Configuring TDD Sync for Asymmetry

LINKPlanner V5.4.0 introduces Asymmetry to the TDD Sync operation and allows users to bias the throughput to either the downlink or uplink direction. The PTP 700 1+1 HSB introduced an extension to the length of the Frame Duration (and in turn to the Burst Durations), which is called Long Frame Duration. This feature can also be enabled on other PTP 700 Link Types, if required, especially if trying to synchronize a number of links using a mix of 1+1 HSB and other link types.

In this document the term “network” refers to the set of links which are in the same frequency group and have Sync enabled (but not set to Internal). There may be other links in the project file which are either in a different frequency group or that are not required to be synchronized, which are not included within the TDD sync network.

Restrictions of use

Asymmetry is not supported in conjunction with the following products or features. If any link in the network is using any of these configurations then the whole network cannot use Asymmetry.

  • E1/T1
  • DFS
  • PTP 650 and PTP 670 (PTP 670 will be available in a future release)

There are some additional limitations:

  • PTP 700 1+1 HSB links must have Long Frame Duration enabled
  • 5, 10 and 15 MHz bandwidths don’t support Long Frame Duration
  • 5 MHz bandwidth only has one burst duration option limiting it to symmetric operation

When designing networks with mixed bandwidths and link types, a common set of parameters need to be found which satisfy all the restrictions. Long Frame Duration can be set to enabled, but it will only be used on bandwidths that support it. Where networks include links that can’t support longer frame durations, the burst duration options chosen have to fit within the standard frame durations. When using asymmetry this can still often include some of the longer burst durations.

Configuring TDD Sync Parameters

If any of the links in the network include any of the first three restrictions on supporting Asymmetry, then the TDD Sync panel will look very similar to earlier releases and the burst and frame durations are configured in the usual way.


As this network is symmetric, Maximum Burst Duration Phase 1 and Maximum Burst Duration Phase 2 will be the same and hence the Phase 2 value is not shown.

When the links can all support the new Asymmetry functionality the default TDD Sync panel will show new options for setting Link Symmetry (default Symmetric) and Long Frame Duration (default Disabled).


To configure Asymmetry set Link Symmetry to Asymmetric and then configure the Maximum Burst Duration for both Phase 1 and Phase 2 before setting the Frame Duration.

Choosing Burst Durations

The options in the burst duration list have been reduced from previous releases to only include those that are valid for the bandwidths used on the links being synchronized. When Long Frame Duration is disabled and if all the network is on the same bandwidth there will be a maximum of five burst duration options. When Long Frame Duration is enabled on a supported bandwidth this list will increase to a maximum of 14 options for a given bandwidth. If the network contains links with different bandwidths then the number of options will continue to increase.

The first entry shown in the Maximum Burst Duration list is the minimum value that can support all the bandwidths used in the network and may be higher than the burst duration configured on individual links.

When setting Asymmetric burst durations, either the Phase 1 or Phase 2 end must be set to the minimum value in the list. Once the Phase 1 burst duration is set to a value above the minimum then the Phase 2 list will automatically reduce to only offering the minimum value.

When TDD Sync is disabled the Symmetry direction is driven from the Master end of the link. When TDD Sync is enabled it is now driven by the Phase, therefore it is important to know which end of the link is on which Phase. By default LINKPlanner will configure the Master end to be Phase 1, but in some cases it is necessary to change this, in which case the symmetry will go with the Phase rather than stay with the Master direction.


Using this convention of Phase 1 on Master then setting Phase 1 high will give symmetries of 2:1, 3:1, etc. in the Master to Slave direction (equivalent to the x:1 setting in LINKPlanner when Sync is disabled). Setting Phase 1 low and Phase 2 high will result in symmetries of 1:2, 1:3 etc in the Master to Slave direction.

Choosing the Frame Duration

Once the burst durations have been configured the Frame Duration can be selected. The number in brackets after a Frame Duration in the list shows how many links cannot support that Frame Duration.

The number of valid Frame Durations is dependent on the topology of the network and the combination of bandwidths used across the links. It is possible that there will be no valid Frame Durations, in which case try reducing the number of different bandwidths being used or reducing the highest burst duration (especially if using burst durations supported with Long Frame Duration in a mixed network with links that can’t support Long Frame Duration).

The estimated best frame duration continues to guide users on the smallest frame duration that can support all the links without interference.

To maximize throughput choose the lowest valid frame duration. Larger frame durations are often used to minimize latency, but at the expense of lower throughput.

Synchronized Links Table

The following new columns are available in the Synchronized Links table (see for more information on customizing the columns visible in a table):

  • Burst Duration P2 (μs)
  • Actual Burst Duration P2 (μs)
  • Symmetry

When planning networks with mixed bandwidths the symmetry may not be the same on all links, therefore it is not possible to define the symmetry as an input to the synchronization process, but displaying the Symmetry column should make it easier to see what has been configured for each link.