Can someone explain the 4 hop rule?

Community Playground General Discussions
1

I am unclear on this rule for Z-wave. Something like a message can only go 4 hops across devices max before its destination??

Is this a Z-wave or Vera rule?

2

This is a zwave protocol spec…

“What Z-Wave does to get range is form a mesh network, where all power-line connected devices act as repeaters and “hop” the message using low power transmissions from device to device to get extended range. The typical range for a Z-Wave device is 20 meters or 60 feet. Z-Wave supports 4 hops in a link so the typical range overall is 4 * 60 or 240 feet.”

Taken from: http://www.zwaveworld.com/ask/ask40.php

3

So, how does that work? Hpow do the devices find the next one to hop? Let’s say that you have 6 devices, each sepparated by 20 feet. Will the signal hop from one to the closest one (20 feet) and so on? In that case the range is only 80 feet … Or will the first device choose one that is at 60 feet (even though there are two other that are closer)?

4

The highest number of possible “hops” is 4: Controller → Receiver 1 → Receiver 2 → Receiver 3 → Receiver 4. However, you would not be able to actually see how the signal is being sent without special equipment. Also you will find that as you increase the number of nodes, the reliability will increase. You cannot rely simply on “line-of-sight” distance. Radio waves are funny things; they reflect and refract off of other objects so that sometimes signals are repeated through distant nodes to get to nodes that are physically closer.

Just to give additional insight into the complex method of routing, here is more detailed information. Routing is done in the layer below anything controlled by us. It is all handled by the ZenSYS IC chip and their firmware. But this is basically how it works:

  1. The controller will try to send its command directly to the intended node.
  2. If it fails to get an acknowledgement, it will try 2 more times (this only takes a few milliseconds).
  3. If it stills fails to get an acknowledgement, it will try a simple 1-hop routed transmission.
  4. If it fails to get an acknowledgement, it will try 2 more times.
  5. If it stills fails to get an acknowledgement, it will try a different 1-hop routed transmission (3 times).
  6. If it stills fails to get an acknowledgement, it will continue to try all other 1-hop routed transmission paths (3 times each).
  7. If it stills fails to get an acknowledgement, it will try a 2-hop routed transmission (3 times).
  8. If it stills fails to get an acknowledgement, it will continue to try all other 2-hop routed transmission paths (3 times each).

This goes on until it has tried all possible routes.

5

This looks like a backtracing algorithm that can last a long time. My question to you is: how long (from your experience) can such an attempt last?