GSM / 2G
GSM underpins SMS delivery, international roaming, and network fallback. Understanding A-interface, MSC, and MSISDN is essential for any telecom or SMS gateway integration.
What It Defines
The Global System for Mobile Communications defines the 2G digital cellular network: TDMA air interface, SIM architecture, MSISDN numbering, HLR/VLR location registration, A5/1 and A5/3 encryption, and the SMS transport layer. First digital cellular standard, deployed commercially in 1991.
Canonical (Normative)
Related References
The global collaboration of telecommunications standards bodies that produces the mobile network specifications: GSM/EDGE, UMTS/HSPA, LTE/4G, 5G NR, and IMS. Technical specifications (TS) and reports (TR) are freely available at 3gpp.org. Releases (Rel-8, Rel-15, Rel-17…) provide versioned capability sets.
Related Specs
SMS is how billions of people receive OTP codes, alerts, and notifications. Understanding PDU format, encoding (GSM-7 vs UCS-2), and concatenation is essential for any platform sending SMS at scale via Twilio, AWS SNS, or direct SMPP.
LTE is the dominant global mobile network. VoLTE, QoS bearers, and EPC architecture are directly relevant when building mobile-connected applications, IoT modules, or carrier infrastructure.
Every phone number your app touches — Twilio, AWS SNS, WhatsApp, SIP — uses E.164. Getting number formatting and parsing right (libphonenumber patterns) requires understanding CC/NDC/SN structure.