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Using Telephone and Cable Networks for Data Transmission

* A home computer can access the Internet through the existing telephone system or through a cable TV system.
* DSL supports high-speed digital communications over the existing telephone local loops.
* ADSL technology allows customers a bit rate of up to 1 Mbps in the upstream direction and up to 8 Mbps in the downstream direction.
* ADSL uses a modulation technique called DMT which combines QAM and FDM.
* SDSL, HDSL, and VDSL are other DSL technologies.
* Theoretically, the coaxial cable used for cable TV allows Internet access with a bit rate of up to 12 Mbps in the upstream direction and up to 30 Mbps in the downstream direction.
* An HFC network allows Internet access through a combination of fiber-optic and coaxial cables.
* The coaxial cable bandwidth is divided into a video band, a downstream data band, and an upstream data band. Both upstream and downstream bands are shared among subscribers.
* DOCSIS defines all protocols needed for data transmission on an HFC network.
* Synchronous Optical Network (SONET) is a synchronous high-data-rate TDM network for fiber-optic networks.
* SONET has defined a hierarchy of signals (similar to the DS hierarchy) called synchronous transport signals (STSs).
* Optical carrier (OC) levels are the implementation of STSs.
* A SONET frame can be viewed as a matrix of nine rows of 90 octets each.
* A SONET system can use the following equipment:
a. STS multiplexer—combines several optical signals to make an STS signal.
b. Regenerator—removes noise from an optical signal.
c. Add/drop multiplexer—adds STSs from different paths and removes STSs from a path.
* SONET is backward compatible with the current DS hierarchy through the virtual tributary (VT) concept. VT's are a partial payload consisting of an m-by-n block of octets. An STS payload can be a combination of several VT's.
* STSs can be multiplexed to get a new STS with a higher data range.