QUESTION What could cause high jitter on a LAN?

nievz

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I built 5 Asterisk servers for my company. They are connected to an AVAYA PABX. There are two cisco switches and a firewall in between. What could cause high jitter between Asterisk and Avaya on the same physical location? Continuous ping from the Avaya server to Asterisk seems consistently in the low 1ms. But tcpdump from the server and Avaya shows jitter consequently causing packet loss. Other phones in the enterprise and the location using the Avaya pbx don't have issues. Could it be something in the five Asterisk servers causing this? One Asterisk server runs on a Power Edge R320 Dell server.
 

nievz

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Thanks for the response. Our network guys re plied with a bunch of ping screens from the switches. Could icmp and rtp taking different priorities? The pings look fine from the Avaya to Asterisk OR the max of 25ms and avg of 3ms could be the problem. Is 25ms a big contributor on jitter?

On the actual audio, there are times when audio disappears for a couple of seconds suggesting discarded packets. This doesn't happen throughout calls but does happen intermittently during.

Repeat count [5]: 500
Datagram size [100]: 1400
Timeout in seconds [2]:
Extended commands [n]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 500, 1400-byte ICMP Echos to x.x.x.x (I omitted the IP), timeout is 2 seconds:
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!
Success rate is 100 percent (500/500), round-trip min/avg/max = 1/3/25 ms


By the way, I think it's important to note that all these testings were done on a Sunday, while noone's in the office, and only me was using the asterisk server - on an active conference call while doing a tcpdump in the server.
 

nievz

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Here's the result of the tcpdump output in the Asterisk Server. First image is traffic from Asterisk to Avaya, 2nd image is Avaya to Asterisk. I sorted by the Jitter column. That part in the capture showing 59.88ms jitter was the point I loss audio on the call for a couple of seconds, listening to music on hold from the Asterisk server, on an Avaya phone off the Avaya PBX.

Asterisk to Avaya.jpg

Avaya to Asterisk.jpg
 

nievz

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I found out today that the Cisco switch where the servers are connected has QoS turned off globally, therefore, contending with other application servers on the device. This is what I think the problem is. Will report back whatever my Data team decides to do.
 

phonebuff

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The MTR tool is a good way to look at all the hops involved in a connection -

JMS.
 

nievz

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We moved the servers to a 'voice' only switch and the issue is fixed. I think there were just too many application servers running on that other vlan and qos was turned off.

Thanks for introducing me to the MTR tool. I never knew it existed until now.
 

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