Subject: [Sip] PING/PONG

From: "Christian Stredicke" <[email-masked]>
Date: Mon, 8 Nov 2004 22:31:15 +0100

Hello Cullen,
 
I think it is no harm if there is a PING message defined in SIP. I
personally think it is overdue anyway. Implementors can then decide if
they are using it or not. Lets leave that decision to the implementors!
 
But we have to consider who is sending keep-alive traffic. "IMHO" is it
definitely better if the UA does this, because then e.g. usually it is
ok to send CRLF keep alive or STUN.
 
We register with a header that incates (a) that the UA is able to do the
refreshing and (b) what the proposed refresh time is. The UA can do all
these tricky NAT measurement tricks and then propose the refresh time.
Stupid UA may just propose a predefined value, e.g. 20 seconds. The
registrar (or whatever is in the path) then can acknowlege the refresh
role and leave the refreshing to the UA. Otherwise, it will send the
refresh messages. In that case, it will probably use PING, cause it
needs a response to keep the NAT alive in all cases - even if it is a
"503 Not Implemented".
 
Christian
 
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