Cabling a Multi-Zone Network

Building the Multi-Zone Wi-Fi Network

There are two general reasons for having more than one wireless access point in a network:

1. Covering a wider physical area; that is, more space.

2. Providing additional bandwidth so that more computers can connect to the network at useful throughput levels, even if they're close enough to reach a single access point.

Roaming

If you simply need to cover a larger home or office, any access points will do. This is especially true if you don't need to support roaming, that is, the ability to walk around with a laptop or Wi-Fi equipped PDA and not lose your connection when you move from the field of one access point to another. Without roaming, you must move to a location and log into the network from that location. Move out of the field of the access point to which you're connected, and your connection vanishes, and you must re-connect from a new location in the field of a different access point.

Roaming has not been implemented consistently on low-end access points. Higherend products (like those from Cisco and Proxim) implement proprietary solutions for roaming that work, but only work when all access points are 'in the family' and support the proprietary technology. The IEEE 802.11f task group defining the Inter Access Point Protocol (IAPP) that will standardize 802.11 roaming is not yet finished, and products conforming to the IAPP specification may not appear before late 2003.

All of this is just to say: If you want reliable roaming, you will have to spend big. Cisco Aironet 350 access points cost $600, not $100, because they support more features-and because they're targeted at corporations more willing to spend money than ordinary people.

The other reason for implementing a multi-zone network may take some explaining. Say you have a cube farm in your office with fifteen workers, each with a computer that needs to be networked through a wireless access point. If all fifteen workers connect to one access point, all fifteen would share that access point's throughput, which might be 4 Mbps. (I cover measurement of throughput later in this chapter.) You might as well put them all on a dialup, especially if their work involves lots of heavy communication among their computers.

Load Balancing

Load balancing in this context means arranging a network so that multiple access points are installed in the same general area, and connections from wireless clients are distributed evenly among them. With three access points, you could have five clients connected to each access point, and your fifteen workers would all have a reasonably brisk network connection.

Load balancing is not a part of the 802.11 specification, and in my experiments has proven remarkably difficult to pull off with low-end hardware. The problem is that in a network with multiple access points, Wi-Fi client adapters want to connect to the access point with the strongest signal. Most client adapters provide no way to force them to associate with a particular access point when several are present on the same network. As with roaming, the higher-end access points from companies like Cisco and Proxim support load balancing through proprietary technology, either from a centrally administered utility or by manually assigning individual client adapters to access points by MAC address.

Be aware that there are only three 802.11b channels that do not overlap in frequency and thus do not interfere with one another: 1, 6, and 11. Doing load balancing with more than three access points in the same area gets very dicey. My suggestion: Move to a technology such as 802.11a, which provides much higher throughput, and allows more client computers to connect to a single access point. 802.11a is especially attractive if you have wide-open areas divided into cubes, especially if you can mount the access point high on a wall or on the ceiling.