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

Figure 6.8 Call control example using REFER

The resulting INVITEmessage (Message 8) would then have the following

form:

INVITE sip:[email protected] SIP/2.0

Via: SIP/2.0/UDP 100.101.102.103:5060

To: <sip:[email protected]>

From: User B <sip:[email protected]>

Call-ID: [email protected]

CSeq: 67 INVITE

Contact: sip:[email protected]

Referred-By: <sip:[email protected]>

Content-Length: ...

The Refer-Toheader in the REFERcontains the URI to whom A is refer-

ring, while the Referred-Byheader identifies A as the referrer, and is passed

to C in the INVITEso that C knows that B has been referred by A in initiating

this session.

User A

1 INVITE

User B User C

5 ACK

7 200 OK

15 200 OK

No More Session

9 NOTIFY

11 200 OK

13 BYE

6 REFER Refer-To: C

Media Session

2 100 Trying

8 INVITE Referred-By: A

14 ACK

10 180 Ringing

12 200 OK

3 180 Ringing

4 200 OK

Media Session

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