1. Field of the Invention
The present invention relates to a method and to a circuit arrangement for determining the quality of virtual connections extending via input lines and output lines of an asynchronous transfer mode (ATM) switching equipment, whereby respective message cells are transmitted according to an asynchronous transfer mode process during the course of these virtual connections and each of these message cells thereby has a cell header available for identifying the respective virtual connection for the input line or, respectively, output line coming into consideration.
2. Description of the Prior Art
The problem generally arises in telecommunication switching systems of monitoring the quality of defined connections in order to be able to provide subscribers with appropriate information, for example, given complaints. The operators of public or private switching equipment, however, also have the need for or, respectively, raise the requirement of being able to measure and monitor the quality of the switching equipment. Quality measurements of this type also enter into the maintenance concepts in order to be able to, for example, avoid predictable deteriorations in quality beyond an allowable tolerance limit.
Given a method and a circuit arrangement of the type initially set forth, it is therefore an object of the present invention to provide a way to determine the quality of virtual connections on the basis of the message cells transmitted during the course of such virtual connections.
In a method of the type set forth above, this object is achieved, according to the present invention, in an improved method for determining the quality of virtual connections extending via input lines and output lines of an ATM switching equipment in which respective message cells are transmitted according to an asynchronous transfer mode during the course of these virtual connections and each of the message cells thereby has a cell header available with which the respective virtual connection for the input line or, respectively, output line coming into consideration is identified, and is particularly characterized in that the plurality of message cells accepted and output are separately acquired in a call-associated manner in the ATM switching equipment on the basis of the cell headers of the message cells accepted via the input lines or, respectively, output to the output lines, and in that, in response to the cleardown of the respective virtual connection, the loss rate of the message cells is calculated as a measure for the quality of the respective virtual connection, being determined from the previously, separately-acquired plurality of accepted and output message cells.
The present invention yields the advantage that the quality of the individual virtual connections can be continuously determined on the basis of the transmitted message cells without significantly dynamically loading an ATM switching equipment for this determination.
According to a particular feature of the invention, the aforementioned improved method is further particularly characterized in that a mean loss rate is formed as quality measure for the ATM switching equipment on the formation being from the identified loss rates of the virtual connections established within a defined time interval. Also, the improved method is particularly characterized in that the loss rate identified for the respective virtual connection is involved in the calculation of charges. This feature and development yields the advantage of a simple determination of the quality of an ATM switching equipment.
The advantage of the improved circuit arrangement set forth above is that only the message quantity forwarded by an ATM switching equipment to a subscriber equipment, in fact, enters into the calculation of charges. Message cells repeatedly transmitted within an ATM switching equipment or, respectively, misrouted message cells due, for example, to transmission malfunctions are left out of consideration for calculating charges.
The circuit arrangement for the implementation of the method set forth above is characterized in that a plurality of counters corresponding in number to the plurality of virtual connections extending via the input lines and the output lines is assigned to the input lines and to the output lines, in that the plurality of counters can be placed into a defined initial counter reading proceeding from a central control device during the respective course of the setup of the allocated virtual connection, in that the individual counters are individually drivable given the appearance of message cells on the allocated input line or, respectively, output line, being individually drivable according to the prescription of the cell header respectively contained in the message cells, and in that the momentary counter reading of a counter is variable by a counting unit proceeding from a defined initial counter reading, the reading being variable with each drive, and in that the momentary counter readings of the counter assigned to a virtual connection can be interrogated at least at the cleardown of the connection by a central control device for calculating the loss rate.
The advantage of the circuit arrangement is thereby that the registration of the message cells transmitted during the course of virtual connections occurs in peripheral equipment so that the central control device of an ATM switching equipment is largely relieved of the determination of the quality of the virtual connections.
According to other features and developments of the invention, the circuit arrangement is particularly characterized in that the momentary counter readings of the counter can be additionally interrogated at fixed time intervals. Also, the arrangement is particularly characterized in that the counters are fashioned as periodically-circulating counters and in that a message signal is separately offered to the central control device before a cleardown of the respective virtual connection each time a defined counter reading is reached. The advantage of these features and developments is that the counters provided for the registration of message cells require only a relatively low counting capacity and, therefore, the required circuit expense can be kept low.