Normal handling of a basic session establishment, up through establishment of the bearer channel and alerting of the destination user or by a previous session redirection after bearer establishment procedure.
Based on a timeout or other indications, UE#2 decides the current session should be redirected to a new destination URI. This new destination URI may be a phone number, an email address, a web page, or anything else that can be expressed as a URI. The Redirect response is sent to P-CSCF#2.
P-CSCF#2 shall revoke any authorization for QoS for the current session.
P-CSCF#2 forwards the Redirect response to S-CSCF#2.
S-CSCF#2 invokes whatever service logic is appropriate for this session redirection. If UE#2 does not subscribe to session redirection service, or did not supply a new destination URI, S-CSCF#2 service logic may supply one or may terminate the session setup attempt with a failure response. The new destination URI may be a phone number, an email address, a web page, or anything else that can be expressed as a URI. If S-CSCF#2 service logic requires that it remain on the path for the redirected request, the service logic generates a private URI, addressed to itself, as the new destination.
S-CSCF#2 sends a SIP Redirect response back to I-CSCF, containing the new destination URI.
I-CSCF sends a Redirect response back to S-CSCF#1, containing the new destination.
S-CSCF#1 service logic may check the number of redirections that have occurred for this session setup attempt, and if excessive, abort the session. If S-CSCF#1 service logic requires that UE#1 not know the new destination URI, the service logic stores the new destination information, generates a private URI addressed to itself pointing to the stored information, and generates a modified Redirect response with the private URI.
S-CSCF#1 sends the Redirect response to P-CSCF#1.
P-CSCF#1 revokes any authorization for QoS for the current session and sends the Redirect response to UE#1.
UE#1 initiates a new INVITE request to the address provided in the Redirect response. The new INVITE request is sent to P-CSCF#1.
P-CSCF#1 forwards the INVITE request to S-CSCF#1.
S-CSCF#1 invokes whatever service logic is appropriate for this new session setup attempt. The service logic may retrieve destination information if saved in step #17.
S-CSCF#1 determines the network operator of the new destination address. If the service logic in step #14 did not provide its private URI as a new destination, the procedure continues with step #26, bypassing steps #24 and #25. If the service logic in step #14 did provide a private URI as a new destination, the INVITE message is sent to I-CSCF#2, the I-CSCF for S-CSCF#2.
I-CSCF forwards the INVITE to S-CSCF#2.
S-CSCF#2 decodes the private URI, determines the network operator of the new destination, and sends the INVITE request to the I-CSCF for that network operator.
The remainder of this session completes as normal.