Method for bit error rate measurements in a cell-based telecommunication system

Abstract

A method for bit error rate measurements in a cell-based telecommunication system is presented, comprising the following steps of generating a first bit pattern at a first location of said telecommunication system, transmitting said first bit pattern from said first location to a second location of said telecommunication system, thereby obtaining a transmitted bit pattern, generating a second bit pattern at said second location, said second bit pattern being identical with the first bit pattern and comparing said transmitted bit pattern with said second bit pattern. The first bit pattern is transmitted in at least one unused cell (U, I), said unused cell (U, I) being generated during normal operation of said telecommunication system in the case of a lack of used cells to be transmitted.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates to a method for bit error rate measurements in a cell-based telecommunication system.[0002]In cell-based telecommunication systems, the information is transferred by means of cells of fixed or variable byte-length. These cells typically have an overhead section wherein control, management and routing information is embedded and a payload section, carrying user information.[0003]Cell-based telecommunication systems comprise for example ATM (Asynchronous Transfer Mode) communication networks. ATM cells for instance have a fixed length of 53 bytes, 8 bytes of which constitute the overhead section or the so called ATM cell header, reserved for overhead information.[0004]The whole transmitted cell-stream in a cell-based network is generally composed of two different types of cells: on the one hand used cells carrying in their payload section the proper user information and on the other hand unused cells with no user informati...

AI Technical Summary

Benefits of technology

[0013]One essential advantage of the invention, compared with conventional methods is that the bit error rate measurements are performed during normal operation of the telecommunication system. Accordingly the telecommunication system has not to be interrupted and brought in a test phase in which no transmission of proper user information is possible.

[0014]In a cell-based telecommunication system, e.g. an ATM-network, where unused cells, carrying no user information, are generally inserted amid the used cells in order to provide a continuous cell-stream between transmitting means and receiving means, bit error rate measurements according to the present method advantageously need no additional bandwidth by using those unused cells.

[0015]It has to be noted, that the generated bit patterns are independent from any transmitted user information and that the bit pattern generated at the first location and the reference bit pattern generated at the second location are identical. This means, that the number of detected discrepancies between the transmitted bit pattern and the second bit pattern really represents a measure for the bit error rate at the moment of transmission, because the bit errors only can occur in the test bit pattern itself. This is not the case in systems, where control information, calculated on the basis of user data to be transmitted, is transmitted together with said user information and the transmitted control information is compared to control information calculated on the basis of the transmitted user data. In fact, in these systems, bit errors can occur as well in the transmitted user data as in the transmitted control information, thus leading to a possible falsification of the measurement results.

[0016]In a preferred embodiment, the steps for bit error rate measurements according to the present method are repeated at each generation of an unused cell. The accuracy of the achieved bit error rates is increasing with the number of repetitions, i.e. with the number of comparisons between transmitted bit patterns and generated bit patterns at the receiver.

[0017]The comparison between the transmitted bit pattern and the second bit pattern is preferably bit synchronised, which enables a fast evaluation of bit error rates during measurements.

[0018]The generation of the second bit pattern may be synchronised with the arrival of the transmitted bit pattern at a comparator means for comparing said transmitted bit pattern with said second bit pattern.

Problems solved by technology

Bit errors which occur during transmission of these cells, have a negative impact onto the quality of the connection.

A bit error which occurs in the payload section of the cell implies a falsification of the transmitted information; wherein a bit error which occurs in the overhead section of the cell potentially implies a falsification of the destination address, and thus a loss of the cell.

Traditional bit error rate measurement methods have the disadvantage, that normal operation of the system has to be interrupted and the system has to be brought in a test phase.

During this test phase, no transmission of proper user information is possible.

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