Mesh network requirements have evolved from their military origins as requirements have moved from the battlefield to the service provider, and residential networking environments. Today, to cover large areas with a single wired Internet link, more cost effective and efficient means of bandwidth distribution are needed. This implies more relay nodes (hops) than were needed before. Further, growing demands for Video and Voice-over-IP require packets to be moved over the mesh at high speeds with both low latency and low jitter. These requirements (more hops to cover large areas, more efficient bandwidth distribution and better latency and jitter for Video and VOIP) has given rise to the newer mesh architectures.
Three Generations of Mesh Architectures
Three generations of mesh architectures are shown above. Note: First and Second, both use a single radio as backhaul:
• First Generation: 1-Radio Ad Hoc Mesh (left). This network uses one radio channel both to service clients and backhaul. This architecture provides the worst of all the options, as expected, since both backhaul and service compete for bandwidth.
• Second Generation: Dual-Radio with Single Radio Ad-Hoc meshed backhaul (center). A single radio ad hoc mesh is still servicing the backhaul, packets traveling toward the Internet share bandwidth at each hop along the backhaul path with other interfering mesh backhaul nodes - all-operating on the same channel. Bandwidth Degradation
• Third Generation: 3-Radio Meshdynamics Mesh (right). Provides separate backhaul and service functionality and dynamically manages channels of all uplink and downlink radios so that each backhaul (hop) is on non-interfering channels.
Meshdynamics Structured MeshTM are multi-radio backhauls. They are the wireless equivalent of (scalable) switch stacks.
Bandwidth degradation on Single Channel Backhauls
With one backhaul radio available for relaying packets, all nodes communicate with each other on one radio channel. For data to be relayed from mesh node to mesh node, that node must repeat it in a store-and-forward manner. A node first receives the data and then retransmits it. These 2 operations cannot occur simultaneously because, with only a single radio channel, simultaneous transmission and reception would interfere with each other.
This inability - to simultaneously transmit and receive - is a serious disadvantage. If a node cannot send and receive at the same time, it loses ½ of its bandwidth as it attempts to relay packets up and down the backhaul path. A loss of ½ with each hop implies that after 4 hops, a user would be left with (½*½*½*½) = 1/16 of the bandwidth available at the Ethernet link. This is 1/(2N) relationship defines the fraction of the bandwidth available to a user after N hops, see Figure 2. .
Fig.2: (left) Competing mesh products suffer from ½ Bandwidth loss with each hop.
Click to Enlarge.
Decoupling the logical channel-selection and topology-definition processes from the specific physical radio in this fashion delivers distributed dynamic radio intelligence benefits for current as well as emerging radio standards.
An additional benefit of decoupling the distributed dynamic radio intelligence software -- controlling channel selection and topology configuration -- from the radio hardware is the potential to incorporate commercial-off-the-shelf (COTS) radio and other modules. This substantially decreases time-to-market and greatly increases manufacturing scale, reducing both development- and unit cost over the use of custom hardware development.
Bridging Across Multiple Networks.
Modular MeshTM products take our radio agnostic MeshControlTM RF Agility one step further. The "RF robot" software runs at a radio-abstracted layer: the same mesh control software supports radios operating on different frequency bands and protocols.
Fig. 4 shows how this level of flexibility is leveraged. There are 4 mini-PCI slots on the board, two on the bottom and two on top. Each of the four slots can house a different frequency radio. This opens up some interesting possibilities including 2.4 GHz backhaul systems being part of a mesh with 5.8 GHz backhauls.
Since the service and backhaul radios are distinct, it is possible to use a service radio to bridge over from a 5.8 GHz backhaul to 2.4 GHz backhaul – as shown in Fig. 5. The 4325 Mobility Relay node on the bottom left has joined the mesh – even though the upper links are 5.8 GHz (blue) – through the service radio (pink). (Click on Figure to Enlarge).
New mesh requirements (more hops to cover larger areas, more efficient bandwidth distribution, better latency and jitter for Video and VOIP) have given rise to the Third Generation of mesh architectures. Third Generation multi-radio backhaul architectures deliver the higher bandwidth and more-deterministic performance necessary to meet these new requirements.
Software-oriented approaches based on distributed dynamic radio intelligence support frequency agility, automated channel selection, dynamic topology configuration, and radio agnostic meshes, provide more effective single framework solutions for larger scale and diverse application environments.
This combination of features delivers higher performance but is also opening many new applications for wireless mesh, see:
The Abstracted Network for Enterprises and the Internet of Things.