$3\mathrm{.}3\mathrm{.}15$ In a packet voice communications system, a source transmits packets contain$-$ ing digitized speech to a receiver. Because transmission errors occasionally occur, an ackno,vledgment $($ACK$)$ or a negative ac$-$ kno,vledgment $($NAK$)$ is transmitted back to the source to indicate the status of each received packet. $\backslash$i$\backslash !$hen the transmitter gets a NAK, the packet is retransmitted. Voice packets are delay sensitive$,$ and a packet can be transmitted a maximum of d times. If a packet transmission is an independent Bernoulli trial with success probability p$,$