18-03-2011, 06:29 PM
|
| M.Arsalan Qureshi | | Join Date: Oct 2008 Location: Garden Town, Multan Cantt
Posts: 616
Program / Discipline: BSTS Class Roll Number: 09-31 | |
Using Telephone and Cable Networks for Data Transmission 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.
__________________ |