In a large distributed wireless mesh network, such as a municipal network that supports public-safety or other vehicle applications, optimized Layer 2 algorithms designed for low latency and high throughput on a large scale work far better than common spanning-tree and related implementations. Layer 2 algorithms enable associated mesh nodes to adapt quickly to the dynamics of mobile nodes while supporting real-time and high-speed applications.
Optimal wireless mesh net
Scalable mesh fast reroute (SMFR) is a new high-performance wireless mesh technology that solves the problems associated with other algorithms. SMFR enables automatic, self-forming and self-healing, topology-independent fast rerouting that supports high-speed mobile roaming, near-zero through- put loss and near-zero latency over multiple hops.
SMFR is a component of an optimal dynamic mesh architecture that takes advantage of wireless mesh network nodes with multiple radios and puts mesh intelligence and decision criteria in each node. The nodes have distributed localized node intelligence, network topology-independent fast rerouting, instant roaming, near-zero through- put loss and near-zero latency over multiple hops.
Regardless of network topology or size, SMFR has the inherent intelligence to locate all network nodes automatically in a mesh via airspace scanning and real-time backhaul-path analysis using round-trip delay, signal-to-noise ratio and other criteria. Each node maintains a table of its associated neighbors initiated through foreground scanning and probe request/response packets. The table is based on real-time information learned at every link-state change and updated via background scans every 5 milliseconds, transmitted via 802.11. During updates, the node reviews preconfigured parameters, checks them against new information and updates all previous information as necessary.
Each node has distributed algorithms to localize the decision-making process based on local traffic measurements and performs intelligent dynamic channel assignment, which is critical to the mesh's performance. Each node also determines best paths for primary and secondary transport; sets quality-of-service and fast mobile-roaming parameters; and handles real-time backhaul path analysis, congestion avoidance and optimal channel reuse. In addition, each node monitors the health of its own area.
Neighboring nodes in the network are aware of the best path for a given user and for backhaul ingress and egress. If the best-path criteria drop below the set threshold or the path is blocked, the system continues the self-healing process. This involves foreground and background wireless-link scanning, in which probes are sent from every node over each link to every adjacent node. If a network failure occurs, a wireless link is switched to the node with the best path, which is based on multiple criteria to ensure the highest possible "score" for zero-loss seamless handoff.
This handoff enables roaming across large geographic areas without the need for user intervention.
SMFR continuously performs self-tuning and self-healing to optimize each path for best performance and congestive redirection, even for mobile nodes moving at 200 miles an hour.
Lab results
Independent testing by Iometrix Inc. shows that multiradio solutions implementing SMFR offer the highest performance over multiple hops and can support the largest number of high-quality voice calls. The test plan developed by Iometrix was based on standards work by the IEEE 802.11 Task Group for Tests. The tests used RF-shielded equipment from Azimuth Systems Inc.
The test plan specified a series of rigorous tests to determine a variety of performance parameters:
• backhaul performance for both data and voice under various conditions of stress;
• maximum client capacity;
• in-motion roaming delays;
• reconvergence times in the event of mesh node failure; and
• voice quality in the presence of data.
The testing results showed that in single-, dual- and some multiradio implementations, throughput tapers off when hop counts increase. With a multiradio mesh implementation employing SMFR, however, maximum throughput was sustained and remained constant over a large number of wireless hops. In addition, SMFR provided extremely low latency, falling well below the requirement for high-speed mobility handoff. And it maintained the highest number of high-quality VoIP calls, regardless of the number of hops.
Many have tried to use single- and dual-radio architectures, as well as Layer 3 IP routing and Layer 2 spanning-treelike algorithms, to build wireless mesh networks. However, these networks have failed to provide the high throughput, low latency and fast roaming handoff required for the wide range of applications used today. Multiradio wireless mesh network products provide a significant performance advantage over single- and dual-radio products. In addition, multiradio products build a mesh network by supporting multiple active associations. With this level of connectivity, the wireless mesh network provides the resilience and performance needed to support a wide range of applications, including not only data but also high-quality voice and video.
Consumers are familiar with the performance of their own broadband Wi-Fi connections at home, and now wireless networking has proven itself to the point where consumers want to remain connected all the time. Wireless mesh networks that use SMFR can provide this level of performance. Moving forward, this technology will continue to be used in large-scale deployments worldwide.
