Subject: Re: [bmwg] [Sip] Comment on Forking option measurement in draft-poretsky-sip-bench-term-04

From: "Vijay K. Gurbani" <[email-masked]>
Date: Wed, 13 Aug 2008 08:43:04 -0500

Hello Ranjit:

     I am redirecting this to sipping since this work is a liaison
     between sipping and bmwg WGs.

Avasarala Ranjit-A20990 wrote:
> 
> Hi
> 
> In the draft: "draft-poretsky-sip-bench-term-04" section 3.3.15 says 
> that the Forking is an optional process and is not standardized. 

Oops, sorry.  The "process is not standardized" bit is a cut-and-
paste error from the previous section.  It will be taken out
in the next draft revision (which is being worked upon.)

> So why is it that the performance of the proxy is impacted by doing 
> this, 

Clearly forking takes up resources in a proxy that would otherwise
not be spent.  For instance, in simultaneous forking, the proxy
will have to (if TCP was being used) spend a socket per down-
stream destination, using up kernel buffers for the TCP blocks.
Then, for parallel forking, it has to keep each of the N
transactions in memory, match the incoming responses, figure out
the best response.  If it sees a 2xx or 6xx, it will have to
generate CANCELs on N-1 branches, if not it will have to
aggregate Authenticate and WWW-Authenticate headers, etc.  All
of this takes up CPU cycles and host resources that would
otherwise be used in servicing other incoming requests.

> rather this could be a separate parameter for measuring proxy 
> performance.

It *is* a separate parameter for measuring proxy performance (if
this is not clear from reading the document, please do let us
know.)  The intent is that the bmwg document produces a metric for
performance without forking and with forking, all other variables
being constant between the two runs.

Thanks,

- vijay
-- 
Vijay K. Gurbani, Bell Laboratories, Alcatel-Lucent
2701 Lucent Lane, Rm. 9F-546, Lisle, Illinois 60532 (USA)
Email: vkg@{alcatel-lucent.com,bell-labs.com,acm.org}
WWW:   http://www.alcatel-lucent.com/bell-labs
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