| 摘要 |
<p>The loopback test consists of a user-application interface that connects the network operator to substantially all of the ATM points in the network. In operation, the network operator selects two ATM points as the loopback and source endpoints for the loopback test. The virtual path identification (VPI), virtual channel identification (VCI) and payload type indicator (PTI) that will be in the address header of the test cell when it arrives at the loopback endpoint location and the identification of the loopback endpoint are transmitted to the loopback endpoint in a setup message via a link from the UAI. The VPI, VCI and PTI that constitute the address header of a test cell injected at the source endpoint and destined for the loopback endpoint, and the location identification of the source endpoint are provided to the source endpoint in a setup message via a separate link from the UAI. The source endpoint formats a test cell based on this information and injects the cell into the network where it is routed based on the address header. The targeted loopback endpoint monitors the node identified in the setup message anticipating the arrival of the test cell. When the test cell arrives, it is captured by the loopback endpoint, examined to ensure that it is the appropriate loopback cell and retransmitted to the source endpoint. <IMAGE></p> |
