G.703 is a 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 (64 kbps). For information about E0 audio see G.711.
G.703 is typically transported over balanced 120 ohm twisted pair cables terminated in RJ48C jacks. However, some telephone companies use unbalanced (dual 75 ohm coaxial cables) wires, also allowed by G.703.
G.704 uses synchronous frame structures used at 1544, 6312, 2048, 8448 and 44 736 kpbs hierarchical levels.