ion, giving examples of the services and their semi-permanent basis via network management. possible applications and defining some of their attributes. Defines a number of uses for pre-assigned VPIs. It deals with the definition of the following: 41.4.4.2 B-ISDN aspects with an impact on services 1. Cell multiplexing and switching: The VC is the basic routing entity for switched services and is handled in VC multiplexers The recommendation also gives guidance concerning some import- and switches. VCs are aggregated in VPCs which are routed ant aspects which need to be taken into account when supporting through VP multiplexers and switches. and developing services for B-ISDN, and also provides an introduc- 2. Quality of service related to VP and VC connections: particular tion to recommendations 1.362 and 1.363 dealing with the ATM QOS classes will be requested at call establishment for both VP adaptation layer. and VC connections. A VPC will carry VCs of various different QOSs. The VPC must meet the most demanding QOS require- Multimedia aspects: ment of the VCs carried. 3. Quality of service related to cell loss priority (CLP): many Deals with the need to separate out connection control from call variable bit rate (VBR) services will require a guarantee of control so that one call can support several types of connection some minimum capacity as well as a peak capacity. When dealing with different (standardised) information types. congested, the network will need to know which cells may be discarded without violating (e.g.) the guaranteed minimum Quality of service aspects: capacity. The CLP bit is set by the user or service provider to indicate such cells. Deals with QOS negotiation and indication options also the need 4. Payload types (user information/network information) and the for the Cell Loss Priority indicator. payload type identifier field. 5. Generic flow control (GFC) mechanism for control of user Service bit-rate aspects: information towards the network at the broadband user-net- work interface (UNI