how do network cables transmit data from thousands of people without interference? Like a phone cable for 5 houses not mixing up calls?
In: Technology
Long story short, each device has an unique number assigned to it and each communication is made using those numbers. Think of it as a a mailman, he has the exact address and gets you your mail. That s how packets work.
For the not mixing part, the switch router theoretically is a small computer as it has it s own memory processing power. Each router stores your exact address 🙂 or a way to get to your address. Hope this helps
Phone wires are dedicated between each house. The copper wires in my phone line do not touch the copper wires of any of my neighbours. That might not have been true ~100 years ago but it is true today.
Now, electrical interference is a thing, and in some cases bad wiring has in fact caused people to be able to hear calls from other people’s houses on their own phone lines. Tell the phone company and they will take it very seriously and get it fixed at no cost to you. However since internet over phone lines (mainly DSL) would never work properly or would run very slowly if there were interference it’s a rare thing these days…. Well, DSL and even land lines are unpopular today so many not as clear cut.
In terms of regular networking, data is in tiny packets – typically 1500 bytes of main data, more for the addressing – that includes information about who the data belongs to. In situations where the wire/cable is shared (eg: cable modems, some forms of fibre) your modem is programmed to ignore data not intended for them by the addressing information. Otherwise the wires are dedicated to you and the internet provider will only send data to you where the address indicates it’s yours.
The word you are looking for is “multiplexing”. There are many ways:
In packet networks you are sending small pieces of data called packets (up to some thousands of bytes), each of them has a header that says where it is coming from and where it is going. The devices at the end of the cable have a queue for packets that should go down that cable. You can get clever about how much of the total bandwidth each of the flows is allowed to use and even more clever about whether other flows can get the bandwidth a flow is allowed to use, but does not. With sufficient cleverness you can make it so you can guarantee someone’s packets will be delivered within a given time if they do not send more than a given amount.
You can assign _time slots_ to flows. Split time into some intervals (called frames, I think), split frames into slots, assign each slot to a flow. If that flow does not use it, no one does. That gives you lower efficiency, but very deterministic timing (this is what we used for phone calls before compression was clever, when we knew exactly how much bandwidth any flow would use).
You can take an optical cable and assign different wavelengths (colours) of light to different flows, then use a prism to split them again. I think you can get about 160 different colours into a single cable.
When you really need lots of bandwidth, you would combine these — send 8 (or 160) different colours down a piece of fiber and on each of them use packet multiplexing.
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