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

Figure 15.5 Session mobility with seamless handover

To avoid the gap for media, the media buffer must be filled before the com-
plete handover to the new SIP UA, and this is accomplished with the header
Require: bufferonly, as shown in the INVITEmessage to the new device
where the session will be transferred to.

SIP Network-Based Fixed-Mobile Convergence

SIP-based application-level mobility is also an enabler for the convergence
between mobile and fixed (wireline) networks, as shown in Figure 15.6.

F1 INVITE

ACK

200 OK

AB

Seamless transfer of handover from A to B

Fill the receive buffer before the transfer

F1: INVITE A -> B

INVITE sips:[email protected] SIP/2.0

Via:SIP/2.0/TLS client.pdnl.example.com:5061;branch=z9hG4bK74bf9

Max-Forwards: 70

From: Alice <sips:[email protected]>;tag=1234567

To: Bob <sips:[email protected]>

Call-ID: [email protected]

CSeq: 314159 INVITE

Contact: <sips:[email protected]>

Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY

Require: bufferonly

Content-Type: application/sdp Content-Length:...

C

INVITE

ACK

MEDIA

200 OK

F2 INVITE

ACK

200 OK

REFER

ACCEPTED

SIP Application Level Mobility 261