Contents

1 History

• Bellcore (now Telcordia Technologies) developed Asymmetric Digital Subscriber Line (ADSL) and filled a patent in 1988.
• Now is the most used method for residential access.

2 Hardware

• Use the same line than the telephone (ordinary copper lines).
• A DSL modem is the device required to connect the computer or the network of the user to the telephone line.
• The local loop (last-mile) must be less than 5.5 kilometers (3.5 miles).
• Voice and data simultaneously (microfilters or splitter (both are a low-pass filter with a cut-off frequency of 4 KHz) must be installed because if the phone is not “DSL friendly”).
• Full-duplex.

3 Modulation

• FDM: voice, upstream and downstream in parallel.
• Data is modulated using:
  • OFDM (Orthogonal Frequency-Division Multiplexing).
• Asymmetric DSL (ADSL) uses a frequency range from approximately 20 kHz to 1 MHz.

4 Multiplexing

• Do not exist (medium is dedicated), although voice and full-duplex data are multiplexed using FDM.

5 Delay

• Delay is minimal because the circuits are dedicated (each user has a separate direct connection to the ISP).
• Jitter is negligible.

6 Bit-rates

• Bit-rates depends on the noise in the line. Tipically:
  1. Download: up to 52 Mbps.
  2. Upload: up to 16 Mbps.