Voice Degradation using FXO Cards in Cisco 2610

[mnlatif]

Hi,

We are facing Voice Degradation wil using FXO cards in 2610 Routers.

The link is through Frame-Relay Voice PVC (32K CIR) over 256K Access Pipe. The same serial interface carries another PVC for Data (96K CIR).

The Voice PVC doesn't carry any other traffic except voice. We have "not" implemented Frame-Relay Traffic-Shapping.

The Voice quality is really bad in ONE Direction (i.e from location1 to location2). However Voice from location 2 - location 1 is without any problems. And at the same time i do see some FECN (at location 2) and BECN (at location 1) indicating congestion.

1. Has any one experienced Bad Voice quality in only one direction ?

2. Would it help to implement Traffic-Shapping ?

3. What percentage of FECN and BECN is normal ?

4. Is 32K BW enough for 4 FXO ports (4 Voice calls) simulteneously ?

[thusain]

To be honest im not surprised you are seeing voice quality problems. And one way is also very common because it depends on bottlenecks. Answers to your questions are :

1. Yes.. it is common.

2. It would help greatly, you should configure it not to burst (mincir = cir = 32 and be = 0).

3. ?

4. depending on what codec, VAD, crTP you use. Typicall 32K will not be enough for 4 calls, even with g729 and VAD on. If you turn on cRTP, then you can shave it down to 12K, but thats still 36K per call.

[doug.lockwood]

"1. Has any one experienced Bad Voice quality in only one direction ? "

Very common.

"2. Would it help to implement Traffic-Shapping ?"

Yes. However, enough bandwith for the number of calls supported needs to be available in order for traffic shaping to be effective.

"3. What percentage of FECN and BECN is normal ?"

FECN and BECN are indications that traffic is being dropped by the FR link.

if 1% of the traffic is dropped, the voice quality is severily lowered on that link.

"4. Is 32K BW enough for 4 FXO ports (4 Voice calls) simulteneously ?"

It depends on the codec and to a lesser extent whether its VOIP or VOFR.

A G.729 VOIP data call requires about 20K of bandwidth over a frame link.

The same call over G.711 VOIP codec requires about 80K per call.

Any routing traffic or CDP on this link will also add traffic.

Other Comments:

Frame relay fragmentation on the data VC will prevent the voice packets from being delayed due to 1500 byte data packets.

Examine VAD. Enabling it can cut bandwidth up to 40%, but the operation of VAD can reduce voice quality.

In a congested Frame Relay network, packet delay can be as important as dropped traffic in lowering voice quality. Check the ping times across the voice network.

HTH

Doug