Most engineers know the QCI numbers, but few understand what they actually mean on a real LTE network.
Hereโs a simple, table-free way to look at QCIs โ keeping icons and normal bold as requested.
First: QCIs = Behavior Profiles
Each QCI defines how the network treats the traffic, based on:
โข Priority
โข Packet Delay Budget (PDB)
โข Packet Loss Rate (PLR)
โข Scheduling behavior
โข GBR / Non-GBR
Think of them as โtraffic personalities.โ
QCI 1 โ VoLTE RTP (Strictest Real-Time)
โข GBR
โข 100 ms PDB
โข Very low PLR
โข Immediate scheduler grants
If QCI 1 suffers, voice suffers instantly.
QCI 2 โ Real-Time Interactive (Video Call, Gaming)
Similar to QCI 1 but slightly softer.
Used for:
โข Video telephony
โข Interactive gaming
โข Low-latency apps
QCI 5 โ IMS Signaling
โข Non-GBR
โข Extremely high priority
โข 100 ms PDB
If QCI 5 is delayed โ IMS registration, SIP INVITE, and VoLTE setup start failing.
QCI 6, 7, 8, 9 โ Internet/Data Traffic
All Non-GBR
Perfect for:
โข Browsing
โข Social media
โข Background traffic
Most devices default to QCI 9 for general data.
QCI 4 โ Streaming / Buffered Video
โข Non-GBR
โข Lower priority
YouTube/Netflix can buffer โ no strict delay needed.
QCI 3 โ Used by Some Operators for Video/Audio Streaming
More priority than QCI 4
Less strict than QCI 1/2
QCIs 65, 66, 69 โ Dedicated EPC Enhancements
Used for:
โข Mission-critical traffic
โข Enterprise APNs
โข Special slices in early 5G NSA
Practical Troubleshooting Rule
If QCI 1 has problems โ check GBR capacity + scheduler.
If QCI 5 has problems โ check signaling, congestion, PGW/MME delays.
If QCI 9 has problems โ check eNodeB load + backhaul.
QCIs tell you where to investigate before you even open the trace.
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