As we discussed in Chapter 3, an access point is a piece of hardware that connects your wireless clients to a wired network (and usually on to the Internet from there). As with any piece of bridging hardware, it has at least two network connections and shuffles traffic between them. The wireless interface is typically an onboard radio or an embedded PCMCIA wireless card. The second network interface can be Ethernet, a dialup modem, or even another wireless adapter.
The access point hardware controls access to and from both networks. On the wireless side, most vendors have implemented 802.11b access control methods (like WEP encryption keys, "closed" network ESSIDs, and MAC address filtering). Some have added proprietary extensions to provide additional security, like public key encryption.[1] Many access points also allow control over what the wired network can send to the wireless clients, through simple firewall rules.
In addition to providing access control, the access point also maintains its own network connections. This includes functions like dialing the phone and connecting to an ISP on demand, or using DHCP on the Ethernet interface to get a network lease. Most access points can provide NAT and DHCP service to the wireless clients, thereby supporting multiple wireless users while only requiring a single IP address from the wire. Some support direct bridging, allowing the wired and wireless networks to exchange data as if they were physically connected together. If the access point has multiple radios, it can bridge them together with the wire, allowing for a very flexible, extendable network.
Another important service provided by APs is the ability to "hand off" clients as they wander between access points. This lets users walk around a college campus, for example, without ever dropping their network connection. Current AP technology only allows roaming between access points on the same physical subnet (that is, APs that aren't separated by a router). Unfortunately, the roaming protocol was left unimplemented in the 802.11 spec, so each manufacturer has implemented their own method. This means that hand-offs between access points of different manufacturers aren't currently possible.
In the last year, at least 20 different access point hardware solutions have hit the consumer market. Low cost models (intended for home or small office use) like the Linksys WAP11 and D-Link DWL-1000AP currently retail for around $200. Higher-end APs like the Orinoco AP-1000 and Cisco Aironet 350 cost over $1000. Typically, higher-priced equipment includes more features, greater range, and generally more stable operations. While every AP will claim 802.11b (or Wi-Fi[2] ) compliance, they are not all alike. Features that set different models apart include:
Wi-Fiis the "marketing friendly" name picked by the WECA (the Wireless Ethernet Compatibility Alliance) to refer to 802.11b-compliant gear. See http://www.weca.net/ if you're so inclined.• Direct bridging to the wired network
• NAT/DHCP service
• Multiple radios (to support more users or for use as a repeater)
• External antenna connectors
• Greater radio output power (most operate at 30mW, while some operate at 100mW or more)
In general, look for an AP in your price range that works for your intended application, with the greatest possible range. Single radio APs can support several users simultaneously, and, as we'll see in Chapter 6, adding APs to your network is probably preferable to adding highergain antennas or amps to your existing AP.