How to limit simultaneous request from a single client?

We provide couple of SOAP web service.

Yesterday our service was down, we couldn't access 开发者_开发百科to the service from the outside (can't even load the wsdl), but we could access to the service if we were connected with terminal service on the server.

The thing is one of our partner was calling our web service with 130 simultaneous threads.

So I think the service was down because this partner was occupying all the available connection. And this limitation is done by .net because I can easily read static file (txt) on my server from the outside, and the service accept the connection if it's from the local IP.

Here is my question : how can I limit the simultaneous connection count for one client ? I know I can do it for every one in IIS Manager, I can do it for outgoing request (connectionmanagement configuration). But I can't find it for incoming request.

It's strange because I think it's one of the first thing I'd set to prevent DOS attack.

(.net 3.5 , IIS 6)