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RE: Logging ISP Download Speed.



Hi,

>>> 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!

One other thing to keep in mind. Usualy when downloading a file with a "chatty protocol", one that needs to confirm downloading a block to the server before the next block is sent, the actual filetransfer wil not fill the full bandwith, in those cases a second download will fill up that available bandwith. I see that a lot when I transfer files via my VPN connection from my Windows PC from/to the Windows server.
With a WAN optimized file protocol that is filling the available bandwith starting a second download at the same time will not help.

Bonno Bloksma


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