A Listener provides a communication channel from a client, such as a 3270 emulator or a batch submission, to a CICS or JES region.
Each Listener is configured to provide one or more channels to a region or regions. Each channel is associated with a TCP port, a protocol such as a TN3270 for CICS or MFBINP for JES, and a CICS or JES region name.
A client connects to the port. The listener does the work needed to set up the conversation, such as identifying an appropriate channel for the client. It then connects to the Dispatcher to establish contact with the region. A listener can also connect directly to one or more SEPs.
Once the communication channel is established, the listener listens for input from all clients and SEPs to which it is connected.
A listener forwards new client input and client sessions to a dispatcher, and receives responses from an SEP to send back to the client. In some cases, a dispatcher can also send a response. For example, when the Clear key is pressed in a CICS session and no next transaction is associated with the session, the dispatcher can free up the keyboard, or send an error response to indicate that the region is not started.
When scaling out, the listener, dispatcher and SEP can operate on different machines. Each machine that has a dispatcher and/or SEP requires an event monitor service. A machine that just runs a listener does not require an event monitor service.
A Listener is hosted as follows:
| Default | Self-hosted |
| Runs as | Windows Micro Focus SEE Listener service1 |
| Started by | Dispatcher, SEP, or User Interface |
| Process | seelistener.exe |
| 1 When the Dispatcher and SEP are self-hosted, the Listener is started as a Windows console application. | |