How does the one internet cable that runs along powerlines handle traffic for dozens of houses without contention?


How does the one internet cable that runs along powerlines handle traffic for dozens of houses without contention?

In: Engineering

a lot of systems and protocols exist for this but the main thing to know is that data is chopped in to smaller frames (technical term for segments of data covered in multiple layers of important info) which also have an address and an ordering number in them, so it can be reassembled at its destination

They don’t run on or directly in contact with powerlines. They use coaxial cable, fiber, or twisted pair. All resist or eliminate interference from power lines. If every user in a neighborhood tries to download a huge file simultaneously, there will be some slowdown.

A phone cable has a pair for each house. Contention doesn’t happen per line but can happen when all the lines come together at the Central Office.

A Cable Co line has more bandwidth available than all the houses use on average. Using more than the total bandwidth causes contention and slows each customer down. Customer complaints will prompt the cable co to improve the lines.

Customers transmitting on the Cable Co line at the same time would cause contention. That’s prevented by using a Token Bus style protocol or transmitting on different frequencies.

Well…actually there very likely is contention. But if you’re not noticing it, then your ISP is probably doing a good job of managing it.

Suppose an ISP has a 1000Mbps internet pipe for a neighborhood to share. Also suppose, for simplicity, that this ISP only offers 50Mbps internet packages to its customers. This means that the ISP would be able to support 20 customers without contention. Every customer would be able to get the full 50Mbps advertised, at all times, regardless of what the other customers are doing.

However, ISPs know that most people spend very little time fully saturating their connection. Most web browsing activity only uses a trickle of data, and even video streaming is unlikely to use a full 50Mbps. Therefore the ISP can get away with oversubscribing. For example, the ISP may decide to implement a 5:1 oversubscription ratio by putting 100 customers, each with a 50Mbps package, on this 1000Mbps internet pipe.

With this oversubscribed setup, most customers will be able to get the 50Mbps they are expecting most of the time. But if for some reason everyone starts downloading at the same time (e.g. new show comes out on Netflix), customers will start experiencing slowdowns because the shared internet pipe doesn’t have enough capacity to give everyone 50Mbps at the same time.

The exact oversubscription ratios ISPs actually use are a closely guarded secret, but I think it’s say that virtually all residential ISPs oversubscribe. It doesn’t make business sense to spend 5x, 10x, or 20x more money on infrastructure to eliminate contention when 99% of customers won’t notice when they occasionally don’t reach the full advertised speed.

If you want to have your speed guaranteed at all times, or if you want a dedicated line for yourself not shared with anyone else, that likely requires an enterprise contract with your ISP which requires much more $$$$$.