Network Working Group P. Saint-Andre
Internet-Draft XMPP Standards Foundation
Intended status: Informational E. Gavita
Expires: July 7, 2008 N. Hossain
S. Loreto
Ericsson
January 4, 2008
Interworking between the Session Initiation Protocol (SIP) and the
Extensible Messaging and Presence Protocol (XMPP): Text Chat
draft-saintandre-sip-xmpp-chat-00.txt
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Copyright (C) The IETF Trust (2008).
Abstract
This document defines a bi-directional protocol mapping for the
exchange of instant messages in the context of a one-to-one chat
session between a user of the Session Initiation Protocol (SIP) and a
user of the Extensible Messaging and Presence Protocol (XMPP).
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Specifically for SIP text chat, this document specifies a mapping to
the Message Session Relay Protocol (MSRP).
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Connection Maintenance . . . . . . . . . . . . . . . . . . 4
1.4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 5
2. Message Sessions . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. XMPP Formal Chat Session to MSRP . . . . . . . . . . . . . 5
2.2.1. Initiating a Formal Session . . . . . . . . . . . . . 6
2.2.2. Accepting a Formal Session . . . . . . . . . . . . . . 9
2.2.3. Terminating a Formal Session . . . . . . . . . . . . . 12
2.2.4. Canceling the Negotiation . . . . . . . . . . . . . . 14
2.2.5. Rejecting a Formal Session . . . . . . . . . . . . . . 15
2.3. XMPP Informal Session to MSRP . . . . . . . . . . . . . . 16
2.4. MSRP to XMPP formal session . . . . . . . . . . . . . . . 16
2.4.1. Initiating a Session . . . . . . . . . . . . . . . . . 17
2.4.2. Accepting a Session . . . . . . . . . . . . . . . . . 20
2.4.3. Completing the Transaction . . . . . . . . . . . . . . 21
2.4.4. Send a Message . . . . . . . . . . . . . . . . . . . . 21
2.4.5. Terminating a Session . . . . . . . . . . . . . . . . 22
2.4.6. Cancel the transaction . . . . . . . . . . . . . . . . 24
2.4.7. Rejecting a transaction . . . . . . . . . . . . . . . 25
2.5. MSRP to an XMPP Informal Session . . . . . . . . . . . . . 26
3. Security Considerations . . . . . . . . . . . . . . . . . . . 26
4. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.1. Normative References . . . . . . . . . . . . . . . . . . . 26
4.2. Informative References . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28
Intellectual Property and Copyright Statements . . . . . . . . . . 29
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1. Introduction
1.1. Overview
Both the Session Initiation Protocol [SIP] and the Extensible
Messaging and Presence Protocol [XMPP] can be used for the purpose of
one-to-one text chat over the Inernet. To ensure interworking
between these technologies, it is important to define bi-directional
protocol mappings.
The architectural assumptions underlying such protocol mappings are
provided in [SIP-XMPP], including mapping of addresses and error
conditions. Mappings for single instant messages (sometimes called
"pager-mode" messaging) are provided in [SIP-XMPP-IM]. This document
specifies mappings for one-to-one text chat sessions (sometimes
called "session-mode" messaging); in particular, this document
specifies mappings between XMPP and the Message Session Relay
Protocol [MSRP]. Mapping of multi-user text chat (sometimes called
"groupchat") is out of scope for this document.
Note: The capitalized 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 RFC 2119 [TERMS].
1.2. Scope
Both XMPP and SIP/SIMPLE technologies enable end users to send
"instant messages" to other end users. The term "instant message"
usually refers to messages sent between two end-users for delivery in
close to real time (rather than messages that are stored and
forwarded to the intended recipient upon request). Generally, there
are three kinds of instant messages:
1. Single messages, which are sent from the sender to the recipient
outside the context of any one-to-one chat session or multi-user
text conference. The message is immediately delivered and not
stored in an inbox. In XMPP a single message is a <message/>
stanza of type "normal" as specified in [XMPP-IM]. In SIP/SIMPLE
a single message is sent via the MESSAGE method as specified in
[MSRP].
2. One-to-one chat messages, which are sent from the sender to the
recipient (i.e., one-to-one) in the context of a "chat session"
between the two entities. In XMPP a chat message is a <message/>
stanza of type "chat". In SIP/SIMPLE a chat message is sent
using an MSRP session.
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3. Groupchat messages, which are sent from a sender to multiple
recipients (i.e., 2 or more) in the context of a "multi-user chat
session" or "text conference". In XMPP a groupchat message is a
<message/> stanza of type "groupchat" that is reflected from the
sender to multiple recipients by a multi-user chat service as
defined in [XEP-0045]. In SIP/SIMPLE a groupchat message is
reflected from the sender to multiple recipients by a conference
server that uses MSRP to handle groupchat sessions.
This document only covers the scenario #2 above for converting XMPP
messages of type "chat" to their corresponding SIP INVITE - MSRP
message types on the SIP/SIMPLE side.
As in [SIP-XMPP-IM] and related documents, the approach taken here is
to directly map syntax and semantics from one protocol to another.
One-to-one chat sessions using XMPP message stanzas of type "chat"
are specified in [XMPP-IM], and a method for formally negotiating
such a session is specified in [XEP-0155]. One-to-one chat sessions
using the SIP MESSAGE method, the SIP INVITE method, and the Message
Session Relay Protocol (MSRP) are specified in [SIP-MSG] and [MSRP].
In particular, this document defines a mapping between XMPP chat
sessions (as specified in [XMPP-IM] and [XEP-0155]) and the Message
Session Relay Protocol (as specified in [MSRP]).
1.3. Connection Maintenance
XMPP makes use of long-lived TCP connections. If mobility affecting
Layer 3 causes a dropped connection, the connection must be re-
established. If mobility preserves the IP address, the TCP
connection will be dropped. Any TLS session and SASL associations
must be re-established if the TCP connection is dropped. XMPP binds
directly to TCP in the core specification, so the TCP session must
remain open for the entire duration of the chat/conversation. The
XMPP Standards Foundation does define protocol extensions enabling
transport of XMPP traffic over HTTP (refer to [XEP-0124] and
[XEP-0206]), so that individual messages are carried using HTTP and
are more robust in environments such as mobile networks, allowing for
better recovery if a TCP session is broken.
SIMPLE is similar when using MSRP. The Message Session Relay
Protocol [MSRP] is a protocol for transmitting instant messages (IM)
in the context of a session. The protocol specification describes
how the session can be negotiated and established with an offer or
answer [OFFER] using the Session Description Protocol [SDP]. In
SIMPLE, this exchange is carried using SIP as the signaling protocol.
After the TCP connection is established, if it fails for any reason,
then an MSRP endpoint MAY choose to re-create such session using a
new SDP exchange in a SIP re-INVITE. SIMPLE also uses MESSAGE
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request for transporting instant messaging outside the context of a
session. The MESSAGE request is sent inside the signaling path
without establishing any dedicate connection.
1.4. Acknowledgements
Some text in this document was borrowed from [SIP-XMPP] and from
[XEP-0155].
2. Message Sessions
2.1. Overview
The traditional model for one-to-one chat "session" in Jabber/XMPP is
for a user to simply send a message to a contact with a thread ID,
but without any formal negotiation of session parameter.
This informal approach to session initiation in XMPP can be mapped
both to SIP pager-mode messaging using the SIP MESSAGE method (as
documented in [SIP-XMPP]) and to a MSRP chat session. How the
Gateway chooses to map the XMPP chat session in the SIP side is a
matter of the implementation.
However, in XMPP it also possibile to formally request a chat session
and negotiate its parameters (e.g., security, privacy, message
logging) before beginning the session. The protocol for doing so is
defined in [XEP-0155]. In this case, the XMPP chat session should be
translated into a MSRP session.
This document covers the mapping of both informal and formally-
negotiated XMPP chat session into a MSRP session.
2.2. XMPP Formal Chat Session to MSRP
XMPP Protocol offers two ways an XMPP user can initiate a 1-1 chat:
the first approach doesn't establish a session (this method is
referred to the "informal session" approach); the second approach
instead involves explicit negotiation of a session (this method is
referred to the "formal session" approach).
This section describes how to map an XMPP "formal session" to an MSRP
session.
The XMPP formal session is based on the protocol described in
[XEP-0155], which enable the initiation, renegotiation, and
termination of a format chat session on the XMPP side. This approach
maps to the semantic of the SIP INVITE and BYE methods.
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XMPP User X2M GW SIP User
| | |
|(F1) (XMPP) Stanza session request |
|------------------------->| |
| |(F2) (SIP) INVITE |
| |------------------------->|
| |(F3) (SIP) 200 OK |
| |<-------------------------|
|(F4) (XMPP) Stanza session acceptance |
|<-------------------------| |
| |(F5) (SIP) ACK |
| |------------------------->|
|(F6) (XMPP) Stanza session completion |
|------------------------->| |
| |(F7) (MSRP) SEND |
| |------------------------->|
|(F8) (XMPP) Stanza session termination |
|------------------------->| |
| |(F9) (SIP) BYE |
| |------------------------->|
| |(F10) (SIP) 200 OK |
| |<-------------------------|
|(F11) (XMPP) Stanza acknoledgment |
| session termination |
|<-------------------------| |
2.2.1. Initiating a Formal Session
When the XMPP user ("Juliet") wants to initiate a negotiated session
with a SIP user ("Romeo"), she sends a <message/> stanza to Romeo
containing a <feature/> child qualified by the
'http://jabber.org/protocol/feature-neg' namespace. The <message/>
stanza must not contain a <body/< child (as specified in [XMPP-IM]),
since thhat child element is used for human-readable text. The
<message/> stanza type should be "normal". The stanza must contain a
<thread/> element for tracking purposes (where the newly-generated
ThreadID is unique to the proposed session). The encapsulated data
form shall contain a FORM_TYPE field whose type is "hidden" and whose
value is "urn:xmpp:ssn"; it must also contain a boolean field named
"accept".
The XMPP user may request a session with a specific resource of the
contact. However in this document the resource identifier will be
ignored and discarded for cross-system interworking.
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Example: (F1) Juliet starts a formal session:
<message type='normal'
from='juliet@example.com'
to='romeo@example.net'>
<thread>711609sa</thread>
<feature xmlns='http://jabber.org/protocol/feature-neg'>
<x xmlns='jabber:x:data' type='form'>
<title>Open chat with Juliet?</title>
<field var='FORM_TYPE' type='hidden'>
<value>urn:xmpp:ssn</value>
</field>
<field label='Accept this session?' type='form' var='accept'>
<value>true</value>
<required/>
</field>
<field label='Primary written language of the chat'
type='list-single' var='language'>
<value>en</value>
<option label='English'><value>en</value></option>
<option label='Italiano'><value>it</value></option>
</field>
</x>
</feature>
</message>
Upon receiving such a session request, the XMPP server to which
Juliet has authenticated attempts to deliver the request to a local
user or attempts to route the request to the foreign domain that
services the hostname in the 'to' attribute. Naturally, in this
document we assume that the hostname in the 'to' attribute is an IM-
aware SIP service hosted by a separate server.
As specified in [XMPP-IM], the XMPP server needs to determine the
identity of the foreign domain, which it does by performing one or
more [DNS-SRV] lookups. For message stanzas, the order of lookups
recommended by [XMPP-IM] is to first try the "_xmpp-server" service
as specified in [XMPP] and to then try the "_im" service as specified
in [IMP-SRV]. Here we assume that the first lookup will fail but
that the second lookup will succeed and return a resolution
"_im._simple.example.net.", since we have already assumed that the
example.net hostname is running a SIP instant messaging service.
(Note: The XMPP server may have previously determined that the
foreign domain is a SIMPLE server, in which case it would not need to
perform the SRV lookups; the caching of such information is a matter
of implementation and local service policy, and is therefore out of
scope for this document.)
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Once the XMPP server has determined that the foreign domain is
serviced by a SIMPLE server, it must determine how to proceed. We
here assume that the XMPP server contains or has available to it an
XMPP-MSRP gateway. The XMPP server would then deliver the message
stanza to the XMPP-MSRP gateway.
The XMPP-MSRP gateway is then responsible for translating the XMPP
session into an MSRP session.
Example: (F2) Juliet starts a formal session (SIP transformation):
INVITE sip:romeo@example.net SIP/2.0
To: <sip:romeo@example.net>
From: <sip:juliet@example.com>;tag=786
Subject: Open chat with Juliet?
Call-ID: 711609sa
Content-Type: application/sdp
c=IN IP4 x2m.example.com
m=message 7654 TCP/MSRP *
a=accept-types:text/plain
a=lang:en
a=lang:it
a=path:msrp://x2m.example.com:7654/jshA7weztas;tcp
There is no direct mapping for the MSRP URIs. In fact MSRP URIs
identify a session of instant message at a particular device; they
are ephemeral and have not meaning outside the scope of that session.
The authority component of the MSRP URI MUST contain the XMPP-MSRP
gateway hostname or numeric IP address and an explicit port number.
Native XMPP supports text (i.e., UTF-8) only, so the "accept-types"
attribute that follows an MSRP media line MUST indicate text/plain as
the only media-type that is acceptable to the endpoint.
As specified in [SIP-XMPP], the mapping of XMPP syntax elements to
SIP and SDP syntax elements SHOULD be as shown in the following
table. (Mappings for elements not mentioned are undefined).
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Table 1: Message syntax mapping from XMPP to SIP/SDP
+-----------------------------+-----------------------------+
| XMPP Element or Attribute | SIP Header or SDP Contents |
+-----------------------------+-----------------------------+
| <thread/> | Call-ID |
| from | From |
| to | To |
| <title/> | Subject |
| xml:lang | a=lang:<language tag> |
| - | a=accept-types:text/plain |
+-----------------------------+-----------------------------+
2.2.2. Accepting a Formal Session
The SIP user agent Romeo receiving the SIP invitation, containing an
offered session description that includes a session of MSRP, accepts
the invitation and includes an answer session description that
acknowledges the choice of media.
Example: (F3) Romeo accepts the request
SIP/2.0 200 OK
To: <sip:romeo@example.net>;tag=087js
From: <sip:juliet@example.com>;tag=786
Call-ID: 711609sa
Content-Type: application/sdp
c=IN IP4 example.net
m=message 12763 TCP/MSRP *
a=accept-types:text/plain
a=lang:it
a=path:msrp://example.net:12763/kjhd37s2s20w2a;tcp
Upon receiving such a response, the MSRP-XMPP gateway SHOULD remember
that this is a response to a SIP transaction related to an XMPP-MSRP
translation. The gateway is responsible for translating the response
into an XMPP message stanza and deliver it from the SIP user back to
the XMPP user deliver.
The MSRP-XMPP gateway MUST include in the response translation values
for all the fields that the XMPP request indicated are required.
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Example: (F4) Romeo accepts the request (XMPP translation)
<message type='normal'
from='romeo@example.net'
to='juliet@example.com'>
<thread>711609sa</thread>
<feature xmlns='http://jabber.org/protocol/feature-neg'>
<x xmlns='jabber:x:data' type='submit'>
<field var='FORM_TYPE'>
<value>urn:xmpp:ssn</value>
</field>
<field var='accept'><value>true</value></field>
<field var='language'><value>it</value></field>
</x>
</feature>
</message>
The gateway MUST also send a SIP ACK to the SIP user.
Example: (F5) The GW sends the ACK to Romeos UA:
ACK sip:romeo@example.com SIP/2.0
To: <sip:romeo@example.net>;tag=087js
From: <sip:juliet@example.com>;tag=786
Call-ID: 711609sa
If Romeo accepted the session Juliet MUST either complete or cancel
the stanza session negotiation. The user's client SHOULD verify that
the selected values of the fields are acceptable before completing
the stanza session negotiation -- and confirming that the session is
open -- by replying with the form 'type' attribute set to 'result'.
The form MUST contain the FORM_TYPE field and the "accept" field set
to "1" or "true". The user MAY include other content "e.g., a
<body/> element in the confirmation stanza:
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Example: (F6) Juliet completes negotiation, confirms session is open
and send a message.
<message type='normal'
from='juliet@example.com'
to='romeo@example.net'>
<thread>711609sa</thread>
<feature xmlns='http://jabber.org/protocol/feature-neg'>
<x xmlns='jabber:x:data' type='result'>
<field var='FORM_TYPE'>
<value>urn:xmpp:ssn</value>
</field>
<field var='accept'><value>true</value></field>
</x>
</feature>
</message>
Upon receiving such stanza completing the session negotiation, the
XMPP server MUST not send any confirmation to the SIP side.
The XMPP-MSRP gateway must create a transaction identifier and use
this and the SEND method to create an MSRP request start line.
The XMPP 'id' attribute is not required in the protocol and there is
not a way to enforce its use for messages. It is RECOMMENDED to add
it as a negotiable item in the XEP-0155, however it may not be
present within the <message/> stanza, in this case the XMPP-MSRP MUST
generate a new unique Message-ID.
Note: If the XMPP user has not explicitly requested message receipts
during the negotiation, it is RECOMMENDED that the XMPP-MSRP inserts
a Failure-Report header field value of "no" during the creation of a
SEND request. The XMPP user can include the requested for message
receipts using the Message Receipts XMPP protocol extension
[XEP-0184].
As specified in [SIP-XMPP], the mapping of XMPP syntax elements to
MSRP syntax elements SHOULD be as shown in the following table.
(Mappings for elements not mentioned are undefined).
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Table 2: Message syntax mapping from XMPP Message to MSRP
+-----------------------------+-----------------------------+
| XMPP Element or Attribute | MSRP Header |
+-----------------------------+-----------------------------+
| to | To-Path |
| from | From-Path |
| <body/> | body of the SEND request |
| - | Content-Type: text/plain |
| id | Message-ID |
+-----------------------------+-----------------------------+
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, Alice's client MUST immediately
generate and send a response.
MSRP d93kswow 200 OK
To-Path: msrp://x2m.example.com:7654/jshA7weztas;tcp
From-Path: msrp://example.net:12763/kjhd37s2s20w2a;tcp
-------d93kswow$
The XML character data of an XMPP message is not limited by the
protocol, but is sometimes limited in deployment. However messages
sent using MSRP can be delivered in several SEND requests, so when
the XMPP-MSRP gateway receives a message longer then 2048, it is
STRONGLY RECOMMENDED it delivers this message using as few chunks (at
least 2048 octets long) as possible.
2.2.3. Terminating a Formal Session
If Juliet decides to terminate the negotiated chat session, her
client sends a <message/> stanza to Romeo containing a data form of
type "submit". The <message/> stanza MUST contain a <thread/>
element with the same XML character data as the original initiation
request. The data form containing a boolean field named "terminate"
set to a value of "1" or "true".
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Example: (F8) Juliet terminates the chat session
<message type='normal'
from='juliet@example.com'
to='romeo@example.net'>
<thread>711609sa</thread>
<feature xmlns='http://jabber.org/protocol/feature-neg'>
<x xmlns='jabber:x:data' type='submit'>
<field var='FORM_TYPE'>
<value>urn:xmpp:ssn</value>
</field>
<field var='terminate'><value>1</value></field>
</x>
</feature>
</message>
Upon receiving such stanza terminating the chat session, the gateway
terminates the SIP session by sending a SIP BYE to tear down the MSRP
session with Romeo's client. Romeo's SIP client then responds with a
200 OK.
Example: (F9) Juliet terminates the chat session (SIP translation)
BYE romeo@example.com sip: SIP/2.0
Max-Forwards: 70
From: <sip:juliet@example.com>;tag=786
To: <sip:romeo@example.net>;tag=087js
Call-ID: 711609sa
Cseq: 1 BYE
Content-Length: 0
Example: (F10) Romeo terminates the chat session
SIP/2.0 200 OK
From: <sip:juliet@example.com>;tag=786
To: <sip:romeo@example.net>; tag=087js
Call-ID: 711609sa
CSeq: 1 BYE
Content-Length: 0
Upon receiving the 200 OK, the GW acknowledges the termination of the
chat session on the XMPP side by sending a <message/> containing a
data form of type "result", and the value of the "terminate" field
set to "1" or "true". The client must mirror the <thread/> value it
received.
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Example: (F11) Romeo terminates the chat session (XMPP translation)
<message type='normal'
from='romeo@example.net'
to=='juliet@example.com'>
<thread>711609sa</thread>
<feature xmlns='http://jabber.org/protocol/feature-neg'>
<x xmlns='jabber:x:data' type='result'>
<field var='FORM_TYPE'>
<value>urn:xmpp:ssn</value>
</field>
<field var='terminate'><value>1</value></field>
</x>
</feature>
</message>
2.2.4. Canceling the Negotiation
XMPP User X2M GW SIP User
| | |
|(F1) (XMPP) Stanza session request |
|------------------------->| |
| |(F2) (SIP) INVITE |
| |------------------------->|
| |(F3) (SIP) 200 OK |
| |<-------------------------|
|(F4) (XMPP) Stanza session acceptance |
|<-------------------------| |
| |(F5) (SIP) ACK |
| |------------------------->|
|(F6) (XMPP) Stanza session canceling |
|------------------------->| |
| |(F7) (SIP) BYE |
| |------------------------->|
| |(F8) (SIP) 200 OK |
| |<-------------------------|
If Romeo accepted the session, but Juliet decides to cancel the
stanza session negotiation, the client must reply with a data form
containing the FORM_TYPE field and the "accept" field set to "0" or
"false":
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Example: (F6) User cancels stanza session negotiation
<message type='normal'
from='juliet@example.com'
to='romeo@example.net'>
<thread>711609sa</thread>
<feature xmlns='http://jabber.org/protocol/feature-neg'>
<x xmlns='jabber:x:data' type='result'>
<field var='FORM_TYPE'>
<value>urn:xmpp:ssn</value>
</field>
<field var='accept'><value>0</value></field>
</x>
</feature>
</message>
Upon receiving such stanza canceling the session negotiation, the
XMPP-MSRP Gateway MUST send a SIP BYE. Once the XMPP-MSRP receives
the 200 OK, the internal session data is removed and the session is
officially canceled also in the gateway.
2.2.5. Rejecting a Formal Session
XMPP User X2M GW SIP User
| | |
|(F1) (XMPP) Stanza session request |
|------------------------->| |
| |(F2) (SIP) INVITE |
| |------------------------->|
| |(F3) (SIP) 4xx/6xx |
| |<-------------------------|
|(F4) (XMPP) Stanza session decline |
|<-------------------------| |
A common scenario occurs when the SIP UA is currently not willing or
able to accept a formal session. The SIP UA declining an offer
contained in an INVITE SHOULD return a 4xx or a 6xx response. Such
response SHOULD include a Warning header field value explaining why
the offer was rejected.
Upon receiving the error response for the SIP INVITE, the XMPP-MSRP
GW will send back a "Session Reject" message back to the XMPP Client.
The data form MUST contain the FORM_TYPE field and the "accept" field
set to "0" or "false". It is reccomended that the form does not
contain any other field even if the request indicated they are
required. The client MAY include a reason in the <body/> child of
the <message/> stanza.
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The content of the Warning header field present in the SIP response
SHOULD be copied in the <body/> child of the <message/> stanza. If
the Warning header it is not present then the descriptive phrase of
the SIP response can be used.
Example: (F4) User declines offer and specifies reason
<message type='normal'
from='romeo@example.net'
to='juliet@example.com'>
<thread>711609sa</thread>
<feature xmlns='http://jabber.org/protocol/feature-neg'>
<x xmlns='jabber:x:data' type='submit'>
<field var='FORM_TYPE'>
<value>urn:xmpp:ssn</value>
</field>
<field var='accept'><value>0</value></field>
</x>
</feature>
</message>
2.3. XMPP Informal Session to MSRP
The "informal session" approach is to simply send someone a <message
type='chat'/> without start any session negotiation before (as
described in [XMPP-IM]). The XMPP "informal session" approach maps
very well into a SIP MESSAGE request, as described in [SIP-XMPP].
Although the mapping to a SIP Message is straightforward, it is also
possible to map an informal session to an MSRP session. The mapping
will be provided in a future version of this specification.
2.4. MSRP to XMPP formal session
Unlike the XMPP protocol, the MSRP protocol only offers one way to
initiate a Chat session, that is typically initiated using the
Session Description Protocol [SDP] via the SIP offer/answer mechanism
[OFFER].
This section will describe how to map a MSRP Chat session to either a
formal or informal XMPP session.
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SIP User M2X GW XMPP User
| | |
|(F1)(SIP) INVITE | |
|------------------------>| |
| |(F2)(XMPP) Stanza session request
| |------------------------->|
| |(F3)(XMPP) Stanza session acceptance
| |<-------------------------|
|(F4)(SIP) 200 OK | |
|<------------------------| |
|(F5)(SIP) ACK | |
|------------------------>| |
| |(F6)(XMPP) Stanza session completion
| |------------------------->|
|(F7)(MSRP) SEND | |
|------------------------>| |
| |(F8)(XMPP) Stanza message |
| |------------------------->|
|(F9)(SIP) BYE | |
|------------------------>| |
| |(F10)(XMPP) Stanza session termination
| |------------------------->|
| |(F11)(XMPP) Stanza acknowledgment
| | session termination
| |<-------------------------|
|(F12)(SIP) 200 OK | |
|<------------------------| |
2.4.1. Initiating a Session
When Romeo wants to start an MSRP message session with Juliet, he
first has to start the SIP session by sending out a SIP INVITE
request containing an offered session description that includes an
MSRP media line accompanied by a mandatory "path" attribute and
corresponding URIs. The MSRP media line is also accompanied by an
"accept-types" attribute used to specify the only media-types
acceptable for Romeo (i.e., text/plain).
In addition to plain text messages, MSRP is able to carry arbitrary
(binary) Multipurpose Internet Mail Extensions [MIME] compliant
content, such as images or video clips.
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Example: (F1) SIP user starts the session:
INVITE sip:juliet@example.com SIP/2.0
To: <sip:juliet@example.com>
From: <sip:romeo@example.net>;tag=576
Subject: Open chat with Romeo?
Call-ID: 742507no
Content-Type: application/sdp
c=IN IP4 example.net
m=message 7313 TCP/MSRP *
a=accept-types:text/plain
a=lang:en
a=lang:it
a=path:msrp://example.net:7313/ansp71weztas;tcp
Upon receiving the INVITE, the MSRP-XMPP gateway needs to determine
the identity of the foreign domain, which it does by performing one
or more DNS SRV lookups [DNS-SRV]. The gateway SHOULD resolve the
address present in the To header of the INVITE to an im, then follow
the rules in [IMP-SRV] regarding the "_im" SRV service for the target
domain contained in the To header. If SRV address resolution fails
for the "_im" service, the gateway MAY attempt a lookup for the
"_xmpp-server" service as specified in [XMPP] or MAY return an error
to the sender (i.e. 502 Bad Gateway).
If SVR address resolution succeeds, the gateway is responsible for
translating the request into an XMPP message stanza to initiate a
negotiated session from the SIP user to the XMPP user.
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Example: (F2) SIP user starts the session (XMPP transformation):
<message type='normal'
from='romeo@example.net'
to='juliet@example.com'>
<thread>742507no</thread>
<feature xmlns='http://jabber.org/protocol/feature-neg'>
<x xmlns='jabber:x:data' type='form'>
<title>Open chat with Romeo?</title>
<field var='FORM_TYPE' type='hidden'>
<value>urn:xmpp:ssn</value>
</field>
<field label='Accept this session?' type='form' var='accept'>
<value>true</value>
<required/>
</field>
<field label='Primary written language of the chat'
type='list-single'
var='language'>
<value>en</value>
<option label='English'><value>en</value></option>
<option label='Italiano'><value>it</value></option>
</field>
</x>
</feature>
</message>
The mapping of SIP and SDP syntax elements to XMPP syntax elements
SHOULD be as shown in the following table. (Mappings for elements
not mentioned in the foregoing table are undefined).
Table 3: Message syntax mapping from SIP to XMPP
+-----------------------------+-----------------------------+
| SIP Header or SDP Contents | XMPP Element or Attribute |
+-----------------------------+-----------------------------+
| Call-ID | <thread/> |
| From | from |
| To | to |
| Subject | <title/> |
| accept-types | - |
| a=lang | xml:lang |
| To | to |
+-----------------------------+-----------------------------+
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2.4.2. Accepting a Session
If the request is accepted then Juliets client MUST include all the
fields that were marked as required in the request message.
In the example below, we assume that Juliet accepts the session and
specifies that she prefers to speak Italian with Romeo.
Example: (F3) Juliet accepts session and specifies parameters:
<message type='normal'
from='juliet@example.com'
to='romeo@example.net'>
<thread>742507no</thread>
<feature xmlns='http://jabber.org/protocol/feature-neg'>
<x xmlns='jabber:x:data' type='submit'>
<field var='FORM_TYPE'>
<value>urn:xmpp:ssn</value>
</field>
<field var='accept'><value>true</value></field>
<field var='language'><value>it</value></field>
</x>
</feature>
</message>
Upon receiving such a response, the MSRP-XMPP gateway SHOULD remember
that this is a response to a stanza related to an MSRP-XMPP
translation. The gateway is responsible for translating the response
into a SIP response and deliver it from the XMPP user back to the SIP
user.
Example: (F4) Juliet accepts session (SIP translation)
SIP/2.0 200 OK
To: <sip:juliet@example.com>;tag=534
From: <sip:romeo@example.net>;tag=576
Call-ID: 742507no
Content-Type: application/sdp
c=IN IP4 m2x.example.net
m=message 8763 TCP/MSRP *
a=accept-types:text/plain
a=lang:it
a=path:msrp://m2x.example.net:8763/lkjh37s2s20w2a;tcp
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2.4.3. Completing the Transaction
In this case, the 200 OK is routed back and is received by Romeo UA.
Finally, Romeos client sends an acknowledgment message, ACK, to
Juliets client to confirm the reception of the final response (200
OK).
Example: (F5) Romeo sends the ACK:
ACK sip:juliet@example.com SIP/2.0
To: <sip:juliet@example.com>;tag=534
From: <sip:romeo@example.net>;tag=576
Call-ID: 742507no
Upon receiving the ACK, the MSRP-XMPP gateway SHOULD remember this is
an acknowledgment to an XMPP formal session. The gateway is
responsible for translating the acknowledgment into a confirmation
stanza, without inserting other content (e.g. a <body/> element can
not be inserted).
Example: (F6) Romeo sends the ACK (XMPP translation)
<message type='normal'
from='romeo@example.net'
to='juliet@example.com'>
<thread>742507no</thread>
<feature xmlns='http://jabber.org/protocol/feature-neg'>
<x xmlns='jabber:x:data' type='result'>
<field var='FORM_TYPE'>
<value>urn:xmpp:ssn</value>
</field>
<field var='accept'><value>true</value></field>
</x>
</feature>
</message>
2.4.4. Send a Message
When Romeo wants to send a message, he creates an MSRP SEND request
that contains message.
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Example: (F7) Romeo send a message.
MSRP ad49kswow SEND
To-Path: msrp://m2x.example.net:8763/lkjh37s2s20w2a;tcp
From-Path: msrp://example.net:7313/ansp71weztas;tcp
Message-ID: 44921zaqwsx
Byte-Range: 1-32/32
Failure-Report: no
Content-Type: text/plain
I forgot what I wanted to say!
-------ad49kswow$
Upon receiving the MSRP SEND request, the MSRP-XMPP gateway SHOULD
remember that the message is for an XMPP user. The gateway is
responsible for translating the MSRP SEND request in an XMPP message
stanza.
Example: (F8) Romeo sends a message (XMPP translation).
<message type='normal'
from='romeo@example.net'
to='juliet@example.com'>
<thread>742507no</thread>
<body>I forgot what I wanted to say!</body>
</message>
The mapping of MSRP syntax elements to XMPP syntax elements SHOULD be
as shown in the following table. (Mappings for elements not
mentioned are undefined).
Table 4: Message syntax mapping from MSRP Message to XMPP
+-----------------------------+-----------------------------+
| MSRP Header | XMPP Element or Attribute |
+-----------------------------+-----------------------------+
| To-Path | to |
| From-Path | from |
| body of the SEND request | <body/> |
| Content-Type: text/plain | - |
| Message-ID | id |
+-----------------------------+-----------------------------+
2.4.5. Terminating a Session
When Romeo wants to terminate the Session, he is required to send a
SIP BYE request.
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Example: (F9) Romeo terminates the session
BYE juliet@example.com sip: SIP/2.0
Max-Forwards: 70
From: <sip:romeo@example.net>;tag=576
To: <sip:juliet@example.com>;tag=534
Call-ID: 742507no
Cseq: 1 BYE
Content-Length: 0
Upon receiving the SIP BYE request, the GW SHOULD translate the
request to a <message/> stanza containing a data form of type
"submit". The <message/> element MUST contain a <thread/> element
with the same XML character data as the original initiation request.
The data form containing a boolean field named "terminate" should be
set to a value of "1" or "true".
Example: (F10) Romeo terminates the session (XMPP translation)
<message type='normal'
from='romeo@example.net'
to='juliet@example.com'>
<thread>742507no</thread>
<feature xmlns='http://jabber.org/protocol/feature-neg'>
<x xmlns='jabber:x:data' type='submit'>
<field var='FORM_TYPE'>
<value>urn:xmpp:ssn</value>
</field>
<field var='terminate'><value>1</value></field>
</x>
</feature>
</message>
Juliet explicitly acknowledges the termination of the chat session on
the XMPP side by sending a <message/> containing a data form of type
"result", and the value of the "terminate" field set to "1" or
"true". The client MUST mirror the <thread/> value it received.
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Example: (F11) Juliet acknowledges the termination of the session.
<message type='normal'
from='juliet@example.com'
to=='romeo@example.net'>
<thread>742507no</thread>
<feature xmlns='http://jabber.org/protocol/feature-neg'>
<x xmlns='jabber:x:data' type='result'>
<field var='FORM_TYPE'>
<value>urn:xmpp:ssn</value>
</field>
<field var='terminate'><value>1</value></field>
</x>
</feature>
</message>
Upon receiving the acknowledgment message, the GW SHOULD translate it
to a SIP answer 200 OK.
Example: (F12) Juliet acknowledges the termination of the session
(SIP translation)
SIP/2.0 200 OK
From: <sip:romeo@example.net>;tag=576
To: <sip:juliet@example.com>;tag=534
Call-ID: 742507no
CSeq: 1 BYE
2.4.6. Cancel the transaction
SIP User M2X GW XMPP User
| | |
|(F1)(SIP) INVITE | |
|----------------------->| |
| |(F2)(XMPP) Stanza session request
| |------------------------->|
|(F3)(SIP) CANCEL | |
|----------------------->| |
| |(F4)(XMPP) Stanza session termination
| |------------------------->|
| |(F5)(XMPP) Stanza acknowledgment
| | session termination
| |<-------------------------|
|(F6)(SIP) 200 OK | |
|<-----------------------| |
A common scenario occurs when the SIP user issues an invitation to
set up a Chat session with an XMPP user and immediately after the SIP
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invitation is sent, the SIP user decides to cancel it. The XMPP-MSRP
GW will receive the CANCEL request and using the the Call-ID, To,
From and CSeq (sequence number only) header field values as a guide,
will issue an XMPP Stanza session termination request to the XMPP
user to cancel the XMPP formal session (assuming that it was already
set up). Once the XMPP-MSRP GW receives an ACK stanza message for
the session termination, the XMPP-MSRP GW will respond with a status
of 200 (OK) back to the SIP user. It is important to note that if
the SIP session transaction does not exist, the XMPP-MSRP GW will
return a status of 481 (Transaction Does Not Exist) back to the SIP
User.
2.4.7. Rejecting a transaction
SIP User M2X GW XMPP User
| | |
|(F1)(SIP) INVITE | |
|-------------------------->| |
| |(F2)(XMPP) Stanza session request
| |------------------------->|
| |(F3)(XMPP) Stanza session decline
| |<-------------------------|
|(F4)(SIP) 4xx/6xx | |
|<--------------------------| |
Another common scenario occurs when the XMPP UA is currently not
willing or able to accept a formal session request. The XMPP UA
SHOULD decline the invitation. The data form MUST contain the
FORM_TYPE field and the "accept" field set to "0" or "false". It is
RECOMMENDED that the form does not contain any other fields even if
the request indicated they are required. The client MAY include a
reason in the <body/> child of the <message/> stanza:
Example: (F3) User declines offer and specifies reason
<message type='normal'
from='juliet@example.com'
to='romeo@example.net'>
<thread>742507no</thread>
<feature xmlns='http://jabber.org/protocol/feature-neg'>
<x xmlns='jabber:x:data' type='submit'>
<field var='FORM_TYPE'>
<value>urn:xmpp:ssn</value>
</field>
<field var='accept'><value>0</value></field>
</x>
</feature>
</message>
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Upon receiving the declined response for the XMPP formal session
request, the XMPP-MSRP GW SHOULD return a 4xx or a 6xx SIP response
back to the SIP client. Any content that is contained in the <body/>
child of the <message/>. stanza SHOULD be copied into the response
Warning header field which explains why the offer was rejected.
2.5. MSRP to an XMPP Informal Session
To follow.
3. Security Considerations
To follow.
4. References
4.1. Normative References
[IMP-SRV] Peterson, J., "Address Resolution for Instant Messaging
and Presence", RFC 3861, August 2004.
[MSRP] Campbell, B., Mahy, R., and C. Jennings, "The Message
Session Relay Protocol (MSRP)", RFC 4975, September 2007.
[OFFER] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
June 2002.
[SIP] 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.
[TERMS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[XEP-0155]
Paterson, I. and P. Saint-Andre, "Stanza Session
Negotiation", XSF XEP 0155, March 2007.
[XMPP] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 3920, October 2004.
[XMPP-IM] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence",
RFC 3921, October 2004.
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4.2. Informative References
[DNS-SRV] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[SDP] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[SIP-MSG] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C.,
and D. Gurle, "Session Initiation Protocol (SIP) Extension
for Instant Messaging", RFC 3428, December 2002.
[SIP-XMPP]
Saint-Andre, P., Houri, A., and J. Hildebrand,
"Interworking between the Session Initiation Protocol
(SIP) and the Extensible Messaging and Presence Protocol
(XMPP): Core", draft-saintandre-sip-xmpp-core-00 (work in
progress), January 2008.
[SIP-XMPP-IM]
Saint-Andre, P., Houri, A., and J. Hildebrand,
"Interworking between the Session Initiation Protocol
(SIP) and the Extensible Messaging and Presence Protocol
(XMPP): Instant Messaging",
draft-saintandre-sip-xmpp-im-00 (work in progress),
January 2008.
[XEP-0045]
Saint-Andre, P., "Multi-User Chat", XSF XEP 0045,
April 2007.
[XEP-0124]
Paterson, I., Smith, D., and P. Saint-Andre,
"Bidirectional-streams Over Synchronous HTTP (BOSH)", XSF
XEP 0124, February 2007.
[XEP-0184]
Saint-Andre, P. and J. Hildebrand, "Message Receipts", XSF
XEP 0184, September 2007.
[XEP-0206]
Paterson, I., "XMPP Over BOSH", XSF XEP 0206, June 2007.
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Authors' Addresses
Peter Saint-Andre
XMPP Standards Foundation
P.O. Box 1641
Denver, CO 80201
USA
Email: stpeter@jabber.org
URI: https://stpeter.im/
Eddy Gavita
Ericsson
Decarie Boulevard
Town of Mount Royal, Quebec
Canada
Email: eddy.gavita@ericsson.com
Nazin Hossain
Ericsson
Decarie Boulevard
Town of Mount Royal, Quebec
Canada
Email: Nazin.Hossain@ericsson.com
Salvatore Loreto
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Salvatore.Loreto@ericsson.com
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