As D- channel (English: data channel) is the term for the ISDN channel for transmission of control information ( signaling ), particularly for setting up and dismantling of the connection. A signaling protocol used in ISDN for example DSS1. The D channel can not be like the B- channel used for ( direct ) communication between two nodes, but is used for communication with the central office. It has a data transmission rate of 16 kbit / s at base terminals and 64 kbit / s primary rate interfaces. Between the exchanges signaling (64 kbit / s ) applies to the so-called central signaling channel instead of on which the ITU -T Signalling System No. 7 is used.
In the point-to- multipoint operation ( such as the S0 bus of a basic access in Mode -multipoint connection) is used as the access method for the D - channel is a CSMA / CA variant.
On the D-channel is a permanent connection to the switching center, which is more efficient, as it is necessary to replace the pure control information. The remaining capacity can be used for example for Datex- P compounds (up to 9600 bit / s). Also, you could be informed earlier with Deutsche Telekom over this channel when e- mail was received on a T- Online Account ( what with competition laws is no longer possible today ).
When establishing a connection can also get more information such as a subaddress or via the D- channel except the phone number - strings are sent that are passed to the called party - a limited degree. This makes it possible to transmit through repeated call attempts complex information to files without a ( paid ) set up connection. For example, there was a Linux project that was used this function and could be used to a very slow indeed, but free data transfer. The Fire Line program uses the method described by text messages to be transmitted. Since this will strain the telephone network, the necessary functions but were turned off by many telephone companies.
The transmitted on the D- channel signaling information can be read with an ISDN monitor and recorded.
In a GSM network, the control channel (CCH ) corresponding to the D channel.
See also: B channel, LAPD