Guidelines for Testing Radio Links with Communication or Reliability Challenges

Products ePMP
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Troubleshooting the radio link

If you are experiencing challenges with your ePMP network, including:

  • no radio communication
  • unreliability
  • low throughput

please see the following sections for general troubleshooing guidelines to help drill-down the the core of the network's issue.

If the ePMP Module has Lost or Does Not Establish Radio Connectivity

When there is no radio link between the modules, begin by verifying the following:

  1. Check that the AP and SMs are configured with the same Frequency Carrier.  If operating in a region where DFS is required, ensure that the SM's Frequency Carrier LIst contains the frequencies configured in the AP's DFS Alternate Frequency Carrier 1/Alternate Frequency Carrier 1 Channel Bandwidth and DFS Alternate Frequency Carrier 2/Alternate Frequency Carrier 2 Channel Bandwidth fields.  This ensures that if a DFS event occurs, the SM will be able to connect to the AP with these configured frequency carriers.
  2. Verify that the Channel Bandwidth is configured the same at the AP and at the SM.  Modules with differing Channel Bandwidth configurations will not establish a radio link.
  3. On the AP, verify that the Max Range setting is configured to a distance slightly greater than the distance between the AP and the furthest SM that must register to the AP.  If an SM is deployed outside of the distance configured by the Max Range parameter, the ePMP system's framing mechanisms will not allow the SM to register.
  4. Check that the AP's Synchronization Source is configured properly based on the network configuration (i.e. is GPS synchronization employed in your network with Synchronization Source set to GPS, CMM3, or CMM4, or if synchronziation is not required, Synchronziation Source is set to Internal). 
  5. Verify the authentication settings on the AP and SM.  If Authentication Type is set to WPA2, verify that the Pre-shared Key matches between the AP and the SM Preferred AP LIst and Configuration > Security settings.
  6. Check that the software at each enf of the link is the same version
  7. Check that the desired APs SSID is configured in the SM Preferred AP List
  8. On the SM Home page, check the Downlink RSSI and Downlink SNR values.  Verify that for the SM installed distance that the values are consistent with the link budget values listed in ePMP User Guide (tables "5 GHz threshold, power and link loss" and "2.4 GHz threshold, power and link loss").
  9. Check the Transmitter Output Power parameter on the AP and the Max Tx Power parameter on the SM.  Too low of a setting may restrict the devices from receiving proper radio signaling.  On the SM, if Max Tx Power is set to Auto, the actual output power may be lower due to Automatic Transmit Power Control (ATPC), where the AP instructs the SM to lower its power to meet the SM target Receive Level configured on the AP.
  10. Check that the link is not obstructed by buildings, seasonal foliage, etc. and that the link is not misaligned (due to wind loading or other factors).
  11. Check the DFS status page (Monitor > System) at each end of the link and confirm that the device is in service on a clean channel (relatively free of DFS events disrupting radio transmission).
  12. If there are no faults found in the configuration and there is absolutely no wireless signal, retry the installation procedure.

If the ePMP Link is Unreliable or Does Not Achieve Data Rates Required

If the ePMP link is active but is unreliable or does not achieve expected data rates, proceed as follows:

  1. Verify that the interference (noise floor) has not increased in the service area by monitoring the SNR (dB) Downlink / Uplink values reported in the AP page Monitor > Wireless Status.  Compare current SNR values with the historical levels of these statistics at the site.
  2. Verify that the RSSI (dBm) Downlink / Uplink values reported at the AP and SM are in general alignment with the values reported in the ePMP User Guide tables "5 GHz threshold, power and link loss" and "2.4 GHz threshold, power and link loss"
  3. Check that the path loss (the loss in signal experienced from the transmitter to the receiver) is low enough for the communication rates (and corresponding MCS rates) required for the site.  
  4. Check that the AP or SM has not become misaligned due to wind loading or other factors.
  5. Review your Quality of Service configuration (Configuration > Quality of Service) and ensure that the data rates are not limited by a certain Maximum Information Rate (MIR) or Traffic Priority profile.  This review should also be conducted for any RADIUS servers in the network which may be configured to automatically limit data rates.
  6. Verify Ethernet Port settings on the AP and SM (Configuration > Network) and sure that the ports are operting as expected

If the ePMP Module has Lost or Does Not Gain GPS Synchronization

To troubleshoot a loss of sync, perform the following steps:

  1. If the AP is receiving synchronization via CMM (Cambium Networks Cluster Management Module), verify that the CMM is properly receiving syn via its attached GPS antenna (see PMP Synchronization User Guide).  Verify that the cables from the CMM to the network switch are at most 30 feet / 9.1 meters (shielded) or 10 feet / 3 meters (unshielded) and that the network switch is not PoE (802.3af)-capable.
  2. If the CMM is receiving GPS synchronization pulses, verify that the AP's Synchronization Source is set to CMM and that the AP's GPS status bar icon is lit green.
  3. If the AP is receiving synchronization via its internal GPS module and an external GPS antenna, verify the cabling from the AP to the GPS antenna and verify that the AP's Synchronization Source is set to GPS.  The GPS antenna should have a relatively clear view of the sky and satellites may be tracked via AP page Monitor > GPS.
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