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CSCvm62742 - ISR4300 shows abnormal large RTT

Level 1
Level 1

We just encountered this on a new ISR4321 turned up over the weekend running 16.3.7. It seems to be routing calls just fine, but we can't trouble-shoot voice quality issues because the stats are all invalid for both live and completed calls. Here are some more details we've noticed:


  • The RoundTripDelay is always 28000+ ms for all legs of a call where one endpoint is our internal Asterisk server. This is true whether the other endpoint of the call is external (Level3) or internal (CUCM device).
  • The RoundTripDelay is always 0ms for every other call leg. No matter what call we look at, we can't seem to get a "normal" RoundTripDelay.
  • All of the other quality stats we check (e.g. ReceiveDelay, LostPackets, LatePackets, EarlyPackets, gaps, HiWaterPlayoutDelay, and LoWaterPlayoutDelay) are always 0 for all call legs no matter where the endpoints are.
  • For the first few days it was up, all of the byte and packet counts were also 0 for about 98% of the calls. After 3 days of missing bandwidth numbers, they just magically started showing up. It happened between 2:00PM and 2:11PM on Tuesday, and there were no configuration changes, restarts, etc. that we can see that would account for the change.

Something is definitely not right.


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