RFC 7702
Interworking between the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol (XMPP): Groupchat
Pages: 43
Proposed Standard
Proposed Standard
Part 1 of 2 – Pages 1 to 25
Internet Engineering Task Force (IETF) P. Saint-Andre Request for Comments: 7702 &yet Category: Standards Track S. Ibarra ISSN: 2070-1721 AG Projects S. Loreto Ericsson December 2015 Interworking between the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol (XMPP): GroupchatAbstract
This document defines a bidirectional protocol mapping for the exchange of instant messages in the context of a multi-party chat session among users of the Session Initiation Protocol (SIP) and users of the Extensible Messaging and Presence Protocol (XMPP). Specifically, this document defines a mapping between the SIP-based Message Session Relay Protocol (MSRP) and the XMPP Multi-User Chat (MUC) extension. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7702.
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Table of Contents
1. Introduction ....................................................4 2. Intended Audience ...............................................4 3. Terminology .....................................................5 4. Architectural Assumptions .......................................5 5. Multi-party Messaging Session from XMPP MUC to MSRP .............8 5.1. Enter Room ................................................11 5.2. Set Nickname ..............................................14 5.3. Conference Subscription ...................................14 5.4. Presence Broadcast ........................................15 5.5. Exchange Messages .........................................19 5.5.1. Send a Message to All Occupants ....................19 5.5.2. Send a Private Message .............................21 5.6. Change Nickname ...........................................22 5.7. Invite Another User to a Room .............................23 5.8. Exit Room .................................................25 6. MSRP Multi-party Messaging Session to XMPP MUC .................25 6.1. Enter Room ................................................28 6.2. Presence Broadcast ........................................30 6.3. Exchange Messages .........................................32 6.3.1. Send a Message to All Occupants ....................32 6.3.2. Send a Private Message .............................34 6.4. Change Nickname ...........................................34 6.5. Invite Another User to a Room .............................35 6.6. Exit Room .................................................36 7. Handling of Nicknames and Display Names ........................37 8. Message Size ...................................................38 9. Security Considerations ........................................38 10. References ....................................................39 10.1. Normative References .....................................39 10.2. Informative References ...................................40 Acknowledgements ..................................................42 Authors' Addresses ................................................43
1. Introduction
Both the Session Initiation Protocol (SIP) [RFC3261] and the Extensible Messaging and Presence Protocol (XMPP) [RFC6120] can be used for the purpose of multi-party text chat over the Internet. To ensure interworking between these technologies, it is important to define bidirectional protocol mappings. The architectural assumptions underlying such protocol mappings are provided in [RFC7247], including the mapping of addresses and error conditions. This document specifies mappings for multi-party text chat sessions (often called "groupchat"); specifically, this document defines a mapping between the XMPP Multi-User Chat (MUC) extension [XEP-0045] and SIP-based multi-party chat using Message Session Relay Protocol (MSRP) [RFC4975] as specified in [RFC7701]. Both MUC and MSRP contain a large set of features, such as the ability to administer rooms, kick out and ban users, reserve a nickname within a room, change room subject, enable room moderation, and destroy the room. This document covers only a basic subset of groupchat features: joining a room, establishing or changing (but not permanently registering) a room nickname, modifying presence information within the room, sending a message to all participants, sending a private message to a single participant, inviting another user to the room, and leaving the room. Future documents might define mappings for additional features beyond this set.2. Intended Audience
The documents in this series are intended for use by software developers who have an existing system based on one of these technologies (e.g., SIP), and who would like to enable communication from that existing system to systems based on the other technology (e.g., XMPP). We assume that readers are familiar with the core specifications for both SIP [RFC3261] and XMPP [RFC6120], with the base document for this series [RFC7247], and with the following groupchat-related specifications: o Multi-party Chat Using MSRP [RFC7701] o Multi-User Chat [XEP-0045]
3. Terminology
A number of technical terms used here are defined in [RFC3261], [RFC4975], [RFC6120], and [XEP-0045]. In flow diagrams, MSRP traffic is shown using arrows such as "%%%>", SIP traffic is shown using arrows such as "***>", XMPP traffic is shown using arrows such as "...>". In protocol flows and examples, provisional SIP responses have been elided for the sake of brevity. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].4. Architectural Assumptions
XMPP and MSRP differ in their assumptions regarding groupchat traffic. In XMPP, a message of type "groupchat" is just another stanza and is handled directly by an XMPP server or routed to an associated server component for multi-user chat. By contrast, sessions (including groupchat sessions) in MSRP are considered to be a type of media (similar to audio/video sessions): signaling to set up, manage, and tear down the session is handled by a "conference focus" [RFC4353] (here we assume via SIP), but the session data itself is handled by a separate entity called an MSRP switch. How the conference focus and MSRP switch communicate is a matter of implementation and deployment. An architectural diagram for a possible gateway deployment is shown below, where the entities have the following significance: o romeo@example.org -- a SIP user. o romeo@example.org;gr=dr4hcr0st3lup4c -- a particular endpoint associated with the SIP user. o example.org -- a SIP proxy with an associated SIP-to-XMPP gateway ("S2X GW") to XMPP. o chat.example.org -- a SIP-based conference focus and MSRP switch with an associated MSRP-to-SIP gateway ("M2X GW") to XMPP. o montague@chat.example.org -- a conference at an MSRP switch; not shown in diagram.
o juliet@example.com -- an XMPP user.
o juliet@example.com/yn0cl4bnw0yr3vym -- a particular endpoint
associated with the XMPP user.
o example.com -- an XMPP server with an associated XMPP-to-SIP
gateway ("X2S GW") to SIP and an XMPP-to-MSRP gateway ("X2M GW")
to MSRP.
o rooms.example.com -- an XMPP MUC service associated with
example.com.
o capulet@rooms.example.com -- a chat room at an XMPP MUC service;
not shown in diagram.
These are logical entities, and several of them might be co-located
in the same physical entity. For example, the SIP conference focus
and MSRP switch and associated gateways, or the XMPP server and MUC
service and associated gateways, might be part of the same deployed
code. In addition, it is likely that an XMPP service would not have
separate gateways for XMPP-to-SIP translation and XMPP-to-MSRP
translation, but would instead have a single gateway.
##################################################################### # # # +------------------+ # # &&&&&&&&&&&&&&&&| chat.example.org |<%%%%%%%%%%% # # & &&&&| (MSRP switch) +-----+ % # # & & +---------------| M2X | % # # & & % | GW | % # # & & % +-----+ % # # & & % : % # # & & % ///////////////////////////////////# # & & % / : % # # & & % / : +-----+ # # & & % / : | X2M | # # & & % / : +-------| GW |---+ # # & & % / :.>| +-----+ | # # & & % / | | # # & +------------------+ % / +-----+ | # # & | chat.example.org |<*******/*| X2S | example.com | # # & | (conference | % **/*| GW | (XMPP server) | # # & | focus) +-----+ % * / +-----+ | # # & +------------| S2X | % * / | +-------------------+ # # & * | GW |......*./....>| | rooms.example.com | # # & * +-----+ % * / +-----| (MUC service) | # # & * % * / ^ : +-------------------+ # # & +---------------+ % * / : : # # &&| example.org |<********* / : : # # | (SIP proxy) +-----+ % / : : # # +-------------| S2X | % / : : # # * | GW |......./........ : # # * +-----+ % / : # # * % / : # # romeo@example.org / juliet@example.com # # ;gr=dr4hcr0st3lup4c / /yn0cl4bnw0yr3vym # # / # # --SIP/MSRP DOMAIN-- / --XMPP DOMAIN-- # # / # ##################################################################### Legend: . = XMPP % = MSRP * = SIP & = unstandardized communication paths / = separation of administrative domains Figure 1: Logical Deployment Architecture
In SIP, there is no necessity for a SIP user such as romeo@example.org to make use of his SIP proxy in order to join a chat room on the XMPP network; for example, he could try to directly find a SIP service at example.com or independently locate a SIP-to- XMPP gateway. Although, as a simplifying assumption, this document shows the more expected path of using one's "home" SIP proxy and shows gateways as associated with the sending domain, nothing in this document ought to be construed as discouraging other deployment architectures or communication paths (e.g., services hosting their own inbound gateways).5. Multi-party Messaging Session from XMPP MUC to MSRP
This section describes how to map an XMPP MUC session to an MSRP Multi-party Messaging session. The following diagram outlines the overall protocol flow of a sample session, which includes some optional exchanges (such as sending messages, changing a nickname, and inviting another user). XMPP XMPP SIP MSRP User Server Conference Switch | + X2S GW Focus + M2X GW | & X2M GW + S2X GW | | | | | | (F1) XMPP | | | | enter room | | | |................>| | | | | (F2) SIP INVITE | | | |****************>| | | | | (F3) | | | | unstandardized | | | | interaction | | | |<&&&&&&&&&&&&&&&>| | | (F4) SIP 200 OK | | | |<****************| | | | (F5) SIP ACK | | | |****************>| | | | (F6) MSRP SEND (bodiless) | | |%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%>| | | (F7) MSRP 200 OK | | |<%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%| | | (F8) MSRP NICKNAME | | |%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%>| | | (F9) MSRP 200 OK | | |<%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%|
| | (F10) SIP | |
| | SUBSCRIBE | |
| | Event: | |
| | conference | |
| |****************>| |
| | (F11) SIP 200 OK| |
| |<****************| |
| | (F12) SIP NOTIFY| |
| |<****************| |
| | (F13) SIP 200 OK| |
| |****************>| |
| (F14) XMPP | | |
| presence | | |
|<................| | |
| (F15) XMPP | | |
| MUC subject | | |
|<................| | |
. . . .
. . . .
| (F16) XMPP | | |
| groupchat | | |
| message | | |
|................>| | |
| | (F17) MSRP SEND |
| |%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%>|
| | (F18) MSRP 200 OK
| |<%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%|
| (F19) XMPP | | |
| groupchat | | |
| message | | |
|<................| | |
. . . .
. . . .
| (F20) XMPP | | |
| private | | |
| message | | |
|................>| | |
| | (F21) MSRP SEND |
| |%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%>|
| | (F22) MSRP 200 OK
| |<%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%|
. . . .
. . . .
| (F23) XMPP | | |
| presence: | | |
| change nick | | |
|................>| | |
| | (F24) MSRP NICKNAME |
| |%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%>|
| | (F25) MSRP 425 Error |
| |<%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%|
| (F26) XMPP | | |
| presence | | |
| error | | |
|<................| | |
. . . .
. . . .
| (F27) XMPP | | |
| message: | | |
| invite | | |
|................>| | |
| | (F28) SIP | |
| | REFER | |
| |****************>| |
| | (F29) SIP | |
| | 200 OK | |
| |<****************| |
| | (F30) SIP | |
| | NOTIFY | |
| |<****************| |
. . . .
. . . .
| (F31) XMPP | | |
| presence: | | |
| exit room | | |
|................>| | |
| | (F32) SIP BYE | |
| |****************>| |
| | (F33) SIP | |
| | 200 OK | |
| |<****************| |
| (F34) XMPP | | |
| presence | | |
| unavailable | | |
|<................| | |
| | | |
Detailed protocol flows and mappings are provided in the following
sections.
5.1. Enter Room
As defined in the XMPP Multi-User Chat (MUC) specification [XEP-0045], when an XMPP user (say, "juliet@example.com") wants to join a groupchat room (say, "montague@chat.example.org"), she sends a directed <presence/> stanza [RFC6121] to that chat room. In her request she also specifies the nickname she wants to use within the room (say, "JuliC"); in XMPP this room nickname is the resourcepart of an occupant JID (thus "montague@chat.example.org/JuliC"). The joining client signals its ability to speak the multi-user chat protocol by including in the initial presence stanza an empty <x/> element qualified by the 'http://jabber.org/protocol/muc' namespace. Example 1: Juliet Enters Room (F1) | <presence from='juliet@example.com/yn0cl4bnw0yr3vym' | to='montague@chat.example.org/JuliC'> | <x xmlns='http://jabber.org/protocol/muc'/> | </presence> Upon receiving such a presence stanza, the XMPP server needs to determine the identity of the domainpart in the 'to' address, which it does by following the procedures discussed in [RFC7247]. Here we assume that the XMPP server has determined the domain is serviced by a SIP server, that it contains or has available to it an XMPP-to-SIP gateway or connection manager (which enables it to speak natively to SIP servers), and that it hands off the presence stanza to the XMPP-to-SIP gateway. Because a multi-user chat service accepts the presence stanza shown above as a request to enter a room, the XMPP-to-SIP gateway transforms it into a SIP INVITE request.
Example 2: SIP Mapping of Room Join (F2) | INVITE sip:montague@chat.example.org SIP/2.0 | To: <sip:montague@chat.example.org> | From: "Juliet" <sip:juliet@example.com>;tag=786 | Contact: <sip:juliet@example.com>;gr=yn0cl4bnw0yr3vym | Call-ID: BC466C1C-E01D-4FD1-B766-9AD174BAF2E7 | CSeq: 1 INVITE | Content-Type: application/sdp | Content-Length: ... | | c=IN IP4 x2s.example.org | m=message 7654 TCP/MSRP * | a=accept-types:text/cpim | a=accept-wrapped-types:text/plain text/html | a=path:msrp://x2m.example.com:7654/jshA7weztas;tcp | a=chatroom:nickname private-messages Here the Session Description Protocol (SDP) offer specifies the XMPP- to-MSRP gateway on the XMPP side (in the SDP 'path' attribute specified in [RFC4975]) as well as other particulars of the session. There is no direct mapping for the MSRP URIs. In fact, an MSRP URI identifies a session of instant messages at a particular device; it is ephemeral and has no meaning outside the scope of that session. The authority component of the MSRP URI here MUST contain the XMPP-to-MSRP gateway hostname or numeric IP address (as well as, in accordance with [RFC4975], an explicit port number). The mapping of XMPP syntax elements to SIP and [RFC4566] syntax elements MUST be as shown in the following table. Table 1: Message Syntax Mapping from XMPP to SIP/SDP +-----------------------------+-----------------------------+ | XMPP Element or Attribute | SIP Header or SDP Contents | +-----------------------------+-----------------------------+ | from | From | | to (without the /nick) | To | +-----------------------------+-----------------------------+ As shown in the foregoing example and described in [RFC7247], the XMPP-to-SIP gateway MUST map the bare JID ("localpart@domainpart") of the XMPP sender to the SIP From header and include the resourcepart of the full JID as the Globally Routable User Agent URI (GRUU)
portion [RFC5627] of the SIP URI. However, note that a SIP response uses the same From and To as in the SIP request, whereas an XMPP response swaps the from and to attributes. Here we assume that the SIP conference focus accepts the session establishment. The Contact header field of the SIP 200 OK response includes the 'isfocus' feature tag specified in [RFC4353] along with other relevant feature tags. The conference focus also includes an answer session description that acknowledges the choice of media, specifies the MSRP URI of the switch (in the 'path' attribute specified in [RFC4975]), and contains the extensions specified in [RFC7701]. Example 3: Chat Room Accepts Session Establishment (F4) | SIP/2.0 200 OK | From: "Juliet" <sip:juliet@example.com>;tag=786 | To: <sip:montague@chat.example.org>;tag=087js | Call-ID: BC466C1C-E01D-4FD1-B766-9AD174BAF2E7 | CSeq: 1 INVITE | Contact: <sip:montague@chat.example.org;transport=tcp>;isfocus | Content-Type: application/sdp | Content-Length: ... | | v=0 | c=IN IP4 example.org | s=- | m=message 12763 TCP/MSRP * | a=accept-types:message/cpim | a=accept-wrapped-types:text/plain text/html | a=path:msrp://chat.example.org:12763/kjhd37s2s20w2a;tcp | a=chatroom:nickname private-messages Upon receiving such a response, the XMPP-to-SIP gateway sends a SIP ACK to the conference focus on behalf of the joining user. Example 4: Gateway Sends ACK to Conference Focus (F5) | ACK sip:montague@chat.example.org SIP/2.0 | To: <sip:montague@chat.example.org>;tag=087js | From: "Juliet" <sip:juliet@example.com>;tag=786 | Call-ID: BC466C1C-E01D-4FD1-B766-9AD174BAF2E7 | CSeq: 2 ACK In accordance with [RFC4975], the gateway sends a bodiless MSRP message (F6) to the switch immediately upon establishing the connection, and the switch acknowledges that message (F7).
5.2. Set Nickname
If the chat room server accepted the session, the XMPP-to-MSRP gateway sets up the nickname as received in the presence stanza (i.e., the resourcepart of the 'to' address, such as "JuliC" in "montague@chat.example.org/JuliC"). This is done using the extension specified in [RFC7701]. Example 5: Gateway Sets Up Nickname (F8) | MSRP a786hjs2 NICKNAME | To-Path: msrp://montague@chat.example.org:12763/kjhd37s2s20w2a;tcp | From-Path: msrp://x2m.example.com:7654/jshA7weztas;tcp | Use-Nickname: "JuliC" | -------a786hjs2 The MSRP switch analyzes the existing allocation of nicknames, accepts the nickname proposal, and answers with a 200 response. Example 6: MSRP Switch Accepts Nickname Proposal (F9) | MSRP a786hjs2 200 OK | To-Path: msrp://x2m.example.com:7654/jshA7weztas;tcp | From-Path: msrp://montague@chat.example.org:12763/kjhd37s2s20w2a | ;tcp | -------a786hjs2 This section assumes that the nickname request is successful. The error flow resulting from a nickname conflict is described under Section 5.6.5.3. Conference Subscription
As mentioned in [RFC7701], the joining user will typically also subscribe to a conference event package (see [RFC4575] and [RFC6502]) at the focus. Although such a subscription is not required by [RFC7701] in practice the temporary and context-dependent presence subscriptions and room rosters involved in joining an XMPP MUC room are best mapped to the conference event package.
Example 7: Gateway Subscribes to the Conference (F10) | SUBSCRIBE sip:montague@chat.example.org SIP/2.0 | To: <sip:montague@chat.example.org>;tag=087js | From: "Juliet" <sip:juliet@example.com>;tag=786 | Contact: <sip:juliet@example.com>;gr=yn0cl4bnw0yr3vym | Call-ID: BC466C1C-E01D-4FD1-B766-9AD174BAF2E7 | CSeq: 3 SUBSCRIBE | Event: conference | Expires: 600 | Accept: application/conference-info+xml | Allow-Events: conference | Content-Length: 0 The focus will accept or reject the request based on local policy. Example 8: Focus Accepts Subscription Request (F11) | SIP/2.0 200 OK | To: <sip:montague@chat.example.org>;tag=087js | From: "Juliet" <sip:juliet@example.com>;tag=786 | Call-ID: BC466C1C-E01D-4FD1-B766-9AD174BAF2E7 | CSeq: 3 SUBSCRIBE | Contact: <sip:montague@chat.example.org;transport=tcp>;isfocus | Expires: 600 | Content-Length: 0 If the conference focus accepts the request to enter a room, the XMPP user expects to receive back presence information from all the existing occupants of the room. To make this happen, the XMPP-to-SIP gateway subscribes to the conference event package [RFC4575] at the focus.5.4. Presence Broadcast
When the conference event package subscription is completed, the focus sends to the XMPP-to-SIP gateway a NOTIFY request containing the presence information of all the existing occupants, represented using the format defined in [RFC4575].
Example 9: Conference Focus Sends Presence Information (F12) | NOTIFY sip:montague@chat.example.org SIP/2.0 | To: "Juliet" <sip:juliet@example.com>;tag=786 | From: <sip:montague@chat.example.org>;tag=087js | Call-ID: BC466C1C-E01D-4FD1-B766-9AD174BAF2E7 | CSeq: 4 NOTIFY | Event: conference | Subscription-State: active;expires=3600 | Content-Type: application/conference-info+xml | Content-Length: ... | | <conference-info version="0" state="full" | entity="sip:3402934234@chat.example.org"> | <conference-description> | <subject>Today in Verona</subject> | <conf-uris> | <entry> | <uri>tel:+18882934234</uri> | </entry> | </conf-uris> | </conference-description> | <users> | <user entity="sip:montague@chat.example.org;gr=Romeo" | state="full"> | <display-text>Romeo</display-text> | <roles> | <entry>participant</entry> | </roles> | <associated-aors> | <entry> | <uri>xmpp:romeo@example.org/dr4hcr0st3lup4c</uri> | </entry> | </associated-aors> | <endpoint entity="sip:montague@chat.example.org;gr=Romeo" | state="full"> | <status>connected</status> | <joining-info> | <when>2013-12-12T10:01:03.691128+01:00</when> | </joining-info> | <media id="211835820"> | <type>message</type> | </media> | </endpoint> | </user> | <user entity="sip:montague@chat.example.org;gr=Ben" | state="full"> | <display-text>Ben</display-text>
| <roles> | <entry>participant</entry> | </roles> | <endpoint entity="sip:montague@chat.example.org;gr=Ben" | state="full"> | <status>connected</status> | <media id="211835821"> | <type>message</type> | </media> | </endpoint> | </user> | <user entity="sip:montague@chat.example.org;gr=JuliC" | state="full"> | <display-text>JuliC</display-text> | <roles> | <entry>participant</entry> | </roles> | <endpoint entity="sip:montague@chat.example.org;gr=JuliC" | state="full"> | <status>connected</status> | <media id="211835822"> | <type>message</type> | </media> | </endpoint> | </user> | </users> | </conference-info> The syntax mapping from the RFC 4575 payload to the XMPP participant list MUST be as shown in the following table. (Mappings for elements not mentioned are undefined.) Table 2: Participant list mapping +--------------------------------+-----------------------------+ | RFC 4575 Element or Attribute | XMPP Element or Attribute | +--------------------------------+-----------------------------+ | <conference-info/> 'entity' | room JID | | <subject/> | room subject | | <user/> 'entity' | occupant JID | | <display-text/> | participant nickname | | <endpoint/> 'entity' | occupant JID | | <user/> 'associated-aors' | user full JID (if avail.) | +--------------------------------+-----------------------------+
Upon receiving such a response, the XMPP-to-SIP gateway sends a SIP 200 OK response to the conference focus (example not shown) and translates the participant list into a series of XMPP presence stanzas. Example 10: XMPP Mapping of Chat Room Presence (F14) | <presence from='montague@chat.example.org/Romeo' | to='juliet@example.com/yn0cl4bnw0yr3vym'> | <x xmlns='http://jabber.org/protocol/muc#user'> | <item affiliation='none' role='participant'/> | </x> | </presence> | <presence from='montague@chat.example.org/Ben' | to='juliet@example.com/yn0cl4bnw0yr3vym'> | <x xmlns='http://jabber.org/protocol/muc#user'> | <item affiliation='none' role='participant'/> | </x> | </presence> | <presence from='montague@chat.example.org/JuliC' | to='juliet@example.com/yn0cl4bnw0yr3vym'> | <x xmlns='http://jabber.org/protocol/muc#user'> | <item affiliation='none' role='participant'/> | <status code='110'/> | </x> | </presence> If the NOTIFY request included a subject, the gateway converts that into a separate XMPP message. Example 11: XMPP Mapping of Chat Room Subject (F15) | <message from='montague@chat.example.org/mayor' | to='juliet@example.com/yn0cl4bnw0yr3vym' | id='mbh2vd68'> | <subject>Today in Verona</subject> | </message> The mapping of SIP and [RFC4575] payload syntax elements to XMPP syntax elements MUST be as shown in the following table. (Mappings for elements not mentioned are undefined.)
Table 3: Message Syntax Mapping from SIP to XMPP +---------------------------------+-----------------------------+ | SIP Header or RFC 4575 Contents | XMPP Element or Attribute | +---------------------------------+-----------------------------+ | <user/> 'entity' | from | | To with <display-text> | occupant JID | | <role>participant</role> | role='participant' | | [N/A] | affiliation='none' | +---------------------------------+-----------------------------+5.5. Exchange Messages
Once the user has joined the chat room, the user can exchange an unbounded number of messages, both public and private. The mapping of XMPP syntax elements to MSRP syntax elements MUST be as shown in the following table. (Mappings for elements not mentioned are undefined.) Table 4: Message Syntax Mapping from XMPP Message to MSRP +-----------------------------+-----------------------------+ | XMPP Element or Attribute | CPIM Header | +-----------------------------+-----------------------------+ | to | To | | from | From | | <body/> | body of the SEND request | +-----------------------------+-----------------------------+5.5.1. Send a Message to All Occupants
When Juliet wants to sends a message to all other occupants in the room, she sends a message of type "groupchat" to the <room@service> itself (in our example, <montague@chat.example.org>). The following examples show an exchange of a public message. Example 12: Juliet Sends Message to All Occupants (F16) | <message from='juliet@example.com/yn0cl4bnw0yr3vym' | to='montague@chat.example.org' | type='groupchat' | id='lzfed24s'> | <body>Who knows where Romeo is?</body> | </message>
Upon receiving such a message, the XMPP-to-MSRP gateway translates it into an MSRP SEND message. Example 13: Gateway Maps XMPP Message to MSRP (F17) | MSRP a786hjs2 SEND | To-Path: msrp://chat.example.org:12763/kjhd37s2s20w2a;tcp | From-Path: msrp://x2m.example.com:7654/jshA7weztas;tcp | Message-ID: 87652491 | Byte-Range: 1-*/* | Content-Type: message/cpim | | To: <sip:montague@chat.example.org> | From: "Juliet" <sip:juliet@example.com> | DateTime: 2008-10-15T15:02:31-03:00 | Content-Type: text/plain | | Who knows where Romeo is? | -------a786hjs2$ Upon receiving the SEND request, if the request either contains a Failure-Report header field value of "yes" or does not contain a Failure-Report header at all, the MSRP switch immediately generates and sends a response. Example 14: MSRP Switch Returns 200 OK (F18) | MSRP d93kswow 200 OK | To-Path: msrp://x2m.example.com:7654/jshA7weztas;tcp | From-Path: msrp://chat.example.org:12763/kjhd37s2s20w2a;tcp | -------d93kswow$ Since an XMPP MUC room could be moderated and an XMPP user cannot be sure whether her message has been accepted without receiving it back from the server, [XEP-0045] states that the sender needs to receive a reflected copy of the message it sent. So, in this scenario, the XMPP-to-MSRP gateway has to reflect the message back to the sender. This procedure only applies to XMPP endpoints. Example 15: Gateway Reflects Message to XMPP User (F19) | <message from='montague@chat.example.org/JuliC' | to='juliet@example.com/yn0cl4bnw0yr3vym' | type='groupchat' | id='ix51z73m'> | <body>Who knows where Romeo is?</body> | </message>
5.5.2. Send a Private Message
Since each occupant has a unique JID, Juliet can send a "private message" to a selected occupant through the service by sending a message to the user's occupant JID. The XMPP message type ought to be "chat" (and is not allowed to be "groupchat"). The following examples show an exchange of a private message. Example 16: Juliet Sends Private Message (F20) | <message from='juliet@example.com/yn0cl4bnw0yr3vym' | to='montague@chat.example.org/Romeo' | type='chat' | id='6sfln45q'> | <body>O Romeo, Romeo! wherefore art thou Romeo?</body> | </message> Upon receiving such a message, the XMPP-to-MSRP gateway translates it into an MSRP SEND message. Example 17: Gateway Maps Private Message from XMPP to MSRP (F21) | MSRP a786hjs2 SEND | To-Path: msrp://chat.example.org:12763/kjhd37s2s20w2a;tcp | From-Path: msrp://x2m.example.com:7654/jshA7weztas;tcp | Message-ID: 87652491 | Byte-Range: 1-*/* | Content-Type: message/cpim | | To: <sip:montague@chat.example.org>;gr=Romeo | From: <sip:juliet@example.org>;gr=yn0cl4bnw0yr3vym | DateTime: 2008-10-15T15:02:31-03:00 | Content-Type: text/plain | | O Romeo, Romeo! wherefore art thou Romeo? | -------a786hjs2$ After acknowledging the message by sending an MSRP 200 OK message (step F22, not shown), the MSRP switch is responsible for sending the message to the intended recipient. When doing so, it modifies the From header to the sender's address within the chat room.
Example 18: Switch Sends Private Message to SIP User | MSRP a786hjs2 SEND | To-Path: msrp://chat.example.org:12763/kjhd37s2s20w2a;tcp | From-Path: msrp://x2m.example.com:7654/jshA7weztas;tcp | Message-ID: 87652491 | Byte-Range: 1-*/* | Content-Type: message/cpim | | To: <sip:romeo@example.org> | From: <sip:montague@chat.example.org>;gr=JuliC | DateTime: 2008-10-15T15:02:31-03:00 | Content-Type: text/plain | | O Romeo, Romeo! wherefore art thou Romeo? | -------a786hjs2$ Note: If an XMPP-to-MSRP gateway has support for private messaging, it MUST advertise that fact by adding a "private-messages" value to the a=chatroom SDP attribute it sends to the conference focus, as specified in [RFC7701]. | a=chatroom:nickname private-messages5.6. Change Nickname
The XMPP user might want to change her nickname. She can do so by sending an updated presence stanza to the room, containing a new nickname. Example 19: Juliet Changes Her Nickname (F23) | <presence from='juliet@example.com/yn0cl4bnw0yr3vym' | to='montague@chat.example.org/CapuletGirl'/> So far we have assumed that the requested nickname did not conflict with any existing nicknames. The following text describes the handling of a nickname conflict. The MSRP switch analyzes the existing allocation of nicknames, and detects that the nickname proposal is already provided to another participant. In this case, the MSRP switch answers with a 425 response.
Example 20: MSRP Switch Does Not Accept Nickname Proposal (F25) | MSRP a786hjs2 425 Nickname usage failed | To-Path: msrp://x2m.example.com:7654/jshA7weztas;tcp | From-Path: msrp://chat.example.org:12763/kjhd37s2s20w2a;tcp | -------a786hjs2 Upon receiving such a response, the XMPP-to-MSRP gateway translates it into an XMPP presence stanza of type "error", specifying a <conflict/> error condition (which implies that the XMPP client will then need to choose another nickname and repeat the process of joining). Example 21: Conflict Error for Nickname (F26) | <presence from='montague@chat.example.org/JuliC' | to='juliet@example.com/yn0cl4bnw0yr3vym' | type='error'> | <x xmlns='http://jabber.org/protocol/muc'/> | <error type='cancel' by='montague@chat.example.org'> | <conflict xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/> | </error> | </presence> Alternatively, the gateway might generate a new nickname request on behalf of the XMPP user, thus shielding the XMPP client from handling the conflict error.5.7. Invite Another User to a Room
In XMPP, there are two methods for inviting another user to a room: direct invitations [XEP-0249] (sent directly from the user's real JID outside the room to the invitee's real JID) and mediated invitations (sent through the room from the user's occupant JID to the invitee's JID). In this document, we cover mediated invitations only. For example, if Juliet decides to invite Benvolio to the room, she sends a message stanza with an invite and Benvolio's JID (which could be his real JID or an occupant JID in another room).
Example 22: Juliet Invites Benvolio to the Room (F27) | <message from='juliet@example.com/yn0cl4bnw0yr3vym' | id='nzd143v8' | to='montague@chat.example.org'> | <x xmlns='http://jabber.org/protocol/muc#user'> | <invite to='benvolio@example.com'/> | </x> | </message> The XMPP-to-SIP gateway then sends a SIP REFER request to the conference focus indicating who needs to be invited in the Refer-To header, as per Section 5.5 of [RFC4579]. Example 23: SIP Mapping of Invite (F28) | REFER sip:montague@chat.example.org SIP/2.0 | To: <sip:montague@chat.example.org> | From: "Juliet" <sip:juliet@example.com>;tag=786 | Call-ID: BC466C1C-E01D-4FD1-B766-9AD174BAF2E7 | CSeq: 5 REFER | Contact: <sip:juliet@example.com>;gr=yn0cl4bnw0yr3vym | Accept: message/sipfrag | Refer-To: <sip:benvolio@example.com> | Supported: replaces | Content-Length: 0 The conference focus then acknowledges the SIP REFER request with a 200 OK response (step F29, not shown). The progress of the invitation will be tracked by the received NOTIFY requests as per [RFC3515]. Example 24: Progress Notification for Invitation (F30) | NOTIFY sip:juliet@example.com SIP/2.0 | To: <sip:juliet@example.com>;tag=786 | From: <sip:montague@chat.example.org>;tag=087js | Call-ID: BC466C1C-E01D-4FD1-B766-9AD174BAF2E7 | CSeq: 6 NOTIFY | Max-Forwards: 70 | Event: refer | Subscription-State: active;expires=60 | Contact: <sip:montague@chat.example.org;transport=tcp>;isfocus | Content-Type: message/sipfrag;version=2.0 | Content-Length: ...
Note: Implementers might want to be aware that several recently published specifications modify the way in which REFER requests handle SIP notifications (see [RFC7647] and [RFC7614]).5.8. Exit Room
If Juliet decides to exit the chat room, her client sends a directed presence stanza of type "unavailable" to the occupant JID she is currently using in the room (here <montague@chat.example.org/JuliC>). Example 25: Juliet Exits Room (F31) | <presence from='juliet@example.com/yn0cl4bnw0yr3vym' | to='montague@chat.example.org/JuliC' | type='unavailable'/> Upon receiving such a stanza, the XMPP-to-SIP gateway terminates the SIP session by sending a SIP BYE to the conference focus and the conference focus responds with a SIP 200 OK (steps F32 and F33, not shown). Juliet can include a custom exit message in the presence stanza of type "unavailable", in which case it is broadcast to other participants using the methods described above. Example 26: Juliet Exits the Chat Room (F31) | <presence from='juliet@example.com/yn0cl4bnw0yr3vym' | to='montague@chat.example.org/JuliC' | type='unavailable'> | <status>O, look! methinks I see my cousin's ghost</status> | </presence>
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