DS3 Breakdown for bandwidth command

ceyko1 20 years ago

Greetings, An friend and I are trying to determine how Cisco arrives at 44736 for a DS3. Furthermore we want to create a table for other speeds within a DS3's capacity.

There is a minor disagreement on how to calculate the bandwidth. I vote

1544 * # of channels. He votes for "10" x 1024 for a 10 meg circuit.

However, I get the feeling we are both not right. Cisco shows examples of bandwith 44736

for a full ds3. However, I don't know how they come up with that...

1544 x 28 = 43232
1544 x 29 = 44776 (CLOSE, but no cigar)

1024 x anything = not close

My understanding is it should be 1544 x 28. I'm told that the extra

1504 for the 44736 is due to framing. I can not find any good information for the framing overhead that equals 1504. I've found some that'll equal 1536. (64 x 24) We use C-bit framing....

Any input on exactly how to calculate these channels and so forth will be appreciated.

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Doug McIntyre 20 years ago

You'll really want to readup on how the information is mashed and splitup inside a DS3. There's several tech articles for the googling..

You're missing all the framing and sub-code information bits stuffed into the mix. 1544*28 is closer, but missing the framing and c-bits.

4 DS1s form a DS2. 7 DS2s form a DS3.

A DS2 M-Subframe takes 12-bits from each of its 4 DS1s, and starts with a frame bit, and seperates each of the 48-bit info blocks with c-bits or frame bits.

A DS2 Multiframe takes its component DS2 M-Subframes and seperates them out with M framing bits, and then you get M23 Stuff blocks from interleaving each of your DS2s.

Finally, you get a DS3 M-Subframe from each of the DS2 M-Subframes, and you stuff those together into the full DS3 Frame with additional framing and c-bits.

Now-a-days, they don't need the clock recovery bits, so the c-bit framing uses them for sub-band signal codes downstream.

Whew.

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ceyko1 20 years ago

Doug, Thank you for the response. It is appreciated.

Take care, ceyko

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