1 This International Standard provides a guide for signal quality requirements for serial data transmission at the interface between start-stop transmission Data Terminal Equipment (DTE) and Data Circuit-terminating Equipment (DCE). The interface referred to in this International Standard conforms to CCITT Recommendations V.24 (telephone networks), X.24 (data networks) and the transmitting/receiving equipment to CCITT Recommendations V.21, V.22, V.22 bis, V.23, V.26 ter, X.20, X.20 bis together with V.28, or X.20 together with X.26 (= V.10) and/or X.27 (= V.11).
The signal quality requirement is limited to start-stop transmission at the interface with asynchronous DCEs or synchronous DCEs such as CCITT type V.22. Signal quality pertaining to synchronous DTEs is not part of this International Standard.
2 This International Standard recognizes the need to have a number of different performance categories of signal quality depending on the type of timing used. Two types of timing are distinguished, electronic timing and mechanical timing, and the appropriate characteristics are indicated in the table.
Four signal quality categories are defined for transmitting DTEs. The categories I and II have been chosen to cover equipment using all electronic signal generation. Category II is for the attachment of start-stop transmitting DTEs to synchronous DCEs. Categories P1 and P2 are provided for DTEs using mechanical timing. Complementary categories for receiving DTEs are shown under the headings A, B, PA and PB.
The signal quality characteristics apply to data circuits regardless of whether or not multiplexing equipment is includ-ed. They do not apply to tandem data circuits where no signal regeneration is provided between interconnected sections.
A number of signal quality categories, therefore, are defined for transmitting equipment and for receiving equipment, the intention being that any receiving equipment may operate with any transmitting equipment, the actual selection being dependent
upon such factors as channel characteristics, and economic considerations of the data communication system.
3 This International Standard is of particular importance when the transmitting or receiving equipment are furnished by different oganizations. It does not attempt to indicate what action, if any, is to be taken if the limits are not met, but it is intended to provide a basis for agreement between parties involved.
4 This International Standard does not describe the signal quality of the DCE or the line associated with it. Neither does it describe any requirement for an acceptable bit error r?te.