Bandwidth throttling

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Introduction

Hosting a website can be fun. But, when you offer big downloads or streaming media, you do not want a visitor to eat up the full bandwidth. Or, maybe, you want to offer a premium account from where users can download without limitation, and a free account where users cannot download faster than 50 kb/s. Here is where throttling comes in.

Bandwidth throttling helps provide quality of service (QoS) by limiting network congestion and server crashes. For example, you make sure a connection does not get more than an X number of bytes per second.

The purpose of this article is to show how to use bandwidth throttling, with a small helper class.

Using the code

Within the source code, you will find a class named ThrottledStream. This class is derived from the abstract Stream that can be found in the System.IO namespace. In the constructor, it accepts a base stream to throttle. Here is a small line of code that shows how to instantiate a ThrottledStream:

Stream throttledStream = new ThrottledStream(Response.OutputStream, 1024);

Now, everything you do with the throttledStream will be limited to 1024 bytes per second, and will be send to or read from the OutputStream that is a member of the Response property that exists within an ASP.NET page.

Because the ThrottledStream is derived from the abstract Stream class, it is easy to add throttling to an existing application or website. For example, when you have a process that sends file content over a Stream and you want to enable bandwidth throttling, you only have to change the initialization of the destination stream.

The old code can look like this:

Stream sourceStream;
Stream destinationStream;

try
{
    sourceStream = new FileStream(@"c:\myfile.bin", 
                       FileMode.Open, FileAccess.Read, FileShare.Read);
    destinationStream = new NetworkStream(mySocket, false);

    byte[] buffer = new byte[1024];
    int readCount = sourceStream.Read(buffer, 0, BufferSize);

    while (readCount > 0)
    {
        destinationStream.Write(buffer, 0, readCount);
        readCount = sourceStream.Read(buffer, 0, BufferSize);
    }
}
finally
{
    if (destinationStream != null)
    {
        destinationStream.Close();
    }
 
    if (sourceStream != null)
    {
        sourceStream.Close();
    }
}

Now, we can easily add throttling support to this process. We only need to change the initialization:

...

Stream originalDestinationStream = new NetworkStream(mySocket, false);
destinationStream = new ThrottledStream(originalDestinationStream, 51200);

...

By adding only one line of code, this full process is throttled to 50 kb/s (51200 b/s). Now, we go even a step further and add throttling that is based on a membership:

...

long bps;

switch( user.Membership )
{
    case MembershipLevel.Bronze:
        bps = 51200;
        break;

    case MembershipLevel.Silver:
        bps = 102400;
        break;

    case MembershipLevel.Gold:
        bps = 153600;
        break;

    case MembershipLevel.Platina:
        bps = ThrottledStream.Infinite;
        break;
}

Stream originalDestinationStream = new NetworkStream(mySocket, false);
destinationStream = new ThrottledStream(originalDestinationStream, bps);

...

Here, we have a situation where a Bronze membership will give you 50 kb/s, Silver 100 kb/s, Gold 150 kb/s, and Platina infinitive - no throttling.

Points of interest

Bandwidth throttling can improve the QoS of your server, and allows you to control the bandwidth for a specified connection. The helper class named ThrottledStream is very easy to use, and can be used in existing scenarios.