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Network Working Group                                          J. LennoxRequest for Comments: 3880                                         X. WuCategory: Standards Track                                 H. Schulzrinne                                                     Columbia University                                                            October 2004Call Processing Language (CPL):A Language for User Control of Internet Telephony ServicesStatus of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2004).Abstract   This document defines the Call Processing Language (CPL), a language   to describe and control Internet telephony services.  It is designed   to be implementable on either network servers or user agents.  It is   meant to be simple, extensible, easily edited by graphical clients,   and independent of operating system or signalling protocol.  It is   suitable for running on a server where users may not be allowed to   execute arbitrary programs, as it has no variables, loops, or ability   to run external programs.Lennox, et al.              Standards Track                     [Page 1]

RFC 3880                          CPL                       October 2004Table of Contents1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .31.1.   Conventions of This Document. . . . . . . . . . . . . .42.  Structure of CPL Scripts . . . . . . . . . . . . . . . . . . .42.1.   High-level Structure. . . . . . . . . . . . . . . . . .42.2.   Abstract Structure of a Call Processing Action. . . . .52.3.   Location Model. . . . . . . . . . . . . . . . . . . . .62.4.   XML Structure . . . . . . . . . . . . . . . . . . . . .63.  Script Structure: Overview . . . . . . . . . . . . . . . . . .74.  Switches . . . . . . . . . . . . . . . . . . . . . . . . . . .84.1.   Address Switches. . . . . . . . . . . . . . . . . . . .94.1.1.  Usage of "address-switch" with SIP. . . . . . .114.2.   String Switches . . . . . . . . . . . . . . . . . . . .124.2.1.  Usage of "string-switch" with SIP . . . . . . .134.3.   Language Switches . . . . . . . . . . . . . . . . . . .144.3.1.  Usage of "language-switch" with SIP . . . . . .144.4.   Time Switches . . . . . . . . . . . . . . . . . . . . .15              4.4.1.  iCalendar differences and implementation                      issues. . . . . . . . . . . . . . . . . . . . .204.5.   Priority Switches . . . . . . . . . . . . . . . . . . .214.5.1.  Usage of "priority-switch" with SIP . . . . . .225.  Location Modifiers . . . . . . . . . . . . . . . . . . . . . .225.1.   Explicit Location . . . . . . . . . . . . . . . . . . .235.1.1.  Usage of "location" with SIP. . . . . . . . . .235.2.   Location Lookup . . . . . . . . . . . . . . . . . . . .245.2.1.  Usage of "lookup" with SIP. . . . . . . . . . .255.3.   Location Removal. . . . . . . . . . . . . . . . . . . .255.3.1.  Usage of "remove-location" with SIP . . . . . .266.  Signalling Operations. . . . . . . . . . . . . . . . . . . . .266.1.   Proxy . . . . . . . . . . . . . . . . . . . . . . . . .266.1.1.  Usage of "proxy" with SIP . . . . . . . . . . .296.2.   Redirect. . . . . . . . . . . . . . . . . . . . . . . .296.2.1.  Usage of "redirect" with SIP. . . . . . . . . .306.3.   Reject. . . . . . . . . . . . . . . . . . . . . . . . .306.3.1.  Usage of "reject" with SIP. . . . . . . . . . .307.  Non-signalling Operations. . . . . . . . . . . . . . . . . . .317.1.   Mail. . . . . . . . . . . . . . . . . . . . . . . . . .317.1.1.  Suggested Content of Mailed Information . . . .327.2.   Log . . . . . . . . . . . . . . . . . . . . . . . . . .328.  Subactions . . . . . . . . . . . . . . . . . . . . . . . . . .339.  Ancillary Information. . . . . . . . . . . . . . . . . . . . .3410. Default Behavior . . . . . . . . . . . . . . . . . . . . . . .3511. CPL Extensions . . . . . . . . . . . . . . . . . . . . . . . .3512. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .3712.1.  Example: Call Redirect Unconditional. . . . . . . . . .3712.2.  Example: Call Forward Busy/No Answer. . . . . . . . . .3812.3.  Example: Call Forward: Redirect and Default . . . . . .39Lennox, et al.              Standards Track                     [Page 2]

RFC 3880                          CPL                       October 200412.4.  Example: Call Screening . . . . . . . . . . . . . . . .4012.5.  Example: Priority and Language Routing. . . . . . . . .4112.6.  Example: Outgoing Call Screening. . . . . . . . . . . .4212.7.  Example: Time-of-day Routing. . . . . . . . . . . . . .4312.8.  Example: Location Filtering . . . . . . . . . . . . . .4412.9.  Example: Non-signalling Operations. . . . . . . . . . .4512.10. Example: Hypothetical Extensions. . . . . . . . . . . .4612.11. Example: A Complex Example. . . . . . . . . . . . . . .4813. Security Considerations. . . . . . . . . . . . . . . . . . . .4914. IANA Considerations. . . . . . . . . . . . . . . . . . . . . .49       14.1.  URN Sub-Namespace Registration for              urn:ietf:params:xml:ns:cpl. . . . . . . . . . . . . . .4914.2.  Schema registration . . . . . . . . . . . . . . . . . .5014.3.  MIME Registration . . . . . . . . . . . . . . . . . . .5015. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . .51A.  An Algorithm for Resolving Time Switches . . . . . . . . . . .52B.  Suggested Usage of CPL with H.323. . . . . . . . . . . . . . .53B.1.   Usage of "address-switch" with H.323. . . . . . . . . .53B.2.   Usage of "string-switch" with H.323 . . . . . . . . . .55B.3.   Usage of "language-switch" with H.323 . . . . . . . . .55B.4.   Usage of "priority-switch" with H.323 . . . . . . . . .55B.5.   Usage of "location" with H.323. . . . . . . . . . . . .56B.6.   Usage of "lookup" with H.323. . . . . . . . . . . . . .56B.7.   Usage of "remove-location" with H.323 . . . . . . . . .56C.  The XML Schema for CPL . . . . . . . . . . . . . . . . . . . .56   Normative References . . . . . . . . . . . . . . . . . . . . . . .70   Informative References . . . . . . . . . . . . . . . . . . . . . .71   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .73   Full Copyright Statement . . . . . . . . . . . . . . . . . . . . .741.  Introduction   The Call Processing Language (CPL) is a language that can be used to   describe and control Internet telephony services.  It is not tied to   any particular signalling architecture or protocol; it is anticipated   that it will be used with both the Session Initiation Protocol (SIP)   [1] and H.323 [16].   CPL is powerful enough to describe a large number of services and   features, but it is limited in power so that it can run safely in   Internet telephony servers.  The intention is to make it impossible   for users to do anything more complex (and dangerous) than describe   Internet telephony services.  The language is not Turing-complete,   and provides no way to write loops or recursion.   CPL is also designed to be easily created and edited by graphical   tools.  It is based on the Extensible Markup Language (XML) [2], so   parsing it is easy and many parsers for it are publicly available.Lennox, et al.              Standards Track                     [Page 3]

RFC 3880                          CPL                       October 2004   The structure of the language maps closely to its behavior, so an   editor can understand any valid script, even ones written by hand.   The language is also designed so that a server can easily confirm the   validity of a script when the server receives it, rather than   discovering problems while a call is being processed.   Implementations of CPL are expected to take place both in Internet   telephony servers and in advanced clients; both can usefully process   and direct users' calls.  This document primarily addresses the usage   in servers.  A mechanism will be needed to transport scripts between   clients and servers; this document does not describe such a   mechanism, but related documents will.   The framework and requirements for the CPL architecture are described   inRFC 2824, "Call Processing Language Framework and Requirements"   [17].1.1.  Conventions of This Document   In this document, the key words "MUST", "MUST NOT", "REQUIRED",   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",   and "OPTIONAL" are to be interpreted as described inBCP 14,RFC 2119   [3] and indicate requirement levels for compliant CPL   implementations.      Some paragraphs are indented, like this; they give motivations of      design choices, advice to implementors, or thoughts on future      development of or extensions to CPL.  They are not essential to      the specification of the language, and are non-normative.2.  Structure of CPL Scripts2.1.  High-level Structure   A CPL script consists of two types of information: ancillary   information about the script, and call processing actions.   A call processing action is a structured tree that describes the   operations and decisions a telephony signalling server performs on a   call set-up event.  There are two types of call processing actions:   top-level actions and subactions.  Top-level actions are actions that   are triggered by signalling events that arrive at the server.  Two   top-level actions are defined: "incoming", the action performed when   a call arrives whose destination is the owner of the script, and   "outgoing", the action performed when a call arrives whose originator   is the owner of the script.Lennox, et al.              Standards Track                     [Page 4]

RFC 3880                          CPL                       October 2004   Subactions are actions which can be called from other actions.  CPL   forbids subactions from being called recursively: seeSection 8.   Ancillary information is information which is necessary for a server   to correctly process a script, but which does not directly describe   any operations or decisions.  Currently, no ancillary information is   defined, but the section is reserved for use by extensions.2.2.  Abstract Structure of a Call Processing Action   Abstractly, a call processing action is described by a collection of   nodes that describe operations that can be performed or decisions   that can be made.  A node may have several parameters, which specify   the precise behavior of the node; they usually also have outputs,   which depend on the result of the decision or action.   For a graphical representation of a CPL action, see Figure 1.  Nodes   and outputs can be thought of informally as boxes and arrows; CPL is   designed so that actions can be conveniently edited graphically using   this representation.  Nodes are arranged in a tree, starting at a   single root node; outputs of nodes are connected to additional nodes.   When an action is run, the action or decision described by the   action's top-level node is performed; based on the result of that   node, the server follows one of the node's outputs, and the   subsequent node it points to is performed; this process continues   until a node with no specified outputs is reached.  Because the graph   is acyclic, this will occur after a bounded and predictable number of   nodes are visited.   If an output to a node does not point to another node, it indicates   that the CPL server should perform a node- or protocol-specific   action.  Some nodes have specific default behavior associated with   them; for others, the default behavior is implicit in the underlying   signalling protocol, or can be configured by the administrator of the   server.  For further details on this, seeSection 10.Lennox, et al.              Standards Track                     [Page 5]

RFC 3880                          CPL                       October 2004        _________________      ___________________    ________  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 Version2.3.  Location Model   For flexibility, one piece of information necessary for CPL is not   given as node parameters: the set of locations to which a call is to   be directed.  Instead, this set of locations is stored as an implicit   global variable throughout the execution of a processing action (and   its subactions).  This allows locations to be retrieved from external   sources, filtered, and so forth, without requiring general language   support for such operations (which could harm the simplicity and   tractability of understanding the language).  The specific operations   which add, retrieve, or filter location sets are given inSection 5.   For the incoming top-level call processing action, the location set   is initialized to the empty set.  For the outgoing action, it is   initialized to the destination address of the call.2.4.  XML Structure   Syntactically, CPL scripts are represented by XML documents.  XML is   thoroughly specified by the XML specification [2], and implementors   of this specification should be familiar with that document.   However, as a brief overview, XML consists of a hierarchical   structure of tags; each tag can have a number of attributes.  It is   visually and structurally very similar to HTML [18], as both   languages are simplifications of the earlier and larger standard SGML   [19].Lennox, et al.              Standards Track                     [Page 6]

RFC 3880                          CPL                       October 2004   See Figure 2 for the XML document corresponding to the graphical   representation of the CPL script in Figure 1.  Both nodes and outputs   in CPL are represented by XML tags; parameters are represented by XML   tag attributes.  Typically, node tags contain output tags, and vice-   versa (with a few exceptions: see Sections5.1,5.3,7.1, and7.2).   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 inSection 8.   The higher-level structure of a CPL script is represented by tags   corresponding to each piece of ancillary information, subactions, and   top-level actions, in order.  This higher-level information is all   enclosed in a special tag "cpl", the outermost tag of the XML   document.   A complete XML Schema for CPL is provided inAppendix C.  The   remainder of the main sections of this document describe the   semantics of CPL, while giving its syntax informally.  For the formal   syntax, please see the appendix.3.  Script Structure: Overview   As mentioned, a CPL script consists of ancillary information,   subactions, and top-level actions.  The full syntax of the "cpl" node   is given in Figure 3.   <?xml version="1.0" encoding="UTF-8"?>   <cpl xmlns="urn:ietf:params:xml:ns:cpl"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">     <subaction>       <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>Lennox, et al.              Standards Track                     [Page 7]

RFC 3880                          CPL                       October 2004         </address>         <otherwise>           <sub ref="voicemail" />         </otherwise>       </address-switch>     </incoming>   </cpl>   Figure 2: Sample CPL Script: XML Version           Tag:  "cpl"    Parameters:  None      Sub-tags:  "ancillary"  SeeSection 9                 "subaction"  SeeSection 8                 "outgoing"   Top-level actions to take on this user's                              outgoing calls                 "incoming"   Top-level actions to take on this user's                              incoming calls   Figure 3: Syntax of the top-level "cpl" tag   Call processing actions, both top-level actions and subactions,   consist of a tree of nodes and outputs.  Nodes and outputs are both   described by XML tags.  There are four categories of CPL nodes:   switches, which represent choices a CPL script can make, location   modifiers, which add or remove locations from the location set,   signalling operations, which cause signalling events in the   underlying protocol, and non-signalling operations, which trigger   behavior which does not effect the underlying protocol.4.  Switches   Switches represent choices a CPL script can make, based on either   attributes of the original call request or items independent of the   call.   All switches are arranged as a list of conditions that can match a   variable.  Each condition corresponds to a node output; the output   points to the next node that should be executed if the condition is   true.  The conditions are tried in the order they are presented in   the script; the output corresponding to the first node to match is   taken.   There are two special switch outputs that apply to every switch type.   The output "not-present", which MAY occur anywhere in the list of   outputs, is true if the variable the switch was to match was not   present in the original call setup request.  (In this document, this   is sometimes described by saying that the information is "absent".)Lennox, et al.              Standards Track                     [Page 8]

RFC 3880                          CPL                       October 2004   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.  SeeSection 10 for   more information on this.   Switches MAY contain no outputs.  They MAY only contain an   "otherwise" output.      Such switches are not particularly useful, but might be created by      tools which automatically generate CPL scripts.4.1.  Address Switches   Address switches allow a CPL script to make decisions based on one of   the addresses present in the original call request.  They are   summarized in Figure 4.          Node:  "address-switch"       Outputs:  "address"         Specific addresses to match    Parameters:  "field"           "origin", "destination",                                   or "original-destination"                 "subfield"        "address-type", "user", "host",                                   "port", "tel", or "display"                                   (also: "password" and "alias-type")        Output:  "address"    Parameters:  "is"              Exact match                 "contains"        Substring match (for "display" only)                 "subdomain-of"    Sub-domain match (for "host", "tel")   Figure 4: Syntax of the "address-switch" node   Address switches have two node parameters: "field" and "subfield".   The mandatory "field" parameter allows the script to specify which   address is to be considered for the switch: either the call's origin   address (field "origin"), its current destination address (field   "destination"), or its original destination (field "original-   destination"), the destination the call had before any earlier   forwarding was invoked.  Servers MAY define additional field values.   The optional "subfield" specifies which part of the address is to be   considered.  The possible subfield values are: "address-type",   "user", "host", "port", "tel", and "display".  Additional subfield   values MAY be defined for protocol-specific values.  (The subfield   "password" is defined for SIP inSection 4.1.1; the subfield "alias-   type" is defined for H.323 inAppendix B.1.)  If no subfield isLennox, et al.              Standards Track                     [Page 9]

RFC 3880                          CPL                       October 2004   specified, the "entire" address is matched; the precise meaning of   this is defined for each underlying signalling protocol.  Servers MAY   define additional subfield values.   The subfields are defined as follows:      address-type: This indicates the type of the underlying address,            i.e., the URI scheme, if the address can be represented by a            URI.  The types specifically discussed by this document are            "sip", "tel", and "h323".  The address type is not case-            sensitive.  It has a value for all defined address types.      user: This subfield of the address indicates, for e-mail style            addresses, the user part of the address.  For a telephone            number style address, it includes the subscriber number.            This subfield is case-sensitive; it may be absent.      host: This subfield of the address indicates the Internet host            name or IP address corresponding to the address, in host            name, IPv4, or IPv6 [4] textual representation format.  Host            names are compared as strings.  IP addresses are compared            numerically.  (In particular, the presence or location of an            IPv6 :: omitted-zero-bits block is not significant for            matching purposes.)  Host names are never equal to IP            addresses -- no DNS resolution is performed.  IPv4 addresses            are never equal to IPv6 addresses, even if the IPv6 address            is a v4-in-v6 embedding.  This subfield is not case            sensitive, and may be absent.            For host names only, subdomain matching is supported with            the "subdomain-of" match operator.  The "subdomain-of"            operator ignores leading dots in the hostname or match            pattern, if any.      port: This subfield indicates the TCP or UDP port number of the            address, numerically, in decimal format.  It is not case            sensitive, as it MUST only contain decimal digits.  Leading            zeros are ignored.      tel:  This subfield indicates a telephone subscriber number, if            the address contains such a number.  It is not case            sensitive (telephone numbers may contain the symbols 'A',            'B', 'C', or 'D'), and may be absent.  It may be matched            using the "subdomain-of" match operator.  Punctuation and            separator characters in telephone numbers are discarded.Lennox, et al.              Standards Track                    [Page 10]

RFC 3880                          CPL                       October 2004      display: This subfield indicates a "display name" or user-visible            name corresponding to an address.  It is a Unicode string,            and is matched using the case-insensitive algorithm            described inSection 4.2.  The "contains" operator may be            applied to it.  It may be absent.   For any completely unknown subfield, the server MAY reject the script   at the time it is submitted with an indication of the problem; if a   script with an unknown subfield is executed, the server MUST consider   the "not-present" output to be the valid one.   The "address" output tag may take exactly one of three possible   parameters, indicating the kind of matching allowed.      is:   An output with this match operator is followed if the            subfield being matched in the "address-switch" exactly            matches the argument of the operator.  It may be used for            any subfield, or for the entire address if no subfield was            specified.      subdomain-of: This match operator applies only for the subfields            "host" and "tel".  In the former case, it matches if the            hostname being matched is a subdomain of the domain given in            the argument of the match operator; thus, subdomain-            of="example.com" would match the hostnames "example.com",            "research.example.com", and            "zaphod.sales.internal.example.com".  IP addresses may be            given as arguments to this operator; however, they only            match exactly.  In the case of the "tel" subfield, the            output matches if the telephone number being matched has a            prefix that matches the argument of the match operator;            subdomain-of="1212555" would match the telephone number "1            212 555 1212."      contains: This match operator applies only for the subfield            "display".  The output matches if the display name being            matched contains the argument of the match as a substring.4.1.1.  Usage of "address-switch" with SIP   For SIP, the "origin" address corresponds to the address in the   "From" header, "destination" corresponds to the "Request-URI", and   "original-destination" corresponds to the "To" header.   The "display" subfield of an address is the display-name part of the   address, if it is present.  Because of SIP's syntax, the   "destination" address field will never have a "display" subfield.Lennox, et al.              Standards Track                    [Page 11]

RFC 3880                          CPL                       October 2004   The "address-type" subfield of an address is the URI scheme of that   address.  Other address fields depend on that "address-type".   For SIP URIs, the "user", "host", and "port" subfields correspond to   the "user," "host," and "port" elements of the URI syntax.  (Note   that, following the definitions ofRFC 3261 [1], a SIP URI which does   not specify a port is not the same as an explicit port 5060; the   former is indicated by an absent port subfield.)  The "tel" subfield   is defined to be the "user" part of the URI, with visual separators   stripped, if the "user=phone" parameter is given to the URI, or if   the server is otherwise configured to recognize the user part as a   telephone number.  An additional subfield, "password", is defined to   correspond to the "password" element of the SIP URI, and is case-   sensitive.  However, use of this field is NOT RECOMMENDED for general   security reasons.   For tel URLs, the "tel" and "user" subfields are the subscriber name;   in the former case, visual separators are stripped.  The "host" and   "port" subfields are both not present.   For h323 URLs, subfields MAY be set according to the scheme described   inAppendix B.   For other URI schemes, only the "address-type" subfield is defined by   this specification; servers MAY set other pre-defined subfields, or   MAY support additional subfields.   If no subfield is specified for addresses in SIP messages, the string   matched is the URI part of the address.  For "is" matches, standard   SIP URI matching rules are used; for "contains" matches, the URI is   used verbatim.4.2.  String Switches   String switches allow a CPL script to make decisions based on free-   form strings present in a call request.  They are summarized in   Figure 5.               Node:  "string-switch"            Outputs:  "string"         Specific string to match         Parameters:  "field"          "subject", "organization",                                       "user-agent", or "display"             Output:  "string"         Parameters:  "is"             Exact match                      "contains"       Substring match   Figure 5: Syntax of the "string-switch" nodeLennox, et al.              Standards Track                    [Page 12]

RFC 3880                          CPL                       October 2004   String switches have one node parameter: "field".  The mandatory   "field" parameter specifies which string is to be matched.   String switches are dependent on the call signalling protocol being   used.   Four fields are defined and listed below.  The value of each of these   fields is a free-form Unicode string with no other structure defined.      subject: The subject of the call.      organization: The organization of the originator of the call.      user-agent: The name of the program or device with which the call            request was made.      display: Free-form text associated with the call, intended to be            displayed to the recipient, with no other semantics defined            by the signalling protocol.   Strings are matched as case-insensitive Unicode strings, in the   following manner.  First, strings are canonicalized to the   "Compatibility Composition" (KC) form, as specified in Unicode   Standard Annex #15 [5].  Then, strings are compared using locale-   insensitive caseless mapping, as specified in Unicode Standard Annex   #21 [6].      Code to perform the first step, in Java and Perl, is available;      see the links from Annex 5 of UAX 15 [5].  The case-insensitive      string comparison in the Java standard class libraries already      performs the second step; other Unicode-aware libraries should be      similar.   The output tag of string matching is named "string", and has a   mandatory argument, one of "is" or "contains", indicating whole-   string match or substring match, respectively.4.2.1.  Usage of "string-switch" with SIP   For SIP, the fields "subject", "organization", and "user-agent"   correspond to the SIP header fields with the same name.  These are   used verbatim as they appear in the message.   The field "display" is not used, and is never present.Lennox, et al.              Standards Track                    [Page 13]

RFC 3880                          CPL                       October 20044.3.  Language Switches   Language switches allow a CPL script to make decisions based on the   languages in which the originator of the call wishes to communicate.   They are summarized in Figure 6.            Node:  "language-switch"         Outputs:  "language"         Specific string to match      Parameters:  None          Output:  "language"      Parameters:  "matches"          Match if the given language                                      matches a language-range of the                                      call.      Figure 6: Syntax of the "language-switch" node   Language switches take no parameters.   The "language" output takes one parameter, "matches".  The value of   the parameter is a language-tag, as defined inRFC 3066 [7].  The   caller may have specified a set of language-ranges, also as defined   inRFC 3066.  The CPL server checks each language-tag specified by   the script against the language-ranges specified in the request.   SeeRFC 3066 for the details of how language-ranges match language-   tags.  Briefly, a language-range matches a language-tag if it exactly   equals the tag, or if it exactly equals a prefix of the tag such that   the first character following the prefix is "-".   If the caller specified the special language-range "*", it is ignored   for the purpose of matching.  Languages with a "q" value of 0 are   also ignored.   This switch MAY be not-present.4.3.1.  Usage of "language-switch" with SIP   The language-ranges for the "language-switch" switch are obtained   from the SIP "Accept-Language" header field.  The switch is not-   present if the initial SIP request did not contain this header field.      Note that because of CPL's first-match semantics in switches, "q"      values other than 0 of the "Accept-Language" header fields are      ignored.Lennox, et al.              Standards Track                    [Page 14]

RFC 3880                          CPL                       October 20044.4.  Time Switches   Time switches allow a CPL script to make decisions based on the time   and/or date the script is being executed.  They are summarized in   Figure 7.   Time switches are independent of the underlying signalling protocol.         Node:  "time-switch"      Outputs:  "time"         Specific time to match   Parameters:  "tzid"RFC 2445 Time Zone Identifier                "tzurl"RFC 2445 Time Zone URL       Output:  "time"   Parameters:  "dtstart"      Start of interval (RFC 2445 DATE-TIME)                "dtend"        End of interval (RFC 2445 DATE-TIME)                "duration"     Length of interval (RFC 2445 DURATION)                "freq"         Frequency of recurrence ("secondly",                               "minutely", "hourly", "daily",                               "weekly", "monthly", or "yearly")                "interval"     How often the recurrence repeats                "until"        Bound of recurrence (RFC 2445 DATE-TIME)                "count"        Number of occurrences of recurrence                "bysecond"     List of seconds within a minute                "byminute"     List of minutes within an hour                "byhour"       List of hours of the day                "byday"        List of days of the week                "bymonthday"   List of days of the month                "byyearday"    List of days of the year                "byweekno"     List of weeks of the year                "bymonth"      List of months of the year                "wkst"         First day of the work week                "bysetpos"     List of values within                               set of events specified   Figure 7: Syntax of the "time-switch" node   Time switches are based closely on the specification of recurring   intervals of time in the Internet Calendaring and Scheduling Core   Object Specification (iCalendar COS),RFC 2445 [8].      This allows CPL scripts to be generated automatically from      calendar books.  It also allows us to re-use the extensive      existing work specifying time intervals.   If future standards-track documents are published that update or   obsoleteRFC 2445, any changes or clarifications those documents make   to recurrence handling apply to CPL time-switches as well.Lennox, et al.              Standards Track                    [Page 15]

RFC 3880                          CPL                       October 2004   An algorithm to determine whether an instant falls within a given   recurrence is given inAppendix A.   The "time-switch" tag takes two optional parameters, "tzid" and   "tzurl", both of which are defined inRFC 2445 (Sections4.8.3.1 and   4.8.3.5 respectively).  The "tzid" is the identifying label by which   a time zone definition is referenced.  If it begins with a forward   slash (solidus), it references a to-be-defined global time zone   registry; otherwise it is locally-defined at the server.  The "tzurl"   gives a network location from which an up-to-date VTIMEZONE   definition for the timezone can be retrieved.   While "tzid" labels that do not begin with a forward slash are   locally defined, it is RECOMMENDED that servers support at least the   naming scheme used by the Olson Time Zone database [9].  Examples of   timezone databases that use the Olson scheme are the zoneinfo files   on most Unix-like systems, and the standard Java TimeZone class.   Servers SHOULD resolve "tzid" and "tzurl" references to time zone   definitions at the time the script is uploaded.  They MAY   periodically refresh these resolutions to obtain the most up-to-date   definition of a time zone.  If a "tzurl" becomes invalid, servers   SHOULD remember the most recent valid data retrieved from the URL.   If a script is uploaded with a "tzid" and "tzurl" which the CPL   server does not recognize or cannot resolve, it SHOULD diagnose and   reject this at script upload time.  If neither "tzid" nor "tzurl" are   present, all non-UTC times within this time switch should be   interpreted as being "floating" times, i.e., that they are specified   in the local timezone of the CPL server.      Because of daylight-savings-time changes over the course of a      year, it is necessary to specify time switches in a given      timezone.  UTC offsets are not sufficient, or a time-of-day      routing rule which held between 9 am and 5 pm in the eastern      United States would start holding between 8 am and 4 pm at the end      of October.   Authors of CPL servers should be careful to handle correctly the   intervals when local time is discontinuous, at the beginning or end   of daylight-savings time.  Note especially that some times may occur   more than once when clocks are set back.  The algorithm inAppendix A   is believed to handle this correctly.   Time nodes specify a list of periods during which their output should   be taken.  They have two required parameters: "dtstart", which   specifies the beginning of the first period of the list, and exactly   one of "dtend" or "duration", which specify the ending time or theLennox, et al.              Standards Track                    [Page 16]

RFC 3880                          CPL                       October 2004   duration of the period, respectively.  The "dtstart" and "dtend"   parameters are formatted as iCalendar COS DATE-TIME values, as   specified inSection 4.3.5 of RFC 2445 [8].  Because time zones are   specified in the top-level "time-switch" tag, only forms 1 or 2   (floating or UTC times) can be used.  The "duration" parameter is   given as an iCalendar COS DURATION parameter, as specified insection4.3.6 of RFC 2445.  Both the DATE-TIME and the DURATION syntaxes are   subsets of the corresponding syntaxes from ISO 8601 [20].   For a recurring interval, the "duration" parameter MUST be small   enough such that subsequent intervals do not overlap.  For non-   recurring intervals, durations of any positive length are permitted.   Zero-length and negative-length durations are not allowed.   If no other parameters are specified, a time node indicates only a   single period of time.  More complicated sets of period intervals are   constructed as recurrences.  A recurrence is specified by including   the "freq" parameter, which indicates the type of recurrence rule.   Parameters other than "dtstart", "dtend", and "duration" SHOULD NOT   be specified unless "freq" is present, though CPL servers SHOULD   accept scripts with such parameters present, and ignore the other   parameters.   The "freq" parameter takes one of the following values: "secondly",   to specify repeating periods based on an interval of a second or   more, "minutely", to specify repeating periods based on an interval   of a minute or more, "hourly", to specify repeating periods based on   an interval of an hour or more, "daily", to specify repeating periods   based on an interval of a day or more, "weekly", to specify repeating   periods based on an interval of a week or more, "monthly", to specify   repeating periods based on an interval of a month or more, and   "yearly", to specify repeating periods based on an interval of a year   or more.  These values are not case-sensitive.   The "interval" parameter contains a positive integer representing how   often the recurrence rule repeats.  The default value is "1", meaning   every second for a "secondly" rule, every minute for a "minutely"   rule, every hour for an "hourly" rule, every day for a "daily" rule,   every week for a "weekly" rule, every month for a "monthly" rule, and   every year for a "yearly" rule.   The "until" parameter defines an iCalendar COS DATE or DATE-TIME   value which bounds the recurrence rule in an inclusive manner.  If   the value specified by "until" is synchronized with the specified   recurrence, this date or date-time becomes the last instance of the   recurrence.  If specified as a date-time value, then it MUST beLennox, et al.              Standards Track                    [Page 17]

RFC 3880                          CPL                       October 2004   specified in UTC time format.  If not present, and the "count"   parameter is not also present, the recurrence is considered to repeat   forever.   The "count" parameter defines the number of occurrences at which to   range-bound the recurrence.  The "dtstart" parameter counts as the   first occurrence.  The "until" and "count" parameters MUST NOT occur   in the same "time" output.   The "bysecond" parameter specifies a comma-separated list of seconds   within a minute.  Valid values are 0 to 59.  The "byminute" parameter   specifies a comma-separated list of minutes within an hour.  Valid   values are 0 to 59.  The "byhour" parameter specifies a comma-   separated list of hours of the day.  Valid values are 0 to 23.   The "byday" parameter specifies a comma-separated list of days of the   week.  "MO" indicates Monday, "TU" indicates Tuesday, "WE" indicates   Wednesday, "TH" indicates Thursday, "FR" indicates Friday, "SA"   indicates Saturday, and "SU" indicates Sunday.  These values are not   case-sensitive.   Each "byday" value can also be preceded by a positive (+n) or   negative (-n) integer.  If present, this indicates the nth occurrence   of the specific day within the "monthly" or "yearly" recurrence.  For   example, within a "monthly" rule, +1MO (or simply 1MO) represents the   first Monday within the month, whereas -1MO represents the last   Monday of the month.  If an integer modifier is not present, it means   all days of this type within the specified frequency.  For example,   within a "monthly" rule, MO represents all Mondays within the month.   The "bymonthday" parameter specifies a comma-separated list of days   of the month.  Valid values are 1 to 31 or -31 to -1.  For example,   -10 represents the tenth to the last day of the month.   The "byyearday" parameter specifies a comma-separated list of days of   the year.  Valid values are 1 to 366 or -366 to -1.  For example, -1   represents the last day of the year (December 31st) and -306   represents the 306th to the last day of the year (March 1st).   The "byweekno" parameter specifies a comma-separated list of ordinals   specifying weeks of the year.  Valid values are 1 to 53 or -53 to -1.   This corresponds to weeks according to week numbering as defined in   ISO 8601 [20].  A week is defined as a seven day period, starting on   the day of the week defined to be the week start (see "wkst").  Week   number one of the calendar year is the first week which contains at   least four (4) days in that calendar year.  This parameter is only   valid for "yearly" rules.  For example, 3 represents the third week   of the year.Lennox, et al.              Standards Track                    [Page 18]

RFC 3880                          CPL                       October 2004      Note: Assuming a Monday week start, week 53 can only occur when      January 1 is a Thursday or, for leap years, if January 1 is a      Wednesday.   The "bymonth" parameter specifies a comma-separated list of months of   the year.  Valid values are 1 to 12.   The "wkst" parameter specifies the day on which the work week starts.   Valid values are "MO", "TU", "WE", "TH", "FR", "SA" and "SU".  This   is significant when a "weekly" recurrence has an interval greater   than 1, and a "byday" parameter is specified.  This is also   significant in a "yearly" recurrence when a "byweekno" parameter is   specified.  The default value is "MO", following ISO 8601 [20].   The "bysetpos" parameter specifies a comma-separated list of values   which corresponds to the nth occurrence within the set of events   specified by the rule.  Valid values are 1 to 366 or -366 to -1.  It   MUST only be used in conjunction with another byxxx parameter.  For   example, "the last work day of the month" could be represented as:      <time -timerange- freq="monthly" byday="MO,TU,WE,TH,FR"            bysetpos="-1">   Each "bysetpos" value can include a positive (+n) or negative (-n)   integer.  If present, this indicates the nth occurrence of the   specific occurrence within the set of events specified by the rule.   If byxxx parameter values are found which are beyond the available   scope (i.e., bymonthday="30" in February), they are simply ignored.   Byxxx parameters modify the recurrence in some manner.  Byxxx rule   parts for a period of time which is the same or greater than the   frequency generally reduce or limit the number of occurrences of the   recurrence generated.  For example, freq="daily" bymonth="1" reduces   the number of recurrence instances from all days (if the "bymonth"   parameter is not present) to all days in January.  Byxxx parameters   for a period of time less than the frequency generally increase or   expand the number of occurrences of the recurrence.  For example,   freq="yearly" bymonth="1,2" increases the number of days within the   yearly recurrence set from 1 (if "bymonth" parameter is not present)   to 2.   If multiple Byxxx parameters are specified, then after evaluating the   specified "freq" and "interval" parameters, the Byxxx parameters are   applied to the current set of evaluated occurrences in the following   order: "bymonth", "byweekno", "byyearday", "bymonthday", "byday",   "byhour", "byminute", "bysecond", and "bysetpos"; then "count" and   "until" are evaluated.Lennox, et al.              Standards Track                    [Page 19]

RFC 3880                          CPL                       October 2004   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 (seeSection 8) to link multiple   outputs to the same subsequent node.   The "not-present" output is never true for a time switch.  However,   it MAY be included to allow switch processing to be more regular.4.4.1.  iCalendar Differences and Implementation Issues   (This sub-sub-section is non-normative.)   The specification of recurring events in this section is identical   (except for syntax and formatting issues) to that ofRFC 2445 [8],   with only one additional restriction.  That one restriction is that   consecutive instances of recurrence intervals may not overlap.   It was a matter of some debate, during the design of CPL, whether the   entire iCalendar COS recurrence specification should be included in   CPL, or whether only a subset should be included.  It was eventually   decided that compatibility between the two protocols was of primary   importance.  This imposes some additional implementation issues on   implementors of CPL servers.Lennox, et al.              Standards Track                    [Page 20]

RFC 3880                          CPL                       October 2004   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 inAppendix A runs in constant time after these   pre-processing steps.   Servers ought to check that recurrence rules do not create any absurd   run-time or memory requirements, and reject those that do, just as   they ought to check that CPL scripts in general are not absurdly   large.4.5.  Priority Switches   Priority switches allow a CPL script to make decisions based on the   priority specified for the original call.  They are summarized in   Figure 8.  They are dependent on the underlying signalling protocol.Lennox, et al.              Standards Track                    [Page 21]

RFC 3880                          CPL                       October 2004             Node:  "priority-switch"          Outputs:  "priority"         Specific priority to match       Parameters:  None           Output:  "priority"       Parameters:  "less"             Match if priority is less                                       than that specified                    "greater"          Match if priority is greater                                       than that specified                    "equal"            Match if priority is equal                                       to that specified   Figure 8: Syntax of the "priority-switch" node   Priority switches take no parameters.   The "priority" tag takes one of the three parameters "greater",   "less", or "equal".  The values of these parameters are one of the   following priorities: in decreasing order, "emergency", "urgent",   "normal", and "non-urgent".  These values are matched in a case-   insensitive manner.  Outputs with the "less" parameter are taken if   the priority of the call is less than the priority given in the   argument, and so forth.   If no priority is specified in a message, the priority is considered   to be "normal".  If an unknown priority is specified in the call, it   is considered to be equivalent to "normal" for the purposes of   "greater" and "less" comparisons, but it is compared literally for   "equal" comparisons.   Since every message has a priority, the "not-present" output is never   true for a priority switch.  However, it MAY be included, to allow   switch processing to be more regular.4.5.1.  Usage of "priority-switch" with SIP   The priority of a SIP message corresponds to the "Priority" header in   the initial "INVITE" message.5.  Location Modifiers   The abstract location model of CPL is described inSection 2.3.  The   behavior of several of the signalling operations (defined inSection6) is dependent on the current location set specified.  Location   nodes add or remove locations from the location set.Lennox, et al.              Standards Track                    [Page 22]

RFC 3880                          CPL                       October 2004   There are three types of location nodes defined.  Explicit locations   add literally-specified locations to the current location set,   location lookups obtain locations from some outside source, and   location filters remove locations from the set, based on some   specified criteria.5.1.  Explicit Location   Explicit location nodes specify a location literally.  Their syntax   is described in Figure 9.   Explicit location nodes are dependent on the underlying signalling   protocol.          Node:  "location"       Outputs:  None        (Next node follows directly)     Next node:  Any node    Parameters:  "url"       URL of address to add to location set                 "priority"  Priority of this location (0.0-1.0)                 "clear"     Whether to clear the location set before                             adding the new value   Figure 9: Syntax of the "location" node   Explicit location nodes have three node parameters.  The mandatory   "url" parameter's value is the URL of the address to add to the   location set.  Only one address may be specified per location node;   multiple locations may be specified by cascading these nodes.   The optional "priority" parameter specifies a priority for the   location.  Its value is a floating-point number between 0.0 and 1.0.   If it is not specified, the server SHOULD assume a default priority   of 1.0.  The optional "clear" parameter specifies whether the   location set should be cleared before adding the new location to it.   Its value can be "yes" or "no", with "no" as the default.   Basic location nodes have only one possible result, since there is no   way that they can fail.  (If a basic location node specifies a   location which isn't supported by the underlying signalling protocol,   the script server SHOULD detect this and report it to the user at the   time the script is submitted.)  Therefore, their XML representations   do not have explicit output tags; the <location> tag directly   contains another node.5.1.1.  Usage of "location" with SIP   All SIP locations are represented as URLs, so the locations specified   in "location" tags are interpreted directly.Lennox, et al.              Standards Track                    [Page 23]

RFC 3880                          CPL                       October 20045.2.  Location Lookup   Locations can also be specified up through external means, through   the use of location lookups.  The syntax of these tags is given in   Figure 10.   Location lookup is dependent on the underlying signalling protocol.          Node:  "lookup"       Outputs:  "success"   Next node if lookup was successful                 "notfound"  Next node if lookup found no addresses                 "failure"   Next node if lookup failed    Parameters:  "source"    Source of the lookup                 "timeout"   Time to try before giving up on the lookup                 "clear"     Whether to clear the location set before                             adding the new values        Output:  "success"    Parameters:  none        Output:  "notfound"    Parameters:  none        Output:  "failure"    Parameters:  none   Figure 10: Syntax of the "lookup" node   Location lookup nodes have one mandatory parameter and two optional   parameters.  The mandatory parameter is "source", the source of the   lookup.  This can either be a URI, or a non-URI value.  If the value   of "source" is a URI, it indicates a location which the CPL server   can query to obtain an object with the text/uri-list media type (see   the IANA registration of this type, which also appears inRFC 2483   [10]).  The query is performed verbatim, with no additional   information (such as URI parameters) added.  The server adds the   locations contained in this object to the location set.   CPL servers MAY refuse to allow URI-based sources for location   queries for some or all URI schemes.  In this case, they SHOULD   reject the script at script upload time.      There has been discussion of having CPL servers add URI parameters      to the location request, so that (for instance) CGI scripts could      be used to resolve them.  However, the consensus was that this      should be a CPL extension, not a part of the base specification.Lennox, et al.              Standards Track                    [Page 24]

RFC 3880                          CPL                       October 2004   Non-URL sources indicate a source not specified by a URL which the   server can query for addresses to add to the location set.  The only   non-URL source currently defined is "registration", which specifies   all the locations currently registered with the server.   The "lookup" node also has two optional parameters.  The "timeout"   parameter specifies the time, as a positive integer number of   seconds, the script is willing to wait for the lookup to be   performed.  If this is not specified, its default value is 30.  The   "clear" parameter specifies whether the location set should be   cleared before the new locations are added.   Lookup has three outputs: "success", "notfound", and "failure".   Notfound is taken if the lookup process succeeded but did not find   any locations; failure is taken if the lookup failed for some reason,   including that the specified timeout was exceeded.  If a given output   is not present, script execution terminates and the default behavior   is performed.5.2.1.  Usage of "lookup" with SIP   For SIP, the "registration" lookup source corresponds to the   locations registered with the server using "REGISTER" messages.5.3.  Location Removal   A CPL script can also remove locations from the location set, through   the use of the "remove-location" node.  The syntax of this node is   defined in Figure 11.   The meaning of this node is dependent on the underlying signalling   Protocol.             Node:  "remove-location"          Outputs:  None               (Next node follows directly)        Next node:  Any node       Parameters:  "location"         Location to remove   Figure 11: Syntax of the "remove-location" node   A "remove-location" node removes locations from the location set.  It   is primarily useful following a "lookup" node.  An example of this is   given inSection 12.8.   The "remove-location" node has one optional parameter.  The parameter   "location" gives the URI of a location to be removed from the set, in   a signalling-protocol-dependent manner.  If this parameter is not   given, all locations are removed from the set.Lennox, et al.              Standards Track                    [Page 25]

RFC 3880                          CPL                       October 2004   The "remove-location" node has no explicit output tags.  In the XML   syntax, the XML "remove-location" tag directly encloses the next   node's tag.5.3.1.  Usage of "remove-location" with SIP   The location specified in the "location" parameter of the "remove-   location" node is matched against the location set using the standard   rules for SIP URI matching (as are used, e.g., to match Contact   addresses when refreshing registrations).6.  Signalling Operations   Signalling operation nodes cause signalling events in the underlying   signalling protocol.  Three signalling operations are defined:   "proxy," "redirect," and "reject."6.1.  Proxy   Proxy causes the triggering call to be forwarded on to the currently   specified set of locations.  The syntax of the proxy node is given in   Figure 12.   The specific signalling events invoked by the "proxy" node are   signalling-protocol-dependent, though the general concept should   apply to any signalling protocol.Lennox, et al.              Standards Track                    [Page 26]

RFC 3880                          CPL                       October 2004         Node:  "proxy"      Outputs:  "busy"         Next node if call attempt returned "busy"                "noanswer"     Next node if call attempt was not                               answered before timeout                "redirection"  Next node if call attempt was redirected                "failure"      Next node if call attempt failed                "default"      Default next node for unspecified outputs   Parameters:  "timeout"      Time to try before giving up on the                               call attempt                "recurse"      Whether to recursively look up                               redirections                "ordering"     What order to try the location set in.       Output:  "busy"   Parameters:  none       Output:  "noanswer"   Parameters:  none       Output:  "redirection"   Parameters:  none       Output:  "failure"   Parameters:  none       Output:  "default"   Parameters:  none   Figure 12: Syntax of the "proxy" node   After a proxy operation has completed, the CPL server chooses the   "best" response to the call attempt, as defined by the signalling   protocol or the server's administrative configuration rules.   If the call attempt was successful, CPL execution terminates and the   server proceeds to its default behavior (normally, to allow the call   to be set up).  Otherwise, the next node corresponding to one of the   "proxy" node's outputs is taken.  The "busy" output is followed if   the call was busy, "noanswer" is followed if the call was not   answered before the "timeout" parameter expired, "redirection" is   followed if the call was redirected, and "failure" is followed if the   call setup failed for any other reason.   If one of the conditions above is true, but the corresponding output   was not specified, the "default" output of the "proxy" node is   followed instead.  If there is also no "default" node specified, CPL   execution terminates and the server returns to its default behavior   (normally, to forward the best response upstream to the originator).Lennox, et al.              Standards Track                    [Page 27]

RFC 3880                          CPL                       October 2004      Note: CPL extensions to allow in-call or end-of-call operations      will require an additional output, such as "success", to be added.   If no locations were present in the set, or if the only locations in   the set were locations to which the server cannot proxy a call (for   example, "http" URLs), the "failure" output is taken.   Proxy has three optional parameters.  The "timeout" parameter   specifies the time, as a positive integer number of seconds, to wait   for the call to be completed or rejected; after this time has   elapsed, the call attempt is terminated and the "noanswer" branch is   taken.  If this parameter is not specified, the default value is 20   seconds if the "proxy" node has a "noanswer" or "default" output   specified; otherwise the server SHOULD allow the call to ring for a   reasonably long period of time (to the maximum extent that server   policy allows).   The second optional parameter is "recurse", which can take two   values, "yes" or "no".  This specifies whether the server should   automatically attempt to place further call attempts to telephony   addresses in redirection responses that were returned from the   initial server.  Note that if the value of "recurse" is "yes", the   "redirection" output to the script is never taken.  In this case this   output SHOULD NOT be present.  The default value of this parameter is   "yes".   The third optional parameter is "ordering".  This can have three   possible values: "parallel", "sequential", and "first-only".  This   parameter specifies in what order the locations of the location set   should be tried.  Parallel asks that they all be tried   simultaneously; sequential asks that the one with the highest   priority be tried first, the one with the next-highest priority   second, and so forth, until one succeeds or the set is exhausted.   First-only instructs the server to try only the highest-priority   address in the set, and then follow one of the outputs.  The priority   of locations in a set is determined by server policy, though CPL   servers SHOULD honor the "priority" parameter of the "location" tag.   The default value of this parameter is "parallel".   Once a proxy operation completes, if control is passed on to other   nodes, all locations which have been used are cleared from the   location set.  That is, the location set is emptied of proxyable   locations if the "ordering" was "parallel" or "sequential"; the   highest-priority item in the set is removed from the set if   "ordering" was "first-only".  (In all cases, non-proxyable locations   such as "http" URIs remain.)  In the case of a "redirection" output,   the new addresses to which the call was redirected are then added to   the location set.Lennox, et al.              Standards Track                    [Page 28]

RFC 3880                          CPL                       October 20046.1.1.  Usage of "proxy" with SIP   For SIP, the best response to a "proxy" node is determined by the   algorithm of the SIP specification.  The node's outputs correspond to   the following events:      busy: A 486 or 600 response was the best response received for the            call request.      redirection: A 3xx response was the best response received for the            call request.      failure: Any other 4xx, 5xx, or 6xx response was the best response            received for the call request.      no-answer: No final response was received for the call request            before the timeout expired.   SIP servers SHOULD honor the "q" parameter of SIP registrations when   determining location priority.6.2.  Redirect   Redirect causes the server to direct the calling party to attempt to   place its call to the currently specified set of locations.  The   syntax of this node is specified in Figure 13.   The specific behavior the redirect node invokes is dependent on the   underlying signalling protocol involved, though its semantics are   generally applicable.             Node:  "redirect"          Outputs:  None         (No node may follow)        Next node:  None       Parameters:  "permanent"  Whether the redirection should be                                 considered permanent   Figure 13: Syntax of the "redirect" node   Redirect immediately terminates execution of the CPL script, so this   node has no outputs and no next node.  It has one parameter,   "permanent", which specifies whether the result returned should   indicate that this is a permanent redirection.  The value of this   parameter is either "yes" or "no" and its default value is "no."Lennox, et al.              Standards Track                    [Page 29]

RFC 3880                          CPL                       October 20046.2.1.  Usage of "redirect" with SIP   The SIP server SHOULD send a 3xx class response to a call request   upon executing a "redirect" tag.  If "permanent" was "yes", the   server SHOULD send the response "301" (Moved permanently), otherwise   it SHOULD send "302" (Moved temporarily).6.3.  Reject   Reject nodes cause the server to reject the call attempt.  Their   syntax is given in Figure 14.  The specific behavior they invoke is   dependent on the underlying signalling protocol involved, though   their semantics are generally applicable.                    Node:  "reject"                 Outputs:  None      (No node may follow)               Next node:  None              Parameters:  "status"  Status code to return                           "reason"  Reason phrase to return   Figure 14: Syntax of the "reject" node   A reject node immediately terminates the execution of a CPL script,   so this node has no outputs and no next node.   This node has two arguments: "status" and "reason".  The "status"   argument is required, and can take one of the values "busy",   "notfound", "reject", "error", or a signalling-protocol-defined   status.   The "reason" argument optionally allows the script to specify a   reason for the rejection.6.3.1.  Usage of "reject" with SIP   Servers which implement SIP SHOULD also allow the "status" field to   be a numeric argument corresponding to a SIP status in the 4xx, 5xx,   or 6xx range.   They SHOULD send the "reason" parameter in the SIP reason phrase.   A suggested mapping of the named statuses is as follows.  Servers MAY   use a different mapping, though similar semantics SHOULD be   preserved.      "busy": 486 Busy Here      "notfound": 404 Not FoundLennox, et al.              Standards Track                    [Page 30]

RFC 3880                          CPL                       October 2004      "reject": 603 Decline      "error": 500 Internal Server Error7.  Non-signalling Operations   In addition to the signalling operations, CPL defines several   operations which do not affect and are not dependent on the telephony   signalling protocol.7.1.  Mail   The mail node causes the server to notify a user of the status of the   CPL script through electronic mail.  Its syntax is given in Figure   15.          Node:  "mail"       Outputs:  None      (Next node follows directly)     Next node:  Any node    Parameters:  "url"     Mailto url to which the mail should be sent   Figure 15: Syntax of the "mail" node   The "mail" node takes one argument: a "mailto" URL giving the   address, and any additional desired parameters, of the mail to be   sent.  The server sends the message containing the content to the   given url; it SHOULD also include other status information about the   original call request and the CPL script at the time of the   notification.      Using a full "mailto" URL rather than just an e-mail address      allows additional e-mail headers to be specified, such as      <mail url="mailto:jones@example.com?subject=Lookup%20failed" />.   A mail node has only one possible result, since failure of e-mail   delivery cannot reliably be known in real time.  Therefore, its XML   representation does not have output tags: the <mail> tag directly   contains another node tag.   Note that the syntax of XML requires that ampersand characters, "&",   which are used as parameter separators in "mailto" URLs, be quoted as   "&amp;" inside parameter values (see Section C.12 of the XML   specification [2]).Lennox, et al.              Standards Track                    [Page 31]

RFC 3880                          CPL                       October 20047.1.1.  Suggested Content of Mailed Information   This section presents suggested guidelines for the mail sent as a   result of the "mail" node, for requests triggered by SIP.  The   message mailed (triggered by any protocol) SHOULD contain all this   information, but servers MAY elect to use a different format.      1. If the "mailto" URI did not specify a subject header, the         subject of the e-mail is "[CPL]", followed by the subject         header of the SIP request.  If the URI specified a subject         header, it is used instead.      2. The "From" field of the e-mail is set to a CPL server         configured address, overriding any "From" field in the "mailto"         URI.      3. Any "Reply-To" header in the URI is honored.  If none is given,         then an e-mail-ized version of the origin field of the request         is used, if possible (e.g., a SIP "From" header with a sip: URI         would be converted to an e-mail address by stripping the URI         scheme).      4. If the "mailto" URI specifies a body, it is used.  If none was         specified, the body SHOULD contain at least the identity of the         caller (both the caller's display name and address), the date         and time of day, the call subject, and if available, the call         priority.   The server SHOULD honor the user's requested languages, and send the   mail notification using an appropriate language and character set.7.2.  Log   The Log node causes the server to log information about the call to   non-volatile storage.  Its syntax is specified in Figure 16.               Node:  "log"            Outputs:  None       (Next node follows directly)          Next node:  Any node         Parameters:  "name"     Name of the log file to use                      "comment"  Comment to be placed in log file   Figure 16: Syntax of the "log" node   Log takes two arguments, both optional: "name", which specifies the   name of the log, and "comment", which gives a comment about the   information being logged.  Servers SHOULD also include other   information in the log, such as the time of the logged event,Lennox, et al.              Standards Track                    [Page 32]

RFC 3880                          CPL                       October 2004   information that triggered the call to be logged, and so forth.  Logs   are specific to the owner of the script which logged the event.  If   the "name" parameter is not given, the event is logged to a standard,   server-defined log file for the script owner.  This specification   does not define how users may retrieve their logs from the server.   The name of a log is a logical name only, and does not necessarily   correspond to any physical file on the server.  The interpretation of   the log file name is server defined, as is a mechanism to access   these logs.  The CPL server SHOULD NOT directly map log names   uninterpreted onto local file names, for security reasons, lest a   security-critical file be overwritten.   A correctly operating CPL server SHOULD NOT ever allow the "log"   event to fail.  As such, log nodes can have only one possible result,   and their XML representation does not have explicit output tags.  A   CPL <log> tag directly contains another node tag.8.  Subactions   XML syntax defines a tree.  To allow more general call flow diagrams,   and to allow script re-use and modularity, we define subactions.   Two tags are defined for subactions: subaction definitions and   subaction references.  Their syntax is given in Figure 17.               Tag:  "subaction"           Subtags:  Any node        Parameters:  "id"              Name of this subaction       Pseudo-node:  "sub"           Outputs:  None in XML tree        Parameters:  "ref"             Name of subaction to execute   Figure 17: Syntax of subactions and "sub" pseudo-nodes   Subactions are defined through "subaction" tags.  These tags are   placed in the CPL script after any ancillary information (seeSection9), but before any top-level tags.  They take one argument: "id", a   token indicating a script-chosen name for the subaction.  The "id"   value for every "subaction" tag in a script MUST be unique within   that script.   Subactions are called from "sub" tags.  The "sub" tag is a "pseudo-   node", and can be used anyplace in a CPL action that a true node   could be used.  It takes one parameter, "ref", the name of the   subaction to be called.  The "sub" tag contains no outputs of its   own, instead control passes to the subaction.Lennox, et al.              Standards Track                    [Page 33]

RFC 3880                          CPL                       October 2004   References to subactions MUST refer to subactions defined before the   current action.  A "sub" tag MUST NOT refer to the action it appears   in, or to any action defined later in the CPL script.  Top-level   actions cannot be called from "sub" tags, or through any other means.   Script servers MUST verify at the time the script is submitted that   no "sub" node refers to any subaction that is not its proper   predecessor.      Allowing only back-references of subs forbids any sort of      recursion.  Recursion would introduce the possibility of non-      terminating or non-decidable CPL scripts, a possibility our      requirements specifically excluded.   Every sub MUST refer to a subaction ID defined within the same CPL   script.  No external links are permitted.   Subaction IDs are case sensitive.      If any subsequent version or extension defines external linkages,      it should probably use a different tag, perhaps XLink [21].      Ensuring termination in the presence of external links is a      difficult problem.9.  Ancillary Information   No ancillary information is defined in the base CPL specification.   If ancillary information, not part of any operation, is found to be   necessary for a CPL extension, it SHOULD be placed within this tag.   The (trivial) definition of the ancillary information tag is given in   Figure 18.      It may be useful to include timezone definitions inside CPL      scripts directly, rather than referencing them externally with      "tzid" and "tzurl" parameters.  If it is, an extension could be      defined to include them here.                            Tag:  "ancillary"                     Parameters:  None                        Subtags:  None   Figure 18: Syntax of the "ancillary" tagLennox, et al.              Standards Track                    [Page 34]

RFC 3880                          CPL                       October 200410.  Default Behavior   When a CPL node reaches an unspecified output, either because the   output tag is not present, or because the tag is present but does not   contain a node, the CPL server's behavior is dependent on the current   state of script execution.  This section gives the operations that   should be taken in each case.      no location modifications or signalling operations performed,           location set empty: Look up the user's location through           whatever mechanism the server would use if no CPL script were           in effect.  Proxy, redirect, or send a rejection message,           using whatever policy the server would use in the absence of           a CPL script.      no location modifications or signalling operations performed,           location set non-empty: (This can only happen for outgoing           calls.)  Proxy the call to the addresses in the location set.      location modifications performed, no signalling operations:  Proxy           or redirect the call, whichever is the server's standard           policy, to the addresses in the current location set.  If the           location set is empty, return a "notfound" rejection.      noanswer output of proxy, no timeout given: (This is a special           case.)  If the "noanswer" output of a proxy node is           unspecified, and no timeout parameter was given to the proxy           node, the call should be allowed to ring for the maximum           length of time allowed by the server (or the request, if the           request specified a timeout).      proxy operation previously taken: Return whatever the "best"           response is of all accumulated responses to the call to this           point, according to the rules of the underlying signalling           protocol.11.  CPL Extensions   Servers MAY support additional CPL features beyond those listed in   this document.  Some of the extensions which have been suggested are   a means of querying how a call has been authenticated, richer control   over H.323 addressing, end-system or administrator-specific features,   regular-expression matching for strings and addresses, and mid-call   or end-of-call controls.   CPL extensions are indicated by XML namespaces [11].  Every extension   MUST have an appropriate XML namespace assigned to it.  The XML   namespace of the extension MUST be different from the XML namespaceLennox, et al.              Standards Track                    [Page 35]

RFC 3880                          CPL                       October 2004   defined inSection 14.  The extension MUST NOT change the syntax or   semantics of the CPL schema defined in this document.  All XML tags   and attributes that are part of the extension MUST be appropriately   qualified so as to place them within that namespace.   Tags or attributes in a CPL script which are in the global namespace   (i.e., not associated with any namespace) are equivalent to tags and   attributes in the CPL namespace "urn:ietf:params:xml:ns:cpl".   A CPL script SHOULD NOT specify any namespaces it does not use.  For   compatibility with non-namespace-aware parsers, a CPL script MAY omit   the base CPL namespace for a script which does not use any   extensions.   A CPL server MUST reject any script containing a reference to a   namespace it does not understand.  It MUST reject any script   containing an extension tag or attribute that is not qualified to be   in an appropriate namespace.      A syntax such as      <extension-switch>        <extension has="http://www.example.com/foo">           [extended things]        </extension>        <otherwise>           [non-extended things]        </otherwise>      </extension-switch>      was suggested as an alternate way of handling extensions.  This      would allow scripts to be uploaded to a server without requiring a      script author to somehow determine which extensions a server      supports.  However, experience developing other languages, notably      Sieve [22], was that this added excessive complexity to languages.      The "extension-switch" tag could, of course, itself be defined in      a CPL extension.   In the XML schema of CPL, we introduce three abstract elements,   namely 'toplevelaction', 'switch', and 'action', which accordingly   have the abstract type 'TopLevelActionType', 'SwitchType', and   'ActionType'.  Any top-level action in a CPL extension MUST be   defined as the substitutionGroup of the abstract 'toplevelaction'   element, and have the type extended from the 'TopLevelActionType'.   Any switch in a CPL extension MUST be defined as the   substitutionGroup of the abstract 'switch' element, and have the typeLennox, et al.              Standards Track                    [Page 36]

RFC 3880                          CPL                       October 2004   extended from the 'SwitchType'.  Any action in a CPL extension MUST   be defined as the substitutionGroup of the abstract 'action' element,   and have the type extended from the 'ActionType'.12.  Examples12.1.  Example: Call Redirect Unconditional   The script in Figure 19 is a simple script that redirects all calls   to a single fixed location.      <?xml version="1.0" encoding="UTF-8"?>      <cpl xmlns="urn:ietf:params:xml:ns:cpl"        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"        xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">        <incoming>          <location url="sip:smith@phone.example.com">            <redirect/>          </location>        </incoming>      </cpl>   Figure 19: Example Script: Call Redirect UnconditionalLennox, et al.              Standards Track                    [Page 37]

RFC 3880                          CPL                       October 200412.2.  Example: Call Forward Busy/No Answer   The script in Figure 20 illustrates some more complex behavior.  We   see an initial proxy attempt to one address, with further operations   if that fails.  We also see how several outputs take the same action   subtree, through the use of subactions.   <?xml version="1.0" encoding="UTF-8"?>   <cpl xmlns="urn:ietf:params:xml:ns:cpl"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">     <subaction>       <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 AnswerLennox, et al.              Standards Track                    [Page 38]

RFC 3880                          CPL                       October 200412.3.  Example: Call Forward: Redirect and Default   The script in Figure 21 illustrates further proxy behavior.  The   server initially tries to proxy to a single address.  If this attempt   is redirected, a new redirection is generated using the locations   returned.  In all other failure cases for the proxy node, a default   operation -- forwarding to voicemail -- is performed.   <?xml version="1.0" encoding="UTF-8"?>   <cpl xmlns="urn:ietf:params:xml:ns:cpl"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">     <incoming>       <location url="sip:jones@jonespc.example.com">         <proxy>           <redirection>             <redirect/>           </redirection>           <default>             <location url="sip:jones@voicemail.example.com">               <proxy/>             </location>           </default>         </proxy>       </location>     </incoming>   </cpl>   Figure 21: Example Script: Call Forward: Redirect and DefaultLennox, et al.              Standards Track                    [Page 39]

RFC 3880                          CPL                       October 200412.4.  Example: Call Screening   The script in Figure 22 illustrates address switches and call   rejection, in the form of a call screening script.  Note also that   because the address-switch lacks an "otherwise" clause, if the   initial pattern does not match, the script does not define any   operations.  The server therefore proceeds with its default behavior,   which would presumably be to contact the user.   <?xml version="1.0" encoding="UTF-8"?>   <cpl xmlns="urn:ietf:params:xml:ns:cpl"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">     <incoming>       <address-switch field="origin" subfield="user">         <address is="anonymous">           <reject status="reject" reason="I reject anonymous calls"/>         </address>       </address-switch>     </incoming>   </cpl>   Figure 22: Example Script: Call ScreeningLennox, et al.              Standards Track                    [Page 40]

RFC 3880                          CPL                       October 200412.5.  Example: Priority and Language Routing   The script in Figure 23 illustrates service selection based on a   call's priority value and language settings.  If the call request had   a priority of "urgent" or higher, the default script behavior is   performed.  Otherwise, the language field is checked for the language   "es" (Spanish).  If it is present, the call is proxied to a Spanish-   speaking operator; other calls are proxied to an English-speaking   operator.   <?xml version="1.0" encoding="UTF-8"?>   <cpl xmlns="urn:ietf:params:xml:ns:cpl"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">     <incoming>       <priority-switch>         <priority greater="urgent"/>         <otherwise>           <language-switch>             <language matches="es">               <location url="sip:spanish@operator.example.com">                 <proxy/>               </location>             </language>             <otherwise>               <location url="sip:english@operator.example.com">                 <proxy/>               </location>             </otherwise>           </language-switch>         </otherwise>       </priority-switch>     </incoming>   </cpl>   Figure 23: Example Script: Priority and Language RoutingLennox, et al.              Standards Track                    [Page 41]

RFC 3880                          CPL                       October 200412.6.  Example: Outgoing Call Screening   The script in Figure 24 illustrates a script filtering outgoing   calls, in the form of a script which prevent 1-900 (premium) calls   from being placed.  This script also illustrates subdomain matching.   <?xml version="1.0" encoding="UTF-8"?>   <cpl xmlns="urn:ietf:params:xml:ns:cpl"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">     <outgoing>       <address-switch field="original-destination" subfield="tel">         <address subdomain-of="1900">           <reject status="reject"               reason="Not allowed to make 1-900 calls."/>         </address>       </address-switch>     </outgoing>   </cpl>   Figure 24: Example Script: Outgoing Call ScreeningLennox, et al.              Standards Track                    [Page 42]

RFC 3880                          CPL                       October 200412.7.  Example: Time-of-day Routing   Figure 25 illustrates time-based conditions and timezones.   <?xml version="1.0" encoding="UTF-8"?>   <cpl xmlns="urn:ietf:params:xml:ns:cpl"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">     <incoming>       <time-switch tzid="America/New_York"           tzurl="http://zones.example.com/tz/America/New_York">         <time dtstart="20000703T090000" duration="PT8H" freq="weekly"             byday="MO,TU,WE,TH,FR">           <lookup source="registration">             <success>               <proxy/>             </success>           </lookup>         </time>         <otherwise>           <location url="sip:jones@voicemail.example.com">             <proxy/>           </location>         </otherwise>       </time-switch>     </incoming>   </cpl>   Figure 25: Example Script: Time-of-day RoutingLennox, et al.              Standards Track                    [Page 43]

RFC 3880                          CPL                       October 200412.8.  Example: Location Filtering   Figure 26 illustrates filtering operations on the location set.  In   this example, we assume that version 0.9beta2 of the "Inadequate   Software SIP User Agent" mis-implements some features, and so we must   work around its problems.  We know that it cannot talk successfully   to one particular mobile device we may have registered, so we remove   that location from the location set.  Once this operation has been   completed, call setup is allowed to proceed normally.   <?xml version="1.0" encoding="UTF-8"?>   <cpl xmlns="urn:ietf:params:xml:ns:cpl"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">     <incoming>       <string-switch field="user-agent">         <string is="Inadequate Software SIP User Agent/0.9beta2">           <lookup source="registration">             <success>               <remove-location location="sip:me@mobile.provider.net">                 <proxy/>               </remove-location>             </success>           </lookup>         </string>       </string-switch>     </incoming>   </cpl>   Figure 26: Example Script: Location FilteringLennox, et al.              Standards Track                    [Page 44]

RFC 3880                          CPL                       October 200412.9.  Example: Non-signalling Operations   Figure 27 illustrates non-signalling operations; in particular,   alerting a user by electronic mail if the lookup server failed.  The   primary motivation for having the "mail" node is to allow this sort   of out-of-band notification of error conditions, as the user might   otherwise be unaware of any problem.   <?xml version="1.0" encoding="UTF-8"?>   <cpl xmlns="urn:ietf:params:xml:ns:cpl"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">     <incoming>       <lookup           source="http://www.example.com/cgi-bin/locate.cgi?user=mary"           timeout="8">         <success>           <proxy/>         </success>         <failure>           <mail url="mailto:mary@example.com?subject=Lookup%20failed"/>         </failure>       </lookup>     </incoming>   </cpl>   Figure 27: Example Script: Non-signalling OperationsLennox, et al.              Standards Track                    [Page 45]

RFC 3880                          CPL                       October 200412.10.  Example: Hypothetical Extensions   The example in Figure 28 shows a hypothetical extension that   implements distinctive ringing.  The XML namespace   "http://www.example.com/distinctive-ring" specifies a new node named   "ring".   <?xml version="1.0" encoding="UTF-8"?>   <xs:schema targetNamespace="http://www.example.com/distinctive-ring"     xmlns="http://www.example.com/distinctive-ring"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xmlns:xs="http://www.w3.org/2001/XMLSchema"     xmlns:CPL="urn:ietf:params:xml:ns:cpl"     elementFormDefault="qualified"     attributeFormDefault="unqualified">     <xs:import namespace="urn:ietf:params:xml:ns:cpl"         schemaLocation="cpl.xsd"/>     <xs:complexType name="DRingAction">       <xs:complexContent>         <xs:extension base="CPL:ActionType">           <xs:attribute name="ringstyle" type="xs:string"               use="optional"/>         </xs:extension>       </xs:complexContent>     </xs:complexType>     <xs:element name="ring" type="DRingAction"         substitutionGroup="CPL:action"/>   </xs:schema>   <?xml version="1.0" encoding="UTF-8"?>   <cpl xmlns="urn:ietf:params:xml:ns:cpl"     xmlns:dr="http://www.example.com/distinctive-ring"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd         http://www.example.com/distinctive-ring distinctive-ring.xsd">     <incoming>       <address-switch field="origin">         <address is="sip:boss@example.com">           <dr:ring ringstyle="warble"/>         </address>       </address-switch>     </incoming>   </cpl>   Figure 28: Example Schema and Script: Hypothetical              Distinctive-Ringing ExtensionLennox, et al.              Standards Track                    [Page 46]

RFC 3880                          CPL                       October 2004   The example in Figure 29 implements a hypothetical new attribute for   address switches, to allow regular-expression matches.  It defines a   new attribute "regex" for the standard "address" node.   <?xml version="1.0" encoding="UTF-8"?>   <cpl xmlns="urn:ietf:params:xml:ns:cpl"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">     <incoming>       <address-switch field="origin" subfield="user"           xmlns:re="http://www.example.com/regex">         <address re:regex="(.*.smith|.*.jones)">           <reject status="reject"               reason="I don't want to talk to Smiths or Joneses"/>         </address>       </address-switch>     </incoming>   </cpl>   Figure 29: Example Script: Hypothetical Regular-Expression ExtensionLennox, et al.              Standards Track                    [Page 47]

RFC 3880                          CPL                       October 200412.11.  Example: A Complex Example   Finally, Figure 30 is a complex example which shows the sort of   sophisticated behavior that can be achieved by combining CPL nodes.   In this case, the user attempts to have his calls reach his desk; if   he does not answer within a small amount of time, calls from his boss   are forwarded to his mobile phone, and all other calls are directed   to voicemail.  If the call setup failed, no operation is specified,   so the server's default behavior is performed.   <?xml version="1.0" encoding="UTF-8"?>   <cpl xmlns="urn:ietf:params:xml:ns:cpl"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xsi:schemaLocation="urn:ietf:params:xml:ns:cpl cpl.xsd ">     <subaction>       <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 ExampleLennox, et al.              Standards Track                    [Page 48]

RFC 3880                          CPL                       October 200413.  Security Considerations   CPL is designed to allow services to be specified in a manner which   prevents potentially hostile or mis-configured scripts from launching   security attacks, including denial-of-service attacks.  Because   script runtime is strictly bounded by acyclicity, and because the   number of possible script operations are strictly limited, scripts   should not be able to inflict damage upon a CPL server.   Because scripts can direct users' telephone calls, the method by   which scripts are transmitted from a client to a server MUST be   strongly authenticated.  Such a method is not specified in this   document.   Script servers SHOULD allow server administrators to control the   details of what CPL operations are permitted.14.  IANA Considerations   This document registers a new MIME type, application/cpl+xml, and a   new URN perRFC 2141 [12],RFC 2648 [13], andRFC 3688 [14].   The XML namespace urn:ietf:params:xml:ns:cpl will only refer to the   version of CPL in this document and will not change.  Any CPL   enhancements MUST be made by extensions and MUST have different   namespaces.14.1.  URN Sub-Namespace Registration for urn:ietf:params:xml:ns:cpl     URI: urn:ietf:params:xml:ns:cpl     Registrant Contact: Jonathan Lennox <lennox@cs.columbia.edu>          Xiaotao Wu <xiaotaow@cs.columbia.edu>          Henning Schulzrinne <hgs@cs.columbia.edu>     XML:           BEGIN           <?xml version="1.0"?>           <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"               "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">           <html xmlns="http://www.w3.org/1999/xhtml">           <head>             <meta http-equiv="content-type"                content="text/html;charset=iso-8859-1"/>             <title>Call Processing Language Namespace</title>           </head>           <body>Lennox, et al.              Standards Track                    [Page 49]

RFC 3880                          CPL                       October 2004             <h1>Namespace for Call Processing Language</h1>             <h2>urn:ietf:params:xml:ns:cpl</h2>             <p><a href="ftp://ftp.rfc-editor.org/in-notes/rfc3880.txt">RFC3880</a>.</p>           </body>           </html>           END14.2.  Schema registration   This specification registers XML Schema for CPL, as per the   guidelines in [14].      URI: urn:ietf:params:xml:schema:cpl      Registrant contact:           Jonathan Lennox <lennox@cs.columbia.edu>           Xiaotao Wu <xiaotaow@cs.columbia.edu>           Henning Schulzrinne <hgs@cs.columbia.edu>      XML: The XML can be found inAppendix C.14.3.  MIME Registration   As an XML type, CPL's MIME registration conforms with "XML Media   Types,"RFC 3023 [15].      MIME media type name: application      MIME subtype name: cpl+xml      Mandatory parameters: none      Optional parameters: charset           As for application/xml inRFC 3023.      Encoding considerations: As for application/xml inRFC 3023.      Security considerations: SeeSection 13, and Section 10 ofRFC3023.      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.Lennox, et al.              Standards Track                    [Page 50]

RFC 3880                          CPL                       October 2004      Applications which use this media type: SIP proxy servers and           other telephony servers, and client software to control           their behavior.      Additional information:           Magic number: None           File extension: .cpl or .xml           Macintosh file type code: "TEXT"      Person and e-mail address for further information:           Jonathan Lennox <lennox@cs.columbia.edu>           Xiaotao Wu <xiaotaow@cs.columbia.edu>           Henning Schulzrinne <hgs@cs.columbia.edu>      Intended usage: COMMON      Author/Change Controller: The IETF.15.  Acknowledgments   This document was reviewed and commented upon by the IETF IP   Telephony Working Group.  We specifically acknowledge the following   people for their help:   The outgoing call screening script was written by Kenny Hom.   Paul E. Jones contributed greatly to the mappings of H.323 addresses.   The text of the time-switch section was taken (lightly modified) fromRFC 2445 [8], by Frank Dawson and Derik Stenerson.   We drew a good deal of inspiration, notably the language's lack of   Turing-completeness and the syntax of string matching, from the   specification of Sieve [22], a language for user filtering of   electronic mail messages.   Thomas F. La Porta and Jonathan Rosenberg had many useful   discussions, contributions, and suggestions.   Richard Gumpertz performed a very useful last-minute technical and   editorial review of the specification.Lennox, et al.              Standards Track                    [Page 51]

RFC 3880                          CPL                       October 2004A.  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 inSection 4.4.1 has been done, it operates in   constant time.  Open-source Java code implementing this algorithm is   available athttp://www.cs.columbia.edu/~lennox/Cal-Code/ on the   world wide web.   This algorithm is believed to be correct, but this section is non-   normative.Section 4.4, andRFC 2445 [8], are the definitive   definitions of recurrences.      1. Compute the time of the call, in the timezone of the time         switch.      2. If the call time is earlier than "dtstart", fail NOMATCH.      3. If the call time is less than "duration" after dtstart, succeed         MATCH.      4. Determine the smallest unit specified in a "byxxx" rule or by         the "freq."  Call this the Minimum Unit.  Determine the         previous instant (before or equal to the call time) when all         the time units smaller than the minimum unit are the same as         those of "dtstart."  If the minimum unit is a second, this time         is the same as the instant.  If the minimum unit is a minute or         an hour, the minutes or the minutes and hours, respectively,         must be the same as "dtstart".  For all other minimum units,         the time-of-day must be the same as "dtstart."  If the minimum         unit is a week, the day-of-the-week must be the same as         "dtstart."  If the minimum unit is a month, the day-of-the-         month must be the same as "dtstart."  If the minimum unit is a         year, the month and day-of-month must both be the same as         "dtstart."  (Note that this means it may be necessary to roll         back more than one minimum unit -- if the minimum unit is a         month, then some months do not have a 31st (or 30th or 29th)         day; if the minimum unit is a year, then some years do not have         a February 29th.  In the Gregorian calendar, it is never         necessary to roll back more than two months if the minimum unit         is a month, or eight years if the minimum unit is a year.         Between 1904 and 2096, it is never necessary to roll back more         than four years -- the eight-year rollback can only occur when         the Gregorian calendar "skips" a leap year.         Call this instant the Candidate Start Time.Lennox, et al.              Standards Track                    [Page 52]

RFC 3880                          CPL                       October 2004      5. If the time between the candidate start time and the call time         is more than the duration, fail NOMATCH.      6. If the candidate start time is later than the "until" parameter         of the recurrence (or the virtual "until" computed off-line         from "count"), fail NOMATCH.      7. Call the unit of the "freq" parameter of the recurrence the         Frequency Unit.  Determine the frequency unit enclosing the         Candidate Start Time, and that enclosing "dtstart".  Calculate         the number of frequency units that have passed between these         two times.  If this is not a multiple of the "interval"         parameter, fail NOMATCH.      8. For every "byxxx" rule, confirm that the candidate start time         matches one of the options specified by that "byxxx" rule.  If         so, succeed MATCH.      9. Calculate a previous candidate start time.  Repeat until the         difference between the candidate start time and the call time         is more than the duration.  If no candidate start time has been         validated, fail NOMATCH.B.  Suggested Usage of CPL with H.323   This appendix gives a suggested usage of CPL with H.323 [16].   Study   Group 16 of the ITU, which developed H.323, is proposing to work on   official CPL mappings for that protocol.  This section is therefore   not normative.B.1.  Usage of "address-switch" with H.323   Address switches are specified inSection 4.1.  This section   specifies the mapping between H.323 messages and the fields and   subfields of address-switches.   For H.323, the "origin" address corresponds to the alias addresses in   the "sourceAddress" field of the "Setup-UUIE" user-user information   element, and to the Q.931 [23] information element "Calling party   number."  If both fields are present, or if multiple alias addresses   for "sourceAddress" are present, which one has priority is a matter   of local server policy; the server SHOULD use the same resolution as   it would use for routing decisions in this case.  Similarly, the   "destination" address corresponds to the alias addresses of the   "destinationAddress" field, and to the Q.931 information element   "Called party number."Lennox, et al.              Standards Track                    [Page 53]

RFC 3880                          CPL                       October 2004   The "original-destination" address corresponds to the "Redirecting   number" Q.931 information element, if it is present; otherwise it is   the same as the "destination" address.   The mapping of H.323 addresses into subfields depends on the type of   the alias address.  An additional subfield type, "alias-type", is   defined for H.323 servers, corresponding to the type of the address.   Possible values are "dialedDigits", "h323-ID", "url-ID",   "transportID", "email-ID", "partyNumber", "mobileUIM", and "Q.931IE".   If future versions of the H.323 specification define additional types   of alias addresses, those names MAY also be used.   In versions of H.323 prior to version 4, "dialedDigits" was known as   "e164".  The two names SHOULD be treated as synonyms.   The value of the "address-type" subfield for H.323 messages is "h323"   unless the alias type is "url-ID" and the URL scheme is something   other than h323; in this case the address-type is the URL scheme, as   specified inSection 4.1.1 for SIP.   An H.323-aware CPL server SHOULD map the address subfields from the   primary alias used for routing.  It MAY also map subfields from other   aliases, if subfields in the primary address are not present.   The following mappings are used for H.323 alias types:      dialedDigits, partyNumber, mobileUIM, and Q.931IE: the "tel" and           "user" subfields are the string of digits, as is the           "entire-address" form.  The "host" and "port" subfields are           not present.      url-ID: the same mappings are used as for SIP, inSection 4.1.1.      h323-ID: the "user" field is the string of characters, as is the           "entire-address" form.  All other subfields are not present.      email-ID: the "user" and "host" subfields are set to the           corresponding parts of the e-mail address.  The "port" and           "tel" subfields are not present.  The "entire-address" form           corresponds to the entire e-mail address.      transportID: if the TransportAddress is of type "ipAddress,"           "ipSourceRoute," or "ip6Address," the "host" subfield is set           to the "ip" element of the sequence, translated into the           standard IPv4 or IPv6 textual representation, and the "port"           subfield is set to the "port" element of the sequence           represented in decimal.  The "tel" and "user" fields are not           present.  The "entire-address" form is not defined.  TheLennox, et al.              Standards Track                    [Page 54]

RFC 3880                          CPL                       October 2004           representation and mapping of transport addresses is not           defined for non-IP addresses.   H.323 [16] defines an "h323" URI scheme.  This appendix defines a   mapping for these URIs onto the CPL "address-switch" subfields, as   given inSection 4.1.  This definition is also available asRFC 3508   [24], which is an excerpt from the H.323 specification.   For h323 URIs, the "user", "host", and "port" subfields are set to   the corresponding parts of the H.323 URL.  The "tel" subfield is not   present.  The "entire-address" form corresponds to the entire URI.   This mapping MAY be used both for h323 URIs in an h323 "url-ID"   address alias, and for h323 URIs in SIP messages.B.2.  Usage of "string-switch" with H.323   For H.323, the "string-switch" node (seeSection 4.2) is used as   follows.  The field "display" corresponds to the Q.931 information   element of the same name, copied verbatim.  The fields "subject",   "organization", and "user-agent" are not used and are never present.      The "display" IE is conventionally used for Caller-ID purposes, so      arguably it should be mapped to the "display" subfield of an      "address-match" with the field "originator".  However, since a) it      is a message-level information element, not an address-level one,      and b) the Q.931 specification [23] says only that "[t]he purpose      of the Display information element is to supply display      information that may be displayed by the user," it seems to be      more appropriate to allow it to be matched in a "string-switch"      instead.B.3.  Usage of "language-switch" with H.323   The language-ranges for the "language-switch" switch are obtained   from the H.323 UUIE "language".  The switch is not-present if the   initial message did not contain this UUIE.B.4.  Usage of "priority-switch" with H.323   All H.323 messages are considered to have priority "normal" for the   purpose of a priority switch (seeSection 4.5).Lennox, et al.              Standards Track                    [Page 55]

RFC 3880                          CPL                       October 2004B.5.  Usage of "location" with H.323   Locations in explicit location nodes (Section 5.1) are specified as   URLs.  Therefore, all locations added in this manner are interpreted   as being of alias type "url-ID" in H.323.   Specifications of other H.323 address alias types will require a CPL   extension (seeSection 11).B.6.  Usage of "lookup" with H.323   For location lookup nodes (Section 5.2), the "registration" lookup   source corresponds to the locations registered with the server using   "RAS" messages.B.7.  Usage of "remove-location" with H.323   Location removal nodes (Section 5.3) remove addresses with the alias   type "url-ID" using verbatim string matching on the URLs.  If a "tel"   URL is specified as the location, matching addresses (ignoring visual   separators) with the alias types "dialedDigits" ("e164"),   "partyNumber", "mobileUIM", or "Q.931IE" are also removed.  No   mechanism is provided to remove other alias types.C.  The XML Schema for CPL   This section includes a full XML Schema describing the XML syntax of   CPL.   Every script submitted to a CPL server SHOULD comply with this   XML Schema.   When parsing scripts comply with the CPL DTD in earlier   documents, the DOCTYPE lines in the scripts should be ignored.  Note   that compliance with this schema is not a sufficient condition for   correctness of a CPL script, as many of the conditions described in   this specification are not expressible in schema syntax.  Figure 31   shows the structure of the schema.  'incoming' and 'outgoing' are   defined as the substitutionGroup of the 'toplevelaction'.  All the   switches are defined as the substitutionGroup of the 'switch'   element.  All the actions are defined as the substitutionGroup of the   'action' element.Lennox, et al.              Standards Track                    [Page 56]

RFC 3880                          CPL                       October 2004         +---------+    +------+                    +--address       +-+ancillary|    |switch|** +--------------+ | +-not-present       | +---------+    +---+--+ **|address-switch+-+-+-address       |                    |    * +--------------+ +--otherwise       | +---------+ +----+ |    *                   +--language       +-+subaction+-+Node| |    * +---------------+ | +-not-present       | +---------+ +----+ |    **|language-switch|-+-+-language       |                    |    * +---------------+ +--otherwise       |                    |    *                   +--priority       |                    |    * +---------------+ | +-not-present       |                    |    **|priority-switch|-+-+-priority       |                    |    * +---------------+ +--otherwise       |                    |    *                 +--string   cpl-+                    |    * +-------------+ | +-not-present       |                    |    **|string-switch|-+ +-string       |                    |    * +-------------+ +--otherwise       |                    |    *               +--time       | +--------------+ +-+--+ * +-----------+ | +-not-present       +-+toplevelaction+-+Node|  *|time-switch|-+-+-time         +-----*--------+ +-+--+   +-----------+ +--otherwise              *             |              +--------+ +----+             *              |            **|location+-|Node|             *              | +--------+ * +--------+ +----+             * +--------+   |-+modifier|** +------+ +-success-Node             **|incoming|   | +--------+ *-|lookup+-+-notfound-Node             * +--------+   |            * +------+ +-failure-Node             *              | +---+      * +---------------+ +----+             * +--------+   +-+Sub+-sub  **|remove-location+-+Node|              *|outgoing|   | +---+        +---------------+ +----+               +--------+   |            +---+                            |          **|log+-Node                            |          * +---+                            |          * +----+                            | +------+ **|mail+-Node                            +-+action|** +----+     +-busy-Node        ----  contains        +------+ * +-----+    |                                       **|proxy+----+-noanswer-Node        ****  substitutes              * +-----+    |                                       * +--------+ +-failure-Node                                       **|redirect| |                                       * +--------+ +-redirection-Node                                       * +------+   |                                        *|reject|   +-default-Node                                         +------+   Figure 31: The structure of the XML schema for CPLLennox, et al.              Standards Track                    [Page 57]

RFC 3880                          CPL                       October 2004   BEGIN   <?xml version="1.0" encoding="UTF-8"?>   <xs:schema targetNamespace="urn:ietf:params:xml:ns:cpl"     xmlns="urn:ietf:params:xml:ns:cpl"     xmlns:xs="http://www.w3.org/2001/XMLSchema"     elementFormDefault="qualified"     attributeFormDefault="unqualified">     <xs:complexType name="TopLevelActionType" abstract="true">       <xs:group ref="Node"/>     </xs:complexType>     <xs:element name="toplevelaction" type="TopLevelActionType"/>     <xs:complexType name="ActionType" abstract="true"/>     <xs:element name="action" type="ActionType"/>     <xs:complexType name="SwitchType" abstract="true"/>     <xs:element name="switch" type="SwitchType"/>     <xs:complexType name="ModifierType" abstract="true"/>     <xs:element name="modifier" type="ModifierType"/>     <xs:element name="location" type="LocationType"         substitutionGroup="modifier"/>     <xs:element name="lookup" type="LookupType"         substitutionGroup="modifier"/>     <xs:element name="remove-location" type="RemoveLocationType"         substitutionGroup="modifier"/>     <xs:element name="sub" type="SubAction"/>     <xs:group name="Node">       <xs:choice>         <xs:element ref="switch" minOccurs="0" maxOccurs="1"/>         <xs:element ref="modifier" minOccurs="0" maxOccurs="1"/>         <xs:element ref="sub" minOccurs="0" maxOccurs="1"/>         <xs:element ref="action" minOccurs="0" maxOccurs="1"/>       </xs:choice>     </xs:group>     <xs:complexType name="OtherwiseAction">       <xs:group ref="Node"/>     </xs:complexType>     <xs:complexType name="NotPresentAction">       <xs:group ref="Node"/>     </xs:complexType>     <xs:simpleType name="YesNoType">       <xs:restriction base="xs:NMTOKEN">         <xs:enumeration value="yes"/>         <xs:enumeration value="no"/>       </xs:restriction>     </xs:simpleType>     <xs:simpleType name="StatusType">       <xs:union>         <xs:simpleType>           <xs:restriction base="xs:NMTOKEN">Lennox, et al.              Standards Track                    [Page 58]

RFC 3880                          CPL                       October 2004             <xs:enumeration value="busy"/>             <xs:enumeration value="notfound"/>             <xs:enumeration value="reject"/>             <xs:enumeration value="error"/>           </xs:restriction>         </xs:simpleType>         <xs:simpleType>           <xs:restriction base="xs:string"/>         </xs:simpleType>       </xs:union>     </xs:simpleType>     <xs:simpleType name="OrderingType">       <xs:restriction base="xs:NMTOKEN">         <xs:enumeration value="parallel"/>         <xs:enumeration value="sequential"/>         <xs:enumeration value="first-only"/>       </xs:restriction>     </xs:simpleType>     <xs:simpleType name="AddressFieldType">       <xs:union>         <xs:simpleType>           <xs:restriction base="xs:NMTOKEN">             <xs:enumeration value="origin"/>             <xs:enumeration value="destination"/>             <xs:enumeration value="original-destination"/>           </xs:restriction>         </xs:simpleType>         <xs:simpleType>           <xs:restriction base="xs:string"/>         </xs:simpleType>       </xs:union>     </xs:simpleType>     <xs:simpleType name="AddressSubfieldType">       <xs:union>         <xs:simpleType>           <xs:restriction base="xs:NMTOKEN">             <xs:enumeration value="address-type"/>             <xs:enumeration value="user"/>             <xs:enumeration value="host"/>             <xs:enumeration value="port"/>             <xs:enumeration value="tel"/>             <xs:enumeration value="display"/>             <xs:enumeration value="password"/>             <xs:enumeration value="alias-type"/>           </xs:restriction>         </xs:simpleType>Lennox, et al.              Standards Track                    [Page 59]

RFC 3880                          CPL                       October 2004         <xs:simpleType>           <xs:restriction base="xs:string"/>         </xs:simpleType>       </xs:union>     </xs:simpleType>     <xs:complexType name="AddressType">       <xs:annotation>         <xs:documentation>Exactly one of the three attributes must             appear</xs:documentation>       </xs:annotation>       <xs:group ref="Node"/>       <xs:attribute name="is" type="xs:string" use="optional"/>       <xs:attribute name="contains" type="xs:string" use="optional">         <xs:annotation>           <xs:documentation>for "display" only</xs:documentation>         </xs:annotation>       </xs:attribute>       <xs:attribute name="subdomain-of" type="xs:string"           use="optional">         <xs:annotation>           <xs:documentation>for "host", "tel" only</xs:documentation>         </xs:annotation>       </xs:attribute>       <xs:anyAttribute namespace="##any" processContents="lax"/>     </xs:complexType>     <xs:complexType name="AddressSwitchType">       <xs:complexContent>         <xs:extension base="SwitchType">           <xs:sequence>             <xs:element name="address" type="AddressType" minOccurs="0"                 maxOccurs="unbounded"/>             <xs:sequence minOccurs="0">               <xs:element name="not-present" type="NotPresentAction"/>               <xs:element name="address" type="AddressType"                   minOccurs="0" maxOccurs="unbounded"/>             </xs:sequence>             <xs:element name="otherwise" type="OtherwiseAction"                 minOccurs="0"/>           </xs:sequence>           <xs:attribute name="field" type="AddressFieldType"               use="required"/>           <xs:attribute name="subfield" type="AddressSubfieldType"               use="optional"/>         </xs:extension>       </xs:complexContent>     </xs:complexType>     <xs:element name="address-switch" type="AddressSwitchType"         substitutionGroup="switch"/>Lennox, et al.              Standards Track                    [Page 60]

RFC 3880                          CPL                       October 2004     <xs:simpleType name="StringFieldType">       <xs:restriction base="xs:NMTOKEN">         <xs:enumeration value="subject"/>         <xs:enumeration value="organization"/>         <xs:enumeration value="user-agent"/>         <xs:enumeration value="display"/>       </xs:restriction>     </xs:simpleType>     <xs:complexType name="StringType">       <xs:group ref="Node"/>       <xs:attribute name="is" type="xs:string" use="optional"/>       <xs:attribute name="contains" type="xs:string" use="optional"/>       <xs:anyAttribute namespace="##any" processContents="lax"/>     </xs:complexType>     <xs:complexType name="StringSwitchType">       <xs:complexContent>         <xs:extension base="SwitchType">           <xs:sequence>             <xs:element name="string" type="StringType" minOccurs="0"                 maxOccurs="unbounded"/>             <xs:sequence minOccurs="0">               <xs:element name="not-present" type="NotPresentAction"/>               <xs:element name="string" type="StringType" minOccurs="0"                   maxOccurs="unbounded"/>             </xs:sequence>             <xs:element name="otherwise" type="OtherwiseAction"                 minOccurs="0"/>           </xs:sequence>           <xs:attribute name="field" type="StringFieldType"               use="required">             <xs:annotation>               <xs:documentation>Strings are matched as case-insensitive                   Unicode strings.</xs:documentation>             </xs:annotation>           </xs:attribute>         </xs:extension>       </xs:complexContent>     </xs:complexType>     <xs:element name="string-switch" type="StringSwitchType"         substitutionGroup="switch"/>     <xs:complexType name="LanguageType">       <xs:group ref="Node"/>       <xs:attribute name="matches" type="xs:string" use="required">         <xs:annotation>           <xs:documentation>The value of one of these parameters is a               language-tag, as defined inRFC3066.</xs:documentation>         </xs:annotation>Lennox, et al.              Standards Track                    [Page 61]

RFC 3880                          CPL                       October 2004       </xs:attribute>       <xs:anyAttribute namespace="##any" processContents="lax"/>     </xs:complexType>     <xs:complexType name="LanguageSwitchType">       <xs:complexContent>         <xs:extension base="SwitchType">           <xs:sequence>             <xs:element name="language" type="LanguageType"                 minOccurs="0" maxOccurs="unbounded"/>             <xs:sequence minOccurs="0">               <xs:element name="not-present" type="NotPresentAction"/>               <xs:element name="language" type="LanguageType"                   minOccurs="0" maxOccurs="unbounded"/>             </xs:sequence>             <xs:element name="otherwise" type="OtherwiseAction"                 minOccurs="0"/>           </xs:sequence>         </xs:extension>       </xs:complexContent>     </xs:complexType>     <xs:element name="language-switch" type="LanguageSwitchType"         substitutionGroup="switch"/>     <xs:simpleType name="FreqType">       <xs:restriction base="xs:NMTOKEN">         <xs:pattern value="[s|S][e|E][c|C][o|O][n|N][d|D][l|L][y|Y]"/>         <xs:pattern value="[m|M][i|I][n|N][u|U][t|T][e|E][l|L][y|Y]"/>         <xs:pattern value="[h|H][o|O][u|U][r|R][l|L][y|Y]"/>         <xs:pattern value="[d|D][a|A][i|I][l|L][y|Y]"/>         <xs:pattern value="[w|W][e|E][e|E][k|K][l|L][y|Y]"/>         <xs:pattern value="[m|M][o|N][n|N][t|T][h|H][l|L][y|Y]"/>         <xs:pattern value="[y|Y][e|E][a|A][r|R][l|L][y|Y]"/>       </xs:restriction>     </xs:simpleType>     <xs:simpleType name="YearDayType">       <xs:union>         <xs:simpleType>           <xs:restriction base="xs:integer">             <xs:minInclusive value="-366"/>             <xs:maxInclusive value="-1"/>           </xs:restriction>         </xs:simpleType>         <xs:simpleType>           <xs:restriction base="xs:integer">             <xs:minInclusive value="1"/>             <xs:maxExclusive value="366"/>           </xs:restriction>         </xs:simpleType>       </xs:union>Lennox, et al.              Standards Track                    [Page 62]

RFC 3880                          CPL                       October 2004     </xs:simpleType>     <xs:simpleType name="DayType">       <xs:restriction base="xs:NMTOKEN">         <xs:pattern value="[m|M][o|O]"/>         <xs:pattern value="[t|T][u|U]"/>         <xs:pattern value="[w|W][e|E]"/>         <xs:pattern value="[t|T][h|H]"/>         <xs:pattern value="[f|F][r|R]"/>         <xs:pattern value="[s|S][a|A]"/>         <xs:pattern value="[s|S][u|U]"/>       </xs:restriction>     </xs:simpleType>     <xs:complexType name="TimeType">       <xs:annotation>         <xs:documentation>Exactly one of the two attributes "dtend" and             "duration" must occur.  None of the attributes following             freq are meaningful unless freq appears.             </xs:documentation>       </xs:annotation>       <xs:group ref="Node"/>       <xs:attribute name="dtstart" type="xs:string" use="required">         <xs:annotation>           <xs:documentation>RFC 2445 DATE-TIME</xs:documentation>         </xs:annotation>       </xs:attribute>       <xs:attribute name="dtend" type="xs:string" use="optional">         <xs:annotation>           <xs:documentation>RFC 2445 DATE-TIME</xs:documentation>         </xs:annotation>       </xs:attribute>       <xs:attribute name="duration" type="xs:string" use="optional">         <xs:annotation>           <xs:documentation>RFC 2445 DURATION</xs:documentation>         </xs:annotation>       </xs:attribute>       <xs:attribute name="freq" type="FreqType" use="optional"/>       <xs:attribute name="interval" type="xs:positiveInteger"           default="1"/>       <xs:attribute name="until" type="xs:string" use="optional">         <xs:annotation>           <xs:documentation>RFC 2445 DATE-TIME</xs:documentation>         </xs:annotation>       </xs:attribute>       <xs:attribute name="count" type="xs:positiveInteger"           use="optional"/>       <xs:attribute name="bysecond" type="xs:string" use="optional">         <xs:annotation>           <xs:documentation>Comma-separated list of seconds within aLennox, et al.              Standards Track                    [Page 63]

RFC 3880                          CPL                       October 2004               minute.  Valid values are 0 to 59.</xs:documentation>         </xs:annotation>       </xs:attribute>       <xs:attribute name="byminute" type="xs:string" use="optional">         <xs:annotation>           <xs:documentation>Comma-separated list of minutes within an               hour.  Valid values are 0 to 59.</xs:documentation>         </xs:annotation>       </xs:attribute>       <xs:attribute name="byhour" type="xs:string" use="optional">         <xs:annotation>           <xs:documentation>Comma-separated list of hours of the day.               Valid values are 0 to 23.</xs:documentation>         </xs:annotation>       </xs:attribute>       <xs:attribute name="byday" type="xs:string" use="optional">         <xs:annotation>           <xs:documentation>Comma-separated list of days of the week.               Valid values are "MO", "TU", "WE", "TH", "FR", "SA" and               "SU".  These values are not case-sensitive.  Each can be               preceded by a positive (+n) or negative (-n)               integer.</xs:documentation>         </xs:annotation>       </xs:attribute>       <xs:attribute name="bymonthday" type="xs:string" use="optional">         <xs:annotation>           <xs:documentation>Comma-separated list of days of the month.               Valid values are 1 to 31 or -31 to               -1.</xs:documentation>         </xs:annotation>       </xs:attribute>       <xs:attribute name="byyearday" type="xs:string" use="optional">         <xs:annotation>           <xs:documentation>Comma-separated list of days of the year.               Valid values are 1 to 366 or -366 to               -1.</xs:documentation>         </xs:annotation>       </xs:attribute>       <xs:attribute name="byweekno" type="xs:string" use="optional">         <xs:annotation>           <xs:documentation>Comma-separated list of ordinals specifying               weeks of the year.  Valid values are 1 to 53 or -53 to               -1.</xs:documentation>         </xs:annotation>       </xs:attribute>       <xs:attribute name="bymonth" type="xs:string" use="optional">         <xs:annotation>           <xs:documentation>Comma-separated list of months of the year.Lennox, et al.              Standards Track                    [Page 64]

RFC 3880                          CPL                       October 2004               Valid values are 1 to 12.</xs:documentation>         </xs:annotation>       </xs:attribute>       <xs:attribute name="wkst" type="DayType" default="MO"/>       <xs:attribute name="bysetpos" type="YearDayType"/>       <xs:anyAttribute namespace="##any" processContents="lax"/>     </xs:complexType>     <xs:simpleType name="TZIDType">       <xs:restriction base="xs:string"/>     </xs:simpleType>     <xs:simpleType name="TZURLType">       <xs:restriction base="xs:anyURI"/>     </xs:simpleType>     <xs:complexType name="TimeSwitchType">       <xs:complexContent>         <xs:extension base="SwitchType">           <xs:sequence>             <xs:element name="time" type="TimeType" minOccurs="0"                 maxOccurs="unbounded"/>             <xs:sequence minOccurs="0">               <xs:element name="not-present" type="NotPresentAction"/>               <xs:element name="time" type="TimeType" minOccurs="0"                   maxOccurs="unbounded"/>             </xs:sequence>             <xs:element name="otherwise" type="OtherwiseAction"                 minOccurs="0"/>           </xs:sequence>           <xs:attribute name="tzid" type="TZIDType"/>           <xs:attribute name="tzurl" type="TZURLType"/>         </xs:extension>       </xs:complexContent>     </xs:complexType>     <xs:element name="time-switch" type="TimeSwitchType"         substitutionGroup="switch"/>     <xs:simpleType name="PriorityValues">       <xs:restriction base="xs:NMTOKEN">         <xs:pattern             value="[e|E][m|M][e|E][r|R][g|G][e|E][n|N][c|C][y|Y]"/>         <xs:pattern value="[u|U][r|R][g|G][e|E][n|N][t|T]"/>         <xs:pattern value="[n|N][o|O][r|R][m|M][a|A][l|L]"/>         <xs:pattern             value="[n|N][o|O][n|N]-[u|U][r|R][g|G][e|E][n|N][t|T]"/>       </xs:restriction>     </xs:simpleType>     <xs:complexType name="PriorityType">       <xs:annotation>         <xs:documentation>Exactly one of the three attributes must             appear </xs:documentation>Lennox, et al.              Standards Track                    [Page 65]

RFC 3880                          CPL                       October 2004       </xs:annotation>       <xs:group ref="Node"/>       <xs:attribute name="less" type="PriorityValues"/>       <xs:attribute name="greater" type="PriorityValues"/>       <xs:attribute name="equal" type="xs:string">         <xs:annotation>           <xs:documentation>case-insensitive</xs:documentation>         </xs:annotation>       </xs:attribute>       <xs:anyAttribute namespace="##any" processContents="lax"/>     </xs:complexType>     <xs:complexType name="PrioritySwitchType">       <xs:complexContent>         <xs:extension base="SwitchType">           <xs:sequence>             <xs:element name="priority" type="PriorityType"                 minOccurs="0" maxOccurs="unbounded"/>             <xs:sequence minOccurs="0">               <xs:element name="not-present" type="NotPresentAction"/>               <xs:element name="priority" type="PriorityType"                   minOccurs="0" maxOccurs="unbounded"/>             </xs:sequence>             <xs:element name="otherwise" type="OtherwiseAction"                 minOccurs="0"/>           </xs:sequence>         </xs:extension>       </xs:complexContent>     </xs:complexType>     <xs:element name="priority-switch" type="PrioritySwitchType"         substitutionGroup="switch"/>     <xs:simpleType name="LocationPriorityType">       <xs:restriction base="xs:float">         <xs:minInclusive value="0.0"/>         <xs:maxInclusive value="1.0"/>       </xs:restriction>     </xs:simpleType>     <xs:complexType name="LocationType">       <xs:complexContent>         <xs:extension base="ModifierType">           <xs:group ref="Node"/>           <xs:attribute name="url" type="xs:anyURI" use="required"/>           <xs:attribute name="priority" type="LocationPriorityType"               use="optional" default="1.0"/>           <xs:attribute name="clear" type="YesNoType" default="no"/>         </xs:extension>       </xs:complexContent>     </xs:complexType>     <xs:complexType name="LookupType">Lennox, et al.              Standards Track                    [Page 66]

RFC 3880                          CPL                       October 2004       <xs:complexContent>         <xs:extension base="ModifierType">           <xs:all>             <xs:element name="success" minOccurs="0">               <xs:complexType>                 <xs:group ref="Node"/>               </xs:complexType>             </xs:element>             <xs:element name="notfound" minOccurs="0">               <xs:complexType>                 <xs:group ref="Node"/>               </xs:complexType>             </xs:element>             <xs:element name="failure" minOccurs="0">               <xs:complexType>                 <xs:group ref="Node"/>               </xs:complexType>             </xs:element>           </xs:all>           <xs:attribute name="source" type="xs:string"               use="required"/>           <xs:attribute name="timeout" type="xs:positiveInteger"               default="30"/>           <xs:attribute name="clear" type="YesNoType" default="no"/>         </xs:extension>       </xs:complexContent>     </xs:complexType>     <xs:complexType name="RemoveLocationType">       <xs:complexContent>         <xs:extension base="ModifierType">           <xs:group ref="Node"/>           <xs:attribute name="location" type="xs:string"               use="optional"/>         </xs:extension>       </xs:complexContent>     </xs:complexType>     <xs:complexType name="LogAction">       <xs:complexContent>         <xs:extension base="ActionType">           <xs:group ref="Node"/>           <xs:attribute name="name" type="xs:string" use="optional"/>           <xs:attribute name="comment" type="xs:string"               use="optional"/>         </xs:extension>       </xs:complexContent>     </xs:complexType>     <xs:element name="log" type="LogAction"         substitutionGroup="action"/>Lennox, et al.              Standards Track                    [Page 67]

RFC 3880                          CPL                       October 2004     <xs:complexType name="IncomingType">       <xs:complexContent>         <xs:extension base="TopLevelActionType"/>       </xs:complexContent>     </xs:complexType>     <xs:element name="incoming" type="IncomingType"         substitutionGroup="toplevelaction"/>     <xs:complexType name="OutgoingType">       <xs:complexContent>         <xs:extension base="TopLevelActionType"/>       </xs:complexContent>     </xs:complexType>     <xs:element name="outgoing" type="OutgoingType"         substitutionGroup="toplevelaction"/>     <xs:complexType name="ProxyAction">       <xs:complexContent>         <xs:extension base="ActionType">           <xs:all>             <xs:element name="busy" minOccurs="0">               <xs:complexType>                 <xs:group ref="Node"/>               </xs:complexType>             </xs:element>             <xs:element name="noanswer" minOccurs="0">               <xs:complexType>                 <xs:group ref="Node"/>               </xs:complexType>             </xs:element>             <xs:element name="failure" minOccurs="0">               <xs:complexType>                 <xs:group ref="Node"/>               </xs:complexType>             </xs:element>             <xs:element name="redirection" minOccurs="0">               <xs:complexType>                 <xs:group ref="Node"/>               </xs:complexType>             </xs:element>             <xs:element name="default" minOccurs="0">               <xs:complexType>                 <xs:group ref="Node"/>               </xs:complexType>             </xs:element>           </xs:all>           <xs:attribute name="timeout" type="xs:positiveInteger"               use="optional" default="20"/>           <xs:attribute name="recurse" type="YesNoType"               use="optional" default="yes"/>Lennox, et al.              Standards Track                    [Page 68]

RFC 3880                          CPL                       October 2004           <xs:attribute name="ordering" type="OrderingType"               use="optional" default="parallel"/>         </xs:extension>       </xs:complexContent>     </xs:complexType>     <xs:element name="proxy" type="ProxyAction"         substitutionGroup="action"/>     <xs:complexType name="RedirectAction">       <xs:complexContent>         <xs:extension base="ActionType">           <xs:attribute name="permanent" type="YesNoType"               default="no"/>         </xs:extension>       </xs:complexContent>     </xs:complexType>     <xs:element name="redirect" type="RedirectAction"         substitutionGroup="action"/>     <xs:complexType name="RejectAction">       <xs:complexContent>         <xs:extension base="ActionType">           <xs:attribute name="status" type="StatusType"               use="required"/>           <xs:attribute name="reason" type="xs:string"               use="optional"/>         </xs:extension>       </xs:complexContent>     </xs:complexType>     <xs:element name="reject" type="RejectAction"         substitutionGroup="action"/>     <xs:complexType name="MailAction">       <xs:complexContent>         <xs:extension base="ActionType">           <xs:group ref="Node"/>           <xs:attribute name="url" type="xs:anyURI" use="required"/>         </xs:extension>       </xs:complexContent>     </xs:complexType>     <xs:element name="mail" type="MailAction"         substitutionGroup="action"/>     <xs:complexType name="SubAction">       <xs:attribute name="ref" type="xs:string" use="required"/>     </xs:complexType>     <xs:complexType name="AncillaryType"/>     <xs:complexType name="SubactionType">       <xs:group ref="Node"/>       <xs:attribute name="id" use="required"/>     </xs:complexType>     <xs:complexType name="CPLType">Lennox, et al.              Standards Track                    [Page 69]

RFC 3880                          CPL                       October 2004       <xs:sequence>         <xs:element name="ancillary" type="AncillaryType" minOccurs="0"             maxOccurs="1"/>         <xs:element name="subaction" type="SubactionType" minOccurs="0"             maxOccurs="unbounded"/>         <xs:element ref="toplevelaction" minOccurs="0"             maxOccurs="unbounded">           <xs:annotation>             <xs:documentation>Any toplevel action MUST NOT appear more                 than once.</xs:documentation>           </xs:annotation>         </xs:element>       </xs:sequence>     </xs:complexType>     <xs:element name="cpl" type="CPLType"/>   </xs:schema>   ENDNormative References   [1]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,        Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:        Session Initiation Protocol",RFC 3261, June 2002.   [2]  Bray, T., Paoli, J., Sperberg-McQueen, C. M., Maler, E., and F.        Yergeau, "Extensible Markup Language (XML) 1.0 (Third Edition)",        W3C Recommendation REC-xml-20040204, World Wide Web Consortium        (W3C), February 2004.  Available athttp://www.w3.org/XML/.   [3]  Bradner, S., "Key words for use in RFCs to Indicate Requirement        Levels",BCP 14,RFC 2119, March 1997.   [4]  Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6)        Addressing Architecture",RFC 3513, April 2003.   [5]  Davis, M. F. and M. Duerst, "Unicode Normalization Forms",        Unicode Standard Annex #15, Unicode Consortium, April 2003.        Revision 23; part of Unicode 4.0.0. Available athttp://www.unicode.org/unicode/reports/tr15/.   [6]  Davis, M. F., "Case Mappings", Unicode Standard Annex #21,        Unicode Consortium, March 2001.  Revision 5; part of Unicode        3.2.0.  Available athttp://www.unicode.org/unicode/reports/tr21/.   [7]  Alvestrand, H., "Tags for the Identification of Languages",BCP47,RFC 3066, January 2001.Lennox, et al.              Standards Track                    [Page 70]

RFC 3880                          CPL                       October 2004   [8]  Dawson, F. and D. Stenerson, "Internet Calendaring and        Scheduling Core Object Specification (iCalendar)",RFC 2445,        November 1998.   [9]  Eggert, P., "Sources for Time Zone and Daylight Saving Time        Data".  Available athttp://www.twinsun.com/tz/tz-link.htm.   [10] Mealling, M. and R. Daniel, "URI Resolution Services Necessary        for URN Resolution",RFC 2483, January 1999.   [11] Bray, T., Hollander, D., and A. Layman, "Namespaces in XML", W3C        Recommendation REC-xml-names-19990114, World Wide Web Consortium        (W3C), January 1999.  Available athttp://www.w3.org/TR/REC-xml-names/.   [12] Moats, R., "URN Syntax",RFC 2141, May 1997.   [13] Moats, R., "A URN Namespace for IETF Documents",RFC 2648,        August 1999.   [14] Mealling, M., "The IETF XML Registry",BCP 81,RFC 3688, January        2004.   [15] Murata, M., St.Laurent, S., and D. Kohn, "XML Media Types",RFC3023, January 2001.Informative References   [16] International Telecommunication Union, "Packet-based multimedia        communication systems", Recommendation H.323, Telecommunication        Standardization Sector of ITU, Geneva, Switzerland, July 2003.   [17] Lennox, J. and H. Schulzrinne, "Call Processing Language        Framework and Requirements",RFC 2824, May 2000.   [18] Raggett, D., Le Hors, A., and I. Jacobs, "HTML 4.01        Specification", W3C Recommendation REC-html401-19991224, World        Wide Web Consortium (W3C), December 1999.  Available athttp://www.w3.org/TR/html4/.   [19] ISO (International Organization for Standardization),        "Information processing -- Text and office systems -- Standard        Generalized Markup Language (SGML)", ISO Standard ISO        8879:1986(E), International Organization for Standardization,        Geneva, Switzerland, October 1986.Lennox, et al.              Standards Track                    [Page 71]

RFC 3880                          CPL                       October 2004   [20] ISO (International Organization for Standardization), "Data        elements and interchange formats -- Information interchange --        Representation of dates and times", ISO Standard ISO        8601:2000(E), International Organization for Standardization,        Geneva, Switzerland, December 2000.   [21] DeRose, S., Maler, E., Orchard, D., and B. Trafford, "XML        Linking Language (XLink) Version 1.0", W3C Recommendation REC-        xlink-20010627, World Wide Web Consortium (W3C), June 2001.        Available athttp://www.w3.org/TR/xlink/.   [22] Showalter, T., "Sieve: A Mail Filtering Language",RFC 3028,        January 2001.   [23] International Telecommunication Union, "Digital Subscriber        Signalling System No. 1 (DSS 1) - ISDN user-network interface        layer 3 specification for basic call control", Recommendation        Q.931, International Telecommunication Union, Geneva,        Switzerland, March 1993.   [24] Levin, O., "H.323 Uniform Resource Locator (URL) Scheme        Registration",RFC 3508, April 2003.Lennox, et al.              Standards Track                    [Page 72]

RFC 3880                          CPL                       October 2004Authors' Addresses   Jonathan Lennox   Dept. of Computer Science   Columbia University   1214 Amsterdam Avenue, MC 0401   New York, NY 10027   USA   EMail: lennox@cs.columbia.edu   Xiaotao Wu   Dept. of Computer Science   Columbia University   1214 Amsterdam Avenue, MC 0401   New York, NY 10027   USA   EMail: xiaotaow@cs.columbia.edu   Henning Schulzrinne   Dept. of Computer Science   Columbia University   1214 Amsterdam Avenue, MC 0401   New York, NY 10027   USA   EMail: schulzrinne@cs.columbia.eduLennox, et al.              Standards Track                    [Page 73]

RFC 3880                          CPL                       October 2004Full Copyright Statement   Copyright (C) The Internet Society (2004).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the IETF's procedures with respect to rights in IETF Documents can   be found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Lennox, et al.              Standards Track                    [Page 74]