Not too long ago Bluetooth® SIG announced that Bluetooth® is going mesh, giving a rise to a new wave of interest to Mesh networking. Although the interest is growing rapidly, solutions available on the market keep using just the trusted star topology. But what are the real possibilities?
Most networks on the market are declared to be “mesh ad hoc,” so in most cases these terms are used together in turn blurring the difference between them. But there is a difference and it’s important to highlight it.
Mesh network is a kind of a network topology where all the possible connections between nodes are established. This leads to the main mesh network feature – self-healing, where broken routes can be restored using different access links between devices.
Ad hoc network is a decentralized wireless network that does not require any infrastructure to form and maintain. Nodes connection depends on its possibility. This network is self-configuring, which means that devices can join or form it on the fly.
In this way, mesh network is the most robust static type of ad hoc networks. But when both terms are used together, they typically mean ad hoc only. Mesh explains just the physical layer of wireless communication that is broadcasting from its nature where all devices that are close enough hear each other (i.e., connected) and form enough links for self-healing. To be completely accurate, it should be mentioned, that “ad hoc” means that the nodes are stationary. There is a term for mobile nodes – Mobile ad hoc networks (MANET’s). But today in PAN/LAN context (Wi-Fi, Bluetooth, ZigBee) nodes are assumed to be static due to their use cases, even if they can be moved sometimes from place to place.
Wi-Fi is an area that already has ad hoc solutions available through documents and open source. Official specification IEEE 802.11S is the less effective and innovative one. It introduces two new kinds of devices: Mesh portals and Mesh points. Mesh portals are ordinary Access points with wired connection to the Internet. Mesh points act as wireless routers between stations and portals. Everything that has “mesh” prefix is connected together where it is possible. The standard is completely the same as B.A.T.M.A.N. adv Wi-Fi mesh that is already included in the Linux core.
In parallel, open source community works on cjdns (Hyperboria) that is a real candidate for the DarkNet set of protocols. Cjdns is developed in the way to create a wireless mesh network that is totally disconnected from the Internet. Its core advantages are:
The last one is a headache for all Wi-Fi ad hoc networks. Old DHCP conflicts with the essence of the ad hoc network and mobility.
Mesh networking using Wi-Fi sounds ready but not for small low-power devices. Thus, we better pay attention to Bluetooth® Low Energy (BLE) and ZigBee®.
The first thing that Mesh-network-sceptics say about Bluetooth® is that it was not designed for Mesh networking. However it is widely spread, so why not to try using it?
Existing solutions on BLE are nothing more than trying to sell things that we already have in ZigBee® under the “Mesh network” label. To build a “mesh” the customer should buy a BLE gateway that forwards packets to the cloud. All main-powered BLE devices act as routers and interconnected with each other, while battery powered devices talk to routers only. Nothing special.
But BLE wins in that it is already in devices that have the Internet connection through 3G, LTE, Wi-Fi, and even the cable. That means that in theory the customer can get more than one gateway connected by the Internet. Moreover, customer’s tablets and smartphones bring the mobility to such network.
The power of the Wi-Fi + BLE collaboration has already been explored by Apple: check out the Multipeer connectivity framework for iOS 7 and, for example, FireChat application that proudly announces “Internet is not needed to chat.”
When talking about ZigBee® one thing should be kept in mind – it was initially designed to be ad hoc. The routing mechanism implemented in ZigBee® is called Ad hoc On-Demand Distance Vector (AODV). Although RFC is operating IP frames, there are no major differences. The algorithm is quite simple for CPU and gentle to ROM and is available even for a bulb or smart socket or any other main-powered device.
As it was mentioned earlier, ZigBee®-based systems on the market currently prefer to use star topology, even though it has everything to be a mesh network and should be used as such. When Wi-Fi or BLE implement mesh, it is not only a technological step forward, but a marketing reason. The truth is ZigBee® is already a step ahead in terms of technology, but maybe a step behind in terms of marketing.
One might mot like that ZigBee® network is not using IPv6. Well, neither does BLE, but it does not disturb it. Nevertheless, there is IEEE 802.15.4 + IPv6 + UDP solution called 6Lowpan and Thread or JupiterMesh built over it. Though they haven’t still made a splash on the market, probably nobody has positioned them as “mesh.”
As we can see, if the market wants mesh/ad hoc/MANET, there are all the pre-requisites for it. It is already around but the customer is not aware of it because either the market is too “shy” or that field has not yet been covered in depth. Anyway, the results will come soon and they will come from Wi-Fi, BLE, ZigBee or even a collaboration between them.