Hi, can anyone tell me how the sides of this cake is done???

http://www.flickr.com/photos/64101107@N03/7009095555/

thanks
 

AI would say a rolling pin.

AOr an impression mat

Maybe a textured mat?  Not sure, but it does add a nice touch to the cake.

It looks like the sides were done using an embossed rolling pin or mat - a design similar to basket weave

Whatever tool is used, I would wrap it instead of cover it so the markings don't stretch. 

Have a look at this post:

http://nyccakegirl.com/2011/08/16/how-to-decorate-a-sweet-wedding-cake-really-this-is-a-step-by-step/