The third level in the European E-carrier digital hierarchy. Designed for long haul transmission in support of interoffice trunking in the public switched telephone network (PSTN), E-3 runs at a signaling rate of 34.368 Mbps. An E-3 actually begins as four E-1s multiplexed into an E-2, by an M13 (Multiplex E-1 to E-3) mux, which then multiplexes four E-2s to yield a signaling rate of 33.792 Mbps. Stuff bits are added as necessary to adjust for variations in the clocking rates of the incoming E-2s, bringing the signaling rate up to 34.368 Mbps, comprising 480 DS-0 channels at 64 kbps for payload, plus 16 embedded channels for signaling and control. See also bit stuffing, channel, digital hierarchy, DS-0, E-carrier, long haul, multiplexer, payload, PSTN, signaling rate, and trunk.