MultiModemISDN User Guide
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LAPB (Link Access Procedure Balanced)—Based on the X.25 Layer 2 specification. A full-duplex, point-to-point, bit-synchronous protoc ol commonly used as a data link control protocol to interface X.25 DTEs. LAPB is the link initialization procedure that establishes and maintains communications between the DTE and the DCE.
LAPD (Link Access Protocol for the
D-Channel)—Based on the ISDN Q.921 specification. A full-duplex point-to-point bit-synchronous link-level protocol for ISDN con nections; different from LAPB in its framing sequence. Transmission is in units called frames, and a frame may contain one or more X.25 packets.
link optimization—An ISDN feature that permits only user data to open the communications link and keeps administrative packets from opening the link. A cost saving feature that ensures that remote connections are not unnecessarily utilized.
local loop—A transmission path, typically twisted-pair wire, between an individual subscriber and the nearest public telecommunications network switching center. Also called the subscriber loop.
LT (loop termination)—A device, similar to an NT1, that terminates the local loop at the carrier’s central switching office. The LT provides the interface to the ISDN U reference point. Contrast ET (exchange termination).
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ML-PPP(Multilink PPP)—An open standard for inverse multiplexing, allowing two 64 bps ISDN B channels to be multiplexed into one 128 Kbps link.
modem—A communications device that enables a computer to transmit information over a telephone line. It converts the computer’s digi tal signals into analog signals to send over a telephone line and converts them back to digital signals at the receiving end. Modems can be internal and fit into an expansion slot, or external and connect to a USB port.
MSN (Multiple Subscriber Number) - Allows a caller to specify an individual terminal adapter when more than one unit is connected to your network terminator. An MSN consists of a base address and a subaddress. If you assisgn a base address only, the unit accepts any incoming call with the same base address, regardless of whether a subaddress is included. If you assign a base address and a subaddress, the unit only accepts calls that match both the base address and the subaddress.
multilink—In point-to-point protocol, literally many links. A procedure used to route data packets over many links for increased bandwidth (e.g., two B-channels on a single BRI for 128 Kbps).
mux (multiplexer)—A device that merges several signals into one composite signal for transmission over a single medium or channel. A demultiplexer, built into most muxes, reverses the process at the receiving end.
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nailed connection—A permanent or dedicated circuit of a previously switched circuit or circuits.
nailed-upcircuit—A semi-permanent circuit established through a circuit-switching facility for point-to-point connectivity.
NAK (negative acknowledgment)—A communications code used to indicate that a message was not properly received, or that a terminal does not wish to transmit. Contrast with ACK.
network—A group of computers connected by cables or other means and using software that enables them to share equipment, such as printers and disk drives to exchange information.
NI-1(National ISDN-1)—A physical standard to make all compliant ISDN lines appear the same. With ISDN-1 installed, additional cost s are not incurred when changing from prestandard ISDN to standard ISDN. Most RBOCs now are moving to ISDN-1.
NI-2(National ISDN-2)—A physical standard subsequent to NI1. When tested and deployed, NI-2 will provide additional features and enhanced plug and play capabilities.
node—Any point within a network that has been assigned an address.
NT (network termination)—Devices that form the boundary between customer premise equipment and telephone company equipment. Two types of NTs are used: NT1 and NT2.
NT1 (Network TerminationType 1)—An interface device used in the BRI portion of ISDN to connect four-wire (S/T) ISDN devices to the two-wire (2BIQ U) IDN. It provides basic rate access in a 2B+D format with two 64 bps channels for voice, data, and video communications. It also provides one 16 Kbps channel for packet-mode signalling, low-speed data and telecommunications services at the OSI Layer 1 level. Similar in function to a DSU/CSU device.
NT2 (Network TerminationType 2)—A device at the customer premise (user) side responsible for the ISDN network connection and for functions such as multiplexing and switching (may be an intelligent device).
NTE (network terminating equipment)—A set of ISDN functions residing at the boundary of the IDN and the subscriber.
NUI (network user identification)—A unique alphanumeric number provided to dial-up users to identify them to packet-switched netwo rks world-wide. The number is used for network access and billing.
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