While UML 1.4 collaboration diagrams at instance level (collaboration diagrams at classifier level are not supported by ARIS UML Designer 7.x) contain objects connected by links with attached stimuli, UML 2 communication diagrams contain lifelines connected by connectors with attached messages.
If a UML 1.4 link occurs in a collaboration diagram and in a class diagram it is migrated into a UML 2 connector and a UML 2 instance specification.
The remarks above about objects and lifelines in sequence diagrams are also valid for communication diagrams.