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Community Member


I'm currently using g729r8 on a cisco mc3810 w/ a frame-relay 128K cir.. with a nortel key system.. no ip phones.. so i guess. you could say VoIP over FR .. my question is.. we have bad delay, static, and echo problems.. we are upgrading to t1's.. but do you suggest to keep the same codec?.. i've heard g711 is good.. any suggestions

Community Member

Re: codecs?

G711 probably won't help, it would require too much bandwidth, it sounds like a QoS problem, do you have any QoS configured ?

check out this link.

Community Member

Re: codecs?

You have told nothing about QoS in your network. While echo is NOT caused by a VoIP network, the existing echo can indeed become worse, more annoyable, because of delay. I don't think your problem is the codec, but it seems to me that there's no queue, fragmentation, interleaving and prioritization set in your network.

Community Member

Re: codecs?

Voice has priority... the precedence is 5

Cisco Employee

Re: codecs?

Giving precedence won't solve your problems on a low bandwidth frame link. My suggestion would be to implement low latency queuing with frame relay traffic shaping and frame relay fragmentation. check out this link:

Cisco Employee

Re: codecs?

Can you please give an example of your map-class for the frame and are you doing any QOS other than setting the IP precedence to 5. I would suggest using LLQ to priortize the voice traffic over the data. Are you doing any fragmentation. Go ahead and post the configs for you serial interface and the map-class and we will try to help you. Assuming you are doing no header compression g.729 is 24k a call and g.711 is 80k a call. I don't think g.711 will help.

Thank you,


Community Member

Re: codecs?

It doesn't seem you need Low Latency Queuing (LLQ) since you only need to priviledge voice transmission (you are not worried about the different classes of data traffic, are?). So I'd suggest:

- LFI - Link Fragmentation and Interleaving

- RTP prioritization (priority queue)

- RTP header compression (this is not essential, but would save you kbps)

- WFQ - Weighted Fair Queue for everything that is NOT RTP

In do this in my network, and the performance is pretty good. Here's an example configuration of my routers (only the essential commands are listed):

interface Serial0/0

bandwidth 384

encapsulation frame-relay

frame-relay lmi-type ansi

frame-relay traffic-shaping


interface Serial0/0.1 point-to-point

bandwidth 384

frame-relay class SUBSCRIBER

frame-relay interface-dlci 101 CISCO

frame-relay ip rtp header-compression

map-class frame-relay SUBSCRIBER

no frame-relay adaptive-shaping

frame-relay cir 384000

frame-relay bc 3840

frame-relay be 0

frame-relay fair-queue

frame-relay fragment 480

frame-relay ip rtp priority 16384 16383 256

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