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Data Packet Loss in a Queue with Limited Buffer SpaceJose Gil, Motorola Research
BackgroundA system that occurs in several contexts in computer and data networks has the generic form shown in Figure 1.
Figure 1: Diagram of system There are N sources, and each source n transmits bursts of data at speed R_{n} packets a second, and they share a medium to which access is controlled by a queueing discipline. The queue has a limited buffer space B, and so in some conditions packets are dropped. The system feeds back to source n the proportion p_{n} of its packets that were dropped, and the source then adjusts its sending rate according to the formula Here K, C and D are to be treated as known dimensionless constants, and RTT_{n} is the roundtriptime of the packets, from the time source n sends them to the time it receives the feedback that a proportion p_{n} of them were dropped.
ProblemThe problem is to find the equilibrium point (R_{n}(p_{n}), p_{n},RTT_{n}), and also information about the statistics of the distribution, eg the variance of the packet loss distribution. Detailed models:Sources:There are 2 cases to consider:
Packet discard policies:There are 2 packet discard policies that might be in operation:
The graphs of packet drop probability against buffer occupancy in these 2 cases are illustrated in Figure 2
Figure 2: Packet loss probability for the two packet discard policies Queueing disciplines:There are 3 queueing disciplines of interest:
The queueing patterns in the first 2 cases are illustrated in Figure 3 Figure 3: FO and round robin queueing systems Service times:The service time per data packet is random, and for the purposes of this study it can be treated as exponentially distributed with a known mean service rate mu_n, different packets being independent. Priorities for the Study Group:The combinations of cases, in order of most interest, are


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