Round-robin with credits: an improved scheduling strategy for rate-allocation in high-speed packet-switching

“Framed non-work conserving” scheduling disciplines have been used to ensure performance guarantees for VBR traffic in ATM. The author presents a modified round-robin scheduling discipline of this type, which uses the notion of “credits”. This scheduler is analysed and shown to give improvements provided the input traffic obeys certain restrictions. It turns out that, the scheduler allows to guarantee a minimum rate for a virtual circuit (VC) at any switch, while also ensuring that higher-rate bursts of a limited length are properly handled. The scheduler is also “self-policing” in the sense that the long-term average rate allocated to the VC is kept dose to the guaranteed minimum. This, in turn, allows suitable rate allocations to be made for other (non delay-sensitive) VCs, and this rate can be guaranteed to such VCs. The analysis also provides a method of computing delay and jitter bounds which can be used to determine suitable parameters for call set-up, as part of the connection admission control