FTZ 1 TR 6
Encyclopedia
FTZ 1 TR 6 is the standard for the obsolete German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 national digital
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...

 signalling protocol (D channel
D channel
D 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 kbit/s on a primary rate interface.For DSS1 signalling, the D channel...

 protocol) used for the ISDN
Integrated Services Digital Network
Integrated Services Digital Network is a set of communications standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network...

. It has been superseded by DSS1 but is still in use on some lines and private exchanges.

1 TR 6 did not support multiple subscriber numbers
Multiple Subscriber Number
Multiple Subscriber Number - a telephone number associated with an ETS 300 BRI line. Providers of ETS 300 often give you three MSNs with a BRI, although additional MSNs can be purchased. An ISDN terminal will "ring" only when calls are made to the MSN entered in that terminal...

 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 line
Leased line
A leased line is a service contract between a provider and a customer, whereby the provider agrees to deliver a symmetric telecommunications line connecting two or more locations in exchange for a monthly rent . It is sometimes known as a 'Private Circuit' or 'Data Line' in the UK or as CDN in Italy...

s that could be temporarily disabled to use the B channel
B channel
B channel is a telecommunications term which refers to the ISDN channel in which the primary data or voice communication is carried. It has a bit rate of 64 kbit/s in full duplex....

for other purposes.

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