[2][3] These service categories provide a method to relate traffic characteristics and QoS requirements to network behaviour.
CBR is tailored for any type of data for which the end-systems require predictable response time and a static amount of bandwidth continuously available for the life-time of the connection.
For telephony and native voice applications CBR provides low-latency traffic with predictable delivery characteristics, and is therefore typically used for circuit emulation.
Sources that use rt-VBR connections are expected to transmit at a rate that varies with time (for example, traffic that can be considered bursty).
ABR provides a best-effort transport service, in which flow-control mechanisms are used to adjust the amount of bandwidth available to the traffic originator.
The ABR service expects the end-system to adapt its traffic rate in accordance with the feedback so that it may obtain its fair share of available network resources.
The goal of ABR service is to provide fast access to available network resources at up to the specified Peak Cell Rate (PCR).
UBR has enjoyed success in the Internet LAN and WAN environments for store-and-forward traffic, such as file-transfers and e-mail.