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ADSL modem 10 years 5 months ago #14364

  • dwyane
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:D Hi guys,
Had a conversation with my friends on the Term ADSL Modem,
wanted to have ur comments on the term " ADSL modem ", is it correct to term it as ADSL modem, iv checked with a previous thread but nothing is clear...

what i understand is :->

from CO--- <<digital signals>>-- DSLAM---<<analog>>---CPE( modem)--

>> digital signals to the computer

what i mean is from CO to DSLAM its digital, after DSLAM its analog to the CPE where the ADSL modem converts analog back to digital and vice a versa... , if this is what the case is then the term ADSL modem is correct as it is modulating and demodulating

wonder if its correct or not.. :roll:
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Re: ADSL modem 10 years 5 months ago #14389

  • jwj
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It is correct calling it a DSL modem. I was actually confused about this until a few months ago when a post here cleared things up. ADSL uses Discrete Multi-tone (DMT) modulation. It separates the analog signal from the CPE to the DSLAM into 255 "bins". These bins are multiples of 4.3125 kHz. The digital bits from your computer to the CPE is encoded into it's respective analog bin using phase-shift keying.

The first bin is reserved for voice. This is why you can use your telephone while your DSL connection is on. There is six bins after that which serve to reduce interference between the voice and data bins. Bins 7 - 31 are for upstream data, and 32 - 255 are for downstream. This explains why downstream is always faster in ADSL.

Anyways, the wikipedia entry for the ITU standard for ADSL, ITU G.992.1 is very informative, and goes even further into this than I did. Hope this helps.
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