RFC 3398 says that when ISUP timer T7 expires before an ACM or CON is received, the gateway should send 504 Server Timeout to the SIP side, not 408.
Checked 2026-10-02
A '504 Server Timeout' SHOULD be sent back to the SIP network.
- Vendor
- not restricted
- Product
- not restricted
- Subsystem
- SIP-ISUP interworking
- Deployment
- any
- Region
- not restricted
- Release range
- RFC 3398, current as of 2026-10-02
- Checked
- 2026-10-02
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 7.1.3 ISUP T7 Expires; Section 7.2.2
Cite this note
APA
WarmTransfer. (2026, October 2). Troubleshooting SIP 408 Request Timeout and calls that get no response: source note sip-408-timeout-troubleshooting-rfc3398-t7-expiry-504. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-408-timeout-troubleshooting-rfc3398-t7-expiry-504
BibTeX
@misc{warmtransfer-claim-sip-408-timeout-troubleshooting-rfc3398-t7-expiry-504,
title = {Troubleshooting SIP 408 Request Timeout and calls that get no response: source note sip-408-timeout-troubleshooting-rfc3398-t7-expiry-504},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-408-timeout-troubleshooting-rfc3398-t7-expiry-504},
note = {Source note sip-408-timeout-troubleshooting-rfc3398-t7-expiry-504, checked 2026-10-02}
}