FAQ - LAN synchronisation

If the DECT connection between base stations seems to be not reliable enough to permanently guarantee a stable DECT over the air synchronization, e.g., because they are separated by iron doors or a firewall, you can determine that synchronisation should take place via LAN. In this case the base station with the higher sync level will act as LAN master, the base station with the lower sync level is a LAN slave. One base station must be explicitly be defined as LAN master. Currently, it must be on DECT sync level 1.

Advantage:

• No Synchronization levels needs to be configured.
• When a base station fails (Not the LAN Master) it will not have any impact on the other base stations.

• Fewer base stations required as the overlapping area of the base stations is smaller. The overlapping area for handset handover can be smaller, because neighboured base stations do not need to receive each other in stable error free quality, but they must still be able to detect each other for the process of dynamic channel selection.

Disadvantage:

• Base stations must be in the same network segment.
• Precision Time Protocol (PTPv2), deviation must be lower then 500 ns (rms).
• High reliable LAN network is needed, see below for the requirements.
  
  

Consider the following network requirements.

• The less switch hops. the lower the transmission delay and its jitter will be.
• The higher the bandwidth or quality of used switches is regarding packet delay and its jitter, the lower the packet delay and the lower the packet delay jitter will be.
• Enhanced packet processing logics (like L3 switching or packet inspection) could have significant negative impact on the resulting packet delay jitter. If possible, they should be deactivated for the N870 base stations connected switch ports.
• Significantly increased traffic load on a switch, in the range of the maximum throughput, could have significant negative impact on the packet delay jitter.
• VLAN based prioritisation of LAN packets could be a fruitful measure to minimize packet delay and its jitter for N870 base stations.

Hints regarding PTP deviation.

LAN synchronisation is based on a two layer design:

• Native PTPv2 is used to synchronise a common reference timer along all base stations involved.
  Target quality benchmark to provide sufficient PTP synchronisation along the base stations, is to have a PTP deviation lower than 500 ns (rms). For this PTP synchronisation a few single deviations > 500 ns are accepted and might just generate first warnings. If the PTP sync packet deviation does continuously exceed this limit of 500 ns, the PTP synchronisation is considered broken and will lead to new start synchronisation procedure.
• Based on the PTP synchronisation LAN master and LAN slave adjust their DECT reference timer to one common offset to the common PTP reference timer. This common offset will be permanently monitored by a proprietary communication.
  The target quality benchmark for this synchronisation level is to see reference timer deviation by this DECT reference timer sync packets: DECT-LAN-Sync deviation lower than 1000 ns. A good mean value would be 500 ns (rms).

To meet this criteria the switches themselves do not necessarily need to be PTP aware. But the network should consider the above mentioned guidelines to meet this criteria.

When using LAN synchronization, it does not mean that the DECT signal quality is not important anymore. You still need to do an DECT measurement.

• Base stations that are synchronized via LAN must be able to see the neighbor base stations via an stable DECT signal.

For this you can use the DECT measurement kit. A value of -75 dBm is enough.

To check if the customers network can be used for LAN synchronisation. You can install an Integrator / DECT manager and some base stations in the customer network that are synchronised via LAN.

From software 2.29.1 we have the LAN sync quality visible in the Base-station events see:  FAQ - Base station events, q-idx-lt, o-thr-exc, d-thr-exc (LAN synchronization)

For previous software, see below.

Enable the CLI access on the Integrator / DECT manager.

Connect a PC to the customer network and run the batch script below that connects with the DECT base stations that are synchronised via LAN. You do not need to connect to the DECT manager.

Run the Batch file below.

1. Results will be written every minute in the c:\temp\ directory when not available change the script to write to another directory.
2. Change the host= to the IP address of your base station.
3. Change the password= to the CLI password.
4. The ssh_client= points to the location of plink.exe that is part of PuTTY. You can find PuTTY on the Internet.

Let it run for a day or longer and check if the values are within the supported limits.

Possible you want to see the results in the syslog so you can send this to your own syslog server.

1. Enable the CLI access on the Integrator / DECT manager.
2. Connect via an SSH client with the DECT base that is a LAN sync slave device.
3. enter "sudo killall -10 dlsd" to activate the logging
   

   user@ubuntu:~$ ssh cli@192.168.3.6
   cli@192.168.3.6's password: 
    _____ _           _       _       ____  
   | ____(_)_ __  ___| |_ ___(_)_ __ |___ \ 
   |  _| | | '_ \/ __| __/ _ \ | '_ \  __) |
   | |___| | | | \__ \ ||  __/ | | | |/ __/ 
   |_____|_|_| |_|___/\__\___|_|_| |_|_____|
   
   V2.8.0-126-gf2e4c3c;einstein-albert;ci-xberry@2018-08-15/14:03:01
   
   cli@base-7c2f80cfdf2a:~$ sudo killall -10 dlsd
   cli@base-7c2f80cfdf2a:~$

4. The syslog send from the DECT slave will contain the same output like described above.

5. To deactivate the syslog output, enter "sudo killall -10 dlsd" a second time
6. If you want to see the output from multiple DECT devices, do the same on the other DECT devices.