Dropped calls can occur for several reasons in a hosted UCaaS environment. This guide will help you investigate and resolve dropped call issues using the platform's tools and associated network diagnostics.

Common Causes of Dropped Calls

Poor network conditions (packet loss, jitter, latency)

• NAT or firewall session timeouts.
• SIP ALG interference.
• Device firmware or configuration issues.
• Media path (RTP) or signalling path issues.
• Incomplete registration or re-registration failure.
• Carrier-side hangups or SIP errors (e.g., 408, 481, 503).

Step-by-Step Troubleshooting 

1. Confirm the Scope of the Issue

• Does it affect one user or multiple users?
• Are calls dropped at a specific time length (e.g., 30 seconds, 2 minutes, 15 minutes, 1 hour)? Calls dropping consistently often point to session timers or firewall/NAT issues.
• Internal, inbound, or outbound calls?

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 to share with the support team.

Look for a BYE or CANCEL and who sent it. If the BYE comes from the user side, it's likely a device, network, or NAT issue. Investigate upstream routing or the SIP trunk if it comes from the carrier.

Identify SIP error codes (e.g., 408 Request Timeout, 481 Call/Transaction Does Not Exist).

 3. Check Device & Network Environment

• Reboot the affected phone or softphone.
• Verify that SIP registration is stable.
• Ensure no double NAT exists in the network path.
• Check for SIP ALG enabled on the router/firewall (should be disabled).
• Review session timeout settings (e.g., UDP timeout < 60s can cause drops) or use TCP.
• Ping and perform traceroutes to SIP/RTP server addresses.
• Run a packet capture (Wireshark) if available. Packet loss is a major culprit for call failures.

 4. Review Device and Firmware Configuration

• Ensure phone firmware is up to date.
• Check SIP session timers (Session-Expires) and keep-alive intervals.
• For ATAs or SIP endpoints, confirm NAT keep-alive is enabled.
• Validate SIP proxy and outbound proxy settings 

Recommendations

Dropped calls are often linked to signalling path instability, NAT/firewall configurations, or SIP session management. Combining call trace analysis with local network and endpoint inspection allows most dropped call issues to be quickly diagnosed and resolved.

Escalation

If the issue consistently occurs on calls to specific numbers or carriers:

• If you have one, share the Call Trace to extract Call-ID and SIP routing path.
• Record the extensions or numbers affected.
• Record the timestamp and time zone.
• Record symptoms and duration.
• Call Trace link.
• Record any relevant IPs or device models.
• Identify any SIP 5xx or 4xx responses on their leg of the call.