For the VoIP example in Section 9.3, 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.  

a. 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, and t_n. 

b. Describe why for Internet telephony, the delay estimate described in Section 9.3 is more appropriate than the delay estimate outlined in part (a).