Guest

T1/E1 & T3/E3

E1 PRI Troubleshooting

Document ID: 14167

Updated: Sep 09, 2005

   Print

Introduction

When troubleshooting a Primary Rate Interface (PRI), ensure that the E1 is running properly on both ends. If Layer 1 problems have been resolved, look for problems on Layers 2 and 3. Use the show controller e1 command to verify that the configuration of the line matches that of the remote end. Ensure that the framing, line coding, and clock source are configured correctly. Refer to the E1 Alarm Troubleshooting and E1 Error Events Troubleshooting documents for more information. Contact your Service Provider for the correct settings.

Before You Begin

Conventions

For more information on document conventions, see the Cisco Technical Tips Conventions.

Prerequisites

There are no specific prerequisites for this document.

Components Used

The information in this document is based on the software and hardware versions below.

  • Cisco IOS® Software Release 12.0

The information presented in this document was created from devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If you are working in a live network, ensure that you understand the potential impact of any command before using it.

Using the show isdn status Command

The show isdn status command displays a summary of all ISDN interfaces. It also displays the status of Layers 1, 2, and 3. Complete the following steps to check the status of the layers:

  1. Verify that Layer 1 is in the ACTIVE state. The status of Layer 1 should always be ACTIVE unless the E1 is down.

    If the show isdn status command output indicates that Layer 1 is DEACTIVATED, then there is a problem with the physical connectivity of the E1 line. If the line is administratively down, use the no shutdown command to restart the interface.

  2. Ensure that Layer 2 is in the MULTIPLE_FRAME_ESTABLISHED state. This is the desired state for Layer 2, indicating that Layer 2 frames are being exchanged and Layer 2 initialization has finished.

    If Layer 2 is not in the MULTIPLE_FRAME_ESTABLISHED state, use the show controller e1 EXEC command to diagnose the problem. For more information, see the E1 Alarm Troubleshooting document.

    Since the show isdn status command displays a summary of the current status, it is possible that Layer 2 is bouncing up and down despite indicating a MULTIPLE_FRAME_ESTABLISHED state. Use the debug isdn q921 command to verify that Layer 2 is stable.

    Following is an example of show isdn status output:

    bru-nas-03#show isdn status
    Global ISDN Switchtype = primary-net5
    ISDN Serial0:15 interface
            dsl 0, interface ISDN Switchtype = primary-net5
        Layer 1 Status:
            ACTIVE
        Layer 2 Status:
            TEI = 0, Ces = 1, SAPI = 0, State = MULTIPLE_FRAME_ESTABLISHED
        Layer 3 Status:
            5 Active Layer 3 Call(s)
        Activated dsl 0 CCBs = 5
            CCB:callid=7D5, sapi=0, ces=0, B-chan=9, calltype=DATA
            CCB:callid=7D6, sapi=0, ces=0, B-chan=10, calltype=DATA
            CCB:callid=7DA, sapi=0, ces=0, B-chan=11, calltype=DATA
            CCB:callid=7DE, sapi=0, ces=0, B-chan=1, calltype=DATA
            CCB:callid=7DF, sapi=0, ces=0, B-chan=2, calltype=DATA
        The Free Channel Mask:  0xFFFF78FC
    ISDN Serial1:15 interface
            dsl 1, interface ISDN Switchtype = primary-net5
        Layer 1 Status:
            ACTIVE
        Layer 2 Status:
            TEI = 0, Ces = 1, SAPI = 0, State = TEI_ASSIGNED
        Layer 3 Status:
            0 Active Layer 3 Call(s)
        Activated dsl 1 CCBs = 0
        The Free Channel Mask:  0xFFFF7FFF
        Total Allocated ISDN CCBs = 5

    Notice that E1 0 (whose D-channel is Serial 0:15) has Layer 1 as ACTIVE and Layer 2 as MULTIPLE_FRAME_ESTABLISHED indicating that the signaling channel is functioning correctly and is exchanging Layer 2 frames with the Telco switch. The D-channel (Serial1:15) for E1 1 has Layer 1 ACTIVE, but Layer 2 is TEI_ASSIGNED. This indicates that the PRI is not exchanging Layer 2 frames with the switch. Use the show controller e1 x command to troubleshoot. Refer to the E1 Troubleshooting flowchart for more information.

Using the debug q921 Command

The debug isdn q921 command displays data link layer (Layer 2) access procedures that are occurring at the router on the D-channel.

Ensure you are configured to view debug messages by using the logging console or terminal monitor command.

Note: In a production environment, verify that console logging is disabled by using the show logging command. If logging is enabled, the access server might intermittently stop working when the console port is overloaded with log messages. Enter the no logging console command to disable logging.

Note: If debug isdn q921 is turned on and you do not receive any debug outputs, place a call or reset the controller to get debug outputs.

Complete the following steps to ensure that the data link layer access procedures are occurring at the router on the D-channel:

  1. Verify that Layer 2 is stable by looking for messages in the debug output. If the line is bouncing up and down, output similar to the following will appear:

    Mar 20 10:06:07.882: %ISDN-6-LAYER2DOWN: Layer 2 for Interface Se0:15, TEI 0 changed to down
    Mar 20 10:06:09.882: %LINK-3-UPDOWN: Interface Serial0:15, changed state to down
    Mar 20 10:06:21.274: %DSX1-6-CLOCK_CHANGE: Controller 0 clock is now selected as clock source
    Mar 20 10:06:21.702: %ISDN-6-LAYER2UP: Layer 2 for Interface Se0:15, TEI 0 changed to up
    Mar 20 10:06:22.494: %CONTROLLER-5-UPDOWN: Controller E1 0, changed state to up
    Mar 20 10:06:24.494: %LINK-3-UPDOWN: Interface Serial0:15, changed state to up
    
    

    If Layer 2 does not appear to be stable, refer to the E1 Error Events Troubleshooting document.

  2. Verify that only service access point identifier (SAPI) messages appear on both the transmit (TX) and receive (RX) sides. For example:

    Mar 20 10:06:52.505: ISDN Se0:15: TX -> RRf sapi = 0 tei = 0 nr = 0
    Mar 20 10:06:52.505: ISDN Se0:15: RX <- RRf sapi = 0 tei = 0 NR = 0
    Mar 20 10:07:22.505: ISDN Se0:15: TX -> RRp sapi = 0 tei = 0 NR = 0
    Mar 20 10:07:22.509: ISDN Se0:15: RX <- RRp sapi = 0 tei = 0 NR = 0
    Mar 20 10:07:22.509: ISDN Se0:15: TX -> RRf sapi = 0 tei = 0 NR = 0
    Mar 20 10:07:22.509: ISDN Se0:15: RX <- RRf sapi = 0 tei = 0 NR = 0 
    
    
  3. Verify that asynchronous balanced mode extended (SABME) messages do not appear. These messages indicate that Layer 2 is trying to reinitialize. The messages usually appear when poll requests (RRp) are transmitted and there is no response from the switch (RRf), or vice versa. Following are examples of SABME messages:

    Mar 20 10:06:21.702: ISDN Se0:15: RX <- SABMEp sapi = 0 tei = 0
    Mar 20 10:06:22.494: ISDN Se0:15: TX -> SABMEp sapi = 0 tei = 0
    
    

    If SABME messages appear, complete the following steps:

    1. Use the show running-config command to ensure that isdn switch-type and pri-group timeslots are configured correctly. Contact your Service Provider for the correct values.

    2. To change the isdn switch-type and pri-group settings, enter the following commands:

      bru-nas-03#configure terminal
      bru-nas-03(config)#isdn switch-type primary-net5
      bru-nas-03(config)#controller e1 0
      bru-nas-03(config-controlle)#pri-group timeslots 1-31
      
      
  4. Ensure the D-channel is up using the show interfaces serial number:15 command, where the number is the interface number.

    If the D-channel is not up, use the no shutdown command to bring it up. For example:

    bru-nas-03(config)#interface serial 0:15
    bru-nas-03(config-if)#no shutdown
    
  5. Ensure encapsulation is PPP. If not, use the encapsulation ppp command to set encapsulation. For example:

    bru-nas-03(config-if)#encapsulation ppp
    
  6. Ensure the interface is in loopback mode. Loopback should be set only for testing purposes. Use the no loopback command to remove loopbacks. For example:

    bru-nas-03(config-if)#no loopback 
    
  7. Power cycle the router.

If the problem persists, contact your Service Provider or the Cisco Technical Assistance Center (TAC).

Related Information

Updated: Sep 09, 2005
Document ID: 14167