[Sip] comments on draft-hilt-sip-correction-503-01

[Jonathan Rosenberg <jdrosen at cisco.com>]

Something that needs to be looked into; I think one of the interworking 
specs to ISUP uses the 503 response code as well to map to certain PSTN 
failure cases. Those need to be looked at to make sure they still fit 
with the proposed new definition.

The draft implies that the Retry-After mechanism provides too 
coarse-grained solution for overload control, and finer-grained controls 
are needed. As you know, some of the solutions being investigated for 
overload algorithms still use on/off behavior but just tune the 
Retry-After more algorithmically. So your statements about this need to 
be tempered a bit.

I'm really unsure about whether this is an essential correction or not. 
Its not a functional bug, but a performance bug. So a system based on 
rfc3261 works, but just not that well under load. I'm a bit worried 
that, in an attempt to squeeze this in as an essential correction, we 
may define the wrong thing so as to minimize change. In particular I 
don't like alternative 2 and think we probably need a new response code.

The other big question is, is it worth defining a new response code now, 
and then later on basically updating it with the right overload handling 
behavior, or do it all at once. I think that requires some discussion.

Thanks,
Jonathan R.
--
Jonathan D. Rosenberg, Ph.D.                   499 Thornall St.
Cisco Fellow                                   Edison, NJ 08837
Cisco, Voice Technology Group
jdrosen at cisco.com
http://www.jdrosen.net                         PHONE: (408) 902-3084
http://www.cisco.com


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