Subject: strange result

From: Harpreet Arora <[email-masked]>
Date: Mon, 29 Oct 2001 18:18:44 -0500

Hi,
I've been using NS-2 to do wireless simulations. While I was trying to
evaluate the effect of Queue length on the network performance, I came
up on a very strange result. I simulated a small network with 5 nodes
and 3 cbr sources, moving in an area of 500m X 500m, at a peak speed of
25 m/s. For a queue length of 20, I performed the simulations by varying
the number of packets sent by each source during each simulation. The
number of packets of each flow dropped was monitored. For one particular
flow, the number of packet drops shows spikes at some points. If these
points are ignored, the graph results in a smooth curve, which is very
logical. The strange part is that, if the spiked points are plotted
separately, it also results in a smooth curve. I have not been able to
understand the phenomenon, even after prolonged investigation of the
trace files. Could someone please explain me the reason for this? The
results of the simulations are shown below. The spikes are shown by flow
2 and 3. Similar results occur with different scenario files and
different Connection Patterns. Is it a bug in the ns-code, or are these
just abberations which should be ignored?

# of packets    # of Packets    # of Packets    # of Packets    Total #
of Packets
per source        of flow 1        of flow 2         of flow
3            dropped (including
                        dropped        dropped
dropped                control packets)
    50     1     0     0     2
    53     1     0     0     2
    54     0     0     0     2
    57     1     0     0     2
    58     1     6     0     8
    61     1     0     0     2
    62     1     0     0     2
    64     1     0     0     2
    66     1     1     0     4
    69     1     0     0     4
    70     1     2     0     4
    73     1     0     0     2
    74     1     1     0     3
    76     1     0     0     2
    78     1     1     0     3
    80     1     0     0     3
    83     1     0     0     2
    85     1     9     0    11
    87     1     0     0     4
    88     1     9     0    11
    90     1     1     0     3
    93     2     0     0     2
    94     1     0     0     2
    97     1     0     0     2
    99     1     1     0     3
   100     2     0     0     2
   103     1     0     0     2
   105     2     0     0     3
   107     1     0     1     3
   108     1     0     2     4
   111     1     0     0     2
   112     1     0     0     2
   115     1     0     0     2
   117     1    12     0    14
   118     1    12     0    14
   120     1     0     0     2
   123     1     0     0     2
   124     1     0     0     2
   127     0     0     0     2
   128     1     0     5     7
   131     1     0     0     2
   132     1    14     0    16
   135     1     0     0     3
   137     1     0     0     2
   138     1     0     0     2
   140     1    14     0    16
   142     1     0     0     2
   145     1     0     0     2
   146     1     0     9    11
   148     1     0     0     2
   151     1     0    10    12
   153     1     0     0     3
   155     1     0     0     2
   156     1     0     0     2
   158     1     1     0     5
   160     1     1     0     3
   162     1     0    12    14
   165     1     0     0     2
   166     1     0    13    15
   169     1     0     0     2
   170     1     1     0     3
   172     1     0     0     2
   175     1     0    15    17
   176     1     0     0     2
   178     0     1     0     2
   180     1     1     0     4
   183     1     0     0     2
   185     1     0     0     2
   187     1     0    17    19
   189     2     0     0     4
   190     1     0     0     3
   192     1    20     0    22
   194     1     0    19    21
   197     1     0     0     2
   199     1     0     0     2
   200     1     0     0     3
   202     1     0     0     2
   205     1    22     0    24
   207     1     0     0     2
   208     1     1    22    25
   211     1     0     0     3
   213     1     1     0     3
   214     1     0    24    26
   217     1     0     0     3
   218     1     0     0     2
   220     1     0     0     2
   223     1     0     0     2
   225     1    23     0    25
   226     1     0     0     2
   229     1     0     0     2
   231     1     0     0     2
   233     1     1    26    29
   235     1     0     0     2
   237     1     0     0     2
   239     1     0    28    30
   241     1     0     0     2
   242     1    24     0    26
   245     1     0     0     2
   247     1     0    29    31
   248     1    29     0    31
   250     1     0     0     2
   252     1     0     0     2
   255     1    31     0    33
   257     1     0    31    33
   259     1     1     0     3
   260     1     0    33    35
   262     1    32     0    34
   264     1     0     0     2
   266     1     0     0     2
   269     1     0     0     2
   271     1    28     0    30
   272     1     0     0     2
   274     1     0    36    38
   277     1     0     0     2
   279     1    35     0    37
   281     1     0     0     3
   282     1     0     0     4
   285     2     0     0     3
   287     1     1     0     3
   289     1     0     0     2
   290     1     1     0     4
   292     1     0     0     3
   295     1     0     0     2
   296     1     1     0     3
   299     1     0     0     2
   300     1     1     0     3
   302     2     0     0     3
   304     1     0    41    43
   306     1     0     0     2
   308     1     1     0     3
   311     1     0     0     2
   313     1     0     0     2
   314     1     0     0     2
   316     1     2     0     4
   318     1     2     2     7
   320     1     2     2     6
   322     1     3     2     8
   324     1     3     4     9
   327     2     3    47    55
   329     1     3     5    10
   331     1    47     6    56
   333     1     5     6    13
   334     1     5     8    17
   336     1     6     9    17
   338     1     6    10    20
   340     2     5    10    18
   342     1     6    11    19
   344     1     7    12    23
   346     1     6    12    22
   349     1     7    14    23
   351     1     8    14    26
   353     1     8    58    68
   354     1     8    59    69
   357     2     9    17    30
   358     2    11    17    32
   360     1    10    18    32
   362     1    11    18    32
   364     1    11    62    75
   367     2    10    20    33
   368     2    43    22    68
   371     2    11    22    36
   372     2    11    23    37
   374     1    14    24    40
   376     2    13    68    84
   379     1    14    26    42
   380     2    14    26    43
   383     2    14    27    45
   385     3    14    28    46
   386     2    46    28    77
   388     1    15    30    49
   391     2    15    31    49
   393     1    15    30    47
   394     1    17    32    51
   396     1    16    75    93
   399     1    17    33    52
   400     1    18    34    54
   403     2    18    78    99
   405     1    20    36    60
   406     1    19    37    58
   409     1    19    37    58
   411     2    21    38    62
   413     1    20    39    61
   414     3    52    40    96
   417     2    20    83   106
   419     1    22    42    67
   420     2    65    42   110
   423     1    22    43    68
   424     2    22    44    70
   426     1    23    45    70
   429     1    25    46    75
   431     2    25    47    77
   432     1    26    47    75
   435     1    25    49    78
   436     1    25    48    75
   439     3    57    50   111
   441     1    25    50    78
   443     1    26    94   122
   444     2    27    52    84
   446     1    29    53    85
   449     1    27    53    84
   451     3    27    98   129
   453     2    30    55    90
   455     1    29    99   130
   457     1    29    57    89
   459     1    29   101   132
   460     1    32    58    92
   463     2    30    59    92
   464     2    30   104   137
   467     1    31    61    94
   468     1    32    61    96
   470     1    31    62    95
   473     1    32    63    97
   475     2    32   107   142
   477     3    33    65   102
   478     1    34    66   102
   480     3    33    66   103
   483     3    79    67   150
   484     1    35    68   105
   486     3    37    69   111
   489     1    36    70   109
   490     3    80    70   154
   493     3    38   114   156
   494     1    38    72   112
   497     3    69    73   146
   498     3    37   117   158

Thanks.

Harpreet.

---

From: "Philippe Jacquet" <[email-masked]>
Date: Tue, 30 Oct 2001 12:07:01 +0100

Looks difficult to investigate. Why flow 1 always experience the same number
of drop (1 or 2). Does it mean that the numbers of packets transmitted vary
only on flow and 3 or does it mean different motion for sources 1 2 3?

Another question: does the nodes follows exactly the same motion path in
every simulations?

Philippe