For the Internet phone example

For the Internet phone example in Section 7.3, we introduced an online procedure (exponential moving average) for estimating delay. In this problem we will examine an alternative procedure. Let t_i be the timestamp of the ith packet received; let r_i be the time at which the ith packet is received. Let d_n be our estimate of average delay after receiving the nth packet. After the first packet is received, we set the delay estimate equal to d₁=r₁-t₁.
Suppose that we would like d_n=(r₁-t₁+r₂-t₂+....+r_n-t_n)/n for all n. Give a recursive formula for d_n in terms of d_n-1, r_n,and t_n.
b. Describe why for Internet telephony, the delay estimate described in Section 7.3 is more appropriate than the delay estimate outlined in Part a.