Re: Help needed on VoIP project

[Jiri Kuthan <>]

At 01:10 AM 3/2/2004, Andrew Rutherford wrote:
>At 7:54 AM -0500 1/3/04, Jon Zeeff wrote:
>
>>This is somewhat off topic, but to me, the most important thing to test is 
>>resistance to packet loss and jitter.
>
>Yes, the difference in phones can be significant. We were called in to look 
>at a 3com quality issue over an 802.11b link. It turned out the switch 
>driving the wireless link was at fault (unable to cope with more than 100 
>packets with prioritization set per second - turned prioritization support 
>off and the problem went away), with on the order of 12% packet loss.
>
>When we went to site we didn't know that, and took some Cisco 7940 phones 
>with us because of their better statistic reporting. With two people on 
>either end of the link, with a 3com handset (sorry, didn't record the model) 
>in one ear and a Cisco 7940 handset in the other, we got scratchy but 
>understandable quality voice on the Cisco 7940, but completely 
>incomprehensible on the 3com. Sniffing showed the incoming packet flows were 
>pretty much identical in terms of loss and jitter between the two audio 
>streams, so the quality you have to test is the audio coming out of the 
>handset, not the packets going in.

That corresponds to our rough observations: 79x0 must have a nice packet loss 
concealm algorithm
built in.

-jiri