The as-yet unratified 802.16d standard, a combination of 802.16a, b and c, supports hundreds of concurrent connections and operates at distances of up to 30 miles (50 kilometers) and speeds as high as 75 Mbps. That's enough for at least 50 businesses to have sustained T1 access. Unlike the 802.11 standard, which uses CSMA/CA as a MAC protocol, the 802.16 MAC employs TDMA (time-division multiple access).
CSMA/CA problems are magnified when you implement 802.11 in a wireless MAN. CSMA/CA doesn't fare well over long distances because it's contention-based and requires that client machines detect collisions. Using directional antennas aggravates the problem. Instead, 802.16 uses TDMA, which allocates time slots so that each node takes a turn in order rather than semirandomly. That means no collisions and better performance. And 802.16 has QoS (quality of service) built into the MAC layer, which lets WMAN providers offer time-sensitive services like VoIP and low-resolution video without additional protocol overhead. It's designed for hundreds of users and works best if a single cell is less than 100 nodes to avoid polling delays. QoS is being added to 802.11.
Unlike conventional 2.5G and 3G data services, latency is not a significant issue in WMANs because most systems can tolerate a 10-ms delay. Wireless MAN distances aren't large, so the delays caused by RF propagation are minimal. That makes optimizing radio-processing crucial. Proxim claims its multipoint products have delays of less than 1 ms. Emerging mesh-based wireless solutions, in which data travels through multiple intermediate router hops, tend to suffer from higher delay.
So should you install your own wireless MAN? Unless the antenna is integrated into the CPE or is designed to be suction-cupped to a window, it's best to have your vendor or other service provider install it for you. That's because most WMAN reliability and performance problems are caused by improperly installed antennas.
And even with WiMAX, it will be some time before true plug-and-play 802.16 exists because the protocol spec is so broad and the number of products so few thus far.
Discover the benefits of scalable backbone and network services for application and cloud providers.
Network automation is gaining momentum. Here's how you can drive this powerful technology to its full potential.
Subsea cable alternatives can provide a level of comfort for those concerned about disruptions. Realistically, they will continue to play a small, but critical role in the short term.
