RFC 
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Network Working Group  C. Jennings 
INTERNET DRAFT  Cisco Systems, Inc. 
<draft-jennings-sipping-instance-id-00.txt>   February 2004 
Category: Informational   
Expires: August 2004   

Instance Identifiers for SIP User Agents
draft-jennings-sipping-instance-id-00.txt

Status of this Memo

This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts.

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

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

The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html.

This Internet-Draft will expire in August 2004.

Copyright Notice

Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

There are places in building SIP [2] based communications systems where it is useful to have a stable identifier for particular user agents that are used for user communications. This draft defines a convention for names that can be used to satisfy these needs.


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Table of Contents

Conventions and Definitions
Introduction and Use Cases
Requirements
Solution
Discussion
BNF
Example
Security Consideration
Open Issues
10  Acknowledgments
§  Normative References
§  Informative References
§  Author's Address
§  Full Copyright Statement


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1  Conventions and Definitions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [3].


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2  Introduction and Use Cases

There are a few cases in which it is convenient to be able to identify instances of a user agent. Some examples are described. They all require the name to be stable across reboots of the device.

In the config framework[4], a user agent sends a subscribe to fetch its configuration. It needs to get the same configuration each time.
A particular user, Alice, has several user agents that all register as Alice. A registrar wishes to report which user agent are currently registered to a network management system. For this reporting to make sense, each of Alice's user agents must have a stable name.
A system that is using the dialog package to monitor a particular user agent would like to be able to assign an alias like "My Office Phone" for display purposes to that particular user agent.
When several presence user agents are providing presence data, it must be possible to correlate a particular set of data with the particular device that provided it.

In all these cases, the user agent could be a software program running on a computer with more than one user.


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3  Requirements

The identifier needs to be unique.

Identifiers are needed for user agents that are in dedicated pieces of hardware such as IP phones.

Identifiers are needed for software user agents running on multi-user computers.

In some of the cases with IP phones, it is desirable for this same identifier to be recorded as a bar code on the outside of the box that the IP phone comes in.


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4  Solution

User agents that follow the convention of this document MUST put a unique identifier in a new tag, called "instance", of the Contact header when sending a SIP request. They MAY omit this for a particular sequence of SIP messages if the user has requested it be removed for privacy reasons.

The unique identifier has no real semantic information other than uniqueness. In cases in which the user agent runs on a single computer and this is the only user agent on that computer, the MAC address of the primary network card is the preferred identifier. In cases in which it is impossible to use the MAC address, then when the user agent is first run, it should generate a random 64 bit number and use this as the identifier. It MUST store this number in some non volatile storage that is stable over reboots and power outages. The user agent SHOULD use the same instance identifier tag even if it is registering different AOR or contacts.

If the identifier is a MAC address, it MUST be formatted as the letters "MAC-" followed by a 12 digit hexadecimal representation of the MAC address. The address can not include ":", whitespace, or other formatting. If the identifier is a random number, it MUST be formatted as the letters "RANID-" followed by a 16 digit hexadecimal representation of the number. Note that the identifiers are case sensitive and all alpha characters are upper case.

The MAC and RANDID identify the namespace for the unique identifier. In the future this unique identifer namespace may be extended with other namespaces that use unique identifiers from things like USB, Bluetooth, or Firewire.

These same identifiers may be used in the user portion of request URIs when that is appropriate. A SUBSCRIBE for configuration information is a good example.


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5  Discussion

The contact header in a SIP request identifies an address that can be used to reach the device that is sending the request. This address may change each time the device running the user agent gets a new IP address, but it is very reasonable for the display name to give a unique identifier for what this instance of the user agent wishes to be known by. Right now SIP does not give any recommendation on what to place in the field. This document suggests a naming convention for this.

MAC addresses are usually put on the outside of the box for IP phones in a form that humans can read and also by a barcode scanner.


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6  BNF

The following ABNF follows the rules in RFC-2234 [1] and updates the BNF in RFC 3261.

   contact-params = c-p-q / c-p-expires / c-p-instance 
                    / contact-extentions
   c-p-intance = "instance" EQUAL uniq-ident
   UHEX  =  DIGIT / %x41-46 ;uppercase A-F
   MAC  =  %x4d.41.43 ; MAC in caps
   RANDID  = %x52.41.4e.44.49.44 ; RANDID in caps
   uniq-ident = ( mac-ident / rand-ident )
   mac-ident = MAC "-" 12UHEX
   rand-ident = RANDID "-" 16UHEX

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7  Example

The following are some valid Contact headers:

Contact: <sip:alice@host22.example.com>;instance=MAC-123456789ABC 
Contact: <sip:alice@host22.example.com>;instance=
         RANDID-0123456789ABCDEF

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8  Security Consideration

The unique identifer reveals further privacy related information to other people that see the SIP signalling. Currently user agents put an IP address or DNS name in the contact header, so the amount of extra information this reveals is very minimal. The MAC address may reveal the manufacturer of the user agent.


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9  Open Issues

Would this be better in an "Instance-ID" header?

Would this be better in the User-Agent header? Some systems are doing already doing this.

Is 64 bits the right size for the random identifier?

Is requiring upper case appropriate?


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10  Acknowledgments

Many thank for the useful comments and improvements from Louis Pratt, Steve Levy, Rohan Mahy, and Randy Baird as well as the list discussion from Jonathan Rosenberg.


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Normative References

[1] Crocker, D.H. and Overell, P., "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997.
[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. and Schooler, E., "SIP: Session Initiation Protocol", RFC 3261, June 2002.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.

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Informative References

[4] Petrie, D, "A Framework for SIP User Agent Configuration", Internet-Draft draft-ietf-sipping-config-framework-00, March 2003.

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Author's Address

  Cullen Jennings
  Cisco Systems, Inc.
  170 West Tasman Dr.
MS: SJC-21/2
  San Jose, CA 95134
  USA
Phone:  +1 408 902 3341
EMail:  fluffy@cisco.com
 

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Full Copyright Statement

Copyright (C) The Internet Society (2004). 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.

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Acknowledgement

Funding for the RFC editor function is currently provided by the Internet Society.