[Asterisk-Users] VoIP Provider problems

[Rich Adamson]

> > The apparent packet loss you are seeing may be just fine tuning
> > of the routers in question.
> 
> This is the conclusion I came to as well; however, with the way 
> PingPlotter works the router is not sending ICMP unreachables but rather 
> ICMP TTL expired responses.  In any case, the routers in question may 
> either be:
> 
> 1) ...intentionally discarding the received UDP "ping" packets (these 
> are not ICMP pings, but rather UDP packets with TTL down to zero when 
> they get to the router), because the router has better things to do.
> 
> 2) ...throttling the ICMP TTL expired responses to a certain rate per 
> period of time, as you suggest.  This would appear as packet loss.
> 
> 3) ...actually congested, with the received UDP "pings" (and other types 
> of packets) getting discarded on the input side at the rate shown in the 
> data.
> 
> I wish there was a way to measure 3) without being affected by 1) and 2).

The deceptive part of doing the above is that once you see
congestion (lack of an icmp response), you still have absolutely
no idea what device was at fault.

In other words, as the ttl value is increased and additional icmps
are sent, you might see what you believe is congestion, but you still
don't have any clue as to whether hop #2, #5, or #10 actually was
involved with that congestion.