Enabling Remote Loopback Testing

You can configure the router to request that compatible devices connected at the following layers enter into a loopback:

• T1 over SONET/SDH VT layer
• T1 over T3 layer
• T3 layer

You can also configure the router to start loopback testing when it receives an appropriate signal from a devices connected at any of these layers.

For a list of the modules that support remote loopback, see ERX Module Guide, Appendix A, Module Protocol Support.

Note: There is no protocol that allows remote loopback on E1 links.

To enable remote loopback:

1. Select a controller.
2. Configure remote loopback at the desired layers in the interface.

path ds1|e1 loopback remote

• Use to place a remote device, connected at the T1 over SONET/SDH VT layer, in loopback.
• Specify one of the following options:
  • line fdl ansi (T1 only)—Sends a repeating 16-bit ESF data link code word (00001110 11111111) to the remote end requesting that it enter into a network line loopback. Specify the ansi keyword to enable the remote line facilities data link (FDL) ANSI bit loopback on the T1 line, according to the ANSI T1.403 specification.
  • line fdl bellcore (T1 only)—Sends a repeating 16-bit ESF data link code word (00010010 11111111) to the remote end requesting that it enter into a network line loopback. Specify the bellcore keyword to enable the remote line FDL Bellcore bit loopback on the T1 line, according to the Bellcore TR-TSY-000312 specification.
  • payload [ fdl ] [ ansi ] (T1 only)—Sends a repeating 16-bit ESF data link code word (00010100 11111111) to the remote end requesting that it enter into a network payload loopback. Enables the remote payload FDL ANSI bit loopback on the T1 line. You can optionally specify fdl and ansi.
• Example

  host1(config-controll)#path 12 ds1 1/3/4 loopback remote line fdl ansi

• Use the no version to send the 16-bit ESF data link code word to deactivate the loopback at the remote end, depending on the last activate request sent to the remote end.
• See path ds1|e1 loopback.

path ds1 remote-loopback

• Use to enable the router to accept remote loopback requests from a remote device connected at the T1 over SONET/SDH VT layer.
• Example

  host1(config-controll)#path 12 ds1 1/3/4 remote-loopback

• Use the no version to restore the default, which is to reject remote loopback requests.
• See path ds1 remote-loopback.

path ds3 equipment loopback

• Use to enable or disable the router’s ability to enter into a loopback initiated by a remote device connected at the T3 layer.

  Note: Remote loopback is available only on frame-based T3 interfaces configured to use C-bit framing.

• Specify one of the following loopback options:
  • customer—Enables the router to enter into loopback when it receives an appropriate signal from the remote interface
  • network—Disables the router’s ability to enter into loopback when it receives an appropriate signal from the remote interface; this is the default behavior
• Examples

  host1(config-controll)#path 12 ds3 2 equipment customer loopback

  host1(config-controll)#path 12 ds3 2 equipment network loopback

• Use the no version to restore the default behavior, which disables the router’s ability to be placed in loopback by a remote device. Using the no version has the same effect as issuing the command with the network keyword.
• See path ds3 equipment loopback.

path ds3 loopback remote

• Use to place a remote device, connected at the T3 layer, in loopback.
• Specify the remote keyword to send a far end alarm code in the C-bit framing, as defined in ANSI T1.404, to notify the remote end to activate or (when you use the no version) deactivate the line loopback.

  Note: Remote loopback is available only on frame-based T3 interfaces configured to use C-bit framing.

• Example

  host1(config)#controller sonet 5/0

  host1(config-controll)#path 12 ds3 1 loopback remote

• Use the no version to turn off the loopback.
• See path ds3 loopback.

path ds3 t1 loopback remote

• Use to place a remote device, connected at the T1 over T3 layer, in loopback.
• Specify one of the following options:
  • line fdl ansi—Sends a repeating 16-bit ESF data link code word (00001110 11111111) to the remote end requesting that it enter into a network line loopback. Specify the ansi keyword to enable the remote line FDL ANSI bit loopback on the T1 line, according to the ANSI T1.403 specification.
  • line fdl bellcore—Sends a repeating 16-bit ESF data link code word (00010010 11111111) to the remote end requesting that it enter into a network line loopback. Specify the bellcore keyword to enable the remote line FDL Bellcore bit loopback on the T1 line, according to the Bellcore TR-TSY-000312 specification.
  • payload [ fdl ] [ ansi ]—Sends a repeating 16-bit ESF data link code word (00010100 11111111) to the remote end requesting that it enter into a network payload loopback. Enables the remote payload FDL ANSI bit loopback on the T1 line. You can specify fdl or ansi.
• Example

  host1(config-controll)#path 12 ds3 2 t1 14 loopback remote payload

• Use the no version to send the 16-bit ESF data link code word to deactivate the loopback at the remote end, depending on the last activate request sent to the remote end.
• See path ds3 t1 loopback.

path ds3 t1 remote-loopback

• Use to enable the router to accept remote loopback requests from a remote device connected at the T1 over T3 layer.
• Example

  host1(config-controll)#path 12 ds3 2 t1 14 remote-loopback

• Use the no version to restore the default, which is to reject remote loopback requests.
• See path ds3 t1 remote-loopback.

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