ADSL and modem notion

Not to discredit this information, but is there a reference I can read about the bins? Thanks, just want to understand this better because I've never seen this info before...all references I've read have said the CPE doesn't modulate/demodulate.

Edit: Nevermind, I looked it up. Interesting stuff on DSL, is there a similar concept to ISDN, or is calling it an ISDN modem erroneous?

ISDN is a different kettle of bytes completely.

ISDN is an all digital comms system comes in to basic variants - Primary Rate & Basic rate.

Primary rate within europe provides 2mb/s connection and can uses a number of different protocols for signalling, namely Q.931, DPNSS & DASS. DPNSS & DASS are older UK specific standard, whereas Q.931 is a etsi (european telecoms standards institute) offering.

With primary rate the signal transmitted digitally as a single frame split into 32 channels, each of 64 kb/s. (Think PCM - voice signal is samples 4000/s at a rate of 8 bits = 64 Kb/s)

Channel 0 is used for frame alignment

Channel 16 (d-channel) is used to carry the Q.931 signalling, but any channel can be specified to carry this (BT use channel 1 I believe, but could be wrong)

The remaining channels (b-channels) can carry traffic - traditionally voice, but data is not a problem.

Basic rate consists of 3 channels 2B + D, or 2 x 64 kb/s+ 16kb/s. The D channel contains the signalling, while the B channels can be used for voice or data.

For Basic rate access the customer requires a Terminal Adapter, this purely provide a termination point for the cabling. However more many modern TA's (such as installed by BT) have the ability to perform the PCM to convert analogue voice to a B-channel. Otherwise an ISDN NIC, or ISDN Phone is required to use the line.

Both B-channels can be combined (bonded) to increase the data rate from 64 kb/s to 128kb/s

Hope that helps

More excellent information from Ranger24!
I have one question back on the subject of DSL. Back in the days when phone lines were just phone lines they could carry 4Khz of voice and that was it. Then with the advent of modems we crawled slowly upwards with the baud rate until we got to the absolute design maximum of 56Kb/s. What have they done to those bits of wet string (wet copper?) that now allow an effective bandwith of a couple of Mhz to be carried without horrendous crosstalk and crippling signal loss over the distances involved?

IN short the wet string has stayed the same, but the mathmaticians have got smarter!

by combining the same technology in a 56k modem (Google: Quad Amplitude Modulation - QAM), and combining this with frequency division Multiplexing on multiple carriers the effective bandwidth of a copperline has moved from 4khz to 2.2 Mhz.

That is as detailed as I am going to get on this one Bishop!

(I don't want everyone thinking I don't have a life!)

thanks for all that stuff...but is dsl really digital.. :

very good ranger24 .. very good.. it seems u got experties on compleate infrastructure of DSL Technology ... wonder u work for any such ISP :roll: