The CCITT, considering (a) that the Recommendation X.1 defines the synchronous user classes of services to be provided by a publicdata network; (b) that Recommendation X.50 defines some envelope data formats which can be used in public data networks; (c) that the use of a full 64 kbit/s data stream for the transmission of a single lower speed synchronous data channel may be economically attractive in some applications, when a low cost 64 kbit/s channel is available; (d) that for customer access to circuit switched data services in the ISDN, a method for adaption of synchronous user data rates to a 64 kbit/s bearer rate is defined in Recommendation X.30, but that in certain applications as mentioned under (c) a simpler method is preferred.
ITU-T X.57-1988 Referenced Document
ISO/IEC 8650-2:1995 Information technology — Open Systems Interconnection — Protocol specification for the Association Control Service Element: Protocol Implementation Conformance Statement (PICS) proforma*， 1995-07-13 Update
ISO/IEC 9594-1:1990 Information technology; open systems interconnection; the directory; part 1: overview of concepts, models and services*， 1990-12-01 Update
ISO/IEC 9646-7:1995 Information technology - Open Systems Interconnection - Conformance testing methodology and framework - Part 7: Implementation conformance statements*， 1995-09-01 Update
ITU Data architecture of one software system Study Group 17*， 2007-02-01 Update
ITU-T X.200-1994 Information Technology - Open Systems Interconnection - Basic Reference Model: the Basic Model - Data Networks and Open System Communications Open Systems Interconnection - Model and Notation 64 pp*， 1994-01-01 Update
ITU-T X.247-1994 (WITHDRAWN) Information Technology - Open Systems Interconnection - Protocol Specification for the Association Control Service Element: Protocol Implementation Conformance Statement (PICS) Proforma - Data Networks and Open System Communications Open Syst*， 1994-07-01 Update
ITU-T X.249 Information Technology - Open Systems Interconnection - Remote Operations: Protocol Implementation Conformance Statement (PICS) Proforma - Data Networks and Open System Communications Open Systems Interconnection - PICS Proformas 17 pp*， 1995-04-19 Update
ITU-T X.581-1995 Information Technology - Open Systems Interconnection - the Directory: Directory Access Protocol - Protocol Implementation Conformance Statement (PICS) Proforma - Data Networks and Open System Communications Directory 28 pp*， 1995-01-01 Update
ITU-T X.57-1988 history
1988ITU-T X.57-1988 METHOD OF TRANSMITTING A SINGLE LOWER SPEED DATA CHANNEL ON A 64 kbit/s DATA STREAM