Question

Consider the following situation, in which hosts A and B are separated by intervening routers R1 and R2. The A—R1 link is instantaneous. The R1⟶R2 and R2⟶B links have a bandwidth of one packet per second in the direction towards B. ACKs are transmitted instantaneously, for an RTT of 2.0 sec. A—————R1—————R2—————B Assume A uses unbounded slow start to begin sending to B, with the initial congestion window (cwnd) equal to one (so A starts by sending a single packet). cwnd is incremented by 1 for each new ACK received, so A sends two new packets for each ACK it gets. Assume R's queue has a capacity of two packets, in addition to the one it is sending. (a) Carry this on until (i) a packet is lost, and (ii) the first two dupACKs (B’s response to packets following the lost packet) arrive back at A. Remember that ACKs are cumulative: if Data[N] is lost, Data[N+1] elicits (at best) ACK[N-1]. Assume the lost packet is not retransmitted. Note that A does not send new data once it starts receiving dupACKs.

Answer 1