The overall process by which a series of tells devices called circuit switches connect a circuit from one customer device to the other, with the device’s logic taking incoming bits on one segment in the link and forwarding those bits out the matching outgoing segment, without storing the bits. Packet switching- The process of forwarding customer data in a WAN by looking at the header of the messages sent into the WAN by the customer and making a per- message (per-packet) decision as to where to forward each message. A physical link between two locations, provided by a tells, that allows two-way communication between sites. Because the customer does not own the physical line between sites, but rather pays a monthly fee for the service, it is called a leased service or leased line. Also known as a dedicated circuit, leased circuit, and point-to-point line.
Time-division- A type of logic used by some networking devices, including circuit switches in the tells, in which the switch divides a faster-speed line into time channels. The TDMA logic takes the bits off slower- peed lines and forwards those bits inside the time channels in the higher-speed line (multiplexing), and when receiving bits on a higher-speed line, finds the bits in each time channel and splits those back out to the correct slower-speed line (timetabling). Multiplexing- he opposite of demodulated. For a multiplexer, the process of taking multiple incoming digital serial bit streams and putting all of them into different channels on a single line that has time channels, like IDS and ADS lines.
T-carrier system- The name of the combination of different hysterical line standards (DISC, IDS, ADS, and others), plus circuit switches that use time-division multiplexing (TDMA) features, that together allowed the phone company to create digital circuits from end to end and create leased-line services for customers. DOS- Digital Signal Level O. One of the physical line standards in the T-carrier system, as originally created by the companies of the Bell System in the United States. DOS runs at 64 Kbps. IDS- Digital Signal Level 1. One of the physical line standards in the T-carrier system, as originally created by the impasses of the Bell System in the United States. IDS runs at 1. 544 Mbps, with a 193-bit frame, 24 DOS channels, and an 8-Kbps overhead channel.
Frame Relay- A widely popular packet-switching technology and service that emerged in the market in the asses, using permanent virtual circuits (PVC) between pairs of routers that can send frames to each other, and data-link connection identifiers (DELI) to address and identify each PVC. Acronyms: AT M: Asynchronous Transfer Mode CO: Central Office DCE: data communications equipment Demark: demarcation line DELI: data-link connection identifier DOS: digital signal level 0 IDS: digital signal level 1 ADS: digital signal level 3 DATE: data terminal equipment SEES: electronic switching system FRR: frame relay forum HEAD: high-level data link control Metro: metro Ethernet MILS: multiprocessor label switching POP: point of presence APP: point-to-point protocol APT: postal, telephone and telegraph PVC: permanent virtual circuits SONNET: Synchronous Optical Network T 1: T-carrier system layer TO: T-carrier system layers TDMA: time-division multiplexing Tells: service provider WAN: wide-area network
