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Table Of Contents  CertiGuide to A+ (Core Hardware)
 9  Chapter 0111:  Peripheral Devices
      9  VII  Modems

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VIII  Printers
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Compression and Errors

The biggest challenge users had with modems was the speed, or rather lack of speed. Long distance rates were about $30 an hour (after 11 PM).

Users wanted faster file transfers. Modem manufacturers wanted to help out since it meant they got to sell newer and more profitable modems. Over the years a whole range of new ways of getting more data down the existing wires was unveiled, until it became a regular bowl of alphabet soup.

The most recent scrap was the 56K Flex verses US Robotics X2. Of course, the two standards didn't interoperate. The battle was ended with the release of the standard set by the International Telecommunications Union (ITU). This example was just the latest of a 20-year battle of different standards.

[spacer]V.xx Standards

The V.xx standards were set by CCITT (Comite Consultatif International de Telegraphique ed Telephonique), now known as ITU-T. The higher the number after the V. the newer the standard. Sometimes this meant full duplex was added; sometimes it meant extending a standard to include higher data rates.

V.42 is an error-detection standard, which competes with the various Microcom Networking Protocol (MNP) versions.


[spacer]V.90

This standard ended the battle between Rockwell/Lucent's K56flex and US Robotics' (now 3COM) entry with X2. The idea behind 56k is simple. Instead of converting the returning signal back to analog, require the service provider to have a direct digital connection, and leave the returning to the V.90 a signal digital.

Line quality and distance will limit the actual throughput of the returning digital data.


V.90 Performance

V.90
modems under ideal conditions are 53kbps to the user (downstream), and 33kpbs from the user (upstream).


Modems in the Real World

The acronym, modem has become part of everyday language. In fact, it is becoming a noun. Cable Internet access providers are saying you need a cable modem to connect between the Ethernet card in the PC and the cable company. The cable companies are offering digital connections, so there is no modulating to an analog signal. No modulation means no demodulation, so no MO-DEMing is happening. However John Q. Public understands the acronym modem, as a word, so the providers refer to their connecting equipment as a modem.



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