Hotels/motels use a PMS (Property Management System) for handling operational data and billing guests (through folios w/room, amenity and other charges). Call accounting systems interface to a PMS so priced call records are posted directly to the guest folios.
Different PMS' use different interfaces. Interfaces differ in how call record data is packaged. Some call accounting systems come pre-programmed from the manufacture, while others must be configured onsite. Most call accounting systems use one of three different types of interfaces: MR (rarely used), and the two most popular, covered here, HB and HX.
PMS-HB. These systems need a line feed (LF) before the call record and three control characters (line feed/LF, carriage return/CR, and form feed/FF) after the call record. PMS-HB systems must recognize one of these three as the "end". In testing, FF may catch installers/techs - FF is a form feed and sends paper or a monitor to "top of page" - look back a page for data!
PMS-HB supports 2-way ("hand-shaking") and 1-way communication between PMS and call accounting systems ("CAS"). In 2-way mode, PMS and CAS can handle acknowledgment or non-acknowledgment with each call record. The CAS is "told" to send or that the call record was received okay or, if not, to hold or that call record needs to be re-sent. Hand-shaking control characters include: ACK (ASCII hex 06) and NAK (ASCII hex 21) - (or lower case "y" and "n"). PMS-HB systems usually do NOT require hand-shaking, so when none exists, CAS systems send call records and assume reception was okay.
PMS-HX. HX call accounting systems ask permission to send call records to ensure the PMS is ready, by first sending ENQ (ASCII hex 05) - an enquiry. If ready, PMS sends an ACK (ASCII hex 06), so the CAS sends an STX (ASCII hex 02) - start-of-text - before the call record, followed by an ETX (ASCII hex 03) - end-of-text and a block check character. The block check character allows the PMS to do a parity check for accuracy of the CR received. If the PMS "likes" the call record, it sends an ACK to the CAS.
It is helpful for installers/techs to use a laptop or monitor on the PMS-to-CAS connection (Laptops are even better w/communication software like HyperTerminal - available on most Windows systems). Some of the communications packages show control characters as icons; e.g. ENQ is a club, ACK an ace, etc. The software often lets you send control characters by pressing ctrl (control key) plus another key. Example: to send ACK, press ctrl with the F key.
Once communication parameters and hand shaking characters are matched up between the CAS and the PMS, you're running! Call accounting manuals usually include very detailed explanations of PMS interface protocols. Manuals or specific tech information can often be downloaded from the CAS manufacturers' site.