: Target Diameter server poorly specified

Description of issue: Target Diameter server poorly specified
Submitter name: Glen Zorn
Submitter email address: [email protected]
Date first submitted: 17 Oct 05
Document: sip
Comment type: T
Priority: S
Section: 5.3
Rationale/Explanation of issue: Paragraph 4 says "SIP server 1 receives
a next SIP REGISTER request containing the user credentials (step 9).
Note that SIP server 1 does not need to keep a
state, and even more, there is no guarantee that the SIP request arrives
at the same SIP server 1; there could be a farm of SIP servers 1
operating in redundant configuration.  The Diameter client in SIP server
1 contacts a Diameter server 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)."  The operation in the last sentence of this passage is made
possible by a previous exchange between a possibly different "SIP server
1" and a Diameter server.  Since the "SIP server 1" is not keeping
state, however, the Diameter server must be.  If that is the case, and
"there is no guarantee that the SIP request arrives at the same SIP
server", then the UAR in step 10 must be sent to the _same_ Diameter
server, not "a Diameter server" (unless we assume essentially
instantaneous state synchronization between the configured Diameter
servers).  This implies that there is either a single Diameter server
for the entire "farm of SIP servers 1 operating in redundant
configuration" or that several steps have been omitted from figure 2
(perhaps exchanges w/the Diameter SL?).
Requested change: Completely the specification.