ISDN PRI - 1.544 Mbps or 1.536 Mbps ?

ISDN PRI - 1.544 Mbps or 1.536 Mbps ?
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Subject Author Date
ISDN PRI - 1.544 Mbps or 1.536 Mbps ? eager 12-20-2007
Posted by eager on December 20, 2007, 12:00 am
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"The Primary Rate Interface consists of 23 B-channels and one 64 kbit/s
D-channel using a T1 line. Thus, a Primary Rate Interface user on a T1 line
can have up to 1.544 Mbit/s service."

If you do the math:
23Bchannels x 64 + 1D channel x64 = 1536 kbps or 1.536Mbit/s.
Even if you divide 1536 : 1024 still doesn't give 1.544 Mbps ....




Pure Networks
Posted by robertwessel2@yahoo.com on December 20, 2007, 1:28 am
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> "The Primary Rate Interface consists of 23 B-channels and one 64 kbit/s
> D-channel using a T1 line. Thus, a Primary Rate Interface user on a T1 line
> can have up to 1.544 Mbit/s service."
>
> If you do the math:
> 23Bchannels x 64 + 1D channel x64 = 1536 kbps or 1.536Mbit/s.
> Even if you divide 1536 : 1024 still doesn't give 1.544 Mbps ....


A T1 line has 8000 frames each second of 192 data bits. When
channelized for voice or ISDN PRI, you have 8 bits for each of the 24
channels in each frame. Each frame also has a framing bit. So
193x8000=1.544mb/s, with 8000bps being overhead. Not unlike a 9600bps
async link really being able to transmit 7680bps of "real" data
(assuming N-8-1 format).

Posted by eager on December 20, 2007, 2:43 am
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>> "The Primary Rate Interface consists of 23 B-channels and one 64 kbit/s
>> D-channel using a T1 line. Thus, a Primary Rate Interface user on a T1
>> line
>> can have up to 1.544 Mbit/s service."
>>
>> If you do the math:
>> 23Bchannels x 64 + 1D channel x64 = 1536 kbps or 1.536Mbit/s.
>> Even if you divide 1536 : 1024 still doesn't give 1.544 Mbps ....
>
>
> A T1 line has 8000 frames each second of 192 data bits. When
> channelized for voice or ISDN PRI, you have 8 bits for each of the 24
> channels in each frame. Each frame also has a framing bit. So
> 193x8000=1.544mb/s, with 8000bps being overhead. Not unlike a 9600bps
> async link really being able to transmit 7680bps of "real" data
> (assuming N-8-1 format).

I do not know where you got that, but even so, PRI _uses_ T1 line, and every
book out there says that PRI consists of 23 B-channels _64kbps_each_ and 1 D
channel also _64kbps.




Posted by =?ISO-8859-2?Q?Hubert_Wi=B6nie on December 20, 2007, 2:54 am
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eager wrote:
>>> "The Primary Rate Interface consists of 23 B-channels and one 64 kbit/s
>>> D-channel using a T1 line. Thus, a Primary Rate Interface user on a T1
>>> line
>>> can have up to 1.544 Mbit/s service."
>>>
>>> If you do the math:
>>> 23Bchannels x 64 + 1D channel x64 = 1536 kbps or 1.536Mbit/s.
>>> Even if you divide 1536 : 1024 still doesn't give 1.544 Mbps ....
>>
>> A T1 line has 8000 frames each second of 192 data bits. When
>> channelized for voice or ISDN PRI, you have 8 bits for each of the 24
>> channels in each frame. Each frame also has a framing bit. So
>> 193x8000=1.544mb/s, with 8000bps being overhead. Not unlike a 9600bps
>> async link really being able to transmit 7680bps of "real" data
>> (assuming N-8-1 format).
>
> I do not know where you got that, but even so, PRI _uses_ T1 line, and every
> book out there says that PRI consists of 23 B-channels _64kbps_each_ and 1 D
> channel also _64kbps.
>
>
>

Hi,

24 * 64kbps + 8kbps management channel used by telco

Hubert

Posted by robertwessel2@yahoo.com on December 20, 2007, 4:28 pm
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> > A T1 line has 8000 frames each second of 192 data bits. When
> > channelized for voice or ISDN PRI, you have 8 bits for each of the 24
> > channels in each frame. Each frame also has a framing bit. So
> > 193x8000=1.544mb/s, with 8000bps being overhead. Not unlike a 9600bps
> > async link really being able to transmit 7680bps of "real" data
> > (assuming N-8-1 format).
>
> I do not know where you got that, but even so, PRI _uses_ T1 line, and every
> book out there says that PRI consists of 23 B-channels _64kbps_each_ and 1 D
> channel also _64kbps.


Right, but what's your question? Just like I said, each T1 frame of
192 data bits (of which there are 8000 each second), carries eight
bits from each of the 24 (23B+1D) 64kbps channels in a PRI (assuming
the T1 is carrying a PRI, of course). And each frame has a 193rd bit
for framing, which is the source of the 8000bps you were missing.

The 193x8000 frame format is inherent in a T1. You can channelize
that many different ways, but with voice-like circuits, the sub
channels are invariably bit sliced across the frame in such a way that
no jitter, burstyness, or lag is introduced. Remember that basic
voice service is 8000 eight bit samples per second, and that you'll
find line/frame formats all over the (telco) network synchronized in
some fashion to the 8000 samples-per-second rate for the precise
reason that you can carry that data rate without jitter, burstyness,
or lag.

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