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Phase Ready?

As you think about the evolution of your network, don't limit your thoughts to the frequency stability you need now. We want to help ensure that network roll-outs today will still be relevant come the explosion of HetNets and Small Cells.

Edge Microwave - Transparent or Boundary Clock?

We've been fortunate enough at Chronos to work with several microwave equipment manufacturers in the last year or so, helping them develop and test their implementations of On Path Support for Edge Phase applications. We have seen some quite astonishing improvements in Packet Delay Variation (PDV) of PTP packets when implementing a Transparent Clock; actually in turning the radio link in to a virtual Transparent Clock.

All the manufacturers we have spoken to (of course this is not ALL manufacturers!) are implementing a version of this Transparent Clock. They have come to this conclusion independently, I think because they realise that the many variations that the radio link can encounter due to loading, bandwidth use, scheduling, weather or other external factors means that simply terminating the PTP flow at the link "Ingress" and generating a fresh flow at the "Egress" will not deliver the standard of output clock needed to support a living and breathing network.

I was surprised therefore when I discovered that manufacturers were under external pressure to deliver Boundary Clock rather than Transparent Clock. The main two reasons seem to be that use of Boundary Clock for Phase is now standardised whereas Transparent Clock is not, and that Transparent Clock breaks OSI Layer boundaries.

We are actually beginning some tests in the next week or so to start to characterise some microwave links' PDV and their effect on Boundary Clock performance. In my opinion the fact the the standards bodies can't keep up with technology should not be a brake on development, and is no surprise to any of us in any case! The Layer Violation argument seems a bolt on excuse to me - if the manufacturers believe Transparent Clock is the best way to deliver On Path Support then we should get on with supporting them in the standards!

A poorly working compromise will simply not do in the urban Small Cells space. We're in a different world now and what works should be what is implemented.

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