For DNS SRV destinations, CUBE marks a destination busyout if it receives a 503 response or no response to the INVITE and tries the next active destination.
Checked 2026-10-02
If CUBE receives a 503 response or no response for the INVITE, CUBE then marks that destination as busyout and attempts call on the next destination that is marked as active.
- Vendor
- Cisco
- Product
- Cisco Unified Border Element
- Subsystem
- options-keepalive
- Deployment
- on-premises
- Region
- not restricted
- Release range
- IOS XE 17.6 onwards
- Checked
- 2026-10-02
Sources
- Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - SIP Trunk Monitoring — Cisco · tier 2 current vendor documentation · OPTIONS Ping for DNS SRV Hosts
Cite this note
APA
WarmTransfer. (2026, October 2). Troubleshooting Unified CM SIP trunks that show No Service: source note cucm-sip-trunk-no-service-troubleshooting-cube-503-busyout. WarmTransfer. https://warmtransfer.net/knowledge/claims/cucm-sip-trunk-no-service-troubleshooting-cube-503-busyout
BibTeX
@misc{warmtransfer-claim-cucm-sip-trunk-no-service-troubleshooting-cube-503-busyout,
title = {Troubleshooting Unified CM SIP trunks that show No Service: source note cucm-sip-trunk-no-service-troubleshooting-cube-503-busyout},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/cucm-sip-trunk-no-service-troubleshooting-cube-503-busyout},
note = {Source note cucm-sip-trunk-no-service-troubleshooting-cube-503-busyout, checked 2026-10-02}
}