To Be Wireless
With the introduction of wireless LAN (WLAN), IP networks are now also available for those applications on which wired technologies are not suitable or no wired connectivity is available at all. The following are a few wireless use cases:
- Home ISP connectivity: Consumer products
- Building-to-building connectivity: Point-to-point and multipoint
- “Last mile” ISP connectivity: Rural Internet access
- Mobility applications: Car rental returns and parcel deliveries
- Enterprise network extension: Reduce, move, add, and change/mobile office environment
Although WLAN appears to be “just another LAN type/protocol,” the nature of wireless is to be a shared medium, and shared not only between a certain workgroup but also shared across the walls, across the building, and with your neighbor. On top of normal networking issues, WLAN adds a couple of new challenges, such as Layer 1 (radio frequency [RF]) issues; a set of L2 protocols, such as IEEE 802.11; and the need for agencies to regulate the use of this shared medium.
Layer 1: Radio Frequencies
Radio frequencies are high-frequency, alternating current (AC) signals that are radiated into the air through an antenna, creating radio waves. Radio waves propagate away from the antenna in a straight line in all directions at once, just like light rays from a bulb. More light bulbs spread around the room will provide better overall lighting. This translates into a stronger average signal for mobile clients. When radio waves hit a wall, door, or any obstruction, there is attenuation of the signal, which weakens the signal and can reduce throughput. The signal can also be reflected or refracted.
Industrial, Scientific, and Medical (ISM) Radio Bands
WLAN devices work in a frequency range (wavebands) that belongs to the industrial, scientific, and medical (ISM) radio bands. The ISM band was originally reserved internationally for the use of RF electromagnetic fields for industrial, scientific, and medical purposes other than communications. In general, communications equipment must accept any interference generated by ISM equipment.
- Within the ISM band, WLAN devices use wavebands as follows:
- Bluetooth 2450-MHz band
- HIPERLAN 5800-MHz band
- IEEE 802.11/WiFi 2450-MHz and 5800-MHz bands
Cisco WLAN technologies use the IEEE 802.11 range, which is what this book focuses on.