Big Latency on SM-AP 900 link

We have an AP and a SM 6 miles apart with RSSI at 1493 and Jitter at 1-2.

Our problem is a lot of glitch for our TDMoIP application. We set up the link for priority traffic and configured the TOS of our TDMoIP equipment to low latency (bit 3 to 1).

We found out that our Round-trip delay is in the 400 ms and our TDMoIP equipment gives us a 56 ms maximum delay deviation between packets!!! In the booklet it is specified at 40 ms for software scheduling and 25 ms scheduling. We are on the former currently.

We also run the same TDMoIP equipment on BH and the max deviation is around 5ms.

On both sides pinging to the AP/SM gives us 1 ms.

Any clue where to look?

Thank you.


How much and what kind of other traffic is on this link?

Watch the counters for the high-priority queue with your TDM equipment active and inactive, to verify that its traffic is being tagged and placed in the high-priority queue, and that no other traffic is being placed in this queue.

Also, when measuring latency, are you using standard ICMP packets without any priority tagging?

If the high priority channel is saturated with traffic from the TDM system, the delay in the normal queue will be high and you may not get an accurate measure with a standard ICMP ping. Try a program like pingplotter that lets you set the DiffServ header manually so the ping packets end up in the high priority queue.