Synchronous mesh offers scalability

This could be the answer to a mesh network's asynchronous MAC protocol.

Wireless mesh networks have become increasingly popular based on their many advantages, but the topology can have an Achilles' heel that is becoming painfully apparent: The network may fail to scale as promised.

The underlying problem is the mesh network's asynchronous media access control (MAC) protocol, which is unable to handle the contention in larger networks. The mesh network eventually breaks down in a mess of self-interference and collisions that degrade throughput and undermine scalability.

A synchronous mesh employs directional antennas and the time division duplex (TDD) protocol to direct and coordinate simultaneous transmissions throughout the wireless mesh topology. By maximizing spatial and spectral reuse, the synchronous mesh is able to deliver substantially greater scalability.

The first requirement of the synchronous mesh involves using directional antennas instead of omnidirectional. Directional antennas dynamically create dedicated point-to-point connections among mesh nodes, which reduces internode interference and collisions. This directional wire-in-the-sky forms the foundation for a scalable mesh network. The higher power levels permissible with switched point-to-point links also afford other advantages, including higher modulation rates and a longer range between nodes.

The second requirement for building a scalable wireless mesh network involves synchronizing all transmissions across numerous directional point-to-point links. This requires a common timing source, such as the one provided by GPS satellites. A common clock allows the synchronous TDD MAC protocol to coordinate precisely directional transmit/receive processes throughout the mesh topology. Transmissions occurring simultaneously in different portions of the mesh network result in maximum spatial and spectral reuse.

With wireless, the only way to overcome the scalability limitations of carrier-sense multiple access-based Wi-Fi mesh networks is to employ dynamic, directional point-to-point links with all traffic flows synchronized and coordinated.

It is important to note that meshwide transmission coordination also makes the synchronous mesh deterministic; the throughput, latency and jitter become predictable, because the traffic flow is no longer subject to variable conditions that cause congestion and collisions. Deterministic QoS is essential in converged networks that must support real-time voice and video communications.

Like previous generations of mesh networks, synchronous mesh supports automatic node discovery for rapid deployment and self-healing failover for dependable operation. Other previously used capabilities also can be implemented in a synchronized mesh without restrictions, such as dynamic link optimization, customizable traffic shaping and prioritization and end-to-end dynamic routing.

When implemented together, the directional antennas and synchronous TDD MAC create a deterministic mesh network that breaks through the performance and scalability barriers encountered in previous generations of wireless mesh solutions.

Further, a growing number of industry analysts say a scalable, high-performance mesh topology can be created only with the spatial and spectral reuse afforded by these twin capabilities.

Jenkins is vice president of product management for SkyPilot Networks. He can be reached at bjenkins@skypilot.com.

The rapid synchronization of concurrent traffic flows through a mesh topology uses spatial reuse to deliver deterministic QoS from source to destination.

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