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Definition
| Local telephone company. Owns the cables and has right of way for leased lines used for WANs. |
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Definition
| A serial communication circuit between two end points, provided by some service provider, typically a telephone company or a telco. Provides basic connectivity between to points. Work with a service provider to install a circuit – connection is always available. Sometimes called leased circuit or Point-to-Point WAN Connection. |
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| Channel Service Unit/Data Service Unit |
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| Channel Service Unit/Data Service Unit (CSU/DSU) |
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Definition
| A device that understands the Layer 1 details of serial links installed by a telco and how to use a serial cable to communicate with networking equipment such as routers. |
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| Central Office (of telco) |
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| Telco point of origin for the four-wire cable from the telco to your building. Cabling runs from CO Wan switch to CSU/DSU to router. |
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| Demarcation point. On network diagrams, "demarc" marks the physical point separating telco-owned equipment from customer-owned. |
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Definition
| Customer Premises Equipment |
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| Customer Premises Equipment (CPE) |
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Definition
| Any equipment related to communications that is located at the customer site, as opposed to inside the telephone company’s network. |
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Definition
| The speed at which a serial link encodes bits on the transmission medium. Also called bandwidth or link speed. |
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Definition
| Various devices must synchronize their clocks so that they run at the exact same speed. Devices operate at close to the same speeds and listen to the speed of the other device on the other side of the link. One side makes small adjustments to match the other side. |
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Term
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Definition
| Synchronization occurs between the two CSU/DSUs on a leased line by having one CSU/DSU (the slave) adjust its clock to match the clock rate of the other CSU/DSU (the master). Networking devices synchronize their clocks several times per second. |
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Definition
| The device providing clocking on a WAN link, typically a CSU/DSU. DCE cables reverse the transmit and receive pins, like a crossover cable in Ethernet. DCE cable has female connectors. |
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Definition
| The device receiving clocking; typically the router. DTE cable sends and transmits from the same pins on both ends, like a straight-through cable in Ethernet. DTE cable has male connectors. |
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Definition
| Data Communication Equipment |
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Definition
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| A 64-kbps line or channel of a faster line inside a telco whose origins are to support a single voice call using the original voice (PCM) codecs. |
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Definition
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Definition
| A 1.544-Mbps line from the telco, with 24 DS0 channels of 64 kbps each, plus an 8-kbps management and framing channel. Also called T1. |
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Definition
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Term
| Pulse Code Modulation (PCM) |
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Definition
| A technique of encoding analog voice into a 64-kbps datat stream by sampling with 8-bit resolution at a rate of 8000 times per second. |
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Term
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Definition
| In Frame Relay, the physical serial link that connects a Frame Relay DTE device, usually a router, to a Frame Relay switch. The access link uses the same physical layer standards as do point-to-point leased lines. |
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Term
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Definition
| A serial link between two routers, created without CSU/DSUs, by connecting a DTE cable to one router and a DCE cable to the other. Typically used in labs to build serial links without the expense of an actual leased line from the telco. |
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Term
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Definition
| The process of supplying a signal over a cable, either on a separate pin on a serial cable or as part of the signal transitions in the transmitted signal, so that the receiving device can deep synchronization with the sending device. |
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Term
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Definition
| An international standard data-link protocol that defines the capabilities to create a frame-switched (packet-switched) service, allowing DTE devices (typically routers) to send data to many other devices using a single physical connection to the Frame Relay Service. |
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Term
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Definition
| Hgh-level Data Link Control |
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Term
| High-level Data Link Control (HDLC) |
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Definition
| A bit-oriented synchronous data layer protocol developed by the International Organization for Standardization (ISO). HDLC has three tasks: 1) detect errors, 2) discard frames with errors, 3) identify the type of packet inside the HDLC frame. |
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Definition
| HDLC header includes Address field and Protocol Type field. HDLC trailer contains FCS (Frame Check Sequence). Cisco proprietary HDLC frame also includes Type field. |
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Term
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Definition
| A generic reference to network services, typically WAN services, in which the service examines the contents of the transmitted data to make some type of forwarding decision. |
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Definition
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Term
| Point-to-Point Protocol (PPP) |
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Definition
| A protocol that provides router-to-router and host-to-network connections over synchronous point-to-point and asynchronous point-to-point circuits. |
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Term
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Definition
| A type of cable with many different styles of connectors used to connect a router to an external CSU/DSU on a leased-line installation. |
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Term
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Definition
| The imposition of time ordering on a bit stream. Practically, a device will try to use the same speed as another device on the other end of a serial link. However, by examining transitions between voltage states on the link, the device can notice slight variations in the speed on each end and can adjust its speed accordingly. |
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Term
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Definition
| A line from a telco that allows transmission of data at 1.544 Mbps, with the ability to treat the line as 24 different 64-kbps DS0 channels (plus 8 kbps of overhead). |
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Definition
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Term
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Definition
| The logical path a frame travels between each pair of routers. In packet (frame) switched services like Frame Relay, VC refers to the ability of two DTE devices (typically routers) to send and receive data directly to each other, which supplies the same function as a physical leased line (leased circuit), but doing so without a physical circuit. |
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Term
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Definition
| Permanent Virtual Circuit |
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Term
| Permanent Virtual Circuit (PVC) |
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Definition
| Virtual Circuit preconfigured by the Service Provider. In contrast to VCs that are configured on an as-needed basis. |
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Term
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Definition
| Committed Information Rate |
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Term
| Committed Information Rate (CIR) |
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Definition
| Guarantee by the service provide in Frame Relay that a particular VC gets at least that much bandwidth. CIR is like the bandwidth or clock rate of a point-to-point circuit except that it is a minimum value – more can actually be sent, in most cases. |
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