GTP-C and GTP-U Finally Separated Control from Subscriber Traffic
GTP made more sense once I stopped treating it as one protocol and separated tunnel-control signalling from the packets that actually carry user traffic.
LTE
QCI 5 for IMS Signalling and QCI 1 for Voice Made QoS Concrete
VoLTE QoS became easier to understand when I separated the persistent IMS signalling bearer from the dedicated low-latency bearer created for voice media.
Open5GS Made the EPC Feel Like a Set of Services Instead of One Big Core
Breaking the EPC into MME, HSS, SGW, PGW and PCRF roles made LTE core traffic much easier to follow in captures and logs.
APNs, PGW Selection and the Path to the Data Network
An APN is more than a label on the handset; it influences how a subscriber session reaches a packet gateway and an external data network.
Dedicated Bearers Stopped Feeling Abstract Once I Traced the Create Bearer Request
Tracing a Create Bearer Request tied policy, QoS and user-plane classification together in one procedure.
The S6a Interface Connected LTE Authentication to the HSS for Me
Tracing S6a made the HSS feel less like a subscriber database and more like an active control-plane participant in LTE attach and mobility.