Using IEEE-1588 transparent clocks to improve system time synchronization accuracy

By Paul Skoog, Symmetricom, Inc.
Embedded.com (11/24/09, 08:25:00 PM EST)

Simply put, time synchronization is setting the time on two or more clocks to be the same. Hidden in this simple sentence are obstacles involved with "setting" the time, the length of time it takes to "set" the time and the varying levels of acceptance of what the "same" time actually is. Just the notion of "same time" conjures up accuracy to the second, millisecond, microsecond, nanosecond, or better.

Key to understanding synchronization is that clocks drift and need to be corrected periodically. This begs the questions, "How long are they 'the same' before they are not 'the same' as they drift apart?"

It takes time to go through the process of correcting the time, and during this process how accurate can we set the time relative to another clock in the first place? This process of correcting the time is challenging and is a limiting factor in how accurately two clocks can be synchronized.

IEEE-1588 defines a process of transferring time. However, before jumping in and demonstrating that Transparent Clocks (aka IEEE-1588 enabled switches) work great to improve IEEE-1588 time transfer accuracy, there are a few fundamentals we need to cover along the lines of offsets and delays and how switches and routers contribute to both.

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