TECH BRIEF

When nanoseconds matter, these products can help

New IEEE 1588 timing products hit the market

Coordinating accurate time across a network has always been a challenge. By the time it takes a data packet with the current time to go from a time server to a client requesting the time, hundreds of milliseconds may have elapsed.

Compounding the problem is that the packet may or may not experience queuing delays of indeterminate lengths as it moves across the switches, routers and other gear in between the source and the destination.

The good news is that for most cases, the Network Time Protocol (NTP) can be used to keep time straight, thanks to various offset mechanisms built into the standard that take network jitter and delay into account. However, in some cases, really exact time measurement is needed, down to the sub-millisecond. For these duties, system builders should look at the Institute of Electrical and Electronics Engineers' IEEE 1588 precision clock synchronization protocol.

"NTP can exchange time stamps about once every 16 seconds, which means the accuracy which we typically derive [from NTP] is about a millisecond," said Paul Skoog, product marketing manager at the Timing, Test and Measurement Division of Symmetricom. "If you have to have to have better than a millisecond, that's when we start talking 1588."

A company that specializes in network time-synchronization products, Symmetricom offers a range of hardware that works with 1588, including dedicated time servers and switches that can maintain the integrity of time packets.

Most recently, the company has released version 4.0 of TimePictra, a package of hardware components that can synchronize time across an Ethernet or Internet Protocol network, using IEEE 1588. With this package, a node manager maintains the correct time, which it communicates with remote clients at the edges of the networks on regular intervals. The company has also released the latest version of its Grandmaster Clock, which features a dedicated 1588 time stamp processor.

The labs of Hewlett-Packard Co., originated IEEE 15888 as a way of synchronizing test and measurement equipment over a network, Stoog said. The chief difference between IEEE 1588 and NTP is that with NTP, the time is generated and adjusted is all in software, while IEEE 1588 uses the underlying hardware as a reference, meaning the time is based off the frequency oscillations of the underlying circuitry. This approach allows time to be measured in about 60 nanosecond intervals (a nanosecond is 0.000001 Milliseconds).

Symmetricom has a number of white papers that explain the internal workings of 1588 in more detail. To download them, visit this page.

Although NTP can handle most synchronization needs in government, there are a number of cases where more exact measurement does come in handy. Military sensor networks, for instance. A testing range may want to carefully document how some explosives detonate, or how quickly an aircraft moves. A testing range could be instrumented with hundreds of sensors to capture data from tests. Coordinating the resulting data would require extremely precise measurement. GPS devices could also provide sub-millisecond accuracy, but pairing GPS devices to each sensor would be prohibitively expensive.

Telecommunication companies are the biggest buyers of the 1588 protocols products. As telcos move to Internet Protocol networks, they lose the built-in time synchronization of circuit networks. A base station cell tower, for instance, may be directly connected to an Ethernet network, rather than to a T-1 line, and would require timing. Using 1588-based synchronization platforms keeps the telco's networks all on the same clock.

Symmetricom is not alone in releasing new 1588 products. Napatech has updated its round of 1 Gigabit and 10 Gb Ethernet adapters to be synchronized via 1588. Napatech is pitching these adapters for use in network performance monitoring, test and measurement, and traffic optimization.

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