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.
