Re: [Sip] Draft: draft-holmberg-sip-keep-00.txt

[jh at tutpro.com (Juha Heinanen)]

  Right, but the whole thing here is the UA doesn't know if the proxy
  supports STUN/CRLF, or is legacy.  If the UA does draft-outbound and
  so does the proxy, it can find out; if it does draft-sip-keep, it can
  find out.  If the UA finds out the proxy can't do it, then it will not
  do it.

hadriel,

that would break currently working nat traversal with proxies that do
not support CRLF keepalive, i.e., that are not able to response to
double-CRLF with a single one.  

a tcp connected sip UA is namely still able to keep its nat binding open
by sending double CRLFs, because it does get back tcp level
acknowledgements even when it does not get back SIP keepalive
acknowledgement (single CRLF).

if it uses the keep param and does not get back keep=yes, it would not
send CRLFs and its nat binding would die away.  this is not a good idea
at all.

- juha
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