Week Six Mini Case

C . A.

Chapter 10 Mini-Case: I. Cathy’s Collectibles

October 8, 2011

The digital subscriber line (DSL) is a family of point-to-point technologies designed to provide high-speed data transmission over traditional telephone lines. The reason for the limited capacity on traditional telephone circuits lies with the telephone and the switching equipment at the end offices. There are many different types of DSL. The most common type of DSL in use today is asymmetric DSL (ADSL). ADSL is called asymmetric because its two data channels have different speeds. The size of the two digital channels depends on the distance from the CPE to the end office. The shorter the distance, the higher the speed, because with a shorter distance, the circuit suffers less attenuation and higher-frequency signals can be used, providing a greater bandwidth for modulation. The ADSL package has a maximum speed of 1.5 Mbps downstream rate and 384 Kbps upstream rate with a maximum length of 18,000 feet for the local loop.

Cable modem architecture is very similar to DSL—with one very important difference. DSL is a point-to-point technology whereas cable modems use shared multipoint circuits. With cable modems, each user must compete with other users for the available capacity. Furthermore, because the cable circuit is a multipoint circuit, all messages on the circuit go to all computers on the circuit. The DOCSIS standard provides many types of cable modems. The maximum speed is about 150 Mbps downstream and about 100 Mbps upstream, although most cable TV companies provide at most 27 Mbps downstream and 10 Mbps upstream. Cable modems can be configured to limit capacity, so the most common speeds offered by most cable providers range from 1–10 Mbps downstream and 256 Kbps to 1 Mbps upstream. Of course, this capacity is shared, so an individual user will only see this when no other computers on his or her segment are active.

The most popular types of fixed wireless are WiMax and wireless DSL,...