Internet Communication Manager (ICM)
The Internet Communication Manager ensures that communication between the SAP System (SAP NetWeaver Application Server) and the outside world via HTTP, HTTPS and SMTP protocols works properly. In its role as a server, the ICM can process requests from the Internet that arrive as URLs with the server/port combination that the ICM can listen to. The ICM then calls the relevant local handler for the URL in question.
You need the ICM if you want your SAP NetWeaver Application Server to communicate with the Internet via HTTP, HTTPS or SMTP, like Web applications do with Web Dynpro ABAP. In AS Java the ICM distributes the incoming requests directly to the Java server processes. For communicating with the client, P4, IIOP and Telnet protocols are used in addition to HTTP(S).
ICM in the SAP NetWeaver Application Server
The ICM is a component of the SAP NetWeaver Application Server. It is implemented as a separate process, which is started and monitored by the ABAP dispatcher. With AS Java the startup framework does this task. You can configure the ICM using profile parameters.
SAP Web Dispatcher
The ICM and the SAP Web Dispatcher use the same code basis. The main difference between them is that the Web dispatcher performs load balancing, and passes requests to ICMs on the connected application servers rather than to work processes. This relationship makes it possible to share profile parameters and administration options. The structure of the documentation makes it clear what applies to the ICM only and what applies also to the Web dispatcher.