Source note · Troubleshooting calls that drop on hold or transfer
On a 491 to a re-INVITE the UAC should wait a random 2.1 to 4 seconds if it owns the Call-ID, or 0 to 2 seconds if it does not, then retry the re-INVITE once more if it still wants the change.
Checked 2026-09-30
- Vendor
- IETF
- Product
- SIP
- Subsystem
- sip-dialog
- Deployment
- any
- Region
- not restricted
- Release range
- RFC as published
- Checked
- 2026-09-30
Sources
- RFC 3261 — SIP: Session Initiation Protocol — IETF / RFC Editor · tier 1 standards and regulators · Section 14.1 (UAC Behavior), 491 timer paragraph
Cite this note
APA
WarmTransfer. (2026, September 30). Troubleshooting calls that drop on hold or transfer: source note sip-reinvite-call-drops-491-retry-timer. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-reinvite-call-drops-491-retry-timer
BibTeX
@misc{warmtransfer-claim-sip-reinvite-call-drops-491-retry-timer,
title = {Troubleshooting calls that drop on hold or transfer: source note sip-reinvite-call-drops-491-retry-timer},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-reinvite-call-drops-491-retry-timer},
note = {Source note sip-reinvite-call-drops-491-retry-timer, checked 2026-09-30}
}