[cisco-voip] RTP arriving early generating ICMP unreachable

[Nick Matthews]

This is normal.  Signaling generally takes a different path than
media.  Many times you will get an unreachable because the media beats
the signaling.  Alternatively, some software may not expect the
packets as fast as soon as they get there, and the socket isn't fully
opened.  I would not consider this cause for concern.  It also happens
on the ending of a session intermittently.

-nick

On Mon, May 17, 2010 at 5:49 PM, Dale Shaw
<dale.shaw+cisco-voip at gmail.com> wrote:
> 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
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