 of an ATM net- work is similar to the ISDN network. ATM is also called broadband ISDN (BISDN) by ITU-T. Figure 3.65 shows the ATM network on the access side. The model depicts one ATM Terminal System (ATM-TS) and an ATM access router. Concepts defined in the ATM standard are rendered in bold. AAL protocols ATM-TS The ATM-CSP ITU-T Q.2931 B-ISUP ATM-DNCPC ATM access router Route Routing Switch Manager controll. Analyser ATM transport link ATM access link vpi.. switch ATM transport link AAL ATM adaption layer TPC terminal process controller ATM asynchronous transfer mode TS terminal system ATMU ATM user VP virtual path ATN access transport network VPI virtual path identifier ATNC ATN concentrator UDT user-data protocol element DNCP distributed network process controller Fig. 3.65 The ATM-CSP on the access side A short description of Fig. 3.65 follows: ATM routers are designed for broadband connectivity services to users over ATM access links. A special feature of ATM compared to other CON networks, is that ATM networks define a two-level structure of channels: virtual path (VP) and virtual channel (VC). A virtual path is a bundle of virtual channels. An ATM link can carry, at a maximum, 256 virtual paths, and each virtual path can carry, at a maximum, 65 536 virtual channels. Virtual paths are identified by virtual path identifiers (VPI), virtual channels by virtual channel identifica- tions (VCI). Virtual channel users are called AAL-UDT. AAL stands for ATM Adaption Layer, and refers to different types of protocols between ATM users (ATMU) (more about AAL later in this section). AAL-UDTs are instantiated inside 3 Logical Network Modelling ATMUs. An end-to-end connection between two AAL-UDTs is a VC connec- tion. A VC connection is established by interconnecting virtual channels in dif- ferent ATM transport links over ATM-switches. Users can also use end-to-end VP connection. A VP connection is established by interconnecting virtual paths in different ATM transport links over ATM switches. ATMUs in ATM Terminal Sy