C# API WebRequest default connection limit is 2. Use the request.ServicePoint.ConnectionLimit to unlock this limitation

TestUnityConnectionLimit.cs

using UnityEngine;
using System.Net;
using System.Threading;

public class TestConnectionLimit : MonoBehaviour
{
    void Download(object arg)
    {
        var sw = new System.Diagnostics.Stopwatch();
        sw.Start();
        string url = arg as string;

        try
        {
            var request = WebRequest.Create(url) as HttpWebRequest;
            // HTTP 1.1 specifies that A single-user client SHOULD NOT maintain more than 2 connections with any server or proxy
            // Use the following code to unlock this limitation
            // request.ServicePoint.ConnectionLimit = 10;
            request.GetResponse(); 
        }
        catch (System.Exception e)
        {
            Debug.LogWarning(e.ToString());
        }
        finally
        {
            Debug.Log(url + " elapsedTimeInMilliseconds: " + sw.ElapsedMilliseconds);
        }
    }

    void DownloadAsync(string url)
    {
        var thread = new Thread(new ParameterizedThreadStart(Download));
        thread.Start(url);
    }

    void Start()
    {
        DownloadAsync("http://mat1.gtimg.com/www/images/qq2012/qqlogo_1x.png");
        DownloadAsync("http://mat1.gtimg.com/www/images/qq2012/qqlogo_1x.png");
        DownloadAsync("http://mat1.gtimg.com/www/images/qq2012/qqlogo_1x.png");
        DownloadAsync("http://mat1.gtimg.com/www/images/qq2012/qqlogo_1x.png");
        DownloadAsync("http://mat1.gtimg.com/www/images/qq2012/qqlogo_1x.png");
    }
}