For the communication process between central and decentralized systems in the R/2-R/3 link, various communication elements are required to make data transfer and the checking of transfer transactions possible.

A central element of the communication process is the communication document. A communication document is created for each data transfer transaction between the systems.

A communication document is a data chain transferred in one transaction. It consists of communication records with the same number. The first and the last record of the communication document are marked. Thus, a communication document can be seen as a logical unit as such.

A communication record is a data extract in R/3 format consisting of the data to be transferred.

Since different data has to be transferred, depending on the transaction and the direction of the communication process, communication records are assigned to specific record types.

A communication record is identified by a record type and a record number. Communication records with the same record number form a communication document, regardless of the record type.

The structure of a communication record is stored in R/3 format in the Data Dictionary and is dependent on the record type. A specific table, where the respective communication records are stored, is defined for each record type.

Communication records are always transferred in R/3 format, regardless of the direction of the communication process. Thus, the recipient is always responsible for the conversion. Therefore, it does not make any difference for the R/2-R/3 link which system is operating as the partner system (R/2 host, non-SAP host).

To enable a communication chain to be created, the communication records are given a record status that determines their position within the communication document during the technical transfer process.

The following table lists possible statuses:

When the system recognizes during a transaction that a communication document must be created, it determines a communication number based on the recipient.

The communication number is the technical definition of the recipient (target system, application, client, receiving program etc.). The communication number is used to determine the key for the queue file.

In a queue, communication records to be transferred are stored in an intermediate file before the transfer takes place.

The communication documents can be sent automatically or manually from the intermediate file to the partner system.

At the time of data transfer a send program is called up that

• creates the communication document
• writes the communication document to the intermediate file

During an automatic transfer, the program carries out the following functions:

• It establishes a connection to the receiving program in the target system.
• It transfers the communication documents using CPI-C.

In the receiving system the communication document is processed by the receiving program. The receiving program has the following functions:

• It writes the individual communication records to the tables defined for the specific record types.
• It creates a status record that you can use to check the communication process.
• It tests the data contents in the communication records.
• It carries out the postings in the receiving system.