ITU X.21:1992
ITU X.21:1992 Interface Between Data Terminal Equipment And Data Circuit-terminating Equipment For Synchronous Operation On Public Data Networks
Table of Contents
Preface1Scope
2DTE/DCEphysicalinterfaceelements
3Alignmentofcallcontrolcharactersanderrorchecking
4Elementsofthecallcontrolphaseforcircuitswitched
service
5Datatransferphase
6Clearingphase
7Testloops
AnnexA-Interfacesignallingstatediagrams
AnnexB-Interfacesignallingsequencediagramsand
time-outoperations
AnnexC-DTEtime-limitsandDCEtime-outs
AnnexD-Formatsofselection,callprogressand
DCE-providedinformationsignals
AnnexE-InterworkingbetweenDTEsconformingto
RecommendationsX.21andX.21bis
AnnexF-CodingofcallprogresssignalsandDTEprovided
information
AnnexG-Facilityrequest,indicatorandparametercoding
AnnexH-InformationcontentofDCE-providedinformation
AnnexI-Referenceandtransitiontables