TABLE OF CONTENTS The following are the cause codes used in Release (REL) messages. These cause codes are typically dependent on implementation, but are fairly self-explanatory. They are included in this appendix as a quick reference.
Cause codes are divided into various classes or groups. The class designation is found in bits 5 through 7. The decimal value for each cause code is shown in parenthesis.
Class 000 and 001, Normal Event
| 0 | 0 | 0 | 0 | 0 | 0 | 1 | (1) | Unallocated (unassigned) number |
| 0 | 0 | 0 | 0 | 0 | 1 | 0 | (2) | No route to specified transit network |
| 0 | 0 | 0 | 0 | 0 | 1 | 1 | (3) | No route to destination |
| 0 | 0 | 0 | 0 | 1 | 0 | 0 | (4) | Send special information tone |
| 0 | 0 | 0 | 0 | 1 | 0 | 1 | (5) | Misdialed trunk prefix (no procedure specified for U.S. networks) |
| 0 | 0 | 0 | 1 | 0 | 0 | 0 | (8) | Preemption |
| 0 | 0 | 0 | 1 | 0 | 0 | 1 | (9) | Preemption circuit reserved for reuse |
| 0 | 0 | 1 | 0 | 0 | 0 | 0 | (16) | Normal clearing |
| 0 | 0 | 1 | 0 | 0 | 0 | 1 | (17) | User busy |
| 0 | 0 | 1 | 0 | 0 | 1 | 0 | (18) | No user responding |
| 0 | 0 | 1 | 0 | 0 | 1 | 1 | (19) | No answer from user (user alerted) |
| 0 | 0 | 1 | 0 | 1 | 0 | 0 | (20) | Subscriber absent |
| 0 | 0 | 1 | 0 | 1 | 0 | 1 | (21) | Call rejected |
| 0 | 0 | 1 | 0 | 1 | 1 | 0 | (22) | Number changed |
| 0 | 0 | 1 | 0 | 1 | 1 | 1 | (23) | Redirect to new destination |
| 0 |
