| A | B |
|---|
| Asynchronous Transfer Mode | International standard for cell relay in which multiple service types (such as voice, video, or data) are conveyed in fixed-length (53-byte) cells |
| Bearer (B) channel | In ISDN, a full-duplex, 64-kbps channel used to send user data |
| central office (CO) | The local telephone company office to which all local loops in a given area connect and in which circuit switching of subscriber lines occurs. |
| Channel service unit. (CSU) | Digital interface device that connects end-user equipment to the local digital telephone loop |
| Circuit switching | WAN switching method in which a dedicated physical circuit is established, maintained, and terminated through a carrier network for each communication session |
| Communication servers | concentrates dial-in and dial-out user communication |
| CSU/DSU | adapts the physical interface on a DTE device (such as a terminal) to the interface of a DCE device (such as a switch) in a switched-carrier network. |
| Data (D) channel | Full-duplex, 16-kbps (BRI) or 64-kbps (PRI) ISDN channel |
| Data communications equipment (DCE) | provides a physical connection to the network, forwards traffic, and provides a clocking signal used to synchronize data transmission at the network end of the user-to-network interface |
| Data service unit. (DSU) | Device used in digital transmission that adapts the physical interface on a DTE device to a transmission facility such as T1 or E1; responsible for such functions as signal timing |
| Dedicated lines | leased lines; provide full-time service; generally provide core or backbone connectivity between major sites |
| Dedicated, full-time connectivity is provided by | point-to-point serial links |
| Dial-on-demand routing (DDR) | a technique in which a router can dynamically initiate and closes circuit-switched sessions when transmitting end stations need them |
| Frame Relay | designed to be used over high-speed, high quality digital facilities |
| ISDN devices | TE1, TE2, TA |
| Terminal Adapter (TA) | device used to connect ISDN Basic Rate Interface (BRI) connections to other interfaces. |
| Link Access Procedure, Balanced (LAPB) | a bit-oriented protocol derived from HDLC |
| local loop | Line from the premises of a telephone subscriber to the telephone company CO |
| Modems | device that interprets digital and analog signals by modulating and demodulating the signal |
| NT1 | Connects four-wire ISDN subscriber wiring to the conventional two-wire local loop facility. |
| NT2 | Directs traffic to and from different subscriber devices and the NT1; is an intelligent device that performs switching and concentrating |
| Packet-switched | WAN switching method in which network devices share a permanent virtual circuit (PVC) |
| Examples of Packet-switched | Frame Relay, SMDS, and X.25 |
| Permanent virtual circuit. (PVC) | saves bandwidth associated with circuit establishment and tear down in situations where certain virtual circuits must exist all the time. |
| Point of presence (POP) | the point of interconnection between the communication facilities provided by the telephone company and the building's main distribution facility |
| Point-to-Point Protocol (PPP) | provides router-to-router and host-to-network connections over synchronous and asynchronous circuits; successor to SLIP |
| Switched connections can be either | circuit switched or packet switched |
| Switched virtual circuit (SVC) | Virtual circuit that is dynamically established on demand and is torn down when transmission is complete.; used in situations where data transmission is sporadic |
| Synchronous Data Link Control (SDLC) | a bit-oriented, full-duplex serial protocol that has spawned numerous similar protocols, including HDLC and LAPB; data link layer communications protocol |
| TA | Converts standard electrical signals into the form used by ISDN so that non-ISDN devices can connect to the ISDN network. |
| TA/NT1 | Modems that interface ISDN services |
| Telephone and data services | most commonly used WAN services |
| terminal adapter (TA) | Device used to connect ISDN BRI connections to existing interfaces such as EIA/TIA-232. Essentially, an ISDN modem. |
| Terminal Equipment 1 (TE1) | Designates a device that is compatible with the ISDN network; connects to an NT of either Type 1 or Type 2. |
| Terminal Equipment 2 (TE2) | Designates a device that is not compatible with ISDN and requires a TA. |
| Two basic WAN link options | dedicated lines and switched connections |
| virtual circuit | Logical circuit created to ensure reliable communication between two network devices |
| WAN switch | typically switches such traffic as Frame Relay, X.25, and Switched Multimegabit Data Service (SMDS); connect to WAN bandwidth for voice, data, and video communication |
