FTZ 1 TR 6

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FTZ 1 TR 6 (short 1 TR 6 is) the signaling protocol ( D-channel protocol) of national ISDNs the former Federal Post , Telecommunications Technical Central Office , (now German Telekom ); it was first used in 1989. It was replaced by the DSS1 protocol for all new connections .

The active marketing of connections of the National ISDN was stopped in the mid-1990s; after several extensions, operations were finally closed at the end of 2006. Telekom AG customers who still had connections to the national ISDN were terminated in September 2006 at the end of the year. The terminated connections were forcibly switched to DSS1 no later than the night of December 28th to December 29th, 2006. This change to DSS1 was free of charge for customers, but the participants concerned usually had to purchase new devices.

Within private telephone systems, a protocol variant (FTZ 12 TR 7) will probably exist for a long time.

Call number system

1 TR 6 does not support MSNs , but uses terminal selection digits ( EAZ ). ISDN customers received a block of ten consecutive numbers with final digits from 0 to 9. These final digits are the EAZ. The EAZ "0" is used for calls that are to be signaled simultaneously on all connected terminals ("global call"). With 1 TR 6 it was not possible to continue using existing (analog) phone numbers.

Device selection

When a call comes in , a broadcast message is sent to all end devices. The message contains compatibility requirements. These would be:

  • Connection indicator (for connections from a non-ISDN network)
  • Transmission service (services such as voice, data)
  • Terminal selection digit (EAZ), subaddress or, if applicable, extension number
  • Requirements for the OSI layers 1 to 7 (transmission rate, data backup, etc.)
  • ISDN number

The device that meets these requirements is allowed to accept the call.

It is also possible to select devices using the device selection number (EAZ). Each device can have an EAZ between 1 and 8. The EAZ of the desired device is then contained in the broadcast message. Each device compares its EAZ with that in the broadcast message. If they match, it takes the call. However, the network operator must be aware that the end devices have a set EAZ.

Semi-permanent connection

A special feature of 1 TR 6 is the semi-permanent connection (SPV) , which was later renamed as pre-ordered permanent dial-up connection (VDV) . This is a dial-up connection to a previously defined connection partner, which is paid for with a lump sum. This service was very popular in Germany because it had similar features to a leased line , but was offered much cheaper. Since the service is not available with Euro-ISDN , many participants did not switch to it, or they continued to explicitly order 1 TR 6 in order to be able to continue using the service.

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