L2TP

See Layer 2 Tunneling Protocol.

LABEL

The MS-DOS command which allows you to give a name to your disk.

LAN

See Local Area Network.

LANE

See LAN Emulation.

LAN Emulation (LANE)

The technology that allows an ATM network to operate as a LAN backbone. To do so, the ATM network is required to provide multicast and broadcast support, address mapping (MAC-to-ATM), SVC management, in addition to an operable packet format. Additionally, LANE defines Ethernet and Token Ring ELANs. See also Emulated LAN.

LAN Emulation Address Resolution Protocol (LE ARP)

The protocol providing the ATM address that corresponds to a MAC address.

LAN Emulation Client (LEC)

Software providing the emulation of the Link layer interface that allows the operation and communication of all higher-level protocols and applications to continue. The LEC client runs in all ATM devices, which include hosts, servers, bridges, and routers. The LANE client is responsible for address resolution, data transfer, address caching, interfacing to the emulated LAN, and driver support for higher-level services. See also Emulated LAN and LAN Emulation Server.

LAN Emulation Configuration Server (LECS)

An important part of emulated LAN services, providing the configuration data that is furnished upon request from the LES. These services include address registration for Integrated Local Management Interface (ILMI) support, configuration support for the LES address and their corresponding emulated LAN identifiers, and an interface to the emulated LAN. See also LAN Emulation Server and Emulated LAN.

LAN Emulation Network-to-Network Interface (LNNI)

In the Phase 2 LANE specification, an interface that supports communication between the server components within one ELAN.

LAN Emulation Server (LES)

The central LANE component that provides the initial configuration data for each connecting
LEC. The LES typically is located on either an ATM-integrated router or a switch. Responsibilties of the LES include configuration and support for the LEC, address registration for the LEC, database storage and response concerning ATM addresses, and interfacing to the emulated LAN. See also Emulated LAN, LAN Emulation Client, and LAN Emulation Configuration Server.

LAN Emulation User-to-Network Interface (LUNI)

Defining the interface between the LAN Emulation Client (LEC) and the LAN Emulation Server, LUNI is the ATM Forum’s standard for LAN Emulation on ATM networks. See also LAN Emulation Server and LAN Emulation Configuration Server.

LAN Manager

The Microsoft brand of a network product jointly developed by IBM and Microsoft that provided an early client/server environment. LAN Manager/Server was eclipsed by NetWare but was the genesis of many important protocols and IPC mechanisms used today, such as NetBIOS, named pipes, and NetBEUI. Portions of this product exist today in OS/2 Warp Server. See also Operating System 2 and Interprocess Communications.

LAN Server

The IBM brand of a network product jointly developed by IBM and Microsoft. See also LAN Manager.

LAN Switch

A high-speed, multiple-interface transparent bridging mechanism, transmitting packets between segments of data links, usually referred to specifically as an Ethernet switch. LAN switches transfer traffic based on MAC addresses. Multilayer switches are a type of high-speed, special-purpose, hardware-based router. See also Multilayer Switch and Store-and-Forward Packet Switching.

LAPB

See Link Accessed Procedure, Balanced.

LAPD

See Link Access Procedure on the D Channel.

Laptop Computer

A small, portable computer that is light enough to carry comfortably, with a flat screen and keyboard that fold together. Advances in battery technology allow laptop computers to run many hours between charges. Laptop computers often have a thin, backlit or sidelit liquid-crystal display (LCD) or a plasma screen. Some models can mate with a docking station to perform as a full-sized desktop system back at the office, and many new laptop computers allow direct connection to the network with PCMCIA network interface cards. In some laptop computers, a set of business applications is built in to ROM. See also Hand-Held Computer, Mobile Computing, Notebook Computer, PC Memory Card International Association, Port Replicator, and Wireless Communications.

LaserJet

The most popular brand of laser printer in the world, manufactured by Hewlett Packard. See also Laser Printers and Ink-Jet Printers.

Laser Printers

Output devices that produce paper copies of computer data by creating an electrostatic charge on a metallic cylinder using a laser, which is then passed through a toner reservior. Toner (ink) sticks to the charged areas of the drum. The toner is pressed into paper and then heat cured. Because of the fine resolution that the extremely narrow laser beam achieves, laser printers create very high quality paper documents. Laser printers are faster than many other printers but are generally more expensive.

Laser Transmissions

High-powered laser transmitters can transmit data for several thousand yards when line-of-sight communication is possible. Lasers can be used in many of the same situations as microwave links without requiring an FCC license.

Last Known Good Configuration

A Windows Advanced Options menu item used to load the control set that was used the last time the computer was successfully booted.

LAT

See Local Address Table.

Latency

Broadly, the time it takes a data packet to get from one location to another. In specific networking contexts, it can mean either 1. the time elapsed (delay) between the execution of a request for access to a network by a device and the time the mechanism actually is permitted transmission, or 2. the time elapsed between when a mechanism receives a frame and the time that frame is forwarded out of the destination port.

Layer

Part of the OSI model, for which there are defined roles during data communications.

Layer 2 Tunneling Protocol (L2TP)

A generic tunneling protocol that allows encapsulation of one network protocol’s data within another protocol. Used in conjunction with IPSec to enable VPN access to Windows networks.

Layer-3 Switch

See Multilayer Switch.

Layered Architecture

Industry standard way of creating applications to work on a network. Layered architecture allows the application developer to make changes in only one layer instead of the whole program.

LazyWriter

A system process responsible for physical I/O. The role of the LazyWriter is to flush pages from cache to disk as free buffers are needed by the system. The LazyWriter differs from the checkpoint in how it performs its work. The checkpoint process executes its work in spikes and then goes back to sleep. The LazyWriter may be continuously active, writing out pages from cache to disk as needed.

LCD

Liquid Crystal Display.

LCP

See Link Control Protocol.

LDAP

See Lightweight Directory Access Protocol (LDAP).

LDIFDE

See LDIF Directory Exchange (LDIFDE).

LDIF Directory Exchange (LDIFDE)

A command-line utility that is used to transfer Active Directory objects between LDIF files and the Active Directory. LDIF files can be read and modified through the use of LDIF-compatible tools.

LDT

See Local Domain Table.

Leaf Object

An object that does not contain any other objects. A mailbox object is an example of a leaf object.

Leaky Bucket

An analogy for the basic cell rate algorithm (GCRA) used in ATM networks for checking the conformance of cell flows from a user or network. The bucket’s “hole” is understood to be the prolonged rate at which cells can be accommodated, and the “depth” is the tolerance for cell bursts over a certain time period.

Learning Bridge

Also known as a transparent bridge. This type of bridge is transparent to the device sending the packet. At the same time, this bridge will learn over time what devices exist on each side of it.

LE ARP

See LAN Emulation Address Resolution Protocol.

Lease

The offer of service provided by a DHCP server to a client upon successful negotiation.

Leased Lines

Telephone lines that are leased for dedicated use by a company or individual.

LEC

See LAN Emulation Client.

LECS

See LAN Emulation Configuration Server.

LES

See LAN Emulation Server.

LH

Loads a program into the upper memory area.

Library File

Library files contain groups of often-used computer code that different programs can share. Programmers who use library code make their programs smaller since they do not need to include the code in their program. A virus that infects a library file automatically may appear to infect any program using the library file. In Windows systems, the most common library file is the Dynamic Link Library (DLL).

License Server

A server that issues licenses to Terminal Services clients. This license is a digitally signed certificate that will remain with the client and cannot be used by any other client. See also
Terminal Services Client.

Lightweight Directory Access Protocol (LDAP)

A standards-based protocol that can be used to interact with conformant directory services. LDAP version 2.0 allows for reading the contents of a directory database, whereas LDAP version 3.0 (defined under RFC 2251) allows users and applications to both read and write to a directory database. LDAP was developed by Tim Howes and the University of Michigan.

Link Access Procedure on the D Channel (LAPD)

The ISDN Data-Link layer protocol used specifically for the D channel and defined by ITU-T Recommendations Q.920 and Q.921. LAPD evolved from LAPB and is created to comply with the signaling requirements of ISDN basic access.

Link Accessed Procedure, Balanced (LAPB)

A bit-oriented Data-Link layer protocol that is part of the X.25 stack and has its origin in
SDLC. See also Synchronous Data Link Control and X.25.

Link Control Protocol (LCP)

The protocol designed to establish, configure, and test data link connections for use by PPP. See also Point-to-Point Protocol.

Link-State Advertisement (LSA)

Contained inside of link-state packets (LSPs), these advertisements are usually multicast packets, containing information about neighbors and path costs, that are employed by link-state protocols. Receiving routers use LSAs to maintain their link-state databases and, ultimately, routing tables.

Link-State Routing Algorithm

A routing algorithm that allows each router to broadcast or multicast information regarding the cost of reaching all its neighbors to every node in the internetwork. Link-state algorithms provide a consistent view of the network and are therefore not vulnerable to routing loops. However, this is achieved at the cost of somewhat greater difficulty in computation and more widespread traffic (compared to distance-vector routing algorithms). See also Distance-Vector Routing Algorithm.

Link-Support Layer (LSL)

An implementation of the Open Datalink Interface (ODI) that works between the NetWare server’s LAN drivers and communications protocols, such as IPX (Internet Package eXchange) or TCP/IP, allowing network interface cards to service one or more protocol stacks. LSL is also used on workstations. See also Multiple-Link Interface Driver and Open Datalink Interface/Network Driver Interface Specification Support

Linux

A free, Unix-compatible, 32-bit operating system developed in 1991 by Linus Torvalds while at the University of Helsinki in Finland. Strictly speaking, Linux is the name of the operating system kernel, the central part of the operating system that manages system services, but many people use the name to refer to the complete operating system package, including utilities, editors and compilers, games, and networking components. Many of these important elements are actually part of the Free Software Foundation’s GNU Project, and others have been written and released by volunteers. Linux is supported and distributed by companies such as Red Hat Software, Caldera Software, Workgroup Solutions, Walnut Creek Software, and S.u.S.E. of Germany. With the increasing use of Linux in the corporate world, several major companies have announced some level of support for the operating system, including Hewlett-Packard, Silicon Graphics, Sun Microsystems, and Intel, and several major application packages have been ported to Linux, including Oracle’s Oracle8, Adaptive Server Enterprise from Sybase, and IBM’s DB2. See also Free Software Foundation and Open Source Software.

Listeners

The configured authentication method for a particular internal network adapter that “listens” for outgoing web requests.

LISTSERV

A mailing list product available from L-Soft International, Inc. LISTSERV runs on Unix, Microsoft Windows, and several other operating systems. See also Listserver and Mailing List.

Listserver

An automatic mailing system available on the Internet. Rather than sending e-mail on a particular topic to a long list of people, you send it to a special e-mail address, where a program automatically distributes the e-mail to all the people who subscribe to the mailing list. Several programs have been written to automate a mailing list; the most common is LISTSERV, but you may also encounter mailserv, majordomo, or almanac. Mailing lists are usually devoted to a particular subject, such as training dogs or playing obscure types of bagpipes, rather than to general interest communications. See also LISTSERV, Mailing List, Newsgroup, and Usenet.

LLAP

See LocalTalk Link Access Protocol.

LLC Sublayer

See Logical Link Control Sublayer.

LMHOSTS File

A file used to map NetBIOS names to computers’ IP addresses. An LMHOSTS file can be used in place of a WINS server. See also IP Address, and WINS Server.

LMI

An enhancement to the original Frame Relay specification. Among the features it provides are a keepalive mechanism, a multicast mechanism, global addressing, and a status mechanism.

LNNI

See LAN Emulation Network-to-Network Interface.

Local Address Table (LAT)

The ISA routing table used to determine if a destination address is local to the network, and therefore should remain internal, or if the destination is external and should be looked for on the Internet.

Local Area Network (LAN)

Broadly, any network linking two or more computers and related devices within a limited geographical area (up to a few kilometers). LANs are typically high-speed, low-error networks within a company. Cabling and signaling at the Physical and Data Link layers of the OSI are dictated by LAN standards. Ethernet, FDDI, and Token Ring are among the most popular LAN technologies. See also Wide Area Network and Data Link Layer.

Local Computer Policy

A Microsoft Management Console (MMC) snap-in used to implement account policies.

Local Delivery

The delivery of a message to a recipient object that resides on the same server as the sender.

Local Domain Table (LDT)

Similar to the Local Address Table (LAT), the LDT allows you to designate particular domain names as local to the ISA network and therefore should not be sought outside. See also Local Address Table.

Local Explorer Packet

In a Token Ring SRB network, a packet generated by an end system to find a host linked to the local ring. If no local host can be found, the end system will produce one of two solutions: a spanning explorer packet or an all-routes explorer packet. See also Spanning Explorer Packet and All-Routes Explorer Packet.

Local Group

Local groups can be created on Windows NT Server or Workstation and can include both user accounts and global groups. Moreover, these groups are assigned permissions. See also
Global Group.

Local Group Policy

A Microsoft Management Console (MMC) snap-in used to implement local group policies, which include computer configuration policies and user configuration policies.

Local Logon

A logon when the user logs on from the computer where the user account is stored on the computer’s local database. Also called an interactive logon.

Local Loop

Connection from a demarcation point to the closest switching office.

Local Policies

Policies that allow administrators to control what a user can do after logging on. Local policies include audit policies, security option policies, and user rights policies. These policies are set through Local Computer Policy. See also Local Computer Policy.

Local Printer

A local printer is a printer that uses a physical port and that has not been shared. If a printer is defined as local, the only users who can use the printer are the local users of the computer that the printer is attached to. See also Printers and Print Device.

Local Procedure Call (LPC)

When a program issues an instruction that is executed on the same computer as the program executing the instruction. See also Remote Procedure Call.

Local Security

Security that governs a local or interactive user. Local security can be set through NTFS partitions. See also Security, Interactive User and New Technology File System.

LocalTalk

A data link layer standard for local area networking used by Macintosh computers. LocalTalk is available on all Macintosh computers. The drawback of LocalTalk is that it transmits at only 230.4 kilobits per second (as opposed to Ethernet, which can transmit at 10 megabits per second). See also Data Link Layer and Macintosh.

LocalTalk Link Access Protocol (LLAP)

In a LocalTalk environment, the data link-level protocol that manages node-to-node delivery of data. This protocol provides node addressing and management of bus access, and it also controls data sending and receiving to assure packet length and integrity.

Local User Account

A user account stored locally in the user accounts database of a computer that is running Windows.

Local User Profile

A profile created the first time a user logs on, stored in the Documents and Settings folder. The default user profile folder’s name matches the user’s logon name. This folder contains a file called NTUSER.DAT and subfolders with directory links to the user’s Desktop items.

Local Users and Groups

A utility that is used to create and manage local user and group accounts on Windows computers and Windows member servers.

Locale Settings

Settings for regional items, including numbers, currency, time, date, and input locales.

Location Transparency

Being able to access resources without knowledge of their physical location.

Lock

A mechanism by which SQL Server manages concurrency. SQL Server places locks on data when it is being accessed by a client application. SQL Server locks are primarily page locks. This means that when a client accesses a single record on an 8KB page, SQL Server will lock the entire page until it is appropriate to release the lock. SQL Server also supports table locks for times when it would make more sense to lock the entire table rather then individual pages. Row-level locking is also supported automatically with SQL Server.

Lockbox

An encrypted secret key that is sent with a message.

Lock Escalation

The SQL Server process of increasing a lock from the page to the table level. When a transaction acquires a configured number of page locks, a table lock is set and the page locks are released. This behavior is configured through lock-escalation thresholds.

Logging

The process of recording information about activities and errors in the operating system.

Logical Drive

An allocation of disk space on a hard drive, using a drive letter. For example, a 5GB hard drive could be partitioned into two logical drives: a C: drive, which might be 2GB, and a D: drive, which might be 3GB.

Logical Drives

A Windows utility used to manage the logical drives on the computer.

Logical I/O

See I/O.

Logical Link Control (LLC) Sublayer

A sublayer in the Data Link layer of the Open Systems Interconnection (OSI) model. The LLC sublayer defines flow control. See also Data Link Layer and Open Systems Interconnection Model.

Logical Port

Printers can be attached to a network through a logical port. A logical port uses a direct connection to gain access to the network. This is done by installing a network card on your printer. The advantage to using logical ports are that they are much faster than physical ports and that you are not limited to the cabling limitations imposed by parallel and serial cable distances allowed when connecting a printer to a PC’s parallel or serial ports. See also Printers and Print Device.

Logical Printer

The software interface between the physical printer (the print device) and the operating system. Also referred to as just a printer in Windows terminology. See also Printers and Print Device.

Logical Topology

Describes the logical pathway a signal follows as it passes among the network nodes.

Logic Bomb

A logic bomb is a type of trojan horse that executes when specific conditions occur. Triggers for logic bombs can include a change in a file, by a particular series of keystrokes, or at a specific time or date. See also Time Bomb.

Login

The term used by Novell NetWare to indicate opening a session with a server by providing a valid user account name and password. See also NetWare and Logon.

Login

A name that, when combined with a password, allows access to SQL Server resources. Logins are stored in the sysxlogins system table. (For easier queries, use the syslogins view.) This table is located in the Master database only, and there is only one per server.

Logoff

The process of closing an open session with a server. See also Logon.

Logon

The process of opening a network session by providing a valid authentication consisting of a user account name and a password to a domain controller. After logon, network resources are available to the user according to the user’s assigned permissions. See also Domain Controller and Logoff.

Logon Scripts

Command files that automate the logon process by performing utility functions such as attaching to additional server resources or automatically running different programs based upon the user account that established the logon. See also Logon.

LOADFIX

Loads a program above the first 64K of memory, and runs the program.

LOADHIGH

Loads a program into the upper memory area.

Long Filename (LFN)

A filename longer than the eight characters plus three-character extension allowed by MS-DOS. In current versions of Windows, long filenames may be up to 255 characters.

LPC

See Local Procedure Call.

LSA

See Link-State Advertisement.

LUNI

See LAN Emulation User-to-Network Interface.