Wireless Concept Basic

Wireless transmission has been used for a very long time to transmit data by using infrared radiation, microwaves, or radio waves through a medium like air. With this type of connection, no wires are used. Typically, three terms are used to group different wireless technologies: narrowband, broadband, and circuit/packet data. Whenever you are choosing a wireless solution for your WAN or LAN, you should always consider the following criteria: speed, distance, and number of devices to connect.

Narrowband solutions typically require a license and operate at a low data rate. Only one frequency is used for transmission: 900 MHz, 2.4 GHz, or 5 GHz. Other technologies—household wireless phones, for instance—also use these technologies. Through the use of spread spectrum, higher data rates can be achieved by spreading the signal across multiple frequencies. However, transmission of these signals is
typically limited to a small area, like a campus network.

The broadband solutions fall under the heading of the Personal Communications Service (PCS). They provide lower data rates than narrowband solutions, cost about the same, but provide broader coverage. With the right provider, you can obtain national coverage. Sprint PCS is an example of a carrier that provides this type of solution.

Circuit and packet data solutions are based on cellular technologies. They provide lower data rates than the other two and typically have higher fees for each packet transmitted; however, you can easily obtain nationwide coverage from almost any cellular phone company.

Wireless is becoming very popular in today’s LANs, since very little cabling is required. Three basic standards are currently in use: 802.11a, 802.11b, and 802.11g, shown in Table 2-2. Of the three, 802.11b has been deployed the most, with 802.11g just introduced as a standard. One advantage that 802.11b and 802.11g devices have over 802.11a is that 802.11b and 802.11g can interoperate, which makes migrating from an all-802.11b network to an 802.11g network an easy and painless process.

Note that 802.11g devices are compatible with 802.11b devices (but not vice versa) and that 802.11a devices are not compatible with the other two standards. Also note that the speeds listed in Table 2-2 are optimal speeds based on the specifications—the actual speeds that you might achieve in a real network vary according to the number of devices you have, the distance that they are from the base station, and any physical obstructions or interference that might exist.

One of the biggest problems of wireless networks is security. Many wireless networks useWired Equivalency Privacy (WEP) for security. This is an encryption protocol that uses 40-bit keys, which is weak by today’s standards. Many vendors use 128-bit keys to compensate this weakness; however, weaknesses have been found in this protocol, and WEP is used with other security measures to provide a more secure wireless network.

The 802.1x/EAP (Extensible Authentication Protocol) is used to provide authentication services for devices: it authenticates devices to an authentication server (typically a RADIUS server) before the device is allowed to participate in the wireless network.

Cisco has developed an extension to this called LEAP, or lightweight EAP. LEAPcentralizes both authentication and key distribution (for encryption) to provide scalability for large wireless deployments.