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A packet communication system consists of a buffer that
Chapter , Problem 5(choose chapter or problem)
A packet communication system consists of a buffer that stores packets from some source, and a communication line that retrieves packets from the buffer and transmits them to a receiver. The system operates in time-slot pairs. In the first slot, the system stores a number of packets that are generated by the source according to a Poisson PMF with parameter \(\lambda\); however, the maximum number of packets that can be stored is a given integer \(b\), and packets arriving to a full buffer are discarded. In the second slot, the system transmits either all the stored packets or \(c\) packets (whichever is less). Here, \(c\) is a given integer with \(0<c<b\).
(a) Assuming that at the beginning of the first slot the buffer is empty, find the PMF of the number of packets stored at the end of the first slot and at the end of the second slot.
(b) What is the probability that some packets get discarded during the first slot?
Questions & Answers
QUESTION:
A packet communication system consists of a buffer that stores packets from some source, and a communication line that retrieves packets from the buffer and transmits them to a receiver. The system operates in time-slot pairs. In the first slot, the system stores a number of packets that are generated by the source according to a Poisson PMF with parameter \(\lambda\); however, the maximum number of packets that can be stored is a given integer \(b\), and packets arriving to a full buffer are discarded. In the second slot, the system transmits either all the stored packets or \(c\) packets (whichever is less). Here, \(c\) is a given integer with \(0<c<b\).
(a) Assuming that at the beginning of the first slot the buffer is empty, find the PMF of the number of packets stored at the end of the first slot and at the end of the second slot.
(b) What is the probability that some packets get discarded during the first slot?
ANSWER:
Step 1 of 3
(a) Let \(X\) be the number of packets stored at the end of the first slot.
For \(x<b\) The probability is the same as the x packets generated by the source.
For \(x=b\) The probability is the same that b or more packets are generated by the source.
So, the PMF of the number of packets at the end of first slot is given by:
\(P(X=x)=\left\{\begin{array}{c} \frac{e^{-\lambda} \lambda^{x}}{x !}, \quad 0 \leq x<b \\ \sum_{x=b}^{\infty} \frac{e^{-\lambda} \lambda^{x}}{x !}, \quad x=b \\ 0, \quad x>b \end{array}\right.\)