Re: : Target Diameter server poorly specified

Glen Zorn (gwz) wrote:

> 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.
> 

It is correct to think that there is a single Diameter server (for a 
given user). But this is already spelled out in Section 4, Applicability 
Statement, when the text reads:

    We assume that the database containing the user-related data
    is located outside the SIP node that requires authorization.  Data
    belonging to different users may be stored in different nodes in the
    Home Realm, but we assume that all the data related to a particular
    user is stored in a single node.


In my opinion we shouldn't be indicating in every place "Please reader, 
note that as we indicated in Section 4, a general assumption of this 
document is that the user data for a given user is stored in a single 
place in the network".

So I will change the "contact a Diameter server" with "contact the 
Diameter server", if that improves the readability.

/Miguel
-- 
Miguel A. Garcia           tel:+358-50-4804586
sip:[email protected]
Nokia Research Center      Helsinki, Finland