8.5.5Multiple Recipient Messages

210 SIP: Understanding the Session Initiation Protocol

MESSAGE sip:nancy-list@csiro.au SIP/2.0

Via: SIP/2.0/TCP unimelb.csiro.au;branch=z9hG4bKhs8asdLs83 Max-Forwards: 70

To: <sip:nancy-list@csiro.au>

From: Nancy Tyson Burbidge <sip:nancy.burbidge@csiro.au> ;tag=Kjd32331

Call-ID: 8uF2sflFSsa CSeq: 98712 MESSAGE

Require: recipient-list-message

Content-Type: multipart/mixed;boundary=”boundary2” Content-Length: 501

--boundary2 Content-Type: text/plain

Hello Everybody!

--boundary2

Content-Type: application/resource-lists+xml Content-Disposition: recipient-list

<?xml version=”1.0” encoding=”UTF-8”?>

<resource-lists xmlns=”urn:ietf:params:xml:ns:resource-lists” xmlns:cp=»urn:ietf:params:xml:ns:copycontrol”>

<list>

<entry uri=”sip:caroline.atkinson@smh.com.au” cp:copyControl=”to” />

<entry uri=”sip:egould@ramsgate.kent.uk” cp:copyControl=”to” <entry uri=”sip:gmolloy@botanicals.org” cp:copyControl=”cc”/> <entry uri=”sip:jasminb@clearwater.tx.us” cp:copyControl=”cc” </list>

</resource-lists> --boundary2--

This MESSAGE has a multipart/mixed body which consists of a Content-

Type: text/plain instant message followed by a Content-Type: application/

resource-lists+xml body, which contains a list. Note that this list format is the same as that used in SUBSCRIBE requests creating resource lists. The copyControl attribute is defined in [26], which allows for the values of to, cc, or bcc that have the same meaning as in e-mail.

8.5.6Session Mode Instant Messaging

The Message Session Relay Protocol (MSRP) [30] was developed to meet the needs of a session mode IM system. For this case, the use of the SIP MESSAGE method was determined to be suboptimal. As a result, this is a non-SIP protocol. MSRP uses a SIP offer/answer exchange to establish the MSRP session using SDP. MSRP messages are either SEND requests, which carry a message or a REPORT request which reports on the status of a previous message. MSRP allows large messages to be sent by breaking the message into chunks which are sent in separate SEND requests. MSRP uses a stream-based transport such as TCP. As a result,

it must provide its own framing. MSRP defines its own URI scheme, which is used when negotiating the session. For example, an SDP offer used to establish an MSRP session:

v=0

o=nancy 2890844526 2890844527 IN IP4 unimelb.csiro.au s=-

c=IN IP4 unimelb.csiro.au t=0 0

m=message 7344 TCP/MSRP * a=accept-types:text/plain a=path:msrp://unimelb.csiro.au:27394/Kdsa2s93i9a;tcp

The media line contains the message media type while TCP/MSRP indicates that MSRP protocol will be used over TCP. An example MSRP exchange is shown in Figure 8.10.

MSRP has defined a number of header fields, listed in Table 8.7, and uses error codes shown in Table 8.8. Table 8.9 lists MSRP message types.

The use and operation of relay with MSRP is defined in [31]. These relays can be used for NAT traversal, logging, and corporate compliance. With MSRP relays, a mechanism for discovery and authentication is defined. An approach to establish MSRP sessions through NATs that uses standard ICE mechanisms is defined in [35]. The usage of MSRP in a multiuser chat is described in [34], which also defines a new MSRP request NICKNAME used to set a temporary name, known as a nickname, which can be used as an alias during the multiuser chat session. MSRP multiuser chat uses CPIM messages and the CPIM header to identify the recipient. The recipient can either be the entire chat room or it can