What is "Wireless DSL?"

If the most common forms of broadband Internet -- Cable, DSL, and Satellite -- are unavailable and/or unattractive in your area, are you out of luck? Maybe not. Fixed terrestrial (as opposed to satellite) wireless, sometimes called "Wireless DSL," is a group of newer technologies that are starting to be deployed in some areas. Here's a quick guide to this type of service:

1. "Wireless DSL" is not really DSL
   Fixed terrestrial wireless is capable of providing a broadband experience comparable to DSL, which is why it's sometimes called "Wireless DSL." However, the term DSL (Digital Subscriber Line) properly refers only to data service over standard copper telephone lines. In addition, there are important technical differences between fixed terrestrial wireless and DSL. Hence the term "Wireless DSL" is descriptive but not really accurate.

1. There's more than one flavor of fixed terrestrial wireless
   Some of the principal technologies:
   1. BroadLink is based on local transceivers with relatively short range (about 4 miles) using the same 11 Mbps IEEE 802.11b technology used in wireless local area networking. The service is somewhat similar to cellular data, and is sold only through ISPs (not direct from BroadLink). Service is currently available in Santa Rosa, California (Sonic.net), Stockton, California (InReach), and is undergoing market trials in Atlanta, Georgia.
   2. Sprint Broadband Direct (no longer available).
   3. WaveRider has both line-of-sight and non-line-of-sight products.

   Service in the first two cases is available only to those with direct line-of-sight to a transceiver, although the technology used by BroadLink tends to provide more complete coverage (less line-of-sight interference) and to be more scalable (fewer subscribers per transceiver). The balance of this section will focus on the technology used by BroadLink.

2. Like Satellite Internet, you need an external antenna
   The BroadLink antenna is about 14.5 inches square. Although it must be mounted with direct line-of-sight to the local transceiver, alignment is less critical than for Satellite Internet. Currently the necessary electronics are mounted in a separate box located near the antenna [picture]; in the next generation the electronics will be smaller and mounted on the back of the antenna. Connection to the subscriber's computer is by standard Category 5 network cable, which carries data as well as power for the electronics.
3. Like Cable Internet, the service is shared
   Unlike true DSL, where each subscriber has a dedicated connection, but like Cable Internet, Wireless DSL subscribers share the capacity of a given transceiver. Hence, it is possible for the service to slow down during periods of high usage if the capacity has been oversubscribed. Nevertheless, like Cable Internet, performance is usually very good. Like typical DSL, the service objective is 1.5 Mbps (down, 128 Kbps up).
4. It's not really 11 Mbps
   Only one transmitter can be sending at any one time on a given segment (serviced by a given local transceiver). Since data cannot flow in both directions (up and down) at the same time, real throughput is much less the raw 11 Mbps transmission speed -- on the order of about 6 Mbps. Nevertheless, that's still enough capacity (augmented by "fairness" algorithms in the network) to provide good service to dozens of typical subscribers on a given segment.
5. Latency is much better than satellite
   Although the other principal form of wireless broadband, Satellite Internet, suffers from very high latency (due to the long round trip that signals must travel) that can adversely affect certain types of Internet use (e.g., real-time gaming), Wireless DSL has latency ("ping" time) comparable to Cable Internet and DSL (typically on the order of 40 ms or less).
6. Premium service
   BroadLink service is available with static IP, either bridged or routed. This means that, for example, you can easily run your own server.
7. Good security
   The basic security of IEEE 802.11b networking (used by BroadLink) is based on WEP (Wired Equivalent Privacy). The bad news is that WEP has been shown to be not terribly secure. The good news is that BroadLink has implemented additional security that keeps subscribers from snooping the traffic of other subscribers.
8. How to get the most out of Wireless DSL
   Because it's so similar to Cable Internet and to DSL, Wireless DSL can be easily optimized using the methods described in this document.
9. Another wireless Internet option
   Metricom's Ricochet service, which has been deployed in a number of areas, provides a different tradeoff for wireless Internet access, the benefit of roaming mobile service (rather than fixed point) at the expense of speed (128 Kbps versus 1.5 Mbps). Unfortunately, Metricom has filed for Chapter 11 bankruptcy protection, and the future of the Ricochet service is uncertain.

http://cable-dsl.navasgroup.com/