1.5 WLANs

1.5 Wireless LANs

With the introduction and adoption of the IEEE 802.11a, 802.11b and 802.11g standards, wireless local networks are gaining popularity and are being used to solve network problems and meet user requirements that are not easily possible with conventional wired networks.

Wireless LANs, although they can be separate, usually connect to a wired network infrastructure. The operation of the wireless is similar to that of a cable network in that network devices require network interface cards (wireless) to be installed and configured, however, one difference is that media access must be performed using CSMA/CA ie: collision avoidance rather than collision detection.

Wireless communications travel through the air and this can take the form of an ad-hoc network, eg: people at a meeting could use wireless to link their laptops, or more typically organised through a wireless device such as an access point in a similar way to a wired network but without the cable.

WLAN Standard: 802.11

802.11 is the reference used for the series of specifications developed by the IEEE for wireless LAN technology.

The three most commonly used are 802.11a, 802.11b and 802.11g.

  • 802.11a – Provides up to 54 Mbps transmission in the 5GHz band
  • 802.11b – Provides up to 11 Mbps transmission in the 2.4 GHz band.
  • 802.11g – Provides up to 54 Mbps transmission in the 2.4 GHz band.

The speed of a WLAN decreases the further away from the access point and is dependant on the number of users.

LANs are inherently more secure than WLANs because LANs are protected by the physicality of their structure. That is because some or all of the network is inside a building then the network can be secured against unauthorized access.

WLANs, which use radio waves, do not have the same physical protection and therefore are more vulnerable to tampering. One method of illegal access and tampering is called War Driving, where a person drives around and uses an antenna to try and pick up unsecured wireless networks. This weakness in security has been one of the reasons for the slow uptake in wireless network technology. An open WLAN is available to anyone with a wireless card.

There are some circumstances when such an open access is desirable, eg: all UK airports now have wireless Internet connections with passengers being able to use their wireless laptop to check their email, etc. Although this is an open network passengers have to subscribe to use it, this involves obtaining a username and password for a fee.

In order to access a closed wireless network a shared key is required, this is set on the access point, and only computers that have the shared key that matches the access point key will be allowed to access the network. This key can be 64 bit or 128 bit. The stronger security key will decrease network performance slightly but the additional security can outweigh the slight loss of performance.

Wired Equivalent Privacy (WEP) is a protocol that is designed to provide the same level of security in a wireless network as that of a wired network. WEP aims to provide security by encrypting data over radio waves so that it is protected as it is transmitted from one end point to another. However, it has been found that WEP is not as secure as once believed. WEP is used at the two lowest layers of the OSI model the data link and physical layers and as such it does not offer end-to-end security.

WLAN Devices

There are two key devices that allow WLANs to work:

  • Access Point
  • Wireless Bridge

A wireless access point (AP) allows wireless devices to communicate and are commonly connected to cabled networks to allow wireless users access to the network.

Wireless bridges can be used to connect networks together and also extend the range of the network. A WLAN bridge can be used to connect networks up to three miles apart with a Long-Range Wireless Bridge allowing communication to take place up to 25 miles apart.

The techniques of wireless transmission are:

  1. Infrared transmission
  2. Spread-spectrum radio transmission
  3. Laser transmission
  4. Narrowband (single-frequency) radio transmission

Wireless mobile networks use telephone carriers and public services to transmit and receive signals using:

  • Packet-radio communication
  • Cellular networks
  • Satellite stations

Travelling employees can use this technology with portable computers, mobile telephones, or Personal Digital Assistants (PDAs) to exchange email messages, files, or other information. Although this type of communication is convenient it is slow with transmission rates ranging from 8 Kbps to 19.2 Kbps.

GPRS is typically referred to in connection to mobile phones. Mobile phones that have the GPRS technology can be used to receive data and information, such as web pages and email.

GPRS in a similar way to broadband is an “always on” technology which means that the mobile phone is always ready to receive data. Time-division duplexing is used all let GPRS phones send and receive data at the same time.

Information that is to be passed to a GPRS mobile phone is divided up into packets. Each packet is given a destination address and travels independently of other packets across any available part of the network. The phone then gathers the incoming packets prior to reassembling them when the final packet arrives.