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# Testing Interfaces

Testing interfaces allows you to troubleshoot problems and to check the quality of links at various layers in the interface stack. The router supports the following test options:

- Transmission of BERT patterns to remote devices
- Local loopback—Loops the data back toward the router; on supported line modules, also sends an alarm indication signal (AIS) out toward the network
- Network loopback—Loops the data toward the network before the data reaches the frame
- Payload loopback—Loops the data toward the network after the framer processes the data
- Remote loopback—Provides the ability to:
  - Request that remote devices enter into loopback
  - Be placed in loopback by remote devices

## Sending BERT Patterns

The router can send BERT patterns from different layers in the interface stack on frame-based T3 interfaces.

For a list of the modules that support bit error rate tests, see ERX Module Guide, Appendix A, Module Protocol Support.

To send BERT patterns:

1. Select a controller.
   `
   host1(config)#controller t3 3/2
   `
2. Configure a specific layer in the interface to generate BERT patterns.
   `
   host1(config-controll)#bert pattern 2^11 interval 10
   `

   For information about BERT patterns, see References.

bert

- Use to enable bit error rate tests using the specified pattern on a T3 interface.
- Unlike other configuration commands, bert is not stored in NVRAM.
- Specify one of the following test patterns:
  - 0s—Repetitive test pattern of all zeros, 00000...
  - 1s—Repetitive test pattern of all ones, 11111...
  - 2^9—Pseudorandom test pattern, 511 bits in length
  - 2^11—Pseudorandom test pattern, 2047 bits in length
  - 2^15—Pseudorandom test pattern, 32,767 bits in length
  - 2^20—Pseudorandom test pattern, 1,048,575 bits in length
  - 2^20-QRSS—Pseudorandom QRSS test pattern, 1,048,575 bits in length
  - 2^23—Pseudorandom test pattern, 8,388,607 bits in length
  - alt-0-1—Repetitive alternating test pattern of zeros and ones, 01010101...
- Specify the duration of the test in the range 1–1440 minutes.
- Example
  `
  host1(config-controll)#bert pattern 2^11 interval 10
  `
- Use the no version to stop the test that is running.
- See bert.

## Enabling Local, Network, and Payload Loopback

To enable local, network, or payload loopback testing of a T3 or E3 line, use the clock source and loopback commands from Controller Configuration mode.

1. Change the clock source to internal.
   `
   host1(config-controll)#clock source internal module
   `
2. Specify a loopback.
   `
   host1(config-controll)#loopback local
   `

## Enabling Remote Loopback

You can enable remote loopback capability on frame-based T3 interfaces configured to use C-bit framing. Remote loopback is not supported on E3 ATM, E3 FRAME, and T3 ATM interfaces.

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

To enable remote loopback:

1. Change the clock source to internal.
   `
   host1(config-controll)#clock source internal module
   `
2. Ensure that the line is configured to use C-bit framing, which is the default for frame-based T3 interfaces.
   `
   host1(config-controll)#framing c-bit
   `
3. Configure one of the following loopback tests:
   - Set the loopback to remote to request that a remote device connected on a T3 interface enter into a loopback.
     `
     host1(config-controll)#loopback remote
     `
   - Configure the T3 interface to enable or disable the ability to enter into a loopback initiated by a remote device, as follows:
     - Issue the equipment customer loopback command to enable the router to enter into loopback when it receives an appropriate signal from the remote device.
       `
       host1(config-controll)#equipment customer loopback
       `
     - Issue the equipment network loopback command to disable the ability to enter into loopback initiated by a remote device.
       `
       host1(config-controll)#equipment network loopback
       `

equipment loopback

- Use to enable or disable the router’s ability to enter into a loopback initiated by a remote device connected on a T3 interface.

  | 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
- Examples
  `
  host1(config-controll)#equipment customer loopback
  host1(config-controll)#equipment network loopback
  `
- Use the no version to disable the router’s ability to be placed in loopback by the remote device.
- See equipment loopback.

loopback

- Use to configure a loopback.
- Specify one of the following loopback options:
  - local—Loops the data back toward the router; on supported line modules, also sends an alarm indication signal (AIS) out toward the network
  - network—Loops the data toward the network before the framer processes the data
  - payload—Loops the data toward the network after the framer processes the data
  - remote—Sends 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-controll)#loopback local
  `
- Use the no version to restore the default configuration, no loopback.
- See loopback.

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