Serial Loops for CTP Bundles Overview
You can use serial loops to diagnose issues in your network. You set up serial loops in the following directions:
Toward the serial interface and the attached customer device.
Toward the IP network and the remote customer device.
Serial loops may not run on transparent circuits. The serial loop function connects the SD and RD signals of the interface (in the direction specified), and will work only if a transparent circuit uses the SD and RD signals to transport data.
Normal Data Flow in the CTP Network
Figure 15 shows the normal data flow through the network.
Serial Loop to the Serial Interface
Figure 16 shows the data flow for a serial loop to the interface and the local customer device.
The serial loop toward the interface loops data arriving from the serial interface that is destined for the IP network back to the serial interface. The data is still transmitted from the serial interface to the IP network, but data from the IP network to the serial interface is blocked.
Serial Loop to the Network
Figure 17 shows the data flow for a serial loop toward the network.
Serial loops toward the IP network loops data arriving from the IP network that is destined for the serial interface back to the IP network and the remote customer device. The data is still transmitted from the IP network to the serial interface, but data from the serial interface to the IP network and the remote customer device is blocked.