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Internet Engineering Task Force                                 IPTEL WG
Internet Draft                                        Lennox/Schulzrinne
ietf-iptel-sip-reg-payload-00.txt                    Columbia University
February 23, 1999
Expires: September 1999


     Transporting User Control Information in SIP REGISTER Payloads

STATUS OF THIS MEMO

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

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

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

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


Abstract

   Several newly developed languages and interfaces, such as the CPL and
   SIP CGI, allow users or administrators to specify how Internet
   telephony servers should process calls. There needs to be a method of
   transporting scripts for such languages between a client and a
   server. This document proposes using the payload of SIP REGISTER
   messages, and their responses, as one method to transport them.



1 Introduction

   Several newly developed languages and interfaces, such as the CPL [1]
   and SIP CGI [2] allow users or administrators to specify how Internet
   telephony servers should process calls. Scripts typically can be
   created on a client, but executed on an Internet telephony server.

   There therefore needs to be a method of transporting these scripts
   from a client to a server, and of retrieving them from the server so



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   the client can know the current status or modify the script. This
   method should integrate cleanly with the existing infrastructure of
   Internet telephony, without requiring significant additional protocol
   traffic or complexity in either a client or a server.

   This document proposes using the payload of SIP [3] REGISTER
   messages, and their responses, as the media to transport these
   scripts to SIP registration servers alongside the user's
   registration.  Since clients typically will need to register anyway,
   and servers will need to have registrars to process the clients'
   registrations, this technique does not impose much additional
   overhead on servers and clients.

   This technique is not appropriate for all environments -- most
   obviously, it is not useful for H.323 [4] servers -- and we do not
   anticipate that it will be the only such transport mechanism
   developed. Other protocols considered have included transporting
   scripts over LDAP [5], ACAP [6], or HTTP file upload [7], or
   transport mechanisms developed from scratch.

2 Transport Details

   To upload a script, the registration client places the script in the
   body of the SIP REGISTER request. Bodies of SIP requests are
   described in [3]. The Content-Type header field is set to the media
   type of the submitted script. Currently, we expect to register
   application/sip-cgi as the content type for SIP CGI scripts, and
   application/cpl for CPL scripts.

   To inform a client of what types of scripts it supports, a server
   SHOULD send the media types of its supported scripts in Accept header
   fields in the response to any successful OPTIONS or REGISTER request.


        Allowing the client to restrict transmitted scripts by
        media type allows clients connected by a low-bandwidth
        network avoid downloading lengthy scripts.


        Note: this is against the strict wording of the SIP
        specification, which says that Accept headers are only
        allowed in requests or 415 (Unsupported Media Type)
        responses. However, it is always legal to include a header
        in any request or response, as clients which do not
        understand it in a given context simply ignore it.

   In a successful response to any REGISTER request, whether or not a
   script payload was included, the server SHOULD return the currently



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   specified script in the response body, with its type specified in
   Content-Type, unless the REGISTER request included a set of Accept
   headers which did not include the type of the registration script.
   The server SHOULD NOT return the currently registered script if
   response to the registration request was an error condition.

   The server MAY perform validation on scripts at the time they are
   uploaded to the server. If the script is not valid, the server SHOULD
   return a 400-class error to the registration request indicating the
   problem.  It MAY include in the body of the response an explanation
   of the problem as, for instance, text/html or text/plain , if the
   client specified such a type in its Accept header.

   When a script of the same type as an existing script is uploaded, the
   script is replaced in the server. Which script applies to calls in
   progress at the time the script was changed is not defined by this
   document, but MAY be specified by specifications of script languages.
   If the current or new script affects the handling of REGISTER
   requests, the registration is handled entirely by the existing
   script; the new script does not take effect until the registration
   process is complete.

   The result of uploading a script of a different type from the one
   currently registered is undefined; if a client wants to change its
   script from one type to another, it SHOULD first delete the old
   script by the method described below, then upload a new one. A server
   MAY support simultaneous registration of separate scripts of
   different types.


        This ambiguity allows a simple server to have a single
        script per user, while a more complex server might allow
        users to specify simultaneous CGI and CPL scripts, for
        example.

   To delete a script, a client sends a REGISTER message with its
   Content-Type set to the type of the current script and a Content-
   Length of 0. If the request specifies a Content-Type other than that
   of a currently defined script, the behavior is undefined. When a
   script is deleted, the server SHOULD return to its default call
   handling behavior for subsequent calls, just as if no script had ever
   been uploaded.


        Question: should this technique have a Require header?
        It's possible someone might use REGISTER bodies for some
        other purpose.




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3 Persistence Model

   Registrations in SIP are normally transient -- the data in the
   Contact header fields last only for the length of time specified in
   the registration's Expires header, and clients must refresh their
   registrations periodically.

   In contrast, scripts sent to registration servers using the method
   described in this document are persistent -- they remain in the
   server until replaced or deleted, and they do not need to be
   refreshed. Servers SHOULD therefore store uploaded scripts in non-
   volatile storage so they persist through server restarts or failures.
   Clients SHOULD only upload scripts when they are explicitly requested
   to, and SHOULD NOT transmit their scripts in every registration
   request.


        The model of standard SIP registrations is that each client
        registers itself; if a location changes or hosts die, old
        registrations naturally time out. Since a user can be
        simultaneously registered from many locations, several
        clients re-registering periodically present no conflicts.

   The model of scripts is quite different. A user only has one script
   (or at least only of a given type) at a time, so if clients
   periodically re-uploaded scripts, two clients with different
   specified scripts would cause "script flapping," as the behavior
   specified in the server changed frequently, with unpredictable and
   probably surprising behavior. Moreover, one of the most important
   purposes of scripts is to control the processing of a user's requests
   when he or she is not registered from any location; if scripts timed
   out and had to be refreshed, this goal could not be accomplished.

4 Examples

   The first example shows a user uploading a simple call-filtering SIP
   CGI script written in Perl to his server. Note that he is
   transmitting both a contact address, which persists only for 30
   minutes, the time specified by the Expires header, and a script,
   which persists indefinitely.  This allows him subsequently to
   register new contact addresses and have his script apply equally to
   them. (See [2] for an explanation of SIP CGI as used in the script.)

   The use of Basic authorization here is for the purposes of the
   example only; in actual practice much more robust authentication
   SHOULD be used. See section 5.





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   REGISTER sip:@sip.example.com SIP/2.0
   From: Joe User <sip:joe@example.com>
   To: "J. User" <sip:joe@example.com>
   CSeq: 18 REGISTER
   Expires: 1800
   Call-ID: 39485832@joespc.example.com
   Contact: sip:joe@joespc.example.com
   Accept: application/sip-cgi, application/sdp, text/html
   Authorization: Basic am9lOnBhc3N3b3JkAFBX
   Content-Type: application/sip-cgi
   Content-Length: 168

   #!/usr/bin/perl
   if ($ENV{HTTP_FROM} =~ /telemarketers.com/) {
       print "SIP/2.0 603 Go awayn"
   } else {
       print "CGI-DEFAULT-ACTION dummy SIP/2.0n"
   }



   In the second example, a few minutes later, the user registers a new
   contact address, but does not change his script. In the response to
   the registration, the server reminds him of his contact addresses and
   his current script.

   His client sends this request:


   REGISTER sip:@sip.example.com SIP/2.0
   From: Joe User <sip:joe@example.com>
   To: "J. User" <sip:joe@example.com>
   CSeq: 19 REGISTER
   Expires: 1800
   Call-ID: 39485832@joespc.example.com
   Contact: sip:joe@joeshome.example.com
   Accept: application/sip-cgi, application/sdp, text/html
   Authorization: Basic am9lOnBhc3N3b3JkAFBX
   Content-Length: 0



   And the server replies with this response:


   SIP/2.0 200 OK
   From: Joe User <sip:joe@example.com>
   To: "J. User" <sip:joe@example.com>



Lennox/Schulzrinne                                            [Page 5]


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   CSeq: 19 REGISTER
   Contact: sip:joe@joespc.example.com
   Contact: sip:joe@joeshome.example.com
   Accept: application/sip-cgi, application/cpl
   Content-Type: application/sip-cgi
   Content-Length: 168

   #!/usr/bin/perl
   if ($ENV{HTTP_FROM} =~ /telemarketers.com/) {
       print "SIP/2.0 603 Go awayn"
   } else {
       print "CGI-DEFAULT-ACTION dummy SIP/2.0n"
   }



   Finally, the user decides to eliminate his script, and the server
   responds in the same manner as it would respond to an ordinary
   registration, as though no script had ever been uploaded:


   REGISTER sip:@sip.example.com SIP/2.0
   From: Joe User <sip:joe@example.com>
   To: "J. User" <sip:joe@example.com>
   CSeq: 20 REGISTER
   Call-ID: 39485832@joespc.example.com
   Contact: sip:joe@joeshome.example.com
   Authorization: Basic am9lOnBhc3N3b3JkAFBX
   Accept: application/sip-cgi, application/sdp, text/html
   Content-Type: application/sip-cgi
   Content-Length: 0




   SIP/2.0 200 OK
   From: Joe User <sip:joe@example.com>
   To: "J. User" <sip:joe@example.com>
   CSeq: 20 REGISTER
   Contact: sip:joe@joespc.example.com
   Contact: sip:joe@joeshome.example.com
   Accept: application/sip-cgi, application/cpl
   Content-Length: 0



5 Security Considerations




Lennox/Schulzrinne                                            [Page 6]


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   Since the scripts transported by this mechanism control how a server
   directs private information intended for a user, the server MUST
   reject all un-authenticated attempts to submit a script, and SHOULD
   require that the authentication method used verifies the integrity of
   the submitted script; for example, by having the entire request,
   including its body, signed with SIP's PGP authentication method.

6 Authors' Addresses

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

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

7 Bibliography

   [1] J. Lennox and H. Schulzrinne, "CPL: A language for user control
   of internet telephony services," Internet Draft, Internet Engineering
   Task Force, Feb.  1999.  Work in progress.

   [2] J. Lennox, J. Rosenberg, and H. Schulzrinne, "Common gateway
   interface for SIP," Internet Draft, Internet Engineering Task Force,
   Nov. 1998.  Work in progress.

   [3] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP:
   session initiation protocol," Internet Draft, Internet Engineering
   Task Force, Jan. 1999.  Work in progress.

   [4] International Telecommunication Union, "Visual telephone systems
   and equipment for local area networks which provide a non-guaranteed
   quality of service," Recommendation H.323, Telecommunication
   Standardization Sector of ITU, Geneva, Switzerland, May 1996.

   [5] T. Howes, S. Kille, and M. Wahl, "Lightweight directory access
   protocol (v3)," Request for Comments (Proposed Standard) 2251,
   Internet Engineering Task Force, Dec. 1997.




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   [6] J. Myers and C. Newman, "ACAP -- application configuration access
   protocol," Request for Comments (Proposed Standard) 2244, Internet
   Engineering Task Force, Dec. 1997.

   [7] E. Nebel and L. Masinter, "Form-based file upload in HTML,"
   Request for Comments (Experimental) 1867, Internet Engineering Task
   Force, Nov. 1995.


   Full Copyright Statement

   Copyright (c) The Internet Society (1999). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS 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.




                           Table of Contents



   1          Introduction ........................................    1
   2          Transport Details ...................................    2
   3          Persistence Model ...................................    4
   4          Examples ............................................    4



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   5          Security Considerations .............................    6
   6          Authors' Addresses ..................................    7
   7          Bibliography ........................................    7
















































Lennox/Schulzrinne                                            [Page 9]


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