Switches Improve WLAN Range and Performance

By Jim Geier

July 02, 2003

Wireless LANs are taking an evolutionary path similar to Ethernet networks. Learn how switch technology is improving range and performance of wireless LANs.

Traditional access points offer a shared medium, wherein clients take turns transmitting data. This is similar to a hub in a wired Ethernet network. Only one access point can transmit at a particular time. It's possible that two or more clients or access points may transmit at the same time, however, which results in a collision and corresponding packet retransmission. This increases the amount of time it takes to transmit packets, which reduces overall throughput of the wireless LAN.

Switched access points, on the other hand, implement a switching technology similar to what you find in traditional Ethernet switches. Switches enable multiple wireless clients to communicate with the same access point simultaneously and eliminate collisions between packets. The overall result is better range and throughput.

How WLAN Switches Work?

There are a couple of different approaches to switched wireless LANs. One is to have a single access point switch that takes the place of multiple access points. Vivato and Bandspeed are the two primary companies implementing this approach.

Vivato's switches use planar phased array antennas to support simultaneous traffic for up to 150 users. The Vivato switch is a rather large (48"x25"x3") wall-mountable panel and is available in both indoor and outdoor versions. The switches connect to the main network through a single Ethernet port, which also provides power-over-Ethernet (PoE). They can operate in either the 2.4GHz or 5GHz bands, making them suitable for supporting a variety of requirements.

The indoor version of the Vivato switch generally installs in the corner of a building and provides coverage for an entire floor of a building. It does this by using highly directive, narrow beams that automatically point to specific clients roaming through the facility. Instead of transmitting RF signals in every direction like traditional access points, Vivato uses their PacketSteering technology to concentrate power into a single directional beam, very much like a movable, high-gain directional antenna.

Since the switches use phased-array antennas, they can send different signals in different directions at the same time. This enables simultaneous, collision free transmission among clients associated with the same access point.

Because they use directed signals, Vivato indoor switches have a range of around 300 meters at their maximum throughput. Vivato's outdoor switches will deliver wireless connectivity to a much larger area, with a range up to 4 kilometers. They can also provide wireless connectivity to an entire multi-level building by mounting a Vivato switch within an adjacent building. The switch will then beam coverage throughout the building. This method of deployment is an ideal solution for areas where there are lots of buildings that are close to each other, such as college campuses.

Bandspeed offers a technology that is very similar to the Vivato switch, except that it is somewhat smaller in size. Named Gypsy, the switch technology uses directional antennas to provide 360 degree coverage with a range similar to that of the Vivato switch. Gypsy also supports both the 2.4GHz and 5GHz bands, making it applicable to 802.11a, 802.11b, and 802.11g networks. Bandspeed doesn't sell these switches directly to the public; rather they supply original equipment manufacturers (OEMs) and original development manufacturers (ODMs) with the technology and products necessary to build the switches and sell to the public.

Another approach to existing switched wireless LAN technology is to have a single Ethernet-based switch that interconnects many small, lower technology access ports (think of them as access points without the brains -- some call them "lite access points") mounted throughout the facility. The access ports offer a low cost method of providing small cells throughout large facilities. This provides users with the performance enhancing qualities of a switch and a highly scalable solution. You can start with a limited solution and add access ports as needed.

The Symbol Mobius System offers this type of technology. Symbol's Axon Wireless Switch runs the control and management functions for the wireless network. All of the intelligence and features found in normal access points fall within the Axon Switch.

The Axon Switch connects to Mobius Access Ports through standard 100BaseT cabling. The relatively small access ports contain the wireless LAN radio and antenna, which you can mount almost anywhere. They support PoE, and also include a second built-in Ethernet port for "daisy chaining" multiple access ports together.

The Mobius system currently supports 802.11a and 802.11b, and is almost ready for 802.11g. The access ports require no configuration because the centralized Axon Wireless Switch includes provides all configuration settings.

The Advantages

Here are some key advantages pertaining to switched wireless LANs:

  • Increased capacity and range: Switched access points allow you to provide greater coverage with less hardware, which can result in cost savings due related to hardware and installation. Through the use of directed beams, for example, Vivato and Bandspeed switches provide increased range of coverage, close to ten times that of regular access points.
  • Simpler installation: The use of switched wireless LANs make installation somewhat easier. For example, the Vivato and Bandspeed approaches limit the need to consider RF channel assignments for access points. The switching mechanisms rather than RF channels keeps users apart from each other.
  • Centralization: There are fewer access points to manage with wireless LAN switches, making configuration and troubleshooting a lot easier. Also, because there are generally fewer components, there is a much lower chance of anything going wrong.
  • Improved security: It's possible to implement tighter security measures, mainly because centralization limits the number of devices that hackers can exploit.

The Disadvantages

As with anything else, there are some disadvantages to deploying switched wireless LANs. One of the disadvantages is initial cost. For example, the Vivato switches range in price from $8,995 for the indoor model to $13,995 for the outdoor model. These prices are rather steep now, but the prices probably will come down in the future as volumes increase. Also keep in mind that the greater coverage of the switch will likely make the installation of a large wireless LAN less expensive than using traditional access points.

Another issue to consider is newness of the technology. There are no standards for switched wireless LANs. The 802.11 standard doesn't come anywhere close to defining switched wireless LAN technology, except for the Point Coordination Function (PCF) that is an optional medium access method that vendors don't implement.

Certainly any enterprise should consider the use of switched wireless LANs for large-scale deployments. Similar to the massive migration from Ethernet hubs to switches in the mid-1990s, IT managers will likely adopt switched wireless LANs as needs for higher performance wireless LANs proliferate.

Jim Geier provides independent consulting services to companies developing and deploying wireless network solutions. He is the author of the book, Wireless LANs and offers computer-based training focusing on wireless LANs.

Join Jim for discussions as he answers questions in the 802.11 Planet Forums.



Comment and Contribute
(Maximum characters: 1200). You have
characters left.