Troubleshooting choppy, garbled and out of sync audio issues in your DECT network can be a difficult task. Incorrect arrangement of the DECT base stations in a multicell is a known reason for many issues including audio.
The M-Series handsets (M25, M65, M70, M80, M85 and M90) have a diagnostic menu that helps to determine if there is a weak or inadequate RF/RSSI signal between the handset and the base unit.
Checking multicell DECT sync source values
If you are using several base stations in a multicell setup, make sure that they are arranged correctly. Click on Multi Cell -> scroll down to Base Station Group to see the list of bases. The table will look similar to the one below. Check under "DECT sync source" and make sure that none of the values are below -75dBm. In the below example, value -86dB is too low and can cause audio issues. If you have any such values, re-assess the arrangement of the base stations (see DECT - 1. Multicell Deployment Guide). You may need to add some additional base stations.
Checking RSSI signal level
If you are experiencing audio issues you should check the RF/RSSI coverage in the areas where you are experiencing the problems. Make sure that the RSSI signal level between handset and its current base is below -75dBm.
Here is how to check the RSSI signal levels between the base stations and the handsets:
- On the M65/M85, press the menu key ; on the M25, press the OK key. The main menu is shown.
- Type *47* on the keypad of the handset.
- The handset will detect all base stations within range and show their MAC addresses on the display. If the handset has detected more than one base, compare them with the MAC address on the type label of your base station to identify and select the right one.
- If necessary, scroll to the MAC address of your base station. The selected item is highlighted in blue and expands to also show the IP address of the base station.
- Press the function key underneath "Select". The selected base station's RFPI and RSSI are shown on the display.
◦ RFPI: The Radio Fixed Part Identity is a unique identifier frequently transmitted by the base station.
◦ RSSI: The Radio Signal
Audio Loopback Testing
You can also do an audio loopback testing to see if the RF signal in those locations your have tested from is a contributing factor of the audio issues.
- Press the green key to establish an audio loopback connection to the base station. You can now speak into the microphone of the handset to hear the echo of your voice.
RTP Collision Detection
You can also try enabling RTP Collision Detection on the base (the setting can be found in the web interface under Network). This setting controls whether the base checks for RTP collision. RTP collision means that the device is receiving RTP packages from more than one source address with same SSRC. Per default, this setting is off.
The Site survey mode can help to check Handover/Roaming scenarios and can give a more complete picture of the DECT conditions on-site (see DECT - 4. Site Survey). Interference due to reflections should be easier to find with this function (error counter: FE). Also, an inconsistent multicell could be detected.
Checking the multicell page can show problems in the DECT tree which must be corrected in order to stay within the recommended values (-75db or better).
Try performing the RSSI and Loopback tests on the affected handsets when the issue occurs and keep a log of the RSS levels and loopback results for Snom Support if you open a ticket. If coverage and RSSI is an issue, adding DECT repeaters to extend converge in your Network may be necessary.
It is also recommended to have the latest stable release of firmware upgraded to the base stations and the handsets. It is also a good practice to gather the syslog and systems, calls, repeater, and DECT statistics and settings files from the Base Stations for further analysis.