You can strip 100rel as long as it's Supported. However, not so good things 
happen if you strip it from Required. :-) 


-- Alex

--
Sent from my Samsung mobile, and thus lacking in the refinement one might 
expect from a proper keyboard. 

Alex Balashov - Principal
Evariste Systems LLC
235 E Ponce de Leon Ave
Suite 106
Decatur, GA 30030
Tel: +1-678-954-0670
Web: http://www.evaristesys.com/Andrew Mortensen <admor...@isc.upenn.edu> 
wrote:Can I safely strip 100rel support from INVITEs sent by callers registered 
to my proxy?

We're using proxy-generated 302 redirects for call forwarding in our 
deployment. In general this works better for us than appending branches, as we 
rapidly ran into branch limits when dealing with large multiple appearance 
lines.

However, we've run into a case where the caller, a Polycom 550, seems to get 
confused when a parallel forked call is redirected, 100rel is in use and the 
redirection target is also a multiple appearance line.

The caller is correctly responding with PRACKs to all 180s, before and after 
the redirection. However, hanging up the call on the caller after the 
redirection, but before any remote party has answered, does *not* cause the 
caller to send a CANCEL to tear down the call. In fact, the caller doesn't send 
anything at all. The remote parties continue to ring until the ring timer 
expires, and the proxy sends CANCELs to all callee endpoints.

That's clearly a Polycom bug, and we'll need to work with them to get it 
resolved.

In the meantime, I'm looking for workarounds. One quick, crude option is to 
strip 100rel from the Supported header in the caller's INVITE. I've tested 
this, and it does solve the problem, but I'm concerned about side effects. I'm 
aware of the value 100rel has for calls to the PSTN, but in this case the calls 
never leave the local network. Are there situations where 100rel is critical 
for a parallel forked call? 

andrew
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