You can perform loopback on a transmission device or a transmission channel by means of hardware or software.
You can learn whether the hardware equipment are working properly and the software parameters are set correctly based on the situation of the transmission equipment, channels, services, and signaling cooperation after the self-loopback. Loopback test is a most often used method of locating transmission faults and faults in trunk parameter setting.
Loopback is classified into timeslot loopback, port loopback, and speech loopback.
Timeslot loopback is used to loop back the data carried by the timeslot in the specified direction. Through the timeslot loopback, you can determine whether the transmission on a speech channel is normal or not. You can determine the loopback direction by selecting a loopback mode.
Timeslot loopback is of two modes: remote loopback and local loopback.
Remote loopback
The signals received on a timeslot are sent out without being processed. Remote loopback refers to the loopback performed on the MSC side.
Local loopback
The signals that should be placed in the sending direction are placed in the receiving direction as the received data. Local loopback refers to the loopback performed on the BSC side.
Port loopback is used to loop back the data received or transmitted by the port in the specified direction. Different interface boards have different port loopback modes. For details, see Table 1.
Interface Board |
Loop Mode |
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|---|---|---|---|
EIU/OIU |
E1/T1 |
Local Loopback: All the signals that should be placed in the sending direction are placed in the receiving direction and returned as the received data. The signals are not sent to the ports on the peer interface board through physical links. Remote Loopback: All the ports that have received signals send the signals back. The board where the ports are located does not process signals. Payload Loopback: A board processes the signals received from ports and then sends the signals back through the ports. |
|
STM-1 |
Optical port |
Regenerator Section Line-side: All the ports that have received signals send the signals back. The board where the ports are located does not process signals. |
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Regenerator Section System Side: All the signals that should be placed in the sending direction are placed in the receiving direction and returned as the received data. The signals are not sent to the ports on the peer interface board through physical links. |
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Optical tributary |
Lower Order Path Line-side Loopback: A board processes the signals received from ports and then sends the signals back through the ports. |
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Tributary Line-side Loopback: All the ports that have received signals send the signals back. The board where the ports are located does not process signals. |
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Tributary System Side Loopback: All the signals that should be placed in the sending direction are placed in the receiving direction and returned as the received data. The signals are not sent to the ports on the peer interface board through physical links. |
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The IP interface board and transmission optimization interface board |
Local Loopback: All the signals that should be placed in the sending direction are placed in the receiving direction and returned as the received data. The signals are not sent to the ports on the peer interface board through physical links. |
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On a speech channel, you can locate the segment where the speech problem occurs by comparing the loopback speech with the original speech.
Speech loopback is classified into remote speech channel loopback and DSP speech channel loopback:
Remote speech channel loopback
You can detect the speech channel fault by performing the remote speech channel loopback on the A interface, GEIUB/GOIUB/GFGUB/GEHUB/GOGUB Abis interface, and PTU Abis interface. If it is the internal problem that results in the speech channel fault, you can start the internal testing to locate the fault.
DSP speech channel loopback