Type of Service
Currently, five ATM Forum-defined service categories exist (see Table 1). The basic differences among these service categories are described in the following sub-sections. These service categories provide a method to relate traffic characteristics and QoS requirements to network behaviour. The service categories are characterised as being real-time or non-real-time. CBR and rt-VBR are the real-time service categories. The remaining three service categories (nrt-VBR, UBR and ABR) are considered non-real-time service categories.
| ATM Forum Traffic Management 4.0 ATM Service Category | ITU-T I.371 ATM Transfer Capability | Typical Use |
|---|---|---|
| Constant Bit Rate (CBR) | Deterministic Bit Rate (DBR) | Real-time, QoS guarantees |
| Real-Time Variable Bit Rate (rt-VBR) | (for further study) | Statistical mux, real time |
| Non-Real-Time Variable Bit Rate (nrt-VBR) | Statistical Bit Rate (SBR) | Statistical mux |
| Available Bit Rate (ABR) | Available Bit Rate (ABR) | Resource exploitations, feedback control |
| Unspecified Bit Rate (UBR) | (No equivalent) | Best effort, no guarantees |
| (No equivalent) | ATM Block Transfer (ABT) | Burst level feedback control |
Read more about this topic: Traffic Contract
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