ISDN Standards

From the end of the 1960s and up to the mid 1980s, a comprehensive set of standards defined the ISDN technology. The T sector of the International Telecommunication Union (ITU-T) was created in 1993 as a replacement for the former Comit Consultatif International T l phonique et T l graphique (CCITT) with an initial 15 study groups. This organization issued protocols in three different series as defined in the sections that follow.

E-Series

E-Series protocols, developed for overall network operation, telephone service, service operation, and human factors, standardize the telephone networks for ISDN. ITU-T recommendation E.167 for example, defines the ISDN network identification codes.

I-Series

I-Series protocols are grouped into three main categories and are designed for the standardization of concepts, terminology, and general methods related to users, User -Network Interfaces (UNIs), and Network-to-Network Interfaces (NNIs). I-Series standards, which are designed for ISDN, start from I.110 and end with I.762. I.431, for example, defines the Primary Rate Interface (PRI), and I.432 defines the BRI.

Q-Series

Q-Series protocols, which are designed for switching and signaling, define the standards of switching and signaling schemes and techniques. The Q.921 standard, for example, describes the ISDN data-link processes of LAPD, which functions as Layer-2 processes in the International Organization for Standardization/Open System Interconnection (ISO/OSI) reference model. Q.931 specifies ISO/OSI reference model Layer 3 functions.