G.703 is a ITU-T standard originally written in 1972[1] but subsequently revised a number of times since.

It defines a physical and electrical interface used for encoding voice or data over 75 ohm co-axial cable terminated in BNC or Type 43 connectors or 120 ohm twisted pair cables terminated in RJ48C jacks.

These are organised as part of a hierarchy of carriers defined in G.702.

A G.703 E1 link is typically, though not necessarily, framed using the G.704 standard which divides the data stream into time slots.

Typically, each time slots represents an E0 (64 kbit/s) voice channel encoded using pulse-code modulation (PCM).