# 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
- Receipt of BERT patterns from remote devices
- Local loopback—The ability to loop the data back toward the router; on supported line modules, also sends an alarm indication signal (AIS) out toward the network
- Network loopback—The ability to loop the data toward the network before the data reaches the frame
- Remote loopback, which provides:
  - The ability to request that remote devices enter into loopback
  - The ability to be placed in loopback by remote devices
- Connectivity tests to remote devices

## Sending BERT Patterns

The router can send BERT patterns from different layers in the interface stack. For a list of the modules that support bit error rate tests (BERTs), see ERX Module Guide, Appendix A, Module Protocol Support.

To send BERT patterns:

1. Select a controller.
2. Configure a specific layer in the interface to generate BERT patterns.

   For information about BERT patterns, see References.

path ds1|e1 bert

- Use to enable bit error rate tests using the specified pattern at the T1/E1 over SONET/SDH VT layer.
- Unlike other configuration commands, path ds1|e1 bert is not stored in NVRAM.
- Specify one of the following options:
  - 2^11—Pseudorandom test pattern, 2047 bits in length
  - 2^15—Pseudorandom test pattern, 32,767 bits in length
  - 2^20-O153—Pseudorandom test pattern, 1,048,575 bits in length
- Specify the duration of the test in the range 1–1440 minutes.
- Optionally, specify the unframed keyword to overwrite the framing bits.
- Example
  host1(config-controll)#path 12 ds1 1/3/4 bert pattern 2^11 interval 10 unframed
- Use the no version to stop the test that is running.
- See path ds1|e1 bert.

path ds3 bert

- Use to enable bit error rate tests using the specified pattern at the T3 layer.
- Unlike other configuration commands, path ds3 bert is not stored in NVRAM.
- Specify one of the following options:
  - 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)#path 12 ds3 2 bert pattern Os interval 10
- Use the no version to stop the test that is running.
- See path ds3 bert.

path ds3 t1 bert

- Use to enable bit error rate tests using the specified pattern at the T1 over T3 layer.
- Unlike other configuration commands, path ds3 t1 bert is not stored in NVRAM.
- Specify one of the following options:
  - 2^11—Pseudorandom test pattern, 2047 bits in length
  - 2^15—Pseudorandom test pattern, 32,767 bits in length
  - 2^20-O153—Pseudorandom test pattern, 1,048,575 bits in length
- Specify the duration of the test in the range 1–1440 minutes.
- Optionally, specify the unframed keyword to overwrite the framing bits.
- Example
  host1(config-controll)#path 12 ds3 2 t1 14 bert pattern 2^11 interval 10 unframed
- Use the no version to stop the test that is running.
- See path ds3 t1 bert.

## Receiving BERT Patterns

The router can receive BERT patterns from a remote device at the T1/E1 over SONET/SDH VT and T1/E1 over T3 layers. To receive BERT patterns, configure the interface on the router for network payload loopback and the remote interface to use the line clock. Inaccurate results might occur if you use other loopback modes or clock sources.

When the router is synchronized with and receiving BERT patterns from a remote device, the router records the number of bit errors and the number of bits received. To view these statistics, issue the show controllers sonet command.

## Enabling Local or Network Loopback

You can enable loopback tests on the router at the following layers in the interface stack:

- SONET/SDH section layer
- T1/E1 over SONET/SDH VT layer
- T3 layer
- T1/E1 over T3 layer

See Interface Stack for a description of the layers.

To enable local or network loopback:

1. Select a controller.
2. Configure local or network loopback at the desired layers in the interface.

loopback

- Use to configure the type of loopback at the SONET/SDH section layer.
- Specify one of the following 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 data reaches the frame.
- Example
  host1(config)#controller sonet 4/0 host1(config-controller)#loopback network
- Use the no version to disable loopback.
- See loopback.

path ds1|e1 loopback

- Use to configure a loopback at the T1/E1 over SONET/SDH VT layer.
- Specify one of the following options:
  - local—Loops the router output data back toward the router at the T1/E1 framer; on supported line modules, also sends an alarm indication signal (AIS) out toward the network.
  - network { line | payload }
    - Specify the line keyword to loop the data back toward the network before the T1/E1 framer and automatically set a local loopback at the HDLC controllers.
    - Specify the payload keyword to loop the payload data back toward the network at the T1/E1 framer and automatically set a local loopback at the HDLC controllers.
- Example
  host1(config-controll)#path 12 ds1 1/3/4 loopback network line
- Use the no version to clear the local loopback configuration.
- See path ds1|e1 loopback.

path ds3 loopback

- Use to configure a loopback at the T3 layer.
- Specify one of the following 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 { line | payload }
    - Specify the line keyword to loop the data toward the network before the data reaches the framer.
    - Specify the payload keyword to loop the data toward the network after the framer has processed the data.
- Example
  host1(config-controll)#controller sonet 5/0 host1(config-controll)#path 12 ds3 1 loopback local
- Use the no version to turn off the loopback.
- See path ds3 loopback.

path ds3 t1 loopback

- Use to configure a loopback at the T1 over T3 layer.
- Specify one of the following options:
  - local—Loops the router output data back toward the router at the T1 framer; on supported line modules, also sends an alarm indication signal (AIS) out toward the network.
  - network { line | payload }
    - Specify the line keyword to loop the data back toward the network before the T1 framer and automatically set a local loopback at the HDLC controllers.
    - Specify the payload keyword to loop the payload data back toward the network at the T1 framer and automatically set a local loopback at the HDLC controllers.
- Example
  host1(config-controll)#path 12 ds3 2 t1 14 loopback network line
- Use the no version to clear the local loopback configuration.
- See path ds3 t1 loopback.

## 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.

## Testing Connectivity

Use the path overhead j1 command to check for connectivity between the router and a SONET/SDH device at the other end of the line. This command defines:

- A message that the router sends from the specified interface to the SONET/SDH device at the other end of the line.
- A message that the router expects to receive on the specified interface from the SONET/SDH device at the other end of the line.

When you define a message that the interface sends, you must monitor receipt of that message at the remote end.

When you define a message that the interface expects to receive, you should configure the remote device to transmit the same message to the interface. You can then use the show controllers sonet command to compare the expected and received messages.

path overhead j1

- Use to define messages that the router sends to or expects to receive from a SONET/SDH device connected to a cOCx/STMx interface.
- Specify a path identifier between 1 and 2,147,483,648 for a cOCx/STMx interface.
- Specify the keyword msg for a message that the router transmits for this path.
- Specify the keyword exp-msg to define a message that the router expects to receive on this path.
- Define a message of up to 62 characters for SONET or up to 15 characters for SDH.
- Configure the remote device to send the same message that the router expects to receive on this path. You can then compare the expected and received messages in the display of the show controllers sonet command.
- Example for cOCx/STMx interface:
  host1(config-controller)#path 2 overhead j1 exp-msg goodbye
- Use the no version to restore the default situation, in which all the characters in the transmitted or expected message are zeros.
- See path overhead j1.