Lowest Data Modulation Mode

PTP 650/700 provide controls for the Lowest Data Modulation Mode attribute in the System Configuration web-page and in the Wireless Configuration page of the Installation Wizard. Here's the control from the Installation Wizard.

The control provides an ordered list of the adaptive modulation modes, sorted according to the capacity provided, just like this:

Mode list for LDMM.PNG

When you set the Lowest Data Modulation Mode (LDMM), you're telling the ODU that you don't want it to bridge data across the wireless link if the link is using a modulation mode lower than the one you selected.

So, why would this be a good idea? In a simply-connected, tree-like, network it is almost never a good idea to set LDMM higher than the minimum of BPSK 0.63. A higher LDMM simply reduces the availability of link.

On the other hand, in a network with multiple paths, for example a network with a wireless mesh or ring topology, the LDMM can be used to stop a link from bridging when the modulation mode drops, so that routers or switches can send traffic over an alternative link. In a mesh or ring network, look at the availability of each of the modulation modes and choose LDMM so that if one link falls below this mode, there is a high probability that an alterative route will offer a better capacity.