It uses two types of standard channels: Bearer channels
, which carry the user's voice, data, image and sound traffic; and Data channels, which carry the call set-up and signaling information.
In ISDN systems, 64 Kbps circuit-switched bearer channels
(B channels) carry both voice and data.
25 and the newest High Density Channelized (HDC) board, which is capable of processing up to 32 SS7 links or 128 HDLC and PCM bearer channels
25 D channel connections and transferring data over the D channel and simultaneously up to two circuit switched Bearer channels