Modem and gateway behavior questions

I am new to the sensors and have been evaluating the hardware to see if it fits our needs. I have a few questions regarding both software and hardware. For any of the questions, please correct me if I am wrong in the understanding.

  • I see network/PAN id used in what appears to be interchangeably in documentation. It is the same thing, correct?

  • When a sensor is in configuration mode, it switches to network/PAN id 7BCD. To then configure that sensor, the wireless modem needs to be on that PAN id as well to configure it. Given that, if a sensor is in configuration mode and you are wanting to configure it via the modem then other sensors that are deployed wouldn’t be able to send their data to the modem while it is on that PAN id reserved for configuration mode. Is that correct?

  • Assuming that previous question is correct, would deploying a modem designated for configuration mode (always set for PAN id 7BCD) and then having another modem designated for sensor data collection on some other PAN id be an ideal setup so no data is lost?

  • When a node is in configuration mode, does the encryption key still need to be the same as the modem it is going to be communicating with?

  • Placing several modems around a location can help propagate signal as a repeater. Will the modem only re transmit if the data it received was on the same PAN id? Will a modem only re transmit if the encryption key on that modem is the same as the originating sensor’s encryption key?

  • Wireless sensor nodes do not act as repeaters from what I understand. I see some wireless sensors have a place for hard-wired power. If a sensor is hard-wired for power and not dependent on battery power do these wireless sensor nodes then act as repeaters in this configuration?

  • What is the primary difference between these two products - PR55-17B and U900HP-S3BMSR_ZIGMO? Is it mainly just that one has a barrel jack for power already in place? If the one with the barrel jack is connected to just power, does it act as a repeater?

  • I was reading the documentation on the digi site for broadcast vs unicast configuration. By default the nodes from NCD are in broadcast mode so that they are picked up by any gateway. The digi documentation states “Sending frequent broadcast transmissions can quickly reduce the available network bandwidth, so this functionality should be used sparingly.” It doesn’t give an exact number of how many would be pushing the limit of broadcast mode, but for the use of the sensors would broadcast be a bad idea? If I had several buildings near by that had maybe 150 sensors that had sample rates ranging from 10 minutes to 90 minutes, would that overwhelm the mesh’s capability in broadcast mode? Is it expected that end users of the products set their sensors up in unicast mode? What about in a situation with 300 or more sensor nodes? I’m just trying to get a estimate as we are currently adding more and more sensors.

I also have some Node-RED questions. I went ahead and made another thread to separate that out. Thread can be found here:



  1. Yes, sensor network ID and PAN ID are same thing .
  2. Yes, during cfg it usages 7BCD. the reason behind that is if you loose/forget your network ID you can still go back to cfg mode and set a new or read the stored one. and also that when its in cfg mode other sensor wont interrupt the process.
  3. cfg is something which is dont only few times in a sensor lifetime. But if you want yes you can have tow separate modems.
  4. Yes, the sensor and modem ENY key should be always same else they wont communicate.
  5. even hardware wired wont act like repeaters. You can use a modem as repeater. all you will need to make sure they have same networks id and same ENY key and is powered up all the time.
  6. correct. i will recommend going with PR55-17A
  7. if you are planning ot send data after 10 or 90 mini then we recommend a max 255 node per gateway.

These were some really excellent questions. :slight_smile:
Let me know if you have any other questions.