Post B7vgAKIt94B1Lxqxeq by argv_minus_one@mastodon.sdf.org
 (DIR) More posts by argv_minus_one@mastodon.sdf.org
 (DIR) Post #B7vUVsYlmIG2ECnAiu by CursedSilicon@social.treehouse.systems
       0 likes, 0 repeats
       
       @argv_minus_one @fivetonsflax @futurebird *Puts hand up* Hi, I have worked in the ISP space before.Cable's asymmetry wasn't an intentional choice. But a design vestige of its history. Originally these systems were designed as a one-to-many (and one way) network. Radio waves were blasted down the wire and into the back of TV setsThe lacking upload speed is because the networks were never *designed* with the idea of broadcasts coming back up the pipe. DOCSIS was grafted on to cable TV networks as an afterthought and required major cleanup of the design of the networks to accommodate them
       
 (DIR) Post #B7vUVsmawtJgv5GDGy by astraleureka@social.treehouse.systems
       0 likes, 0 repeats
       
       @CursedSilicon @argv_minus_one @fivetonsflax @futurebird yep, I came here to explain this but you already covered the bases. It's a similar story with ADSL/VDSL as well - symmetric DSL variants DO exist, but they have significantly reduced downstream bandwidth compared to their asymmetric cousins. Given the general traffic mix of a residential connection, the asymmetric profiles were generally a sensible tradeoff. Fun fact about DOCSIS: one of the side effects of grafting data service on top of cable TV networks is that all traffic is encapsulated in MPEG-2 transport stream frames - 188 byte (iirc?) chunks. Downstream traffic is also broadcast, so on early networks it was possible to see traffic destined for other customers. An encryption layer (BPI) was eventually added, giving each cable modem a separate encryption key
       
 (DIR) Post #B7vgAKIt94B1Lxqxeq by argv_minus_one@mastodon.sdf.org
       0 likes, 0 repeats
       
       @astraleureka Residential fiber works the same way, according to Wikipedia, even though it's a new network specifically designed for full-duplex transmission. https://en.wikipedia.org/wiki/Passive_optical_network@CursedSilicon @fivetonsflax @futurebird
       
 (DIR) Post #B82b2RNTxUp1E0yVl2 by CursedSilicon@social.treehouse.systems
       0 likes, 0 repeats
       
       @argv_minus_one @fivetonsflax @futurebird That one I'm surprisingly less familiar with why it's asymmetric, despite growing up with it in AustraliaI'd defer to telco nerds on that ;-;
       
 (DIR) Post #B82b2Ri2j3GiFmavo0 by brouhaha@mastodon.social
       0 likes, 0 repeats
       
       @CursedSilicon @argv_minus_one @fivetonsflax @futurebird It was asymmetric because they want to partition the frequency spectrum used into separate upward and downward bands, to avoid the computationally heavy need for full echo cancellation, and they both expected and wanted end users to be mostly consumers of content, not producers.There was no _techincal_ reason it couldn't be reverse in the other direction, or fully symmetric (which existed: SDSL).1/
       
 (DIR) Post #B82b2SBSxenvj2MQfQ by oscherler@tooting.ch
       0 likes, 0 repeats
       
       @brouhaha I once heard that the asymmetry of ADSL is because the hardware in your home is cheap shit with bad SNR, but the hardware at your ISPs is much more performant. But now that I think about it, it seems it’s the wrong way around.@CursedSilicon @argv_minus_one @fivetonsflax @futurebird
       
 (DIR) Post #B82b2SH8cZLE0d0xVY by brouhaha@mastodon.social
       0 likes, 0 repeats
       
       @CursedSilicon @argv_minus_one @fivetonsflax @futurebird Making the frequency/direction control dynamically adjust was entirely possible, but would have made the DSLAM and modems a little more expensive, so they chose not to.2/
       
 (DIR) Post #B82b2SkCsUarSmcAoi by mirabilos@toot.mirbsd.org
       0 likes, 0 repeats
       
       @oscherler @brouhaha @CursedSilicon @argv_minus_one @fivetonsflax @futurebird I’ve been reliably (apprenticeship at telco) informed that it is because of cross-talking.In the downstream direction, the signal from the DSLAM is still strong where there’s the most cross-talking (in the thick wire bundle near the VSt), in the upstream direction the most cross-talk is where the signal is weak (most distance from sender).