This part of ISO/IEC defines abstract test suite for testing the conformance of the Data Link Layer of an IUT with respect to ISO/IEC 7776 or the CCITT Recommendation X.25 (1980, 1984).

Conformance of a Data Terminal Equipment (DTE) to the above ISO International Standard or CCITT Recommendation is tested using a dedicated circuit between the tester and the DTE. It is noted that CCITT Recommendation X.25 (1984) are written form the perspective of a DCE and therefore do not always explicitly specify the DTE's operation. In such cases it is assumed that recommended operation of a DTE is included by implication because of the need to communicate with X.25 DCEs. This part of ISO/IEC 8882 excludes the testing of the LAP procedures given in the CCITT Recommendations.

NOTE Test cases for extended mode operation (Moduio 128), multilink procedure and DTE-DTE operation as per ISO/IEC 7776 are for further study.

The tests in this part of ISO/IEC 8882 are designed for three possible interworking situations, shown in Figure 1. This part specifies tests for all three cases shown in Figure 1 but recognizes that not every test may apply to a performed to determine the applicability of a test to a particular DTE. Such selection will be based on the PICS and the PIXIT.