Fiber Optic Wiki

Digital subscriber line

December 14, 2011

Digital subscriber line (DSL) is a family of technologies that provides digital data transmission over the wires of a local telephone network. DSL originally stood for digital subscriber loop. In telecommunications marketing, the term DSL is widely understood to mean Asymmetric Digital Subscriber Line (ADSL), the most commonly installed DSL technology.

Theory behind DSL

December 14, 2011

Theory behind DSL, like many other forms of communication, can be traced back to Claude Shannon's seminal 1948 paper: A Mathematical Theory of Communication. An early patent was filed in 1987 for the use of wires for both voice phones and as a local area network.

Early DSL service required a dedicated dry loop

December 14, 2011

Early DSL service required a dedicated dry loop, but when the U.S. Federal Communications Commission (FCC) required ILECs to lease their lines to competing DSL service providers, shared-line DSL became available. Also known as DSL over Unbundled Network Element, this unbundling of services allows a single subscriber to receive two separate services from two separate providers on one cable pair.

Primary Rate Interface

December 13, 2011

The other ISDN access available is the Primary Rate Interface (PRI), which is carried over an E1 (2048 kbit/s) in most parts of the world. An E1 is 30 'B' channels of 64 kbit/s, one 'D' channel of 64 kbit/s and a timing and alarm channel of 64 kbit/s.

The bearer data channel

December 13, 2011

The bearer channel (B) is a standard 64 kbit/s voice channel of 8 bits sampled at 8 kHz with G.711 encoding. B-Channels can also be used to carry data, since they are nothing more than digital channels.Each one of these channels is known as a DS0.Most B channels can carry a 64 kbit/s signal, but some were limited to 56K because they traveled over RBS lines. This was commonplace in the 20th century, but has since become less so.

ISDN is used heavily by the broadcast industry

December 13, 2011

ISDN is used heavily by the broadcast industry as a reliable way of switching low latency, high quality, long distance audio circuits. In conjunction with an appropriate codec using MPEG or various manufacturers proprietary algorithms, an ISDN BRI can be used to send stereo bi-directional audio coded at 128 kbit/s with 20 Hz-20 kHz audio bandwidth, although commonly the G.722 algorithm is used with a single 64 kbit/s B channel to send much lower latency mono audio at the expense of audio quality.

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