Wireless Technologies

Wireless Technologies and Devices

• In addition to the wired network, various technologies exist that allow the transmission of information between hosts without cables. These are known as wireless technologies.
• Wireless technologies use electromagnetic waves to carry information between devices. An electromagnetic wave is the same medium that carries radio signals through the air.
• The electromagnetic spectrum includes such things as radio and television broadcast bands, visible light, x-rays and gamma-rays. Each of these has a specific range of wavelengths and associated energies as shown in the diagram.
• Some types of electromagnetic waves are not suitable for carrying data. Other parts of the spectrum are regulated by governments and licensed to various organizations for specific applications. Certain areas of the spectrum have been set aside to allow public use without the restriction of having to apply for special permits. The most common wavelengths used for public wireless communications include the Infrared and part of the Radio Frequency (RF) band.

Infrared

• Infrared (IR) is relatively low energy and cannot penetrate through walls or other obstacles. However, it is commonly used to connect and move data between devices such as Personal Digital Assistants (PDAs) and PCs.
• A specialized communication port known as an Infrared Direct Access (IrDA) port uses IR to exchange information between devices. IR only allows a one-to-one type of connection.
• IR is also used for remote control devices, wireless mice, and wireless keyboards. It is generally used for short-range, line-of-sight, communications.
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Radio Frequency (RF)

• RF waves can penetrate through walls and other obstacles, allowing a much greater range than IR. Certain areas of the RF bands have been set aside for use by unlicensed devices such as wireless LANs, cordless phones and computer peripherals. This includes the 900 MHz, 2.4 GHz, and the 5 GHz frequency ranges. These ranges are known as the Industrial Scientific and Medical (ISM) bands and can be used with very few restrictions.
• Bluetooth is a technology that makes use of the 2.4 GHz band. It is limited to low-speed, short-range communications, but has the advantage of communicating with many devices at the same time. This one-to-many communications has made Bluetooth technology the preferred method over IR for connecting computer peripherals such as mice, keyboards and printers.

Benifits of Wireless Technology

• One of the main advantages is the ability to provide anytime, anywhere connectivity. The widespread implementation of wireless in public locations, known as hotspots, allows people to easily connect to the Internet to download information and exchange emails and files.
• Wireless technology is fairly easy and inexpensive to install. The cost of home and business wireless devices continues to decrease.
• Wireless technology enables networks to be easily expanded, without the limitations of cabled connections. New and visiting users can join the network quickly and easily.

Limitations of Wireless Technology

• First, Wireless LAN (WLAN) technologies make use of the unlicensed regions of the RF spectrum. Since these regions are unregulated, many different devices make use of them. As a result, these regions are congested and signals from different devices often interfere with each other.
• Second, a major concern with wireless is security. Wireless provides ease of access. It does this by broadcasting data in a manner that allows anyone the ability to access it. However, this same feature also limits the amount of protection wireless can provide for the data. It allows anyone to intercept the communication stream, even unintended recipients.

Types of Wireless Networks

Wireless networks are grouped into three major categories: Wireless Personal Area networks (WPAN), Wireless Local Area networks (WLAN), and Wireless Wide Area networks (WWAN).

• WPAN

  This is the smallest wireless network used to connect various peripheral devices such as mice, keyboards and PDAs to a computer. All of these devices are dedicated to a single host with usually use IR or Bluetooth technology.

• WLAN

  WLAN is typically used to extend the boundaries of the local wired network (LAN). WLANs use RF technology and conform to the IEEE 802.11 standards. They allow many users to connect to a wired network through a device known as an Access Point (AP). An Access Point provides a connection between wireless hosts and hosts on an Ethernet wired network.
• WMAN
• A metropolitan area network (MAN) is a computer network larger than a local area network, covering an area of a few city blocks to the area of an entire city, possibly also including the surrounding areas.
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• WWAN

  WWAN networks provide coverage over extremely large areas. A good example of a WWAN is the cell phone network. These networks use technologies such as Code Division Multiple Access (CDMA) or Global System for Mobile Communication (GSM) and are often regulated by government agencies.

WLANs and SSID

When building a wireless network, it is important that the wireless components connect to the appropriate WLAN. This is done using a Service Set Identifier (SSID).

The SSID is a case-sensitive, alpha-numeric string that is up to 32-characters. It is sent in the header of all frames transmitted over the WLAN. The SSID is used to tell wireless devices which WLAN they belong to and with which other devices they can communicate.

Regardless of the type of WLAN installation, all wireless devices in a WLAN must be configured with the same SSID in order to communicate.

Ad-hoc

• The simplest form of a wireless network is created by connecting two or more wireless clients together in a peer-to-peer network. A wireless network established in this manner is known as an ad-hoc network and does not include an AP.
• All clients within an ad-hoc network are equal. The area covered by this network is known as an Independent Basic Service Set (IBSS). A simple ad-hoc network can be used to exchange files and information between devices without the expense and complexity of purchasing and configuring an AP.
• Static assignment of addressing information can provide increased control of network resources, but it can be time consuming to enter the information on each host. When entering IP addresses statically, the host only performs basic error checks on the IP address. Therefore, errors are more likely to occur.

Infrastructure Mode

Although an ad-hoc arrangement may be good for small networks, larger networks require a single device that controls communications in the wireless cell. If present, an AP will take over this role and control who can talk and when. This is known as infrastructure mode.