Source note · Troubleshooting calls that drop on hold or transfer
When re-INVITE glare occurs, the UAS returns 491 (Request Pending) and the UAC retries the offer after a randomly selected time that depends on which user agent owns the dialog's Call-ID, as specified in RFC 3261 sections 14.1 and 14.2.
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 6141: Re-INVITE and Target-Refresh Request Handling in the Session Initiation Protocol (SIP) — IETF / RFC Editor · tier 1 standards and regulators · Section 3.5 (Glare Situations)
Cite this note
APA
WarmTransfer. (2026, September 30). Troubleshooting calls that drop on hold or transfer: source note sip-reinvite-call-drops-491-glare-rule. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-reinvite-call-drops-491-glare-rule
BibTeX
@misc{warmtransfer-claim-sip-reinvite-call-drops-491-glare-rule,
title = {Troubleshooting calls that drop on hold or transfer: source note sip-reinvite-call-drops-491-glare-rule},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-reinvite-call-drops-491-glare-rule},
note = {Source note sip-reinvite-call-drops-491-glare-rule, checked 2026-09-30}
}