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16.1 INTRODUCTION 503TABLE 16.1-4Component TypesComponent Acronym Function ROSEComponent-HandlingTC PrimitiveInvoke INV Request an Operation Y TC-INVOKEReturn Result, Last RR-L Final responseY TC-RESULT-Lto an InvokeReturn Error RE Error was detected Y TC-U-ERRORReject RJ Invalid Operationwas receivedY TC-U-REJECTTC-R-REJECTTC-L-REJECTReturn Result,Not LastRR-NLNonfinal responseto an InvokeNTC-RESULT-NLcomponent is about 240 octets. Most operations yield information that fits withinone component and, if the information is longer, it is segmented and carried inone or more RR-NL components plus one RR-L component.A TCAP message can carry multiple components.16.1.6 Optional Dialog-Control APDUsIn addition to exchanging components, an AE can engage in an exchange of informationwith its remote peer to negotiate and agree upon the application context(Section 16.1.1). That takes place when a dialog-handling TC primitive includes adialog control APDU containing an AC name as a parameter. The APDU withthe AC name is passed to the remote node in the optional dialog control portionof a TCAP message (Section 16.2.2). The remote node can accept or reject the proposedAC name. Dialog control APDUs and their mapping to dialog-handling primitivesare shown in Table 16.1-5.When there is no AC negotiation, dialog control APDUs are not used and dialogsare managed by the transaction portion of TCAP messages (Section 16.2.2).16.1.7 TCAP Message SequenceFigure 16.1-4 shows examples of TCAP message sequences in transactions thatinvolve ASE-1 and ASE-2. The transactions are initiated by ASE-1, which sendsa Begin message with Invoke 1. The vast majority of transactions require just twomessages: Begin and End (cases (a) and (b)). In case (a), the invoked operationresults in an instruction, which is returned in an End message with Invoke 2. InTABLE 16.1-5 Dialog Control APDUsAPDU Acronym Dialog-Handling TC PrimitiveDialog UNI [unstructured dialog] AUDT TC-UNIDialog Request AARQ TC-BEGINDialog Response [accept] AARE [accept] TC-CONTINUE, TC-ENDDialog Response [rejected] AARE [rejected] TC-U-ABORTDialog Abort Dialog ABRT TC-U-ABORT