Convergence Channel: Deploying Wireless Networks

What’s the Frequency, Kenneth?

Another important aspect of wireless implementation is choosing the appropriate frequencies. But to be perfectly honest, the choice of frequencies actually isn’t much of a choice anymore. There are two main frequency ranges for public wireless network usage: 2.4GHz and 5.8GHz. There is also an available range of frequencies at 4.9GHz, but these are reserved for public safety agencies and operations.

The reason I say there’s not much of a choice anymore is that the available channels in the 2.4GHz range are pretty much saturated now. This consists of every 802.11b or g wireless system out there, which is pretty much all of the consumer-level devices. If you’re in the big city, finding empty 2.4GHz channels will be a challenge. If you live out away from heavily populated areas you may still be in luck, although I wouldnt count on that lasting too much longer.

Wireless 802.11a and n devices use the much less crowded 5.8GHz band, although that too is filling up fast. Networks classified as 802.11n in fact can use either 2.4GHz or 5.8GHz, depending on the device. The 802.11n class is fast becoming the new consumer standard for home wireless networking, and 5.8GHz cordless phones are starting to emerge in the market as well, further muddying up the wireless waters.

Earlier I mentioned the 4.9GHz range and how these frequencies are reserved for public safety agencies. There are specifications for fixed and portable operations. If you are planning a wireless system for municipal or other government use it is worth looking into these frequencies. Unlike the 2.4GHz and 5.8GHz bands, 4.9GHz is in fact-regulated and an application must be submitted by the requesting agency. A regional coordinator addresses any interference issues between 4.9GHz systems that might arise.

A Review of Wireless Topology

Just to go back over some basics, there are three general types of wireless networks: point-to-point, point-to-multipoint and mesh.

The point-to-point and point-to-multipoint networks are pretty self-explanatory. A point-to-point network will have a single transmitter and a single receiver, sending a single stream of data. For an installation sending one device back to one point (like a parking lot camera back to a guard building), this is the way to go.

A point-to-multipoint network will generally have a single receiving antenna, with multiple transmitting radios feeding into it. A case for this topology would be multiple parking lot cameras shooting back to a single building. Depending on the needs, the single receiving antenna can either connect directly to a wired network, or it can also redirect the traffic to a second radio with a higher-bandwidth wireless connection to another location. This application is called a backhaul.

A mesh network has multiple nodes, usually consisting of both a transmitting and a receiving radio. Each node is constantly in contact with other nodes, sending data back and forth. One of the benefits of a wireless mesh network is if a node goes offline, other nodes adjacent to it can detect the failure and reroute the data around the affected node. This is called a self-healing mesh.

A mesh network is commonly used in citywide video policing systems or for campus-wide video security. In some cases, the wireless nodes can have multiple radios in them. These can provide either a high bandwidth backhaul link or sometimes the second radio can be used for public access WiFi. This application can be used as a revenue generator in some circumstances.

Design Is Divine

As I often preach in this column, the work put in upfront is everything. If the network is designed correctly, whether wired or wireless, many problems can be solved
before they occur. Unlike with wired networks, however, it is important to remember that a wireless environment can change at any time. This is not to say you shouldnt think about doing wireless installs. You just need to be careful with what you promise the customer.

MCSE- and CCNA-certified Steve Payne has more than 15 years of industry experience and heads Convergence Consulting, an IP and security solutions consulting firm. Be sure to also read his “Integrated Thoughts” blog.

 

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