Consider the following network, with each link other than the first having a bandwidth delay of 1 packet/second. Assume ACKs travel instantly from B to R (and thus to A). Assume there are no propagation delays, so the RTT_noLoad is 4; the bandwidthRTT product is then 4 packets. If A uses sliding windows with a window size of 6, the queue at R1 will eventually have size 2.

Suppose A uses threshold slow start (13.2.2 Threshold Slow Start) with ssthresh = 6, and with cwnd initially 1. Complete the table below until two rows after cwnd = 6; for these final two rows, cwnd has reached ssthresh and so A will send only one new packet for each ACK received. How big will the queue at R1 grow?

T	A sends	R1 queues	R1 sends	B receives/ACKs	cwnd
0	1		1		1
1
2
3
4	2,3	3	2	1	2
5			3		2
6
7
8	4,5	5	4	2	3

Note that if, instead of using slow start, A simply sends the initial windowful of 6 packets all at once, then the queue at R1 will initially hold 6-1 = 5 packets.

1 pkt/sec 1 pkt/sec 1 pkt/sec infinitely fast 1 pkt/sec 1 pkt/sec 1 pkt/sec 1 pkt/sec infinitely fast 1 pkt/sec