[c-nsp] diagnosing output drops on a PA-GE

[Ed Ravin]

According to the SNMP counters, we're seeing some output drops on
a PA-GE in a 7206VXR NPE-400, IOS 12.4.9T.  Looking at the interface
counters at the CLI, it's a bit more subtle than that:

  [...]
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops:
244912
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  30 second input rate 155770000 bits/sec, 27686 packets/sec
  30 second output rate 155664000 bits/sec, 27664 packets/sec
     374597076 packets input, 1315914071 bytes, 0 no buffer
     Received 66571 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 31170 ignored
     0 watchdog, 39822 multicast, 0 pause input
     0 input packets with dribble condition detected
     374202979 packets output, 1091146185 bytes, 0 underruns
     0 output errors, 0 collisions, 4 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 151259 pause output
     0 output buffer failures, 0 output buffers swapped out

What does "151259 pause output" mean here?  Also, I see at the controller
level:

Router#show controllers gigabitEthernet 2/0 | begin FX1000 Stat
FX1000 Statistics (PA2)
  CRC error        0             Symbol error     0           
  Missed Packets   0             Single Collision 0           
  Excessive Coll   0             Multiple Coll    0           
  Late Coll        0             Collision        0           
  Defer            3541666       Receive Length   0           
  Sequence Error   0             XON RX           0           
  XON TX           8546          XOFF RX          53          
  XOFF TX          655230        FC RX Unsupport  0           
  Packet RX (64)   388           Packet RX (127)  10116843    
  Packet RX (255)  373860        Packet RX (511)  594955      
  Packet RX (1023) 926790        Packet RX (1522) 8700212     
  Good Packet RX   2989515386    Broadcast RX     3312539     
  Multicast RX     2717883       Good Packet TX   0           
  Good Octets RX.H 1             Good Octets RX.L 1774992269  
  Good Octets TX.H 1             Good Octets TX.L 2534893275  
  RX No Buff       299951        RX Undersize     0           
  RX Fragment      0             RX Oversize      0           
  RX Octets High   1             RX Octets Low    1774990773  
  TX Octets High   1             TX Octets Low    2536093853  
  TX Packet        20708399      RX Packet        20713049    
  TX Broadcast     1853          TX Multicast     330         
  Packet TX (64)   2146814       Packet TX (127)  10388628    
  Packet TX (255)  445116        Packet TX (511)  665522      
  Packet TX (1023) 777636        Packet TX (1522) 6267591     

What are "Defer", "XON TX" and "XOFF TX"?  Is this flow control with the
switch?