Interoperability relates to the ability of equipment to work fully with another manufacturers` equipment. After establishing a connection (call) between two similar types of equipment, all features and functions may not be recognized and processed by one-another. This may be caused by non-standard protocols in the equipment` design.

Interoperability tests are carried out as far as reasonably possible to ensure that most typical call scenarios, equipment models, and manufacturer permutations will recognize and process all functions and features that are possible during the call.