Subject: RE: [Sip] Keepalive on media protocols while mute / on-hold etc, & SIP INVITE

From: "Christian Jansson" <[email-masked]>
Date: Fri, 2 Apr 2004 14:13:24 +0200

comments inline

> A "NAT-friendly" RTP implementation could periodically send 
> no-ops or silence (depending on the payload types already 
> negotiated) if it is not sending anything else - or is this 
> outlawed by being set to "recvonly" or "inactive"?

Do we really have to use special no-ops or silence RTP packets? Why not
just send zero length payload UDP packets, then we do not have to invent
something new. An RTP stack should already today handle this, otherwise
that would be a simple attack method. As long as the UDP packets pass
through the NATs and firewalls it does not matter whether the receiver
is implemented to understand the zero length packet or not.

/ Christian Jansson, Hotsip

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