erv- ice user data terminations (TE-UDT). Since the primary goal of a telecom network is to connect TEUs, no matter what they are and what they communicate, TEUs are also separated in the model from all other entities. We have thereby identified one of the boundaries of a tel- ecom system. To control the use of resources of the distributed resource system, the proc- ess control system must also be distributed into two types of entities. The tele- service network process controller (TEP-NPC) controls the telecom resources in the network and handles the teleservice access protocol on the network side as well as the OM interfaces (Operation and Management). A number of entities on the terminal side, teleservice terminal process controllers (TE-TPC) control the TE-UDTs and communicate with users who order teleservices, called tele- service user controllers, TEC. In order to control the distribution of resources inside the network, the TE-NPC will most likely also be separated into remote entities, as described later in this section. Figure 2.1 deliberately separates network termination entities into two cate- gories: TE-NPC and TE-UDT. A TPC handles the teleservice service access protocol on the terminal side. It also acts as the resource controller of UDTs, and it communicates with TECs. A UDT handles a teleservice protocol and the information flows to/from its TEUs. One reason for separating TPCs and UDTs is that there are many telecom applications where a common entity acts as the TPC on behalf of many UDTs. One example is the ISDN. Another example is the establishment of semiperma- nent connections between UDTs. These connectivity services are normally ordered from a central point in relation to a set of physically dispersed UDTs. Interface types: The model in Fig. 2.1 combines flows of control information with user-data flows. When two entities are assumed to be physically separated, the flows are remote, otherwise they are local. Control information is part of the dialogue between the entities. There are three 