tive is to provide a standard timer value, which then requires the standard to be identified by an ASN.1 object identifier and a timer identity, e.g. 0017921 T202, which is the identifier for the T202 timer in ITU-T recommen- dation Q.921. 7.5 Behaviour Descriptions By definition, user-defined properties are not handled by any AML built-in mechanism. The AML model only acts as a place-holder for such properties. User- defined properties that have been used in the past are "priority", as well as informa- tion that directs test-case generation, like relative frequency of occurrence of the operation. Properties that are used often can later be made AML built-in properties. Figure 7.37 shows the operation specification from Fig. 7.36, extended with the headings for these optional properties. As a general recommendation for all infor- mation elements in AML, a DESCRIPTION should also be included that describes the operation to readers that are not familiar with the formal expressions. Operation specification for callnfo: OPERATION callnfo PROPERTIES {selector,synchronous) Request (INTEGER{time(0), day(1), date(2)} DEFAULT 0) Confirm (CHOICE{[0]Time, [1]DayInWeek, [2]Date}) Time::=SEQUENCE{hour INTEGER SIZE (0..24), ".", minute INTEGER SIZE (0..60) OPTIONAL) DaylnWeek::=IA5String{"Monday","Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"} Date::=SEQUENCE{Month, "/", DayInMonth} Month::=IA5String{"January", "February", "December"} DayInMonth::=INTEGER SIZE (1..31) Refuse (cause INTEGER{watchBroken(0), noWatch(1)) TIME CONSTRAINTS ACTIVITY TIME 0.5 ms USER-DEFINED PROPERTIES DESCRIPTION Fig. 7.37 An example showing all headings in an operation specification Behaviour Descriptions 7.5.1 Introduction The behaviour of a service network is created by the behaviour of its service objects. The only way to observe and define behaviour in a service network is to describe the behaviour in service relations. The behaviour in a service relation depends on the behaviour that the service-providing object allows and t