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Terminologies Simplified

Locally Administered Address (LAA) A parameter used by a 3174 controller to determine whether a node can access a mainframe computer connected to a Token Ring network.

LocalTalk Link Access Protocol (LLAP) A parameter used by a 3174 controller to determine whether a node can access a mainframe computer connected to a Token Ring network.

LocalTalk network A proprietary network architecture from Apple Computer, Inc., consisting of a system of twisted-pair cables, cable extenders, and connectors (DB-9, DIN-8, or DIN-3) that connects computers and network devices to create an AppleTalk network. Using Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) and the LocalTalk Link Access Protocol (LLAP), up to 255 nodes can be separated by up to 1,000 feet. LocalTalk operates at the Data-Link Layer (Layer 2) and Physical Layer (Layer 1) of the OSI Reference Model.

Locked file A file whose attributes have been set so the file may be operated and read, but not written to, deleted, or changed in any way.

Locking A process to ensure two network users or programs cannot try to access the same data simultaneously.

An advisory lock issues a warning and can be overridden. A physical lock is a control mechanism that cannot be overwritten. With a file lock, a file server prevents users from accessing any part of a file, while another user is accessing the same file. With a record lock, a file server prevents users from accessing a record in a file, while another user is accessing the same record. With a logical lock, logical units (LUs) in a file are inaccessible. With a physical lock, sectors or groups of sectors on a hard disk are inaccessible.

Logical Address A network or node address assigned during installation of a network or addition of a workstation.

The installation software assigns a logical address; the hardware manufacturer assigns a hardware address.

Logical Channel A mechanism that allows multiple, simultaneous virtual circuits (VCs) across one physical link on a network.

Logical Channel Number (LCN) A unique number assigned to each virtual circuit (VC) and attached to each packet in a call. The LCN differentiates the packet from other packets generated by users issuing other calls.

Logical Device Name A name used by the operating system to identify a DOS device.

Logical Drive An internal representation used by an operating system to refer to an actual disk device or to a group of directories specified by the DOS SUBST command.

Logical Link Control Type 2 (LLC2) A protocol and packet format commonly used in Systems Network Architecture (SNA) networks and more widely supported than the Synchronous Data Link Control (SDLC) protocol.

Logical Topology A networks logical layout that specifies which path information takes through a network, how the information is transmitted, and how the elements in the network communicate with each other. The two most common types of logical topology are bus and ring.

Logical-Link Control (LLC) A sublayer in the Local Area Network Reference Model (LAN/RM) that provides an interface and services for the network-layer protocols, and mediates between the higher-level protocols and lower media-access protocols. The LLC resides above the Media Access Control (MAC) sublayer and, when combined, the LLC and MAC sublayers are equivalent to the Data Link Layer (Layer 2) of the OSI Reference Model. The LLC is similar to the Synchronous Data Link Control (SDLC) link-layer protocol

Long Fat Network (LFN) A long distance network that has bandwidths of several hundred megabits per second, which can cause performance and packet-loss problems with Transmission Control Protocol/Internet Protocol (TCP/IP).

Long-haul Carrier A description of the cabling and signaling specifications for a carrier system responsible for long-distance telecommunications signals. Coaxial cabling and analog signaling are characteristics of this carrier; they provide tremendous capacity, but are expensive to use.

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