line speeds - is speed quoted both ways?

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Aug 10th, 2009
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Hi all

If I have a 2 meg wan circuit for example, is it 2 meg down and 2 meg up, at the same time, or would it be possible only to upload at 1 meg and download at 1 meg at the same time ?

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Rick Morris Mon, 08/10/2009 - 06:29
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It depends on the carrier, ISP.

If you get a DSL you are not getting the same upload and download speed. If you get a T-1 you are getting the same. This should not be confused with throughput though.


Throughput is the amount of bandwidth at any given time. If all you have is 1.5Mb pipe then that is all you are going to get total up and down. However, if you have no other traffic you will be able to upload the whole amount, minus any overhead, or download to the full potential, again minus overhead.


to answer your question with your example. if you have a 2Mb line you will get 2Mb total on the line used in any combination up and down, but you will not get 2 up and 2 down, this would be 4 in throughput if used all together. You would get the 1 up and 1 down, but don't forget about overhead.

carl_townshend Mon, 08/10/2009 - 07:59
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what about 100 meg full duplex, this means 100 meg both ways right ?

mlund Tue, 08/11/2009 - 02:09
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Hi Carl


I don't agree with Rick

If you have a 2M (E1) circuit you have the possibilty to use 2M simultaneous in both direction. 2M up and 2M down, total 4M.

The same also for 100M full duplex. 100M up and 100M down, total of 200M.


This is how all duplex (also called "full duplex") links works. They give you the possibility to both send and receive at the same time.

The opposite is half duplex, where traffic can only flow in one direction at the time.


/Mikael

Rick Morris Tue, 08/11/2009 - 04:35
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Explain throughput and how it is measured. If you only have a 2M WAN link why is it I can nover get more than 2M throughput on the line? I do not get 2 up and 2 down. When a carrier quotes lines via DSL or cable they never, NEVER quote a total speed, they tell you your cap at down and up speed and your upload speed is almost never the same. When you fill up a line, WAN link as the original question asked you will not get 2+2, you get total throughput quoted.

mlund Tue, 08/11/2009 - 05:36
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Hi


My explanation wasn't so clear, I see that now.


I did not meant You got 4M of throughput.

Of course, You are right, the throughput is not getting higher than the linkspeed.

On a 2M (E1) the speed is symmetric, you got 2M up and 2M down. Max throughput will not exceed 2M, and that is including the layer2 overhead.


And what Carl asked, is, if he can upload 2M and at the same time download 2M. The answer for that is, Yes he can.


/Mikael

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