Quality of Service
During connection setup the end stations can request bandwidth allocation from the switched network. The ATM User to Network Interface (UNI) is used to establish dedicated levels of bandwidth to stations and applications.
CBR - Constant Bit Rate. Useful in multimedia applications for time sensitive traffic such as video, audio or interactive sessions requiring rapid response (virtual reality applications for example). CBR easiest to implement with PVC.
VBR - Variable Bit Rate. Realtime and non-realtime. Useful for LAN Emulation and attaching to best-effort legacy networks such as Ethernet
ABR - Available Bit Rate. Best effort service based on Mimimum Cell Rate (MCR) with low cell loss
UBR - Unspecified Bit Rate. Makes use of excess bandwidth. Subject to increased cell loss and discard of complete packets