Re: [sipcore] RFC4244bis

 I think "not put in response" is probably the 
best option and if we want to keep the semantics 
of option tag in supported for hist-info, then we 
should probably change the MUST to SHOULD 
with "unless" statement mentioning the message 
size. 

 Regards
  Shida

On Sep 3, 2010, at 5:17 PM, Elwell, John wrote:

> Yes, that is certainly another option.
> 
> John 
> 
>> -----Original Message-----
>> From: Hadriel Kaplan [mailto:HKaplan@acmepacket.com] 
>> Sent: 03 September 2010 08:29
>> To: Elwell, John
>> Cc: sipcore@ietf.org
>> Subject: Re: [sipcore] RFC4244bis - size of responses
>> 
>> 
>> On Sep 3, 2010, at 3:13 AM, Elwell, John wrote:
>> 
>>> The History-Info header field can get quite lengthy where a 
>> request has undergone a great deal of branching and 
>> retargeting. The entire accumulated set of hi-entries is 
>> reflected in the response. Thus a response can be 
>> considerably larger than a request from an H-I point of view, 
>> although other material in the request and not in the 
>> response might negate this. It does mean, however, that H-I 
>> can take some responsibility for a response being 
>> considerably larger overall than a request in some 
>> circumstances, particularly on the earlier hops (not on the 
>> final hop, of course). If an earlier hop has a low MTU size, 
>> this could cause a problem with UDP. Existing RFC 3261 
>> guidance on maximum request sizes to be sent over UDP (200 
>> bytes below maximum MTU size) might not be sufficient to cover this.
>>> 
>>> At present the inclusion of H-I in a response is subject to 
>> the option tag being placed by the UAC in the Supported 
>> header field. However, the need for this is being challenged 
>> in another thread, so it could be that H-I will be 
>> unconditionally reflected in the response. In any case, a UAC 
>> will not know about MTU sizes on downstream links, so this 
>> the option tag is not a solution to the response size problem.
>>> 
>>> What are the possible solutions?
>>> - Override the RFC 3261 guidance on maximum request size 
>> for sending over UDP by specifying a larger contingency, 
>> sufficient to accommodate most H-I response scenarios.
>>> - Specify that TCP is to be used when H-I is used.
>>> - Specify that H-I should be dropped from a response to be 
>> sent over UDP if it would cause the response to exceed the 
>> maximum MTU size.
>> You missed one:
>> - Not put H-I in any responses
>> 
>> 
>> 
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