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Mobility during a Call (re-Invite)

For the period of a session, a mobile device may also change its IP address as it changes between one wireless networks to another. Basic SIP supports this situation, as a re-INVITE in a dialog can be used to update the Contact URI and modify the media information in the SDP.

The call flow is explained below;

1. Bowditch detects a new wireless network,

2. Using a DHCP to acquire a new IP address, and

3. Then performs a re-INVITE to allow the signaling and media flow to the new IP address.

If the UA can receive media from both networks, the interruption is unimportant. If this is not the case, a few media packets may be lost, resulting in a minor disturbance to the call.

The re-INVITE carries Bowditch’s new IP address in the Via and Contact header fields and SDP media information

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