mation unit) and SERVid (identifies the requested service). serviceRequest(SERVid,SAPI) sendInfoOrder(SIU) provider provider serviceConfirm() receivelnfoReportConfirm(SIU) Fig. 3.20 ASPs in teleservice network service interfaces Figure 3.21 shows the ASPs for using CNL-SAPs. 3 Logical Network Modelling sendCnlOrder(ToSAPI,SDU) provider receiveCnlReportConfirm(FromSAPI,SDU) Fig. 3.21 ASPs used in CNL-SAPs The name of the operations are, in this case, sendCnl and receiveCnl. The parameters are SAPI and SDU. The SAPI-value in the sendCnl-operation refers the receiver. The SAPI-value in the receiveCnl-operation refers the sender. In the absence of a connection, this is the method used to support a dialogue between two CNL users. If the operations defined in SM&AML are compared to the ASPs that were defined in the OSI RM, there is another important difference as well, as shown in Fig. 3.22. OSI Service Provider definition of operations: DATA request DATA indication OSI-CSP DATA - a global transfer operation SM&AML definition of operations: receiveCnl sendCnl receiveCnl sendCnl CNL-CSP receiveCnl sendCnl operation operation sendCnl Packet-switched receiveCnl operation network operation CNL-UDT CNL-UDT Fig. 3.22 The operation concept in OSI and in SM&AML In OSI RM a set of ASPs were defined (called DATA request, DATA indication, etc.) that relate ASPs of both endpoints to a global transfer operation (DATA) that combines send and receive events over SAPs at both endpoints. This approach does not easily support logical network modelling. This view most likely contrib- uted to the fact that OSI RM never captured the interest of network architects. 3.2 The Communication Service Provider SM&AML takes a different approach: the operations used in each endpoint are independent of each other, in the sense that they refer to two different operations, a send and a receive operation that exist at both ends. This view supports logical net- work modelling. More interesting than the type of operations that are used over different type