Source note · Calls that drop after about 30 seconds
When a request carries rport, the server must set rport to the request's source port. It then sends responses to the IP in 'received' and the port in 'rport', so the responses follow the NAT binding the request created.
Checked 2026-09-25
- Vendor
- IETF
- Product
- SIP
- Subsystem
- NAT traversal / Via
- Deployment
- any
- Region
- not restricted
- Release range
- RFC 3581
- Checked
- 2026-09-25
Sources
- RFC 3581: An Extension to the Session Initiation Protocol (SIP) for Symmetric Response Routing — IETF / RFC Editor · tier 1 standards and regulators · Server behaviour section
Cite this note
APA
WarmTransfer. (2026, September 25). Calls that drop after about 30 seconds: source note sip-calls-drop-30-seconds-rport-server. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-calls-drop-30-seconds-rport-server
BibTeX
@misc{warmtransfer-claim-sip-calls-drop-30-seconds-rport-server,
title = {Calls that drop after about 30 seconds: source note sip-calls-drop-30-seconds-rport-server},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-calls-drop-30-seconds-rport-server},
note = {Source note sip-calls-drop-30-seconds-rport-server, checked 2026-09-25}
}