In normal dialog mode, one transport connection exists between a terminal and a UTM application on the processor. In order for a user to be able to call the services of an application, the user must open a session with the application, i.e. a communication
relationship between two addressable units in the network. A session setup generally means that the user must provide identification to the application. This can also occur implicitly.
OMNIS now offers you the option of connecting simultaneously to several UTM applications, even on different processors. However, you are only actually connected to one communication partner (namely OMNIS). The Session Manager now transmits the input messages (user jobs) to the applications with which you are connected.
Transport connections and sessions exist on both links of the communication relationship, i.e. the link from user -> Session Manager and from Session Manager -> application. This is illustrated in the diagram below:
Figure 15: Transport connections and sessions when multiplexing
A transport connection is a connection between two programs or between one program and a terminal, via which messages can be exchanged. A transport connection has a defined beginning (connection setup) and a defined end (connection shutdown) and is known to the transport system.
A session is one of several completely different data streams, which is maintained via a transport connection. A session has a defined start (session setup) and a defined end (session shutdown) and is known to the transport system. In the special case of OMNIS and openUTM, a session is understood to be a communication relationship between a UTM application and an OMNIS terminal, which begins with the logical opening of the session and ends when the session is closed.
A one-to-one assignment between transport connection and session exists on the link from terminal -> Session Manager.
This one-to-one assignment is cancelled on the link from Session Manager -> application and several sessions can be assigned to a transport connection. In this way, a number of terminals can “multiplex”, i.e. connect to an application via a transport connection. In extreme cases, all sessions between the Session Manager and the application can be processed via a single transport connection.