recurse       (yes|no) "yes"
      ordering      (parallel|sequential|first-only) "parallel"
   >

   <!ELEMENT busy ( %Node; ) >
   <!ELEMENT noanswer ( %Node; ) >
   <!ELEMENT redirection ( %Node; ) >
   <!-- "failure" repeats from lookup, above. -->
   <!ELEMENT default ( %Node; ) >



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   <!ELEMENT redirect EMPTY >
   <!ATTLIST redirect
      permanent     (yes|no) "no"
   >


   <!-- Statuses we can return -->

   <!ELEMENT reject EMPTY >
   <!-- The value of "status" is (busy|notfound|reject|error), or a SIP
        4xx-6xx status. -->
   <!ATTLIST reject
      status        CDATA    #REQUIRED
      reason        CDATA    #IMPLIED
   >

   <!-- Non-signalling actions: actions that don't affect the call -->

   <!ELEMENT mail ( %Node; ) >
   <!ATTLIST mail
      url           CDATA    #REQUIRED
   >

   <!ELEMENT log ( %Node; ) >
   <!ATTLIST log
      name          CDATA    #IMPLIED
      comment       CDATA    #IMPLIED
   >


   <!-- Calls to subactions. -->

   <!ELEMENT sub EMPTY >
   <!ATTLIST sub
      ref           IDREF    #REQUIRED
   >


   <!-- Ancillary data -->

   <!ENTITY % Ancillary 'ancillary?' >

   <!ELEMENT ancillary EMPTY >


   <!-- Subactions -->

   <!ENTITY % Subactions 'subaction*' >



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   <!ELEMENT subaction ( %Node; )>
   <!ATTLIST subaction
      id            ID       #REQUIRED
   >


   <!-- Top-level actions -->

   <!ENTITY % TopLevelActions 'outgoing?,incoming?' >

   <!ELEMENT outgoing ( %Node; )>

   <!ELEMENT incoming ( %Node; )>

   <!-- The top-level element of the script. -->

   <!ELEMENT cpl  ( %Ancillary;,%Subactions;,%TopLevelActions; ) >



D Changes from Earlier Versions


        [Note to RFC Editor: please remove this appendix before
        publication as an RFC.]

D.1 Changes from Draft -05

   The changebars in the Postscript and PDF versions of this document
   indicate significant changes from this version.

        o Clarified that switch nodes are allowed to be degenerate --
          they can have no outputs, and they can have only an
          "otherwise" output.

        o Clarified the (non-) usage of the special language-range "*".

        o Clarified that the Candidate Start Time can be equal to the
          call time.

        o Modified the DTD to require that the "not-present" output
          appear only once.

        o Added DTD entries for the "time-switch" attributes re-added in
          draft -05.

        o Updated the reference to ISO 8601 to cite 8601:2000.




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        o Updated all H.323 references to cite H.323v4.

        o Corrected some spelling errors.

D.2 Changes from Draft -04

        o Broke out language switches into their own switch node.

        o Restored the full iCalendar COS recurrence specification.
          Added text describing the consequences of this for
          implementors, and expanded somewhat on the recurrence
          algorithm.

        o Clarified when time zones are resolved.

        o Spelled out "iCalendar" rather than abbreviating it "iCal."

        o Clarified some points about host and port matching.

        o Whole-address matching in SIP uses the standard SIP URL-match
          rules.

        o Specified that proxy and lookup timeouts are positive integer
          number of seconds.

        o Specified that "subaction" "id" parameters must be unique.

        o Corrected example scripts' namespace and DTD references
          indicating older drafts of this document.

        o Deleted an unused subaction from the "Call Forward: Redirect
          and Default" example script.

        o Made empty switches legal in the DTD.

        o Made the legal values for the "proxy" "ordering" parameter
          explicit in the DTD.

        o Made the "success" output of "lookup" optional in the DTD. It
          can trigger a default action, just like anything else.

        o Clarified that the time-switch resolution algorithm is non-
          normative.

        o Updated references to previously-unpublished RFCs, now
          published.

        o Thanked Richard Gumpertz.



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D.3 Changes from Draft -03

        o Removed an obsolete reference to a usage in examples which
          wasn't actually used anywhere.

        o Added forward references to "remove-location", "mail" and
          "log", as well as "location", in the XML syntax as examples of
          nodes that don't have explicit output tags.

        o Made the usage of some terminology more consistent: "output"
          vs. "next node"; "action" vs. "operation" vs. "behavior";
          "sub-actions" and "subactions"; "other operations" and "non-
          call operations" and "non-signalling operations"; "meta-
          information" and "ancillary information."

        o The "tel" subfield of addresses which come from sip URIs
          should have its visual separators stripped.

        o The default value of the "priority" value of the "location"
          node is 1.0.

        o Corrected the media type of a set of URIs to text/uri-list,
          and added a reference to it.

        o Added some wording clarifying how URI-based lookup queries
          work.

        o Corrected the syntax of "duration" parameter in the examples.

        o Performed some pre-RFC textual cleanups (e.g. removing the
          reference to the Internet-Draft URL from the XML namespace
          identifier).

        o Re-worded text in the description of the Ancillary tag which
          implied that information could be placed in that node in the
          base CPL specification. Clarified that the tag is for use by
          extensions only.

        o Expunged some references to sub-daily recurrences which had
          accidentally been left in the text.

        o Updated bibliography to refer to the latest versions of the
          cited documents.

        o Fixed a number of typographical errors.

D.4 Changes from Draft -02




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        o Reduced time-switches from the full iCal recurrence to an iCal
          subset. Added an appendix giving an algorithm to resolve
          time-switches.

        o Added the extension mechanism.

        o Made explicit how each node is dependent on protocol handling.
          Separated out protocol-specific information -- for SIP in
          subsections of the main text, for H.323 in a non-normative
          appendix.

        o Clarified some address mapping rules for H.323.

        o Corrected the name of the "Redirecting number" in Q.931.

        o Clarified that address matching on the "password" subfield is
          case-sensitive.

        o Added a recommendation that TZID labels follow the usage of
          the Olson database.

        o Added the "priority" parameter to "location" nodes.

        o Added the "default" output to the "proxy" node.

        o Made the meaning of the "proxy" node's outputs explicit.

        o Added suggested content for the e-mail generated by "mail"
          nodes.

        o Pointed out that "&" must be escaped in XML (this is relevant
          for "mailto" URIs).

        o Pointed out that log names are logical names, and should not
          be interpreted as verbatim filenames.

        o Added some examples.

        o Clarified some wording.

        o Fixed some typographical errors.

D.5 Changes from Draft -01

        o Completely re-wrote changes to time switches: they are now
          based on iCal rather than on crontab.

        o Timezone references are now defined within time switches



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          rather than in the ancillary section. The ancillary section is
          now empty, but still defined for future use. To facilitate
          this, an explicit "ancillary" tag was added.

        o Added XML document type identifiers (the public identifier and
          the namespace), and MIME registration information.

        o Clarified that the "not-present" output can appear anywhere in
          a switch.

        o Re-wrote H.323 address mappings. Added the "alias-type"
          subfield for H.323 addresses.

        o Added the "language" and "display" string switch fields.

        o Clarified why useless "not-present" outputs can appear in time
          and priority switches.

        o Added the "clear" parameter to "location" and "lookup" nodes.
          (It had been in the DTD previously, but not in the text.)

        o Weakened support for non-validating scripts from SHOULD to
          MAY, to allow the use of validating XML parsers.

        o Added "redirection" output of "proxy" nodes.

        o Clarified some aspects of how proxy nodes handle the location
          set.

        o Added "permanent" parameter of "redirect" nodes.

        o Add example script for outgoing call screening (from Kenny
          Hom)

        o Updated example scripts to use the public identifier.

        o Add omitted tag to example script for call forward busy/no
          answer

        o Clarified in introduction that this document mainly deals with
          servers.

        o Updated reference to RFC 2824 now that it has been published.

        o Added explanatory text to the introduction to types of nodes.

        o Numerous minor clarifications and wording changes.




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        o Fixed copy-and-paste errors, typos.

D.6 Changes from Draft -00

        o Added high-level structure; script doesn't just start at a
          first action.

        o Added a section giving a high-level explanation of the
          location model.

        o Added informal syntax specifications for each tag so people
          don't have to try to understand a DTD to figure out the
          syntax.

        o Added subactions, replacing the old "link" tags. Links were
          far too reminiscent of gotos for everyone's taste.

        o Added ancillary information section, and timezone support.

        o Added not-present switch output.

        o Added address switches.

        o Made case-insensitive string matching locale-independent.

        o Added priority switch.

        o Deleted "Other switches" section. None seem to be needed.

        o Unified "url" and "source" parameters of "lookup".

        o Added caller prefs to "lookup".

        o Added location filtering.

        o Eliminated "clear" parameter of location setting. Instead,
          "proxy" "eats" locations it has used.

        o Added "recurse" and "ordering" parameters to "proxy".

        o Added default value of "timeout" for proxy.

        o Renamed "response" to "reject".

        o Changed "notify" to "mail", and simplified it.

        o Simplified "log", eliminating its "failure" output.




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        o Added description of default actions at various times during
          script processing.

        o Updated examples for these changes.

        o Updated DTD to reflect new syntax.

E Authors' Addresses

   Jonathan Lennox
   Dept. of Computer Science
   Columbia University
   1214 Amsterdam Avenue, MC 0401
   New York, NY 10027
   USA
   electronic mail: lennox@cs.columbia.edu

   Henning Schulzrinne
   Dept. of Computer Science
   Columbia University
   1214 Amsterdam Avenue, MC 0401
   New York, NY 10027
   USA
   electronic mail: schulzrinne@cs.columbia.edu

F Bibliography

   [1] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP:
   session initiation protocol," Request for Comments 2543, Internet
   Engineering Task Force, Mar. 1999.

   [2] International Telecommunication Union, "Packet based multimedia
   communication systems," Recommendation H.323, Telecommunication
   Standardization Sector of ITU, Geneva, Switzerland, Nov. 2000.

   [3] T. Bray, J. Paoli, and C. M. Sperberg-McQueen, "Extensible markup
   language (XML) 1.0 (second edition)," W3C Recommendation REC-xml-
   20001006, World Wide Web Consortium (W3C), Oct. 2000.  Available at
   http://www.w3.org/XML/.

   [4] J. Lennox and H. Schulzrinne, "Call processing language framework
   and requirements," Request for Comments 2824, Internet Engineering
   Task Force, May 2000.

   [5] S. Bradner, "Key words for use in RFCs to indicate requirement
   levels," Request for Comments 2119, Internet Engineering Task Force,
   Mar. 1997.




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

   [7] 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,
   Oct. 1986.

   [8] M. Murata, S. S. Laurent, and D. Kohn, "XML media types," Request
   for Comments 3023, Internet Engineering Task Force, Jan. 2001.

   [9] R. Hinden and S. Deering, "IP version 6 addressing architecture,"
   Request for Comments 2373, Internet Engineering Task Force, July
   1998.

   [10] M. Davis and M. Duerst, "Unicode normalization forms," Unicode
   Technical Report 15, Unicode Consortium, Aug. 2000.  Revision 19;
   part of Unicode 3.0.1. Available at
   http://www.unicode.org/unicode/reports/tr15/.

   [11] M. Davis, "Case mappings," Unicode Technical Report 21, Unicode
   Consortium, Oct. 2000.  Revision 4.3. Available at
   http://www.unicode.org/unicode/reports/tr21/.

   [12] H. Alvestrand, "Tags for the identification of languages,"
   Request for Comments 3066, Internet Engineering Task Force, Jan.
   2001.

   [13] F. Dawson and D. Stenerson, "Internet calendaring and scheduling
   core object specification (icalendar)," Request for Comments 2445,
   Internet Engineering Task Force, Nov. 1998.

   [14] P. Eggert, "Sources for time zone and daylight saving time
   data." Available at http://www.twinsun.com/tz/tz-link.htm.

   [15] 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,
   Dec. 2000.

   [16] M. Mealling and R. Daniel, "URI resolution services necessary
   for URN resolution," Request for Comments 2483, Internet Engineering
   Task Force, Jan. 1999.

   [17] H. Schulzrinne and J. Rosenberg, "SIP caller preferences and



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   callee capabilities," Internet Draft, Internet Engineering Task
   Force, Nov. 2001.  Work in progress.

   [18] S. DeRose, E. Maler, D. Orchard, and B. Trafford, "XML linking
   language (XLink) version 1.0," W3C Candidate Recommendation CR-
   xlink-20000703, World Wide Web Consortium (W3C), July 2000.
   Available at http://www.w3.org/TR/xlink/.

   [19] T. Bray, D. Hollander, and A. Layman, "Namespaces in XML," W3C
   Recommendation REC-xml-names-19900114, World Wide Web Consortium
   (W3C), Jan. 1999.  Available at http://www.w3.org/TR/REC-xml-names/.

   [20] T. Showalter, "Sieve: A mail filtering language," Request for
   Comments 3028, Internet Engineering Task Force, Jan. 2001.

   [21] D. C. Fallside, "XML schema part 0: Primer," W3C Candidate
   Recommendation CR-xmlschema-0-20001024, World Wide Web Consortium
   (W3C), Oct. 2000.  Available at http://www.w3.org/TR/xmlschema-0/.

   [22] 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,
   Telecommunication Standardization Sector of ITU, Geneva, Switzerland,
   Mar. 1993.

   [23] O. Levin, "H.323 URL scheme definition," Internet Draft,
   Internet Engineering Task Force, Nov. 2001.  Work in progress.


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   revoked by the Internet Society or its successors or assigns.

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