One of the new and exciting features we added to the VCFMW ShadyTel exhibit this year that almost no-one would have seen or realized existed was an actual high precision master frequency reference for our TDM network. This post will dig into what this device is, what it does, and why we use it.

What is a Frequency Reference?

The ShadyTel core network is entirely TDM, also known as Real Telephony. Since this is a Time Division Multiplexing network, the timing on the network is fairly important. Its worth understanding that in this context, timing is not absolute wall clock time in the sense of NTP or PTP, but instead refers to a stable frequency reference used for clocking synchronous serial interfaces.

Another year has gone by, and another VCF has happened. This was the largest VCF in history, occupying the entire 100,000 square foot Discovery Hall at the Schaumburg convention center in Schaumburg, Illinois. It featured an unprecedented number of exhibits, guests, and talks, and ran from September 11Th through the 13Th. In this post, I’d like to talk a look at the IP network, and the technologies that supported this massive show.

This is the third year I have stood up SneakyNet, my fake telephone company at the Southwest Vintage Computer Festival. SneakyNet supplies dial-tone and IP transit to exhibitors around the show, and does so with a mix of period correct and modern hardware. I thought it would be fun to take a step back and talk about how this whole network is put together, and how things actually work.

Before we dive too deeply, more documentation than you could ever want can be found on the main SneakyNet docs site: https://docs.sneaky.nonroutable.network/.

I have recently been doing a lot of work with Cisco IOS Interactive Voice applications written in TCL. This is a dated technology at this point, but still a very stable one. In my application, I wanted to be able to have a duration spoken aloud. Getting the duration itself is not hard, IOS provides a robust timer system to meter calls and set deadlines for actions. Speaking the duration on the other hand is much harder because the Cisco ISR platform lacks the hardware for real-time speech synthesis.

In the last post I showed how my cluster is maintained day to day and using various industry standard tools. This is a fairly robust process as I build out the cluster, but just having a cluster isn’t particularly useful. To build upon this we need to put up a means for outside network traffic to come into the cluster and become inside network traffic. This traffic might be HTTP destined for a service, TCP as a lower level application protocol, or some kind of UDP ingress to a specialized application.