Valid for:

N610

N670

N870

N870E

Embedded Integrator

Virtual Integrator

This White-paper describes the LAN synchronisation.

  1. LAN synchronisation
  2. Network requirements
  3. LAN synchronisation quality information
  4. Detailed LAN sync information
  5. Installation planning and measurement
    1. LAN synchonisation measurement
  6. PTP Domains / Clusters
  7. Set Master / Slave
  8. Distance between base stations
  9. FAQ (examples)

1. 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 you can switch to LAN synchronization where you also need to work with PTP master.


DECT synchronisation is the preferred synchronisation method !!!

LAN synchronisation can look to be more easy then DECT synchronisation, but the Customers network has to be very reliable and network knowledge is required. 

Gigaset offers the possibility to measure the delay/quality but we can not advise you how to configure your switches as we are not the experts for these switches.

In case of bad network quality, it can take some seconds before the synchronization is lost. When this happens, all active calls of this base station are disconnected. It can take up to some minutes before synchronization is active again.

Advantage of LAN synchronization

  • Higher flexibility in the arrangement of the base stations as no synchronisation chains need to be formed
  • 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 neighbored 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

  • Configuration of the system is simplified as all base stations can be synchronised on one synchronisation master

Disadvantage of LAN synchronization

  • 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 this white-paper for the requirements
  • You need to be the customer network administrator or be supported by the existing administrator


2. Network requirements

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To be able to use LAN synchronisation, consider the following network requirements:

Precision Time Protocol (PTPv2), deviation must be lower then 500 ns (rms)

Accuracy: How accurate the slave clock is to the master. Every clock, even an atomic clock, has some deviation from the actual time. The lower, the better.

The DECT measures the PTP deviation and shows/counts if the value > 500ns on the device status page: o-thr-exc  

Base stations must be in the same network segment


Minimum packet delay jitter is crucial for successful synchronisation over LAN. As multiple LAN traffic parameters could have an impact on packet delay and its jitter, specific switches and maximum number of switch hops are required, to guarantee sufficient maximum packet delay jitter.

The experience from real customer installations is that after 3 switches the LAN synchronisation quality could already be at the minimum. This can be measured using the LAN measurement setup.


The less switch hops. the lower the transmission delay and its jitter will be.

Each switch in the network has to forward the PTP messages, this takes time and adds delay. (Indicated with the blue arrows)


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.

VLAN disconnection from other network devices is mandatory.

DSCP (Differentiated Services Codepoint) based QoS could be even more efficient. 

DSCP tagging:

Sync via LAN: PTPv2, DLS (proprietary):  DSCP=CS7=56

RTP:  DSCP=EF=46

SIP:  DSCP=AF41=34

Synchronisation via LAN makes intensive use of IP multicasts which have to be supported by the switches.

Multicast destination address and ports: 

PTPv2: 224.0.1.129 UDP via ports 319/320

Proprietary DLS protocol: 239.0.0.37 UDP via ports 21045/21046

Cascaded switches might need uplink switching of these multicast packets to allow interswitch LAN synchronisation. Otherwise you need isolated LAN-sync clusters, inter-cluster-synchronized via DECT.

IGMP snooping is supported and shall be supported by the switch, to configure and minimize multicast distribution only to the LAN synchronising base stations.


Switch port

The DECT system must be connected to an switch port with:

  • Minimum 100 Mbit/s full-duplex speed
  • Allow multicast / broadcast messages
  • PoE IEEE 802.3af < 3.8 W (Class 1)

  • VLAN disconnection from other network devices is mandatory.

  • Supports VLAN tagging

  • Activation of Quality of Service mechanisms is mandatory

  • DECT Manager and all base stations in the same layer 2 segment

  • The whole Layer 2 network in which the BS/DMs are operating have to IP/Ethernet Multicast enabled in case of Synchronisation via LAN

3. LAN synchronisation quality information

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The DECT system offers the possibility to show information about the LAN synchronisation quality:

In the web-interface go to: Status - Statistics - Base stations - Click on to show the columns:

  • q-idx-it
  • o-thr-exc
  • d-thr-exc

LAN synchronization quality - q-idx-it

Consists of classified values that are weighted and summarized to one resulting index value.
This value offers a fast indication whether synchronization quality is sufficient or not.

  • Q-idx-lt > 93% are good values. (tick)
  • Q-idx-lt > 90% means LAN sync is functional. Remaining 10% evaluate synchronization quality (info)
  • Q-idx-lt < 90% low quality (error)

PTP offset threshold exceeded - o-thr-exc

If the PTP deviation > 500 ns seconds, the counter is increased.

That the counter is increased means that the network does not meet the requirement that the PTP deviation is < 500 ns.

  • Values > 500 ns are accepted and might just generate some warnings.
  • Values > 500 ns for a longer time or very high over the 500 ns will result in an A-synchronization where all calls via this DECT base are disconnected.

DECT base that loses synchronization needs up to 30 seconds to synchronize again (When the LAN synchronization can be started again)

DLS offset threshold exceeded - d-thr-exc

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).

If the DLS deviation > 1000 ns seconds, the counter is increased.

Asynchronisation

The column Async must also be used to check if the network is LAN synchronization capable. You can see in the picture that we have many PTP threshold exceeded (13379) but there is no Synchronization loss.

Theoretical it would not provide problems. But you can expect that if the PTP deviation is getting worse, it will result in synchronization loss.

You should fix the PTP deviation for this base station to avoid complaints later.

Gigaset can not guarantee seamless working system if the values exceed the by Gigaset provided requirements. Support can't be provided if the network is not LAN capable.

4. Detailed LAN sync information

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We offer the possibility to see detailed information (over time) about the LAN synchronisation.

These statistics are offered by the DECT base-station.

LAN synchronisation must be enabled for this base to see the correct information.

In the web-interface go to: SETTINGS - Base stations - Synchronisation and click on the Base station name

It will open the base station web-interface, login using

  • Username: admin
  • Password: admin password

You will see the following information.

  • DECT LAN Sync (DLS) long term statistics 
  • DECT LAN Sync (DLS) statistics overview table
  • DECT LAN Sync (DLS) log


DECT LAN Sync (DLS) long term statistics:

  • ptp-d: ptp clock delay. ptp clock offset to master clock. This value should not exceed 500ns for a longer time
  • dls-d: Measured offset of the local DECT-SYPO signal to the master DECT-SYPO signal. This is the DECT-SYNC criteria and should not exceed 1000ns for a longer time
  • ptp-pd: ptp path delay. This is an indication of the transmission path quality. The account of switches and their processing speed and queue delay's influence this value. Jitter should be as less as possible.

DECT LAN Sync (DLS) statistics overview table

The latest LAN sync output for more detailed information see this wiki page.

Some values, we describe below:

  • QUALITY-async: async counter

  • QUALITY-o_thr_exc: Out of sync threshold exceeded

  • ptp-pd: ptp path delay
    This is an indication of the transmission path quality.
  • ptp-d: ptp clock delay
    Ptp clock offset to master clock
    This value should not exceed 500ns for a longer time
  • dls-d: Measured offset of the local DECT-SYPO signal to the master DECT-SYPO signal.
    This is the DECT-SYNC criteria and should not exceed 1000ns for a longer time


DECT LAN Sync (DLS) log

LAN sync log messages.


Aug 18 06:06:39.897 dlsd[3736]: >>> ptp-pd overshot/peak detected: obsrv-act[ns]:      22355 | obsrv-mean[ns]:      14663 | delta[ns]:       7692 | delta-rel[%]:         52
Aug 18 06:13:21.504 dlsd[3736]: >>> ptp-pd overshot/peak detected: obsrv-act[ns]:      25887 | obsrv-mean[ns]:      14629 | delta[ns]:      11258 | delta-rel[%]:         76
Aug 18 06:13:22.299 dlsd[3736]: >>> ptp-d overshot/peak detected: obsrv-act[ns]:       9534

5. Installation planning and measurement

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Below the steps described for the installation planning of the DECT installation using LAN synchronisation:




LAN synchronisation measurement

If you want to know if the network of the customer can be used for LAN synchronization, you can use the N870 to check the network.

The first you need to do is to configure the customer network, conform the above requirements.


How to use the N870 to check if the network is suitable for LAN synchronization.

Install in the customer network at some strategic points the N870 with some base-stations. They do not have to mounted to the wall, but connected to the switch.

Like in the example below. We installed some N870 base-stations in the customer network, Every base station is connected to one of the customers switches.



  1. In the Nx70 web-interface, Clear the Statistics 
  2. Let the system run for a week and check the LAN synchronisation quality 
    1. The most important is to check how many Async's the DECT base-stations had. (Column "Async")
      1. Each Async will cause customer complaints
      2. Check if the Async's are caused by bad LAN sync quality or other reasons
    2. Check the LAN sync quality (Column "q-idx-it")
      1. The value should be > 93 %
    3. Check the PTP offset threshold exceeded (Column "o-thr-exc")
      1. Values > 500 ns are accepted and might just generate some warnings
      2. Values > 500 ns for a longer time or very high over the 500 ns will result in an A-synchronization where all calls via this DECT base are disconnected
      3. High counter values could indicate that in the future LAN sync issues can be expected


6. PTP Domains / Clusters

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A domain is an interacting set of clocks that synchronize to one another using PTP. Clocks are assigned to a domain by virtue of the contents of the Subdomain name fields in PTP messages they receive or generate. Domains allow multiple clock distribution systems to share the same communications medium.

Using PTP domains, you could for example have 2 or more PTP masters in the same network. Some DECT bases sync with the PTP master of domain 21 and some with the PTP master of domain 28. This is done via the Cluster configuration in the DECT system web-interface.

The DECT bases will see both PTP masters but only Synchronise with it's own master.

In the DECT system you can create Clusters : SETTINGS - Base stations - Synchronization. These clusters are used for DECT and LAN synchronization.

Cluster selective LAN synchronisation

LAN synchronisation consists of two layers:

  • Standard PTP which is shared within a multicast IP domain between all DECT managers (cluster numbers 1-c to 7-c)
  • Proprietary DLS (DECT over LAN Sync) which synchronises the clusters isolated within one DECT manager (cluster numbers 8-i to 15-i)

Cluster numbers from 1-c to 7-c

  • Build up one common PTP sync domain
  • DECT manager can be splitted in multiple DLS domains (clusters):
    • Maximum one LAN master per cluster
    • Intra-DECT manager split in clusters is possible for LAN sync,
    • Same way as for DECT sync
  • DLS sync master and slave do care for matching DECT manager and cluster numbers
  • Multiple DLS domains possible per DECT manager as DECT manager clusters
  • Inter-DM-LAN sync is only possible with matching cluster number (independent from the PTP domain)

Clusters numbers 8-i to 15-i

  • Build up an isolated PTP sync domain per each such cluster number
  • DECT manager can be splitted in multiple DLS domains (clusters):
    • Maximum one LAN master per cluster
    • Intra-DECT manager split in clusters is possible for LAN sync
    • Same way as for DECT sync
  • DLS sync master and slave do care for matching DECT manager and cluster numbers
  • Multiple DLS domains possible per DECT manager as DECT manager clusters
  • Inter-DM-LAN sync is only possible with matching cluster number (independent from PTP-domain)

The settings below shows dependent on the selected cluster, which PTP domain will be used

A cluster forming an isolated PTP domain needs to have one LAN master of its own.

DECT managers forming one common LAN synchronisation domain need to use a cluster number from common domain (1..7) or an identical cluster number of isolated domain (8..15).

DECT managers using different PTP domains (cluster numbers 8..15) cannot be synchronised by inter-DECT manager LAN synchronisation rule (Reference=LAN Master of DMx), but only by inter-DM DECT synchronization rule.

The mentioned PTP domain in aspect of cluster numbers is only relevant for LAN master and LAN slave base stations. For DECT synchronisation, cluster numbers do not have any additional rele-vance beside just identifying different clusters.

Clusters / PTP sub domains

Based on the cluster setting in our DECT system, the device will be member of the PTP subdomain in the table below. 

N870 Common PTP domain

PTP subdomain number

Cluster 1-c / 7-c

21

Cluster 8-i

28

Cluster 9-I

29

Cluster 10-I

30

Cluster 11-I

31

Cluster 12-I

32

Cluster 13-i

33

Cluster 14-I

34

Cluster 15-i

35

In a wireshark trace you would see the following:


Precision Time Protocol (IEEE1588)

0000 .... = transportSpecific: 0x0

.... 0000 = messageId: Sync Message (0x0)

.... 0010 = versionPTP: 2

messageLength: 44

subdomainNumber: 21

flags: 0x0200

0... .... .... .... = PTP_SECURITY: False

.0.. .... .... .... = PTP profile Specific 2: False

..0. .... .... .... = PTP profile Specific 1: False

.... .0.. .... .... = PTP_UNICAST: False

.... ..1. .... .... = PTP_TWO_STEP: True

.... ...0 .... .... = PTP_ALTERNATE_MASTER: False

.... .... ..0. .... = FREQUENCY_TRACEABLE: False

.... .... ...0 .... = TIME_TRACEABLE: False

.... .... .... 0... = PTP_TIMESCALE: False

.... .... .... .0.. = PTP_UTC_REASONABLE: False

.... .... .... ..0. = PTP_LI_59: False

.... .... .... ...0 = PTP_LI_61: False

correction: 0.000000 nanoseconds

correction: Ns: 0 nanoseconds

correctionSubNs: 0 nanoseconds

ClockIdentity: 0x589ec6fffe0d8c73

SourcePortID: 1

sequenceId: 5275

control: Sync Message (0)

logMessagePeriod: -1

originTimestamp (seconds): 0

originTimestamp (nanoseconds): 0



7. Set Master / Slave

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In the DECT system web-interface: SETTINGS - base stations - Synchronisation you can:

  • Select to which Cluster / PTP domain the device is member of
  • Define the LAN master for the cluster / PTP domain
  • Select to which Cluster / PTP domain the DECT base is Slave

8. Distance between base stations

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DECT synchronisation

Distance between DECT base is measured with the SPK and should be -65 / -70 dBm


LAN synchronisation

The DECT base must be able to see the neighbor base via the DECT protocol.

The visualization tool can be used to check this.

9. FAQ (examples)

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Example 1: All-in-one system with Pure LAN or DECT-LAN mixed synchronisation

Example 1: Small/Medium system with Pure LAN or DECT-LAN mixed synchronisation

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3 Comments

  1. Lenfort, Christoph

    I would not create so many example.
    We need to have more compact rules and process steps.
    Of course: System is highly flexible. But explaining just by many examples may hide the important rules.

  2. Lenfort, Christoph

    I am afraid  here we could easily overload the customer with information, in a way, that he misses the important things.

    1. Baremans, Eric

      Yes, I have the same worries (smile)

      We have for this topic:

      • Wiki articles
      • Documentation in the installation manual
      • Training documentation 

      Now I have it in one whitepaper, but to understand it you need to explain it in a DECT training