Carrier Call Status Explanation

Hi,
Can anyone kindly explain to me what does cancel mean in the carrier call status? Also, whats the major diff of chan unavail and congestion so I can avoid these things from happening.
Please see my data below:
---------- CARRIER CALL STATUSES
+----------------------+------------+
| STATUS | CALLS |
+----------------------+------------+
| ANSWER | 1536 |
| BUSY | 21 |
| CANCEL | 1540 |
| CHANUNAVAIL | 9 |
| CONGESTION | 25 |
+----------------------+------------+
| TOTAL | 3131 |
+----------------------+------------+
Thanks in advance
Can anyone kindly explain to me what does cancel mean in the carrier call status? Also, whats the major diff of chan unavail and congestion so I can avoid these things from happening.
Please see my data below:
---------- CARRIER CALL STATUSES
+----------------------+------------+
| STATUS | CALLS |
+----------------------+------------+
| ANSWER | 1536 |
| BUSY | 21 |
| CANCEL | 1540 |
| CHANUNAVAIL | 9 |
| CONGESTION | 25 |
+----------------------+------------+
| TOTAL | 3131 |
+----------------------+------------+
Thanks in advance