How many total bandwidth for ISDN BRI?

coz, I referred to a study note, it says ISDN BRI consists of 192kbps, the D channel is 64K that is divided between 16K used for call-set-up and 48K used for signalling.

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But you can utilize only B channels because D channel is used for signalling and call set up as you said. So, the available bandwidth is 2B = 2x64 = 128 kbps.

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That is somewhat correct. The other 48K is used for framing. The two B channels ARE your available bandwidth, 128K.

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I think this falls under the category of how is the question asked. If the question is how much available bandwidth for user data, then you are looking at 128K. If the question is the total bandwidth of ISDN BRI then the answer would 192K.

Reamer

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But I thought: ISDN BRI is 2B +D
which D is nly 16k.
So, 2*128 + 16 =144
isn't it?

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An ISDN BRI is composed of 2 B channels at 64,000 bps each and 1 D channel at 16,000 bps as you have mentioned. This would provide a total "payload" of 144,000 bits/second. There are also additional bits of overhead required for synchronization and management purposes.

If you were connecting to an S/T connector, realize this interface operates at 192,000 bps. So you have another 48,000bps to carry the framing and management data.

If this was a U interface, there would be an additional 16,000 bps instead of the 48, for the framing and management.

You might want to look at the different types of line coding and/or attributes for a deeper discussion.

HTH

Reamer

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