Wireless LAN Requirements
A wireless LAN must meet the same sort of requirements typical of any LAN, including high capacity, ability to cover short distances, full connectivity among attached stations, and broadcast capability. In addition, a number of requirements are specific to the wireless LAN environment. The following are among the most important requirements for wireless LANs:
Throughput. The medium access-control (MAC) protocol should make as efficient use as possible of the wireless medium to maximize capacity.
Number of nodes. Wireless LANs may need to support hundreds of nodes across multiple cells.
Connection to backbone LAN. In most cases, interconnection with stations on a wired backbone LAN is required. For infrastructure wireless LANs, this is easily accomplished through the use of control modules that connect to both types of LANs. There may also need to be accommodation for mobile users and ad hoc wireless networks.
Service area. A typical coverage area for a wireless LAN has a diameter of 100 to 300 m.
Battery power consumption. Mobile workers use battery-powered workstations that need to have a long battery life when used with wireless adapters. This suggests that a MAC protocol that requires mobile nodes to monitor access points constantly or engage in frequent handshakes with a base station is inappropriate. Typical wireless LAN implementations have features to reduce power consumption while not using the network, such as a sleep mode.
Transmission robustness and security. Unless properly designed, a wireless LAN may be interference-prone and easily eavesdropped. The design of a wireless LAN must permit reliable transmission even in a noisy environment and should provide some level of security from eavesdropping.
Collocated network operation. As wireless LANs become more popular, it's quite likely that two or more wireless LANs will operate in the same area or in some area where interference between the LANs is possible. Such interference may thwart the normal operation of a MAC algorithm and may allow unauthorized access to a particular LAN.
License-free operation. Users would prefer to buy and operate wireless LAN products without having to secure a license for the frequency band used by the LAN.
Handoff/roaming. The MAC protocol used in the wireless LAN should enable mobile stations to move from one cell to another.
Dynamic configuration. The MAC addressing and network management aspects of the LAN should permit dynamic and automated addition, deletion, and relocation of end systems without disruption to other users.
A set of wireless LAN standards has been developed by the IEEE 802.11 committee. Let's look first at the services defined for IEEE 802.11 and then at the various options supported by the standard.