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Versions: 00                                                            
SIMPLE                                                        M. Isomaki
Internet-Draft                                                     Nokia
Intended status: Informational                              J. Rosenberg
Expires: December 24, 2006                                 Cisco Systems
                                                           June 22, 2006

   Advanced Instant Messaging Requirements for the Session Initiation
                             Protocol (SIP)

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
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Copyright Notice

   Copyright (C) The Internet Society (2006).


   Session Initiation Protocol (SIP) supports the basic instant
   messaging service in both page and session mode.  This document
   defines a set of requirements for instant messaging capabilities that
   are beyond the scope of the baseline specifications.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Instant Messaging Disposition Notifications  . . . . . . . . .  3
   4.  Is-Composing . . . . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Content Capabilities . . . . . . . . . . . . . . . . . . . . .  7
   6.  Page-Mode Groups . . . . . . . . . . . . . . . . . . . . . . .  8
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  8
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     10.1.  Normative References  . . . . . . . . . . . . . . . . . .  8
     10.2.  Informative References  . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
   Intellectual Property and Copyright Statements . . . . . . . . . . 11

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1.  Introduction

   The Session Initiation Protocol (SIP) defines several specifications
   that support Instant Messaging (IM).  The SIP MESSAGE method [3]
   allows for "page-mode" messaging, offering a service in some aspects
   similar to Short Message Service (SMS) in wireless networks.  A more
   advanced capability, called session mode messaging, uses the SIP
   INVITE method to establish a session where messages are transported
   using Message Session Relay Protocol (MSRP) [9].  This makes it
   possible to combine messaging with other media such as audio and
   video.  Also, many regular SIP capabilities to be directly applied to
   instant messaging, such as conferencing [10].

   However, there are many additional features that exist in current,
   proprietary IM systems.  Some of these features do not require
   protocol extensions in order to be deployed (IM message archival, for
   example).  However, others do.

   This document provides requirements for a number of advanced IM
   features which require additional standardization activity in
   addition to the basic SIP MESSAGE and MSRP work.  For some of the
   requirements presented here the relevant standardization work has
   actully been already concluded.  In those cases the related
   specifications are called out and referenced.

2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
   described in BCP 14, RFC 2119 [1] and indicate requirement levels for
   compliant implementations.

3.  Instant Messaging Disposition Notifications

   In most cases, an IM is delivered immediately to the recipient.
   Indeed, this is the principal motivation behind the "Instant" in
   "Instant Messaging".  However, in many systems, an instant message
   can be sent even when the recipient is not available.  Indeed, even
   if they are available when the message is sent, the user may log off
   before the message can be delivered.  In addition to basic delivery
   reporting, the sender may be interested when the recipient has
   actually "read" the message or the message has been at least
   displayed to the user in some way.

   Typically, this is dealt with through a combination of two features.

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   The first is message archival and retrieval.  These features allow
   the intended recipient to retrieve their messages at a later time.
   To support this, the receiving domain stores the content of the IM,
   allowing the user to fetch it later.  In this regard, it is very
   similar to existing email systems.  Existing protocols, such as IMAP4
   [8], can be used for the retrieval functions of IM.

   The second feature is message disposition notification.  This feature
   allows the sender to be notified when the message has been delivered
   to the recipient and when the recipient has "read" the message.  This
   feature exists in SMS, email [11] and several commercia IM systems.
   A similar function is needed for SIP-based instant messaging.

   Certainly, much of the email specifications for message delivery
   confirmation can be reused for IM.  However, much of it is email-
   specific, and IM introduces some new requirements.  The following
   requirements apply to IM disposition notifications:

      REQ-DISNOT-1: It MUST be possible for the sender of an IM to
      request a delivery notification and/or a read notification.

      REQ-DISNOT-2: It MUST be possible for the recipient of the message
      to immediately indicate to the sender that the recipient supports
      delivery and/or read notifications.

      REQ-DISNOT-3: It MUST be possible that the disposition
      notifications can be sent and received at any point in the future
      after the actual IM has been sent, without introducing any limits
      on such a time window.

      REQ-DISNOT-4: The delivery notification MUST be capable of
      indicating that the message was delivered to the intended target.

      REQ-DISNOT-5: The delivery notification MUST be capable of
      indicating whether the message was delivered successfully, or
      whether, when it was delivered, the recipient geneeated an error.
      It MUST be possible for the sender to learn the specific error

      REQ-DISNOT-6: The disposition notification MUST indicate the time
      when the message was delivered or read.

      REQ-DISNOT-7: The disposition notification MUST contain enough
      information to allow the sender of the original IM to correlate
      the notification with the correct message, provided that the
      sender has stored the contents of the sent message.  In addition
      the notification MUST be able to carry information that might be
      helpful to a sender who no longer has the original message

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      available, such as the original To, From, Content-Type and
      Content-Length headers.

      REQ-DISNOT-8: It MUST be possible for the message sender (the
      recipient of the notification) to authenticate the sender of the
      notification.  There is no explicit requirement for confidentialy
      of the notification.

      REQ-DISNOT-9: As it is anticipated that this mechanism will be
      used frequently from wireless devices, it SHOULD keep overhead to
      a minimum, and in particular, SHOULD NOT provide extraneous
      information not relevant to the above requirements.

      REQ-DISNOT-10: When an IM is sent to an intermediary that will
      relay it to a group of recipients, it MUST be possible for the
      sender to ask that disposition notifications are generated by each
      final recipient separately.

      REQ-DISNOT-11: When an IM is sent to an intermediary that will
      relay it to a group of recipients, it MUST be possible for the
      sender to ask that the intermediary will generate summary reports
      based on reports it receives from each final recipient.  [OPEN
      ISSUE: Is this needed?]

      REQ-DELNOT-12: Any error condition reported by the notification
      MAY contain a textual description of the error meant for human
      consumption [OPEN ISSUE: How about internationalization?]

      REQ-DELNOT-13: If an IM is being relayed through a gateway, for
      example, to SMS, the delivery report SHOULD be able to indicate
      such a condition [OPEN ISSUE: Is this needed?]]

4.  Is-Composing

   Many commercial instant messaging and presence systems provide a
   feature generally referred to as "is-typing".  This feature is used
   during instant messaging chat sessions.  Whenever one user is in the
   process of typing a message to another user, the recipient-to-be can
   see that a message is in progress.  This avoids a common problem
   where both participants are typing replies at the same time, so that
   the resulting stream of converation is not well synchronized.

   Generalizing this concept, the idea is really to allow one
   participant to inform another participant that they are composing a
   message of some type.  By conveying a type, a broader set of features
   can be enabled.  For example, if one user indicates that they are

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   composing a message of type audio/basic, the other user will know
   that a voice IM is coming.

   The specification of how is-composing indicators are generated and
   represented is available as RFC 3994 [13].  It has been designed
   based on the requirements listed in this Section.

      REQ-COMP-1: The is-composing feature MUST work with instant
      messaging sessions [9].

      REQ-COMP-2: Either side in the session should be able to indicate
      that they can receive the indicators.  The indicators MUST NOT be
      sent from A to B if B does not explicitly indicate that they can
      receive them.

      REQ-COMP-3: It MUST be possible for indicators to be sent in only
      one direction, i.e., A sends them to B, but B does not send them
      to A.

      REQ-COMP-4: It MUST be possible for usage of the indicators to be
      added or removed to any IM session after the session has begun.

      REQ-COMP-5: The indicator MUST be able to inform the recipient
      that the sender has begun composing a message.

      REQ-COMP-6: The indicator MUST be able to inform the recipient
      that the sender has stopped composing a message.

      REQ-COMP-7: The indicator MUST be able to convey the MIME type of
      the message that is being composed.

      REQ-COMP-8: The indicator must be synchrnonized with the message
      stream itself.  That is, if a recipient gets an indicator that a
      user has stopped composing a message, and they also get a message,
      the recipient must be able to know which came first.

      REQ-COMP-9: It must be possible to provide end-to-end message
      integrity and authentication over the indicators.

      REQ-COMP-10: It must be possible to associate the is-composing
      indicator with a particular instant messaging session.

      REQ-COMP-11: It should be possible to interwork is-composing
      indicators between CPIM compliant systems, possibly with some loss
      of functionality, but with integrity and authentication in tact.

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      REQ-COMP-12: It should be possible for is-composing indicators to
      work, possibly with loss of functionality, in page mode.

      REQ-COMP-13: The is-composing indicator should not result in an
      increase on the load of proxies.

      REQ-COMP-14: It must be possible to receive delivery confirmation
      reports for is-composing indicators [OPEN ISSUE: This is related
      to the question on whether disposition notifications will be
      supported for session-mode messaging.]

      REQ-COMP-15: The overhead of the indicators should be minimal.

5.  Content Capabilities

   Although traditionally used with text, an IM can contain any kind of
   content.  There is an increasing trend to send multimedia content,
   including audio, video, and even applications, over IM.  However,
   recipients may not wish to receive content that they do not
   understand, or is over a particular size limit.

   Handling these "content capabilities" is done differently for page
   mode and session mode.  In session mode, the initial offer/answer
   exchange [4] can be used to convey content capabilities.  Indeed, the
   messaging sessions mechanism allows for negotiation of supported
   content types.  However, some additional aspects of negotiation are

      REQ-CONTENT-1: A UA MUST be able to indicate the maximum message
      size it is willing to receive.

      This requirement has been met in MSRP via the a=max-size

   In page mode messaging, a 413 response can be sent if a MESSAGE
   request is too large.  However, there is no way to indicate what the
   largest allowed size is:

      REQ-CONTENT-2: A 413 response MUST be capable of indicating the
      maximum allowed message size.  [OPEN ISSUE: Is this needed?]

   Note that, there is no requirement to support transcoding of content
   at an intermediary in order to reduce the size of a sent message to
   match that of a recipient.

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6.  Page-Mode Groups

   The baseline SIP MESSAGE specification does not have explicit support
   for sending page mode messages to groups or multiple recipients.
   This capability is addressed by the Multi-recipient MESSAGE request
   [12] specification to meet the following requirements.

      REQ-GROUP-1: It MUST be possible to address a page-mode IM to a

      REQ-GROUP-2: Each recipient of a group page IM MUST be capable of
      determining the set of other recipients that got the request.

      REQ-GROUP-3: It MUST be possible for a user to send to an ad-hoc
      group, where the identities of the recipients are carried in the
      message itself.

      REQ-GROUP-4: It MUST be possible for the recipient of a group IM
      to send a message to all other participants that received the same
      group IM (i.e., Reply-To-All).

7.  IANA Considerations

   There are no IANA Considerations associated with this specification.

8.  Security Considerations

   Security requirements are discussed above where relevant.

9.  Acknowledgments

   This draft includes requirements contributed by Aki Niemi [14].  Eric
   Burger, Ben Campbell, Hisham Khartabil, Paul Kyzivat, Aki Niemi, Sean
   Olson and Robert Sparks provided valuable comments.

10.  References

10.1.  Normative References

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

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10.2.  Informative References

   [2]   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.

   [3]   Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C., and
         D. Gurle, "Session Initiation Protocol (SIP) Extension for
         Instant Messaging", RFC 3428, December 2002.

   [4]   Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
         Session Description Protocol (SDP)", RFC 3264, June 2002.

   [5]   Day, M., Aggarwal, S., Mohr, G., and J. Vincent, "Instant
         Messaging / Presence Protocol Requirements", RFC 2779,
         February 2000.

   [6]   Day, M., Rosenberg, J., and H. Sugano, "A Model for Presence
         and Instant Messaging", RFC 2778, February 2000.

   [7]   Vaudreuil, G. and G. Parsons, "Voice Profile for Internet Mail
         - version 2", RFC 2421, September 1998.

   [8]   Crispin, M., "Internet Message Access Protocol - Version
         4rev1", RFC 2060, December 1996.

   [9]   Campbell, B., "The Message Session Relay Protocol",
         draft-ietf-simple-message-sessions-14 (work in progress),
         February 2006.

   [10]  Rosenberg, J., "A Framework for Conferencing with the Session
         Initiation Protocol (SIP)", RFC 4353, February 2006.

   [11]  Moore, K. and G. Vaudreuil, "An Extensible Message Format for
         Delivery Status Notifications", RFC 3464, January 2003.

   [12]  Garcia-Martin, M. and G. Camarillo, "Multiple-Recipient MESSAGE
         Requests in the Session Initiation Protocol  (SIP)",
         draft-ietf-sipping-uri-list-message-07 (work in progress),
         February 2006.

   [13]  Schulzrinne, H., "Indication of Message Composition for Instant
         Messaging", RFC 3994, January 2005.

   [14]  Niemi, A., "Requirements for Instant Messaging in 3GPP Wireless
         Systems", draft-niemi-simple-im-wireless-reqs-02 (work in
         progress), October 2003.

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Authors' Addresses

   Markus Isomaki
   Keilalahdentie 2-4
   Helsinki,   02150

   Phone: +358 50 5225984
   Email: markus.isomaki@nokia.com

   Jonathan Rosenberg
   Cisco Systems
   600 Lanidex Plaza
   Parsippany, NJ  07054

   Phone: +1 973 952-5000
   Email: jdrosen@cisco.com
   URI:   http://www.jdrosen.net

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