Welcome to the chapter on Wireless networking. This chapter negotiations about the rudimentss of radio networking, puting up of a radio web and security issues related to wireless webs.
A wireless local country web ( WLAN ) is a information transmittal system designed to supply location-independent web entree between calculating devices by utilizing wireless moving ridges instead than a overseas telegram substructure.
Wireless webs operate at the same OSI beds and use the same protocols as wired webs. What differs is the type of media used and the methods for accessing the media.
5.1 Wireless Basicss
Wireless web manners
In its simplest signifier, a radio web consists of two or more Personal computers pass oning straight with each other without telegraphing or intermediary hardware. The more complicated radio webs use an entree point to centralise wireless communicating, every bit good as to bridge radio web sections to wired web sections. These two different methods, or manners, are called ad hoc manner and substructure manner.
Ad-hoc manner radio web:
Each wireless node is in direct contact with each of the other radio nodes in the web. Ad hoc manner does non utilize an entree point ; it uses a mesh topology alternatively.
Two or more wireless nodes pass oning in ad hoc manner form an Independent Basic Service Set ( IBSS ) . This is a basic unit of organisation in radio networks. Ad hoc web can non be used to link to other webs unless one of the machines is running Internet Connection Sharing ( ICS ) .
Therefore, Ad hoc manner webs are good for little groups of computing machines that need to reassign files or portion pressmans and as impermanent webs to be used as survey groups or for concern meetings. ( Refer figure 5.1 )
Infrastructure manner radio web
Wireless entree points ( WAPs ) are used to link the radio web nodes centrally in instance of radio webs running in substructure manner. The constellation is similar to the star topology of a wired web.
The substructure manner besides enables connexion of radio web sections to wired sections in the web. To put up a radio web for a big figure of Personal computers, substructure manner is used. WAPs allow control of wireless webs from a cardinal location. This permits better control and filtration of web traffic.
A Basic Service Set ( BSS ) is a individual WAP serving a given country. More entree points can be added to widen this service country and is called an Extended Service Set ( ESS ) .
Infrastructure manner is used for concern webs or webs that need to portion dedicated resources such as Internet connexion and centralised databases ( Refer to calculate 5.1 )
Figure 5.1: Infrastructure manner
Wireless Hardware
If a little group of computers are being connected into a decentralized workgroup so merely wireless arrangers are needed but if wireless web sections are to be connected to wired web, the Wireless entree point ( WAP ) is needed. It connects wireless web nodes to wireless or wired webs. A basic WAP maps like a hub and works at OSI Layer 1. Combination devices are besides used in wireless webs. These work as a high-velocity hub or switch, span, and router at the same time. Such devices can work at many different OSI beds.
Wireless Network Card
A radio web card is necessary for each device on a radio web. A laptop typically has an enlargement ( PCMCIA ) slot in which the web card tantrums. A desktop computing machine needs an internal card, which has an aerial on it. These aerials are optional on most equipment and aid to increase the signal on the card.
Figure 5.2: Radio web card ( NIC )
Wireless Access Point
The wired portion of the radio web is connected to the radio a device in the web with a WAP.WAP allows multiple devices to link through it so that they can entree the web. A WAP can besides work as a router so that informations transmittal can be extended and passed from one entree point to another.
Figure 5.3: Wireless entree point
5.1.1 Standards
Broadcasting Frequency
Wireless devices operate on specific airing frequences to forestall intervention from other wireless devices runing on the same radio set. The original 802.11 criterions use the 2.4-GHz frequence. Later criterions use either 2.4-GHz or 5.0-GHz frequences. Knowing these wireless frequence ranges enable trouble-shooting intervention issues from other devices runing in the same wireless set.
Airing Methods
802.11 define three different spread-spectrum broadcast medium methods used in execution of radio webs these are:
Direct-sequence spread spectrum ( DSSS ) ,
Frequency skiping dispersed spectrum ( FHSS )
Extraneous frequency-division multiplexing ( OFDM ) .
Darmstadtium
DSSS sends informations out on different frequences at the same clip. It uses a bandwidth of 1 MHz. DSSS is capable of greater information throughput but more prone to intervention.
FHSS
FHSS sends informations on one frequence at a clip, invariably switching frequences. It uses a bandwidth of 1 MHz. Throughput lesser than DSSS and less prone to interference every bit compared to DSSS
OFDM
OFDM is the latest method. It combines the usage of multiple frequences as in DSSS and the capableness of switching frequences as in FHSS.
802.11 criterions
The 802.11 criterion defines the security protocols, quality of service and mechanism of radio webs. All these criterions use the Ethernet protocol and the CSMA/CA entree method for radio webs. The criterions are used for both substructure and an ad-hoc web design.
802.11n is the latest criterion that uses two new characteristics Multiple input multiple end products ( MIMO ) and Channel bonding. MIMO is the usage of multiple aerials to accomplish more throughputs as compared to a individual aerial. Channel bonding allows 802.11n to convey informations over two channels to achieve more throughputs. Given below is a tabular array of all the 802.11 criterions.
802.11a
802.11b
802.11g
802.11n
Frequency
5 GHz
2.4 GHz
2.4 GHz
5/2.4 GHz
Transportation rate
54 Mbps
11 Mbps
54 Mbps
Up to 600 Mbps
Scope
150 Foot
300 Foot
300 Foot
300 Foot
Compatibility
802.11a
802.11b/g/n
802.11b/g/n
802.11a/b/g 802.11 Collision Avoidance
The 802.11 standard defines two methods of hit turning away:
Distributed Coordination Function ( DCF )
Point Coordination Function ( PCF )
Current CSMA/CA devices use the Distributed Coordination Function ( DCF ) method for hit turning away.
DCF specifies strict regulations for directing informations onto the web media.It defines a backoff period above the normal IFS delay period before a radio web node can seek to entree the web once more when the web is busy. Recieving nodes are required to direct an recognition ( ACK ) for every package that they process.
The ACK includes a value that tells other wireless nodes to wait a certain period before seeking to entree the web media. This period is calculated as the clip taken by the information package to make its finish and is based on the package ‘s length and information rate. In instance the directing node does n’t have an ACK, it retransmits the same information package until it gets a verification that the package has reached its finish.
5.1.2 Channelss
Channelss
The channel is a part of the frequence scope available to the radio web to pass on. Therefore, each frequence scope is a channel. The 802.11 criterion defines 14 channels. These channels have some convergence, therefore two nearby WAPs must non utilize close channels like 6 and 7. Most WAPs usage channel 1, 6, or 11 by default this keeps the channels as far apart from each other as possible.
Channels
Frequency Range
1
2.3995 GHz – 2.4245 GHz
2
2.4045 GHz – 2.4295 GHz
3
2.4095 GHz – 2.4345 GHz
4
2.4145 GHz – 2.4395 GHz
5
2.4195 GHz – 2.4445 GHz
6
2.4245 GHz – 2.4495 GHz
7
2.4295 GHz – 2.4545 GHz
8
2.4345 GHz – 2.4595 GHz
9
2.4395 GHz – 2.4645 GHz
10
2.4445 GHz – 2.4695 GHz
11
2.4495 GHz – 2.4745 GHz
12
2.4545 GHz – 2.4795 GHz
13
2.4595 GHz – 2.4845 GHz
Note: A radio web can be all right tuned by traveling WAPs to other channels as this avoids overlaps when many radio webs portion the same physical infinite.
5.1.3Authentication and Encryption
Procuring Radio
Implementing a Wireless Network
Configuring the Access Point
Configuring the Client
Infrared and Bluetooth
Infrared
Bluetooth
1.7 Chapter Review Questions
RJ-45 connections are used with______________________
( A )
coax
( C )
Fiber-optic
( B )
1000Base-LX
( D )
10BASE-T
10Base-2 is besides referred to as______________________
( A )
Thicknet
( C )
Unshielded Twisted-pair
( B )
Thinnet
( D )
Class 3
Ringing topology is an?
( A )
Dynamic topology
( C )
Active topology
( B )
Passive topology
( D )
Inactive topology
The maximal section length of 100Base-FX at half semidetached house is.
A )
412 metres
( C )
2000 metres
( B )
200 metres
( D )
1000 metres
The maximal transportation velocity of 10Base-5 is_____________________
( A )
100 mbps
( C )
1 Gaps
( B )
2 Mbps
( D )
10 Mbps
Fibre Distributed Data Interface, portions many of the same characteristics as?
( A )
Ethernet
( C )
Intranet
( B )
Token rings
( D )
Wireless Ethernet
Fibre webs use what sort of connections?
( A )
Scandium
( C )
RJ-45
( B )
BNC
( D )
RJ-11
( A )
Star
( C )
Mesh
( B )
Bus
( D )
HierarchicalWhat topology provides each device with a point-to-point connexion to every other device in the web?
Ethernet is besides known as.
( A )
802.5
( C )
802.11b
( B )
802.2
( D )
802.3
Summary:
In this chapter, we have learnt to:
Identify the features of a web
Identify types of web topologies
Discuss web media and connections
Describe entree methods
Describe web architectures
Explain web runing systems
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