Voice over GPRS?

Andreas Kostyrka andreas at kostyrka.org
Fri Feb 2 17:50:51 CET 2007

* Robert Michel <openmoko at robertmichel.de> [070202 17:06]:
> Salve!
> Does anybody has experiances/ideas about Voice over GPRS?
> How long is the delay? It could maybe used for asyncron
> voice communication Talk2Talk (instead of pushing a button)

The lag with E+ for GPRS/UMTS is at best in my experience 300ms,
and sometimes goes up into seconds.

Please consider also the fact, that GPRS is a low priority service.
Hence for GPRS you get the following fascinating list of properties:
a) high latency
b) non uniform distribution of latency and bandwidth.
c) at best analog modem speeds, albeit only download wise, upload wise
you are often limited to 1 channel with 9600bps.
d) no QoS support

So the only "sensible" voice application over GPRS might be
push-to-talk, which by the way is offered by some carries over GPRS :)

> By using 1KB/s for audio and some overhead, let

In many cases you won't be able to upload 1KB/s.

> us say 2 KB/s 0.24Euro/MB = 24 Cent for 500 seconds,
> 60 seconds makes then about 3 cents. When both using 
> this 6 cents. Hmm that would be interesting when
> the user makes often make brakes/pause in their talk.

No way you can think of doing sensible full-duplex two way discussions.

As an example, take WLAN. VoIP over WLAN works, because the involved
bandwidths have a completly different ratio: Most sip providers claim
2x100kilobits/s as requirement, and even 11mbps WLAN has an useable
bandwidth of 4-5mbps.


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