Abstract Syntax Notation One (ASN.1) is a standardized interface description language used in telecommunications, networking, and cryptography. In 3GPP LTE and 5G NR, all RRC protocol messages (e.g. SIBs, Setup, Configuration, and Measurement Commands) are defined formally using ASN.1 syntax.
3GPP RRC ASN.1 SyntaxRRC schemas define structured messages using sequences (`SEQUENCE`), choices (`CHOICE`), enumerations (`ENUMERATED`), and primitive types (integers, strings). Spec definitions are parsed dynamically from TS 38.331 and TS 36.331 specifications and compiled here for quick lookups.
BER vs. PER encoding rulesWhile certificates and PKCS cryptographic keys use **BER/DER (Basic/Distinguished Encoding Rules)** which contain explicit tag and length prefixes, 3GPP wireless signals use **UPER (Unaligned Packed Encoding Rules)**. UPER strips tags and aligns elements to the nearest bit rather than byte to conserve radio airtime, requiring the pre-compiled schema to decode.