Channel exit programs are programs that are called at defined places in the processing sequence of an MCA. Users and vendors can write their own channel exit programs. Some are supplied by IBM®.
There are several types of channel exit program, but only four have a role in providing link level security:
Security exit
Message exit
Send exit
Receive exit
These four types of channel exit program are illustrated in Figure 1 and are described in the following topics.
Figure 1. Security, message, send, and receive exits on a message channel
