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New Member

VoIP over Frame Relay

I configured the Frame Relay connection using traffic shaping with 1 MB bw in HQ and bandwidth 64kbps with cir=48kbps in branch offices. Without traffic shaping, the connection (5 min in/out) reach 64000 bps but with traffic shaping, it dropped into 58000 bps.

the config as follow:

serial 0

encap frame-relay

fr lmi-ty ansi

fr ip rtp header compression

fr traffic-shaping

serial 0.1 point-to-point

fr int-dlci 110

ip addr

fr class VoIPovFR

map-class frame-relay VoIPovFR

fr cir 64000

fr bc 640

fr mincir 48000

fr fragment 80

fr ip rtp prority 16384 16383 64

According to cisco book,

cir is the bandwidth

mincir is the guaranteed rate.

Tc = bc/cir

10 ms = 640/64000

therefore bc = 640

fragment = 10ms * 64000/8 = 80

I tried to change the cir=48000 & the fragment=60

but then the transfer rate can only be 48000 instead of 64000. As the fragment is reduced from 80 to 60, the voice quality is dropped.

Could any one give me a help.

New Member

Re: VoIP over Frame Relay

I can't see the problem from the information you provided. You should troubleshoot this with Cisco's tech's and let me know what you come up with.

New Member

Re: VoIP over Frame Relay

Mr. bwalchez, after I gave those traffic-shaping commands, it turns the traffic rate from 64kbps to 58kbps. It means I lost 4000 bps.

And where is cisco's tech's ?

New Member

Re: VoIP over Frame Relay

Come back after they help you and let us know what you came up with.

New Member

Re: VoIP over Frame Relay


FRF12 fragmentation is going to put an overhead on the data stream. Each FRF12 fragment is going to require a header! This may account for the loss of the 4K. Try increasing the fragment size - hence reducing the overhaed. But watch out - increasing the fragment size may reduce voice quality.

Another thing you can try is RTP header compression. This can reduce the voip streams down from 32K to 12K.



New Member

Re: VoIP over Frame Relay


There is a recommendation what say that fragment seize with Ip rtp header compresison >= 80 for dont lose quality voice.

Other recomendation is cir = bandwidth in your case

cir = 48000 , but if you use frame relay adaptive shapping then cir= 64000 and mincir =48000 but isnt recommendable

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