Справочник Пользователя для Netopia R2020

The Netopia R2020 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.