It is well known that the Selective-Repeat ARQ protocol has, among all error detection and retransmission schemes, the best throughput efficiency. However, this protocol has the disadvantage that data blocks may be received out of order, such that some reordering is required at the receiver side, before the blocks can be delivered to their destination. In order to accomplish this reordering, the receiver must dispose of a theoretically infinite amount of buffer space for the storage of correctly received blocks which cannot be delivered yet. The purpose of the paper is to study the statistical behavior of this receiver buffer, under the assumption of independent transmission errors.
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The study results in an explicit expression for the probability generating function of the number of blocks stored in the receiver buffer (observed at the discrete time epochs when blocks arrive at the receiver side), under the (worst-case) assumption that data blocks are available without interruption at the transmitter side. From this expression several interesting characteristics, such as the mean and variance of the buffer occupancy and the overflow probability of the buffer (if finite) can be derived with arbitrary accuracy. Previous article in issue. Next article in issue.
The recent trend towards low-latency wireless communication requires a notion of non-ergodic capacity that deals with delays. Significant research has contributed such results for relevant physical layer aspects. Less attention has been paid to actual implementations of link layer automatic repeat request protocols.
Instead, error-free transmission using instantaneous channel state information, simple stop-and-wait protocols, or instantaneous feedback are frequently assumed. In this work, we investigate protocols with pipelining that deal with packet errors under non-negligible round-trip-times. We define a stochastic service curve model of a general class of automatic repeat request protocols with pipelining and derive statistical waiting time and sojourn time bounds. We discover two regimes: under low to moderate load retransmissions cause the largest part of the sojourn time, whereas under high load the waiting time dominates the sojourn time. Generally, with increasing round-trip-time the basic cases of stop-and-wait protocols or instantaneous feedback neglect relevant effects and provide less accurate estimates. Previous article in issue. Next article in issue.
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