Death of the Serial Cable

I’ve been on a mission the last few years:  No serial cables, no multiplexors.  Getting rid of the multiplexors was pretty easy from a technical standpoint, that was more of a culture challenge.  Ethernet is a much bigger challenge because not only do you need to have an Ethernet capable modem on your end, you need to have one on the distant end as well. (For any of the non-military readers, most of our WAN connections go over satellite communications (SATCOM), so your router needs to connect to a SATCOM modem).

It finally happened.  Without having to buy anything extra you can go Ethernet from your router to your FDMA (Frequency Division Multiple Access) or TDMA (Time Division Multiple Access, which have always been Ethernet for us) modems.  This might not sound like a lot, but lets go over how much we can remove from the equipment string by doing this:  Three serial cables, two signal converters, one fiber cable, one external encryption device and one external serial timing device (GPS).  A problem with any one of these devices or cables could stop your WAN connection from working.  Not having to deal with serial timing alone would make this compelling.  When you consider how much cheaper and easier Ethernet is to work with, this one is a no-brainer.  Add in not having to work with an external encryptor and you’ve got a much more stable equipment string.  Not all of our FDMA modems have the ability to do this.  If you have an EBEM (Enhanced Bandwidth Efficient Modem) with an ESEM (Ethernet Service Expansion Module), you will be able to go Ethernet right into the back of the modem.

A couple of things you want to keep in mind:

• Ethernet will be oversubscribed in your employment.  This means the physical ports will negotiate a speed that is faster than the modem is capable of (physical port capable of 10/100/1000).  In cases of oversubscription you will want to shape your traffic to get the most efficient use of your bandwidth.  For more on this, see the “QoS Demystified” post.
• This is not yet a standard practice.  You will need to specifically ask to use Ethernet.  If you are using Ethernet and the distant end is using serial, it won’t work.