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# Configuration Tasks

The following sections describe how to configure the layers on cOCx/STMx interfaces.

## SONET/SDH Configuration Tasks

To configure SONET/SDH on a cOCx/STMx interface:

1. Select an interface.
2. Specify a clock source for the interface.
3. Specify that the mode be SDH, or accept the default mode, SONET.
4. (Optional) Assign a text description or an alias to the interface.
5. (Optional) Disable processing of SNMP link status information for the section and line layers of the interface.
6. Configure the path for the interface.
7. (Optional—not recommended) Overwrite the automatic setting for the path signal label (C2) byte.
8. (Optional) Enable processing of SNMP link status information for the path layer of the interface.
9. (Optional) Configure the router to use remote defect indications (RDIs) at the path layer to determine the operational status of a path.
10. (MPLS fast reroute over SONET/SDH interfaces) Specify the time duration after which the router sets an alarm when it records a defect at the path layer.
11. (MPLS fast reroute over SONET/SDH interfaces) Specify the time duration after which the router sets an alarm when it records a defect at the line or section layer.
12. Configure APS/MSP for the interface.

    For information about configuring APS/MSP, see Configuring APS/MSP in Configuring Unchannelized OCx/STMx Interfaces .

You must now configure the next layer on the interface: E1, T1, or E3. See T1/E1 Configuration Tasks or T3 Configuration Tasks.

clock source

- Use to configure the transmit clock source for the interface.
- For production networks, configure all STMx ports on the line module for internal chassis timing. You must also ensure that the chassis reference clock is of good quality — Stratum 3 or better, recovered either from a known good STM port or from one of the BITS inputs.
- Although the CLI enables you to specify the keywords internal module to use the line module’s internal clock, in a production network we recommend that you do not do this. Instead, specify the keywords internal chassis to use the router’s internal clock.
- For production networks, never specify the keyword line to use the line’s receive clock as the transmit clock. Although the CLI enables this configuration, it is not supported because jitter transfer is not compliant for this timing and because pointer adjustments takes place on the outgoing link.
- In a nonproduction network, you can configure some ports with internal clock sources and others with line clock sources. However, all ports with internal clock sources must use either the router’s clock or the module’s clock. You cannot configure some ports on the I/O module to use the router’s clock and others to use the module’s clock.
- To change the clock source of the ports on a cOC3/STM1 I/O module from the router’s clock to the module’s clock or vice versa, first change the clock source of all ports to the line setting, and then to the new internal clock setting.
- Example
  `
  host1(config-controll)#clock source internal chassis
  `
- Use the no version to revert to the default, line.
- See clock source.

controller sonet

- Use to select an interface on which you want to configure channelized SONET or SDH.
- Example
  `
  host1(config)#controller sonet 4/0
  `
- There is no no version.
- See controller sonet.

description

- Use to assign a text description or an alias to a channelized SONET interface.
- You can use this command to help you identify the interface and keep track of interface connections.
- The description or alias can be a maximum of 64 characters.
- Use the show controllers sonet command to display the text description.
- Example
  `
  host1(config-controll)#description boston-sonet-interface
  `
- Use the no version to remove the text description or alias.
- See description.

path

- Use to configure paths over channelized SONET and SDH interfaces.
- Specify the correct identifier for the type of interface. See Interface Types and Specifiers in JUNOSe Command Reference Guide for details of the syntax.
- Example for a cOC3/STM1 interface
  `
  host1(config-controller)#path 2 oc1
  `
- Example for a cOC12/STM4 interface in SONET mode
  `
  host1(config-controller)#path 2 oc1 1/2
  `
- Example for a cOC12/STM4 interface in SDH mode
  `
  host1(config-controller)#path 2 stm1 2
  `
- Use the no version to delete a SONET or SDH path.
- See path.

path description

- Use to assign a text description or an alias to a channelized SONET path.
- You can use this command to help you identify the interface and keep track of interface connections.
- The description or alias can be a maximum of 64 characters.
- Example
  `
  host1(config-controll)#path 2 description westford
  `
- Use the no version to remove the description.
- See path description.

path overhead c2

- Use to overwrite the automatic setting for the path signal label (C2) byte.
- By default, the value of the C2 byte for the path is determined by the layers configured above the SONET/SDH interface and set automatically. The E Series router sets this default value in accordance with RFC 2558. (See References.)

  | Caution: Use this command only if you know that the automatic setting does not match the setting on the remote device. Otherwise, the remote device might send an unexpected value, and the router might lose data.

- Example
  `
  host1(config-controll)#path 2 overhead c2 20
  `
- Use the no version to restore the default setting, in which the value of the C2 byte is determined by the layers configured above the SONET/SDH interface.
- See path overhead c2.

path shutdown

- Use to disable a specified path.
- Paths are enabled by default.
- Example
  `
  host1(config-controll)#path 2 shutdown
  `
- Use the no version to restart a disabled path.
- See path shutdown.

path snmp trap link-status

- Use to enable SNMP link status processing for the path layer of the interface.
- The default is disabled.
- Example
  `
  host1(config-controll)#path 2 snmp trap link-status
  `
- Use the no version to disable SNMP link status processing.
- See path snmp trap link-status.

path trigger alarm prdi

- Use to configure the router to use remote defect indications (RDIs) at the path layer to determine the operational status of a path.
- Example
  `
  host1(config-controll)#path 2 trigger alarm prdi
  `
- Use the no version to restore the default setting, in which the software uses loss of pointer and AIS defects at the path layer to determine the operational status of a path.
- See path trigger alarm prdi.

path trigger delay

- Use to set the time duration after which the router sets an alarm when it records a defect at the path layer.
- Change this value from the default only when you are using MPLS fast reroute over a SONET/SDH interface.
  - Specify a value of 0 milliseconds if this interface does not use APS/MSP or if MPLS should have priority over APS/MSP.
  - Specify a value of at least 100 milliseconds if this interface uses APS/MSP and if APS/MSP should have priority over MPLS.
- Example
  `
  host1(config-controll)#path 2 trigger delay msec 1000
  `
- Use the no version to restore the default setting, 2500 milliseconds.
- See path trigger delay.

sdh

- Use to specify that the interface supports SDH.
- Example
  `
  host1(config-controller)#sdh
  `
- Use the no version to revert to SONET operation on this interface.
- See sdh.

snmp trap link-status

- Use to enable SNMP link status processing for the section and line layers of the interface.
- The default is enabled.
- Example
  `
  host1(config-controll)#no snmp trap link-status
  `
- Use the no version to disable SNMP link status processing.
- See snmp trap link-status.

trigger delay

- Use to set the time duration after which the router sets an alarm when it records a defect at the line or section layer.
- Change this value from the default only when you are using MPLS fast reroute over a SONET/SDH interface.
  - Specify a value of 0 milliseconds if the interface does not use APS/MSP or if MPLS should have priority over APS/MSP.
  - Specify a value of at least 100 milliseconds if this interface uses APS/MSP and if APS/MSP should have priority over MPLS.
- Example
  `
  host1(config-controll)#trigger delay msec 1000
  `
- Use the no version to restore the default setting, 2500 milliseconds.
- See trigger delay.

### Configuring Higher Layers

You must now configure the next layer on the interface: E1, T1, or T3. See T1/E1 Configuration Tasks or T3 Configuration Tasks.

## T1/E1 Configuration Tasks

Before you configure T1 or E1 on an interface, you must configure SONET or SDH. See SONET/SDH Configuration Tasks.

To configure a T1 or an E1 over SONET or SDH on a cOCx/STMx interface:

1. Configure a tributary for the path.
2. (Optional) Assign a text description or an alias to the interface.
3. Configure one of the following:
   - An unframed E1 line. (See Configuring T1 and E1 Lines .)
   - A T1 or an E1 line. (See Configuring T1 and E1 Lines .)

For detailed examples, see Configuration Examples.

path ds1|e1

- Use to create and configure SONET tributaries, SDH tributaries, and T1 or E1 on the path.
- Example
  `
  host1(config-controller)#path 2 ds1 1/7/4 vt15
  `
- Use the no version to delete SONET and SDH tributaries.
- See path ds1|e1.

path ds1|e1 description

- Use to assign a text description or an alias to a T1/E1 over SONET/SDH VT layer on channelized SONET and SDH interfaces.
- You can use this command to help you identify the interface and keep track of interface connections.
- The description or alias can be a maximum of 80 characters.
- Use show controllers sonet ds1|e1 to display the text description.
- Example
  `
  host1(config-controller)#path 2 ds1 1/7/4 description nyc01
  `
- Use the no version to remove the text description or alias.
- See path ds1|e1 description.

### Configuring an Unframed E1 Line

Use the following command to configure an unframed E1 line.

path e1 unframed

- Use to configure an unframed E1 on the path.
- You cannot configure a mixture of T1 and E1 lines on the same cOCx/STMx line module.
- When you issue this command, the router creates one channel for the unframed E1 line, and assigns the number one to that channel.
- Example
  `
  host1(config-controller)#path 1 e1 1/7/4
  host1(config-controller)#path 1 e1 1/7/4 unframed
  `
- Use the no version to delete an unframed E1 interface from the path.
- See path e1 unframed.

### Configuring T1 and E1 Lines

You can configure T1 and E1 interfaces on paths and tributaries. To do so, complete the following steps:

1. Configure the clock source. You must coordinate this setting with the other end of the line to establish which end is the transmit (internal) clock and which is the receive (line) clock.
2. (Optional) Configure the framing format.
3. (Optional) Enable processing of SNMP link status information about an interface and its associated tributary.
4. Configure the T1 or E1 line parameters.
5. (Optional) Enable processing of SNMP link status information about a channel group.
6. (Optional—T1 only) Configure FDL messages.
7. (Optional) Assign a text description or an alias to the interface.

path ds1|e1 channel-group description

- Use to assign a text description or an alias to a DS1 (T1) or an E1 channel group for channelized SONET and SDH interfaces.
- You can use this command to help you identify the interface and keep track of interface connections.
- The description or alias can be a maximum of 80 characters.
- Use show controllers sonet ds1|e1 to display the text description.
- Example
  `
  host1(config-controller)#path 10 e1 1/5/1 channel-group 4
  description westford e1 151.4
  `
- Use the no version to remove the text description or alias.
- See path ds1|e1 channel-group description.

path ds1|e1 channel-group shutdown

- Use to disable a T1 or an E1 channel group.
- T1 and E1 channel groups are enabled by default.
- Example
  `
  host1 (config-controll)#path 12 e1 1/4/1 channel-group 2 shutdown
  `
- Use the no version to restart a disabled channel group.
- See path ds1|e1 channel-group shutdown.

path ds1|e1 channel-group snmp trap link-status

- Use to enable SNMP link status processing for a T1 or an E1 channel group.
- The default is disabled.
- Example
  `
  host1(config-controll)#path 2 ds1 1/1/1 channel-group 2 snmp trap link-status
  `
- Use the no version to disable SNMP link status processing for a T1 or an E1 channel group.
- See path ds1|e1 channel-group snmp trap link-status.

path ds1|e1 channel-group timeslots

- Use to configure T1 or E1 line parameters.
- You cannot configure a mixture of T1 and E1 lines on the same cOCx/STMx line module.
- Specify a T1 or E1 channel group number, and assign a range of timeslots.
- To configure a whole T1 or E1 line, assign all the timeslots to the channel group.
- You can specify a line speed that applies to all DS0 timeslots assigned to a channel group.
- Example
  `
  host1(config-controll)#path 2 ds1 1/1/1 channel-group 2 timeslots 5-6
  `
- Use the no version to remove the timeslots from the channel group.
- See path ds1|e1 channel-group timeslots.

path ds1|e1 clock source

- Use to configure the transmit clock source for the T1 or E1 interface.
- Select a clock as follows:
  - Specify the keyword line to use a transmit clock recovered from the line’s receive data stream.
  - Specify the keywords internal module to use the line module’s internal clock.
  - Specify the keywords internal chassis to use the router’s clock.
- You can usually accept the default option, line, to use a transmit clock recovered from the line’s receive data stream, except in rare cases such as back-to-back router tests. When performing back-to-back router tests, configure one end of the line as internal and the other end as line.
- On a cOC3/STM1 I/O module, you can configure some interfaces with internal clock sources and others with line clock sources. However, all interfaces with internal clock sources must use either the router’s clock or the module’s clock. You cannot configure some interfaces on the I/O module to use the router’s clock and others to use the module’s clock.
- To change the clock source of the interfaces on a cOC3/STM1 I/O module from the router’s clock to the module’s clock or vice versa, first change the clock source of all ports to the line setting, and then to the new internal clock setting.
- Example
  `
  host1(config-controll)#path 12 e1 1/4/1 clock source line
  `
- Use the no version to restore the default value, line.
- See path ds1|e1 clock source.

path ds1|e1 framing

- Use to configure the framing format for a T1 or an E1 interface.
- For T1, specify esf (extended superframe) or sf (superframe). The default is esf.
- The HDLC idle character differs from non–E Series implementations. For T1 interfaces, if you configure SF, the router sets the HDLC idle character to 0xFF. If you configure ESF, the router sets the HDLC idle character to 0x7E.
- For E1, specify crc4 or no-crc4. The default is crc4.
- Choose a framing format that is compatible with the framing format at the other end of the line.
- Example
  `
  host1(config-controll)#path 12 e1 1/4/1 framing no-crc4
  `
- Use the no version to restore the default value.
- See path ds1|e1 framing.

path ds1|e1 snmp trap link-status

- Use to enable SNMP link status processing for a T1 or an E1 interface and its associated tributary.
- The default is disabled.
- Example
  `
  host1(config-controll)#path 2 ds1 1/1/1 snmp trap link-status
  `
- Use the no version to disable SNMP link status processing.
- See path ds1|e1 snmp trap link-status.

### Configuring T1 Interfaces to Send FDL Messages

You can configure a T1 interface to send FDL messages. To configure FDL:

1. Specify a SONET interface.
   `
   host1(config)#controller sonet 8/0
   `
2. Specify the standard for transmission of FDL messages on both ends of the T1 connection.
   `
   host1(config-controll)#path 2 ds1 1/1/1 fdl ansi
   `
3. (Optional) Configure the interface to operate in an FDL carrier environment.
   `
   host1(config-controll)#path 2 ds1 1/1/1 fdl carrier
   `
4. (Optional) Specify the FDL messages.
   `
   host1(config-controll)#path 2 ds1 1/1/1 fdl string eic "ERX-1410"
   host1(config-controll)#path 2 ds1 1/1/1 fdl string lic "Bldg 10"
   host1(config-controll)#path 2 ds1 1/1/1 fdl string fic "GY788"
   host1(config-controll)#path 2 ds1 1/1/1 fdl string unit 080001
   `
5. Enable transmission of FDL messages.
   `
   host1(config-controll)#path 2 ds1 1/1/1 fdl transmit idle-signal
   `

path ds1 fdl

- Use to specify the FDL standard for the interface.
- Specify the keyword ansi to support the ANSI FDL standard (see References).
- Specify the keyword att to support the AT&T FDL standard (see References).
- Specify the keyword all to support both the ANSI and AT&T standards.
- Specify the keyword none to remove the current FDL mode settings.
- You can configure a different standard on each T1 channel.
- Example
  `
  host1(config-controll)#path 2 ds1 1/1/1 fdl att
  `
- Use the no version to restore the default, none.
- See path ds1 fdl.

path ds1 fdl carrier

- Use to specify that an interface is used in the carrier environment.
- Example
  `
  host1(config-controll)#path 2 ds1 1/1/1 fdl carrier
  `
- Use the no version to restore the default situation, in which the T1 interface does not operate in the carrier environment.
- See path ds1 fdl carrier.

path ds1 fdl string

- Use to configure an FDL message as defined in the ANSI T1.403 specification.

  | Note: The router sends these FDL messages only if you have issued the path ds1 fdl command with the ansi or all keyword and then issued the path ds1 fdl transmit command.

- Example
  `
  host1(config-controll)#path 2 ds1 1/1/1 fdl string eic "ERX-1440"
  `
- Use the no version to restore the default value to the specified FDL message or to all FDL messages.
- See path ds1 fdl string.

path ds1 fdl transmit

- Use to configure the router to send the specified type of FDL message on the T1 channel.
- By default, the router sends no FDL messages.

  | Note: The router sends FDL messages specified with the path ds1 fdl string command only if you have issued the path ds1 fdl command with the ansi or all keyword. If you specified the att keyword with the path ds1 fdl command, the router sends only performance data.

- Specify the keyword path-id to transmit path identifications every second.
- Specify the keyword idle-signal to send idle signals every second.
- Specify the keyword test-signal to transmit test signals every second.
- Example
  `
  host1(config-controll)#path 2 ds1 1/1/1 fdl transmit path-id
  `
- Use the no version to disable transmission of the specified FDL message or all FDL messages.
- See path ds1 fdl transmit.

### Disabling Interfaces and Channel Groups

To disable interfaces and channel groups, use the following commands.

path ds1|e1 shutdown

- Use to disable a T1 or an E1 interface.
- T1 and E1 interfaces are enabled by default.
- Example
  `
  host1 (config-controll)#path 12 e1 1/4/1 shutdown
  `
- Use the no version to restart a disabled interface.
- See path ds1|e1 shutdown.

### Configuring Higher Layers

You must configure HDLC over the top layer of the T1/E1 interface. See HDLC Channel Configuration Tasks.

## T3 Configuration Tasks

Before you configure T3 on an interface, you must configure SONET or SDH on the interface. See SONET/SDH Configuration Tasks.

To configure T3 over SONET or SDH on a cOCx/STMx interface, complete the following actions:

1. Configure a T3 path over the SONET and SDH interfaces.
2. Configure T3 line parameters (for both clear channel T3 lines and multiplexed T3 lines composed of fractional T1 lines).
3. (Optional) Configure T1 or fractional T1 line parameters.

For detailed examples, see Configuration Examples.

path ds3

- Use to create and configure a T3 path over SONET and SDH interfaces.
- Example
  `
  host1(config-controller)#path 2 ds3 1 channelized
  `
- Use the no version to delete a path.
- See path ds3.

### Configuring T3 Line Parameters

Complete the following steps to configure T3 line parameters. Configure these parameters for both clear channel and multiplexed T3 lines.

1. Configure the clock source. You must coordinate this setting with the other end of the line to establish which end is the transmit (internal) clock and which is the receive (line) clock.
2. (Optional) Assign a text description or an alias to the interface.
3. (Optional) Configure the framing format.
4. (Optional) Enable processing of SNMP link status information about an interface.
5. (Optional) Configure MDL settings.
6. (Optional) Configure T1 channels.

path ds3 clock source

- Use to configure the transmit clock source for the T3 line.
- Select a clock as follows:
  - Specify the keyword line to use a transmit clock recovered from the line’s receive data stream.
  - Specify the keywords internal module to use the line module’s internal clock.
  - Specify the keywords internal chassis to use the router’s clock.
- You can usually accept the default option, line, to use a transmit clock recovered from the line’s receive data stream, except in rare cases such as back-to-back router tests. When performing back-to-back router tests, configure one end of the line as internal and the other end as line.
- On a cOC3/STM1 I/O module, you can configure some interfaces with internal clock sources and others with line clock sources. However, all interfaces with internal clock sources must use either the router’s clock or the module’s clock. You cannot configure some interfaces on the I/O module to use the router’s clock and others to use the module’s clock.
- To change the clock source of the interfaces on a cOC3/STM1 I/O module from the router’s clock to the module’s clock or vice versa, first change the clock source of all ports to the line setting, and then to the new internal clock setting.
- Example
  `
  host1(config-controll)#path 12 ds3 1 clock source line
  `
- Use the no version to restore the default value, line.
- See path ds3 clock source.

path ds3 description

- Use to assign a text description or an alias to a T3 (DS3) over channelized SONET/SDH interface.
- You can use this command to help you identify the interface and keep track of interface connections.
- The description or alias can be a maximum of 80 characters.
- Use show controllers sonet ds3 to display the text description.
- Example
  `
  host1(config-controller)#path 12 ds3 1 description boston_t3
  `
- Use the no version to remove the text description or alias.
- See path ds3 description.

path ds3 framing

- Use to configure the framing format for a T3 interface.
- Specify c-bit parity framing or m23 multiplexer framing.
- Example
  `
  host1(config-controll)#path 12 ds3 1 framing m23
  `
- Use the no version to restore the default value, c-bit parity framing.
- See path ds3 framing.

path ds3 shutdown

- Use to disable a T3 interface.
- T3 interfaces are enabled by default.
- Example
  `
  host1(config-controll)#path 12 ds3 1 shutdown
  `
- Use the no version to restart a disabled interface.
- See path ds3 shutdown.

path ds3 snmp trap link-status

- Use to enable SNMP link status processing for a T3 interface.
- The default disables SNMP link status processing.
- Example
  `
  host1(config-controll)#path 12 ds3 1 snmp trap link-status
  `
- Use the no version to disable SNMP link status processing.
- See path ds3 snmp trap link-status.

### Configuring T3 Interfaces to Send MDL Messages

You can configure a T3 interface to send MDL messages. MDL messages are supported only when the T3 framing is set for C-bit parity, the default setting.

To configure a T3 interface to send MDL messages:

1. Specify a SONET interface.
   `
   host1(config)#controller sonet 8/0
   `
2. (Optional) Configure the interface to operate in an MDL carrier environment.
   `
   host1(config-controll)#path 12 ds3 1 mdl carrier
   `
3. Specify the MDL messages.
   `
   host1(config-controll)#path 12 ds3 1 mdl string eic "ERX 1410"
   host1(config-controll)#path 12 ds3 1 mdl string fic "FG786"
   host1(config-controll)#path 12 ds3 1 mdl string lic "Bldg 2"
   host1(config-controll)#path 12 ds3 1 mdl string pfi "Site 1"
   host1(config-controll)#path 12 ds3 1 mdl string port 0800
   host1(config-controll)#path 12 ds3 1 mdl string unit 080001
   `
4. Enable transmissions of MDL messages.
   `
   host1(config-controll)#path 12 ds3 1 mdl transmit path-id
   host1(config-controll)#path 12 ds3 1 mdl transmit idle-signal
   host1(config-controll)#path 12 ds3 1 mdl transmit test-signal
   `

path ds3 mdl carrier

- Use to specify that an interface is used in the carrier environment.
- Example
  `
  host1(config-controll)#path 12 ds3 1 mdl carrier
  `
- Use the no version to restore the default situation, in which the interface does not operate in the carrier environment.
- See path ds3 mdl carrier.

path ds3 mdl string

- Use to specify an MDL message.
- Example
  `
  host1(config-controll)#path 12 ds3 1 mdl string port 0800
  `
- Use the no version to restore the default value to the specified MDL message or to all MDL messages.
- See path ds3 mdl string.

path ds3 mdl transmit

- Use to enable transmission of MDL messages.
- Specify the keyword path-id to transmit path identifications every second.
- Specify the keyword idle-signal to send idle signals every second.
- Specify the keyword test-signal to transmit test signals every second.
- Example
  `
  host1(config-controll)#path 12 ds3 1 mdl transmit test-signal
  `
- Use the no version to disable transmission of the specified type of MDL messages or all MDL messages.
- See path ds3 mdl transmit.

### Configuring T1 Channels on T3 Interfaces

To configure T1 and fractional T1 channels over T3 interfaces:

1. Configure the T1 path.
2. Configure the clock source.

   You must coordinate this setting with the other end of the line to establish which end is the transmit (internal) clock and which is the receive (line) clock.

3. (Optional) Assign a text description or an alias to the interface.
4. (Optional) Configure the framing format.
5. (Optional) Enable processing of SNMP link status information about an interface.
6. Configure the T1 line parameters.

   You can specify parameters for a single channel, multiple individual channels, ranges of channels, or any combination of the three types of specifications. For example:

   `
   host1(config-controll)#path 12 ds3 1 t1 25-28
   `
7. (Optional) Enable processing of SNMP link status information about a channel group.

path ds3 t1

- Use to create and configure the T1 path over SONET and SDH interfaces.
- Example
  `
  host1(config-controll)#path 12 ds3 1 t1 25-28
  `
- Use the no version to delete a path.
- See path ds3 t1.

path ds3 t1 clock source

- Use to configure the transmit clock source for the T3 line.
- Use a transmit clock recovered from the line’s receive data stream, except in rare cases such as back-to-back router tests. When performing back-to-back router tests, configure one end of the line as internal and the other end as line.
- Specify the keyword line to use a transmit clock recovered from the line’s receive data stream.
- Specify the keywords internal module to use the line module’s internal clock.
- Specify the keywords internal chassis to use the router’s clock.
- On a cOC3/STM1 I/O module, you can configure some ports with internal clock sources and others with line clock sources. However, all ports with internal clock sources must use either the router’s clock or the module’s clock. You cannot configure some ports on the I/O module to use the router’s clock and others to use the module’s clock.
- To change the clock source of the ports on a cOC3/STM1 I/O module from the router’s clock to the module’s clock or vice versa, change the clock source of all ports first to the line setting, and then to the new internal clock setting.
- Example
  `
  host1(config-controll)#path 12 ds3 1 t1 28 clock source internal chassis
  `
- Use the no version to restore the default value, line clocking.
- See path ds3 t1 clock source.

path ds3 t1 description

- Use to assign a text description or an alias to a T1 or fractional T1 channel on a T3 (DS3) over channelized SONET/SDH interface.
- You can use this command to help you identify the interface and keep track of interface connections.
- The description or alias can be a maximum of 80 characters.
- Use show controllers sonet ds3 to display the text description.
- Examples
  `
  host1(config-controller)#path 12 ds3 1 t1 28 description boston_t1_on_t3
  host1(config-controller)#path 12 ds3 1 t1 28/5
  description washington_fractional_t1_on_t3
  `
- Use the no version to remove the text description or alias.
- See path ds3 t1 description.

path ds3 t1 framing

- Use to configure the T1 framing format for a T3 interface.
- You must specify either esf (extended superframe) or sf (superframe) framing.
- The framing format you choose must be compatible with the framing format at the other end of the line.
- Example
  `
  host1(config-controll)#path 12 ds3 1 t1 28 framing sf
  `
- Use the no version to restore the default value, esf framing.
- See path ds3 t1 framing.

path ds3 t1 shutdown

- Use to disable T1 channels or a subchannel.
- T1 channels and subchannels are enabled by default.
- Examples
  `
  host1(config-controll)#path 12 ds3 t1 5,9,14-17 shutdown
  host1(config-controll)#path 12 ds3 t1 28/5 shutdown
  `
- Use the no version to restart a disabled interface.
- See path ds3 t1 shutdown.

path ds3 snmp trap link-status

- Use to enable SNMP link status processing for T1 channels or a subchannel.
- The default disables SNMP link status processing.
- Examples
  `
  host1(config-controll)#path 2 ds3 3 t1 28 snmp trap link-status
  host1(config-controll)#path 2 ds3 3 t1 28/5 snmp trap link-status
  `
- Use the no version to disable SNMP link status processing for a T1 channel.
- See path ds3 snmp trap link-status.

path ds3 t1 timeslots

- Use to assign a range of DS0 timeslots to a subchannel as a single data stream.
- You can specify a line speed for all DS0 timeslots assigned to a subchannel.
- Examples
  `
  host1(config-controll)#path 2 ds3 1 t1 28 timeslots 1-10
  host1(config-controll)#path 2 ds3 1 t1 28/1 timeslots 1-10 speed 56
  `
- Use the no version to delete the fractional T1 circuit.
- See path ds3 t1 timeslots.

### Configuring T1 Channels to Send FDL Messages

To configure T1 channels to send FDL messages:

1. Specify a SONET interface.
   `
   host1(config)#controller sonet 8/0
   `
2. Specify the standard for transmission of FDL messages on both ends of the T1 connection.
   `
   host1(config-controll)#path 2 ds3 1 t1 28 fdl ansi
   `
3. (Optional) Configure the interface to operate in an FDL carrier environment.
   `
   host1(config-controll)#path 2 ds3 1 t1 28 fdl carrier
   `
4. (ANSI signals) Specify the FDL messages.
   `
   host1(config-controll)#path 2 ds3 1 t1 28 fdl string eic "ERX-1410"
   host1(config-controll)#path 2 ds3 1 t1 28 fdl string lic "Bldg 10"
   host1(config-controll)#path 2 ds3 1 t1 28 fdl string fic "GY788"
   host1(config-controll)#path 2 ds3 1 t1 28 fdl string unit 080001
   `
5. Enable transmission of FDL messages.
   `
   host1(config-controll)#path 2 ds3 1 t1 28 fdl transmit idle-signal
   `

path ds3 t1 fdl

- Use to specify the FDL standard for the interface.
- Specify the T1 channels in the range 1 through 28.
- Specify the keyword ansi to support the ANSI FDL standard (see References).
- Specify the keyword att to support the AT&T FDL standard (see References).
- Specify the keyword all to support both the ANSI and AT&T standards
- Specify the keyword none to remove the current FDL mode settings
- You can configure a different standard on each T1 channel.
- Example
  `
  host1(config-controll)#path 2 ds3 1 t1 20-28 fdl att
  `
- Use the no version to restore the default, no specified FDL standard.
- See path ds3 t1 fdl.

path ds3 t1 fdl carrier

- Use to specify that T1 channels are used in the carrier environment.
- Example
  `
  host1(config-controll)#path 2 ds3 1 t1 4,6,10-14 fdl carrier
  `
- Use the no version to restore the default situation, in which the T1 channel does not operate in the carrier environment.
- See path ds3 t1 fdl carrier.

path ds3 t1 fdl string

- Use to configure an FDL message as defined in the ANSI T1.403 specification.

  | Note: The router sends these FDL messages only if you have issued the path ds3 t1 fdl command with the ansi or all keyword and then issued the path ds3 t1 fdl transmit command.

- Example
  `
  host1(config-controll)#path 2 ds3 1 t1 28 fdl string eic "ERX-1440",
  `
- Use the no version to restore the default value to the specified FDL message or to all FDL messages.
- See path ds3 t1 fdl string.

path ds3 t1 fdl transmit

- Use to configure the router to send the specified type of FDL message.
- By default, the router sends only FDL performance data messages.

  | Note: The router sends FDL messages specified with the path ds3 t1 fdl string command only if you have issued the path ds3 t1 fdl command with the ansi or all keyword. If you specified the att keyword with the path ds3 t1 fdl command, the router sends only performance data.

- Specify the keyword path-id to transmit path identifications every second.
- Specify the keyword idle-signal to send idle signals every second.
- Specify the keyword test-signal to transmit test signals every second.
- Example
  `
  host1(config-controll)#path 2 ds3 1 t1 28 fdl transmit path-id
  `
- Use the no version to disable transmission of the specified FDL message or all FDL messages.
- See path ds3 t1 fdl transmit.

### Configuring Higher Layers

You must configure HDLC over the top layer of the T3 interface. See HDLC Channel Configuration Tasks.

## HDLC Channel Configuration Tasks

You must configure HDLC over the T3, T1, unframed E1, or fractional T1/E1 line that you configure on an interface. As Figure 8 shows, HDLC must be the top layer of the interface stack.

To configure an HDLC channel, specify a serial interface. For example:

`

host1(config)#interface serial 4/0:1/1/1/1

`

### Optional Tasks

The following configuration tasks are optional when you configure an HDLC channel on a channelized T3 interface:

- Configure the CRC.
- Configure the HDLC idle character.
- Enable data inversion on the interface.
- Set the MRU.
- Set the MTU.
- Assign a text description or an alias to the serial interface.

crc

- Use to configure the size of the CRC.
- Specify the number of bits (16 or 32) that are used to calculate the frame check sequence (FCS). Both the sender and receiver must use the same setting.
- The CRC is an error-checking technique that uses a calculated numeric value to detect errors in transmitted data.
- A 32-bit CRC should be used to protect longer streams at faster rates and, therefore, provide better ongoing error detection.
- Example
  `
  host1(config-if)#crc 32
  `
- Use the no version to restore the default, 16.
- See crc.

idle-character

- Use to configure the HDLC idle character.
- The idle character is sent between HDLC packets.
- Specify one of the following idle characters:
  - flags—Sets the idle character to 0x7E
  - marks—Sets the idle character to 0xFF
- Example
  `
  host1(config-ifs)#idle-character marks
  `
- Use the no version to restore the default value, 0x7E (flags).
- See idle-character.

interface serial

- Use to specify a serial interface.
- Example for unframed E1 interface
  `
  host1(config)#interface serial 4/0:1/1/1/1/1
  `
- Example for fractional T1/E1 interface
  `
  host1(config)#interface serial 4/0:1/1/1/1/1
  `
- Example for unchannelized T3 interface
  `
  host1(config)#interface serial 4/0:1/1
  `
- Example for T3 interface channelized to fractional T1
  `
  host1(config)#interface serial 4/0:1/1/10/22
  `
- Use the no version to remove the interface.
- See interface serial.

invert data

- Use to enable data stream inversion for the interface.
- Enable data stream inversion only if it is turned on at the other end of the line.
- Example
  `
  host1(config-if)#invert data
  `
- Use the no version to disable the feature.
- See invert data.

mru

- Use to configure the MRU size for the interface.
- Specify a value in the range 4–9996 bytes.
- Coordinate this value with the network administrator on the other end of the line.
- If you set this value with a different value for another protocol, such as IP, the router uses the lower value. The lower MRU might cause unexpected results in the network.
- Example
  `
  host1(config-if)#mru 1500
  `
- Use the no version to restore the default, 1600 bytes.
- See mru.

mtu

- Use to configure the MTU size for the interface.
- Specify a value in the range 4–9996 bytes.
- You should coordinate this value with the network administrator on the other end of the line.
- You can set a different MTU value in higher-level protocols, such as IP. If you do, the router uses the lower value. The lower MTU might cause unexpected results in the network.
- Example
  `
  host1(config-if)#mtu 1500
  `
- Use the no version to restore the default, 1600 bytes.
- See mtu.

serial description

- Use to assign a text description or an alias to a serial HDLC interface.
- You can use this command to help you identify the interface and keep track of interface connections.
- The description or alias can be a maximum of 80 characters.
- Use show interfaces serial to display the text description.
- Example
  `
  host1(config-if)#serial description ottawa012 hdlc channel
  `
- Use the no version to remove the text description or alias.
- See serial description.

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