This article walks through common causes and step-by-step troubleshooting for a desktop phone that does not ring, despite calls reaching the user's extension in a hosted UCaaS setup.

Initial Verification

Confirm Extension Behaviour

• Use Call Trace/SIP Flow in the Portal to confirm that:
  • The call is routed to the intended user. 
  • The call completes and is not rejected, sent directly to voicemail, or missed.
  • Check for any unusual SIP response codes (e.g., 486 Busy Here, 480 Temporarily Unavailable).

Use the Cradle to Grave and SIP Flow Tools

Log in to the portal, navigate to Call History 

Filter by:

• Source/Destination Number
• Date/Time Range
• Domain

Analyze the SIP messages:

Cradle to Grave: In the portal, navigate to Call History and filter the results to find the calls with quality issues. Select the "Cradle-to-Grave" icon to view the user-friendly call flow. 

The Cradle to Grave screen opens.

SIP Flow and Link: In the portal, navigate to Call History and filter the results to find the calls with quality issues. Select the "SIP Flow" icon to view the SIP flow detail. 

The SIP Flow screen opens. Click the "Share" button to copy the link to your clipboard. If you escalate the issue, retain this link and share it with the support team.

Use the SIP Ladder in the SIP Flow/Call Trace Tool

• Identify whether a 180 Ringing SIP message is being sent and acknowledged.
• Check  183 Session Progress without 180 Ringing as a possible indicator of a missing alert.

Device Logs (Optional)

• Pull logs from the phone's local admin interface to verify whether it received an INVITE and how it handled the SIP alerting.
• Check for any unusual SIP response codes (e.g., 486 Busy Here, 480 Temporarily Unavailable).

Check Other Devices

• Determine if the extension is registered on multiple devices (e.g., mobile app, softphone).
• Confirm whether the call is ringing on other registered devices.

Device-Level Troubleshooting

SIP Registration Status

Manager Portal > Users >  Select the user> Phones Tab

• Confirm the desktop phone is registered and has a valid IP address and user.
• If not registered:
  • Check the local network.
  • Reboot the phone.
  • Verify SIP credentials.

Common Indicators of Problems

Phone Ringer Settings

• Ensure the phone is not set to Do Not Disturb (DND).
• Check volume and ringer settings on the physical device.
• Confirm no custom ringtone is muted or corrupted.

Check Line Assignment

• Ensure the SIP account is assigned to an active line appearance on the phone.

Firmware Version

• Verify the firmware is current and supported.
• Consider updating if issues persist with multiple devices of the same model.

Call Flow & Routing Issues

Forwarding or Ring Group Conflicts

• Check Call Forwarding Settings
  • Look for forwarding set to voicemail, external numbers, or other users.
• Call Queues / Ring Groups
  • If part of a ring group:
    • Verify the user is included in the group's routing list.
    • Confirm the user is logged in (if login is required for that queue).

Network and QoS Considerations

• SIP/RTP Blocked by Network
  • Confirm that the local firewall or router is not blocking SIP ports (typically UDP 5060 and RTP 10000–20000).
  • Test with a direct connection to an alternate network if possible.
• Multiple NATs or SIP ALG
  • Disable SIP ALG on routers/firewalls.
  • Avoid double NAT setups, which may break inbound audio/ringing.

Resolution Checklist