I have worked as a Sr. Network Engineer for around 15 years now. I can add my viewpoint and tell you it perplexes me a great deal to see that these internet providers are not working to keep their customers at the best possible speeds. In most (probably all) cases it's not even a matter of having to keep their equipment current. Certainly not to give customers a symmetrical upload and download speed. To bring the old 56k modem days into it just clouds the issue. We have advanced WELL beyond those days. But even during those days, none of us had 56k download and 1k uploads. It was always 56k by 56k right? When we moved to ISDN, I had 128k down (with 2 B channels and 1 D channel -- remember guys?) and 128k up. If anything, it might have had to do with a device called a DSLAM. (At least in the DSL days) A Digital Subscriber Line Access Multiplier. And that's just a guess. Multiplexers could always be a little hinky and I could see it getting hung up with acknowledgments. In fact, see RFC5690 and see if anyone can make sense of it. But this occurs even with Fiber.
Maybe we should look at it from a different direction. At home I have 1.5 Mbps upload and 27 Megabit downloads. Maybe some ISP's only give you enough upload speed so that you can send enough acknowledgements for the size of your download speeds. In other words, I can't have 27 Megabit downloads with a 56k upload speed. It would never be able to acknowledge the packets it has received, thus tons of retransmissions. So what is the ISP's problem? Are you afraid we'll start running servers at home? We already do!
Bottom line is, there is no good reason for an ISP to slow down an upload speed. There's got to be an ulterior motive here:
Is it:
A.) The ISP wants to stop or discourage file sharing.
B.) The ISP wants to discourage running home-based servers.
C.) All of the above.
Sorry for the long thread... But I think I just stumbled onto the answer.... At least this would make the most sense to me:
This might just be some sort of weird overlap within a company. When Verizon launched FIOS, I want to say that FIOS was a whole new business unit for Verizon. AT&T likely just ported a lot of its infrastructure over from the DSL side of the business. So it might be that Verizon FIOS started fresh, not having to deal with legacy policies, legal issues, boilerplate contracts, etc. and AT&T did. It might have made sense somehow in the DSL world, like I described above with the DSLAM, for AT&T to keep the speeds non-symmetrical, but Verizon didn't have that issue in the fiber world. Maybe AT&T just needs to update a little bit and get with the times. non-symmetrical circuits are nonsensical. I want to think that AT&T wants to give their customers what they want, but they might just be a little out of touch with their customer base. Maybe when Google Fiber comes to town, they'll ask the question, "Where'd everyone go?"