D-Link DWL-2210AP Router Manual PDF (Setup & Configuration Guide)

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171

Glossary

DOM

The

Document Object Model

(DOM) is an interface that allows programs and scripts to dynamically

access and update the content, structure, and style of documents. The DOM allows you to model

the objects in an HTML or XML document (text, links, images, tables), deﬁning the attributes of

each object and how they can be manipulated.

Further details about the DOM can be found at the

W3C

.

DTIM

The

Delivery Trafﬁc Information Map

(DTIM) message is an element included in some

Beacon

frames. It indicates which stations, currently sleeping in low-power mode, have data buffered on

the

Access Point

awaiting pickup. Part of the DTIM message indicates how frequently stations

must check for buffered data.

Dynamic IP Address

See

IP Address

.

EAP

The

Extensible Authentication Protocol

(EAP) is an authentication protocol that supports

multiple methods, such as token cards, Kerberos, onetime passwords, certiﬁcates, public key

authentication, and smart cards.

Variations on EAP include EAP Cisco Wireless (LEAP), Protected EAP (PEAP), EAP-TLS, and

EAP Tunnelled TLS (EAP-TTLS).

ESS

An

extended service set

(ESS) is an

Infrastructure Mode Wireless Networking Framework

with

multiple access points, forming a single subnetwork that can support more clients than a basic

service set (

BSS

). Each access point supports a number of wireless stations, providing broader

wireless coverage for a large space, for example, an ofﬁce.

Ethernet

is a local-area network (

LAN

) architecture supporting data transfer rates of 10Mbps to

1Gbps. The Ethernet speciﬁcation is the basis for the

IEEE 802.3

standard, which speciﬁes the

physical and lower software layers. It uses the

CSMA/CA

access method to handle simultaneous

demands.

Ethernet supports data rates of 10 Mbps,

Fast Ethernet

supports 100 Mbps, and

Gigabit Ethernet

supports 1Gbps. Its cables are classiﬁed as “

X

base

Y

”, where

X

is the data rate in Mbps and

Y

is the category of cabling. The original cable was

10base5

(Thicknet or “Yellow Cable”). Some

others are

10base2

(Cheapernet),

10baseT

(Twisted Pair), and

100baseT

(Fast Ethernet). The

latter two are commonly supplied using

CAT5

cabling with

RJ-45

connectors. There is also

1000baseT

(Gigabit Ethernet).

ERP

The

Extended Rate Protocol

refers to the protocol used by

IEEE 802.11g

stations (over 20 Mbps

transmission rates at 2.4GHz) when paired with Orthogonal Frequency Division Multiplexing

(OFDM). Built into ERP and the IEEE

802.11g

standard is a scheme for effective interoperability

of IEEE 802.11g stations with IEEE 802.11b nodes on the same channel.

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172

Glossary

Legacy IEEE 802.11b devices cannot detect the ERP-OFDM signals used by IEEE 802.11g

stations, and this can result in collisions between data frames from IEEE 802.11b and IEEE

802.11g stations.

If there is a mix of 802.11b and 802.11g nodes on the same channel, the IEEE 802.11g stations

detect this via an ERP ﬂag on the access point and enable

request to send

(

RTS

) and

clear to

send

(

CTS

) protection before sending data.

See also

CSMA/CA

protocol.

Frame

A

Frame

consists of a discrete portion of data along with some descriptive meta-information

packaged for transmission on a wireless network. Each frame includes a source and destination

MAC

address, a control ﬁeld with protocol version, frame type, frame sequence number, frame

body (with the actual information to be transmitted) and frame check sequence for error detection.

A Frame is similar in concept to a

Packet

, the difference being that a packet operates on the

Network layer (layer 3 in the OSI model) whereas a frame operates on the Data-Link layer (layer

2 in the OSI model).

Gateway

A

gateway

is a network node that serves as an entrance to another network. A gateway also often

provides a proxy server and a ﬁrewall. It is associated with both a router, which use headers and

forwarding tables to determine where packets are sent, and a switch or bridge, which provides

the actual path for the packet in and out of the gateway.

Before a host on a

LAN

can access the Internet, it needs to know the address of its

default

gateway

.

HTML

The

Hypertext Markup Language

(

HTML

) deﬁnes the structure of a document on the World Wide

Web. It uses tags and attributes to hint about a layout for the document.

An HTML document starts with an

<html>

tag and ends with a

</html>

tag. A properly

formatted document also contains a

<head>

...

</head>

section, which contains the metadata

to deﬁne the document, and a

<body>

...

</body>

section, which contains its content. Its

markup is derived from the

Standard Generalized Markup Language

(SGML), which is deﬁned

in

ISO 8879:1986

.

HTML documents are sent from server to browser via

HTTP

. Also see

XML

.

HTTP

The

Hypertext Transfer Protocol

(

HTTP

) deﬁnes how messages are formatted and transmitted

on the World Wide Web. An HTTP message consists of a

URL

and a command (GET, HEAD,

POST, etc.), a request followed by a response.

IAPP

The

Inter Access Point Protocol

(IAPP) is an

IEEE

standard (

802.11f

) that deﬁnes communication

between the access points in a “distribution system”. This includes the exchange of information

about mobile stations and the maintenance of bridge forwarding tables, plus securing the

communications between access points.

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173

Glossary

IBSS

An

independent basic service set

(IBSS) is an

Ad hoc Mode Wireless Networking Framework

in

which stations communicate directly with each other.

IEEE

The Institute of Electrical and Electronic Engineers (IEEE) is an international standards body

that develops and establishes industry standards for a broad range of technologies, including the

802 family of networking and wireless standards. (See

802

,

802.1x

,

802.11

,

802.11a

,

802.11b

,

802.11e

,

802.11f

,

802.11g

, and

802.11i

.)

For more information about IEEE task groups and standards, see

http://standards.ieee.org/

.

Infrastructure Mode

is a

Wireless Networking Framework

in which wireless stations communicate

with each other by ﬁrst going through an

Access Point

. In this mode, the wireless stations can

communicate with each other or can communicate with hosts on a wired network. The access

point is connected to a wired network and supports a set of wireless stations.

An infrastructure mode framework can be provided by a single access point (

BSS

) or a number

of access points (

ESS

).

Intrusion Detection

The

Intrusion Detection System

(IDS) inspects all inbound network activity and reports suspicious

patterns that may indicate a network or system attack from someone attempting to break into the

system. It reports access attempts using unsupported or known insecure protocols.

IP

The

Internet Protocol

(IP) speciﬁes the format of packets, also called datagrams, and the addressing

scheme. IP is a connectionless, best-effort packet switching protocol. It provides packet routing,

fragmentation and reassembly. It is combined with higher-level protocols, such as

TCP

or

UDP

, to

establish the virtual connection between destination and source.

The current version of IP is

IPv4

. A new version, called IPv6 or IPng, is under development. IPv6

is an attempt to solve the shortage of IP addresses.

IP Address

Systems are deﬁned by their

IP address

, a four-byte (octet) number uniquely deﬁning each host

on the Internet. It is usually shown in form 192.168.2.254. This is called dotted-decimal notation.

An IP address is partitioned into two portions: the network preﬁx and a host number on that network.

A

Subnet Mask

is used to deﬁne the portions. There are two special host numbers:

• The

Network Address

consists of a host number that is all zeroes (for example, 192.168.2.0).

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174

Glossary

• The

Broadcast Address

consists of a host number that is all ones (for example,

192.168.2.255).

There are a ﬁnite number of IP addresses that can exist. Therefore, a local area network typically

uses one of the

IANA

-designated address ranges for use in private networks. These address

ranges are:

10.0.0.0 to 10.255.255.255

172.16.0.0 to 172.31.255.255

192.168.0.0 to 192.168.255.255

A

Dynamic IP Address

is an IP address that is automatically assigned to a host by a

DHCP

server

or similar mechanism. It is called dynamic because you may be assigned a different IP address

each time you establish a connection.

A

Static IP Address

is an IP address that is hard-wired for a speciﬁc host. A static address is

usually required for any host that is running a server, for example, a Web server.

IPSec

IP Security

(IPSec) is a set of protocols to support the secure exchange of packets at the

IP

layer.

It uses shared public keys. There are two encryption modes: Transport and Tunnel.

•

Transport

mode encrypts only the data portion (payload) of each packet, but leaves the headers

untouched.

• The more secure

Tunnel

mode encrypts both the header and the payload.

ISP

An

Internet Service Provider

(ISP) is a company that provides access to the Internet to individuals

and companies. It may provide related services such as virtual hosting, network consulting, Web

design, etc.

Jitter

is the difference between the latency (or delay) in packet transmission from one node to

another across a network. If packets are not transmitted at a consistent rate (including

Latency

),

QoS

for some types of data can be affected. For example, inconsistent transmission rates can

cause distortion in VoIP and streaming media.

QoS

is designed to reduce jitter along with other

factors that can impact network performance.

Latency

, also known as

delay

, is the amount of time it takes to transmit a

Packet

from sender to

receiver. Latency can occur when data is transmitted from the access point to a client and vice

versa. It can also occur when data is transmitted from access point to the Internet and vice versa.

Latency is caused by

ﬁxed network

factors such as the time it takes to encode and decode a

packet, and also by

variable network

factors such as a busy or overloaded network.

QoS

features

are designed to minimize latency for high priority network trafﬁc.

LAN

A

Local Area Network

(LAN) is a communications network covering a limited area, for example,

the computers in your home that you want to network together or a couple of ﬂoors in a building.

A LAN

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175

connects multiple computers and other network devices such as storage and printers.

Ethernet

is the most common technology implementing a LAN.

Wireless Ethernet (

802.11

) is another very popular LAN technology (also see

WLAN

).

LDAP

The

Lightweight Directory Access Protocol

(LDAP) is a protocol for accessing online directory

services. It is used to provide an authentication mechanism. It is based on the X.500 standard,

but less complex.

Lease Time

The

Lease Time

speciﬁes the period of time the

DHCP

Server gives its clients an

IP Address

and other required information. When the lease expires, the client must request a new lease.

If the lease is set to a short span, you can update your network information and propagate the

information provided to the clients in a timely manner.

LLC

The

Logical Link Control

(LLC) layer controls frame synchronization, ﬂow control, and error

checking. It is a higher level protocol over the

PHY

layer, working in conjunction with the

MAC

layer.

MAC

The

Media Access Control

(MAC) layer handles moving data packets between

NIC

s across a

shared channel. It is a higher level protocol over the

PHY

layer. It provides an arbitration mechanism

in an attempt to prevent signals from colliding.

It uses a hardware address, known as the

MAC address

, that uniquely identiﬁes each node of a

network.

IEEE 802

network devices share a common 48-bit MAC address format, displayed as a

string of twelve (12) hexadecimal digits separated by colons, for example FE:DC:BA:09:87:65.

MDI and MDI-X

Medium Dependent Interface

(MDI) and

MDI crossover

(MDIX) are twisted pair cabling

technologies for Ethernet ports in hardware devices. Built-in twisted pair cabling and auto-sensing

enable connection between like devices with the use of a standard Ethernet cable. (For example, if

a wireless access point supports MDI/MDIX, one can successfully connect a PC and that access

point with an Ethernet cable rather than having to use a crossover cable).

MSCHAP V2

Microsoft Challenge Handshake Authentication Protocol Version 2

(MSCHAP V2) provides

authentication for

PPP

connections between a Windows-based computer and an

Access Point

or other network access device.

MTU

The

Maximum Transmission Unit

is the largest physical packet size, measured in bytes, that a

network can transmit. Any messages larger than the MTU are fragmented into smaller packets

before being sent.

Glossary

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