 the connection- which are identified by (N)-connection-endpoint-identifiers. A mode. A discussion regarding the use at different layers is included layer boundary may support more than one SAP between the same later in this chapter. or different entities of the (N)-layer and (N+1)-layer. In the future, the upper layers directly supporting applications The provision of (N)-titles is used to uniquely identify individual may also use the connectionless-mode for certain operations, such (N)-entities to facilitate the routing and relaying functions. An as broadcast to multiple APs. (N)-directory is the function that is used to translate a global title into an (N-1)-address to which the (N)-entity is attached. The 12.3.5 Relaying complex and abstract subject of Naming and Addressing is dealt with in detail in Part 3 to ISO 7498, and the provisions for global A layer entity can also provide a relaying function to facilitate the Network SAP addressing is defined in the OSI Network Layer routing of data along the path to the destination system. An (N)- Service Definition ISO 8348 AD2. The addressing structure of the relay-entity does not provide any service to an (N+1)-entity but only upper layers is defined in the Application Layer Structure of ISO uses the services from a receiving (N-1)-entity. It processes the 9545. incoming data unit and forwards it to the (N-1)-entity associated with the next path for the data to flow through. This concept is 12.3.7 Data units illustrated in Figure 12.8. The relay system is identified between the two end systems, which are the source and destination systems for As discussed earlier in this chapter, a communication activity from the instance of communication. an AP in a system progresses from layer to layer as the required A relay system may have a number of possible paths to select from functions are initiated to support the communication. In turn, at the for routing data to the addressed destination, as illustrated by the destination system, the incoming communication ascends thro