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 centralised infrastructure network. Provided there are a sufficient number of nodes, the network is able to sustain temporary congestion, individual node failure and localised interference. The built-in ability to find neighbour 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.
- Discovery and association.
- Medium-access coordination.
- Compatibility to 802.11 services.
- 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.
The current crop of 802.11 products work well for traditional applications that focus on Internet-centered activities such as e-mail, Web surfing, downloads, some video streaming and IP telephony. Even multimedia applications are adequately supported with more advanced 802.11n devices.
As wireless networking moves into more heavy-use environments where the amounts of data increase, even 802.11n capability may not be enough. When high-definition multimedia needs to be moved between local devices for rendering, the current wireless hub-and-spoke model will experience limitations.
Wireless meshes offer the solution to this problem. Wireless devices are able to communicate directly without going through a central point (the access point). With mesh topology, traffic can flow via the most optimal path. The Internet access device, which is commonly collocated with the access point, need not become the bottleneck. These networks can even be created without the need for an access point at all, where information will be kept local between the peer devices.
Wireless mesh, as a replacement for the dysfunctional ad hoc mode (one of two ways to currently approach mesh today, the other being wireless distribution system, WDS), also will enable personal area networking. Devices such as smartphones can easily mesh with personal media players and video cameras without an dedicated intermediate device such as an access point. If infrastructure is available, these meshed devices will be able to use it to access Internet-based resources as well. This will create opportunities for new types of devices and services.
In industrial environments there has long been a need for wireless mesh solutions. Wireless in general is ideally suited for applications that require easy, inexpensive deployment, resilient and manageable operation, extended range and more uniform coverage. Wireless mesh networks that use off-the-shelf hardware that is on the standards track is ideally suited. The use cases include telematics, sensors, surveillance and security, process controls and robotics.
The ability for meshed devices to offload high-capacity data streams from the access point and distribute the data directly between nodes, and the network infrastructure benefits of mesh topology, signal that the time is right for strong, marketable solutions based on 802.11s. The combination of market needs, emerging trends and the demands for interoperability will finally make meshing a common feature of wireless networks after years of being "right around the corner."
Gurevich is vice president of engineering at PacketHop. This article appeared in Network World.
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