Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
Community Member

VoIP or Vo ATM


I need to know the different between Real time circuit and a CBR circuit. I want to pass voice, video and data. What is your recommendation. What should a use???


Community Member

Re: VoIP or Vo ATM


I am using two 2621 routers with AIM ATM boards. I have two PVCs one for voice and one for data. I have used both CBR abd VBR-RT on the voice pipe and always use UBR on the data pipe. While CBR provides a constant minimum bandwidth, VBR-RT adjusts acording to your average bandwidth, burst bandwidth and burst cell rate.

I have performed several tests over the link (T1) and have found that using VBR-RT for voice traffic has a lower average delay and fewer lost packets than CBR. This is especially true at high volumes.

Using basic destination routing, I have been able to run 15 concurrent voice calls very high quality. The 16th has marginal quality. All the while, I am flooding the data link with FTP, HTTP and generic UDP traffic. When using source address based routing, the results have been less desirable, but are getting better.

Community Member

Re: VoIP or Vo ATM

Interesting. i have a similar case and I am pondering whether LLQ is needed to prioritize voice over data. I think I don't because vBR-rt has natural priority over ubr already at egress port of router. just want to know your experinece as well.

I'm not using PVC bundle as signalling and media paths are different

Community Member

Re: VoIP or Vo ATM

Using LLQ, my quality dropped quite a bit. Not what I expected at all.

CreatePlease to create content