Internet Communications Using SIP : Delivering VoIP and Multimedia Services With Session Initiation Protocol {2Nd Ed.}

Figure 6.9 Preconditions of call setup using UPDATEand PRACK

Nonsession-Related Functions

Some SIP functions do not relate directly to session setup. These functions can
occur outside of a session established using SIP.

SIP User Agent

1 INVITE

Proxy Server SIP User Agent

9 183 Session Progress

11 PRACK

2 INVITE

3 100 Trying 5 INVITE

4 100 Trying

6 100 Trying

7 183 Session Progress

8 183 Session Progress

10 PRACK

14 200 OK

QoS SETUP

12 PRACK

Media Session with QoS

16 UPDATE

28 ACK

29 ACK

30 ACK

17 UPDATE

18 UPDATE

13 200 OK

19 200 OK

20 200 OK

21 200 OK 22 180 Ringing

23 180 Ringing

24 180 Ringing 25 200 OK

26 200 OK

27 200 OK

15 200 OK

Proxy Server

SIP Overview 123