What’s So Different About IEEE 1588v2 Sync Over Microwave Backhaul?

The beauty of IEEE 1588v2 (i.e., Precision Time Protocol) synchronization is that it is a bookended solution. In theory, there is no need to worry about what is in between or underneath—from a Layer 1 transport perspective. While in principle this is accurate, there are a couple “unique” aspects of running 1588v2 over a microwave network that should be carefully considered in your deployment plans.

First, the infamous “last mile” is in reality typically many miles across multiple microwave radio hops—which may consist of a mix of linear, ring and hub-and-spoke configurations. Unfortunately, more hops introduce more packet transmission delay and delay variation over the backhaul—a potentially lethal mix for sync transport—the amount of which is proportional to the number of microwave hops. Careful design and engineering are required. On a bright note, Aviat Networks and Symmetricom recently validated <1.5ms delay could be achieved across 10 hops—well within the requirements for mobile backhaul.

Second, most advanced microwave systems now support Adaptive Coding and Modulation (ACM), a key benefit for microwave transport that allows the effective throughput of the microwave link to be dynamically changed to accommodate for radio path fading, typically due to changes in the weather. If bandwidth is reduced as a result of an ACM change, it is critical that advanced traffic and QoS management techniques be applied in the microwave systems to ensure that 1588v2 traffic (packets carrying timestamps) are given the highest/strict priority for transmission, and are not subject to delay or discard. On a brighter note, Aviat Networks and Symmetricom recently validated that 1588v2 could operate over a highly loaded (approaching 100 percent) microwave network running ACM.

In a nutshell, there are some unique considerations for running 1588v2 over microwave – but the outcome can be predictably bright with proper engineering.

Check out the Aviat Networks website for more information on the Aviat Networks/Symmetricom partnership and 1588v2 network synchronization over microwave backhaul.

Errol Binda

Senior Solutions Marketing Manager, Aviat Networks

Comments

    Rakesh Tiwari June 12, 2011/ Reply

    Good to see progress: Finally some real 1588v2 solutions over microwave, after seeing it in all the vendors’ datasheets last year.

    Are the latency variations due to ACM profile changes, and is the asymmetric modulation in RF out/out direction taken care of in this joint design?

    Regards,
    Rakesh

    aviatnetworks June 20, 2011/ Reply

    Hi Rakesh,

    Thanks for your feedback. Yes, we ran a variety of tests to validate latency separately in both forward and reverse microwave paths and plotted MTIE and TDEV results against the ITU benchmarks. We also ran these tests in both static modulation and adaptive modulation conditions to ensure the quality was maintained when the radios underwent various ACM changes.

    Regards,
    Aviat Networks


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