said by Darknessfall:said by telcodad:I think the worst ratio though is the "Extreme Pro" 400/10 plan, with a 40x slower upload, and therefore only 2.5% of download speed!
Does anyone know how much upload is needed per Mbps of download of traffic due to ack packets or whatever? Isn't it riding it close?
Edit: One person here said that when downloading 840 Mbps, it used 21 Mbps upload (40x) »
Re: why are upload/download ratios so horrible in Canada?Wouldn't a light bandwidth upload on 400/10 basically kill the download speeds?
So, I actually did some extensive testing on this.
You end up with some strange efficiency that works in Comcast's favor here ... Some amount of packet loss on ACK's is acceptable because each ACK packet basically means that every thing prior to that byte counter has been received ... Normally, ACK's are sent for every-other packet, but the sending side is also sending a window of packets at a time, (ie, dozens, or even hundreds of packets may be 'in flight' before an ACK is received for what was sent).
Because of this dynamic, significant amounts of the ACK packets can be dropped while full speed is achieved, as long as there is no packet loss in the downstream direction, in which case the limitations of the upstream are more problematic.
The absolute bare minimum I've found to be able to achieve a 1Gbps download when all other conditions are ideal is 7.38 Mbps upstream capacity.
Keep in mind that this number would make the service really, really, really annoying to use, as it would mean that any interactive service would be completely unusable during a download (ie: a game would flat out be impossible), and also any packet loss at all would drastically reduce performance. Packet loss always hurts, but this would make it much more extreme.
At 400Mbps, that would mean that technically they could get away with a minimum of 3Mbps, if they didn't care about providing service which was usable for anything interactive, or working in anything less than perfectly ideal situations.
Also, any upload /at all/ would drastically cut download speeds in this sort of scenario. Like, even sending an email with a jpeg attached would hurt your download speeds, if the upstream was cut this low.
In order to have something that is able to handle even moderately less than ideal scenarios, 24 Mbps upstream would again be the 'bare minimum' for 1Gbps downstream. On a 400 Mbps service, that would work out to about 9.6Mbps. So, that's probably where comcast arrived at 400/10.