The IP Multimedia Subsystem (IMS) is the platform behind modern mobile voice. VoLTE carries calls over the LTE packet core, VoWiFi extends the same IMS services over untrusted Wi-Fi access through the ePDG, and VoNR does the same over 5G Standalone. All of them depend on SIP signalling between the device and the CSCF chain, on Diameter or HTTP/2 interfaces to subscriber data and policy, and on correctly provisioned application servers.
When voice services fail, the root cause can sit almost anywhere — in the device, the access network, the packet core, the IMS core or an interconnect. KL-UK helps teams isolate faults methodically and validate that services behave as designed.
Capabilities
- IMS architecture and integration
- VoLTE engineering support
- VoWiFi and Wi-Fi Calling
- SIP signalling analysis
- Registration and authentication troubleshooting
- Call setup and call-flow investigation
- Voice service validation
- Interoperability testing
- Fault isolation
- Technical and operational support
Typical IMS and voice issues we investigate
- IMS registration failures, including IMS-AKA authentication challenges and IPsec security association problems
- Calls that fail during setup, ring without answer or drop after connection
- Missing or incorrect dedicated bearers for voice media
- One-way or no audio caused by SDP negotiation, codec or media path problems
- VoWiFi failures at the ePDG, including IKEv2 and tunnel establishment issues
- Supplementary service behaviour that differs from the subscriber profile
Evidence-led troubleshooting
We work from SIP and Diameter traces, device logs and node logs to reconstruct the full call flow — REGISTER, INVITE, provisional responses, PRACK and UPDATE where preconditions apply, through to the final response and ACK. Comparing what happened with the expected procedure usually pinpoints where a call went wrong and which element is responsible.
Findings are recorded with the supporting trace evidence, so your engineering, vendor and operations teams can act on them with confidence.
How an engagement works
- Discuss — tell us about your requirements, environment and timescales.
- Agree scope — we confirm deliverables, approach, availability and any onsite or on-call arrangements.
- Deliver — we carry out the agreed engineering, testing or support activities.
- Document and hand over — findings, configurations and procedures are recorded for your teams.
Further reading
Read our article IMS Fundamentals: Registration, Signalling and Voice Services.