How do I understand the message structure of the Micros 2700/3700/4700 interface that we utilize for postings from Aireus and other cloud POS systems?

The following message types are utilized in IP-based interface communication based on the MICROS classic interface.

PL - Posting Listing. This is the response from the PMS containing the Room #, Guest Name and Booking #.
PR - Posting Request. This is a message from the POS attempting to post to the PMS.
PA - Posting Answer. This is the response from the PMS to the POS Posting Request message.

ISISPOS/Aerius has two options in the Payment tab that will result in message communcation with our servers. Room Inquiry and Room Charge.

Room Inquiry will send a PR and expects a PL. Here is an example of the message flow of a simple Room Inquiry request.

16-NOV-2012@22:02:11 S:PL|SOROGERS|WS359-3|ID1|RN201|G#1665569|GNChieppa, Jesse|P#1|
287665 16-NOV-2012@22:02:11 R:PR|SOROGERS|WS359-3|ID1|PI201|DA121116|TI230211|P#1|PMROOM|
287664 16-NOV-2012@22:02:11 New connection from 184.168.116.173

Room Charge will send a RP which expects a PL. It will then send a PR and expect a PA in return from us. Below is an end to end example of a Room Charge sequence.

287673 16-NOV-2012@22:02:59 S:PA|SOROGERS|WS359-3|ID1|RN201|G#1665569|GNChieppa, Jesse|ASOK|DA121116|TI220259|P#4|
287671 16-NOV-2012@22:02:59 R:PR|SOROGERS|WS359-3|ID1|RN201|G#1665569|GNChieppa, Jesse|TA1665|S11500|T1090|T2075|SC000|C#30077|DA121116|TI230259|CV2|P#4|PMROOM|
287670 16-NOV-2012@22:02:59 New connection from 184.168.116.173
287669 16-NOV-2012@22:02:56 S:PL|SOROGERS|WS359-3|ID1|RN201|G#1665569|GNChieppa, Jesse|P#2|
287668 16-NOV-2012@22:02:56 R:PR|SOROGERS|WS359-3|ID1|PI201|DA121116|TI230256|P#2|PMROOM|
287667 16-NOV-2012@22:02:56 New connection from 184.168.116.173

Understanding Categories in messages.

SO: Sales Outlet. We expect only the hotel identifier (SITEID) to be sent in this message.  This is how we identify the Site/Hotel sending the messages.  In the examples above, the SOROGERS is SO + ROGERS (the ID of this hotel that BookingCenter will provide to you).
WS: Workstation ID.
ID: User ID.
RN: Room Number.
G# Guest ID.
GN: Guest Name
DA: Date.
TI: Time.
P#: Posting Sequence Number.
PM: Payment Method.
TA: Total Posting Amount.
S#: Posting Total for each Sales Department. I.E. S11500 in the message above means $15.00 in Sales Department 1.
T#: Posting Total for each Tax Bucket. I.E. T1090 in the message above means $0.90 in Tax 1.
SC: Posting Total for Service Charges.
C#: Check #. This is generated by Aireus and we insert this into the Description during the posting for reference.
TI: Posting Total for Tips.
AS: Answer Status from the PMS.