In asynchronous processing, the intersystem session is used only to pass an initiation request, together with various items of data, from one system to the other. All other processing is independent of the session that is used to pass the request.
IMS V13 supports connectivity with CICS TS over IPIC. This offers an alternative to LU6.1 connection for asynchronous communication. For more information about this interface see ISC TCP/IP enhancement