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However, a number of customers have recently asked how they can get started with HttpWatch and VB.Net. HttpWatch includes automation samples in C# and in a previous post we used C# to create simple empty cache and primed cache tests. Jin Automation, HttpWatch, Internet Explorer Consider using a Content Delivery Network (CDN) or geo-locating your web servers.Don’t blame your ISP for poor downloads from distant web sites.

#Httpwatch basic download download#

Distance doesn’t just increase round trip times it can also reduce download speeds.For example, the ping time to Mars can be up to 40 minutes and would limit TCP throughput to approximately 142 bits / sec! With this in mind an interplanetary version of TCP/IP has been designed: In the case of interplanetary spacecraft, the round trip time may be colossal. Unfortunately, many routers and modems not support it

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RFC1323 allows larger window sizes over IPv4 and is enabled by default in Windows Vista.

There are two solutions to this issue but neither is in widespread use: You really need to geographically position your web server(s) or content close to your users if you want to offer the best possible performance over high bandwidth connections. But with today’s high bandwidth connections, this limit becomes much more significant. In the past, with dialup connections the maximum throughput value was much higher than the 56 Kbps available bandwidth. This value agrees fairly well with the measured figure. The 1.5 factor in the equation represents the overhead of the IP / TCP headers on each network packet and may be a a little too high explaining some of the difference. For large downloads in IE the TCP window starts at 16 KB but is automatically increased to 64 KB. Let’s try putting some numbers into the bandwidth equation to see if it matches our results. The ping time determines how many TCP windows can be acknowledged per second and is often the limiting factor on high bandwidth connections as the maximum window size in standard TCP/IP is only 64 KB.

It allows the receiver to request re-transmission of the last data block, if it detects data corruption or the loss of packets.

This is particularly important for memory challenged mobile devices

It avoids the receiver getting swamped with data that it cannot process quickly enough.

The sender will not start transmitting the next block data until it receives the acknowledgement from the receiver for the previous block. This upper limit is caused by the TCP flow control protocol, It requires each block of data, know as the TCP window, to be acknowledged by the receiver. ping time) imposes an upper limited on maximum throughput. Slide 7 of his talk shows that with standard TCP connections the round trip time between client and server (i.e. The reason for this behavior became clear when we saw Aladdin Nassar’s talk about Hotmail Performance Tuning at Velocity 2008: However, when we tried using other networks to perform transatlantic downloads we could never get more than about 3 – 4 Mbps. This time the download speed was 372 KB/s or 2.91 Mbps – less than 15% of the advertised internet connection speed.Īt first we thought this was some sort of bandwidth throttling of transatlantic traffic by our ISP. It has a ping time of 137 ms from our office in the UK: However, the situation was quite different with our own web site that’s located in Dallas. That’s quite respectable if you allow you the overhead of the IP and TCP headers on each network packet. 1.57 x 8 for 8 bits per byte) was over 60% of the theoretical maximum for the internet connection. The download speed of 1.57 MB /s or 12.56 Mbps (i.e. When we tested this out using a local UK based website with a ping time of 13 ms we saw this: If you just think of network connections as a simple pipe, then you might expect the download speed to be approximately the same as the slowest network connection, i.e. What download speed would you expect in this scenario? The Surprising Effect of Distance on Download Speed