Internet Engineering Task Force Rohan Mahy Internet Draft Ilya Slain Document: draft-mahy-sipping-message-waiting-00.txt Cisco Systems Expires: May 2002 Nov 2001 SIP Event Package for Message Waiting Indication 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 document is an individual submission to the IETF. Comments should be directed to the authors. 1. Abstract This draft proposes an event package for SIP to carry message waiting status and message summaries from a messaging system to an interested User Agent. 2. Conventions used in this document 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. Background and Appropriateness Messaging Waiting Indication is a common feature of telephone networks. It typically involves playing a special dial tone (called message-waiting dial tone), lighting a light or indicator on the phone, or both. Message-waiting dial tone is similar but distinct from stutter dial tone. Both are defined in [GR506]. The methods in SIP 2.0, as defined in RFC2543 [SIP], were only designed to solve the problem of session initiation for multimedia Mahy, Slain Expires: May 2002 [Page 1] Internet Draft SIP Message Waiting Nov 2001 sessions, and rendezvous. Since Message Waiting Indication is really status information orthogonal to a session, it was not clear how an IP telephone acting as a SIP User Agent would implement comparable functionality. Members of the telephony community viewed this as a shortcoming of SIP. Users want the useful parts of the functionality they had using traditional analog and PBX telephones. It is also desirable to provide comparable functionality in a flexible way that allows for more customization and new features. SIP Specific Event Notification [Events] is an appropriate mechanism to use in this environment, as it preserves the user mobility and rendezvous features which SIP provides. Using SIP-Specific Event Notification, A Subscriber User Agent (typically an IP phone or SIP software User Agent) subscribes to the status of their messages. A SIP User Agent acting on behalf of the user's messaging system then notifies the Subscriber whenever the account's messages have changed. The Notifier sends this message summary information in the body of the NOTIFY, encoded in a new MIME type defined later in this draft. A User Agent can also explicitly fetch the current status. A SIP User Agent MAY subscribe to multiple accounts (distinguished by the URL in the To header). Multiple SIP User Agents MAY subscribe to the same account. Before any subscriptions or notifications are sent, each interested User Agents must be made aware of its messaging server(s). This MAY be manually configured on interested User Agents, manually configured on an appropriate SIP Proxy, or dynamically discovered using caller preferences [Caller-Prefs]. (For more information on usage with caller preferences, see section 5.2) 4. Event Package Formal Definition 4.1. Event Package Name This document defines a SIP Event Package as defined in [Events]. The event-package token name for this package is: "message-summary" 4.2. Event Package Parameters This package does not define any event package parameters. 4.3. SUBSCRIBE Bodies This package does not define any SUBSCRIBE bodies. Mahy, Slain Expires: May 2002 [Page 2] Internet Draft SIP Message Waiting Nov 2001 4.4. Subscription Duration Subscriptions to this event package MAY range from minutes to weeks. Subscriptions in hours or days are more typical and are RECOMMENDED. 4.5. NOTIFY Bodies A simple text-based format is proposed to prevent an undue burden on low-end user agents, for example, inexpensive IP phones with no display. Although this format is text-based, it is intended for machine consumption only. A future extension MAY define other NOTIFY bodies. If no "Accept" header is present in the SUBSCRIBE, the body type defined in this document SHOULD be assumed. The format specified in this proposal attempts to separate orthogonal attributes of messages as much as possible. Messages are separated by media type (audio, text, image, and video); by message status (new and old); and by urgent and non-urgent type. The text format begins with a simple status line, and optionally a summary line per media type. Valid media types are Voicemail (audio), Email (text), Fax (image), and Video (video). For each media type the total number of new and old messages is reported in the new and old fields. messsage-summary = status-line [*(summary-line)] [ mheaders ] status-line = "Messages-Waiting: " status CRLF summary-line = media-type ": " new "/" old [ urgent ] CRLF urgent = "(" new-urgent "/" old-urgent ")" status = "yes" | "no" In some cases, detailed message summaries are not available. The status line allows messaging systems or messaging gateways to provide the traditional boolean message waiting notification. Messages-Waiting: yes In the example that follows, more functionality is available to User Agent. There are one new and three old voice messages. Voicemail: 1/3 After the summary, the format can optionally list a summary count of urgent messages. Of the one new and three old voice messages, none of the new messages are urgent, but one of the old messages is. Voicemail: 1/3 (0/1) Optionally, after the summary counts, the messaging systems MAY append message headers, which further describe newly added messages. Mahy, Slain Expires: May 2002 [Page 3] Internet Draft SIP Message Waiting Nov 2001 A messaging system which includes message headers in a NOTIFY, MUST provide an administrator configurable mechanism for selecting which headers are sent. Likely headers for inclusion include To, From, Date, Subject, Message-ID, and Priority. Note that the syntax for these headers is more restrictive than for [SMTP]. Mapping local message state to new/old message status and urgency is an implementation issue of the messaging server. Message servers which use [IMAP4] SHOULD follow the most current recommendations of the [VPIM] Working Group. For SMTP encoded messages, messaging systems SHOULD follow the recommendations of the VPIM Working Group using either MIME type information or [Message-Context] to map messages to a specific media type. Systems using other encodings MAY define their own mappings. 4.6. Subscriber generation of SUBSCRIBE requests Subscriber User Agents will typically SUBSCRIBE to message summary information for a period of hours or days, and automatically attempt to re-SUBSCRIBE when the subscription is half-expired. If re- subscription fails, the Subscriber SHOULD periodically retry again (for example, after the subscription is 66%, 75%, 80%, 85%, 90%, 95%, and 99% expired) until a subscription is successful. The example retry sequence is similar to that used by [DHCP] Clients trying to renew a lease. If a subscription has expired, the Subscriber MAY attempt to renew the expired subscription in intervals of about 10% of the expires period of the original or requested subscription. These new subscriptions MUST use a new Call-ID. The Subscriber SHOULD SUBSCRIBE to that user's message summaries whenever a new user becomes associated with the device (a new login). The Subscriber MAY also explicitly fetch the current status at any time. The subscriber SHOULD renew its subscription immediately after a reboot, or when the subscriber's network connectivity has just been re-established. The Subscriber MUST be prepared to receive and process a NOTIFY with new state immediately after sending a new SUBSCRIBE, a SUBSCRIBE, renewal, an unSUBSCRIBE or a fetch; or at any time during the subscription. When a user de-registers from a device (logoff, power down of a mobile device, etc.), subscribers SHOULD unsubscribe by sending a SUBSCRIBE message with an Expires header of zero. 4.7. Notifier processing of SUBSCRIBE requests When a SIP Messaging System receives SUBSCRIBE messages with the message-summary event-type, it SHOULD authenticate the subscription request. If authentication is successful, the Notifier SHOULD limit Mahy, Slain Expires: May 2002 [Page 4] Internet Draft SIP Message Waiting Nov 2001 the duration of the subscription to an administrator defined amount of time. 4.8. Notifier generation of NOTIFY requests Immediately after a subscription is accepted, the Notifier MUST send a NOTIFY with the current message summary information. This allows the Subscriber to resynchronize its state. This initial synchronization NOTIFY MUST NOT include the optional message headers. When the status of the messages changes sufficiently for a messaging account to change the number of new or old messages, the Notifier SHOULD send a NOTIFY message to all active subscribers to that account. NOTIFY messages sent to subscribers of a group or alias, MUST place the account name in the user part of the Contact header URL. A Messaging System MAY send a NOTIFY with an "Expires" header of "0" before a graceful shutdown. 4.9. Subscriber processing of NOTIFY requests Upon receipt of a valid NOTIFY request, the subscriber SHOULD immediately render the message status and summary information to the end user in an implementation specific way. The Subscriber MUST be prepared to receive NOTIFYs from different Contacts corresponding to the same SUBSCRIBE. (the SUBSCRIBE may have been forked). 4.10. Handling of Forked Requests Forked requests are allowed for this event type and may install multiple subscriptions. The Subscriber MAY render multiple summaries to the user, or MAY merge them as described below. If any of the "Messages-Waiting" status lines report "yes", then the merged state is "yes"; otherwise the merged state is "no". status-line = "Messages-Waiting: " status CRLF status = "yes" | "no" The Subscriber MAY merge summary lines in an implementation-specific way if all notifications contain at least one summary line. summary-line = media-type ":" SP new "/" old [ urgent ] CRLF urgent = "(" new-urgent "/" old-urgent ")" A Subscriber MAY use an "alias" or "group" in the To header and/or Request-URI if that name is significant to the messaging system. Mahy, Slain Expires: May 2002 [Page 5] Internet Draft SIP Message Waiting Nov 2001 User Agents SHOULD tolerate non-SIP URI schemes in the To and From fields. 4.11. Rate of notifications A Notifier MAY choose to buffer NOTIFY responses for a short administrator-defined period (seconds or minutes) when the message status is changing rapidly. This buffering behavior is RECOMMENDED. Note that timely notification of a newly added message is probably more significant to the end user than notifications of newly deleted messages. Also note that in SIP, NOTIFY transactions MUST NOT overlap each other. The rate of Notifications is effectively limited by the round trip time between the Notifier and Subscriber. Notifiers SHOULD NOT generate NOTIFY requests more frequently than once per second. 4.12. State Agents Implementers MAY create a service which consolidates and summarizes NOTIFYs from many Contacts. This document does not preclude implementations from building state agents which support this event package. 4.13. Behavior of a Proxy Server There are no additional requirements on a SIP Proxy, other than to transparently forward the SUBSCRIBE and NOTIFY methods as required in SIP. However, Proxies SHOULD allow non-SIP URLs. Proxies and Redirect servers SHOULD be able to direct the SUBSCRIBE request to an appropriate messaging server User Agent. Proxies are encouraged to support routing to Contacts based on the existence of methods="SUBSCRIBE" and feature="voice-mail" parameters in a Request-Contact header (as specified in the caller preferences specification). 5. Examples of Usage 5.1. Example Message Flow The examples shown below are for informational purposes only. For a normative description of the event package, please see sections 4 and 6 of this document. In the example call flow below, Rohan's IP phone subscribes to the status of Rohan's messages. Via headers are omitted for clarity. Subscriber Notifier | | | A1: SUBSCRIBE (new) | |---------------------->| Mahy, Slain Expires: May 2002 [Page 6] Internet Draft SIP Message Waiting Nov 2001 | A2: 200 OK | |<----------------------| | | | A3: NOTIFY (sync) | |<----------------------| | A4: 200 OK | |---------------------->| | | | | | A5: NOTIFY (change) | |<----------------------| | A6: 200 OK | |---------------------->| | | | | | A7: (re)SUBSCRIBE | |---------------------->| | A8: 200 OK | |<----------------------| | | | A9: NOTIFY (sync) | |<----------------------| | A10: 200 OK | |---------------------->| | | | | | A11: (un)SUBSCRIBE | |---------------------->| | A12: 200 OK | |<----------------------| | | | A13: NOTIFY (sync) | |<----------------------| | A14: 200 OK | |---------------------->| A1: Subscriber (Rohan's phone) -> Notifier (Rohan's voicemail gateway) Subscribe to Rohan's message summary status for 1 day. SUBSCRIBE sip:rohan@vmail.cisco.com SIP/2.0 To: From: ;tag=78923 Date: Mon, 10 Jul 2000 03:55:06 GMT Call-Id: 1349882@rmahy-phone.cisco.com CSeq: 4 SUBSCRIBE Contact: Event: message-summary Expires: 86400 Accept: application/simple-message-summary Content-Length: 0 Mahy, Slain Expires: May 2002 [Page 7] Internet Draft SIP Message Waiting Nov 2001 A2: Notifier -> Subscriber SIP/2.0 200 OK To: ;tag=4442 From: ;tag=78923 Date: Mon, 10 Jul 2000 03:55:07 GMT Call-Id: 1349882@rmahy-phone.cisco.com CSeq: 4 SUBSCRIBE Event: message-summary Expires: 86400 Content-Length: 0 A3: Notifier -> Subscriber (immediate synchronization of current state: 2 new and 8 old [2 urgent] messages) NOTIFY sip:rohan@rmahy-phone.cisco.com SIP/2.0 To: ;tag=78923 From: ;tag=4442 Date: Mon, 10 Jul 2000 03:55:07 GMT Call-Id: 1349882@rmahy-phone.cisco.com CSeq: 20 NOTIFY Contact: Event: message-summary Content-Type: application/simple-message-summary Content-Length: 45 Messages-Waiting: yes Voicemail: 2/8 (0/2) A4: Subscriber -> Notifier SIP/2.0 200 OK To: ;tag=78923 From: ;tag=4442 Date: Mon, 10 Jul 2000 03:55:08 GMT Call-Id: 1349882@rmahy-phone.cisco.com CSeq: 20 NOTIFY Event: message-summary A5: Notifier -> Subscriber This is a notification of new messages. Some headers from the new messages are appended. NOTIFY sip:rohan@rmahy-phone.cisco.com SIP/2.0 To: ;tag=78923 From: ;tag=4442 Date: Mon, 10 Jul 2000 04:28:53 GMT Contact: Call-ID: 1349882@rmahy-phone.cisco.com CSeq: 31 NOTIFY Event: message-summary Mahy, Slain Expires: May 2002 [Page 8] Internet Draft SIP Message Waiting Nov 2001 Content-Type: application/simple-message-summary Content-Length: 420 Messages-Waiting: yes Voicemail: 4/8 (1/2) To: From: Subject: carpool tomorrow? Date: Sun, 09 Jul 2000 21:23:01 -0700 Priority: normal Message-ID: 13784434989@vmail.cisco.com To: From: Subject: HELP! at home ill, present for me please Date: Sun, 09 Jul 2000 21:25:12 -0700 Priority: urgent Message-ID: 13684434990@vmail.cisco.com A6: Subscriber -> Notifier SIP/2.0 200 OK To: ;tag=78923 From: ;tag=4442 Date: Mon, 10 Jul 2000 04:28:53 GMT Call-ID: 1349882@rmahy-phone.cisco.com CSeq: 31 NOTIFY Event: message-summary Content-Length: 0 A7: Subscriber -> Notifier Refresh subscription. SUBSCRIBE sip:rohan@vmail.cisco.com SIP/2.0 To: ;tag=4442 From: ;tag=78923 Date: Mon, 10 Jul 2000 15:55:06 GMT Call-Id: 1349882@rmahy-phone.cisco.com CSeq: 8 SUBSCRIBE Contact: Event: message-summary Expires: 86400 Accept: application/simple-message-summary Content-Length: 0 A8: Notifier -> Subscriber SIP/2.0 200 OK To: ;tag=4442 From: ;tag=78923 Date: Mon, 10 Jul 2000 15:55:07 GMT Mahy, Slain Expires: May 2002 [Page 9] Internet Draft SIP Message Waiting Nov 2001 Call-Id: 1349882@rmahy-phone.cisco.com CSeq: 8 SUBSCRIBE Contact: Event: message-summary Expires: 86400 Content-Length: 0 A9: Notifier -> Subscriber (immediate synchronization of current state) NOTIFY sip:rohan@rmahy-phone.cisco.com SIP/2.0 To: ;tag=78923 From: ;tag=4442 Date: Mon, 10 Jul 2000 15:55:07 GMT Call-Id: 1349882@rmahy-phone.cisco.com CSeq: 47 NOTIFY Contact: Event: message-summary Content-Type: application/simple-message-summary Content-Length: 45 Messages-Waiting: yes Voicemail: 4/8 (1/2) A10: Subscriber -> Notifier SIP/2.0 200 OK To: ;tag=78923 From: ;tag=4442 Date: Mon, 10 Jul 2000 15:55:08 GMT Call-Id: 1349882@rmahy-phone.cisco.com CSeq: 47 NOTIFY Contact: Event: message-summary A11: Subscriber -> Notifier Un-subscribe after "rohan" logs out. SUBSCRIBE sip:rohan@vmail.cisco.com SIP/2.0 To: ;tag=4442 From: ;tag=78923 Date: Mon, 10 Jul 2000 19:35:06 GMT Call-Id: 1349882@rmahy-phone.cisco.com CSeq: 17 SUBSCRIBE Contact: Event: message-summary Expires: 0 Accept: application/simple-message-summary Content-Length: 0 A12: Notifier -> Subscriber Mahy, Slain Expires: May 2002 [Page 10] Internet Draft SIP Message Waiting Nov 2001 SIP/2.0 200 OK To: ;tag=4442 From: ;tag=78923 Date: Mon, 10 Jul 2000 19:35:07 GMT Call-Id: 1349882@rmahy-phone.cisco.com CSeq: 17 SUBSCRIBE Contact: Event: message-summary Expires: 0 Content-Length: 0 A13: Notifier -> Subscriber (immediate synchronization of current state, which the subscriber can now ignore) NOTIFY sip:rohan@rmahy-phone.cisco.com SIP/2.0 To: ;tag=78923 From: ;tag=4442 Date: Mon, 10 Jul 2000 19:35:07 GMT Call-Id: 1349882@rmahy-phone.cisco.com CSeq: 56 NOTIFY Contact: Event: message-summary Content-Type: application/simple-message-summary Content-Length: 45 Messages-Waiting: yes Voicemail: 4/8 (1/2) A10: Subscriber -> Notifier SIP/2.0 200 OK To: ;tag=78923 From: ;tag=4442 Date: Mon, 10 Jul 2000 19:35:08 GMT Call-Id: 1349882@rmahy-phone.cisco.com CSeq: 56 NOTIFY Event: message-summary Content-Length: 0 5.2. Example Usage with Caller Preferences The use of caller preferences is purely optional but its use is encouraged. If caller preferences is used, a messaging server MAY REGISTER a Contact with a "SUBSCRIBE" methods tag. If SUBSCRIBE is used by other services, the messaging server MAY also REGISTER as a Contact with the feature="voice-mail" tag. An example of this kind of registration follows below. REGISTER sip:sip3-sj.cisco.com SIP/2.0 To: Mahy, Slain Expires: May 2002 [Page 11] Internet Draft SIP Message Waiting Nov 2001 From: ;tag=4442 ... Contact: ;feature="voice-mail";methods="SUBSCRIBE" The following SUBSCRIBE message would find the Contact which registered in the example above. SUSBCRIBE sip:rohan@cisco.com SIP/2.0 ... Accept: application/simple-message-summary Request-Contact: *;feature="voice-mail";methods="SUBSCRIBE" 6. Formal Syntax The following syntax specifications use the augmented Backus-Naur Form [BNF] as described in RFC-2234. 6.1. New event-package definition The syntax of the Event header is defined in [Events] as shown below. Event = ( "Event" | "o" ) ":" event-type *(( ";" parameter-name ["=" ( token | quoted-string ) ] ) event-type = event-package *( "." event-subpackage ) event-package = token-nodot event-subpackage = token-nodot token-nodot = 1*( alphanum | "-" | "!" | "%" | "*" | "_" | "+" | "`" | "'" | "~" ) This document defines a new event-package as shown below. event-package = message-event | token-nodot message-event = "message-summary" 6.2. Body Format Syntax The formal syntax for application/simple-message-summary is below: messsage-summary = status-line [*(summary-line)] [ mheaders ] status-line = "Messages-Waiting: " status CRLF summary-line = media-type ":" SP new "/" old [ urgent ] CRLF urgent = "(" new-urgent "/" old-urgent ")" status = "yes" | "no" media-type = "Voicemail" | "Email" | "Fax" | "Video" mheaders = *(CRLF 1*(message-headers)) message-headers = hname ":" SP hvalue CRLF hname = #( alphanum | "-" | "_" ) Mahy, Slain Expires: May 2002 [Page 12] Internet Draft SIP Message Waiting Nov 2001 hvalue = alphanum = lowalpha | upalpha | DIGIT new = WHOLENUMBER old = WHOLENUMBER new-urgent = WHOLENUMBER old-urgent = WHOLENUMBER WHOLENUMBER = *DIGIT DIGIT = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" upalpha = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z" lowalpha = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z" CTL = %0x00-1f | %0x7f ; (0-31 or 127) CRLF = %d13 %d10 SP = %d32 7. IANA Considerations 7.1. SIP Event Package Registration for message-summary Package name: message-summary Type: package Contact: [Mahy] Published Specification: This document. 7.2. MIME Registration for application/simple-message-summary MIME media type name: application MIME subtype name: simple-message-summary Required parameters: none. Optional parameters: none. Encoding considerations: This type is only defined for transfer via [SIP]. Security considerations: See the "Security Considerations" (Section 8) section in this document. Interoperability considerations: none Published specification: This document. Mahy, Slain Expires: May 2002 [Page 13] Internet Draft SIP Message Waiting Nov 2001 Applications which use this media: The simple-message-summary application subtype supports the exchange of message waiting and message summary information in SIP networks. Additional information: 1. Magic number(s): N/A 2. File extension(s): N/A 3. Macintosh file type code: N/A 8. Security Considerations At a minimum, SUBSCRIPTION requests for message waiting, and message waiting NOTIFY messages SHOULD be authenticated. Because of the potential privacy implications, encrypting NOTIFY messages is encouraged to keep potentially sensitive information private. Additionally, SUBSCRIPTION requests MAY be encrypted. Hop-by-hop encryption could discourage unauthorized disclosure of the address or location of the user's account. Additional security considerations are covered in [SIP] and [Events]. 9. Changes from draft-mahy-sip-message-waiting-02 The only change is the name of the internet draft which is reported to the SIPPING WG. 10. Changes from draft-mahy-sip-message-waiting-01 1) This draft is now formatted as a SIP Event Package as defined in Section 4 of [Events]. 2) The event-package name is now "message-summary", to allow for other bodies to extend the package. 3) The "urgent" token was missing from the BNF. 11. Changes from draft-mahy-sip-message-waiting-00 This draft greatly simplifies and shortens the -00 version. 1) The generic behavior of SUBSCRIBE/NOTIFY is now greatly clarified in [Events] and made consistent with PINT and SIP for presence. This message waiting draft is now consistent with [Events]. 2) The XML format has been removed due to lack of immediate interest. At a future date, similar functionality may be added as another body definition with an appropriate MIME type. Mahy, Slain Expires: May 2002 [Page 14] Internet Draft SIP Message Waiting Nov 2001 3) An IANA Considerations section was added to register the new "application/simple-message-summary" MIME type and the "simple- message-summary" SIP event package. 4) The "flag-list" was removed due to lack of interest and to encourage simplicity. 5) Due to synchronization issues, and the recommendation of the VPIM Working Group, support for message count "deltas" was removed. 6) The Messages-Waiting line in the body is now mandatory. 7) This version of the draft clarifies the role of caller preferences as optional but encouraged. 8) A set of SMTP-like headers from the triggering messages may now optionally follow the message summaries, provided that the resulting NOTIFY on UDP fits in a single datagram. 12. References [RFC2026] S Bradner, "The Internet Standards Process -- Revision 3", RFC2026 (BCP), IETF, October 1996. [SIP] M. Handley, E. Schooler, and H. Schulzrinne, "SIP: Session Initiation Protocol", RFC2543, Internet Engineering Task Force, Nov 1998. [Events] Adam Roach, "SIP-Specific Event Notification ", Internet Draft , IETF; July 2001. Work in progress. [RFC2119] S. Bradner, "Key words for use in RFCs to indicate requirement levels," Request for Comments (Best Current Practice) 2119, Internet Engineering Task Force, Mar. 1997. [GR506] "GR-506: Signaling for Analog Interfaces, Issue 1, Revision 1", Telecordia, November 1996. [Caller-Prefs] H. Shulzrinne and J. Rosenberg, "SIP caller preferences and callee capabilities," Internet Draft , Internet Engineering Task Force, June 2001. Work in progress. [DHCP] R Droms, "Dynamic Host Configuration Protocol", RFC2131, IETF, March 1997. [SMTP] Crocker, D., "Standard for the Format of Arpa Internet Messages", RFC822, IETF, August 1982. Mahy, Slain Expires: May 2002 [Page 15] Internet Draft SIP Message Waiting Nov 2001 [IMAP4] M Crispin, "Internet Message Access Protocol - Version 4rev1", RFC2060, IETF, December 1996. [VPIM] Vaudreuil, G., and G. Parsons, "Voice Profile for Internet Mail - version 2", RFC 2421, September 1998. [Message-Context] Burger, E., et al, "Message Context for Internet Mail", Internet Draft , Internet Engineering Task Force, June 2001. Work in progress. [BNF] D Crocker, P Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC2234, IETF, Nov 1997. [UTF-8] Yergeau, F., "UTF-8, a transformation of ISO 10646," RFC2279, IETF, Jan 1998. 13. Acknowledgments Thanks to Dave Oran, Bill Foster, Steve Levy, Denise Caballero- McCann, Jeff Michel, Priti Patil, Satyender Khatter, Bich Nguyen, Manoj, Bhatia, David Williams, and Bryan Byerly of Cisco; Jonathan Rosenberg of Dynamicsoft; and Adam Roach of Ericsson. 14. Author's Addresses Rohan Mahy Cisco Systems 170 W Tasman Dr, MS: SJC-I/2/3 San Jose, CA 95134 USA Phone: +1 408 526 4000 Email: rohan@cisco.com Ilya Slain Cisco Systems 170 W Tasman Dr, MS: SJC09/2/2 San Jose, CA 95134 USA Phone: +1 408 527 9446 Email: islain@cisco.com Mahy, Slain Expires: May 2002 [Page 16] Internet Draft SIP Message Waiting Nov 2001 Full Copyright Statement "Copyright (C) The Internet Society (date). 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. Mahy, Slain Expires: May 2002 [Page 17]