Hardware – Equalization and Pre-emphasis

Screen Shot 2014-02-09 at 9.39.58 AMBefore we look at equalization and pre-emphasis, we should examine some fundamentals of waves and signals. A perfect square wave is a really useful way of representing a waveform in the time-domain, but it’s not the only way of looking at the signal.The name ‘time-domain’ may be new but the view is familiar to us all, you have amplitude on the vertical axis and time you have time on the horizontal scale.

Ideal square waves need infinite bandwidth

The square wave is easy to understand, but unfortunately the ‘perfect’ square wave is a purely theoretical construct. A square wave is actually constructed of many sine waves of different frequencies and amplitudes added together [1]. The fundamental frequency of the signal (e.g. 10Khz) is a sine wave and has the highest amplitude. However there are other many other frequencies called harmonics, which must be successfully received and added to the fundamental signal to ‘square out’ the waveform. To view these signals we need to switch to a new view, the ‘frequency-domain’.  Continue reading

Hardware – Clock and Data Recovery

Clock and data recovery is an essential physical-layer function of modern switch and router hardware. Digging deep into the electronics of a router may not be your thing, but clock recovery is a fundamental building block for other network hardware functions. For example, serial to parallel data conversions require reliable clock and data recovery (CDR) to function effectively. It’s hard to understand serial to parallel conversions or signal conditioning without learning about CDR first.

Continue reading

Test – Throughput alchemy using a snake topology

Sometimes it’s best not to trust network vendor datasheets.  Nothing quite beats a controlled test of a network device in your lab with your config and your required features. But if you want to load test multiple ports on your 10G device-under-test (or DUT), then things can get very expensive, very fast.  In this post I’ll show a test topology that will help you turn 10Gbps of test traffic into 640Gbps or more.

Continue reading

Video – 10G Fiber Transceivers – Network Sherpa

I’ve just recorded a quick video about 10Gbps fiber transceivers, There’s a first for everything I guess.  It’s a cheat sheet which describes the different transceivers, where they’re commonly found and the connectors you use.

I’d love to hear your take on the video.  Too long… too short, music too cheesy (yeah I know!), etc.   All constructive feedback is welcomed.