G.703 is a 2016 ITU-T standard for transmitting voice or data over digital carriers such as T1 and E1. G.703 provides specifications for pulse code modulation (PCM).
G.703 also specifies E0 (64kbit/s). For information about E0 audio see G.711.
G.703 is either transported over 75 ohm co-axial cable terminated in BNC or Type 43 connectors or 120 ohm twisted pair cables terminated in RJ48C jacks. The choice is carrier- and region-dependent.