Leased Line -
Dedicated Line. A dedicated line
that is leased exclusively to connect two points, 24 hours a day, 7 days a week. A leased line,
usually a T1 or
T3 line, gives the highest-speed connection.
Before the days of the internet
and digital communications, a
leased line was a private analog
telephone circuit that directly connected two points; in the case of data
transmission, both end
points are computers. A modem
was still needed to translate the computer's digital signals into phone
line analog signals and vice-versa.
Typically, large companies rent
leased lines to interconnect different geographic locations in their
company. The alternative is to buy and maintain their own private lines or
to use the public POTS
lines with secure message protocols.
The advantages are that leased
lines provide always-on reliable, high-speed connectivity, whereas
dial-up connections are occasional.
The quality of the connection is far superior to what is normally
available through dialup, because of the digital signaling, less noise,
fewer exchanges etc
Costs are higher than
if the connection is to the internet
(instead of directly to another computer), the always-on connectivity
means always-on exposure to hackers and things like virus and
denial of service attacks.
However, using the leased line in Virtual
Private Network mode reduces the security risks considerably.
Legacy System - A computer system
application which continues to be
used because of the cost of replacing or redesigning it and often despite
its poor competitiveness and compatibility with modern equivalents. The
implication is that the system is large, monolithic and difficult to modify.
- If legacy software only runs on antiquated
hardware the cost of maintaining this
may eventually outweigh the cost of replacing both the software and hardware
unless some form of emulation or
backward compatibility allows the software to
run on new hardware.
Sometimes, the legacy system is
one that is running perfectly well, and satisfying all business needs, but
doesn't have the latest trendy eBusiness technology or business process
built-in, and so is perceived as outdated and in need of replacement --
regardless of whether the trendy new eBusiness technology or business process
is going to be utilized.
Level - Relative hierarchical position of a data segment within a message,
e.g. "header level", "line item level", etc.
Lexical Ambiguity - See
Local Area Network (LAN) - Grouping of computers connected to a main unit called the server.
Log off - Disconnect from a host system.
Log on - Process of connecting to another computer and successfully gaining access by entering
the proper identification. Also; (log in) Connect to a host system or public-access site.
Log-in security - Procedure
used network systems to gain access to the system by typing in a
previously defined password or code word pertaining to a particular account.
Coupled - Describes system components - software applications or hardware -
that work together but have a low dependence on one another. When
components are loosely coupled, changes to one component are unlikely to affect
other components. See also Coupling,
- If software components - applications, modules,
subprocesses, etc. - are "loosely coupled", there is no assumption (or
requirement) that all the components be available at the moment when one
component needs to interact with the other component to send or retrieve
data, or to execute a process such as a web service. The
component requesting the interaction needs to have some logic built in
that tells it what to do if the other component is not available.
For example, the requesting component might have logic to keep retrying
the connection over a period of time, and send out an error notification
if the retries are still unsuccessful at the end of the specified period
Lurk -Read messages in a Usenet newsgroup without ever saying anything.