[Speex-dev] jitter buffer

[Jamey Hicks]

Danny Chan wrote:

>Hi Farhan,
>
>It is interesting that GPRS is 9.6 kps, as per GPRS standard it should
>be 115kps ? if it is 9.6kps is true then I would use speex codec on GPRS
>for my project, since in some country they charge GPRS on flat rate
>rather than expensive airtime.
>
>  
>
GPRS can be configured in multiples of 9.6Kbps at the discretion of the 
network provider.  For example, T-Mobile in the US provides 4 timeslots 
downstream and 1 slot upstream.  So voice on this would have to fit into 
9.6Kbps to fit in the upstream channel. 

Another big problem with GPRS wrtp VOIP is that its latency is really 
high.  I measured average 1 second for a 1 way trip across the GPRS 
network here.  I believe this is caused by the block error correction 
scheme that they use on the data channel -- quite a few bits are encoded 
together leading to high latency.  The phone companies just didn't 
understand that there are higher layer protocols for handling data 
integrity.

Jamey