Using the Intersystem Communication link
XRF can make effective use of an intersystem communication link (ISC) session between the active IMS and the alternate IMS.
The session is useful because:
- As surveillance, it alerts the alternate IMS to failures in the active IMS.
- During the synchronization phase, it allows the active IMS to take a SNAPQ checkpoint without operator intervention.
The ISC link is a normal VTAM® APPL-to-APPL session and can be a route through any of the following:
- A channel-to-channel protocol (CTC or 3088)
- A 37x5 Communication Controller with channel paths to both systems
- Separate 37x5 Communication Controllers through a teleprocessing (TP) line
The following figure illustrates the three kinds of ISC links. The numbers correspond to the numbers in the previous list. Generally, the more hardware units there are on the route, the slower the communication and the greater the chance for failure. Choose the most reliable routes you can for surveillance and other communication.
