SQN Sync in IMS AKA Was the Authentication Detail I Kept Missing
IMS AKA stopped looking like a simple password check once I traced the sequence number and resynchronization path.
TOPIC
Mobile Networks
Lessons, explainers, experiments, and implementation notes.
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.
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.
APN in LTE and DNN in 5G Core Are Similar Until the Architecture Matters
APN and DNN both identify data-network intent, but the surrounding EPC and 5GC procedures are different enough that treating them as pure renames is misleading.
freeDiameter Taught Me Why a DRA Is More Than a TCP Proxy
Diameter routing depends on realms, applications and peer capabilities, so a routing agent has to understand more than destination IP addresses.
Gx Charging Rules Only Made Sense After I Followed the TFT
A charging rule becomes concrete when its packet filters are followed all the way into bearer treatment.
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.
PCF and Policy Control Made 5G Sessions Feel Less Static
Policy is not just a config file on the gateway; in 5GC it can actively influence session behavior through dedicated network functions.
Diameter Started Making Sense When I Followed CER and CEA First
Before looking at subscriber procedures, I needed to understand how Diameter peers identify themselves, advertise applications and establish a usable relationship.
Walking a VoLTE Call End to End Connected the EPC, IMS and RTP Pieces
Following one VoLTE call from LTE attachment through IMS registration, SIP session setup, bearer creation and RTP finally connected the year's separate labs.
A 5G Registration Trace Is Easier When I Follow the State Machine
Following registration as a state transition is more useful than memorizing a long list of NAS messages.
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.
PFCP Was the Missing Link Between the SMF and UPF
5G user-plane programming became clearer once I followed PFCP instead of treating the UPF as a static router.
CPRI and eCPRI Made the RAN Transport Boundary Much Clearer
The move from digitized radio samples toward packetized fronthaul explains a lot about modern RAN architecture.
N2 and N3 Helped Me Draw a 5G Call Path Without Hand-Waving
Separating N2 signalling from N3 user traffic made the gNB-to-core boundary much easier to troubleshoot.
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.
Charging Records Are Easier to Trust When I Trace the Event That Created Them
Usage records become meaningful only when they can be tied back to the session, rule and network event that produced them.
32x32 MIMO Made More Sense When I Stopped Counting Antennas
Large antenna arrays are interesting because of beams, spatial layers and RF chains, not because the front panel contains a big number of elements.