TechNet Magazine has the following information about ECP.
The Exchange Control Panel is a Web application that runs on a Client Access Server providing services for the Exchange organization. This Exchange Control Panel is installed automatically when you install a Client Access server. To manage Exchange from just about anywhere, you simply need to enter the URL path for the application in your browser’s Address field. You can then access the Exchange Control Panel. By default, the Exchange Control Panel URL is https://yourserver.yourdomain.com/ecp.
The Client Access server to which you connect processes your remote actions via the ECP application running on the default Web site. The physical directory for this application is %ExchangeInstallPath%\ClientAccess\Ecp. And it runs in the context of an application pool named MSExchangeECPAppPool. In the %ExchangeInstallPath%\ClientAccess\Ecp directory on your server, you’ll find a web.config file that defines the settings for the ECP application.