GPON is TDM (Time Division Multiplexing).  The downstream is essentially OC-48 (2.4Gbps).   The OLT sets the clock and each ONT has a specific timeslot for uploading.  Some vendors can adjust the timeslot reservations to ‘guarantee’ specific upload speeds to specific ONTs

From: NANOG <nanog-bounces+matthew=corp.crocker.com@nanog.org> on behalf of Mel Beckman <mel@beckman.org>
Date: Thursday, June 9, 2022 at 7:31 PM
To: Adam Thompson <athompson@merlin.mb.ca>
Cc: nanog@nanog.org <nanog@nanog.org>
Subject: Re: Upstream bandwidth usage

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Adam,

Your point on asymmetrical technologies is excellent. But you may not be aware that residential optical fiber is also asymmetrical. For example, GPON, the latest ITU specified PON standard, and the most widely deployed, calls for a 2.4 Gbps downstream and a 1.25 Gbps upstream optical line rate.

 -mel

> On Jun 9, 2022, at 3:08 PM, Adam Thompson <athompson@merlin.mb.ca> wrote:
> However, if you're talking about fiber service, it's pretty much pure marketing-dept-driven BS, combined with some vague justification of not letting TOR nodes or copyright-ignoring seeders/Warez-providers/etc. overwhelm the network in unexpected ways.