Comments on "Evaluation of the mean error-free interval of a noisy data channel"

|This paper corrects a few results reported in 1]. It shows that, for very long data strings, the Mean Error-Free Interval as a function of the packet error rate P is not discontinuous. In addition, the corrected results are extended to point-to-multipoint environment. In 1], Georganas et al. derived expressions for the Mean-Error Free Interval (MEFI) in a data string of B packets in a packet-oriented data transmission system. An Error-Free Interval (EFI) was deened as the number of consecutive error-free packets between two packets in error. Expressions were derived for the conditional (given that i packets out of B are in error) and unconditional MEFI's. However , as will be shown in this letter, the evaluation of these MEFI's must take into account that the length K of an EFI can be equal to zero and not only for K = 1; 2 An EFI of length zero corresponds to the interval between two contiguous packets in error. The notation and assumptions utilized in this correspondence are identical to those in the mentioned paper. Thus, the packets have L bits, including overhead, the Bit Error Rate (BER) is p, the errors are statistically independent, the probability of a packet being in error is: and the probability of i packets being in error among the total B is given by the binomial distribution: Using the same steps utilized in 1], it is not diicult to show that equation 3 also is valid for K = 0. Hence, equation 3 becomes valid for 0 K B ?i. This correction implies that the expressions for E(B; i) (equation 5), E 1 (B) (equation 8) and E 1 (1) (equations 9 and 10) in 1] must also be corrected. The corrected expression for the Mean Error-Free Interval given that i packets out of B are in error (E(B; i) in Proposition 2 of 1]) is: The corrected expression for the unconditional Mean Error-Free Interval in a data string of B packets, measured in packet lengths (E 1 (B) in Proposition 3 of 1]), is: (9) The same result can be obtained by a diierent way: given that a packet has been received in error, the probability of the EFI length, between itself and the next packet