Introduction to ISUP Release :

Release codes are usually used to identify and debug any events occurring in ISUP

ISDN User Part

The ISDN User Part or ISUP is part of the Signaling System #7 which is used to set up telephone calls in Public Switched Telephone Networks...

 signaling. Every event in ISUP signaling generates a release code number. Even for a normal ISUP call a release code is generated.There are lot of applications developed based on the release code from ISUP signaling. Similarly Telecom operators trace for Release codes to debug any call failures.
So the release code plays a very important role in Telecom signaling.

Following are the List of releases codes used

Number in Release Cause

1. Unallocated (unassigned) number
2. No route to specific transit network
3. No route to destination
4. Send special info tone
5. Misdialed trunk prefix
   Trunk prefix
   A trunk prefix is the number to be dialed in a domestic telephone call, preceding any necessary area codes and subscriber numbers. When the number is called from overseas, the trunk prefix is omitted by the caller. In most countries, such as Australia, Germany and the United Kingdom, the trunk...
   
   
6. Channel unacceptable
7. Call awarded and being delivered in established channel
8. Preemption
9. Preemption - circuit reserved for reuse
10. 10
11. 11
12. 12
13. 13
14. 14
15. 15
16. Normal call clearing
17. User busy
18. No user responding
19. No answer from user (user alerted)
20. Subscriber absent
21. Call rejected
22. Number changed
23. 23
24. 24
25. Exchange routing error
26. Non-selected user clearing
27. Destination out of order
28. Invalid number format
29. Facility rejected
30. Response to STATUS ENQUIRY
31. Normal, unspecified
32. 32
33. 33
34. No circuit/channel available
35. 35
36. 36
37. 37
38. Network out of order
39. Permanent frame mode connection out of service
40. Permanent frame mode connection operational
41. Temporary failure
42. Switching equipment congestion
43. Access information discarded
44. Requested channel/circuit not available
45. 45
46. Precedence call blocked
47. Resources unavailable, unspecified
48. 48
49. Quality of service
    Quality of service
    The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
    
     unavailable
50. Requested facility not subscribed
51. 51
52. 52
53. Outgoing calls barred within CUG
54. 54
55. Incoming calls barred within CUG
56. 56
57. Bearer capability
    Bearer Capability
    Bearer Capability is one of the Information Elements of the Q.931 SETUP message. It is used by the calling party to specify the kind of B channel that is being requested....
    
    not authorized
58. Bearer capability not presently available
59. 59
60. 60
61. 61
62. Inconsistency in designed outg. access inf. and subscr. class
63. Service or option not available, unspecified
64. 64
65. Bearer capability not implemented
66. Channel type not implemented
67. 67
68. 68
69. Requested facility not implemented
70. Only restricted digital bearer cap. is available
71. 71
72. 72
73. 73
74. 74
75. 75
76. 76
77. 77
78. 78
79. Service or option not implemented, unspecified
80. 80
81. Invalid call reference value
82. Identified channel does not exist
83. A suspended call exists, but this call identity does not
84. Call identity in use
85. No call suspended
86. Call having the requested call identity has been cleared
87. User not member of CUG
88. Incompatible destination
89. 89
90. Non-existing CUG
91. Invalid transit network selection
92. 92
93. 93
94. 94
95. Invalid message, unspecified
96. Mandatory information element is missing
97. Message type non-existing or not implemented
98. Message incompatible with call state or mesg type non-existent or not implemented
99. Information element non-existent or not implemented
100. Invalid information element contents
101. Message not compatible with call state
102. Recovery on timer expiry
103. Parameter non-existent or not implemented - passed on
104. 104
105. 105
106. 106
107. 107
108. 108
109. 109
110. Message with unrecognized parameter discarded
111. Protocol error, unspecified
112. 112
113. 113
114. 114
115. 115
116. 116
117. 117
118. 118
119. 119
120. 120
121. 121
122. 122
123. 123
124. 124
125. 125
126. 126
127. Interworking, unspecified

Release only with number doesn’t define and it is possible to use them for proprietary solution.