[plug] Mailing list archive

[Richard Sharpe]

At 05:26 PM 9/6/00 +0800, Matt Kemner wrote:
>On Wed, 6 Sep 2000, Bret Busby wrote:
>
>> perhaps you could explain whether T1 lines are used in Australia?

Hmmm, there seems to be a number of errors here. Hopefully, I will not add
to them.

>Australia uses E1 lines, which are 2Mb as opposed to 1.5Mb which also

That should be 2.048Mbps as opposed to 1.544Mbps. T1 consistes of a frame
containing 24 channels (8 bits) and a framing bit for a total of 193 bits
in 125 microSeconds, or 1.544Mbps. A superframe, containing 12 or 24
frames, makes the framing bits more useful as they can be used for
signalling as well as framing.  In T1, one data channel is often used for
signalling as well (sometimes divided into 4 D channels of 16kbps each).

E1, OTOH, consists of 32 channels (8 bits) in 125 microSeconds, or
2.048Mbps. Users are only given 30 channels, and the other two are used for
framing and signalling.

>means when you buy a Prime Rate ISDN (PRI) for a digital modem box, they

Primary Rate Interface. They are ISDN, and they are channelized. That is,
you get no choice. With E1 they are 30 channels each of 64kbps, and if what
you wanted was 2.048Mbps, you have to use multilink PPP and you don't quite
get it anyway, as two channels are not available.

If you buy Frame Relay, OTOH, you get X.21, and that can go up to almost
2.048Mbps as one data stream, over which you use PVCs (or SVCs).

There is mucho info on this in books like: Understanding SONET/SDH and ATM
by Stamatios V Kartalopoulos.

The Ex and Tx signalling rates and framing are examples of SDH, the
Synchronous Digital Hierarchy.

>contain 30 lines, not 23 like in the U.S.
>(which is why a Cisco AS5200, for example, in the U.S. holds 46 modems,
> where the Australian version holds 60)

[Deletia]

> - Matt


Regards
-------
Richard Sharpe, sharpe at ns.aus.com
Samba (Team member, www.samba.org), Ethereal (Team member, www.zing.org)
Contributing author, SAMS Teach Yourself Samba in 24 Hours
Author, Special Edition, Using Samba