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What Is Mesh Topology?

Mesh topology is a type of networking where all nodes cooperate to distribute data amongst each other.  This topology was originally developed 30+ years ago for military applications, but today, they are typically used for things like home automation, smart HVAC control, and smart buildings. Within this article, we’ll provide a general overview of how mesh topology works, the benefits and considerations associated with mesh networks, industry standards, and alternatives.

How do mesh topologies work?

Many mesh networks allow radios to spontaneously organize themselves by using something called ad hoc on-demand distance vectoring. This is a reactive protocol using some characteristics of proactive routing—meaning the developer creates some of the routes and identifies nodes to play different roles, like an end node or repeater. In simplified terms, an endpoint doesn’t just act as destination and a source of data, but also as a relay point.

Mesh systems usually rely on a routing table, which tells every node (a) how to communicate with the access point, and (b) how a node should direct traffic that is trying to go somewhere. The routing table assumes that there is not direct communication anywhere in the network except by nodes that have a route to the access point. It’s like a big game of telephone—if you don’t know the route, then you send the message to someone that has the route established. Routing tables are comprised of:

  • Source identifier
  • Destination identifier
  • Source sequence number
  • Destination sequence number
  • Broadcast identifier
  • Time to live

(These are fairly technical topics, and we won’t cover them in much detail here.)

Mesh networks operate in two ways: by either routing the data or flooding the data. When you’re routing a message in a mesh network, it propagates along a predefined path, hopping from node to node until it reaches its destination. In order to establish these routes and ensure that the paths are available, the network needs to be continuously connected and configuring itself. In other words, it has to constantly work to find broken paths and create self-healing algorithms to build route tables. Because there’s a lot of layer two (MAC) traffic flowing on the network to establish this route, mesh networks can be less efficient than star networks (which we’ll cover in a moment).

A simpler mesh network takes a flood approach, where the data flows continuously throughout the network. If a module sees data with its address, it simply grabs it. This works because of the time to live, or TTL, value where messages are allowed to propagate through the mesh for only a fixed number of hops before they are removed.

Benefits

  • You can move a lot of data around the network if the mesh is operating properly.
  • It is relatively power efficient, and thus allows for decent battery life.
  • There are plenty of low-cost mesh radio hardware out there, like ZigBee.
  • There is less of a connection setup delay with mesh networks.

Considerations

  • If you don’t have distributed nodes throughout a building (or wherever you’re trying to go), you can end up with chokepoints and link problems. ZigBee, for example, can transmit only about 30 to 50 feet from node to node. This can be a problem if you don’t have really dense sensor deployment throughout the building.
  • Mesh networks are very short range by nature. We’ve talked with an HVAC installer who admitted to adding extra thermostats in a building just so the links could be made properly.

Industry Standards Around Wireless Mesh Topologies

One of the most popular and well-known mesh network is ZigBee. Other well-known mesh topologies include:

  • Z-Wave
  • 802.15.4
  • DASH7
  • 6LoWPAN
  • ANT
  • One-Net
  • MiWi
  • WirelessHART
  • Wibree

An Alternative To Mesh Topology

Mesh networks are not the only way to solve low power network needs for enterprise and industrial smart applications. In fact, a wide majority of low power, wide-area network (LPWAN) technologies use a star-topology network, where the endpoints are connected directly to the access point. Make sure you do your due diligence on all network types before arriving upon which topology will work best for you.


IoT Protocol Selection White Paper

Written by Brian Ray

Brian is the Founder and CTO of Link Labs. As the chief technical innovator and leader of the company, Brian has led the creation and deployment of a new type of ultra long-range, low-power wireless networking which is transforming the Internet of Things and M2M space.

Before starting Link Labs, Brian led a team at the Johns Hopkins University Applied Physics Lab that solved communications and geolocation problems for the national intelligence community. He was also the VP of Engineering at the network security company, Lookingglass, and served for eight years as a submarine officer in the U.S. Navy. He graduated from the U.S. Naval Academy and received his Master’s Degree from Oxford University.

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