By default both IIS and WCF are somewhat restrictive in their default settings. Executing a large number of concurrent call’s will not have much effect as by default only 2 concurrent connections per IP are allowed.
However there are some simple configuration changes that you can make on machine.config and IIS to give your web applications significant performance boost. These are simple harmless changes but makes a lot of difference in terms of scalability.
To learn how to do this, read this article “Quick ways to boost performance and scalability of ASP.NET, WCF and Desktop Clients” written by Omar Al Zabir.