RFC Errata
RFC 4458, "Session Initiation Protocol (SIP) URIs for Applications such as Voicemail and Interactive Voice Response (IVR)", April 2006
Note: This RFC has been updated by RFC 8119
Source of RFC: IETF - NON WORKING GROUPArea Assignment: rai
Errata ID: 4266
Status: Reported
Type: Technical
Publication Format(s) : TEXT
Reported By: Franz Edler
Date Reported: 2015-02-09
Section 2.2 Cause says:
+---------------------------------+-------+
| Redirecting Reason | Value |
+---------------------------------+-------+
| Unknown/Not available | 404 |
| User busy | 486 |
| No reply | 408 |
| Unconditional | 302 |
| Deflection during alerting | 487 |
| Deflection immediate response | 480 |
| Mobile subscriber not reachable | 503 |
+---------------------------------+-------+
It should say:
+---------------------------------+-------+
| Redirecting Reason | Value |
+---------------------------------+-------+
| Unknown | 404 |
| User busy | 486 |
| No reply | 408 |
| Not available | 503 |
| Unconditional | 302 |
| Deflection during alerting | 487 |
| Deflection immediate response | 480 |
| Mobile subscriber not reachable | 503 |
+---------------------------------+-------+
Notes:
The two redirect reasons "Unknown" and "Not available" are totally different in their meaning. In the first case the user is unknown, whereas in the second case it is a valid address but not reachable.
Unfortunately 3GPP TS 24.604 "Communication Diversion" refers to RFC 4458 and in case of "communication forwarding not logged in" it therefore requests cause value 404 in the meaning of "not available". This cause value is mapped to "unknown" in interworking SIP to ISUP (3GPP TS 29.163 Table 7.4.6.2.2.4) and therefore a missed call notification cannot be sent to a subscriber which is not logged in.
"Not available" should use the same value as "Mobile subscriber not reachable".