OSI/MHS Gateway Programmatic Interface (GPI) Reference Manual

Glossary

OSI/MHS Gateway Programmatic Interface (GPI) Reference Manual—522223-001

Glossary-21

PDAU (physical delivery access unit)

PDAU (physical delivery access unit). A commonly-used type of access unit (AU) within

an EDI messaging system as defined in CCITT Recommendation X.435. The PDAU

provides the ability to send messages to EDIMS users (recipients) through a physical

delivery system (PDS). Other types of access units (for example, facsimile machines)

may be the subject of future CCITT standards.

PDU (protocol data unit). An information unit that contains control and address information

and possibly data, and is exchanged between peer entities. Two types of PDUs relevant

to X.400 are:

PDU ID. An identifier generated by OSI/MHS for internal use. A PDU ID is not the same as

the MPDU ID defined by X.400.

PDU store. The database that stores messages in an X.400 system. A PDU store consists of a

data file and a log file. Each MR, MS, RS, and LO group has its own PDU store.

Physical Layer. Layer 1 in the OSI Reference Model. This layer establishes the actual

physical connection between the network and the computer equipment. Protocols at the

Physical Layer include rules for the transmission of bits across the physical medium and

rules for connectors and wiring.

Port Access Method (PAM). A Compaq communications subsystem that provides an

independent interface to allow applications access to token-ring or Ethernet local area

networks (LANs) on Himalaya S-series servers. The PAM subsystem provides a port

interface that applications can use by making file-system procedure calls. The PAM

subsystem implements, for LANs, the services of the Data Link Layer and layers below.

PAM replaces the Tandem LAN Access Method (TLAM) for G06 and later releases.

port address. For X25AM lines, the logical port number used to specify the address of the

connection to the X.25 network. For TLAM lines, the address used by TLAM to specify

the address of the connection to a LAN controller.

positive notification (PN). An EDIN that reports responsibility for an EDIM has been

accepted. A positive notification is generated by a receiving EDI-UA, EDI-MS, or

PDAU when EDIM responsibility can be given to the associated user. A positive

notification is generated only if it had been requested by the originator of the EDIM.