Strain relief

I’ve got a problem with sagging cables, and I’ve got a simple solution. Examine the side-by-side images below which show the same fiber connection between a switch and a firewall. The image on the left shows a sagging cable which crosses in front of the switch in the rack unit just below it.

As you may know, this cabling install is a violation of the 167th rule of networking:

Thou shalt contain your cables to your own rack unit and shalt not, under any circumstances, impede access to other rack units or blades.

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Network config backups – just the beginning

An emergency switch replacement can ruin your day. However, having network config backups is not enough. Restoring full service may not be as easy as just copying the running configuration from your RANCID CVS repo, or your colleagues hard drive. Restoring the ‘identity’ of your original switch is a multi-step and somewhat complicated process.

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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 – Differential Signaling

I’m planning a series of blog posts that delve deeper into the way networking hardware works. This started with an idea for a single blog post on PHY-chips but I found that there were too many fundamental concepts that I was ‘assuming’ were already known. I’m not an electronics expert, but I hope that I can explain just enough fundamentals to help explain the bigger picture.

The first topic I want to cover is called differential signaling. Differential signaling is used in just about every important communication interface; PCIe, SATA, InfiniBand, 10GigE XAUI and many more. I want to cover this because it is a fundamental component of network systems and secondly because it is just simple and elegant engineering.

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Airflow is important – terminology is key

Data center cooling and large chassis

As a network engineer you need to be aware of the data-center environment where your chosen device will be deployed.  A huge wedge of the cost of running a datacenter are spent trying to keep it cool.  So preserving hot-aisle and cold-aisle airflow containment is a big deal for your data-center manager.  But it’s pretty easy to order hardware that messes with the datacenter airflow.  You need to watch for context and read the fine print to avoid unneeded data-center headaches.

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