This is more "home networking" than "homelab," but I imagine the people here might be familiar with what in talking about.
I'm trying to understand the logic behind ISPs offering asymmetrical connections. From a usage standpoint, the vast majority of traffic goes to the end-user instead of from the end-user. From a technical standpoint, though, it seems like it would be more difficult and more expensive to offer an asymmetrical connection.
While consumers may be connected via fiber, cable, DSL, etc, I assume that the ISP has a number of fiber links to "the internet." Those links are almost surely some symmetrical standard (maybe 40 or 100Gb). So if they assume that they can support 1000 users at a certain download speed, what is the advantage of limiting the upload? If their incoming trunks can support 1000 users at 100Mb download, shouldn't it also support 1000 users at 100Mb upload since the trunks themselves are symmetrical?
Limiting the upload speed to a different rate than download seems like it would just add a layer of complexity. I don't see a financial benefit either; if their links are already saturated for download, reducing upload speed doesn't help them add additional users. Upload bandwidth doesn't magically turn into download bandwidth.
Obviously there's some reason for this, but I can't think of one.
There's a fixed amount of available bandwidth (signaling) on a given connection, regardless of directionality.
That really depends on the technology used. For example, all modern Ethernet standards (which includes both copper and fiber optic) are full duplex, meaning they can provide the full bandwidth in both directions at once. So a gigabit Ethernet link can do a gigabit in one direction AND a gigabit in the other direction at the same time (but not two gigabits in one direction).
This is only true when you have a single transmission medium and a fixed band. Cable internet is a great example; you only have a few MHz of bandwidth to be used for data transmission, in any direction; the rest is used up by TV channels and whatever else. WiFi is also like this; you may have full-duplex communications, but you only have a very small portion of the 2.4Ghz or 5Ghz band that your WiFi router can use.
Ethernet is not like this. You have two independent transmission lines; each operates in one direction, and each is completely isolated from any other signals outside the transmitter and receiver. If your ethernet hardware negotiates a 10Gb connection, you have 10Gb in one direction and 10Gb in the other. Because the transmission lines are separate, saturating one has absolutely no effect on the other.
This is only the theory. In the end there is still a chip doing the routing that has a total throuput it is capable of regardless of the direction.