Transmissions and Channels

To understand fully how wireless local area networks (WLANs) function requires a complete understanding of computer networking and, for that matter, computers themselves. So we’ll start from the premise that local area networks function just fine, and go from there.

WLANs incorporate all the concepts of wired LANs, including data transfer (sending and receiving data), data throughput (the amount of data transmitted in any given chunk of time), and addressing (making sure the data gets to the right place).

The only difference between a LAN and a WLAN, in fact, is the medium of transmission—wires for the former, radio waves for the latter. When it comes to setting up and maintaining a WLAN, to say nothing of designing the technology behind it, the medium of transmission is a major difference.

Wired networks provide more reliability than wireless, along with greater speed, in everything from establishing and maintaining a connection through transferring data and enforcing security.

Wireless networks require a different degree of configuration, and an understanding of how the data gets from one PC to the next can help considerably when it comes to configuration and troubleshooting.

Of course, the same is true to a degree of wired networks, but given the ubiquity of the Ethernet standard, under which the vast majority of smaller PC-based networks operate, wired networking at the small network level has become much easier to achieve than at any time in the past.

Wireless, while getting easier, still demands more of both the network builder and the network user. Wireless networks are based on the IEEE 802.11 standard, developed in 1997 to specify how to format and structure data for wireless transmission, and how devices will transmit and receive the data structures.

802.11 governs the three elements that constitute wireless networking: the network structure itself, the format and structure of the data that moves through the network, and the technical details of the radio signals over which the data structures travel.

The standard determines how network adapters (everything from PC and USB cards to access points) convert computer data into radio signals and vice versa, outlining precisely what each byte of data needs to effect this conversion without data loss or corruption.

Although the 802.11 standard covers multiple types of wireless networking, you’ll find only three of its subsequent standards in widespread use today: 802.11b, 802.11g, and the much less common 802.11a.

These standards are outlined here only briefly because of their importance in understanding the workings of WLANs. 802.11b and 802.11g both transmit at 2.4 GHz, with 802.11a at 5 GHz.

The higher the frequency, the greater the data transfer speed (theoretically, at least), and you can see the difference readily between 802.11b, the first common wireless standard, and 802.11a, which reached the market a couple years later.

802.11b possesses a maximum 11 Mb/sec (megabits per second), while 802.11a can reach 54 Mb/sec. 802.11g, the natural successor to 802.11b and the most popular standard in commonly available wireless products today, manages to achieve 802.11a’s 54 Mbit/sec capability even on 802.11b’s 2.4 Mhz frequency.

The result is a nice blend between 11a and 11b, with 11b’s greater physical signal range and 11a’s speed. For this reason, 11a devices have largely disappeared from the marketplace, while 11b products hang on primarily because they can be sold reasonably inexpensively. 802.11g is currently at the center of the wireless networking universe.

Today’s wireless networks use a radio technology known as Direct Sequence Spread Spectrum, abbreviated to DSSS. DSSS divides radio transmissions into channels to avoid interference between channels and the multiple error connections caused by an older technology called Frequency Hopping Spread Spectrum (FHSS).

DSSS allows 802.11 protocols to take advantage of the 11 channels available in the range of frequencies near 2.4 GHz reserved throughout the world for unlicensed transmissions (that is, transmissions without need for regulation).

The 802.11 technologies send messages, broken into tiny packets, through these channels with addressing information, initiating handshaking (communication) with devices along the way.

The job of the network adapters in your PCs and the access points on your network is to ensure that the data flows into the PCs in the correct format and to the right locations.