H channels are multiplex channels in ISDN with predefined speed. They are also referred to as high-speed channels and extend from the primary multiplex connection( PRI) on the transmitting side through the complete ISDN network to the PRI interface on the receiving side. H channels are based on the B channels and provide transmission rates of more than 64 kbps. Only user data and no signaling is transmitted in the H channels.
The H channels form a multiplex hierarchy, based on 64 kbit/s: H-0 with a bit rate of 384 kbit/s consists of 6 DS-0 channels(64 kbit/s) connected to each other, H-10 for North America with 1,472 kbit/s for the T1 line, corresponding to 23 64 kbit/s channels. H-11 is also used in North America and has a transmission speed of 1,536 kbit/s, which corresponds to a transmission capacity of 24 interconnected DS-0 lines and represents the complete T1 primary, except for 8-kbit/s framing.
H-12 is the European version with a primary multiplex rate of 1,920 kbit/s, which corresponds to a complete E1 interface with 30 64-kbit/s channels, excluding the signaling and service channel. H-2 is a switched multiplex channel consisting of four H-12 channels and a transmission rate of 7.68 Mbit/s. The H-3 channel has a transmission rate of 34 Mbit/s in Europe and 45 Mbit/s in the U.S., and the H-4 channel forms a multiplex structure of H-3 channels. In Europe, H-4 consists of four H-3 channels, corresponding to a transmission rate of 136 Mbit/s, and in the U.S., H-4 is formed of three H-3 channels, corresponding to a transmission rate of 135 Mbit/s.