Subject: RE: [Sip] Outbound-04 and "max-flow" in 200 OK for REGISTER

From: "Christer Holmberg \(JO/LMF\)" <[email-masked]>
Date: Thu, 29 Jun 2006 09:18:33 +0200

Hi,

I agree with Erkki.

Regards,

Christer

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] 
Sent: 29. kesäkuuta 2006 10:04
To: [email-masked]; Christer Holmberg (JO/LMF)
Cc: [email-masked]; [email-masked]; [email-masked]
Subject: [Sip] Outbound-04 and "max-flow" in 200 OK for REGISTER

Hi,

>> FIFTH, related to the second, third and fourth issues, we discussed 
>> that that the network should be able to provide a "max-flow" number 
>> to the client.
>
>the maximum number of flows is the number of outbound-proxy-set URIs.  
>If you want to come up with another piece of configuration data (by the 
>very broad definition of configuration we are using) that is a set of 
>candidate URIs for the outbound-proxy-set which are chosen at random up 
>to some maximum to form the outbound-proxy-set,

>you are free to do so.

I would like to point out two emails in the thread where this "max-flow" issue was discussed:

http://www1.ietf.org/mail-archive/web/sip/current/msg14745.html
http://www1.ietf.org/mail-archive/web/sip/current/msg14753.html

In that thread a solution was outlined as follows:

"Network must provide max-flows in Register response.
 Client must not exceed max-flows when establishing flows.
 Client should attempt to equal max-flows if terminal capabilities allows."

To me this sounds a good idea due to the following facts:

- Instead of explicit configuration the UA might find the
  proxies supporting outbound e.g. from DNS

- The number of proxies configured in DNS does not necessarily
  equal to the number of flows the UA should set up. For instance
  the service provider might have there many proxies to do load
  balancing but targets to have reliability on other means than
  the UAs maintaining multiple flows.

Thus I was also expecting the proposed a solution to appear in
outbound-04 (or later version). In sip-outbound-discovery-02 there is text like this:

   Whether the UA actually sets up one single flow or two redundant
   flows, is determined in the following ways:

   o  When the network responds to the primary REGISTER with 200 OK, the
      response may contain an indication telling the maximum number of
      flows the network expects the UA to use.  The UA SHOULD create two
      flows if the indicated value is at least two or if the network
      does not give the indication at all.  [[OPEN: the details of this
      indication are still to be defined but are not in scope of this
      spec]]

I have not seen any serious comments given why this could not be specified like proposed and would thus vote for adding it to outbound -05.

Regards,

Erkki
____________________________________

  Erkki Koivusalo
  Nokia Mobile Software
  tel:+358 40 7571197
  mailto:[email-masked]
____________________________________ 

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