The recommendation V.24 of UIT-T (ex CCITT) defines the circuits of junctions used during the exchange of information between a terminal of data (called DTE in English for Data Final Equipment or ETTD in French) and equipment of communication (called DCE in English for Data Circuit terminating Equipment or ETCD in French).

In general a numerical junction between a ETTD and a ETCD of level 1 (in accordance with OSI model) is defined by 3 parameters (electric circuits, levels and the stitching). For example, to make a data transmission between a terminal (ETTD) and a modem of the type A.F (ETCD), the junction could be V24/V28/iso 2110.

It is necessary to understand by:

• V24 the definition of the circuits of junctions series 100 (102 common return, 103 emission of data, 104…)
• V28 the electric standard dissymmetrical junction (a circuit of data (103-ED/TD and 104-RD/RD) must have a ddp < with -3V to represent the binary state 1 and > +3V for the binary state 0 )
• Iso 2110 relates to the assignment of these circuits of junctions in a connector dB 25 points (ex: ED/TD 103 stitch 2)

Bonds

See RS-232, DB9/DB25 or Recommendation.