The constraints part is used for describing the values sent or received. The structured types PDUs and ASPs defined in the declarations part are used as models to describe the messages sent on the PCOs. The actual instantiation of these are defined in the same way, using either TTCN or ASN.1 value notation. The instances used for sending must be complete, but for receiving there is the possibility to define incomplete values using wild cards, ranges, and lists. To enable the reuse of different constraints, these can be parameterized and the actual value assigned dynamically to the specific component stated for the argument (see Figures 11 and 12).
Figure 11. Example of a TTCN Constraint Declaration

Figure 12. Example of an ASN.1 Constraint Declaration