Message 3SIP/2.0 200 OK
Via: SIP/2.0/TCP proxy.domain.com;branch=z9hG4bK123
;received=192.0.2.1
Via: SIP/2.0/TCP user1pc.domain.com
;branch=z9hG4bK77; received=1.2.3.4
From: <sip:[email protected]>;tag=49394
To: <sip:[email protected]>;tag=ab8asdasd9
Call-ID: [email protected]
CSeq: 1 MESSAGE
Content-Length: 0Message 4SIP/2.0 200 OK
Via: SIP/2.0/TCP user1pc.domain.com
;branch=z9hG4bK77; received=1.2.3.4
From: <sip:[email protected]>;tag=49394
To: <sip:[email protected]>;tag=ab8asdasd9
Call-ID: [email protected]
CSeq: 1 MESSAGE
Content-Length: 0Presence and IM have serious security issues that are part of the larger secu-
rity aspects for SIP discussed in Chapter 9, “SIP Security.”
Summary
Presence and instant messaging are new forms of communications made pos-
sible by the advent of the Internet. SIP presence is a subset of SIP events, and
there is an increasingly long list of communications and applications based on
presence. The standard for the presence information data format (PIDF) has
been enhanced with the Rich Presence Information Data format (RPID) that is
tailored to communicate presence directly to machines.
IM can be text-based, but can also support audio visual communications. IM
modes are the pager mode and the session mode using the Message Session
Relay Protocol (MSRP).
IM and presence can work both in the client-server and peer-to-peer modes.
Presence and Instant Messaging 241