Answer
Exp 1
NetGear
Input Rate (Mb/s)
Flow 1
100
100
100
100
Flow 2
500
500
500
500
Flow 3
300
500
800
1000*
Output Rate (Mb/s)
Drop Rate
Flow 1
Flow 1
33
9
8
7
Flow 2
Flow 3
56
45
36
31
Flow 2
Flow 3
11
46
56
62
3COM
Input Rate (Mb/s)
Flow 1
100
100
100
100
Flow 2
500
500
500
500
Flow 3
300
500
800
1000*
Output Rate (Mb/s)
Drop Rate
Flow 1
Flow 1
11
10
10
10
Flow 2
56
45
46
46
Flow 3
Flow 2
Flow 3
33
45
44
44
Analysis
(1) What is the Netgear switch’s service capacity? When the sum of input flow rates is
smaller than the line rate, do you observe packet loss? How about the 3COM
switch?
Answer: both switches are able to handle packets at line rate around 988Mb/s
(1Gb/s in theory). No packet losses are observed when the sum of flow rates is
smaller than the line rate.
(2) When the sum of the three input flows is greater than the line rate, how does the
bandwidth distributed among the three flows for the NetGear switch?
Answer: When the total input rate exceeds the maximum service rate, the NetGear
switch dropped frames in all the three flows and the drop rate is almost same.
(3) How about the 3COM switch?
Answer: for the 3COM switch, we observed that
(1) All frames in flow 1 (100 Mb/s) were received
(2) Frames in flow 2 and 3 (around 500 Mb/s) equally share the remaining
bandwidth. The implication is that all flows have the same bandwidth
reservation (333 Mb/s) and the switch served the connections in proportion to
their reservation, and then distributes the extra bandwidth equally among the
active flows.
(4) Does the NetGear switch use work-conserving or non-work-conserving scheduling?
How about the 3COM?
Answer: both use work-conserving scheduling
(5) What scheduling policy might be deployed in both switches based on the collected
data?
Answer: NetGear uses FIFO, 3COM uses fair queueing.
(6) Can you think of some applications in which one switch may be better than the
other? Give one example for each.
Open Answer
Exp 2
Input Rate (Mb/s)
NetGear Delay (µs)
3COM Delay (µs)
100
13
18
1000
13
18
(1) Plot the delay of the 50 packets for the 1Gb/s sending rate case for both netgear
and 3COM switches.
(2) Is this delay mainly due to the processing delay or the queueing delay?
Answer: processing delay
Exp 3
Input Rate (Mb/s)
Flow 1
Flow 2
Flow 3
99
889
988
494
494
988
889
99
988
NetGear Output Rate (Mb/s)
3COM Output Rate (Mb/s)
Flow 1
Flow 1
Flow 2
Flow 3
Flow 2
Flow 3
(3) What is the impact of flow 2 on flow 1 for the NetGear switch?
(4) How about the 3COM switch?
Answer: Therefore, flow 2 does not affect flow 1 at all.
(5) Explain your observation for both switches and what buffering mechanism might
be used in both switches?
Answer: This can be explained by the virtual output queue, in which frames are
classified according to their destination MAC addresses upon arrival at the input
port. The frames with different destination MAC will then be processed
independently.
Reference
Input Rate (Mb/s)
NetGear Output Rate (Mb/s)
3COM Output Rate (Mb/s)
Flow 1
Flow 2
Flow 3
Flow 1
Flow 2
Flow 3
Flow 1
Flow 2
Flow 3
99
889
988
99
466
521
99
493
495
198
790
988
197
435
552
197
491
497
329
659
988
329
404
583
329
492
496
494
494
988
493
338
649
493
492
496
659
329
988
658
258
729
658
329
658
790
198
988
790
167
820
790
197
790
889
99
988
888
90
897
888
99
888
Input Rate (Mb/s)
Flow 1
100
100
100
100
100
100
100
100
100
100
Flow 2
499
499
499
499
499
499
499
499
499
499
Flow 3
100
200
299
399
499
599
699
799
899
988
Output Rate (Mb/s)
Drop Rate
Flow 1
Flow 1
100
100
100
100
100
100
100
100
100
100
Flow 2
499
499
499
486
443
443
443
443
443
442
Flow 3
100
200
299
399
442
442
442
442
442
443
0
0
0
0
0
0
0
0
0
0
Flow 2
0
0
0
0.03
0.11
0.11
0.11
0.11
0.11
0.11
Flow 3
0
0
0
0
0.11
0.26
0.37
0.45
0.51
0.55