SIP trunking has changed the landscape of communication for businesses and is an efficient, flexible alternative to physical phone lines. But like any other technology, SIP trunking brings about its challenges. So if you are facing some SIP trunking issues, you are certainly not alone! Common issues and their remedies are discussed below.
1. Call Quality Issues (Jitter, Latency, and Packet Loss)
Indicators:
- Delayed audio
- Choppy or robotic voice
- There was an echo or static.
Causes & Fixes:
Congested Network: SIP trunk relies on an established internet connection under a reasonable load. Other data traffic interferes with voice quality. Use Quality of Service (QoS) settings in your router to prioritize voice traffic.
Not Enough Bandwidth: Verify that the internet connection can sustain the present volume of calls. If not, consider increasing the bandwidth.
Jitter and Packet Loss: Consider using a Jitter Buffer that can take some of the rough edges of the inconsistent performance. If Packet Loss continues to be a culprit, check the network for faulty cables or routers that might be configured incorrectly.
2. One or the Other, or No Audio
Symptoms:
- One side of the call can hear each other, while others can’t.
- There is dead air after the call is dialed.
Causes & Fixes:
NAT Issues: SIP is highly dependent upon working NAT settings. Make sure that your firewall is processing SIP packets properly.
Firewall Blocking RTP Packets: Inspect firewall rules and make ports open as required (usually UDP 5060 for SIP, and a range for RTP).
Codec Mismatch: Confirm that both endpoints support the same audio codecs, commonly G.711 and G.729.
3. Registration Failures
Symptoms:
- The SIP trunk will not connect.
- Authentication errors.
Causes & Fixes:
Bad Credentials: Confirm your username, password, and domain are correct.
Firewall Blocking SIP Traffic: Allowlist SIP provider IPs, and make sure your PBX is not blocked.
SIP ALG Interference: Some routers come with a SIP ALG Application Layer Gateway feature that modifies SIP packets, generating failures in most cases. Disable in Router settings.
4. Dropped Calls
Symptoms:
- Random drops of calls.
- Drop calls after a fixed time for example 30 seconds, or 60 seconds.
Causes & Fixes:
SIP Session Timeout: Align session timers with those of your provider.
Firewall Timeout Settings: Certain firewalls close SIP sessions too soon. Extend SIP session timeouts.
Issues with the ISP: Calls will drop if the Internet connection is unstable. Carry out a ping test throughout the day for packet loss.
5. Calls Not Connecting or Failing
Symptoms:
- Calls failed.
- Fast busy tone/immediate disconnect.
Causes & Fixes:
Dial Plan Error: Ensure that numbers outgoing from your PBX are formatted correctly (examples: country/area codes need to be added where necessary).
Provider Issues: Sometimes the matter is on the provider’s end. Check their status page or contact their support.
Blocked Caller ID: Some carriers block calls from numbers that do not provide an incoming caller ID. Ensure that your SIP trunk is sending any valid caller ID.
6. Calls-Related Echo
Symptoms:
- A person on the other side hears his voice.
Causes & Fixes:
Acoustic Echo: Reduce speaker volume or use a headset.
Network Latency: High delay may result in echo. Optimize network settings; do not allow unnecessary traffic.
Mismatch of Impedance: In the case of using an Analog Adapter, check impedance settings.
7. Faxing Issues over SIP (T.38 Problems)
Symptoms:
- Fax transmissions either fail or send poorly with only partial pages.
Causes & Fixes:
Codec Issues: Faxes do not work well with compressed codecs such as G.729, but work with G.711 or use T.38 encoding within SIP for reliable work.
Packet Loss: Slight loss is disruptive to faxing. Confirm connections are sound.
Final Thoughts
SIP trunking is such an excellent tool, but sometimes troubleshooting can be challenging. Most issues tend to arise either from network settings, firewall settings, or some limitations placed by the service provider. While troubleshooting these common issues involves due diligence, it will in turn help guarantee a quality voice service from here on.
As a next step, if problems persist, it would be a good idea to contact your SIP provider’s support. They can help further identify any carrier-side issues that may be not visible to your side.
