Some specific question

How does 802.11a differ from 802.11b?
Both IEEE 802.11a and IEEE 802.11b are wireless LAN technology standards.
• Like Ethernet and Fast Ethernet, 802.11b and 802.11a use an identical MAC. However, while Fast Ethernet uses the same physical-layer encoding scheme as Ethernet-only faster-802.11a uses an entirely different modulation scheme called orthogonal frequency division multiplexing (OFDM).
• Because 802.11a has a range approximately half that of 802.11b, more access points are required to cover the same area in a building.

Will 802.11a replace 802.11b?
No. It's believed that the emerging IEEE 802.11a standard for wireless LANs will complement and co-exist rather than compete with the 802.11b standard. The higher data rate will prove beneficial when wireless video and multimedia applications become widespread. If you need to increase bandwidth, you can begin by deploying pockets of 802.11agear right alongside your 802.11b installation. Wi-Fi's greater range and sustainable 11 Mbps data rate complement802.11a's shorter range and 54 Mbps data rate. Because the two standards can coexist without interference risk, products could even be deployed that use both standards simultaneously, such as dual-radio access points.

Are 802.11a products backward compatible with 802.11b products?

No. Short of replacing the radios, there is currently no defined upgrade path between 2.4 GHz and 5 GHz technologies. This could prove to be a difficult selling point for 802.11a-only vendors.

What are the likely applications for 802.11a?

It's expected that 802.11a equipment makers will market products to home and SOHO users. This market segment is likely to deploy Wi-Fi for shared Internet access, and a higher bandwidth standard like 802.11a for video streaming and video sharing applications. This is because of the higher data rate and the fact that the shorter range limitations would be less of a factor for these users. Equipment using this standard could network gaming applications, devices like high definition televisions, and multiple streaming audio and video devices. The enterprise market segment will likely have deployments of both 802.11a and 802.11b for a number of years. As Wi-Fi is a much further developed standard, the following trends will persist:

• Its popularity will continue to drive down costs

• Wi-Fi certified interoperability will continue to be a catalyst for wide-spread adoption

• The risk-averse enterprise segment will continue to focus on cost savings and increasing the return on investment in Wi-Fi

• As all public access wireless deployments today are based on 802.11b, mobile professionals will continue to support Wi-Fi, as 802.11a cards won't offer connectivity.802.11a technology will likely be limited to these types of applications:

• Building-to-building connections

• Video and audio conferencing/streaming video and audio

• Data mining• Large file transfers, such as engineering CAD drawings

• Faster web access and browsing

• High worker density or high throughput scenarios, such as a trading floor with multiple net-works and numerous PCs running graphics-intensive applications