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The benefits of 802.11s wireless mesh nets

By David Gurevich, special to Network World
May 28, 2008 02:48 PM ET
This vendor-written tech primer has been edited by Network World to eliminate product promotion, but readers should note it will likely favor the submitter's approach.

Network World - Mesh networking has been hyped as the next big thing in wireless, but the current IEEE 802.11 standard does not define it. That hasn’t stopped vendors from trotting out proprietary mesh gear to meet market demand, and the IEEE 802.11s Working Group was formed to address that. A draft standard is reportedly now feature complete.

Why the interest in mesh? There are four major benefits:

* Range extension is one of the primary arguments for mesh networks. In situations where wired access-point connectivity is too expensive to implement or impractical due to environmental conditions, the ability to deploy a node that can receive and forward traffic can make wireless mesh the only solution. Because wired infrastructure is not required, mesh can be set up faster, cheaper and with less expertise.

* Mesh nodes can be deployed anywhere there is power, with the resulting network architecture providing better coverage. Nodes can be put in with no regard to the wired backbone. The only limitation is power and radio propagation. Due to the properties of radio-frequency propagation, higher capacity is an added benefit. The closer the radio links between nodes, the higher the modulation rate. The higher the modulation rate, the higher the effective network throughput. Without mesh this can only be achieved with expensive and complicated antenna technology. In the mesh network, any standard off-the-shelf client is able to achieve the highest possible throughput.

* A wireless mesh inherently is more resilient and fault tolerant than a centralized infrastructure network. Provided there are a sufficient number of nodes, the network is able to sustain temporary congestion, individual node failure and localized interference. The built-in ability to find neighbor nodes, set up connections, find optimal traffic paths – all these standard features make the products based on 802.11s mesh less failure-prone.

* Mesh devices can be set up to create a high-bandwidth network among themselves without the need for a central access point. This ability for peer-to-peer connectivity opens a host of new applications in the enterprise and home markets.

The IEEE task group assigned to address mesh networks was formed in 2005 and plans to have the 802.11 “s” addendum (now at Version 2.0) out by the end of 2009 to address:

* Topology learning, routing and forwarding.

* Security.

* Measurement.

* Discovery and association.

* Medium-access coordination.

* Compatibility to 802.11 services.

* Interworking.

* Configuration and management.

The core functionality has been defined so vendors can design and deliver products and claim draft-level support. The pre-standard products usually leverage existing off-the-shelf hardware components and firmware, and modify and extend the standard 802.11 media-access-control layer to enable link establishment and management, path selection, data forwarding and security.

There are multiple benefits for vendors willing to start the evaluation and product development cycle. The current products offer functionality equivalent to the forthcoming standard. To the upper-layer protocol, such as IP, the pre-802.11s wireless mesh will behave exactly the same as the final standard 802.11s mesh, so customers do not have to worry about modifying products once the fully standard implementation is available.

The main limitation with the pre-standard mesh implementations is the lack of product interoperability. But if the customer has a standard 802.11 access network, some mesh vendor’s products will interoperate with the legacy access points transparently. This is particularly useful in the enterprise and consumer entertainment applications, where mesh offers much promise.

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