The iNomads single port option uses only a single declared port between the web server (I.e Apache or EZWeb) and the server running the application.
When a new session starts iNomads launches a process on the application server to do the actual processing. In a single port setup the web server keeps the connection to the application server open between requests from the workstation, in a non single port setup each application process has to have a unique port number assigned to it so when subsequent requests for the same session arrive it gets routed to the applicable process based on it port.
The issue with IIS is keeping the connection active after the ASP request completes whereas with Apache and EZWeb we maintain a table active sessions and their related open tcp connection to the application server.
The single port setting is not directly related to using simple CS.