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Some tests were done on Comcast networks on cable plant. Slide deck below explains it: https://datatracker.ietf.org/meeting/118/materials/slides-118-tsvwg-ses
by vkdelta 3y ago
Some tests were done on Comcast networks on cable plant.
Slide deck below explains it:
https://datatracker.ietf.org/meeting/118/materials/slides-118-tsvwg-sessa-61-l4s-experience-00 https://datatracker.ietf.org/meeting/118/materials/slides-11...
Not sure where this leads but I guess ISPs will start charging toll for express lanes
- jesperwe 3y agoL4S is not really an express lane. It is a way for applications to know when their traffic is congested, enabling them to scale DOWN their traffic to alleviate the congestion. Less congestion means less latency.
- polonbike 3y agoI guess ISPs will start charging toll for congestionless lanes...
- jlivingood 3y agoSee my comment above - doubt this will happen - rather it will become a differentiator like thoughput.
- kmeisthax 3y agoThey already did that, L4S or no. "Fast lanes" usually come in the form of peering links or colocated cache servers, both of which involve actual new capacity. Prioritizing individual flows of traffic over ordinary transit links based on monetary value is something IP is uniquely ill-suited to do.
- Phelinofist 3y agoHow is that different to TCP congestion control?
- flumpcakes 3y agoCongestion control with TCP will eventually still need to send the same number of bytes down a pipe, albeit with added latency. After a while an application could notice and make a change, but it would be long enough for a user to notice poor service.
- sznio 3y agoThis signals congestion explicitly, by a device declaring the link congested and asking others to slow down. TCP congestion control works by detecting when packets are dropped because devices can't keep up. Also, when the congestion signal disappears you can try to push the transfer speed up immediately, rather than slowly ramping back up like with TCP.
- ajb 3y agoTCP congestion control can use this new signal, if present. An update to the TCP protocol which allows it to do is going through IETF at present: https://datatracker.ietf.org/doc/draft-ietf-tcpm-accurate-ecn/ https://datatracker.ietf.org/doc/draft-ietf-tcpm-accurate-ec...
- Phelinofist 3y agoCan anyone guess a timeline when this will be available in OSes, middleboxes and whatnot? So when can we reap the benefits?
- ajb 3y agoThe slowest part is likely to be the network component, and there you can look at the experimental deployment by Comcast, that others have linked to in comments. So far I have not heard of moves by other network providers. Apple already has experimental L4S support for QUIC and TCP: https://developer.apple.com/documentation/network/testing_and_debugging_l4s_in_your_app https://developer.apple.com/documentation/network/testing_an...
- toomim 3y agoTCP congestion control relies on packets being dropped to signal that a link is congested. L4S actually includes an extra bit of information in IP packets that routers can mutate to explicitly say when they are congested. This means that you (a) don't need to play exponential backoff games, (b), don't need to re-send redundant packets, and (c) don't need big buffers in routers. You need big buffers in routers because otherwise exponential backoff goes crazy. But when you add big buffers, you get latency, which is another kind of suck. In order to avoid latency, you need to avoid buffers, which is hard unless you avoid exponential backoff. To avoid exponential backoff, you need routers to actually communicate their congestion, by sending more information. L4S does that by using an unallocated bit in IP packets.
- jlivingood 3y ago100% agree - read my IETF Internet Draft for more on that. :-) https://www.ietf.org/archive/id/draft-livingood-low-latency-deployment-03.html https://www.ietf.org/archive/id/draft-livingood-low-latency-...
- fotta 3y agoOh wow, I did not know this is what’s behind their low latency trials I’ve seen on dslreports.
- jlivingood 3y ago> "Not sure where this leads but I guess ISPs will start charging toll for express lanes" Doubtful IMO. I think latency becomes another competitive differentiator, much like throughput/speed is today. (this is a personal comment but I work at Comcast)