Understanding telecommunications networks is not an easy undertaking. The infrastructure is quite complex and ever-changing. Your company may manage a telecom network today, or perhaps it will be inheriting one in the future. This article will attempt to explain the fundamentals of the logical network within the physical network, how logical circuit provisioning works, and how this all integrates into a GIS world.
The Basics: What are Circuits and Logical Circuits?
We define a “circuit ” as the physical path between two points in a network. An individual circuit terminates at a port on a network device, often a multiplexer. By itself, a circuit does not define the number of concurrent communications that can occur over it. In order to do so, engineers need a method to facilitate multiple conversations over a circuit.
This is where logical circuits come in. We define these circuits as “logical” because they aren’t defined by physical connectivity, but rather as logical divisions of the physical circuits.
A “channel” is the time slot on which a single communication flows. The number of channels on a circuit defines the number of simultaneous communications that can take place. This correlates to the amount of bandwidth available on a circuit. The fundamental standard for a unit of bandwidth is 64Kbps, commonly known as a DS-0. This is derived from the amount of bandwidth required to carry voice in a phone line. Combining multiple DS-0 channels together allows for larger amounts of bandwidth that we use today.
Another important device in telecom networks are multiplexers. These devices provide a way for multiple digital signals to combine into one over a shared medium. In other words, these are the devices that how and when a signal is transferred across the network.
Think of a highway as the circuit, the lanes on the highway as channels, multiplexers are traffic controllers, and the cars moving along the highway as data packets. The number of lanes on the highway determine how many cars can travel along simultaneously. If you started your journey from Salt Lake City, Utah, and head to Denver, you would get on the highway, choose a lane, and make your way towards Denver. This would be one circuit. When you get to Denver, you will arrive at the multiplexer, or traffic controller. The traffic controller will have you wait until a lane is available for you to take to your next destination, Fort Collins, Colorado. Now you will get on another circuit from Denver to Fort Collins, use the allotted channel, and move along until you arrive. Once there, you will come to another multiplexer that will route you to another circuit, and channel, to your house.
Now, let’s say an engineer would like to create a route from Salt Lake City to your house in Fort Collins. He or she would thus need to provision new roads and lanes along which your car could travel. Provisioning a logical circuit includes creating new circuits, if they don’t exist, and creating the channels with large enough bandwidth for the data packet to utilize.
How does logical circuit provisioning tie into GIS? GIS gives us the capability to spatially track the locations and routes that a logical circuit travels through. We can walk the path that an individual logical circuit takes and identify each location that it touches. The distance that a packet of communication takes is easier to see visually and gives us an idea of the total area that a circuit traverses.
I hope this article provided a better understanding of the basics of telecom networks and will give you a head start in your next fiber implementation. At the very least you will be thinking about fiber networks on your next roadtrip!