Wireless Mesh Networks

Roland Piquepaille writes "Robert Poor is CTO of Ember Corporation. He contends that point-to-point or point-to-multipoint networks typical of industrial wireless communications systems have limited scalability and reliability. 'In contrast, wireless mesh networks are multihop systems in which devices assist each other in transmitting packets through the network, especially in adverse conditions. You can drop these ad-hoc networks into place with minimal preparation, and they provide a reliable, flexible system that can be extended to thousands of devices.' The article is pretty technical and contains several illustrations and a case study about the deployment of a wireless mesh network in a water treatment plant. Check this column for Poor's conclusions or read this Sensors article if you have more time."

Comments

Simulations? Hard numbers?

[Quixote]

Common sense tells you that if the number of nodes connected to the (wired) 'net is significantly less than the number of nodes not connected (i.e. on the mesh alone), then you'll have a bottleneck.

Has someone done any simulations on the behaviour of these mesh networks as the number of nodes increases, without an increase in the number of connected (with one foot in each domain) nodes?

Also, will the "max flow min cut" theorem come into play at some point? Will some poor sod who happens to be the "cut point" get hammered beyond belief by having to route all packets?

It looks to me (and I could be totally wrong here, its been known to happen quite often) that this "mesh networks" craze is similar in vein to the "P2P" and "distributed computing" crazes that came along a couple of years ago.

Mesh = Unduly Trusted?

[Shoten]

Ok then...as I can understand it (and maybe I'm missing the point here), for objects in the mesh to assist in carrying its traffic, you have to entrust them to be part of its infrastructure. This leads to the obvious question: would you allow just anyone to put their router (or device that acts like a router and does god knows what else) between you and your endpoint? For that matter, would you trust a network made entirely of network devices that everyone and their brother contributed, with those devices able to come and go like thieves in the night?

It seems to me that a mesh network would inherently place trust in all users, in a world where it's clear that all users should not be trusted, just some...and there's no way yet to sort out the good from the bad. Even if you restricted the use/deployment of the network to a single organization, it still poses an absolute nightmare that an insider could subvert the functions of a node.

I love the notion of minimal centralization (if any) and the fault tolerance that can come with it, but I think that the security risk is waaaaaay too great.

One day, when all connections between points (I doubt this day will come, btw) are encrypted, this could work, but only as long as the mesh itself could detect and isolate the source of DoS behavior against the rest of the net. Remember, encryption keeps information secret, but it doesn't keep anyone from just plain breaking stuff :)

Re:Cells just get smaller

[James_Duncan8181]

And if the cells get smaller, the amount of routing hops increases, and my friend's bandwidth goes down as his node fetches and sends me, my other buddy, my dog, and my neighbour files off Kazaa because he is nearest to the wired pipe. There is fundamentally only so much bandwidth in the air, and it is not enough to support ubiquitous wireless use. The failure here seems to be not appreciating that people will all want to connect to certain nodes, as they supply the (wired) bandwidth.

My biggest problem with this type of network.

[gmplague]

My biggest problem with this type of network is the battery life. Sure, maybe the logistics of the network architecture are sound or whatever, but if my cell phone or my laptop is constantly rebroadcasting packets whenever it's in range of the network, then I'm pretty sure there'll be a substantial drain on my battery life. Maybe when battery life is basically a non-issue this type of network will be feasible, but until then, bleh!

Are they really sure this will scale?

[zerofoo]

It seems that every node must be "connected", that is every node must "touch" every other node. Is that the way this technology works? I couldn't tell from the article. If so, it doesn't look like this type of network will scale very well. (Much like p2p networks...they work around this problem by limiting the amount of nodes any other node can see). I remember talking about this type of network (and its limitations) in college in a graph theory class.

-ted
-ted

Been there, done that...

[erc]

Been there, done that. I designed a wireless tactical network based on this idea back in 1995 or 1996. What I discovered is that it's tricky to get routing right if you use a broadcast type of protocol where each node automatically retransmits anything it hears, because the network quickly gets swamped with retransmissions unless you're careful about the timing of retransmissions. The other way to do it (which I implemented) is to exchange routing information throughout the network - sharing information on which nodes any particular node can hear - then it becomes easy to route packets efficiently through the network.

APRS does a similar sort of thing as the former - it uses a decaying algorithm to determine when to retransmit messages, and so (mostly) avoids the congestion problems inherent in such a design.