iPhone slows down entire home network

Ever since the automatic upgrade to iOS 7, an iPhone that connects to my Linksys WRT54GL router running DD-WRT, slows down all other connections, from any other device. Download speed is reduced by a factor of 3 to 5, and ping times jump from 33ms to 600 - 800ms. This makes it frustratingly slow to use any web application, and appears to happen when some update is going on on the iPhone. However, the last episode has been going on non-stop for more than 12 hours. At a 1.5Mbps DSL, I have no idea what sort of update could take that long, or if something other than an update is going on.

I only have limited access to the iPhone (it's not mine and the owner got quite annoyed with my requests to use their mobile data plan), but I have full control of the router. Banning it by its MAC isn't exactly a solution. What else can be done? I've read through some posts on Apple's board but they didn't offer a clear solution.

Solution 1:

Since you are using the DD-WRT on your router there is a set up you can use to limit the bandwidth for specific IP or MAC.

Here are the instructions how to set up the QoS (Quality of Services)

and more instructions here.