[VoiceOps] Malformed ACKs/sequential request lines

Alex Balashov abalashov at evaristesys.com
Thu Jul 29 10:15:45 EDT 2010

Found the answer to this.  In retrospect, my first clue should have 
been that the UAC in this situation does not include a branch 
parameter in the Via header it inserts at all, let alone one with a 
branch ID starting with "z9hG4bK", the magic cookie indicating 3261 

RFC 2543, the obsolete first-generation spec, dictates that the 
behaviour I described is actually exactly how the UA should behave in 
this situation, as spelled out in Section 6.29 ("Record-Route"):

     Unless this would cause a loop, any client MUST send any
     subsequent requests for this call leg to the first Request-URI
     in the Route request header field and remove that entry.

In other words, consuming the first URI in the Route set and using it 
as the target for sequential requests is normal in 2543-land.

2543 UAs do not understand the ;lr parameter in the Record-Route 
header, and hence don't do 3261-style loose routing.

Alex Balashov - Principal
Evariste Systems LLC
1170 Peachtree Street
12th Floor, Suite 1200
Atlanta, GA 30309
Tel: +1-678-954-0670
Fax: +1-404-961-1892
Web: http://www.evaristesys.com/

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