Thread: Dr. Ari Jaaksi on Maemo 5
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pixelseventy2 is offline pixelseventy2
2008-09-20 , 15:00
Posts: 357 | Thanked: 115 times | Joined on Sep 2007 @ Sunny England :)
#276
Originally Posted by Jerome View Post
I think that the people who think that voip over cellular data is an option forget something important:
-cellular bandwidth is limited
The problem tends to be one of latency, rather than bandwidth. I've used SIP with the G729 and GSM codecs quite happily (as an experiment) over GPRS. But the same wasn't practical over 3G (UMTS) because of the latency. However, HSPA has much lower latency than UMTS, so should be more feasible.

Originally Posted by Jerome View Post
sip uses more bandwidth than voice
SIP is a protocol, not a voice technology. And saying that it uses more bandwidth than voice is a misnomer. Voice on POTS is transmited at 64k, either u-law or a-law, and this is _usually_ the default codec used for SIP-based VOIP providers.

Voice over GSM uses, unsurprisingly, the GSM codec, which was created for transmitting voice over the limited bandwidth. So comparing u-law over 3G to GSM isn't a fair comparison.

Considering the minor difference in compression, the G729 codec offers a surprising quality boost over GSM. Plus, it is supported by the N8x0 SIP client and GSM isn't.
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