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| The Diameter Sip Application : General |
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SIP server 2 creates a SIP 401 (Unauthorized) SIP response (step 7)
based on the challenge included in the MAA message, including the
authentication material needed by the SIP User Agent Client (UAC) to
include the appropriate credentials. SIP server 1 forwards the SIP
response to the SIP UAC (step 8).
The SIP server 1 receives the next SIP REGISTER request containing
the user credentials (step 9). Because SIP server 1 does not need to
keep a state (and there is no guarantee that the SIP request arrives
to the same SIP server 1), the Diameter client in SIP server 1
contacts the Diameter server again by sending a Diameter UAR message
(step 10) to determine the SIP server allocated to the user. The
Diameter server sends the SIP or SIPS URI of SIP server 2 in a
Diameter UAA message (step 11).
SIP server 1 forwards the SIP REGISTER request to SIP server 2 (step
12). SIP server 2 validates the credentials by comparing the
response supplied by the SIP UA with the expected response calculated
by the SIP server 2 (based on the H(A1) received from the Diameter
server).
If the credentials are valid, SIP server 2 sends a Diameter
Server-Assignment-Request (SAR) message (step 13) requesting the
Diameter server to confirm the completion of the authentication
procedure and to confirm the SIP or SIPS URI of the SIP server that
is currently serving the user. The Diameter SAR message also serves
the purpose of requesting that the Diameter server send the user
profile to the SIP server. The Diameter server responds with a
Diameter Server-Assignment-Answer (SAA) message (step 14). If the
Result-Code AVP value does not inform SIP Server 2 of an error, the
SAA message can include zero or more SIP-User-Data AVPs containing
the information that SIP server 2 needs in order to provide a service
to the user.
SIP server 2 generates a SIP 200 (OK) response (step 15), which is
forwarded to SIP server 1 and eventually to the SIP UAC (step 16).
