stems (ATM-TS) are connected to an ATM access router over ATM access and transport links. ATM access links can be based on different types of media, even the twisted copper-pair that connects ordinary tel- ephone users to PSTN and ISDN. Transmission protocols, in that case, are, e.g. asymmetric digital subscriber line (ADSL) or high-bitrate digital subscriber line (HDSL). Bitrates over access links are from 2 Mbps up to 622 Mbps, depending on the type of transmission solution. ATM transport links are based on PDH or SDH connections over coax or optical transmission networks. Bitrates over SDH connections are from 155 Mbps up to 622 Mbps. On the terminal side, the access link discriminates between two SAPs; the SAP that connects the ATMU is used for user-data flows. The other SAP (denoted vpi0) is used for process control data. Concentration of traffic between access links and the transport links that termi- nate in ATM routers is done in the concentration network part (called ATM- ATNC) of the ATM-ATN. Inside the ATM-ATNC statistical multiplexing of packages is performed. Statistical multiplexing is typical for packet networks. It considers the statistical distribution of packets on access links, and multiplexes packets from all access links on one or several transport links with lower capac- ity than the sum of the capacities of all access links. Setting up connections between ATMUs requires a process control function (ATM-DNPC) for VC handling in the ATM router, and a terminal process con- troller (ATM-TPC) in ATM terminal systems. The ATM-DNPC communicates with ATM-TPCs over the service access protocol ITU-T Q.2931 (which is a modified version of the ISDN protocol ITU-T Q.931). This communication uses vpi0 over ATM access links. The ATM-DNPC communicates with other ATM routers over the service distribution protocol B-ISUP (which is a modified version of the ISDN ISUP-protocol). Figure 3.65 shows that ATM provides a solution to the discrimination function in routers, which takes the separation between the resou