Switch Bandwidth

Posted on 2005-04-07
Last Modified: 2007-12-19
We have a network of 4 computers using a switch and one broadband connection of 1mbps. I wanted to know a few things.

1. Does this mean each of us gets 1mb every second, or does each of us get 1mb for 1/4 second(since my understanding is that access to the bandwidth is "switched" among the four comps very fast.

2.Does it matter if we are all downloaading movies or playing online games. I mean, does the downloading by one user affect the speed of the other users in my house?

3. If a computer is connected to the switch but is not accessing the internet, does it mean when it is his turn, the bandwidth is wasted?

Thanks, and I would really appreciate a detailed yet clear and easy to understand answer. I will not hesitate to increase the points if I find the answer given worthy of it.

Thanks in advance.

Question by:obajaber
    LVL 13

    Assisted Solution

    1.  A switch does not lower your bandwidth by sharing it, so each port can deliver what you have it set for: 100Mbps actually = 200Mbps at full duplex.

    2. Downloading affects the "pipe" going to the internet and therefore affects all users.  If you have 1 Mb and are using 600k to download, 400 k is left to share.  The internet pipe is shared, so-to-speak.

    3. No.  If that machine is not accessing the internet, it's not sucking up bandwidth; and it can't get updates either ;-)

    Overall, your switch is a good choice for separating the machines from sharing internal bandwidth.  As for the internet connection, it's not uncommon to have 100s or 1000s of machines reliant upon one pipe.
    LVL 8

    Assisted Solution

    1Mbps is 1 mega BIT per second, which is 1/8th as fast as 1Megabyte per second, that is a common confusion.

    Typically you will be using a 100bT switch which is 100 times faster than your broadband connection, this just points out that your broadband internet is always going to be your bottleneck.

    When you have 4 people sharing the same internet connection, it is essentially shared amongst those that are using it, a portion is not reserved for someones use even if they aren't online.  For example, if it is just you online, and you're downloading a movie at 768Kbps, and all of a sudden 3 other people start using the connection, you will see your download speed deteriorate appropriately.

    Keep in mind that with a 1Mpbs (or 1000Kbps) connection, you will never see a download occur at that speed, at minimum you will lose some of the bandwidth due to overhead (packets being used for control of the line).

    A computer that is turned on, but not accessing the internet, won't have an affect on others download speed.  (However, most systems these days will download stuff automatically such as virus definitions or security updates)

    I hope this helps.
    LVL 8

    Accepted Solution

    1. You all share 1mb.  If only one user is browsing the internet, he/she should be getting 1mb speeds.  'switching' is happening within milliseconds.  If four machines start downloading at the same time, then each will approx get 256mb, some slightly fast than others but this is dependant on various connections of the performance of each PC and where its being downloaded from.

    2. It usually doesn’t matter, but yes each user is affecting other users download speed.  When browsing the internet, it not usually noticed because you are only using the internet for the time a page is being loaded to the screen, once the page is on the screen your computer is not using the internet (usually).  But playing online games is quite different, since most games require an instant response from the internet.  If someone else is using the internet at the same time, you will notice the effect on the game.

    3. Nope.  If the a user is connected but not using the internet, its not a waste, that connection is not in use, so the full bandwidth is available for all other connected machines instead.  Note, if you have auto-updated running, then you may find machines downloading from Microsoft when the machine is not in use.

    Usually connecting a number of machines connected to use one internet connection is always beneficial , as usually everyone benefits.  The only real downside is online gaming, to get the most from your game you need to tell everyone to stop using the internet...!!

    The other advantage is sharing resources.  You only need one printer/scanner.  When setup correctly, all other users can use the same devices.  You can also share files to other machines easily as well.  Have one machine with all the mp3 on, and everyone has access to the same songs.  Your switch is probably 100mbs switch, so you can access other machines 100 times faster than accessing the internet.

    Author Comment


    So basically, what happens when all the users are downloading movies, or want to play bandwidth intensive online games at the same time. Does it mean that some users will get higher bandwidth or is it divided equally? Is thier a priority system in the switch or how does it deal with this situation? I don't think it can give 900kb to one user and leave the other 100kb to be shared by the rest , right?
    LVL 13

    Expert Comment

    You'd have to have a managed switch to assign bandwidth.  So, some will get higher bandwidth than others.  If you want a managed switch, you'll need a layer 3; and that's a whole other game then.
    LVL 5

    Expert Comment

    # Is this a shared line from your ISP? do they dedicate that 1 Mbps to you? Thinking they do, each of you dont get that 1 Mbps. its being shared (eually or non equally-depending upon the usage- web, mail, ftp, how many web pages opend at a time, etc services).

    ## It does matter, bandwidth(bw) will be shared according to the usage, and downloading files' size/types.

    ### No, the bandwidth is not wasted when any pc stays idle or doesnt request for any files from the web or doesnt send any request to the ISP for anything. the only thing this pc could do is to send a few IP packets to the switch to make sure its getting response from the switch. Only if any of the PC is infected with virus, trojans, ads, spywares, it'll waste your bandwidth  
    LVL 8

    Expert Comment

    Only very special switches can manage who gets what bandwidth.  Most switches just moves data as its being received from the internet, which is usually received packs of one thing then packs of something else as being fed from the ISP.

    Imagine your 4 users being fed internet information from a funnel through the roof.  Each user shouting up for a response from the server above.  The server then feeds the data requested into the funnel.  Each of the requests will come almost equally depending on when the server starts feeding and how much data is already in the funnel.  If the funnel is empty the data comes through almost instantly, if data is getting filled up in the funnel then you will start seeing delays.


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