[Asterisk-Users] Calculating required bandwidth

[Andrew Kohlsmith]

On December 16, 2004 02:00 pm, Damon Estep wrote:
> A TDM channel (POTS/PRI) consists of 64k of real-time data, VoIP with no
> compression (g.711) consists of 64k plus IP protocol overhead for a
> total bandwidth or 80 to 90k required per uncompressed channel. So a IP
> T1 carrying VoIP without compression has lower capacity that a Voice T1.
> A t1 for voice typically carries 23 b channels and 1 d channel, so 23
> conversations not 24.

Voice channelized T1 (also known as CAS T1 in Canada) is 24 channels.

PRI is (simplified explanation) out of band signalling on a DS1, but uses 1 
channel for signalling (it's out of band now, so it has to go somewhere) so 
you get 23 channels of voice and 1 for the signalling.

Data T1 carrying VOIP traffic will be able to handle about 21 channels of 
G.711 RTP audio due to RTP and IP overhead, and does not include SIP/H.323 
signalling, although the signalling overhead should be able to fit in the 
remainder of the T1.

> Uncompressed the answer is probably closer to 15 to 18 RTP streams
> across a dedicate T1 IP link.

That few?  I would be surprised if the signalling overhead is that enormous.  
With 21 channels of RTP G.711 audio I have 64kbps of bandwidth available, at 
least according to my calculations.

-A.