Loopback Testing of TDM Ports

You can use loopbacks as a maintenance function to help you isolate faults in a transmission path.

Applying a remote loopback at the port (DS1 level) enables you to test the Ribbon Signaling Systems’ connection to the SS7 network. You can apply a local loopback to check the continuity of the communication path of the TDM channel at the I/O port on the T1 or E1 interface card (see Applying and Removing Loopbacks at the T1, E1, or J1 Port).

The Ribbon Signaling Systems support the following loopback features for the ports on an I/O card at DS1 level:

• REMOTE PAYLOAD (remote loop after the framer)
  
  
• REMOTE LINE (remote loop at the line interface before the framer)
  
  
• LOCAL LINE (local loop internal to the framer)
  
  
• DISABLED (no loopback or echo)

Applying and Removing Loopbacks at the T1, E1, or J1 Port

You can apply a remote or a local loopback to any port on the T1 or E1 interface card. To remove an applied loopback, you must manually set the loopback field to DISABLED.

The following figure shows the signal path for both remote and local loopbacks.

Local and Remote Loopbacks

Remote Loopback

During a remote loopback, all incoming timeslots on the T1 or E1 link are looped back at the interface card port and returned to the adjacent node on the SS7 network. This is useful for testing the connectivity of the physical T1 or E1 links or of the full circuit path.

If the Ribbon Signaling Systems are connected to a node in remote loopback mode, link alignment fails at MTP3 because the SLTM/SLTA exchange fails. If the circuit path is well established, the links cycle through MTP2 alignment (L2 proving then L2 in service then L3 failure). MTP3 does not go into service until the loopback is removed.

Local Loopback

A local loopback loops all LSL Channels internally at the port. This is useful to verify the integrity of the signaling path internal to the I/O card. All timeslots on the physical T1 or E1 link are disconnected at the SS7 interface card port during a local loopback.

Much like a remote loopback, link alignment fails at MTP3, because the SLTM/SLTA exchange fails. The links cycle through MTP2 alignment (L2 proving, then L2 in service, then L3 failure). MTP3 does not go into service until the loopback is removed.

To apply or remove a loopback on the T1, E1 or J1 port

1. From the Main Menu, click the required I/O card on the Hardware image.
   
   
2. Click the required I/O card.
   
   
3. Click the port you want to loopback.
        
   
        
4. In the Loopback Mode drop-down list, select the required option.
   
   
5. Click Continue.