n neither ROSE nor AMLn: TC-TIMER-RESET, TC-L-CANCEL, and TC-U-CANCEL. In relation to ROSE, these are necessary operations. The reason is that TCAP relies on ROSE operation classes, some of which cannot be used without time supervision. For example, in ROSE operation class 3, one TC user generates a TC-INVOKEre- quest which has no defined result. The TC user expects however to be informed if the operation did not succeed. The response time depends on real time factors, including congestion, execution time, and transport delays. If a response does not turn up in a reasonable time, the generating TC user cannot know if that implies that the execution succeeded, or if there are processing and transmission problems. To control this situation, TCAP offers TC users timer and cancel operations, the latter to be used when the TC user is tired of waiting. Timer val- ues are associated to operations and given to TCAP in TC-INVOKEs (the Time- Out parameter in Fig. 6.6). AML deals with this issue in a completely different way: the operation classes defined in AMLs define operations from a pure functional point of view, i.e., without any considerations of real time issues. For example, the ROSE opera- tion class 3 is a confirming operation class (class REQUEST) in AMLs where the confirm primitive just does not have any result parameters. If an implemen- tor wants to implement this as a ROSE operation class 3, either a maximum response time value in the corresponding AMLs operation specification may be added, or the TCAP timer operations (or something similar) may be imple- mented. 3. TCAP defines an extra reject operation, the TC-L-REJECT, in addition to the two that ROSE defines. This is used by a TCAP element to reject its own TC user's invocation request before sending any messages. Thus, this operation is not related to anything that is visible on the network level, which is why it is defined neither in ROSE nor in AMLn. Let's now summarize the characteristics of TCAP, in relation to the ROSE/ ACSE and AMLn agent layers: 