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TOPIC: ADSL and modem notion

ADSL and modem notion 13 years 1 month ago #12602

  • ikaros
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Yesterday I was present in a conversation regarding ADSL. The conversation was around the subject of ADSL and if the term modem should be used for ADSL devices.

I and some other fellows were saying the word modem should not be used for ADSL as it's a digital protocol with no modulation-demodulation happening. On the "opposition" there was the argument that all ADSL devices have written on their boxes and manuals the word ADSL modem, same thing in their web sites. Also sites like use the term ADSL modem.

If it was misused then all this time someone whould have corrected it and one company after the other whould do the same.

So my question is "Is the term ADSL modem used correctly, or we should use the term ADSL device?" and I think the same thing applies for ISDN device and not ISDN modem.

Re: ADSL and modem notion 13 years 1 month ago #12604

  • jwj
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At the very least, a DSL "modem" is an ATM (Asynchronous Transfer Mode) bridge or in many cases, also a router. Calling it a modem is technically incorrect, but is so widespread that it will never be termed correctly. Companies that make these modems know this, but they probably call it a modem so as to not confuse people switching from dial-up to DSL. In ISDN's case, your computer plugs into a Terminal Adapter, and sends it to a Network Terminator 1 device, which will also be on the customer's site. From there, the signal goes to the phone company. So, ISDN does not use modems either.

Re: ADSL and modem notion 13 years 1 month ago #12610

well describe the TA as"essentially an isdn modem" :!:

Re: ADSL and modem notion 13 years 1 month ago #12613

  • jwj
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Regardless of what Cisco says, it's still not modulating or demodulating anything because ISDN is all digital. Many people and companies refer to it as a modem probably to not further confuse the average user.

Re: ADSL and modem notion 13 years 1 month ago #12656

Hi Guys,

Offically (see DSL Forum docs) an ADSL modem is referred to as either a CPE (Customer Premises Equipment) or RG (Routing Gateway).

The majority of users will have a CPE, as this is designed to work in an ATM based DSLAM access network - See my post regarding DSLAMs elsewhere.

The RG is a more complicated CPE designed for the next generation of Broadband network which will based around Ethernet networks.

The Term ADSL Modem is not incorrect however as the CPE is effectively a combination of 256 modems, each transmiting in a 4.3Khz band with a data capacity of 60kb/s.

For ADSL the phone line has an effective band width of 1.1 Mhz, This is divided in to 256 x 4.3khz bins.

Bin 0 (0 - 4.3khz) is reserved for voice traffic so cannot be used.

Bin 256 is never used

Bins 6 -30 are used for Upstream traffic providing a theoritical throughput upstream of 24 * 60 Kbs = 1.44 Mb/s with a data rate of 1 MB/s max.

Bins 31-254 are used for downstream providing a possible max of 223 * 60kb/s = 13.3 Mb/s throughput, with a max data rate of approx 8mb/s.

Probably doesn't make the issues any clearer ;-)

Patience - the last reserve of the any engineer

Re: ADSL and modem notion 13 years 1 month ago #12657

  • DaLight
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Excellent post, Ranger24 like the one on DSLAMs . You have a talent for presenting information in a clear and easy-to-read manner.
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