rtual chan- nel, etc.). Obviously, since the CNL-CSP connects many SAP users (the Internet connects hundreds of millions), a user who sends an SDU in his SAP also must provide an address (SAPI) to the receiving SAP user for each SDU (the SAPI in IP is called IP address). This fact explains why in CNL-CSPs (contrary to TE, CS and CON-CSPs), every SAP must have a unique SAPI value. One of the characteristics of an IP network (like the Internet or private IP net- works, often called "Intranets") is that it does not comprise its own solution to the problem of connecting the users terminal systems (referred to as hosts in IP net- works) to IP routers. This connection problem must be solved by using diverse LAN technologies (like the Ethernet) and WAN technologies (interconnections over PSTN, ISDN, etc.). Figure 3.72 shows one possible solution. In this network, IPUs are connected to an IP router over the ISDN packet access service. This service is based on connecting hosts to the ISDN connection service (CN connections, one or several B-channels) and routers to a packet handler, which is regarded as part of the ISDN. The hosts and the packet handler communicate by means of the LAPB-protocol, in order to provide a packet switched SAP for the IP- UDTs, and to handle biterrors over the CN connection. The IP router is connected to another router over an ATM VC connection. An AAL3/4 protocol would be used over the VC connection. The AAL3/4 layer is designed to support multiplexing of traffic between many hosts and a remote router over a single VC connection. In CNL networks there are no connections to be set up, and therefore no need for a process control function for connection handling. There is also no parameter in the IP-PDU for discrimination. This is a major difference from models of CS and CON networks. However, routing, relaying, as well as QoS handling, must still be performed by the router, although CNL routers perform those functions individ- ually for each message. 3.4 Modelling Telecom Resource Systems IP-TS (