Assume the following network scenario. Flow BA direction, all transmissions are
ID: 3591417 • Letter: A
Question
Assume the following network scenario. Flow BA direction, all transmissions are infinitely fast, i.e. zero delay; this is often a good approximation because ACK packets are what travel in that direction and they are negligibly small. In the AB direction, we will assume that the AR1 link is infinitely fast, but the other four each have a bandwidth of 1 packet/second (and no propagation-delay component). This makes the R1R2 link the bottleneck link; any queue will now form at R1. The “path bandwidth” is 1 packet/second, and the RTT is 4 seconds. Questions: provided a winsize=3, complete the following table whenever there is a packet available.
Note: the brief pile-up at R1 (the bottleneck link!) on startup. However, in the steady state, there is no queuing. i.e At T=3, R1 has just finished sending Data[3] as Data[4] arrives from A; R1 can begin sending packet 4 immediately. No queue will develop. Real sliding-windows protocols generally have some way of minimizing this “initial pileup”.
1 pkt/sec 1 pkt/sec 1 pkt/sec 1 pkt/sec R1 R2 R3 R4 R1 Time | A T sends queues sends sends sends sends |ACKs 0 1,2,3 2,3 1 4 45Explanation / Answer
Time
A
R1
R1
R2
R3
R4
B
T
SENDS
QUEUES
SENDS
SENDS
SENDS
SENDS
ACKs
0
1,2,3
2,3
1
1
1
1
2
1
3
2
2
2
2
0
2
3
3
3
3
1
3
4
4
4
4
4
2
4
5
5
5
5
5
0
5
6
6
6
6
6
1
6
7
7
7
7
7
2
TO MINIMIZE INITIAL PILE_UP WE USE WINSIZE=1 THEN THERE IS NO NEED QUEUE PACKETS AT R1.
Time
A
R1
R1
R2
R3
R4
B
T
SENDS
QUEUES
SENDS
SENDS
SENDS
SENDS
ACKs
0
1,2,3
2,3
1
1
1
1
2
1
3
2
2
2
2
0
2
3
3
3
3
1
3
4
4
4
4
4
2
4
5
5
5
5
5
0
5
6
6
6
6
6
1
6
7
7
7
7
7
2
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