A terminating provider that blocks a call under 47 CFR 64.1200 must immediately return a SIP 603 (or 607/608 family) response on IP networks, or ISUP cause code 21 on non-IP networks.
Checked 2026-10-02
- Vendor
- not restricted
- Product
- not restricted
- Subsystem
- FCC call blocking redress
- Deployment
- carrier
- Region
- us
- Release range
- current as of 2026-10-02
- Checked
- 2026-10-02
Sources
- 47 CFR § 64.1200 - Delivery restrictions — Legal Information Institute, Cornell Law School (reproducing the eCFR) · tier 1 standards and regulators · 47 CFR 64.1200(k)(9)
Cite this note
APA
WarmTransfer. (2026, October 2). Troubleshooting STIR/SHAKEN attestation levels on outbound calls: source note stir-shaken-attestation-troubleshooting-cfr-block-sip-603. WarmTransfer. https://warmtransfer.net/knowledge/claims/stir-shaken-attestation-troubleshooting-cfr-block-sip-603
BibTeX
@misc{warmtransfer-claim-stir-shaken-attestation-troubleshooting-cfr-block-sip-603,
title = {Troubleshooting STIR/SHAKEN attestation levels on outbound calls: source note stir-shaken-attestation-troubleshooting-cfr-block-sip-603},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/stir-shaken-attestation-troubleshooting-cfr-block-sip-603},
note = {Source note stir-shaken-attestation-troubleshooting-cfr-block-sip-603, checked 2026-10-02}
}