cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
338
Views
0
Helpful
3
Replies

192kbps over BRI?

xianglingzj
Level 1
Level 1

"BRI also provides for framing control and other overhead, bringing its total bit rate to 192 kbps. "

-- Cisco Internetworking Technology Handbook

http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/isdn.htm

I'm confused by the statement above. Isn't BRI have a total capability of 2B+D = 2*64+16 = 144kbps ? Can framing control increase bandwidth? Anybody can clarify this? Thanks in advance.

3 Replies 3

rgodden
Level 3
Level 3

You have to look at in timeslots as it running over a time division network.information in each time slot is 8 bits and sampled 8000 times per second to give the 64kbps.

The b channel will fill the whole timeslot, the d timeslot will have 16kbs of info and the rest is filler.

When the data is sent over layer 1 the frames consists of bits from the 2 d channels, 1 b channel framing bit dc balancing bit d-echo channel bit and and seven other types of bit.

A good book is isdn explained by john m griffiths.

a slight correction is required.

On isdn 2, the layer 1 frames are 48 bits long and are samples 4000 times a second to give the 192kbps.

each frame consists bits from 2b and d channels plus a few others.

You can think of the total bandwidth of ISDN BRI as 3 X 64 = 192 Kbps = 2 X B (2 X 64K) + 1 X D (16) + 48 Kbps (framin, synchronization etc. overhead.). The last part of 48 K is out of use.

Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: