Bandwidth again


How much bandwidth is required for a conversation between 2 people using G711

a) 64K + IP Overhead
b) 128K + IP Overhead

I expect you answered B - if so

Why is it you get a two way call down a 64K ISDN channel, do they use compression?

If you answered A, then I don’t understand how. Can you help?

Just as a though, aren’t audio channels generally designated as Kbps, aka Kilobits per second. Internet connections can be measured in KBps or Kbps, the first being Kilobytes per second.

128Kbps = about 16KBps, if memory serves.

I’m purdy sure thats the answer to your question.

AIUI, an 8K sample of a voice takes up 64 Kilo Bytes of bandwidth.

If this is so and you need two of these per two way conversation, I am still at a loss as to how you get 24 two way conversations down a T1 @ 1.544MBps

Help understanding it appreciated.

btw, in a T1, you probably wont get 24… because you need 1 D channel for call control (but true, you can have like 1 D channel for multiple T1’s).

T1 is 1.5Mbps Upload AND 1.5Mbps Download

the g711 itself encodes voice at 64kbps so 1.5*1024 / 64 = 24

And usually a conversation is two-way, but that just means you upload as much as you download… So it will just use both UL and DL.

As for SIP g711, bandwith usage depends on packet size:
5ms: payload: 40Bytes, Overhead: 54Bytes => 150.4 kbps
20ms: payload: 160Bytes, Overhead: 54Bytes => 85.6 kbps
That will always be more than voice T1

Your mistake is thinking ‘two way call down’ when actually it’s one way UP, one way DOWN