[cisco-voip] RTP arriving early generating ICMP unreachable

[Dale Shaw]

Hi,

Disclaimer: The scenario I describe below is not present in a Cisco
deployment -- at the moment I'm just trying to get a feel from this
audience for how normal (or not) this behaviour is in other voice over
IP environments.

I'm investigating a situation at the moment where IP phones are
generating an ICMP unreachable (destination port unreachable) packet
on receipt of the first RTP packet during voice mail access.

To me, it indicates a signalling timing/sequencing problem -- the
phone is indicating it wasn't yet ready to process RTP and effectively
wasn't listening. A very short time later, RTP begins flowing
bi-directionally and everything is OK.

Is there a generic explanation for this behaviour? Is it 'normal'? If
you saw this in your network, would you investigate and tune?

cheers,
Dale