FTZ 1 TR 6 (or 1 TR 6) is the standard for the obsolete German national digital signalling protocol (

D channel D channel (delta channel) is a telecommunications term which refers to the ISDN channel in which the control and signalling information is carried. The bit rate of the D channel of a basic rate interface is 16 kbit/s, whereas it amounts to 64 kb ...

protocol) used for the

ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Work ...

. It has been superseded by

DSS1 Digital Subscriber Signalling System No. 1 (DSS1) is a digital signalling protocol (D channel protocol) used for the ISDN. It is defined by ITU-T I.411 (ETS 300 102). It supports Bearer Capability, Low Level Compatibility and High Level Compat ...

but is still in use on some lines and private exchanges. 1 TR 6 did not support multiple subscriber numbers but featured an ''Endgeräteauswahlziffer'' (''EAZ'', German "user device selection digit"). ISDN subscribers would get a sequence of 10 subsequent subscriber numbers, the last digit of which being the EAZ. The EAZ "0" was used for "global calls" to all connected devices. 1 TR 6 also offered ''semipermanent connections'', which were (comparatively cheap) leased lines that could be temporarily disabled to use the

B channel {{for, Indonesian television network formerly known as B-Channel, RTV (Indonesian TV network) B channel (bearer) is a telecommunications term which refers to the ISDN channel in which the primary data or voice communication is carried. It ha ...

for other purposes. It is said that the "TR" simply stands for "technische Richtlinie" (technical guidelines).

External links

* . {{DEFAULTSORT:Ftz 1 Tr 6 Integrated Services Digital Network