The following is an example of the nicstat command. It prints statistics 
for the network interfaces such as Kb/sec read and written. Here we run it
with an interval of 1 second,

 $ nicstat 1
     Time   Int   rKb/s   wKb/s   rPk/s   wPk/s    rAvs    wAvs   %Util     Sat
 12:33:04  hme0    1.51    4.84    7.26   10.32  213.03  480.04    0.05    0.00
 12:33:05  hme0    0.20    0.26    3.00    3.00   68.67   90.00    0.00    0.00
 12:33:06  hme0    0.14    0.26    2.00    3.00   73.00   90.00    0.00    0.00
 12:33:07  hme0    0.14    0.52    2.00    6.00   73.00   88.00    0.01    0.00
 12:33:08  hme0    0.24    0.36    3.00    4.00   81.33   92.00    0.00    0.00
 12:33:09  hme0    2.20    1.77   16.00   18.00  140.62  100.72    0.03    0.00
 12:33:10  hme0    0.49    0.58    8.00    9.00   63.25   66.00    0.01    0.00
 12:33:11  hme0   12.16 1830.38  185.06 1326.42   67.26 1413.06   15.09    0.00
 12:33:12  hme0   19.03 3094.19  292.88 2229.11   66.53 1421.40   25.50    0.00
 12:33:13  hme0   19.55 3151.87  301.00 2270.98   66.50 1421.20   25.98    0.00
 12:33:14  hme0   11.99 1471.67  161.07 1081.45   76.25 1393.49   12.15    0.00
 12:33:15  hme0    0.14    0.26    2.00    3.00   73.00   90.00    0.00    0.00
 12:33:16  hme0    0.14    0.26    2.00    3.00   73.00   90.00    0.00    0.00
 12:33:17  hme0    0.14    0.26    2.00    3.00   73.00   90.00    0.00    0.00
 [...]

at 12:33:11 an scp was run on the system that sent several Mb to another host. 
The details of this can be seen above, with an increase in write Kb/sec,
write Packets/sec, and in overall utilisation. The maximum Average write 
packet size of around 1420 bytes reflects the MTU size.




This is an example of nicstat running on a system with several interfaces,
this time with a 5 second interval,

 $ nicstat 5
     Time   Int   rKb/s   wKb/s   rPk/s   wPk/s    rAvs    wAvs   %Util     Sat
 00:58:02  hme0    0.12    0.01    1.05    0.04  113.53  238.16    0.00	   0.00
 00:58:02  qfe0    2.94    0.53    5.97    3.70  504.29  147.69    0.03	   0.00
 00:58:02  qfe1    6.79   26.37   17.71   25.47  392.55 1060.22    0.27	   0.00
 00:58:02  qfe2    0.27    7.78    3.24    6.10   86.74 1306.18    0.07	   0.00
 00:58:02  qfe3    1.15   20.30    8.09   15.78  145.72 1317.10    0.18	   0.00
     Time   Int   rKb/s   wKb/s   rPk/s   wPk/s    rAvs    wAvs   %Util     Sat
 00:58:07  hme0    0.00    0.00    0.00    0.00    0.00    0.00    0.00	   0.00
 00:58:07  qfe0    0.04    0.25    0.60    0.80   60.00  316.25    0.00	   0.00
 00:58:07  qfe1    0.00    0.00    0.00    0.00    0.00    0.00    0.00	   0.00
 00:58:07  qfe2    0.00    0.00    0.00    0.00    0.00    0.00    0.00	   0.00
 00:58:07  qfe3    0.14    0.19    0.60    0.60  246.67  319.67    0.00	   0.00
     Time   Int   rKb/s   wKb/s   rPk/s   wPk/s    rAvs    wAvs   %Util     Sat
 00:58:12  hme0    0.00    0.00    0.00    0.00    0.00    0.00    0.00	   0.00
 00:58:12  qfe0   10.34    1.10   19.76   12.18  535.81   92.59    0.09	   0.00
 00:58:12  qfe1    0.00    0.00    0.00    0.00    0.00    0.00    0.00	   0.00
 00:58:12  qfe2    0.00    0.00    0.00    0.00    0.00    0.00    0.00	   0.00
 00:58:12  qfe3    0.14    0.19    0.60    0.60  246.67  319.67    0.00	   0.00
 [...]

the example above shows only a small amount of activity.