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I skimmed the report, but one point caught my attention: VoIP services, which can be used with a data rate as low as 100 kilobits per second (kbps) Isn't this
by Shenglong 15y ago
I skimmed the report, but one point caught my attention:
VoIP services, which can be used with a data rate as low as 100 kilobits per second (kbps)
Isn't this quoted number a little high? If I remember correctly, Ventrilo on a good codec was only 4kb/person/second.
- ww520 15y agoThat's true. Modem was at 56kps max mostly on regular phone line. Voice requires much less than 56kps. Voice on old line sounds crisp and clear. Are they planning for mulit-VoIP sessions or video VoIP?
- adestefan 15y agoA POTS line is analog so even though you can run a 56kbps modem, the actual data is transmitted via an analog signal. G.711 is the raw digital voice benchmark and encodes at a constant 64kbps PCM a-law or u-law ecoding (8 kHz sampling frequency x 8 bits per sample). This is the reason why digital carrier lines are always multiples of 64. A DS-0 is one 64kbps channel, a DS-1 is 1.54 Mbps (24 * 64), an E1 is 2.048 Mbps (32 * 64), etc.
- wmf 15y agoFor low latency, the IP/UDP/RTP headers are much bigger than the audio in many cases. So a "64 kbps" codec is actually ~96 kbps (IIRC) and the overhead gets worse at lower bitrates.
- adestefan 15y agoG.711 (no compression) is 64kb/sec. G.729* is 8kb/sec. The real problem with VoIP is you need low latency. I believe 80ms is where you can start getting into the area where people notice the delay. * EDIT: I forgot to mention that G.729 is encumbered by a number of patents.