Netopia R2121, User Reference Manual

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About 56K Line Access H-1
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The Netopia R2121 with Dual Analog is capable of 56Kbps per line connections. This means that if you use
both onboard modems, you can achieve inbound data transfer rates of up to 112Kbps. Using a third modem
bumps the theoretical speed limit to 168Kbps.
This section describes some practical limitations on the previous statements.
A current FCC limitation will only permit a maximum speed of 52Kbps over analog phone lines using combined
analog/digital technology. Also, the data transfer rates are for
inbound data only. Outbound data is limited to
the current transfer rates for analog phone lines alone which is 33.6Kbps. So, using both onboard modems
under optimal conditions, will yield an inbound data transfer rate of 104Kbps and an outbound rate of
67.2Kbps. This means that your incoming email, file transfers and downloads, web browsing, and so on, occur
at 104Kbps, while your outgoing information, such as outbound email, travels at 67.2Kbps. With a third
modem, the rates become 156Kbps inbound and 100.8Kbps outbound. Also, to achieve the maximum inbound
rates, the ISP-side data must be digitally sourced.
Above a cer tain threshold (called Shannon's Limit) the signal-to-noise ratio of any medium becomes too low to
reliably transfer data. The analog phone line is the limiting factor in the speed of data transmission because of
the inherent noise it contributes.
Today's telephone network is increasingly digital. In par ticular, the por tion of the phone connection between the
phone company and the Internet Ser vice Provider (ISP) is often digital. Digital lines still have noise, and are still
subject to Shannon's limit, but they have less noise and a higher ceiling.
Several companies have created techniques that take advantage of the digital por tion of the phone network to
achieve higher speeds than were possible with a purely analog pathway.
33.6K
33.6K
67.2K
56K
56K
112K
Outbound data
Inbound data