Rate-Controlled Static-Priority Queueing

		Hui Zhang and Domenico Ferrari

We propose a new service discipline, called the Rate-Controlled
Static-Priority (RCSP) queueing discipline, that can provide throughput, 
delay, delay jitter, and loss free guarantees in a connection-oriented 
packet-switching network. Previously proposed solutions are based on 
either a time-framing strategy, or a sorted priority queue mechanism. 
Time-framing schemes suffer from the dependencies that they introduce
between the queueing delay and the granularity of bandwidth allocation; 
sorted priority queue may be difficult to  implement. 

The proposed RCSP queueing discipline decouples the allocation of delay and 
bandwidth by separating rate-control and delay-control functions in the design
of the server. A RCSP server consists of a rate-controller and a scheduler: 
the rate-controller enforces the traffic characteristics for each connection by
assigning each packet an eligibility time and holds the packet till this
time before passing it to the scheduler; the scheduler services eligible 
packets using a non-preemptive static priority discipline. We give the 
admission control conditions for RCSP and also propose an implementation that 
is simple enough to run at very high speed. 

We compare the RCSP discipline with the previously proposed solutions and 
show that nearly identical mechanisms in different service disciplines are 
used to achieve  such desired features as bounded delay, bounded delay jitter,
decoupling of delay and bandwidth allocation, evenly distributed buffer space
reservation to prevent packet loss, and easy implementation in high-speed 
switches. 

The key idea of RCSP is to separate rate-control and delay-control in the
design of a server: the rate-controller does not only allocate bandwidth, 
but also isolates the interactions  between adjacent switches, and controls 
jitter; the scheduler services packets with different priorities to meet a 
variety of  delay requirements. Generalizing this idea by having combinations
of different rate-controllers and schedulers, we get a class of service
disciplines, of which RCSP is an instance.