56 kbps x 64kbps channels in T1

[Jose' Cordeiro]

Hi,

I've read in various places that a T1 is comprised of 24 voice channels.
Each channel is sampled at 8000 Hz with 7 bits giving 56kbps per
channel. The 8-th bit is used for signaling and which ones are used
depends on whether you're using SF or ESF. I've also read hints that
when configured for data transmission, each channel is capable of
64kbps, giving a total throuput of 1.536 Mbps. The problem is I can't
see how to achieve 64kbps when the 8-th bit is still used for signaling.

I would appreciate wise comments on this... Thanks for all!

PS: I've searched for a FAQ about T1 and related topics but couldn't
find one. Does anyone know if such a FAQ exists (and where) ?

Jose' Cordeiro
cord...@uninet.com.br

[David Richards]

In article <334AE1...@uninet.com.br>,

Jose' Cordeiro <cord...@uninet.com.br> wrote:
>I've read in various places that a T1 is comprised of 24 voice channels.
>Each channel is sampled at 8000 Hz with 7 bits giving 56kbps per
>channel. The 8-th bit is used for signaling and which ones are used
>depends on whether you're using SF or ESF. I've also read hints that
>when configured for data transmission, each channel is capable of
>64kbps, giving a total throuput of 1.536 Mbps. The problem is I can't
>see how to achieve 64kbps when the 8-th bit is still used for signaling.

The easy answer is that when the line is configured as a leased line
carrying data directly from one specific site to another, there is no
need for signalling, so no need to rob bits.

Where you do need to accept or originate individual calls at 64K, you'd
use PRI (Primary Rate ISDN), where 23 of the T1 channels are used for 64K
data, and the remaining channel is used as a 'D' channel, carrying call
setup and other messages. If you have multiple PRI's served from the same
switch, you can use NFAS to combine the messages for several PRIs into a
single 64K channel.

--
David Richards Ripco, since Nineteen-Eighty-Three
My opinions are my own, Public Access in Chicago
But they are available for rental Shell/SLIP/PPP/UUCP/ISDN/Leased
d...@ripco.com (773) 665-0065 !Free Usenet/E-Mail!

[David Lesher]

Jose' Cordeiro <cord...@uninet.com.br> writes:

>Hi,

>I've read in various places that a T1 is comprised of 24 voice channels.

Not exactly. See my last post on this...

But with CT1 carried over that DS1 channel....

>Each channel is sampled at 8000 Hz with 7 bits giving 56kbps per
>channel. The 8-th bit is used for signaling and which ones are used
>depends on whether you're using SF or ESF. I've also read hints that
>when configured for data transmission, each channel is capable of
>64kbps, giving a total throuput of 1.536 Mbps. The problem is I can't
>see how to achieve 64kbps when the 8-th bit is still used for signaling.

You don't. You get 64K with "PRI" -- a different application carried
over that 1.544 DS1 data channel. PRI gives you 23 of those 64K's,
and one separate signal channel.

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

[Bill Horne]

You may configure a T1 service to deliver 24 64 Kbps channels, by using
B8ZS line coding and appropriate plugs in the channel banks at each end.
This "clear channel" configuration does NOT provide signalling.

This setup assumes 24 separate users for the channels. It's much more
common for an ISP or other data user to buy a DS1 "pipe", and use it at
full speed to carry packet switched traffic.

Bill

cord...@uninet.com.br wrote:
: Hi,

: I've read in various places that a T1 is comprised of 24 voice channels.

: Each channel is sampled at 8000 Hz with 7 bits giving 56kbps per

: channel. The 8-th bit is used for signaling and which ones are used
: depends on whether you're using SF or ESF. I've also read hints that
: when configured for data transmission, each channel is capable of
: 64kbps, giving a total throuput of 1.536 Mbps. The problem is I can't
: see how to achieve 64kbps when the 8-th bit is still used for signaling.

: I would appreciate wise comments on this... Thanks for all!

: PS: I've searched for a FAQ about T1 and related topics but couldn't
: find one. Does anyone know if such a FAQ exists (and where) ?

: Jose' Cordeiro
: cord...@uninet.com.br

--

Bill Horne
bho...@lynx.neu.edu