High jitter/delay with LLQ

[drobel]

Hello!

I have the following output policy on a Serial interface:

class-map match-all VoiceSignaling3

description --= CCM 4.1 uses CS3 =--

match dscp cs3

class-map match-all Voice3

match dscp ef

policy-map L3-to-L2

description --= LAN COS setting based on DSCP =--

class VoiceSignaling3

set cos 3

class Voice3

set cos 5

policy-map WAN512

class VoiceSignaling3

bandwidth 16

class Voice3

priority 96

class class-default

fair-queue

random-detect

If there are a lot of conversations through the interface the delay of the voice traffic can reach even 3000 ms!

During "normal" congestion the LLQ works well.

What can be the source of this problem?

Thanks,

Bela

[tdrais]

How many calls are you tring to run with this configuration. Depending on the codec you use you may be lucky to get 1. 96k is not a lot of bandwidth. Even using high compression you might get 5 calls.

I also cannot see how you can get delays of 3000ms for voice data. It will either transmit it using low latency or drop it. If you are getting delays then your traffic is mis classified

[drobel]

hi!

we use g729 codecs, and only 4 calls are allowed on the leased line.

The problem exests even if there are only one call through this interface.

As you can see, we do the classification with Cos. All switches trust cos from cisco phones, but rewrites the cos from other sources.

Regards,

Bela

[network.king]

Hi

LLQ is fine from your end . How abt the reverse from the provider or from the other end . In case if your reverse traffic peaks and no QOS done , then any traffic coming return would be in default queue .

Pls check the other side and configure LLQ for ur Voice traffic to solve the problem.

Hope this helps

regards

vanesh k

[drobel]

Hi!

The configuration is simmetric. The high Jitter/delay occures only from the previously sent end of the leased line.

Regards,

Bela

[network.king]

Hi

As said by Tim ,Might be your LLQ might be full . Can u give the output of " show policy-map interface s0 " output when u have the problem.

regards

vanesh k

[drobel]

Hi!

I try, but this is a rare problem, and only one branch is affected.

Thanks,

Bela

[rabeder]

hi,

first of all you should check if voice traffic is in the right queue.

you can check this with "sh policy-map int"

and look how high this queue is utilizized or if there are dropped packets when a call is placed.

!

[drobel]

Hi!

The voice call are in the right queue, with no drops at all.

Bela

[drobel]

sh policy-map interface multilink 1 output class Voice3

Multilink1

Service-policy output: WAN384

Class-map: Voice3 (match-all)

90330 packets, 5545648 bytes

30 second offered rate 0 bps, drop rate 0 bps

Match: dscp ef (46)

Queueing

Strict Priority

Output Queue: Conversation 136

Bandwidth 96 (kbps) Burst 2400 (Bytes)

(pkts matched/bytes matched) 90330/2160261

(total drops/bytes drops) 0/0