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New Member

Bandwidth for VoIP H323 signaling channels


I have a VoIp application between two LANs connected by FR WAN.

I use two cisco1751 routers as gateway.

I would use LLQ and other QoS features on cisco gateway to prioritise VoIP streams.

access-list 100 permit udp host host range 16384 32767

access-list 101 permit tcp host host eq 1720



class-map voip-media

match access-group 100



class-map voip-signaling

match access-group 101



policy-map qos-voip

class voip-media

priority 12 (* number of VoIP channels)

class voip-signaling

bandwidth XXX

class class-default



Using g.729a codec and vad.....I would reserve 12kbps for each VoIp media channel (RTP) in the strict priority queue.

How many bandwith must I give to VoIP signaling (RTCP, H225) for each voIp channel ?


Cisco Employee

Re: Bandwidth for VoIP H323 signaling channels

With G.729 codec & Voice payload of 40 bytes, VAD, cRTP, FRF12, you need 6.3kbps bandwidth.

Here is the excellant url which talks about Per Call Bandwidth Consumption for VoIP calls for different media.

Based on that you can do the math for the bandwidth required.

Also here is the url which talks about QoS over Frame-relay for VoIP calls

New Member

Re: Bandwidth for VoIP H323 signaling channels


I have a similar problem, I have voice over IP running over frame relay between a 7500 & a 3600 router. Doing DTS on the 7500 side. Everything works fine but when I try to use rtp compression to save some seems like "even though the command for rtp header-compresion are accepted on the interface configuration" Compression is actually not happening. Monitoring through EMCOM..sindle takes about 32K..i am suspecting that due to DTS on 7500 side..I am missing something....

Is there any good url can suggest me....As far as enabling rtp header compression is concerned it is very straight forward...the requirement is that ditsributed CEF be enabled globally & interface level which I am already doing...


New Member

Re: Bandwidth for VoIP H323 signaling channels

I too have observed similiar problem as above when I was using different series of routers.But when I connected 1751 routers at both sides with rtp compression, the compression is successful.

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