Google threw up all sorts of possibilities but the more things we tried (and that failed) the more I couldn’t escape from the idea that it must be some network related issue. I got to thinking about the nature of VPN and how there is an initial connection and then a large stream of UDP packets over the tunnel for the data transfer. That’s when a light bulb switched on - I’d seen something like that before in my Draytek router settings.

Draytek have a nice selection of anti denial of service features which I have activated to protect my network. Some of these concern certain types of flood defense; where a count of packets is maintained and if it exceeds a certain threshold then the connection will be dropped for a period of time. This would result in the appearance of a stall for any file transfer caught up in the melé. Bingo!

The culprit setting is shown in the screen shot below, “Enable UDP flood defense”. Originally this was set to 150, I had to set it to 1000 in order to eliminate that VPN issue.

It’s worth discussing why the number has to be so high for my fix and why it may not need to be so high for you. Most home connections over VPN end up being below 5Mbit or so with the corporate end point on the other hand being capable of 100Mbit. This results in the overall speed obviously being tied to your 5Mbit speed. In my case I use the FTTC technology and thus have speeds up to 80Mbit. This means I can transfer many more packets per second than most people on home connections so it is likely that you won’t have to go so high as 1000 to get the desired result in the Draytek settings.

I hope this helps someone out, feel free to get in touch with me if you have any questions.

Shweta gave me this wonderful 3D Christmas card on her arrival in Swindon this weekend

While leaving the Hyde Park Christmas market last evening I snapped this great shot of the setting sun through the trees

Upon leaving the Christmas market by the Royal Festival hall I spotted this sand sculpture being created on the South bank of the Thames

In order to publish my photos to the web I have to extract image data from the RAW files my camera generates and compress into a JPEG file that can be delivered to and opened by a web browser. To to this I make use of dcraw, a nifty little application authored by Dave Coffin. This will pass data out from the RAW file to be collected on stdout by a program such as cjpeg.

As I like to publish exactly what my camera has stored to the file (with a little compression for portability) I don’t use many of the options on dcraw, just invoking the ones that read the values from the file it’s self and use those. Looking down at the parameter list I suddenly wondered if perhaps I’d mistakenly used the wrong parameter somewhere, so I started to check each one I’d used against the documentation.

Everything checked out apart from one very small anomaly; -w was documented but -W was not. The documentation states that -w tells dcraw to use the white balance value stored in the RAW file when processing which is what I wanted but -W seemingly did nothing except it threw no errors when used so must have some function.

Plunging deeper into the documentation I found the bombshell I was looking for; -W is used for switching off the exposure compensation value contained within the file! I ran a quick test and changed to lower case while decoding a photo I’d taken recently and the effect was perfect, the correct brightness and also the correct white balance (it hadn’t been far wrong but was much better now).

I’ve now updated my script that I use to call dcraw to invoke the correct parameters and hopefully dark photos will be a thing of the past on my website. The thought of having to re-decode some 3000 odd photos that have already been uploaded doesn’t fill me with joy though…

As Christmas nears and the brights lights go up around London, Shweta and I stopped to take a few pictures in Covent Garden

Not only has Woolworth now closed down but they hadn’t given out bags like this for years

At a distance this looks like a no smoking sign. Upon closer inspection it gave rise to precisely what it was requesting passers by not to do!

I went out for a walk through Central London late in November and took a number of Autumnal pictures with ShwetaLast update: 02 December 2011

I carved out a spooky pumpkin for Halloween to keep the trick or treaters away. Seeing as that won’t actually stop my house being egged, I also bought a bumper pack of fun size chocolate bars!