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| The Diameter Sip Application : General |
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Page 6 of 10
6.4. SIP Server Requests Authentication and Authorization
Figure 4 depicts a typical scenario where a stateless SIP proxy
requests authentication information and authorization to a Diameter
server, for the purpose of providing SIP routing services to a SIP
User Agent. The SIP proxy server may be configured as an outbound
SIP proxy, so that all the requests initiated by the SIP UA traverse
the SIP proxy.
According to Figure 4, a SIP User Agent sends a SIP request to its
outbound SIP proxy server. In this case, the message is a SIP INVITE
request (see step 1), but it could be any other SIP request. We
assume that this SIP request does not contain any credentials at this
time. The outbound SIP proxy server needs to authenticate and
authorize the proxy services offered to the user. The Diameter
client in the SIP server sends a Multimedia-Auth-Request (MAR)
message (step 2). The Diameter server generates a nonce and sends a
Multimedia-Auth-Answer (MAA) message (step 3) that includes the nonce
and the rest of the data necessary for the SIP server to challenge
the user, typically with HTTP Digest Authentication indicated in the
MAA message. This data enables the SIP server to create a SIP 407
(Proxy Authentication Required) response (step 4) that contains a
challenge. The SIP UA creates a new INVITE request (step 5) that
contains the credentials. The Diameter client in the SIP server
sends the credentials to the Diameter server in a new Diameter MAR
message (step 6). The Diameter server validates the credentials and
authorize the SIP transaction in a Diameter MAA message (step 7).
The SIP server forwards the SIP INVITE request to its destination
(step 8) as per regular SIP procedures. Eventually, the session
setup is confirmed with a SIP 200 (OK) response (step 9) that is
forwarded to the SIP UA (step 10). The session setup is complete.
+--------+ +--------+
|Diameter| | SIP |
| server | | server |
+--------+ +--------+
| |
| |
1. SIP INVITE |
----------------------------------->|
| 2. MAR |
|<------------------|
| 3. MAA |
|------------------>|
| |
4. SIP 407 (Proxy |
Authentication Required) |
<-----------------------------------|
| |
5. SIP INVITE |
----------------------------------->|
| 6. MAR |
|<------------------|
| 7. MAA |
|------------------>| 8. SIP INVITE
| |---------------->
| | 9. SIP 200 (OK)
10. SIP 200 (OK) |<----------------
<-----------------------------------|
| |
Figure 4: SIP server requests authorization
