why aren’t internet upload speeds comparable to download speeds?

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Yes, I know, people use download bandwidth far more than they need upload bandwidth. But I don’t get why it isn’t comparable anyway. Why is it always so much lower?

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You ISP sets this configuration for user experience. They could set if, if they wanted, to be symmetrical but in the days of coaxial there are many people with speeds like 30mb/s or 50mb/s and as you can imagine, getting your download speed cut in half for an upload speed 99% of customers are almost never using is just a waste of cable. Instead they give you around 75-90% download speed to 10-25% upload speed ratio. This makes a better user experience for streaming and downloading new files. There are other configurations and plans at most(if not all) companies for people that run servers and host games that need the faster upload speeds instead of just a consumer configuration.

Because the transmission medium is divided into “channels”. Each channel can transmit a certain amount of data per second, and only in one direction at a time. Higher data-rate connections transmit data over multiple channels at the same time and in that scenario you just don’t assign as many channels for upload as you do download.

For example, my own cable internet modem uses 22 8MHz channels for downlink and 5 6.4 MHz channels for uplink.

Because, why would an ISP dedicate more of his limited ressources than necessary?

Back in the day when streaming (as in broadcasting to twitch etc), file sharing, or even high-performance online gaming wasn’t a thing for everyone and their grandma yet, there was no need for large upload capacity. ISPs would dedicate only so much bandwidth for upload as was necessary for basic web-browsing. At transport level the necessary acknowledgement packets that tell a server that you received (downloaded) a specific piece of data are round about 15-20 times smaller than the actual data packets that you receive. That’s where the familiar up/downstream ratios like 500/50 or 400/25 mbps come from.

Today, as upload-heavy use cases emerge, ISPs offer optional upload packages, but still the most users don’t need them.

Money.

A signal can only be sent down a wire one way at any moment in time. Any upload subtracts from the download. Most Internet connections are contended. The contention ratio can be anywhere from 1:1 (dedicated) for an expensive business connection, to 1:50 for a domestic connection (50 houses share the pool!). By limiting upload speeds, the ISP can guarantee download speeds for at a higher contention ratio since less of the pool can be used up by uploads. Most users don’t care that much about upload speeds so the ISP gets away with it. (It also doesn’t make much difference to many users).

It does however make a very big difference for a business user who has servers which need to send and receive significant quantities of data. Forcing domestic connections to be asymmetric (different upload/download) means a domestic connection can’t be used for a business purpose. Lots of domestic connections are actually pretty fast download nowadays and would be perfect for many small businesses if it weren’t for the comparatively slow upload speed.

ISP’s charge way more for symmetric (same upload/download) connections since they know businesses need them and have no choice but to pay. A not particularly fast (100Mbps) uncontented 1:1 upload/download connection might be £250 per month in the UK.