Good presentation, nicely done, relieved a lot of concerns of the unknown. Actually very reminiscent of most network topology and protocol studies, concepts not unfamiliar to me, now particularized for this particular application ...
@pauln: slide 15 is good as it stands to show the protocol layers, but to convey the increasing number of "onion layers" as one moves down the chart, it might work even better with the arrows starting close together and getting further apart as you move down the slide, and maybe even color coding to show the portion of the layer above that is wrapped with additional protocol in the next layer below.
@pauln: Any comments as to why the contention-free period follows the contention (CSFM-CA) period when using a beacon? I would think the period immediately following the beacon would provide the greatest confidence about where the contention-free time slots lie.
Actually it's a bit of a mesh, with repeaters as required. We need E2E comm but have little say as to where the radios are positioned, as they have other purposes, although roughly in a line. Don't want to tie you up Paul.
If I were to build a large (many nodes and large distances) I would consider using IP before I invented my own protocol. Designing network protocols (such as IP) is a very complicated business, in the sense that there are a lot of things that go wrong. And, as you learn more about networking technologies, you would probably end up adding more features that are already provided by IP. Or, perhaps not adding them, even though they are needed to meet your requirements.
And, if you have more than a trivial topology, you probably want some sort of automatic routing. There are numerous routing protocols available for use in IP networks. And, desiging a routing protocol is very complicated, in that many problems can be very subtle.
@bbauer - you may be looking at trying to use the intermediate radios as "repeaters" (store and forward) unless you wish to have real-time or connectivity part way along the line. (like at substations)
On a 100 km network, you need to think about what you are doing end-to-end. You probably need separate hop-by-hop and end-to-end protocols. For example, do you ack hop-by-hop, end-to-end or both.
Zigbee is a suite of protocols. Some protocols may have more problems with the propagation delay of such a network, while other protocols might work OK.
I suspect that the CSMA-CA protocol (if you are really using that on each hop) seems likely to perform poorly. This is analogous to the maximum size of an Ethernet network, which is limited by propagation delay.
The ack mechanism probably works poorly, because of the long delay between a packet transmission and the reception of the ack.
The limitation of having only one outstanding (unacknowledged) frame at a time is a problem with a network this large.
Paul, do you think Zigbee is suitable for real-time applications?
My current project needs a rapid response to an input. We originally tried to apply sub-1G with simple peer-to-peer network. But latter, we have to deal with expanding the wireless coverage. Mesh network such as Zigbee is perfect for our purpose, but I am not sure whether it can provide good real-time performance, say less than 100ms average delay for about 30 nodes. For example, the frequency we are choosing is 2.4GHz and average payload is 40 bytes long.
@bbauer - Sounds like you want to use radios as a back haul with Zigbee on either end of the back haul. Or are you trying to use zigbee for the entire link?
A 100 km long network might be a little exagerated, but we expect to have at least 100 radios per line. I'm just wondering if anyone has a protocol for this, or if we need to write our own.
I have an application that involves a linear network of radios, say spread out over 100 km of power transmission lines. Would Zigbee provide end-to-end communication using radios as relays?
The sync problem is also present on Cell phones. The difference being that cell phones can tolerate a few bytes being lost without having voice communications suffer. Our ears are amazing at filtering through issues.
Paul - you have lots of vintage radios - any that transmit?
For those of you just joining us, today's questions so far are: 1) What network topologies have you implemented, or are going to implement, in your network? 2) Has anyone implemented a non-beacon, low-power network?
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@bit_slicer Yes and no. I'm trying to stuff as much data passing on one channel as I can, bi-directional, but sometimes I grow impatient getting two devices to talk. :)
I have plenty of leftovers from Halloween, mini Snickers bars. (I usually buy about four times more than I suspect I'll give away, last me until Easter.) :)
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