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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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One or more of the 24 channels (but not all) of a T1 connection.
fractional T1
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A technology that enables several communication streams to travel simultaneously over the same cable segment
multiplexing
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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 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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An ISDN version that provides two 64 Kbps B-channels. Generally used for remote connections.
Basic Rate Interface (BRI)
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An ISDN version that provides 23 64-Kbps B-channels.
Primary Rate Interface (PRI)
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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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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 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 logical sequence of connections with bandwidth allocated for a specific transmission pathway.
virtual circuits
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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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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 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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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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A device that supports X.25 communications for low-speed, character-based terminals.
packet assembler/disassembler (PAD)
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A guaranteed minimum transmission rate offered by the service provider.
Committed Information Rate (CIR)
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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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The equipment at the customer site that’s usually the responsibility of the customer.
customer premises equipment (CPE)
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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 connection between a WAN’s demarcation point and the central office (CO). See also last mile.
local loop
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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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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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