Short Message Service
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.
What It Defines
SMS defines store-and-forward 160-character (7-bit GSM encoding) or 140-byte (8-bit) text messaging over cellular networks. TS 23.040 covers the SM-TL (transfer layer), SM-RL (relay layer), PDU format, concatenated SMS (UDH), validity periods, delivery reports, and the SMSC (Short Message Service Centre) architecture.
Canonical (Normative)
Convenient (Practical)
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
GSM underpins SMS delivery, international roaming, and network fallback. Understanding A-interface, MSC, and MSISDN is essential for any telecom or SMS gateway integration.
RCS is replacing SMS for brand messaging, OTP, and consumer engagement. Every major US/EU carrier now supports RCS Universal Profile. If you build SMS communications today, you need to understand RCS UP for 2025+ deployments.
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.