ADSL Modems
Downstream vs. Upstream
An ADSL connection requires a twisted-pair telephone wire and an ADSL modem in each side of the connection.
This regular phone line is split to 3 different channels:
* A high-speed downstream channel – up to 8 Mbps.
* A medium-speed upstream channel – up to 640 kbps.
* A Plain Old Telephone Service (POTS) – for voice
ADSL succeeds because it takes advantage of the fact that most of the applications that are used by users today requires high download speed and relatively low upload speed. Such applications are internet surfing, video-on-demand, and home shopping.
ADSL download and upload rates depend on several factors, including the length of the copper wire (the distance between the modems in the two edges), and the wire's size. The line performance increases as the wire length is reduced and its size increases, as shown in the table below:
|
Wire Size (mm) |
Distance (km) |
Rate (Mbps) |
|
0.5 |
5.5 |
1.5-2 |
|
0.5 |
3.7 |
6.1 |
|
0.4 |
4.6 |
1.5-2 |
|
0.4 |
2.7 |
6.1 |
ADSL Modems
Downstream vs. Upstream