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Glossary
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Ethernet
A LAN specification developed jointly by Xerox, Intel and Digital Equipment Corporation. Ethernet
networks transmit packets at a rate of 10 Mbps.
G
Gateway
A local device, usually a router, that connects hosts on a local network to other networks.
I
ICMP
See “Internet Control Message Protocol”
IEEE
Institute of Electrical and Electronics Engineers. This American organization was founded in 1963 and sets
standards for computers and communications.
IETF
Internet Engineering Task Force. An organization responsible for providing engineering solutions for TCP/
IP networks. In the network management area, this group is responsible for the development of the SNMP
protocol.
IKE
Internet Key Exchange. An automated method for exchanging and managing encryption keys between two
VPN devices.
Infrastructure Mode
An 802.11 networking framework in which devices communicate with each other by first going through an
Access Point (AP). In infrastructure mode, wireless devices can communicate with each other or can
communicate with a wired network. When one AP is connected to wired network and a set of wireless
stations it is referred to as a Basic Service Set (BSS). An Extended Service Set (ESS) is a set of two or more
BSSs that form a single subnetwork. Most corporate wireless LANs operate in infrastructure mode because
they require access to the wired LAN in order to use services such as file servers or printers.
Internet Control Message Protocol
ICMP is an extension to the Internet Protocol (IP) that supports packets containing error, control, and
informational messages. The PING command, for example, uses ICMP to test an Internet connection.
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Glossary
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Internet Protocol
The method or protocol by which data is sent from one computer to another on the Internet. Each computer
(known as a host) on the Internet has at least one IP address that uniquely identifies it among all other
computers on the Internet. When you send or receive data (for example, an e-mail note or a Web page), the
message gets divided into little chunks called packets. Each of these packets contains both the sender's
Internet address and the receiver's address. Any packet is sent first to a gateway computer that understands a
small part of the Internet. The gateway computer reads the destination address and forwards the packet to an
adjacent gateway that in turn reads the destination address and so forth across the Internet until one gateway
recognizes the packet as belonging to a computer within its immediate neighborhood or domain. That
gateway then forwards the packet directly to the computer whose address is specified.
Because a message is divided into a number of packets, each packet can, if necessary, be sent by a different
route across the Internet. Packets can arrive in a different order than they were sent. The Internet Protocol
just delivers them. It's up to another protocol, the Transmission Control Protocol (TCP) to put them back in
the right order. IP is a connectionless protocol, which means that there is no continuing connection between
the end points that are communicating. Each packet that travels through the Internet is treated as an
independent unit of data without any relation to any other unit of data. (The reason the packets do get put in
the right order is because of TCP, the connection-oriented protocol that keeps track of the packet sequence in
a message.) In the Open Systems Interconnection (OSI) communication model, IP is in Layer 3, the
Networking Layer. The most widely used version of IP today is IP version 4 (IPv4). However, IP version 6
(IPv6) is also beginning to be supported. IPv6 provides for much longer addresses and therefore for the
possibility of many more Internet users. IPv6 includes the capabilities of IPv4 and any server that can
support IPv6 packets can also support IPv4 packets.
IP
See “Internet Protocol”
IP Address
A four-byte number uniquely defining each host on the Internet, usually written in dotted-decimal notation
with periods separating the bytes (for example, 134.177.244.57). Ranges of addresses are assigned by
Internic, an organization formed for this purpose.
ISP
Internet service provider.
L
LAN
See “Local Area Network”
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Glossary
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Local Area Network
A communications network serving users within a limited area, such as one floor of a building. A LAN
typically connects multiple personal computers and shared network devices such as storage and printers.
Although many technologies exist to implement a LAN, Ethernet is the most common for connecting
personal computers and is limited to a distance of 1,500 feet. LANs can be connected together, but if
modems and telephones connect two or more LANs, the larger network constitutes what is called a WAN or
Wide Area Network.
M
MAC
(1) Medium Access Control. In LANs, the sublayer of the data link control layer that supports
medium-dependent functions and uses the services of the physical layer to provide services to the logical
link control (LLC) sublayer. The MAC sublayer includes the method of determining when a device has
access to the transmission medium. (2) Message Authentication Code. In computer security, a value that is a
part of a message or accompanies a message and is used to determine that the contents, origin, author, or
other attributes of all or part of the message are as they appear to be. (
IBM Glossary of Computing Terms
)
MAC address
The Media Access Control address is a unique 48-bit hardware address assigned to every network interface
card. Usually written in the form 01:23:45:67:89:ab.
Maximum Receive Unit
The size in bytes of the largest packet that can be sent or received.
Maximum Transmit Unit
The size in bytes of the largest packet that can be sent or received.
Mbps
Megabits per second.
MDI/MDIX
In cable wiring, the concept of transmit and receive are from the perspective of the PC, which is wired as a
Media Dependant Interface (MDI). In MDI wiring, a PC transmits on pins 1 and 2. At the hub, switch,
router, or access point, the perspective is reversed, and the hub receives on pins 1 and 2. This wiring is
referred to as Media Dependant Interface - Crossover (MDI-X).
MTU
The size in bytes of the largest packet that can be sent or received.
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Glossary
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P
packet
A block of information sent over a network. A packet typically contains a source and destination network
address, some protocol and length information, a block of data, and a checksum.
Point-to-Point Protocol
PPP. A protocol allowing a computer using TCP/IP to connect directly to the Internet.
PPP
A protocol allowing a computer using TCP/IP to connect directly to the Internet.
PPPoA
PPPoA. PPP over ATM is a protocol for connecting remote hosts to the Internet over an always-on
connection by simulating a dial-up connection.
PPPoE
PPPoE. PPP over Ethernet is a protocol for connecting remote hosts to the Internet over an always-on
connection by simulating a dial-up connection.
PPP over ATM
PPPoA. PPP over ATM is a protocol for connecting remote hosts to the Internet over an always-on
connection by simulating a dial-up connection.
PPP over Ethernet
PPPoE. PPP over Ethernet is a protocol for connecting remote hosts to the Internet over an always-on
connection by simulating a dial-up connection.
PPTP
Point-to-Point Tunneling Protocol. A method for establishing a virtual private network (VPN) by embedding
Microsoft’s network protocol into Internet packets.
Protocol
A set of rules for communication between devices on a network.
PSTN
Public Switched Telephone Network.
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Glossary
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Q
QoS
See “Quality of Service”
Quality of Service
QoS is a networking term that specifies a guaranteed level of throughput. Throughput is the amount of data
transferred from one device to another or processed in a specified amount of time - typically, throughputs are
measured in bytes per second (Bps).
R
RADIUS
Short for Remote Authentication Dial-In User Service, RADIUS is an authentication system. Using
RADIUS, you must enter your user name and password before gaining access to a network. This
information is passed to a RADIUS server, which checks that the information is correct, and then authorizes
access. Though not an official standard, the RADIUS specification is maintained by a working group of the
IETF.
RFC
Request For Comment. Refers to documents published by the Internet Engineering Task Force (IETF)
proposing standard protocols and procedures for the Internet. RFCs can be found at
www.ietf.org
.
router
A device that forwards data between networks. An IP router forwards data based on IP source and
destination addresses.
S
SSID
A Service Set Identification is a thirty-two character (maximum) alphanumeric key identifying a wireless
local area network. For the wireless devices in a network to communicate with each other, all devices must
be configured with the same SSID. This is typically the configuration parameter for a wireless PC card. It
corresponds to the ESSID in the wireless Access Point and to the wireless network name.
See also
Wireless
Network Name and ESSID.
Segment
A section of a LAN that is connected to the rest of the network using a switch, bridge, or repeater.

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