Re: Logging ISP Download Speed.
On Thursday 23,August,2012 03:34 PM, Bob Proulx wrote:
> lina wrote:
>> Once I used the wget to download one file from debian repository, on
>> another terminal I with to use the wget to get another file at the same
>> time from the same repository.
>
> And if you needed both files then that seems fine to me.
>
>> I was discouraged to do that, and was also told that, two wget
>> downloading would deduce the downloading speed, I should have waited one
>> finished before download another one.
>
> *Should* is too strong. It doesn't hurt anything to download two
> files at the same time. Or three. A hundred is probably too many
> though. But really there isn't any difference in the overall results
>
>> It's happened two years ago, but I still remembered that suggestions.
>> Even later in my life I still download two or more at the same time.
>
> Sure. I often have multiple things happening at the same time. It is
> why I use a multitasking operating system.
>
>> Here my question is that, is it true that open two wget will affect the
>> downloading speed? better one by one, just suspect it.
>
> Let's assume you have a 1.0 Mbit/s download connection. Because it
> makes the math easier. And assume you need a 1.0 Mbyte file. With no
> other overhead it will take aproximately 10 seconds to download.
>
> Now let's assume that you download two of those files at the same
> time. You still only have 1.0Mbit/s download speed. But now you are
> downloading 2.0Mbytes of data in total. Obviously the total download
> will take aproximately 20 seconds to download.
>
> If you ran them sequentually then the first one would finish in 10
> seconds and then the second one would start and it would finish 10
> seconds later. So it would take 20 seconds in total for both to
> download both of those files.
>
> If you ran them both at the same time then neither would be able to
> get the full 1.0Mbit/s download speed. It should balance out between
> them and each would get about 0.5Mbit/s download speed. Which would
> double the amount of time each would take. Each would take about 20
> seconds to download those files but both are running at the same
> time. So once again it would take 20 seconds in total for both to
> download those files. No difference!
>
> Now if you needed *one* of those files first then you would download
> it first and not start any of the others until you had what you needed
> first. You would prioritize. You would get the high priority items
> first. Because then in 10 seconds you would have something you needed
> first. You would hold off the lower priority items that could wait to
> get the ones that you wanted soonest.
>
> Hopefully all of that makes sense and enables you to do whatever makes
> the most sense at that moment in time. If the bottleneck in speed is
> your local network connection to the Internet then you would whatever
> you wanted to make your task easiest.
>
> Now here is a twist. This is a obtuse thing but useful to know about.
> If the bottleneck is competition with other people then the situation
> is different. Let's say you are working at a small business or school
> or coffee shop along with nine other people for ten total people
> downloading things. There is still a 1.0Mbit/s download capacity.
> But now ten people are using it. So you are only getting 0.1Mbit/s
> download speed. Getting that 1.0Mbyte file now takes 100 seconds
> instead of 10 seconds. Because nine others, all ten of you in total,
> are all downloading all at the same time and the system is sharing the
> bandwidth across all of you. So now it takes 100 seconds.
>
> Now here is the twist. If you can split that file up into nine parts
> and then start nine downloads in parallel you will get the total
> 1Mbyte file downloaded in 50 seconds. That is now twice as fast as
> the 100 second case! The system doesn't know about users. The system
> knows about download connections. If you have nine downloads going at
> once but your nine other coworkers each have one that is 18 total
> downloads going at once. The system will share the bandwidth across
> all 18 of those. But 9 of those are yours and 9 belong to the rest of
> your coworkers. So you are getting half of the available bandwidth
> and starving your coworkers out of their fair share.
>
> Better if you split the file into 27 parts and ran 27 downloads in
> parallel then you would have 27 and your coworkers would have 9 and
> you would have 27/(27+9)=3/4 of the bandwidth and they would have
> 9/(27+9)=1/4 of the bandwidth. You would be able to download a
> 10Mbyte file in 13.3 seconds. The system divides bandwidth up between
> the connections so if you have more connections then you get more
> bandwidth. You could keep going with this but at some point the
> overhead prevents further progress. This is what some file download
> manager programs do. This is part of what makes bittorrent so
> effective.
>
> Meanwhile your coworkers might be a little bit upset that you were
> starving them out. In response they might start doing the same thing
> and running a parallel download manager. This becomes an "arms race"
> with all sides trying to get more than their fair share at the expense
> of others. Now if everyone in your group all did the same thing then
> the result is that you would be right back where you started before,
> with 1/10 of the bandwidth of the ten of you in the group.
>
> I hope this was interesting and useful.
Indeed, very interesting explaination, and now I start to understand why
some "download manager" software are banned here.
Thanks Bob for your time.
Best regards,
>
> Bob
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