A network with hundreds of routers.

Reading the data sheet on the XBEE Pro OEM development kit that I just purchased I’m worried now whether it can actually do what I thought it could.

I’ve an application that may involve more than 100 nodes but where the distance between nodes is such that at any location 3 or 4 nodes can communicate with each other. Say a network where there is a node every 100m for a distance of 10km.

I’m perfectly alright with say, if node 75 wanting to report to the coordinator, broadcasts a message that is relayed all the way back through 74 nodes to node #1.

The nodes are powered off the AC line and the uC also has a unique serial # in addition to XBEE serial number so I will now physically where the node is. I don’t need ad hoc node # assignment.

I realize there are some significant issues here. The coordinator may find that the channel that is best where it’s located is wrong channel for the other end of the network.

I’d like to have a router type application that could perhaps work with multiple channels; upstream and downstream. Each node is a router and the system works out for the local nodes which channel is best.

Am I stretching what is possible with ZigBee or 802.15.4?

If you have part of your network on one channel and the other on another channel I don’t know how you could easily get data across the entire network. You could sudivide the network (have two or more separate networks) and then bridge them with a cable or hard wired connection. But an entire network can’t jump channels on the fly and still hold on to the data being transmitted in the network.

Also, keep in mind that with XBee Zigbe there is a limitation on how many times a packet can hop – it’s based on the timeout - which is how long a transmitter will wait after sending a packet to receive an acknowledgmenet. The maximum timeout on the XBee ZB firmware is about 12-13 seconds (see the NH parameter in manual). This translates roughly to about 60 hops as the maximum allowed within in a network. (possibly could go 10Km depending on the spacing).

Just a suggestion, you might want to consider using a hybrid system of radios. This might include using the Xtend radios as a backbone system since you have AC power to transmit data over long distances but use the Xbees to get the data to the Xtend radios and to reduce costs.

Looking further into the protocol it appears that any node will accept messages that contain a broadcast address and ACKs and Retries aren’t done.

But does the network first have to be established? Can the XBEE PRO be used in a sort of raw 802.15.4 mode where the DSSS transmission ensures adequate distance but the real protocol of who does what with what is all in the body of the message.


Just a quick check: are you talking about series 1 XBees here, or series 2? This is the series 1 forum, and I don’t know any way to get series 1 modules to do routing, even by clever use of broadcast.

So, if you’re using series 1 modules the answer may be that you’ll want to switch to series 2. But check with the good folks at Digi support - I’d hate my answer to cause you to make an expensive mistake.

On the other hand, if your modules are series 2, then you’re likely to have more replies in that forum. Good luck anyway!

(Jay: I hesitate to take issue with such an authority as yourself - but if we’re talking series 1, does the NH parameter really apply?)

Yes. I was under the impression that help was needed in making a decision about which module would be best for his purposes. Since the design requirements immediately rule out 802.15.4 maybe it’s best to move the thread to the Zigbee forum.

We can do that, no problem :wink:

I’m planning starting a network with about 100 devices. The will be one API Coordinator (data collector) and AT Routers with conneced rs485 meters.

  1. How will routers know the shortest way to the coordinator? I will set AR parameter in coordinator so that from time to time it will send broadcast transmission and every AT router will store it’s transmission way to collector. Am I thinking right? Is it enough?

  2. The first problem in my case will be when coordinator wants to collect data from one of the devices. Problem is that I will not know the xbee address of that device but only identificator of the meter connected to xbee adapter. My idea is to send a broadcast message. I will then get response only from that xbee module which is connected to correct meter, so other questions can be send to known xbee address via source routing. Is it correct way of thinking? Beter ideas? The problem is I can’t connect meter id with xbee module address because meters and xbee modules can be freely replaced.

  3. Well… to be able of using source routing I have to get Route Record Indicator from every device. How it can be achived? Am I thinking right that every time coordinator sends aggregate route broadcast transmission (AR) it gets RRI from every device?