What is MRO - Multi Region Operation! Why is it useful! How is TOR, AOR and FOR linked?

               Using Intercommunication Features in CICS

MRO - Multi Region Operation is used connect CICS region running on the same processor. 

Each System has its own address space independently, hence if any region goes down others are not affected.

Typical MRO includes

• TOR - Terminal Owning Region which owns all the Terminal
• AOR - An Application Owning Region that owns all the Applications
• FOR - File Owning Region that owns all the Files

How transaction routes from TOR to AOR?

The PCT entry in the Terminal Owning Region is defined as below:

Terminal Owing Region (PRVT)

Transaction: ABC1
Type:       Remote
Sysid:          PRVA

Application Owing Region(PRVA)

Transaction: ABC1
Type:           Local
Program: XYZ123P

- Any transaction is triggered in the TOR terminal. It checks PCT entry for type and sysid for AOR
- Transactions then routes to the AOR where its defined local in PCT and hits program defined in it.
- Any I/O transaction to be done is routed back to TOR 

How transaction is shipped from AOR to FOR?

In Application Owing Region(PRVA)

XYZ123P
Reads Customer1

File Control Table Definition in AOR
Type: Remote
File : Customer1
SYSID: PRVF
Reclen: 258
Key: 25

In File Owing Region(PRVF)

File Control Table Definition in FOR
Type: Local
File : Customer1
Access: VSAM KSDS

• Function shipping allows to access resource defined in the other region.
• If Program defined in AOR, needs to access file which is defined local in other region, FCT entry is defined with sysid of the FOR region and file type is defined as remote
• Once the program needs to read this file, the control is transferred to the FOR region where file is residing as local. 
• Program accesses required information and passes control back to AOR region.