ADSL overview

Differences between common V90 modems and ADSL

Unlike V90 protocol (common 56k analog modems), ADSL allows voice and data to be transferred by means of the same line in a simultaneous manner, meaning that you can speak on the phone and transfer data simultaneously. In fact, by means of the ADSL technology, voice and data use different frequencies (300Hz to 3,400Hz for voice and above 4KHz for data). If you have an ISDN line, you can ask your ISP (or your telephone company) for a new analog line (ADSL) or replace it with the old analog line (digital ISDN lines are not compatible with analog ADSL lines). On the contrary, V90 modems and ADSL modems are compatible, because V90 modems use the voice spectrum frequencies whereas ADSL modems use the data spectrum frequencies. Anyway, you need filters to separate voice from data (splitters). In fact, splitters use low pass filters to separate the low end frequencies of the telephone audio spectrum from the higher frequencies of the xDSL signals. After plugging the splitter into the phone socket, you can plug the phone and the ADSL modem into the two different socket of the splitter. Main differences between common analog lines (56k/V90 modems) and ADSL lines are summarized here:

- Symmetric speed (V90): upstream and downstream use the same bandwidth
- Asymmetric speed (ADSL): upstream and downstream use *different* bandwidth

- Voice lines carry both voice and data but they are not concurrent (V90): when you are connected to the Internet, your phone line is busy, so you can't receive calls
- Voice lines (or even data lines) carry voice and data at the same time (ADSL): you can speak on the phone while you are connected to the Internet

- Dial up modem (V90): you must dial in to be connected to the Internet
- Always on (ADSL): you have not to dial in to be connected to the Internet (you *CANNOT* get tricked by 'dialers')

- Low bandwidth (V90): up to 56 kbps
- High bandwidth (ADSL): up to 8 Mbps

- Dynamic IP address (V90): your ISP gives you a dynamic IP address, meaning that every times you dial in, you get a different IP address
- Dynamic/Static IP address (ADSL): your ISP can give you a static IP address, meaning that your IP address never changes

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