Subject: Re: [Sip] Progress draft-holmberg-sip-keep

From: Hadriel Kaplan <[email-masked]>
Date: Fri, 27 Jun 2008 12:34:50 -0400

> >>    A typical example is emergency calls.
> >
> > I don't get this one. You don't need to send keep-alive packets to make
> > an outbound call (be it urgent or not).

You need to send keepalives to keep the signaling path open, so that the other side can send back requests during the duration of the call. (in fact, the PSAP could send an UPDATE every 30 seconds to force that in case there is no keepalive)

> Also frequent UDP keep-alives are a total non-starter for mobile handsets, due
> to excessive battery consumption. Yet mobile handsets are probably the most
> common way to do emergency calls nowadays, for obvious availability reasons.

Christer's talking about unregistered devices making an emergency call, and keeping that call alive and usable. (since at least in the US, we have requirements to allow mobile sets and landlines to be able to make emergency calls regardless of paid service subscription)
I assume battery usage for SIP requests during an emergency call is not an issue, since it's already sending RTP the whole time, no?

-hadriel
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