Creating a wireless mesh from scratch

Am 03.12.2014 um 23:36 schrieb tim.....:

^^^^ Someone just called, ranting about about some kind of slip of his he'll never hear the end of; does the name "Freud" ring any bell?

;-]

I can see how an environment might be too noisy "in", "on", or maybe "all across" a given frequency band, but "for" it? Sounds like "customer is basing requirements on hearsay" to me. Not to mention that the restriction to the 2.4 GHz band feels somewhat arbitrary.

They need to think again, then. Are they building to deploy MAN networks? My understanding is that that market is oh so very dead.

Mesh over Zigbee sounds bloody painful.

These are available as COTS for next to nothing on 802.11g and such. AliExpress has a node for $45.

I know it's comp.arch.embedded but Ethernet is a thing now, guys.

Mesh isn't that hard - it's just an extension of a bridge. There are things called "mesh bridges" but I have no idea what those are.

Might be. Might not be.

No, but I worked on the firmware the original mesh.com guys put together well after Moto bought 'em.

--
Les Cargill

Hello Tim,

"tim....." wrote in news: snipped-for-privacy@mid.individual.net:

It sounds like they don't have the requirements nailed down yet. Any single candidate won't be able to solve their issue in the time they want.

You could have inquired about the requirements for the project, what issues they were having, and how you might go about solving their problem ("get a solid communications network for their product").

That was a wise decision. However if you have a good grounding in communications applications you might be able to get up to speed on what is needed.

I've been in that situation too, and the time frame is what worried me most about your call. They were looking for a savior as well as someone to solve a vague set of requirements.

With enough communication background or interest in their product you might have gone on to a second interview which might have led you to people who could have told you what the facts really were about their goals.

Hopefully they'd build on an existing hardware/firmware/communications stack and have you, or your team, solve the problem from there. 9-12 months isn't long for an outsider to make a great solution that would be production worthy. They might take that long to evaluate possible communications technologies if they haven't already done so.

The length of time depends mostly on the complexity and richness of the product. Suppose you have radios and stacks that provide the ability to monitor other stations in your area and a store/forward communication protocol. A simple application could take relatively short time. A more complex application would have more problems to solve to evolve a solid solution. Again, this presumes they really do need a mesh network.

Good luck,

David

it's been part of the spec since the beginning, though I don't know how well it works, it's probably been 8 years since I worked on zigbee

these are ~$5 in onesies

but I don't see wifi being more robust in noise than Zigbee

-Lasse

"They thought"... what? That they needed a wireless mesh network? That the RF environment was too polluted (at least around 2.4G)?

Did they rule out a *wired* network? What sort of traffic were they looking at? Were nodes mobile or stationary? How robust did the mesh need to be? etc.

I'd decline based on "insufficient detail"! :-/

There are just too many details missing, here, to even begin to see what their *real* requirements are likely to be. There's a huge difference between a general purpose, dynamically reconfigurable mesh and, for example, a very

*static* mesh. Likewise, data rates, error protocols, etc.: "How much of the data *must* get through? What guarantees can you provide as to the cleanliness of the spectrum in band selected?"

A mesh network may be attractive in very low duty cycle applications, say each node sends some measurements for a few hundred milliseconds every minute, but in a larger network based on half duplex single frequency store and forward using CSMA band access, will quickly become jammed.

This is especially the case, if the stations are too close together that they also hear other stations beyond the nearest few neighbors.

Perhaps "too noisy" refers to the interference created by their _own_network_nodes operated geographically at a larger distance, than the nearest nodes used for actual mesh communication.

If this mesh is connected to the external world, the stations closest to the gateway node will quickly consume the whole RF bandwidth.

You are absolutely correct - I was thinking of something else.

No, I wouldn't think so.

--
Les Cargill

OLPC is supposed to self-organise a mesh when it finds itself in range of other nodes. However, you may rule it out on other grounds.

I would have stated that there should be a feasibility study done first, which would involve getting in a spectrum analyser and a sensitive wide band receiver to see what his wireless environment looked like (for real). You would, at least have been able to make a proper report of the environment anyone else would be working in and would have a good knowledge of whether any other solution might have suggested itself as you wandered around his plant.

--
******************************************************************** 
Paul E. Bennett IEng MIET..... 
Forth based HIDECS Consultancy............. 
Mob: +44 (0)7811-639972 
Tel: +44 (0)1235-510979 
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk.. 
********************************************************************

A Mesh network requires having enough residual bandwidth for each node that it can repeat frames intended for another node between two nodes not able to link directly.

Node 1 message meant for node 3 is received by node 2 then gets repeated to node 3 by node 2.

--
******************************************************************** 
Paul E. Bennett IEng MIET..... 
Forth based HIDECS Consultancy............. 
Mob: +44 (0)7811-639972 
Tel: +44 (0)1235-510979 
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk.. 
********************************************************************

Did the indicate which band? If so and it isn't an ISM band, have they budgeted the time/money to get the appropriate licences?

Maybe I'm being too cynical, but have they sold a concept and are now having to develop it? Or maybe they are just looking for free consultancy?

Good choice!

Depends on where you start. IIRC Linear Technology are claiming inroads into this kind of area for "IoT" devices.

Not without a /requirements/ specification!

A mesh (wireless or not) can also be used to provide some measure of comms redundancy and/or recovery. Implemented incorrectly (or, applied to an improperly constrained set of nodes), they can lead to a very brittle infrastructure (e.g., potentially having large portions of the network reliant on a *single* node for connectivity to the balance of the network)

Wireless meshes have advantage in *mobile* and/or reconfigurable networks where one or more nodes may enter or leave the mesh AT A PARTICULAR "SPOT" over time. But, *expecting* the entire network to remain "connected" without other constraints in place is just wishful thinking.

The OP's client hasn't (from the OP's reporting) even ensured a mesh (of any technology) is feasible for the (unnamed) application!

You might study the history of AX.25 packet radio systems used by radio amateurs since the 1980's and find out what kind of problems were encountered.

"Modern" mesh systems try to solve some of these problems e.g. by spread spectrum., but even with SS a large number nodes too close will degrade the SNR and hence bit rates.

Might find that more nodes in the mesh is far cheaper than a custom solution.

Ham radio guys have a thing called HSMM-mesh...although I think they recently renamed it. It's custom firmware on commercial routers. There are all kinds of regulatory issues if you tried to use it for commercial applications. But there may be some lessons to be learned from it.

[%X]

Which is why I suggested the RF survey be conducted. Doing studies like that gives you a good look around the plant while taking some real measurements and can lead to ideas forming about how to solve his problem. Ogf course, just doing the survey and making a report is chargeable work and whether or not he got the subsequent job he would have been paid to explore the opportunity a bit more.

--
******************************************************************** 
Paul E. Bennett IEng MIET..... 
Forth based HIDECS Consultancy............. 
Mob: +44 (0)7811-639972 
Tel: +44 (0)1235-510979 
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk.. 
********************************************************************

Realistically, we both understand that *many* clients balk at this sort of thing. They've already got an idea (or a deadline) in their head and just want someone to say, "Sure, I'll do it!". That shifts the responsibility off their shoulders (for the "uninformed" decision) and onto the contractor.

In the OP's situation, I'd have (casually) grilled the client as to why he/they had come to that "conclusion". And, if there didn't seem to be some genuine science involved, take that as a sign that this relationship would turn ugly, at some point (in the near future!). I don't try to "force" a (better!) solution on a client -- but, don't accept jobs where the solution I'm being asked to pursue "feels wrong".

I pitched a wireless mesh solution to a local firm some years back (as a favor -- I wasn't interested in the business, just giving them an idea). It was the *ideal* solution to their problem (they were currently shipping MILES of cable around the globe for each job). But, they were afraid of the "new technology" (outright said so) and comfortable shlepping all that wire around. Someday, their customers won't be willing to pay those costs (or, a competitor will pop up with lower bids) and they'll be forced to rethink their decision. But, by then, they will *see* it as "old, proven technology".

Or, find another line of work! :>

I took this path earlier in my career, it didn't end well :-(

I'm too old to try it again

tim

what market is that?

They are not planning on making a generic network solution to sell on

They have their own specialist data collection (slave) modules which need to send that data back to a master wirelessly (and that need is absolute, a wired solution is impossible). They have a (presumably patented) unique product that they sell into specialist markets with little competition.

Currently they create a one to many, star network but that has a maximum range of about 40 metres.

they want to extend that range (to several 100 metres) by creating a mesh from the slaves

Personally, I would have suggested multiple masters connected together on a point to point basis, but I guess that they have already thought of this.

I don't think the costs of the radio is significant, but the power consumption almost certainly is

that really is impossible, yes really!

tim

You didn't expound on the requirements in your initial post. Just said: "(they thought) their problem required a wireless mess solution" That suggests that there may have been other alternatives -- or, that it would be "wireless or impossible to produce".

Over the years, I've found that folks who "think" they need something are just looking for an alternative to another option that they have decided (rightly or not) is "too hard" and are hoping that something they don't completely understand may, magically, save their asses.

When they discover/decide that they can't have their wireless mesh solution (in the allotted time), they may "suddenly" decide that the "too hard" approach bears revisiting. And, perhaps with this greater motivation, come up with a viable solution!

[There are some interesting texts/research that suggest the quality of the solution (to any problem) rises to meet the constraints placed upon it. I.e., people only tend to look for "difficult solutions" when they have been convinced they *must*]