[time-nuts] What was 50.791095 MHz used for?

[ed breya]

Does anyone know what 50.791095 MHz was used for? I assume it was 
some sort of telecom clocking rate - perhaps obsolete. I 
serendipitously discovered that I have some VCXO modules of this 
frequency, that will likely solve a problem on one of my projects. 
I'm now curious about what they may have been used for, and if that 
is a "standard" frequency that will be available for future use. 
Online searching seems to indicate it is very common, but doesn't say what for.

Ed