One-Way Audio During Calls (No Sound)
Let's examine a situation where a call seems to have connected, buttons are being pressed, the timer is running — but there is actually no conversation. More precisely, audio works for only one side. Someone cannot hear someone else, creating the feeling that telephony is "half broken."
How the Issue Appears
Agents usually describe the problem very emotionally and in slightly different ways, but the meaning is the same:
- "Telephony isn't working"
- "I can't hear the client"
- "The client can't hear me"
- "There's no sound in the call at all"
From the outside, it looks strange: the call is connected, the conversation is ongoing — but someone is silent. Sometimes both sides are silent, sometimes only one side.
Clarifying the Symptoms
To avoid guesswork, ask two simple questions:
— Does adjusting the volume make any difference?
— Is there sound in the call recording?
The typical answer is:
"Adjusting the volume doesn't change anything."
"There's no sound from one side in the call recording."
This is important: if there's no sound even in the recording, the problem is not with the speaker or headphones.
What Is Actually Happening
If you check the logs, the picture looks quite "healthy" at first glance.
- The call connects successfully — incoming or outgoing.
- All SIP events are present, with no errors.
- Diagnostic information and call statistics are available.
But then a key detail emerges: the number of packets sent or received is zero.
In other words, the call technically exists, but no audio is being transmitted between the parties.
How to Diagnose
First, confirm the symptom itself:
- The call connects.
- One side (or both) cannot hear anyone.
- Adjusting the volume doesn't help.
- The call recording lacks audio from one side.
Then, check the logs and call statistics.
If packets are not being sent or received — this is exactly the one-way audio situation.
Possible Causes
In the context of this issue, consider the following possibilities:
- Working behind a firewall or NAT, where the PC can send but cannot receive;
- Incorrect addressing through NAT;
- RTP ports are blocked;
- Antivirus blocking traffic;
- Incorrect audio devices selected;
- The operating system lacks microphone access.
What to Do
In such cases, try these solutions:
- Configure SIP client operation through NAT (IP rewriting, STUN).
- Check and configure the allowed RTP port range.
- Add the SIP client to trusted applications in the firewall and antivirus.
- Check audio device settings and OS permissions.
If you cannot resolve it on your own, involve a system administrator or provider to investigate why RTP traffic (voice packets) is not reaching the agent.
Key Point
If the call connects but there's no sound on one side, always check the RTP packet statistics.
The presence of a successful SIP session with zero RTP packets almost always indicates network issues such as blocked ports, NAT problems, or firewall restrictions.