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Cheap Modems: Pro et Contra

What’s new

Over the past year in the world of modems it was really only one significant event: the adoption in February 1998 protocol V.90. First there were two standard 56K connection: K56Flex, developed by a consortium of Lucent and Rockwell, and X2, promoted by US Robotics (now 3COM). Incompatible standards hurt everyone: users did not understand how to buy a modem providers suffered with a choice of routers.

V.90 was obtained by merging X2 and K56Flex, and it allowed to accumulate in the new standard best demonstrated these protocols, without giving preference to any of them. Supports V.90 can be installed in the vast majority of X2 and K56Flex-MOfleMOB. To do this, simply update their internal software. Moreover, you can upgrade to V.90 modems, some V.34 (33,600). It is important to know and the fact that many manufacturers have stopped producing models that do not support V.90.

V.90 and all-all-all

I stress that the V.90 (X2 as a K56Flex) — unbalanced protocol. That is 56 kilobits per second — the maximum data transfer rate from the provider to the user.

How We Tested

Testing was conducted using a phone line simulator SIM-3 firms "Analyst TC". However, we believe that few users will be engaged in this kind of experiments.

ATA command reference modem switches to full answer and to test the modem to command dial ATD. After connecting to the modem test be forwarded zip-file. Each experiment was carried out 13 times.

Modem connects the telephone line through the simulator SIM-3. Testing was conducted on three types of lines: "good". "average" and "bad".

Beneath "good" we mean line line with greater than -45 dB ratio "S / N", 21-29 dB attenuation frequency response and lack of progress, jitter and amplitude, pulse and other interference.

To "average" line allowed attenuation of 18 dB, the interference signal level floating in the range -44 dB — -38 dB impulse noise with a frequency of 18.8 Hz and a signal level floating in the range of -44 to -26 dB.

To "bad" line, we have increased the incidence of noise and impulse noise and set the damping response within 21-29 dB.

Unfortunately, our available equipment does not allow to test the performance of 56K protocols. All tests were performed at the connection protocol V.34.

"AWACS Jaguar 56 RE" $ 140

In addition to the standard for the modern fax modem feature set and protocols, "Jaguar 56 RE" support technology and AudioSpan DSVD. Their essence is this: allow users to communicate with each other voice without breaking the connection. AudioSpan different from DSVD only by mixing voice and data. The first technology combines the channels into analog form, the second digital. Naturally, the use of each of them leads to a decrease in the data rate.

To use AudioSpan and DSVD need to establish a direct connection between the two modems simultaneously supports one of these protocols. Neither of which connect through the Internet we can not go. AT "User’s Guide "Jaguar 56 RE" (unfortunately only available in electronic format and in English) given initialization strings for each of the voice protocols. In order to communicate in parallel with the data transfer, just connect a microphone and speakers (headset) for both modems, correct them (modems) and initiate a connection. It’s all. You can talk. No additional software is needed. In principle, this is very convenient. Imagine being able to finish off an opponent in deathmatch’e and then sympathetically ask his health. The only pity is that the game can be only two.

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