Contents

1 History

• Cable television first began in Pennsylvania in 1948.
• In the 90’s, there is a large infrastructure of cable TV systems. Some channels are used to transmitt data instead of TV signals to the home of the users (residential access).

2 Hardware

• A cable modem is the device required to connect the computer to the coaxial cable.
• Links are full-duplex, althought shared between several neighbors.

3 Modulation

• Downstream frequencies are in the range of 50 to 860 MHz.
• Upstream frequencies are in the range of 5 to 42 MHz.
• In a modern HFC network, typically 500 to 2,000 active data subscribers are connected to a cable network segment, all sharing the upstream and downstream bandwidth.
• 6 MHz/channel.
• Modulation techbiques:
  • QPSK (Quadrature Phase Shift Keying).
  • QAM (Quadrature Amplitude Modulation).

4 Multiplexing

• CDMA (Code division multiple access).

5 Delay

• Minimal (the bandwidth in a CDMA scheme is reserved).
• Jitter is negligible.

6 Bit-rates

• The actual bandwidth for Internet service over a cable line can be up to 27 Mbps on the download path to the subscriber and about 2.5 Mbps of bandwidth on the upload path. Based on the cable network architecture, cable operator provisioning practices, and traffic load, an individual subscriber can typically get an access speed of between 256 kbps and 6 Mbps.
• When high usage causes congestion, the cable operator can add additional bandwidth for data services by allocating an additional TV channel for high-speed data. This addition may effectively double the downstream bandwidth that is available to subscribers. Another option is to reduce the number of subscribers served by each network segment. To reduce the number of subscribers, the cable operator further subdivides the network by laying the fiber-optic connections closer and deeper into the neighborhoods.