Share this Page URL

Chapter 3. How Wireless Works > Other Wireless Standards - Pg. 50

How Wireless Works NOTE 50 7. Wi-Fi may seem a lot like wired Ethernet, and it is: Wi-Fi shares most of its inner work- ings with wired Ethernet and differs only in the limited part of the specification that covers the physical part of moving bits around using radio signals instead of pushing electrons down a physical wire. If the client is configured to accept an IP address automatically and the access point or network is set to assign an IP address via a DHCP server, that dance occurs, and the client now has an Internet address, often a private network address that can't be reached from the outside world. (See "Network Protocols" in Chapter 2, Networking Basics.) Ad Hoc Mode 802.11b also offers an ad hoc mode, in which two or more computers exchange data directly with a central access point, much like in the old days of using an Ethernet crossover cable or plugging a null modem cable between two computers' serial ports. In ad hoc mode, one computer creates a network, after which the other computers see it (see step 3 in the previous section, "Connecting with 802.11b."). Alternately, each user can type in the same information for a network, and they de facto join up. The difference between ad hoc mode and a software or hardware access point, is that ad hoc connections don't have a central point of authority. Ad hoc connections are entirely private among the machines in question. (You can set up one computer as a gateway to the Internet, sharing its connection; we discuss how to handle this in Chapter 5, Building Your Wireless Network. ) Because ad hoc connections exist only among two or more computers, they're useful primarily for transferring files--if you need to give a colleague a file and have no other way to do it, turning on file sharing and setting up an ad hoc network works well. Next time you have a few extra minutes, we recommend figuring out how to set up an ad hoc network and transfer files, since working through the steps while away from home or the office, possibly with someone you don't know well, can be a bit tricky. Ad hoc mode is one of the few aspects of Wi-Fi that isn't part of the certification process for devices made before 2002. Older equipment, or equipment that doesn't have the latest internal software (called firmware ) updates, won't all necessarily use ad hoc mode in the same way. The Wi-Fi Alliance added an ad hoc standard to its Wi-Fi certification in late 2001, so all new equipment must work together. That said, equipment from the same manufacturer, such as all of Apple's AirPort cards, generally support ad hoc mode with no troubles. Other Wireless Standards Although 802.11b is the most common wireless networking standard in the U. S. and elsewhere, three other specifications are worth a brief look, although we don't cover them to the same extent throughout the rest of the book. These three specifications are a higher-speed but similar version of 802.11b, called 802.11a; a short-range, battery-friendly cable replacement named Bluetooth; and HomeRF, a consumer-oriented way to tie together cordless phones, multimedia devices, cable TV control boxes, and the Internet.