SIP Mobility during Handover (Pre-call)

SIP Mobility during Handover (Pre-call)

Registration in SIP for the short term binds a user’s AOR (Address of Record) URI with a Contact URI of a particular device. As a device’s IP address changes, registration allows this information to be automatically updated in the SIP network.

An end device can also move between service providers using multiple layers of registrations, in which a registration is actually executed with a Contact as an AOR with another service provider.

For example, see the UA in the Image above, which has temporarily acquired a new SIP URI with a new service provider. The UA then performs a double registration:

1. The first registration is with the new service provider, which binds the Contact URI of the device with the new service provider’s AOR URI.

2. The second REGISTER request is routed back to the original service provider and provides the new service provider’s AOR as the Contact URI.

When a request comes in to the original service provider’s network, the INVITE is redirected to the new service provider who then routes the call to the user.