ISDN Protocols
ISDN protocols fall in one of three categories: E-series protocols, I-series protocols and Q-series protocols.
• The E-series protocols include E.163 and E.164, both of which are used for the international telephone numbering plan and international ISDN addressing.
• The I-series protocols include the I.100 series and I.400 series. The I.100 series includes a number of recommendations that describe and define the principles and the terminology used in ISDN, while the I.400 series is mainly concerned with standardisation of the User-Network Interface (UNI).
• The Q-series protocols include Q.921 and Q.931. Q.921 is also referred to as Link Access Protocol - D Channel (LAPD) and is the data-link protocol used over ISDN's D channel while Q.931 is used for the ISDN call establishment, maintenance, and termination of logical network connections between two devices.