Real-time testing of wireless ATM Cell Transfer Performance

1. Question proposal
When an ATM switch is connected through a wireless transmission link, due to the high error rate in the wireless transmission environment, standard cells are converted into wireless ATM cells before entering the wireless channel. There are two methods to test the transmission performance of wireless ATM cells. One is to use an expensive dedicated ATM tester, which must be connected to the ATM tester through a standard cell interface of the ATM switch, then, a PVC connection is established and switched to the wireless cell interface for measurement. The other is to send test cells through the test software to perform a rough test on the transmission performance. The two test methods are the same in principle. First, you need to establish a test PVC connection, and then stop the service transmission or take up part of the bandwidth to send test cells. This is not only tedious, in addition, the normal transmission of business information is inevitably affected. In addition, the real-time performance is poor, which cannot reflect the transmission performance of wireless ATM cells over time-changing wireless channels. This article introduces a method that can test the transmission performance of wireless ATM cells in real time without affecting service transmission.
2 Working Principle of wireless ATM Cell Interface Unit
Wireless ATM cells are different from standard ATM cells. Standard ATM cells only control the error of the cell header and do not process the load in the cell. Wireless ATM cells perform Error Correction Codes on both the cell header and load. The working principle of the wireless port interface unit is described as follows:
* Sending direction: Standard ATM cells from the switching unit are error-corrected to form a wireless ATM cell to be sent to the frame structure generator and sent according to the designed frame structure. If no information needs to be sent, then, empty cells are inserted for sending. In this way, the wireless transmission device sends a wireless ATM Cell stream that conforms to the encoding rules according to the designed frame structure.
* Receiving direction: extract the frame synchronization signal from the information received by the transmission device, and establish frame synchronization with the sending end based on the Anti-fading frame synchronization scheme, decode the received information. Discard empty cells, discard unrecoverable error cells or send them to the switching unit as needed, and send the cells with correct error decoding to the switching unit for processing.
3 wireless ATM cell transfer real-time test method
The implementation principle of wireless ATM Cell Transfer Performance Testing is as follows:
It is learned from the working principle of this unit that frames are received on the premise of setting up frame synchronization. If frames cannot be set up at the receiving end, the wireless link cannot be connected at this time.
When frame synchronization has been established, the transmission performance of wireless ATM cells can be accurately measured. Because the sender sends a continuous wireless ATM Cell stream that complies with the encoding rules, the receiver only needs to perform error correction and Decoding Based on the local receiving information including null cells, the cells with the correct decoding are recorded as correct cells, the cells with the wrong decoding but the correct cell header are recorded as wrong cells, and the mature and correct decoding but cell header is recorded as wrong cells, the cells with incorrect decoding errors and incorrect cell headers are recorded as discarded cells, and various received cells are counted respectively to obtain the transmission performance parameters such as CER and CLR of wireless ATM cells. CER and CLR are defined as follows:
CER = number of error cells/number of sent Cells
= Number of error cells/number of correct cells + number of error cells + number of discarded cells)
CER = number of discarded cells/number of sent Cells
= Number of discarded cells/number of correct cells + number of error cells + number of discarded cells)
Compared with the common test method, this method has the following advantages:
* Simple. You do not need to establish a PVC connection for the test, and do not need to send test cells separately.
* The test does not have to interrupt the service, and can be performed simultaneously with the service transfer.
* Accurate. The length of wireless cells is fixed, and the number of received elements per unit time is fixed. As long as the processing capability of the Error Correction decoding part meets the requirements, the receiving part cannot receive more or less cells. Therefore, the measurement results are accurate and credible based on the actual number of received cells, which is an important basis for evaluating the performance of wireless cell Error Correction in vivo.
* The real-time performance is good. The measurement results are displayed in real time per unit time, allowing you to have an intuitive understanding of the link status for ease of problem analysis.
4 Conclusion
In this paper, we propose a method for wireless link diagnosis and real-time testing of wireless ATM cell transfer performance from the perspective of activation and operation of the network for the special application of the ATM switch using wireless relay networking. This method is simple, practical, accurate, and practical, and does not affect the transmission of business information, it facilitates network activation and real-time monitoring of Error-related transmission performance of wireless ATM cells in the wireless environment, it provides an important basis for correcting wireless ATM cells and evaluating network performance. In addition, the test method described in this article is also applicable to non-wireless ATM cells, as long as the sending information is a continuous code stream conforming to the encoding rules.