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hi all, Some routers can do bandwidth mangement to limit users' bandwidth, but I want to know how does the router mange to do this(bandwidth management), any details or links ...
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  1. #1
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    Smile A question about router


    hi all,

    Some routers can do bandwidth mangement to limit users' bandwidth,

    but I want to know how does the router mange to do this(bandwidth management),

    any details or links about this problem will be quite appreciate,

    thanks a lot!

  2. #2
    Linux Guru jmadero's Avatar
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    This is all done through the firmware I believe. The firmware of a piece of hardware is basically a mini OS which communicates with the item and the main system (or any other hardware that can receive/send packets). So the firmware works similar to a piece of software you install on your computer to do the exact same thing. It simply tells the router to allow X amount to Y IP address or MAC address
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    thanks, jmadero
    I think the key point is: "It simply tells the router to allow X amount to Y IP address or MAC address"!
    I wonder how does the router "allow X amont", no more, no less, I know that a tcp sender will increase its congestion window when the sender receives an ack,, therefore, so long as the acks arrive at the sender, the congestion window will increase, and the sender will achieve higher bandwidth. So I wonder how does the router control the bandwidth, does it just drop the packets sent by the tcp sender or througth any other ways?
    Thanks,

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    Quote Originally Posted by pingpingping View Post
    thanks, jmadero
    I think the key point is: "It simply tells the router to allow X amount to Y IP address or MAC address"!
    I've never that, especially not on a LAN enviroment. You could start tunnelling - something like a GRE tunnel I guess. As a router guy I'm too busy making sure the network works rather than telling a user he can only use 10meg a week.

    Generically a router will just keep shunting data until buffers are full, then it'll start dropping data. Different queuing methods, fifo - first in first out, WFQ, wieghted fair queuing to fiddle with what drops.

    If you want to specify what data gets dropped, you then start getting into the black arts of QoS - Quality of Service; where you start configuring traffic to have different priorities. ie VoIP RTP traffic is the highest, and ftp pretty low down the food chain.

    Different circuits also have different factors as well frame relay, you can do burst traffic, where by the circuit is dynamically increased. This is set up on the switch thou really, not the router.

    The there's traffic management for ISP broadband links. The one's I've worked in the UK have all controlled bandwidth with the atm network/dslam. They put 20 users with 8 meg circuits on a 2 meg circuit and call it a 20:1 contention ratio. If one user is a p2p download addict, they'll monitor it, and when he's cap'ed they'll alter the service in various way. Early days of broadband in the UK none monitored this... they do now.

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    Quote Originally Posted by CmdoColin View Post
    I've never that, especially not on a LAN enviroment. You could start tunnelling - something like a GRE tunnel I guess. As a router guy I'm too busy making sure the network works rather than telling a user he can only use 10meg a week.

    Generically a router will just keep shunting data until buffers are full, then it'll start dropping data. Different queuing methods, fifo - first in first out, WFQ, wieghted fair queuing to fiddle with what drops.

    If you want to specify what data gets dropped, you then start getting into the black arts of QoS - Quality of Service; where you start configuring traffic to have different priorities. ie VoIP RTP traffic is the highest, and ftp pretty low down the food chain.

    Different circuits also have different factors as well frame relay, you can do burst traffic, where by the circuit is dynamically increased. This is set up on the switch thou really, not the router.

    The there's traffic management for ISP broadband links. The one's I've worked in the UK have all controlled bandwidth with the atm network/dslam. They put 20 users with 8 meg circuits on a 2 meg circuit and call it a 20:1 contention ratio. If one user is a p2p download addict, they'll monitor it, and when he's cap'ed they'll alter the service in various way. Early days of broadband in the UK none monitored this... they do now.
    thank you,CmdoColin

    After reading your reply, I guess you are experienced in router and the work of managing network. From your reply I know that different traffics can be configured to have different priorities, that is to say I can configure the router to drop special types of flow, ie. ftp,http and so on.
    but here I doubt whether I can configure the router to drop packets from special IP address in order to keep the bandwidth of that IP under a certain value(ie.10M), if it does, can you explain more in more details for me, or e-mail me some articles about this(my email address is : liucheng@net.pku.edu.cn), if router can't do that do you know how those network managers manage to control the bandwidth of a special IP Address, through software or some other ways?

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    On a Cisco running IOS, I'd possibly use QoS with a policy map with bandwidth statements. - but I'd have to do some reading on it... =P I *think* the bandwidth statements in a policy map actually do enforce b/w used rather than the interfaces statements which are mainly used to calculate routing metrics. I can't remember if it's a min or max though. It's from a vague memory, so I'd definately not say that to a customer. So beware my comments about bandwidth that could be garbage.

    If I'm correct, and it's Cisco kit you're using, as long as you're familiar with acl's its actually not too painful to do. No idea on the others, I've 'played' on them, but have really had to do everything to complex on them.

    As I say I'd have to read up on it. I've never been asked to limit different users/vLANs to set traffic levels. QoS yes, but not deliberately limiting someones bandwitdh. More likely I'm looking to remove traffic that shouldn't be on the link, or looking to upgrade the device/circuit.

    From experience its more likely excess traffic would just be dev/null'ed with an ACL. eg voice calls quality is bad or can't connect and everyones watching youtube 24-7, you'd soon find youtube would be stopped either on the router or via an acl or firewall.

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