A European format for digital transmission. E1 supports signals at 2 Mbps (32 channels at 64Kbps, with 2 channels reserved for signaling and controlling), versus the T1, which carries signals at 1.544 Mbps (24 channels at 64Kbps).
Allows users tracking the condition of the other telephone or the subscriber, for example, there will appear a signal on the screen of the telephone device informing that the subscriber is on the line and is temporarily unavailable.