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Communication in which data travels in the download direction at a speed different from the speed of the upload direction.
asymmetric communication
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A digital telecommunications technology that uses different speeds for downloading and uploading data.
Asymmetric Digital Subscriber Line (ADSL)
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A communication method that sends data in a stream with start and stop bits that indicate where data begins and ends.
Asynchronous
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An ISDN version that provides two 64 Kbps B-channels. Generally used for remote connections.
Basic Rate Interface (BRI)
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A measurement of modem speed that describes the number of state transitions occurring per second on an analog phone line.
baud
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One of the primary synchronous communication protocols.
Binary Synchronous (bisync)
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Networking devices that work at the Data Link layer of the OSI model. They filter traffic according to a packet’s hardware destination address.
bridges
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A reference table created by a bridge to track hardware addresses and to track on which network segment each address is located.
bridging table
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An ISDN variation that supports much higher data rates than standard ISDN and works with other technologies, such as ATM, SONET, and frame relay.
Broadband ISDN (B-ISDN)
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A phenomenon that occurs when a network device malfunctions and floods the network with broadcast packets.
broadcast storm
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A device that links a computer or network to a DDS communications link.
Channel Service Unit/Data Service Unit (CSU/DSU)
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A guaranteed minimum transmission rate offered by the service provider.
Committed Information Rate (CIR)
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The equipment at the customer site that’s usually the responsibility of the customer.
customer premises equipment (CPE)
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The fastest switching method, in which the switch reads only enough of the incoming frame to determine where to forward the frame.
cut-through switching
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The device that sends data to (and receives data from) the local loop, usually a CSU/DSU or modem.
data circuit-terminating equipment (DCE)
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The device that passes data from the customer LAN to the DCE, usually a router.
data terminal equipment (DTE)
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The point at which the CPE ends and the provider’s equipment responsibility begins.
demarcation point
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The Windows program (beginning with Windows 95) that allows connectivity to servers running RAS or RRAS.
Dial-Up Networking (DUN)
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A type of point-to-point synchronous communication link offering 2.4, 4.8, 9.6, or 56 Kbps transmission rates.
Digital Data Service (DDS)
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A hardware device used to transmit digital signals across an ISDN link.
digital modem
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One method of determining the best route available for a packet. Distance-vector protocols count the number of routers (hops) between the source and destination. The best path has the least number of hops.
distance-vector algorithm
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The process by which routers dynamically learn from each other the available paths.
dynamic routing
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One or more of the 24 channels (but not all) of a T1 connection.
fractional T1
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A switching method in which the switch reads in enough of the frame to guarantee that the frame is not less than the minimum frame size allowed for the network type.
fragment-free switching
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A frame error that occurs because the frame is less than the allowable minimum size for the network type. A ____ __________ usually occurs because of a collision or a device malfunction.
frame fragment
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A point-to-point permanent virtual circuit (PVC) technology that offers WAN communications over a fast, reliable, digital packet-switching network
frame relay
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A networking device that translates information between protocols or between completely different networks, such as from TCP/IP to SNA.
Gateway
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One of the primary synchronous communication protocols.
High-level Data Link Control (HDLC)
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A packet traveling through a router on its way to the destination network.
hop
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A WAN technology that offers increments of 64 Kbps connections, most often used by SOHO (small office/home office) users.
Integrated Services Digital Network (ISDN)
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The connection between a WAN’s demarcation point and the central office (CO). See also local loop.
last mile
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A feature that sustains a consistent transmission rate, improves overall quality, and reduces interference noise levels.
line conditioning
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A method used by routers to determine a packet’s best path. In addition to the number of routers involved, routers using link-state algorithms take network traffic and link speed into account to determine the best path.
link-state algorithm
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The connection between a WAN’s demarcation point and the central office (CO). See also last mile.
local loop
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A value that describes the distance to the destination network.
metric
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A device computers use to convert digital signals to analog signals for transmission over telephone lines. The receiving computer then converts the analog signals to digital signals.
modem
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A technology that enables several communication streams to travel simultaneously over the same cable segment
multiplexing
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A device that supports X.25 communications for low-speed, character-based terminals.
packet assembler/disassembler (PAD)
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Pathways between two communication points that are established as permanent logical connections; therefore, the pathway exists even when it’s not in use.
permanent virtual circuits (PVCs)
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Also known as PSTN, the normal telephone communications system. See also public switched telephone network (PTSN).
plain old telephone service (POTS)
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A remote access protocol that supports many protocols, including IP, NetBEUI, and IPX.
Point-to-Point Protocol (PPP)
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An ISDN version that provides 23 64-Kbps B-channels.
Primary Rate Interface (PRI)
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Signal delay created when a number of repeaters connect in a line. To prevent this, many network architectures limit the number of repeaters on a network.
propagation delay
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WAN services, usually provided by private companies, for the purpose of enabling WAN technologies, such as X.25.
public data networks (PDNs)
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Another term for the public telephone system.
public switched telephone network (PSTN)
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A technique for digitizing analog signals. PCM introduces less noise into the signal than traditional modulation/demodulation techniques, thus boosting the total number of bits per second.
pulse code modulation (PCM)
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Networking devices that operate at the Network layer of the OSI model. A router connects networks with different physical media and translates between different network architectures, such as token ring and Ethernet.
routers
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A reference table that includes network information and the next router in line for a particular path.
routing table
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The dial-up protocol originally used to connect PCs directly to the Internet.
Serial Line Internet Protocol (SLIP)
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A type of bridge used in IBM token ring networks that learns its bridging information from information in the frame’s structure.
source-routing bridges
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A type of routing in which the router is configured manually with all possible routes.
static routing
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A switching method in which the switch reads the entire frame to check for errors before forwarding the frame.
store-and-forward switching
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Digital point-to-point leased communication links offered by local and long-distance telcos. Lease terms are based on per-minute use charges, not on 24-hour, seven-day dedicated circuits.
switched 56K
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A communication circuit that’s established when needed and then terminated when the transmission is completed.
switched virtual circuits (SVCs)
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A digital telecommunications technology that uses equivalent speeds for downloading and uploading data.
Symmetric Digital Subscriber Line (SDSL)
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A communication method in which computers rely on exact timing and sync bits to maintain data synchronization.
synchronous
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One of the primary synchronous communication protocols.
Synchronous Data Link Control (SDLC)
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A DDS technology that uses two two-wire pairs to transmit full-duplex data signals at a maximum rate of 1.544 Mbps.
T1
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A communication line that has 28 T1s or 672 channels and supports a data rate of 44.736 Mbps.
T3
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A type of bridge that can translate between network architectures.
translation bridges
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Generally used in Ethernet networks, these bridges build their bridging tables automatically as they receive packets.
transparent bridges
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A logical sequence of connections with bandwidth allocated for a specific transmission pathway.
virtual circuits
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A feature of switches that allows network administrators to group users and resources logically, regardless of their physical location.
virtual local area networks (VLANs)
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The ITU standards that specify how data communication takes place over the telephone network.
V-series
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A WAN protocol that defines how devices communicate over an internetwork. X.25 networks are SVC networks, meaning they create the best available pathway for transmission at the time of transmission.
X.25
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