Telecom Systems
SS7 and SIGTRAN, SIP, SMPP, USSD, SMSC, Asterisk and core telco architecture.
Telecom Systems articles
GTP and the Mobile Packet Core
GTP is the tunnelling protocol that carries subscriber data through the mobile core. Here's GTP-C (signalling) vs GTP-U (user plane), TEIDs, bearers, and GTP security.
October 24, 2026eSIM and Remote SIM Provisioning
An eSIM is a reprogrammable chip (eUICC) that holds downloadable operator profiles. Here's the GSMA RSP architecture — SM-DP+, SM-DS, LPA — and the profile lifecycle.
October 24, 2026VoLTE and IMS Registration Flow
VoLTE is voice as SIP over the LTE data network, anchored in IMS. Here's the CSCF roles, the SIP REGISTER over IPsec, the QCI-1 bearer, and the common failure points.
October 24, 2026SS7 Security and Signalling Firewalls
SS7 was built for a closed club of trusted operators. That assumption broke. Here's the attack classes and what a signalling firewall (per GSMA FS.11) actually filters.
October 24, 2026RTPengine for NAT Traversal and Transcoding
RTPengine is a media proxy that rewrites SDP and relays RTP so calls work through NAT. With a kernel module it forwards packets at line rate. Here's how it fits with a SIP proxy.
October 24, 2026Number Portability and ENUM
A ported number no longer belongs to the original operator's range, so routing needs a database lookup. Here's MNP mechanics and how ENUM maps numbers to SIP.
October 24, 2026Kamailio vs Asterisk: When to Use Each
Kamailio routes SIP signalling at massive scale but touches no media. Asterisk is a full PBX with media. Most real deployments use both — here's the split.
October 24, 2026SS7 vs Diameter
SS7/MAP handled 2G/3G subscriber and mobility signalling; LTE and IMS moved to Diameter. Same jobs — authentication, location, policy, charging — different protocol.
October 24, 2026SMPP: Bind Types and Message Flow
SMPP is the protocol between an application and an SMSC. Learn the three bind types, the submit_sm/deliver_sm flow, and how DLRs and windowing actually work.
October 24, 2026SS7 vs SIGTRAN
SS7 is the signalling network behind calls and SMS; SIGTRAN is SS7 carried over IP. Same upper layers, different transport — here's the stack and the mapping.
October 24, 2026USSD Session Flow, Explained
USSD is the *123# menu system. It's session-based, real-time, and network-mediated — here's the message flow from dial to menu to selection, and where apps plug in.
October 24, 2026Telecom Charging: Online vs Offline
Prepaid needs a real-time credit check before the call connects; postpaid just records what happened. Here's the OCS reservation model and the offline CDR pipeline.
October 24, 2026