3Com Corporation
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area served.
L
LAN:
A local area network (LAN) is a group of
computers and associated devices that share a
common communications line and typically share
the resources of a single processor or server within
a small geographic area (for example, within an
office building). Usually, the server has applications
and data storage that are shared in common by
multiple computer users. A local area network may
serve as few as two or three users (for example, in
a home network) or many as thousands of users
(for example, in an FDDI network).
M
MAC:
Medium Access Control. In a WLAN network
card, the MAC is the radio controller protocol. It
corresponds to the ISO Network Model's level 2
Data Link layer. The IEEE 802.11 standard specifies
the MAC protocol for medium sharing, packet
formatting and addressing, and error detection.
N
NAT:
NAT (Network Address Translation) is the
translation of an Internet Protocol address (IP
address) used within one network to a different IP
address known within another network. One
network is designated the inside network and the
other is the outside. Typically, a company maps its
local inside network addresses to one or more
global outside IP addresses and unmaps the global
IP addresses on incoming packets back into local IP
addresses.
NAT is included as part of a router and is often part
of a corporate firewall.
P
POP3:
POP3 (Post Office Protocol 3) is the most
recent version of a standard protocol for receiving
e-mail. POP3 is a client/server protocol in which
e-mail is received and held for you by your Internet
server. Periodically, you (or your client e-mail
receiver) check your mail-box on the server and
download any mail. POP3 is built into the
Netmanage suite of Internet products and one of
the most popular e-mail products, Eudora. It's also
built into the Netscape and Microsoft Internet
Explorer browsers.
PPP:
PPP (Point-to-Point Protocol) is a protocol for
communication between two computers using a
serial interface, typically a personal computer
connected by phone line to a server. PPP uses the
Internet protocol (IP) (and is designed to handle
others). It is sometimes considered a member of the
TCP/IP suite of protocols. Relative to the Open
Systems Interconnection (OSI) reference model,
PPP provides layer 2 (data-link layer) service.
Essentially, it packages your computer's TCP/IP
packets and forwards them to the server where they
can actually be put on the Internet.
PPP is a full-duplex protocol that can be used on
various physical media, including twisted pair or
fiber optic lines or satellite transmission. It uses a
variation of High Speed Data Link Control (HDLC)
for packet encapsulation.
PPP is usually preferred over the earlier de facto
standard Serial Line Internet Protocol (SLIP)
because it can handle synchronous as well as
asynchronous communication. PPP can share a
line with other users and it has error detection that
SLIP lacks. Where a choice is possible, PPP is
preferred.
PPPoE:
PPPoE (Point-to-Point Protocol over
Ethernet) is a specification for connecting multiple
computer users on an Ethernet local area network
to a remote site through common customer
premises equipment, which is the telephone
company's term for a modem and similar devices.
PPPoE can be used to have an office or building-full
of users share a common Digital Subscriber Line
(DSL), cable modem, or wireless connection to the
Internet. PPPoE combines the Point-to-Point
Protocol (PPP), commonly used in dialup
connections, with the Ethernet protocol, which
supports multiple users in a local area network. The
PPP protocol information is encapsulated within an
Ethernet frame.
PPPoE has the advantage that neither the
telephone company nor the Internet service
provider (ISP) needs to provide any special support.
Unlike dialup connections, DSL and cable modem
connections are "always on." Since a number of
different users are sharing the same physical
connection to the remote service provider, a way is
needed to keep track of which user traffic should go
to and which user should be billed. PPPoE provides
for each user-remote site session to learn each
other's network addresses (during an initial
exchange called "discovery"). Once a session is
established between an individual user and the
remote site (for example, an Internet service
provider), the session can be monitored for billing
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