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| The Diameter Sip Application : General |
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Page 7 of 10
6.5. Locating the Recipient of the SIP Request
Figure 5 shows the scenario where SIP server 1 may be configured as a
SIP edge proxy server, processing SIP traffic at the edge of a
network. SIP server 1 receives a SIP INVITE request (step 1). SIP
server 1 needs to find the address of SIP server 2, which is serving
the recipient of the SIP request. The Diameter client in SIP server
1 sends a Diameter Location-Info-Request (LIR) message (step 2) to
the Diameter server. The Diameter server responds with a Diameter
Location-Info-Answer (LIA) message (step 3) that contains the SIP or
SIPS URI of SIP server 2. SIP server 1 then forwards the SIP INVITE
to SIP server 2 (step 4). SIP server 2 eventually forwards the SIP
INVITE to the appropriate UAS (step 5).
+--------+ +--------+ +--------+
| SIP | |Diameter| | SIP |
|server 1| | server | |server 2|
+--------+ +--------+ +--------+
| | |
1. SIP INVITE | | |
-------------->| 2. LIR | |
|---------------->| |
| 3. LIA | |
|<----------------| |
| 4. SIP INVITE |
|--------------------------------->|
| | | 5. SIP INVITE
| | |-------------->
| | |
| | |
Figure 5: Locating the SIP server of the recipient
Although the example shows the connection between a SIP INVITE
request and the Diameter LIR message, any SIP request other than
REGISTER (such as SUBSCRIBE, OPTIONS, etc.) would trigger the same
Diameter message. (A SIP REGISTER request will trigger a Diameter
UAR message, as indicated in Figure 2 and Figure 3.)
The scenario described in this section is also applicable in case an
outbound SIP server is not interested in authenticating the user, but
is required to locate a further SIP server to route the outbound SIP
requests. In this case, the outbound SIP server is mapped to SIP
server 1 as shown in Figure 5.
