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

Figure 15.3 Terminal mobility: Mid-call scenario using SIP re-INVITE

When moving from one foreign network to another, the mobile host uses the
Layer 2 link indications to acquire a new IP address and to communicate the
new address to the home network. The mobile host will also send a re-INVITE
[11] message to the corresponding host on the Internet so the SIP session can
continue with the new network address.
As mentioned in Table 15.1, personal mobility enables the discovery and
calling of someone on several devices, possibly at the same time. This is shown
in Figure 15.4.

Foreign Network 1

Mobile

Station

1 INVITE Send reINVITE with

Contact header field

and updated SDP

3 ACK

2 200 OK

3 MEDIA

Foreign Network 2

Mobile

Station

Move

Home Network

Home

Registrar

and Proxy

Internet

Corresponding

Station

SIP Application Level Mobility 259