Time to rethink time precision and accuracy: for effective network monitoring, analysis, test and measurement precise Ethernet frame time stamping and accurate time synchronization is essential. As line rates increase the challenge for OEM appliance vendors is ensuring continued precision and accuracy. What are the technology choices available and which of these can help in meeting these challenges?

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The Internet and IP networks are now the de-facto standard platform for new communication service developments, such as converged data centers, cloud computing, unified communications or high-speed financial trading. Most of these services need to adhere to strict quality of service requirements requiring Service Level Agreements (SLAs).

To assure Ss, network managers need not only to know what is happening in their networks, but also when it is happening.

In addition, they need to know the latency of their networks to measure both Application and Transaction Response Times (ART and TRT) as many new services are time critical, such as financial transactions, delivery of voice or video or ensuring fast response when accessing a cloud computing service.

In network analysis and latency measurement applications, each Ethernet frame is time-stamped to allow time registration and latency measurements to be made. With line interface speeds increasing, network managers and OEM appliance vendors are facing a number of challenges:

* How to ensure more precise time stamping as interface speeds increase?

* What time synchronization solutions are required?

* How can time synchronization be deployed cost effectively?

RETHINKING TIME STAMP PRECISION

At I Gbps, a 64-byte Ethernet frame can be sent every 670ns. If you need to ensure that all Ethernet frames have been uniquely time stamped for analysis, then your time stamp precision needs to be lower than this number.

At 10 Gbps, a 64-byte frame Ethernet frame is sent every 6ns and at 40Gbps this is further reduced to I 7ns.

RETHINKING TIME SYNCHRONIZATION

Most network analysis and latency measurement appliances need to perform analysis and measurement on a number of ports at once. It is therefore essential that the time-stamps on frames from different ports are synchronized to ensure that measurements are made correctly.

Accurate time stamps also allow data from multiple ports in a system to be merged for efficient analysis. This enables OEM vendors to develop multi-port 10G and 40G appliances with attractive price points.

In this regard, there are two types of synchronization:

* Relative or Frequency synchronization-where two independent clock frequencies are synchronized

* Absolute synchronization--where the absolute time of day is synchronized

Clock frequency synchronization can be achieved using a I Pulse Per Second (IPPS) signal between the clocks. This can provide accuracy in the range of lOns.

This is sufficient for measuring jitter between received frames, but not enough for latency measurement. Here it is also important to know the absolute time, so the synchronization mechanism must include both...

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