To perform an inloop ATM test on a remote NE, engineers connect an AIX 4000 tester to a local NE, as shown in the figure. During the test, however, services are unavailable.
Set the VCI to a number other than 0 on the AIX 4000.
1. According to the configurations, the remote NE changes the VPI of an ATM service from 40 to 0. The local NE maintains the VPI 40 for an ATM service.
2. The AIX 4000 connected to the local NE sends a cell with VPI of 40 and VCI of 0. The remote NE converts the cell into a new cell with VPI of 0 and VCI of 0 and loops it back to the local NE. The local NE considers the cell with VPI of 0 and VCI of 0 an idle cell. Therefore, the local NE directly discards the cell instead of converting it into a cell with VPI of 40 and VCI of 0. As a result, the service is unavailable.
By default, the AIX 4000 sends a cell with VCI of 0. When the VPI is possible 0, disable the AIX 4000 from sending a cell with VCI of 0. That is, set the VCI to a number other than 0 on the AIX 4000.
In practice, the equipment does not send a cell with VCI of 0 when the VPI is possibly 0. Therefore, such a fault does not occur.