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  • LAN (Local Area Network) A communications system that links computers into a network, usually via a wiring-based cabling scheme. LANs connect PCs, workstations and servers together to allow users to communicate and share resources like hard disk storage and printers. Devices linked by a LAN may be on the same floor or within a building or campus. It is user-owned and does not run over leased lines, though a LAN may have gateways to the PSTN or other, private, networks.
  • LAN Manager for Unix Systems An implementation of LAN Manager for use with Unix. Known colloquially as LM/X.
  • LAN Manager LAN Network Operating System developed by Microsoft which runs or top of OS/2 and recently Windows NT.
  • LAN Network Manager IBM's network management software for Token Ring networks.
  • LAN Segment A part of a LAN that is separated from the rest by one or more bridges.
  • LAN Server IBM version of IBM LAN Manager.

  • LAP (Link Access Protocol) The Data Link or OSI Layer Two protocol specified by the ITU-TS for the X.25 interface standard.
  • LAP-B: A link set-up routine to establish and maintain links between DCE and DTE. Lap-D: The Layer Two protocol for an ISDN D-channel specified in the ITU-TS recommendation Q.921. It is a framed, bit-oriented protocol similar to Lap and Lap-B protocols specified for X.25 circuits. Lap-M: A variation of Lap-B used in the V.42 modem error control standard.
  • LAT (Local Area Transport protocol) A DecNet specific protocol for the exchange of small packets of data between typically Dec Vax host computers and terminal servers in a LAN.
  • Layer Description of divisions in specifications Such as OSI and SNA communications protocols. Functions are grouped together that comprise one step in the hierarchy necessary for successful data communications.
  • Line conditioning A collection of techniques for keeping the quality of transmissions within specified parameters.
  • Line driver A signal converter that conditions the digital signal transmitted by an RS232 interface to extend reliable communication beyond the 50ft RS232 limit up to several miles. It is a baseband transmission device.
  • Line turnaround The interval on a transmission link between the time one block of data was sent and received and the time the next one can be sent.
  • Line signal standards In the US: T1 carries data at 1.544Mbit/s and has 24 voice circuits; T1C 3.152 Mbit/s with 48 voice circuits; T2 6.312Mit/s with 96 voice circuits, and T3, 44.736Mbit/s. In Europe, the standards are of the form En. E1 line speed is 2.048Mbit/s with 3C voice circuits; E2 is 8.448Mit/s with 120 voice channels. E3 is 34.368Mbit/s with 480 voice circuits. In the UK, E1 is often referred to as MegaStream, a BT label for its 2Mbit/s leased circuits.
  • Link state algorithm A routing algorithm such as OSPF which takes into account lowest delay when choosing a route: link speed and congestion as well as hop count.

  • LLC (Logical Link Control) A data link protocol based or HDLC, developed for LANs by the IEEE 802 Committee and consequently common to all LAN standards for Data Link OSI Layer Two transmission.
  • Local bridge Bridge that links two local LANs: in the same building, for example.
  • Local security A security method available for 386 and 486 servers running HPFS386. This method extends LAN Manager security measures to protect the files on a server by restricting access of the users working at the server. With local security, a user must be assigned permissions to access any file or directory in an HPFS386 partition, whether or not the resource is shared as part of a LAN Manager resource.
  • LocalTalk An Apple cabling scheme underlying its low-cost LANs. A 230Kbit/s baseband network primarily for Mac computers and LaserWriter printers, it uses the CSMA/CA media access method. The current Phase II allows theoretically unlimited networks.
  • Lobe The cable between a Token Ring station and the Trunk Coupling Unit to which it is connected. Lobe length comprises a patch cable from the TCU to the main wiring panel, the length of the main wiring to the user station's location, then a patch cable from a floor/desk socket to the station.
  • Logon script A batch program containing LAN Manager, NetWare and other operating system commands used to configure workstations. Logon scripts can be written for one or more users.
  • Logon server For a domain, a logon server is the primary domain controller and the backup domain controllers. For a user, the server that processes the user's logon request.
  • Loopback A diagnostic test that returns the transmitted signal back to the sending device after it has passed through a network or across a particular link. The returned signal can then be compared to the transmitted one. The discrepancy between the two help to trace the fault. When trying to locate a faulty piece of equipment, loopbacks will be repeated, eliminating satisfactory machines until the problem is found.

  • LU (Logical Unit) An IBM SNA network function defined in layers four, five and six (Transmission Control, Data Flow Control and Presentation Services) of the SNA architecture. In the SNA network, corresponding LUs are able to exchange information. Originally, particular types of LU has specific functions: LU1 for printers, LU2 for displays and so on. As SNA has developed, new types of LU have been introduced that support a broader range of communications facilities. LUs are normally associated with particular Physical Units (PUs), or network devices. LUs provide the services required by Applications (APs) in the IBM SNA environment, sitting between the APs and the PUs. A Dependent LU relies on the host for activation, physically and logically, while an Independent LU can initiate a session without host involvement.
  • LU 6.2 An IBM SNA Logical Unit that provides general communications functions, including the communications functions necessary for peer-to-peer networking. Underlying LU 6.2 is a type of node: node type 2.1, which facilitates peer-to-peer networking. Two SNA units which implement rode type 2.1 can set up a full peer-to-peer session without invoking SSCP capabilities in a host processor. This is defined as SNA Low-Entry Networking.

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