Funktionsweise Datex-P
function mode DATEX p

DATEX p is the product designation of the German Telekom for a communications network for the data communication, which on the X.25 - interface minutes for the packet switching are based. It was introduced 1980 to Germany by the Federal Post Office (Federal Post Office). The data transmission rate can be selected of 50 Baud (acoustic coupler - speed) up to 64.000 bit/s. After the number of the mains connections in the start time increased very rapidly, it was continued to develop with the technology of the Canadian manufacturer Northern Telecom, which had already equipped 1976 the Canadian DATAPAC net. This technology had the advantage of the doubling: In case of failure a tax processor can the spare processor the tasks directly take over. Thus the Datex-P-Netz achieves also a high availability, how she is very important for example in the financial trade. In the meantime however the need at faster data communication rose substantially, so that as follow-up technology now Frame Relay is preferably used.

The Datex-P-Netz brought a set of advantages:

  • Adjustment of different interface minutes of the terminals
  • sequence safety device of the packages, river control, speed adjustment
  • secured transmission (repetition of incorrect packages), thereby improvement of the bit error rate in relation to the telephone network around a factor of approx. 100.000
  • optional service attributes as in the telephone network: Acceptance of the fees, closed user group, barriers of a connection for arriving or outgoing calls

during the package-obtained transmission from data to X.25-Protokoll, which is used in the Datex-P-Netz, does not exist exclusively reserved line from the transmitter to the receiver. Instead a virtual connection between transmitter and receiver is developed, which receive a connecting identification. That has the advantage that a transmitter can at the same time maintain a larger number from virtual connections to different receivers at different locations, and but only one connecting cable needs. For example the computing centre of a savings bank needs only one connecting cable, in order to give over the Datex-P-Netz the computers in all savings bank branches access for its volume of data.

The data which can be transmitted are packed of length defined by the terminal into packages and provided depending upon receiver with a connecting identification. By the nodes, the switching centers of the Datex-P-Netzes, are passed on these packages on the basis the connecting identification to the receivers. A terminal has (e.g. „a stupid “ ASCII - terminal “) the ability to package data and drive the X.25-Protokoll, cannot be attached it to a PAD (package assembler these assembler), which takes over these tasks for it.

In the X.25-Terminologie become the terminals as “DTE” (DATA terminal equipment), which calls switching centers “DCE” (DATA Circuit Teminating equipment). Transit switching centers are called “DSE” (DATA Switching Exchange).

For the connection of terminals to the Datex-P-Netz own modems were made available, „the data switching-in devices “. They offer the well-known interfaces of the V-series and the X-series, work in the baseband, both in the synchronous duplex - and in the half duplex - to enterprise, have however a smaller power output as the usual modems for the telephone network. That was not necessary, since they were not laid out for the entire absorption, which can occur in the telephone network between two participants, but only for the relatively short distance up to the next switching center.

DATEX p represented the first entrance available for everyone into the late 1980er year into a global data network. The 16 bits home computers made an inexpensive terminal emulation possible, and one needed only one network user ID (NUI) of the post office or a private offerer around itself by modem or acoustic coupler to in-select. Popular NUAs (network user address) was z. B. CompuServe the portal with numerous services or the legendary Chat on the servers of the company Altos.

See also: DATEX j, DATEX l, DATEX m, IDN


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