MIM CTC paths configuration clarification

Products

• MIM Resource Sharing (MIM)
• MIM Data Sharing (MII)
• MIM Tape Sharing (MIA)
• MIM Message Sharing (MIC)

Issue/Introduction

   We have the following configuration in our MIMINIT
   CTCPATH FROMSYSTEM=SYSA ADDRESS=(545,547) TOSYSTEM=SYSC        
   CTCPATH FROMSYSTEM=SYSC ADDRESS=(54D,54F) TOSYSTEM=SYSA
      Device 545 is specified as primary for SYSA but no device number is specified for SYSC.
      Device 54D is specified as primary for SYSC but no device number is specified for SYSA.
            
Now drawing analogy with how we specify PATHIN and PATHOUT devices for CTC XCF communication in COUPLExx, are the device numbers specified in the above MIM config statements PATHOUT or PATHIN?
In other words, is 545 a PATHOUT (or PATHIN) device on SYSA and how does it know that is the PATHIN (or PATHOUT) device on SYSC?
Similarly, is 54D a PATHOUT (or PATHIN) device on SYSC and how does it know that is the PATHIN (or PATHOUT) device on SYSA?
It may be noted that these are all FICON CTC devices.
And would it be any different if these devices were ESCON CTCs instead of FICON CTCs?

Environment

Release : 12.5

Component : MIM

Resolution

Some basic information:
XCF CTC devices are uni-directional - data flows in only one direction on each CTC.
MIM's CTC are bi-directional - data can flow in either direction.


Example:
CTCPATH FROMSYSTEM=SYSA ADDRESS=(545,547) TOSYSTEM=SYSC
CTCPATH FROMSYSTEM=SYSC ADDRESS=(54D,54F) TOSYSTEM=SYSA

MIM automatically determines which devices are connected by sending handshake I/Os during startup. For example, if MIM sends an IO on device 54D from SYSC to SYSA, then SYSA receives the I/O on device 545, then MIM knows that 54D and 545 are connected. If COMPATLEVEL=12.0, the order of the devices on the ADDRESS parm doesn't matter. If COMPATLEVEL<12.0, the first device on SYSC must connect to the first device on SYSA, and so on.

We describe the process in more detail here.
https://techdocs.broadcom.com/us/en/ca-mainframe-software/traditional-management/ca-mim-for-z-os/12-5/programming/ca-mim-programming/ca-mim-advanced-topics/how-you-define-ctc-devices-for-use-in-vcf-environments.html