alf-duplex, and there are specializations for simplex-send-only and for simplex- receive-only. The CSI symbol comes in two shapes: one that denotes that only one of the par- ties provides services to the other (i.e., the parties are user-provider related), another that denotes that both parties provide services to each other (the parties are peer related). A CSI specifies which services are provided and which services are used by the unit in its communication with other units. In model fragments, port symbols are used to refer to a party in another model fragment (the not connected notation) or to show communication relations in model fragments (the connected notation), see Fig. 3.23. Note that, with the 3 Logical Network Modelling exception of the peer-CSI symbol, the symbols always indicate the providers and the users of services, whether the connected or the non-connected notation is used. The SAPs and CSIs of logical network models and logical network structures can be annotated with the type of primitive services9 they provide. A SAP provides only a single type of primitive service, while a CSI can provide many types of primitive services. Figure 3.24. defines how SAPs and CSIs can be annotated with primitive service names. Annotation principle: <Name of provided primitive services> {<List of names of provided primitive services>} {<List of names of provided primitive services>} {<List of names of used primitive services>} Annotation examples: Description Type of Notational style annotation A SAP that provides the Port notation X.25VC X.25VC connectivity service X.25VC, which is a switched, Notation in send-receive CON service communication X.25VC relations Port notation CSI, used for {TECS} {TECS} ordering teleservices (TECS=Teleservice Control Notation in Service) communication {TECS}< relations CSI where one party Port notation {Y,W,W} {Y,W,W} provides service X, the other party services Y, Z Notation in and W communication > {Y,Z,W} relations Fig. 3.24 Annotation of SAP and CSI The annotation is construc