Onsdag,
Well, no. A T1 is twenty-four 64,000 bps channels, plus 8,000 bps
overhead for framing and other signalling. That's where 1,544,000 bps
comes from. Note that bandwidth K are not 1024, but 1000. The actual
payload capacity for user data is 1,536,000 bps.
An E1 (or PCM-30) circuit consists of 32 64 kbps channels, totaling
2,048,000 bits per second. The PCM-30 standard allocates 30 channels
to voice or ISDN data, and two channels (128 Kbps) for framing
overhead and various signalling purposes.
The European standard is much more sensible, because everything
comes out as nice even (in base 2) numbers. The E1 standard is more
sensible because it came out long after the U.S. T1 standard, and
those clever Europeans learned from our mistakes. The U.S. T1
standard is an adaptation of AT&T's voice digitization scheme from
the 1960's, which did not consider data at all in its original
conception.
The 56 kbps per channel you're thinking of comes from old "robbed
bit" line supervision signaling, in which one bit out of every 8-bit
PCM sample could be consumed for the state of the line (on hook or
off hook) and dialing codes. Because data doesn't fly well if one bit
out of eight can't be guaranteed, the earliest data over T1 schemes
used only seven of the eight bits.
Then along came Extended Super Frame (ESF), which is what we now
use (in conjunction with B8ZS, but that's another story), to permit
full 64 kbps per channel, often called "clear channel" for short.
O'reilly has a great book, "T1: A Survival Guide," that covers most
of these details. http://www.oreilly.com/catalog/t1survival/
-mel
At 1:30 AM +0100 11/28/02, Jakob Peterh�nsel wrote:
Hi All.
Well, I guess theres no need to answer this, since I agree with you all.
I can only add to the comments, that those two circuits need to be
wired correctly, or it will not work.
In europe, the specs are a bit different (E1, ... En) since we use a
base of 64k lines, where US lines use 56k base lines (a T1/E1 is
equal to an ISDN30) It's 30 ISDN circuits in one line, that the
hardware controls.
Hope it helps...
On onsdag, nov 27, 2002, at 16:53 Europe/Copenhagen, Richard E. Brown wrote:
Folks:
There's a controversy about the amount of traffic that a T1 circuit
can carry.
Obviously, it can send, or receive, 1.544 Mbps per second.
But can it send *and* receive 1.5 Mbps simultaneously? Or does the total data
carried (send plus receive) max out at 1.5 Mbps?
I've heard people who ought to know give both answers. So I'll open
the question
to the world's experts and ask this list.
There's a T-shirt for the best answer. Extra credit will be given
for a tutorial
(or links to tutorial information) about how this stuff works. Thanks!
Rich Brown [EMAIL PROTECTED]
Dartware, LLC http://www.dartware.com
10 Buck Road, PO Box 130 Telephone: 603-643-2268
Hanover, NH 03755-0130 USA Fax: 603-643-2289
PS Happy American Thanksgiving! We'll be out of the office through
the weekend.
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Jakob Peterh�nsel
"Tell me why, don't we try, not to break our hearts
and make it so hard for our selfs"
P.S.B. 1987
Email: [EMAIL PROTECTED]
AIM: Marook
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