ficance or information. 20.7 SERVICES: CONNECTION-ORIENTED AND CONNECTIONLESS tables, which differ at every node, must be maintained in a quasi-real-time fashion. This will have to be done by some kind of routing protocol. One way to resolve this problem is to make it an internal network problem and use a connectionless service as described in ITU-T Rec. I.364 (Ref. 11). We must keep in mind that ATM is basically a connection-oriented service. Here we are going to adapt it to provide a connectionless service. 20.7.1 Functional Architecture The provision of connectionless data service in the B-ISDN is carried out by means of ATM switches and connectionless service functions (CLSF). ATM switches support the transport of connectionless data units in the B-ISDN between specific functional groups where the CLSF handles the connectionless protocol and provides for the adaptation of the connectionless data units into ATM cells to be transferred in a connection-oriented environment. It should be noted that CLSF functional groups may be located outside of environment. It should be noted that CLSF functional groups may be located outside of the B-ISDN, in a private connectionless network or with a specialized service provider, or inside the B-ISDN. The ATM switching is performed by the ATM nodes (ATM switch/cross-connect), which are a functional part of the ATM transport network. The CLSF functional group terminates the B-ISDN connectionless protocol and includes functions for the adaptation of the connectionless protocol to the intrinsically connection-oriented ATM layer protocol. These latter functions are performed by the ATM adaptation layer type 3/4 (AAL-3/4), while the CLSF group terminations are carried out by the services layer above the AAL called the CLNAP (connectionless network access protocol). The connectionless (CL) protocol includes functions such as routing, addressing, and QoS (quality of service) selection. In order to perform the routing of CL data units, the CLSF has to interact with the control/manage