An Introduction to Wireless Technology, Second Edition

5.4 Compression / Throughput Issues

The theoretical maximum throughput for a given radio frequency, design

implementation and product, and the effective data transmission rate for the

same seldom coincide. This is because throughput is a function of several

factors:

•

Signal rate

•

Signal/Noise ratio

•

Rejection of and immunity to signal interference

•

Protocol overhead

•

Redundant data transmissions

•

Error detection and/or correction codes

•

Latency

•

Environmental factors

•

Compression techniques

The signaling rate (for example, 2 Mbps for direct-sequence spread spectrum in

the ISM bands) is often mistakenly referred to as the data transmission rate.

The signaling rate is the clock frequency of the radio itself. The IBM Wireless

LAN frequency-hopping spread spectrum system signals at 1 Mbps. In

conjunction with an IBM-unique hardware data compression feature, it can

achieve higher effective data throughput rates than DSSS systems that proclaim

their higher clock signaling rate as equivalent to increased throughput.

5.5 Security Aspects

One of the main concerns often expressed when installing wireless LANs is the

question of data security. These concerns are valid and may be addressed as

follows:

There are three types of security risks:

•

Attack by casual listener

•

Attack by professional hacker

•

Attack by insiders

5.5.1 Attack by Casual Listener

A casual listener might be someone in a neighboring building using the same

type of equipment. Each WLAN system must be capable of identifying those

workstations authorized to participate in that LAN, and deny unauthorized

workstations to access the WLAN. It should not be possible for unauthorized

workstations to overhear and interpret data traffic on a WLAN.

5.5.2 Attack by Professional Hacker

A

passive

attack could come from someone receiving the WLAN radio signal and

using sophisticated tools to try to interpret the data content of the radio signal

heard. An

active

attack could originate within transmission range of the WLAN

but outside the facility. Eavesdropping by attempting to insert an unauthorized

wireless workstation into an existing WLAN is one example.

Chapter 5. Radio Communication in LANs 111