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T1 Carriers.

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lord loh.

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We are being taught T1 Carriers in our class (reference : Advanced Electronic Communication Systems - Wayne Tomasi)...

The T1 system signal DS1 is supposed to be made of 24 DS0 signals. Each channel is 8 bit wide and is sampled at 8KHz. (8x8000=64 Kbps). This is the D1 channel.

24channels of 64Kbps (24x64Kbps=1536Kbps or 1.536Mbps)

Each frame consists of 24 channels ech of 8 bits.(8x24=192bits)

Then a framing bit is added to each frame (193 bits now). And 8000 frames are sent per second. This is the DS1 signal.

(193x8000=1544000 bps or 1.544Mbps).

So the total speed is 1.544 Mbps.

Now the book mentions that this 8Kbps framing bits that were used for inter office signalling was considered excess and some modifications were made. And then came the super frame format that consisted of A highway and B highway of 6 frames each. So the super frame consisting of 12 frames had a signaling bit in every 6th frame. So the signaling rate is now 8Kbps/6=1.333Kbps.

Now I am not clear what happens to the extra framing bit framing bit that was added? If that bit is not deleted, the total overhead signalling is now 9.333 Kbps.
The illustrations in the book show that the framing bits remain and even the calculations of the number of bits in a super frame and the T1 line rate of 1.544 Mbps remains.

Can any one please explain me what exactly is happening ?

Thanks a lot.
 
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