When used to transmit data (whether its voice encoded over IP or streaming video, etc) both technologies operate at the physical and data-link layers of the OSI network model. Both accept data from one port (ATM, Ethernet, etc) and send it out the other port (802.11b Radio, Microwave Radio, etc) and vice versa.
The differences are found we begin to examine the speeds at which they can operate, the frequencies in which they operate, the distances over which they can operate and the restriction that are placed on technologies using the different frequency spectrums.
In many countries the IEEE 802.11b standard operates within an Industry/Scientific/Medical (ISM) band which does not require those using the technology to purchase a spectrum license from the FCC (US), ACA (Australia) or ETSI (Europe), etc. Digital microwave technology operates anywhere between 6 GHz and 30 GHz and thus requires anyone wishing to use the technology to purchase the spectrum from the appropriate regulatory authority. Due to the unlicensed nature of 802.11b many regulatory authorities have placed power output restrictions on the devices to limit the interference that each device can create with other devices operating in the same frequency band.
A key differentiator is the throughput capable of each technology. Whilst 802.11b has an aggregate throughput of 11Mbps, digital microwave technology operates at up to 155Mbps to cater for ATM (OC1) networks.
The wavelength used by each technology is one of the key determinants of the effective range of each device. Generally speaking, the wavelength of the technology is inversely proportionate to the rate of absorption and hence the effective transmission distance – i.e. the higher the frequency, the shorter the effective distance.
However, whilst 802.11b operates at a lower frequency than digital microwave technology, devices operating in the ISM band have had power output restriction placed on the units. Unlike the spectrum that 802.11b operated within, the 6 GHz to 30 GHz spectrum is not as highly regulated and operators are able to use much higher power levels and obtain much further distances.
Unfortunately, I can't tell you which one you should use. If you're looking for a cost-effective solution over a moderate distance and don't need more than 6-8 Mbps data throughput then look to 802.11b. If you need some more speed but the distance isn't that great look to 802.11a bridges – The Cisco 1400 series or the Proxim Tsunami product range are both great places to start looking. Above that I would look to free-space optics (laser), which uses light, not radio frequency, for short-range speeds of around 100Mbps up to 2Gbps. If you need long distance and high speeds then you should make some commercial inquiries into Digital Microwave technology.
This was first published in August 2003