Wireless Networking | Red Hat Fedora 5 Unleashed

As stated earlier, Linux has had support for wireless networking since the first standards were developed in the early 1990s. With computers getting smaller and smaller, the uses for wireless networking increased; meanwhile, the transmission speeds are increasing all the time. There are several different ways to create a wireless network. The following sections introduce you to several Linux commands you can use to initialize, configure, and manage wireless networking on your Fedora system.

Support for Wireless Networking in Fedora

The Linux kernel that ships with Fedora provides extensive support for wireless networking. Related wireless tools for configuring, managing, or displaying information about a wireless connection include

iwconfig Sets the network name, encryption, transmission rate, and other features of a wireless network interface
iwlist Displays information about a wireless interface, such as rate, power level, or frequency used
iwpriv Uses i to set optional features, such as roaming, of a wireless network interface
iwspy Shows wireless statistics of a number of nodes

Support varies for wireless devicesmost likely in the form of a PCMCIA adapteralthough some USB wireless devices now work with Linux. In general, Linux wireless device software (usually in the form of a kernel module) supports the creation of an ethernet device that can be managed by traditional interface tools such as ifconfigwith wireless features of the device managed by the various wireless software tools.

For example, when a wireless networking device is first recognized and initialized for use, the driver will most likely report a new device:

wvlan_cs: WaveLAN/IEEE PCMCIA driver v1.0.6 wvlan_cs: (c) Andreas Neuhaus <andy@fasta.fh-dortmund.de> wvlan_cs: index 0x01: Vcc 3.3, irq 3, io 0x0100-0x013f wvlan_cs: Registered netdevice eth0 wvlan_cs: MAC address on eth0 is 00 05 5d f3 1d da

This output (from the dmesg command) shows that the eth0 device has been reported. If DHCP is in use, the device should automatically join the nearest wireless subnet and be automatically assigned an IP address. If not, the next step is to use a wireless tool such as iwconfig to set various parameters of the wireless device. The iwconfig command, along with the device name (eth0 in this example), will show the status:

# iwconfig eth0 eth0   IEEE 802.11-DS ESSID:"GreyUFO" Nickname:"Prism I"        Mode:Managed Frequency:2.412GHz Access Point: 00:02:2D:2E:FA:3C        Bit Rate:2Mb/s Tx-Power=15 dBm Sensitivity:1/3        RTS thr:off Fragment thr:off        Encryption key:off        Power Management:off        Link Quality:92/92 Signal level:-11 dBm Noise level:-102 dBm        Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0        Tx excessive retries:0 Invalid misc:4  Missed beacon:0

This example shows a 2Mbps connection to a network named GreyUFO. To change a parameter, such as the transmission rate, use a command-line option with the iwconfig command like so:

# iwconfig eth0 rate 11M

Other options supported by the iwconfig command include essid, used to set the NIC to connect to a specific network by named; mode, used to enable the NIC to automatically retrieve settings from an access point or connect to another wireless host; or freq, to set a frequency to use for communication. Additional options include channel, frag, enc (for encryption), power, and txpower. Details and examples of these options are in the iwconfig manual page.

You can then use the ifconfig command or perhaps a graphical Fedora tool to set the device networking parameters, and the interface will work as on a hardwired LAN. One handy output of the iwconfig command is the link quality output, which can be used in shell scripts or other graphical utilities for signal monitoring purposes (refer to Chapter 15 for an example).

Cellular Networking

The ads are starting to crop up on TV: This cellular service allows you to check your email anywhere your cellular phone can reach; that cellular company provides news and other information via the Internet to your phone. Personal digital assistants have cellular addons or even built-in options.

For example, if your laptop has a cellular modem, you can use it to dial in to your network. This is not truly wireless networking if the network dialed in to is wired, but it illustrates how far-reaching wireless networks can go. As long as your cellular service follows you, you can dial in to any network you have access to (be it home or office) from any location in the world to check your email and use it to send electronic files to your associates. And many newer cell phones can be used as a modem by attaching a cable from the phone to a serial or USB port on a laptop. As with most devices, the majority of brand-name PCMCIA cards work with Linux. A lot of generic equipment (such as serial I/O cards) should work, but you are taking a chance if the card is not supported (see the section "Managing PCMCIA" in Chapter 4, "Post-Installation Configuration").

Advantages of Wireless Networking

Advantages of wireless networking are its mobility and potential range. If you have a large enough antenna network, your network can stretch many miles. This would be an expensive network, but one that would easily break out of the brick and mortar confines of the office.

Wireless networking would also be a great advantage to college campuses to eliminate the need to tear through walls to install cabling because more and more students expect to have a network connection in their dorm rooms. Wireless networking cards are becoming more reasonable in price and can easily be issued to each student as he requires them.

Home networkers can also benefit from wireless networking. For those who cannot make wired network modifications to their homes, wireless networking removes the unsightly wires running along baseboards and ceilings that are required to connect computers in different rooms. With a wireless home network, you are not even confined to inside the house. Depending on the transmit power of your router, you can sit out in your backyard and watch clouds drifting by as you type away. Wireless routers are coming down in price with each passing day.

Choosing the right types of wireless devices is an important decision. The next sections discuss some of the basic differences between current protocols used for wireless networking.

Choosing from Among Available Wireless Protocols

The Institute of Electrical and Electronics Engineers (IEEE) started to look seriously at wireless networking in 1990. This is when the 802.11 Standard was first introduced by the Wireless Local Area Networks Standards Working Group. The group based the standard roughly around the architecture used in cellular phone networks. The wireless network is controlled by a base station, which can be just a transmitter attached to the network or, more commonly these days, a router.

Larger networks can use more than one base station. Networks with more than one base station are usually referred to as distribution systems. A distribution system can be used to increase coverage area and support roaming of wireless hosts. You can also employ external omnidirectional antennas to increase coverage area, or if required, use point-to-point, or directional antennas to connect distant computers or networks. Right now, the least expensive wireless Linux networks are built using devices (such as access points or NICs) supporting 802.11b, although prices are rapidly dropping for faster 802.11g devices.

An early standard, 802.11a, offers greater transmission rates than 802.11b, and a number of 802.11a wireless NICs are available (some products provide up to 72Mbps, but will not work with 802.11b devices). Wireless networking devices based on 802.11g, which has the speed improvement of 802.11a and is compatible with 802.11b, are more widely available. Other wireless protocols include Bluetooth, which provides up to 720Kbps data transfers. Bluetooth is intended for short-range device communications (such as for a printer) and supports a typical range of only 10 meters. Bluetooth is unlike IrDA, which requires line-of-sight (devices that are aimed at each other). Bluetooth use conflicts with 802.11 networks because it also uses the 2.4GHz band. You can find out more by browsing to http://www.bluetooth.com/.

The 802.11 standard specifies that wireless devices use a frequency range of 24002483.5MHz. This is the standard used in North America and Europe. In Japan, however, wireless networks are limited to a frequency range of 2471MHz2479MHz because of Japanese regulations. Within these ranges, each network is given up to 79 nonoverlapping frequency channels to use. This reduces the chance of two closely located wireless networks using the same channel at the same time. It also allows for channel hopping, which can be used for security.