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Chapter 2, Wireless Protocols

There are two major types of wireless protocol in use in the modern WISP arena: Wi-Fi based systems, and proprietary systems. In reality, the majority of WISPs operate a hybrid of the two. This section explains the differences between Wi-Fi, proprietary Wi-Fi extensions such as AirMAX, and purely proprietary systems such as WiMAX or LTE.

There are two major types of wireless protocol in use in the modern WISP arena: Wi-Fi based systems, and proprietary systems. In reality, the majority of WISPs operate a hybrid of the two.

Wi-Fi based systems are typically the least expensive, but can suffer from inherent flaws resulting from the 802.11 standards: “hidden nodes” can cause performance problems, Wi-Fi congestion handling assumes that a client will stop broadcasting when it encounters interference (the “backing off” problem), and – particularly on older Wi-Fi standards – large guard frequency areas and relaxed timing requirements can lead to lower overall throughput. The advantage of a pure Wi-Fi system is that you have near-limitless choice in vendors: there is a lot of Wi-Fi equipment available, for just about any need.

Proprietary systems, such as Motorola Canopy (now Cambium) utilize a vendor-designed protocol. This allows them to avoid the downsides of Wi-Fi, but at the expense of compatibility: every participating radio must comply with that vendor's protocol if it is to connect to the network. This tends to result in much higher equipment costs, and significantly reduced choice in systems.

Ubiquiti and Mikrotik have independently developed their own hybrid systems. Both utilize Wi-Fi as the base system, taking advantage of the widespread availability of Wi-Fi systems to offer a large range of low-cost systems with which to power your WISP. Both add a layer on-top of Wi-Fi that alleviates the hidden-node problem, and replaces the “back-off” system with a strict time-division multiplexed (TDMA) system that divides the chosen frequency into small time-slices, and strictly governs when a unit may broadcast within these time slices. This leads to significant performance improvements, while only sacrificing some of the flexibility of pure Wi-Fi (additionally, both Ubiquiti and Mikrotik offer the option to turn off their proprietary layer, and operate as pure Wi-Fi when compatibility with other units is required). Ubiquiti name their system AirMax, while Mikrotik name theirs N-Stream. The two are incompatible, but serve similar purposes.

The majority of WISPs start with either Ubiquiti or Mikrotik, utilizing their TDMA systems. As funds become available, some WISPs find it advantageous to expand into Canopy/Cambium and similar systems, others invest in WiMAX, LTE or other large-scale systems – and many simply stick with hybrid TDMA systems (the largest WISP in Texas reports 150,000 customers utilizing AirMax – and with careful planning have avoided the need for a more expensive system).

System Advantages Disadvantages
Pure 802.11x Wi-Fi Compatible with everything. Protocol back-off, hidden node problems.
Pure Proprietary Higher performance. Compatible only with devices from that vendor.
Hybrid (e.g. AirMax / nStream) Fixes major Wi-Fi problems, performance somewhat higher Compatible only with devices from that vendor, but can generally be disabled for Wi-Fi compatibility.
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