How to Fix One-Way Audio After Changing SIP Server IP on NEC SL2100
Introduction
We migrated our NEC SL2100 SIP environment from the default network to our own IP range to support SIP phones.
After changing the SIP server or migrating the PBX to a different IP subnet, we experienced one-way audio during SIP calls. The issue was traced to Program 84-26 (VOIPDB Basic Setup - DSP), where the DSP IP address still pointed to the previous network.
Symptoms
After changing the SIP server IP:
| Test | Result |
|---|---|
| Internal Call (100 ↔ 101) | ✅ Two-way audio |
| Incoming SIP Call | ❌ Remote party could not hear extension |
| Outgoing SIP Call | ❌ Remote party could not hear extension |
| Hold Music | ✅ Remote party could hear music |
| Direct phone connected to TM Biz Voice | ✅ Working normally |
Cause
The SIP server IP address had been changed successfully.
However, Program 84-26 (VOIPDB Basic Setup - DSP) was still using the old IP address.
Because the DSP continued sending RTP audio using the old IP configuration, SIP calls experienced one-way audio even though registration and call setup worked correctly.
Solution
Login to NEC SL2100 and Navigate to:
84-26
VOIPDB Basic Setup (DSP)
Update:
01 - IP Address
to the same valid IP address used by the SIP network.
Example:
Old
172.16.0.20
↓
New
192.168.x.x
After saving the changes:
- Reboot the NEC SL2100.
- Restart the SIP phones (if required).
- Test incoming and outgoing calls again.
Result
After updating Program 84-26:
✅ Two-way audio restored.
✅ Incoming calls working normally.
✅ Outgoing calls working normally.
✅ SIP phones working correctly on the new network.
Important Note
Whenever changing the SIP network or moving the PBX to another subnet, remember to verify that Program 84-26 (VOIPDB Basic Setup - DSP) is using the correct IP address.
If this setting still points to the previous network, one-way audio issues may occur even though SIP registration is successful.
Troubleshooting Checklist
Before changing additional SIP settings, verify the following:
- ☑ SIP Trunk is registered.
- ☑ Internal extension calls work normally.
- ☑ Hold Music can be heard.
- ☑ Program 84-26 → IP Address matches the current LAN IP.
- ☑ Reboot the PBX after changing the DSP IP address.
Note: If some of the screenshots or steps viewed here are different from the ones in the current system, this is due to our continuous effort to improve our system from time to time. Please notify us at info@ksecure.com.my or WhatsApp 019-390 6861 (Emrick), we will update it as soon as possible.
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