Source note · SS7 and carrier interworking concepts
RFC 3398 maps ISUP cause value 21 (call rejected) to the SIP response 403 Forbidden.
Checked 2026-09-24
- Vendor
- IETF
- Product
- SIP-ISUP gateways
- Subsystem
- ISUP-to-SIP cause mapping
- Deployment
- carrier, on-premises
- Region
- not restricted
- Release range
- current as of 2026-09-24
- Checked
- 2026-09-24
Sources
- RFC 3398: Integrated Services Digital Network (ISDN) User Part (ISUP) to Session Initiation Protocol (SIP) Mapping — IETF / RFC Editor · tier 1 standards and regulators · Section 7.2.4.1 ISDN Cause Code to Status Code Mapping, table
Cite this note
APA
WarmTransfer. (2026, September 24). SS7 and carrier interworking concepts: source note ss7-carrier-interworking-cause21-to-403. WarmTransfer. https://warmtransfer.net/knowledge/claims/ss7-carrier-interworking-cause21-to-403
BibTeX
@misc{warmtransfer-claim-ss7-carrier-interworking-cause21-to-403,
title = {SS7 and carrier interworking concepts: source note ss7-carrier-interworking-cause21-to-403},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/ss7-carrier-interworking-cause21-to-403},
note = {Source note ss7-carrier-interworking-cause21-to-403, checked 2026-09-24}
}