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Mbps V MBps leased line option!!

Discussion in 'Networks' started by garyb, May 9, 2007.

  1. garyb

    garyb Byte Poster

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    Hi,
    I have got myself in a right twist this morning!! We have what BT term a 2Mbps leased line. I always thought this was 2 megabytes per second rather than megabits per second, but BT contract team assure me it is 2Mbps which I think is 0.25 MBps or 256kbps [Slow!]. Can anyone shed any light on what the hell it is as I am stumped at the moment:eek:

    Running various speed tests I can download files at 1694kbps download & 1689kbps upload so the figures of 2mbit seem worng to me!!

    Help please, my head is going to explode:blink
    G
     
    WIP: MCSA 2003
  2. r.h.lee

    r.h.lee Gigabyte Poster

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    Garyb,

    The download and upload speeds you are getting may be based on the actual data received and sent. You have to remember that during the encapsulation process of the data you're uploading, TCP or UDP adds a transport layer header, IP adds a network layer header, Ethernet adds a frame header and frame trailer, all before your data that you're uploading to the 2Mbps. So the "lost bandwidth" may be accounted by the transport layer header, network layer header, data link layer header and trailer which is collectively known as "network overhead."

    The reason why your download speed may be relatively low is because the host on the other side also has to add some network overhead.

    I hope this helps.
     
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  3. garyb

    garyb Byte Poster

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    Thanx for your prompt reply. I am simply not getting this at all:oops: I think the upload/download speeds are fine & way above what I would be getting if its a 2megabit line? Surely with these transfer rates it is 2megabyte line?

    All I am trying to do is calculate our web server bandwidth requirements, and its taking me all morning!!!:ohmy

    G
     
    WIP: MCSA 2003
  4. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    A 2M line is indeed 2Megabits/sec. But it is 2M *both* ways.
    (Note - in the telco world 2M is 2,000,000 - not a power of 2).

    As r.h.lee pointed out - there are overheads from the protocols involved, so the actual speed will be less than 2M. If this is a BT line then I suspect that the bottom layer will be ATM, which is not very efficient for overheads, but is good for fast switching in a big network.

    Your tests show about 1.7M on the line, so the overhead seems to be about 15%.

    Harry.
     
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  5. garyb

    garyb Byte Poster

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    Hi,
    Thanx again for your reply, I may have mislead you with my previous question, we have our wires crossed or you are telling me tha answer & I cant see it!!:blink

    I am not querying whether the line speed is good or not, just simply trying to work out if BT have correctly stated its 2Mbps or what I think it is, 2Mbps?

    If the service is 2Mbps, then surely the line speed detailed above is over what we are supposed to have? With speeds like this it must be a 2MBps leased line, would you not agree?

    download speed of 1694kbps = 1.61 MBps = :eek: 12.87 Mbps

    Looking at this calculation, if we had a 2Mbps leased line as BT say, then:

    download speed of 256kbps = 0.25 MBps = 2Mbps

    Does that make sense to anyone...

    ta..
     
    WIP: MCSA 2003
  6. Tinus1959

    Tinus1959 Gigabyte Poster

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    In the protocols it is normal to use the b for bits and B for bytes. So the 256 kbps in your first post should in fact read 256 KBps. That could allready shed some light on the matter.
    In the Netherlands there is a website called www.speedtest.nl where you can test the speed of the link. I'm sure there is also something like that in the UK. You could in fact use that site, but the text is off course in Dutch.
     
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  7. garyb

    garyb Byte Poster

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    Similiar site results which they post in b not B-
    [​IMG]

    Am I correct in saying that is near enough 1.7MBps upload speed, suggesting we have a 2MBps leased line:cry:

    Cheers

    G
     
    WIP: MCSA 2003
  8. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    You are getting your Bs and bs muddled. Because it is so easy to do I tend, in these situations, to write the word explicitly.

    Er - you say 2Mbps and 2Mbps! What's the difference? :p
    No - it is a 2Mbps line.

    No - 1694kbps = 1.6 Mbps (note the b - not a B). Just slide the decimal point 3 places to convert k to M.

    You are getting bs and Bs muddled again.

    Dowload speed on a 2Mbps line will be a little under 2Mbps - or in bytes/sec a little under 200kBps.

    (I use a 10:1 conversion between bits and bytes here as this approximates the protocol overheads, and is easy to do in my head)

    Harry.
     
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  9. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    That image clearly shows a b - not a B. So you have about 1700kbps, which is 1.7Mbps. You have a 2Mbps line.

    Harry.
     
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  10. garyb

    garyb Byte Poster

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    Thanx to you all, can finally see the bloody wood from the trees now..

    Maybe I need an line upgrade, our dev team have implemented Anthem which is polling the SQL server from the client every 20 secs and pulling back all the data each time! 7 external users have dragged over a gb of data today, so 70 users may struggle a tad:rolleyes:

    Ta
     
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  11. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    A leased line of more than 2Mbps will cost an absolute bomb, depending on distance.

    You might want to look into a LES circuit - although they have distance limitations.

    But the system you describe seems to be designed to be bandwidth wasteful! Why not pull one copy then only pull updates?

    Harry.
     
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  12. garyb

    garyb Byte Poster

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    £12,000 for 10Mbps, it is a lot but not if you consider we pay £8000 for 2Mbps currently..

    We have used LES circuits previously, but they wouldnt help in this scenario as its a public facing site. Our LES10 [Lan Extension Circuit 10MBps] ran 8km office to office and simply provided a private LAN between offices. On top of that they are way more expensive than leased lines where I live..

    Good question!
    I am unsure why they dont do that, but will mention it to them. The site is built in .NET with SQL2000 backend. On the client browser a list of customers records are displayed, every 20 seconds these are refreshed to bring back new data so you can imagine why we are pulling over 1GB data. We intend to roll this out to over 100 users later this year which is why I am trying to forecast bandwidth usage..:eek:

    Cheers
    G
     
    WIP: MCSA 2003
  13. BrizoH

    BrizoH Byte Poster

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    Gary is your £12000 10Mb quote with BT?

    We too are paying £8k for 2Mb (in Glasgow, £6k for London) but I think I could talk the bosses into paying extra for the jump in bandwidth.
     
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  14. garyb

    garyb Byte Poster

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    Yeh, that was our BT account manager who quoted in Feb this year. This is for BT Net Premium, formerly BT Flex Net and is based on our distance from the nearest Exchange.

    I cant quite justify this to the board until I assure them it will bring in more business, which I cant, thats their job:p !!

    Cheers

    G
     
    WIP: MCSA 2003
  15. Tinus1959

    Tinus1959 Gigabyte Poster

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    WOW, I pay 29 euro (thats 20 pound) per month for 1 mbps ADSL
     
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  16. garyb

    garyb Byte Poster

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    Yep, but thats your max rate & you are probably on 50:1 contention ratio, I imagine you would do well to get 256Kbps upload and 750Kbps download. With the leased line you get the full quota minus the overheads, so essential for business's like ours who run Site 2 Site VPNs, Mail servers, web hosting etc.

    I may be wrong but with ADSL you dont get SLAs either, which would be a disaster if the lines went down..:eek:

    G
     
    WIP: MCSA 2003
  17. BrizoH

    BrizoH Byte Poster

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    Very interesting, we're on BTNet Premium too. Thanks for the info
     
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  18. garyb

    garyb Byte Poster

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    Hmmm, as a matter of interest what are BT Net stats like from speedtest.com [http://www.speedtest.net/]?

    I have a 2Mbps line in 2 seperate offices that get different results when run at the same time!

    [​IMG]

    G
     
    WIP: MCSA 2003
  19. Tinus1959

    Tinus1959 Gigabyte Poster

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    You have a point there, but the figures are better. Ratio is 20:1
    upload is 512 kbps, download is 1 mbps. Speedtest is according to these figures.
    I was just a bit astonished by the amount, that's all.
     
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  20. garyb

    garyb Byte Poster

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    I totally agree with you, it astonishes me they charge that too, especially as in London it would only be around £5500 for the same service!

    Saying that when we first took out this line it was £12,500:ohmy on a 36 month contract, fair play to BT though, they do reduce the cost fairly frequently.

    I guess it all depends on your needs at the time, but your 1Mbps ADSL line seems to return decent figures, I take it, its a business line if your on 20:1, is it BT?

    Cheers

    G
     
    WIP: MCSA 2003

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