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difference between throughput , bandwidth , connection speed and channel capacity ?

Discussion in 'Networks' started by kobem, Dec 19, 2007.

  1. kobem

    kobem Megabyte Poster

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    i suppose i could know these but something stupid arose in my head.......


    1-for example my LAN connection speed is 100 Mbps but what is bandwidth for this LAN ?

    2-what is the max. data rate i can transfer at a time ?

    3- also i have a dsl connection and it is said connection speed for it is 1024 Kbps
    in fact this is the download speed and regarding to this 1024/8 = 128 KBps is a number


    but this 128 is throughput or bandwidth ?

    i can not distinguish these !

    4- in LAN , 100 Mbps is the max data rate that i can transmit a time ? if not what?
     
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  2. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Depends on your precise definition of bandwidth, but I'd say 100Mbps was the figure. If you are looking at the frequency bandwidth on the copper then the figure would be higher.
    100Mbps
    In this case 128KBps is an approximation to the download speed in bytes per second.
    Er - distinguish from what?
    100Mbps or a bit less.

    Harry
     
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  3. drum_dude

    drum_dude Gigabyte Poster

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    Don't think that 100mbit on ethernet means you'll transfer at 100mbit - according to Douglas Comer - the frame size is still the size as it is on 10mbit ethernet. All the 100mbit means is that more hosts can sit on the wire compared to 10mbit ethernet. You can liken it to an extra lane added to a motorway but the vehicles stay at the same speed but more can be on the road at the same time. Yes there will be a slight increase in speed as the congestion is less but the highest transfer speed I've seen on my 100mbit home LAN (2 PCs on the wire) is 3.8 Megabytes a second...you would think that 100mbit would give you over 10megabytes a second but I don't think it works that way!

    Douglas Comer is the author of this book

    Someone correct me if I've spouted utter shite...
     
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  4. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    First - something odd with this post - there is more in the edit buffer than appears on the screen!
    Edit - we seems to have clashed on edits - hence the confusion!

    If you get 3.8MBytes with 100BaseT that is faster than 10Base can do! In fact with many machines, particularly with some versions of Windows, there are so many overheads that you rarely get the maximum speed. Try transferring a *large* file and see what happens to the indicated speed.

    I often see speeds fairly close to 10MBytes/sec on good networks between Unix boxes.

    An excellent book, but I doubt you are quoting him quite correctly.

    Harry.
     
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  5. drum_dude

    drum_dude Gigabyte Poster

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    Luckily I have the book to hand:

    At this particular part of the book headed: Fast and Gigabit Ethernet where Douglas Comer discusses faster ethernet technologies: 1000BaseT and 100BaseT. He states:

    "To understand the significance of increase in capacity, it is important to understand two facts. First, although computers have become faster, few computers can transmit at a sustained rate of 1 Gbps. Second, the NEW versions of Ethernet [100baseT and 1000baseT] did not change other parts of the standard. In particular, the maximum packet size remains the same as 10BaseT. These two facts imply that higher-speed Ethernet technologies were not optimized to provide the highest possible throughput between a pair of computers. Instead, the design is optimized to allow more stations and more total traffic."

    Source: Internetworking with TCP/IP, Douglas E Comer, Pearson Prentice Hall, 5th Edition, Page 18.

    :biggrin
     
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  6. drum_dude

    drum_dude Gigabyte Poster

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    Yeah but it ain't 100mbit or even close to it!
     
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  7. drum_dude

    drum_dude Gigabyte Poster

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    But then again my test wasn't exactly a scientific one!! LOL
     
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  8. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    This is what I meant by 'not quite correctly'! :biggrin

    First - he is talking about Gigabit and 100Base, not 100Base and 10Base. And the problems he mentions are slowly going away - some good pieces of hardware plus a good OS will now get close to filling a Gigabit pipe (think PCI-E gigabit cards and a good server OS)

    He is right in many respects - it is just that nowadays it is fairly easy to get top speed from 100Base links despite the frame size limitation.

    Harry.
     
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  9. drum_dude

    drum_dude Gigabyte Poster

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    Yes yes...I see what you mean now, that makes a lot of sense! Cheers Harry!

    :)
     
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  10. kobem

    kobem Megabyte Poster

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    people sorry to make you wait! :(

    i am not in agood mood in these hours , i will return to you later
     
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  11. BosonMichael
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    BosonMichael Yottabyte Poster

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    Keep in mind that file transfer speeds you see on a PC are different from the bit transfer speeds you get on a connection because there's packet overhead involved... the data in the files you are transferring are only a piece of the entire packet.

    There's an app that I like to use to determine actual bit transfer rate on a link - it's called NetCPS. It measures the number of characters (bytes) that traverse a network between two computers running NetCPS. Quite handy for determining if problems exist within your network infrastructure, particularly for WANs. I've seen it use 9.8 Mbps of a 10Mb point-to-point link.
     
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  12. kobem

    kobem Megabyte Poster

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    people sorry to make you wait! :(

    i am not in a good mood in these hours , i will return to you later
     
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  13. drum_dude

    drum_dude Gigabyte Poster

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    Yes I used it the other day to test the transfer speed between 2 servers, 1 in edinburgh and 1 in Rotherham. I was trialing two Packeteer PacketShaper 1700s as I was interested to see the benefits of the compression between the 2 sites. I was quite impressed! From Edinburgh to Rotherham (2mbit up @ Edin and 1mbit down at Rotherham) I was getting an average transfer speed of 96 Kilobytes per second without compression. With compression switched on Netcps reported the transfer at an average of 215Kilobytes per second!!! Unfortunatley the Acceleration on the PacketShaper took the transfer down to an appalling 20kilobytes a second!!! But the netcps is a great tool!

    By the way, does netcps perform a CIFs transfer? I'm sure it does - CIFs is one of our biggest bandwidth consumers!
     
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  14. BosonMichael
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    BosonMichael Yottabyte Poster

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    No idea... that'd be a question for Jarle Aase. :)
     
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  15. Firemouse

    Firemouse Bit Poster

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    Bandwidth is your maximum capacity, throughput is the rate you actually transmit at. Bandwidth can be be specified in Hertz but is most commonly prsented in bps.
     
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  16. kobem

    kobem Megabyte Poster

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    lets think using an example :

    consider you have a "wireless pc" or a laptop , if it is 802.11b/g , connection speed
    is 54 Mbps lets assume.


    first

    what is bandwidth value in that enviro.. ? 54 Mbps ?
    if so , why are there two distinct terms : bandwidth and connection speed ?
    and throughput value ?



    second

    also we often hear the 2.4 GHz frequency value in wireless .

    And lets combine : why 2.4 GHz not 2.4 GB ... ?

     
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  17. Fergal1982

    Fergal1982 Petabyte Poster

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    Look, we've covered this in your other thread. GHz is NOT a measure of Bytes per second. GHz is the frequency at which the device is operating.
     
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  18. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Because they don't all mean the same thing, and some are somewhat vague.
    802.11g has a maximum raw data speed of 54Mbps, but can be quite a bit less if conditions are less than perfect. Bandwidth is a bit fuzzy in this enviroment, but might be used to indicate the maximum rate that you could push application data through such a link. Because of protocol overheads this is going to be about 20Mbps or so.
    Throughput might describe the actual real-world result of transferring some files via the link - which may well be less than the 'bandwidth' because of overheads on the machines in question, like opening files and so on.
    Because 2.4GHz is the frequency 802.11g (and other devices such as microwave ovens) operates on. Bits have nothing to do with it. That band is one of a number known as ISM (Industrial, Scientific and Medical) - see here for more info on ISM.

    Harry.
     
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