VoLTE failures are rarely isolated.
They ripple across multiple network nodes, and unless you trace each layer, the root cause stays buried.
Here’s a proven node-by-node strategy to troubleshoot VoLTE issues – from SIP delays to silent calls 
eNodeB – Radio Layer Issues
Check: RRC logs for drops, poor SINR/RSRP, or T304 timer expiry
Look for:
Uplink/Downlink gaps
Handover failures
Bearer mapping consistency post-HO
Cross-check with X2/S1 logs if HO occurred
MME – EPC & NAS Signaling
Check: Bearer setup/modify/delete events
Look for:
Missing Create Dedicated Bearer Request
Unexpected Bearer Release Command mid-call
GTP-U Tunnel tear-down during ongoing RTP
PGW / SGW – QoS & IP Transport
Check: Gx/Gy sessions, IP flow continuity
Look for:
DSCP markings mismatch (QoS downgrade)
PCRF rejects or modifies QCI mapping
NAT/PAT logs for session expiry or collision
IMS Core (P/I/S-CSCF) – SIP Signaling & Session Control
Check: Full SIP call flow
Look for:
SIP 408, 487, 503 → Where exactly it originates
Registration refresh or session collision
Delayed 183/200 OK or missing ACK
RTP Media Path – Quality & Continuity
Check: Packet loss, jitter, codec negotiation
Look for:
Asymmetrical RTP flow
Codec mismatch (AMR-WB vs NB)
Media stops while SIP session remains alive (NAT/Firewall)
Your VoLTE Trace Checklist
RRC logs
NAS signaling
Bearer management
GTP-U paths
SIP messages
RTP stream analysis
What’s your go-to first step when a user says “the call dropped”?
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