Building Metro Scale WiFi Mesh Networks
for High-Speed Wireless Internet Access Service

Figure 3: Three Competing mesh architectures (L=>R): Ad Hoc, 1-Radio Meshed Backhaul, Multiradio Backhaul

1. 1-Radio Ad Hoc mesh shown on the left uses one radio to service both clients and the mesh - the ad hoc mesh marked AH, is also a client to the mesh. A comparative performance analysis indicates this architecture is the worst of all worlds, as expected - backhaul and service compete for bandwidth.
 
2. 1-Radio Meshed Backhaul - one radio services client while the other forms an ad hoc mesh. In the center figure the pink radio services the laptops. The blue radio forms a single radio ad hoc mesh. In most cases  the two radios operating in different bands. a 2.4 GHZ  802.11 b/g radio is typically used for service and an 802.11a (5.8 GHZ ) radio is used exclusively for backhaul. 

This a + b/g configuration is sometimes called a Dual Radio Mesh - though only one radio participates in the mesh. Competing products claiming dual radio mesh do not support dual backhaul radios.
 
Separating the service from the backhaul improves performance when compared with conventional ad hoc mesh networks. But the backhaul is still being serviced by a single radio ad hoc mesh - since only one radio communicates as part of the mesh. Packets traveling toward the Internet share bandwidth at each hop along the backhaul path with other interfering mesh backhauls - all operating on the same channel. 
 
Note that the mesh behaves like a hub (all mesh radios on one "wire"). Hubs are inherently inefficient.

Figure 4: MeshDynamics 3-Radio Structured Mesh has a true dual radio backhaul

3.  3-Radio Structured Mesh. The best of all possible worlds is to provide separate backhaul and service functionality and dynamically manage channels of all radios so that all radios within range are on non interfering channels. The 3 Radio Structured Mesh does just that, in one integrated package.
 
Note that the two backhaul radios are of the same type - not to be confused with dual radio meshes where one radio is typically of type a (backhaul) and the other of type b/g (service). The backhauls are both of the same type and are both providing backhaul functionality.  This configuration emulates wired switches. Switches make scalable, efficient networks.
 

Figure 5: MeshDynamics 3-Radio supports high client density deployments

In the figure above the backhaul radios communicate with each other on a different channel, depicted by the different colors of the dashed lines.  Note also that the service radios (shown as ovals) are also on different channels and in a different band (802.11b/g vs. 802.11a) as the service radios. Thus, backhaul paths do not interfere or contend with any of the service radios and there are sufficient available channels (in 802.11a) to ensure that the backhaul radios do not interference with each other.

The two backhaul radios operate independently and their channels are allocated automatically to minimize interference between service sets. Bandwidth degradation effects endemic to single radios are eliminated - since each service set operates independently and simultaneous send/receives are now possible. 
 
Bandwidth preservation claims for the 3-radio modules were verified by tests conducted at a USAF lab.

MeshDynamics 2-Radio Structured Mesh^TM (Two Radio Shared Backhaul)

Figure 6: Shared Backhaul and service for light to moderate usage situations

2-radio units are like 3 radio units without a service radio- one backhaul radio doubles as both a service radio and a backhaul. Where client density is low - as in rural areas - 2-radio performance is adequate. As client density increases, 2-radio systems deployed on 4 mini-PCI slot platforms can be easily upgraded to 3-radio units by adding one more a/b/g radio and upgrading the software.
 
2-Radio units are thus a cost effective, scalable starter unit for WISPs covering low density areas or smaller area - but supports a migration strategy from 2-radio to 3-Radio when subscriber base increases.
 
2-radio units also serve as high performance meshed backhauls - both radios act as backhauls. OEMs and wireless backhaul vendors now have to an alternative to Point-to-Point and Point-to-Multi-point wireless solutions that lack the redundancy and re-configurability of Mesh.

Wireless Mesh Networks Value Proposition for WISPs

Competing mesh technologies lack the ability to distribute bandwidth over wide areas requiring multiple hops of the mesh backhaul. As a result, they need to be "re-charged" every few hops - through an Ethernet link. Costs of additional Ethernet links must be added to compare the overall deployment cost, especially for large Hotspots and city-wide HotZones requiring many nodes (see grids below).
 

 
Figure 7: Structured Mesh Networks do not need to be "re-charged" every 2-3 hops

 
In dense areas with many simultaneous accessing users per node, conventional mesh cannot deliver better than "dialup" bandwidth beyond 3 hops. A city wide wireless network therefore requires additional Ethernet links if each mesh is limited to 2-3 hops. 
 
Each Point to Point Ethernet link to the mesh adds increased capital equipment expenses. Also, each Ethernet feed service adds to the running cost of the network. For wide area, city wide WiFi deployments,  Structured Mesh is by far the most cost effective means of providing VOIP and data coverage. 

More Mesh Network Information:

• Various Approaches of Mesh Networking
• Hybrid Mesh Networks
• Wireless ISP Mesh Networks
• Technical Overview of Mesh Networks
• Advantages of Structured Mesh Network Modules
• Mesh Network Management Platform
• Benefits of a Mesh Control Layer
• Performance Analysis of Mesh Networks
• Test Results of Mesh Networks Real World Testing
• Deploying Wi-Fi Cellular Networks for Voice over IP Services