Frame Relay - for Faster and More Efficient Data Communications ...

39Fig. 8Levels of abstraction in a Layered Network; exampleSubnetworktion Points (TCP). A Network Connectioncontains either Link Connections (LC) orSub-Network Connections (SNC), orboth- The Transport Entity "Connection" is responsiblefor the transfer of informationbetween Connection Points (CP). AConnection can be a Sub-Network Connectionor a Link Connection- The Sub-Network Connection transfersinformation transparently across a subnetwork.The connectivity of a Sub-NetworkConnection can be controlled by amanagement process- The Link Connection transfers informationtransparently across a link betweentwo subnetworks. The connectivity of aLink Connection cannot be changed bya management process.Fig. 5 shows that Transport Functions, i.e.Transport Processing Functions andTransport Entities, are separated by oneTransport Reference Point. In addition, amanagement reference point S is providedfor management information to andfrom each Transport Function. The input/outputconcept is related to TransportFunctions and should not be interpreted asindicating signal directions. "Input" representsthe input, "output" the output part ofthe function.The use of the Transport Functions is illustratedin Fig. 6." Fig. 7 is a simplified versionof Fig. 6 and does not show the AccessPoints (AP) explicitly.The Functional Model can be used to modelthe telecommunication network to thedesired degree of detail. Forexample, NetworkElements and parts of Network Elementscan be represented. Fig. 8 showsSub-Network Connections and Link Connectionswhich belong to the same transportlayer, and which in turn can be partitionedinto subnetworks showing variousdegrees of detail.The NET 1 level shows SNC1s, LC1s,CP1 s and TCP1 s, i.e. the greatest degreeof detail. The NET 2 level - less detailed- shows SNC2s, LC2s, CP2s and TCP2s.In this way various degrees of detail (levelsof abstraction) can be chosen, dependingon the purpose of the Functional Model.The network connection in the NET 4level is that of a single SNC4 between twoTCPs. From a management point of view,NET 1 provides the details required at theERICSSON REVIEW No. 1-2, 1992