Why limit the bandwidth but not throughput?

It’s a nice sunny afternoon in the library. So I tried to start a video chat to share this sunshine with her. However, she denied my request. She said that there is a limit on the bandwidth of 1GB per week with the broadband network in her residence.

Bandwidth, is a measure of the amount of data that can be transferred between computers in a network within a specific period.

I’ve been thinking about this for a while: Why do the Internet service providers want to limit the bandwidth? Well, the most reason I’ve heard is that they want to protect the network device from being overloaded and avoid other network users from squeezed out of the information highway.

Hmm, how can they do that by limiting the bandwidth? Let’s take an example in real world. Say there is a bridge on a river and people walk through the bridge from one side to the other side every day. Unfortunately there is a policy from the bridge owner that the bandwidth, the number of times one person allowed to walk through the bridge, is 10 times per day. Sadly, most people need to use the bridge several times only in the morning. It turns out that there are about 100 people walking on the bridge and each person go back and forth 10 times during that time. They don’t really need the bridge for the rest of the day except in the morning. Bridge is overloaded and few guys with bad luck fell into the river because of that.

I think, what the bridge owner really mean, is to limit the throughput.

Throughput, is a measure of the amount of data that can be transferred in a time unit between computers in a network.

It means that, if I am the bridge owner, I don’t care how many time you walk through the bridge everyday. But you must follow the rule that you are allowed to using that bridge for at most twice per hour! So no one will be waiting by the entrance and the bridge is always is good shape.

It’s the same for the computer network. Why can’t they just limit the throughput to, say 256kb per second? Doesn’t that make more sense?

4 Responses to “Why limit the bandwidth but not throughput?”

  1. ZJP Says:

    xiaohu,
    小女子最近在研读通信网络的例子。 以我的理解,bandwidth原是指频率范围(单位为Herts)。 用在信号系统方面,是指数居的传输速率(单位为bit/s)。
    我想sever说的是数据量的限制,而不是速率。 
    refer to:
    http://en.wikipedia.org/wiki/Bandwidth

  2. wangxiaohu Says:

    ZIP, Bandwidth确实是这个定义。可是后来我看 ISP 的协定,上面都说 Bandwidth 一个月 30GB,确实不违背 Bandwidth 的定义,只不过这个时间单位变成了一个月。所以我才会想到另外一个 Throughput,来和被 ISP 扭曲的所谓 Bandwidth 作比较。

  3. ZJP Says:

    sorry, should be “seven”. an unintentinal typo..

  4. 皮帽子 Says:

    Bandwidth is the width of your frequency response. This measures the capability of delivery data with high speed.

    What the ISP limit is “bandwidth USAGE”, which is the integral of data flow.

    Thoughtput is the maximum capable speed after all the protocol/collision overhead adjustments.

    Why would ISP limit your bandwidth usage? Because they want to advertise as “boardband” service (high bandwidth), but don’t want you to suck their resources 24/7 (hence you can enjoy the high bandwidth only to a certain extend). It’s a marketing strategy, not a technical one.

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