Troubleshooting VoIP problems: no ringing, one-way audio and dropped calls
As of October 18, 2026. If a VoIP conversation does not take place or one side cannot hear anything, orderly isolation is more helpful than making changes based on suspicion. The guide separates call setup, audio and network environment. It does not replace checking the specific system and router configuration.
Short conclusion
First check what exactly is going on: Ringing and connection setup are done via SIP signaling; the conversation audio is transmitted as an RTP media stream. A successfully connected call therefore does not prove that the audio transmission works in both directions. Compare one affected device with another, note the location, time and network connection and narrow down the symptom. Do not open any router ports as a precaution and do not switch off protective functions across the board.
Classify symptom first
Placetel describes SIP for call signaling – such as ringing, transferring and hanging up – and RTP for audio transmission. The IETF also maintains SIP as a protocol for setting up, changing and ending sessions; RFC 3550 describes RTP for real-time data. The following table therefore lists test directions, not a reliable remote diagnosis.
| Observation | First test level | Meaningful next comparison |
|---|---|---|
| No ringing or no connection established | Call destination, routing, registration and SIP signaling | Call a second extension; check whether several users or just one device are affected. |
| Call is on but no one hears anything | Audio transmission and RTP in both directions | Perform a cross-check with a second device and a different network connection. |
| Only one side listens | Media transfer direction, network path and device settings | Keep track of which side hears whom; then compare device, network and time. |
| Sound is delayed, choppy or calls break down | Network path stability and concurrent utilization | If possible, compare WLAN and cable, note the VPN status and compare several test times. |
| Problem only affects one extension | End device, user mapping, headset or local configuration | Compare with a working extension without sharing access data or customer data. |
Systematically isolate errors
- Describe the error pattern. Note: outgoing or incoming call, no ringing or no tone, one- or two-way audio, affected extensions, terminal device, time and whether the error occurs permanently or sporadically. A specific symptom is much more helpful for support than “telephony doesn’t work.”
- Start with a comparison test. Test a second extension and - if available - another telephone or softphone. If the fault only occurs on one device, the next test will be there or at its connection. If multiple devices are affected at the same time, consider the shared facility or shared network path. That narrows it down, but doesn't prove a cause.
- Compare network connections. Check whether WLAN, wired network or a VPN is used. Placetel's help lists WLAN, VPN, router configuration and SIP ALG as possible influencing factors. Only change one variable at a time and document the result. Which ports or rules are required depends on the current service and device configuration; Please adopt the current official specifications.
- Check status and changes. Ask the team whether routers, firewalls, Internet connections, devices or policies have recently been changed. Check the provider's official service status and their current network requirements. An inconspicuous status page does not rule out local disturbances.
- Escalate in a targeted manner. Collect error time, affected extensions, device type and the comparison tests carried out. Do not share passwords, access tokens, or full call details publicly. In the event of a business-critical disruption, the responsible administration should consult the provider's current documentation or call in qualified support.
Common Misconceptions
- “The call is connected, so the telephone system is OK.” Signaling and audio are separate test levels; an accepted call does not say that both audio directions work.
- “I just open all VoIP ports.” Blanket port forwarding can create unnecessary attack surfaces and does not solve every cause. The official requirements for the specific service and your own network structure are decisive.
- “It has to be up to the provider.” Provider status, end device, WLAN, VPN and local router/firewall configuration must be distinguished from each other. Comparative tests help to narrow down the responsible authority.
Complementary Placetel facility and support
If you are planning a new cloud telephone system or would like to have an existing setup checked, you can find our Telecommunications and Placetel overview. The Placetel professional cloud telephone system and - if messaging and meetings are also needed - Webex Voice for Placetel go well with this. Our PBX setup, the Placetel setup page and the Quotation request are available for setup. Additional support is described in the maintenance contract for up to 20 extensions or the maintenance contract for 21 extensions or more. For frequent or incoming calls outside of business hours, a voice assistant for Placetel can also be checked; It does not replace fault diagnosis of the telephone system.
Video: Basic functions of a Placetel system
The following official Placetel video shows basic settings such as routing plan, announcement and availability. It is a supplemental setup aid, not a guide to troubleshooting every audio or network error.
Video source: Placetel - set up basic functions in under 5 minutes. Channel: Placetel's YouTube channel. The video is embedded unchanged via YouTube; Viewing and title verification via oEmbed on October 18, 2026. If the player is blocked, open the video directly on YouTube.
Sources and test basis
- Placetel: Network configuration - SIP/RTP basics and possible influences of the network environment.
- IETF RFC 3261: SIP – Session Initiation Protocol.
- IETF RFC 3550: RTP – A Transport Protocol for Real-Time Applications.
- Placetel online help - current instructions and service information.
- Placetel: Set up basic functions in under 5 minutes - official video channel, routing and basic system functions.
Review date: October 18, 2026. Protocol bases were aligned against IETF specifications and Placetel help. The diagram is its own schematic summary, not a test and not a representation of a real user interface.