Common ISDN Problems

Problem	Possible Cause	Possible Solution
An ISDN Basic Rate Interface (BRI) or Primary Rate Interface (PRI) connection is slow, or data is corrupted in transit.	Excessive errors on the ISDN line.	Diagnose with the show isdn command. An error count greater than 20 indicates a problem at the telephone company. (See page 5-2 for BRI connections and page 5-5 for PRI connections.)
The PortMaster cannot establish or maintain an ISDN BRI connection.	An incorrect configuration on the port	Use the show isdn command to check the status and configuration of the port (page 5-3).
The PortMaster cannot establish or maintain an ISDN PRI connection.	Failed circuit. Failed D channel. Incorrect configuration on the port. No synchronization with the T1 switch. PRI connection needs to be reset at the switch.	Use the procedure on page 5-5 to verify the status and configuration of an ISDN PRI port. Use the procedure on page 5-6 to determine if the PortMaster and the T1 switch are synchronized. Use the set line0 loopback command to reset the PRI connection at the switch (page 5-8)
The PortMaster cannot establish or maintain an ISDN connection.	Problems with ISDN negotiation or packet exchange.	Use the set debug isdn commands to display ISDN negotiation and packet exchange information to the console (page 5-9).

Troubleshooting an ISDN BRI Connection

Verifying LEDs

1. Check the LED states as follows and compare its behavior to Table 5-2:
   • On an Office Router OR-U, check the NT1 LED.

   • On a PortMaster 2E, PortMaster 2Ei, or PortMaster 2i, check the appropriate BRI status LED on the back of the five-BRI expansion board.

   Table 5-2 ISDN BRI LED Indications

   LED Behavior	Indication
   Solidly lit	Synchronization and SPID registration
   Flashing slowly	Synchronization only
   Flashing rapidly	No synchronization or SPID registration

2. If the LED indicates no SPID registration, check the SPID and directory number with the show isdn D0 command.

   Verify that the configured SPID and directory number match those given to you by the telephone company, as described in Step 3 on page 5-4.

3. If the LED indicates no synchronization, check the state of the D channel.

Verify that the D channel is functioning properly by using the show isdn command. The interface state should be F7. If the interface state is not F7, do the following:

• Check that the cables are properly installed.

• Call the telephone company and ask them to check the line to ensure that it is functioning properly.

Checking the Physical Interface with show isdn

1. Enter the show isdn command.

The output displays D channel status for the ISDN BRI ports.

Command> show isdn
D	Ports	Bri Layer1		Inits	Uptime	Change	In	Out	Err
----	-----	----------		-----	------	------	---	----	----
D00	(S01/02)	F7-active		1	4days	4days	74974	79221	0

See the PortMaster Command Line Reference for an explanation of this output.

1. Check the D channel information.

You can display comprehensive information about each BRI port by using the show isdn command and specifying either a logical serial port number associated with the port or a D channel number. For example:

Interface state: F7- active
Init count: 1 uptime: 10days last state change: 10days
recv count: 201647 xmit: 217352 errors: 0
numberplan type: Local plan: ISDN E.164

S0 ---------------------------------------------------------------

Ces state: Connected last change: 10days Port state: ESTABLISHED
Directory: 4684400 SPID: 510468440000 regs: 1
Called: Caller: Flags: 0x00
Connects: 1 last connect: 10days b channel: 1 0
Setup: 04 03 08 00 10 18 02 01 01 34 01 4f 70 09 04 01
34 36 38 34 34 30 30 04 02 88 90 18 01 89 34 01

S1 ---------------------------------------------------------------

Ces state: Registered last change: 10days Port state: IDLE

Directory: 4684401 SPID: 510468440101 regs: 1
Called: Caller: 5107352832 Flags: 0x02
Connects: 56 last connect: 0 b channel: 2 1
Setup: 04 03 08 00 10 18 02 01 02 34 01 4f 6c 0c 02 01
35 31 30 37 33 35 32 38 33 32 70 09 04 01 34 36

17210455: msg 5 Disconnect, cause 11 User Busy
17210753: msg 5 Disconnect, cause 1C Invalid Number Format
17268550: msg 5 Disconnect, cause 10 Normal Clearing

1. Use the following information to diagnose ISDN BRI problems:
   • Interface state-indicates the physical interface layer state. This can be down, pending, or active.

   • CES state-on an active ISDN connection, the connection establishment sessions (CES) state must be connected. If the CES state is idle, but the interface state is active, it indicates that the D channel is down.

   • Directory and SPID-Check these values against the information given to you by the telephone company. If either the directory number or service profile identifier (SPID) is not configured correctly, use the following commands to reconfigure them:

     Command> set S0 dn Number

     Command> set S0 spid Number

For more information about configuring the PortMaster for ISDN, see the PortMaster Configuration Guide.

• Number plan and number type-These are numbering formats for the telephone numbers the telephone company uses for ISDN connections. The PortMaster learns these automatically unless a particular number plan or number type has been entered manually with the following commands:

  Command> set isdn-numberplan Plan

  Command> set isdn-numbertype Type

For more information about configuring the PortMaster for ISDN, see the PortMaster Configuration Guide. For more information about these commands, see the PortMaster Command Line Reference.

• Cause Codes-ISDN cause codes are standard messages that are received from networks conforming to the European Telecommunication Standards Institute (ETSI), ISDN2, and INS Net64 Japanese specifications. See Appendix A, "ISDN Cause Codes," for a full description.

Troubleshooting an ISDN PRI Connection

1. Use the show isdn command to display the status of the D channels for ISDN PRI ports.

The output shows

• Whether the circuit is connected-active. The D channel must be in an active state.

• Whether the D channel is operational-carrying data. If the In and Out columns display 0s, the D channel is not carrying data.

• Whether an ISDN connection exists.

  Command> show isdn

  D Ports State Change Start Up Down Time Sess In Out Err

  -- ------- --------- ------ ----- ----- ----- ----- ------ ------- -------

  0 Active 25days 0 4 504 504 61 0 0 0 0

See the PortMaster Command Line Reference for an explanation of this output.

1. Use the show line0 and show line1 commands to display information about the physical interface.

The following example is from a PortMaster with a PRI EI line:

Command> show line0
----------------------- line0 - E1 Primary Rate ISDN -----------------------
Status: DOWN	F3	Framing: FAS	Encoding: HDB3	PCM: a-law
		Violations
		---------------------------------
		Bipolar	1209159
		CRC4	0
		E-bit	0
		FAS	0

High numeric values indicate a possible configuration problem. Changing the framing and encoding with the following commands might solve the problem:

Command> set line0 encoding b8zs|ami|hdb3

For more information about these commands, see the PortMaster Command Line Reference.

Establishing Synchronization for an ISDN PRI Connection

1. Set the console and turn on ISDN frame debugging:

   Command> set console
   Setting CONSOLE to admin session

   Command> set debug isdn-d
   Setting ISDN debugging

The following debug output is from a PortMaster 3 with a nonfunctioning ISDN PRI circuit. Physical connectivity might exist between the digital facility demarcation point and the PortMaster 3, but the ISDN PRI D channel is still not operating. The D0: send 00 01 7f pattern originates from the PortMaster 3 and is sent to the switch via the digital facility. The PortMaster 3 normally receives the D0: recv 00 01 73 patterns in response from the switch.

1. Check the red and green LEDs on the back of the PortMaster 3.

If the LEDs are solidly lit, the PortMaster is synchronized with the switch and the PRI facility is functioning.

1. Confirm physical synchronization with the switch by using the show line0 or show line1 command:

 

Command> show line0
------------------------- line0 - T1 Primary Rate ISDN ---------
Status: UP	Framing: ESF	Encoding: B8ZS	PCM: u-law
Receive Level:	+2dB to -7.5dB
Alarms		Violations
------------------------------------		---------------------------------
Blue	0	Bipolar	102
Yellow	0	CRC Errors	1
Receive Carrier Loss	0	Multiframe Sync	9
Loss of Sync	0

If the switch and the PortMaster are synchronized, the line status is up and the amplitude range for the receive level is approximately 9.5 decibels (dB). This command monitors only physical connectivity (PRI facility status).

If the PortMaster PRI facility is not connected to and synchronized with the switch, the show line0 command provides no output.

Resetting a PRI Connection at the Switch

Command> set line0 loopback on
Loopback set ON for Line0

Command> set line0 loopback off
Loopback set OFF for Line0

Interpreting Send and Receive Patterns

If you see recv patterns only and no send patterns, a problem exists with the PortMaster 3. Try the following:

• Verify the line configuration. If you make any changes to the ISDN or to Line1 or Line0 configuration, you must use the save all command and reboot the PortMaster for the changes to take effect.

• Reset the D channel with the reset D0 command.

• Reboot the PortMaster.

  When a D channel becomes operational, the green LED is on and the red LED is off and set debug isdn-d output is similar to the following example:

  D0: Data Link Down
  D0: send 00 01 7f
  D0: recv 00 01 73
  D0: Data Link UP
  D0: send 00 01 01 01
  D0: recv 00 01 01 01
  D0: send 00 01 01 01
  D0: recv 00 01 01 01
  D0: send 00 01 01 01
  D0: recv 00 01 01 01
  .
  .
  .

  The following example shows normal PRI D channel activity with no incoming calls:

  D0: send 00 01 01 2f
  D0: recv 00 01 01 2f
  D0: send 00 01 01 2f
  D0: recv 00 01 01 2f
  D0: send 00 01 01 2f
  D0: recv 00 01 01 2f

  This pattern repeats. Other data passes as calls are connected to B channels.

Using Debug ISDN Commands

set debug isdn	Displays ISDN debugging information on the console.
set debug isdn D0	Displays the status of a single BRI.
set debug isdn-d	Displays ISDN frame debugging information on the console.
set debug isdn-d D0	Displays ISDN frame debugging for a single BRI.
set debug termination	Displays detailed port termination information.
set debug off	Clears all debug settings-except ISDN debug settings for a specific D channel-currently active on the PortMaster.

The following is example output from the set debug isdn d0 command:

Command> set debug isdn d0
Enabling isdn tracing d0

isdn_dial; S1 CRN7770
isdn_dodial S1 (0:1) Sending Call Request - 7770
0: Received Call Sent
07 00 01 80
S1 (0:1) DISCONNECT Unassigned Number
S1 (0:1) CALL_CLEAR
S1: Redialing at alternate 56Kbps rate
isdn_dodial S1 (0:1) Sending Call Request - 7770
0: Received Call Sent
07 00 01 80
S1 (0:1) DISCONNECT Unassigned Number
S1 (0:1) CALL_CLEAR

To disable ISDN debugging, issue the command again:

Command> set debug isdn d0
Disabling isdn tracing d0

By using the D0 keyword, you can specify a BRI line to debug:

Command> set debug isdn-d d0

Enabling isdn D tracing d0
D0: send 00 f3 01 03
D0: recv 00 f3 01 03
D0: send 00 f1 01 0f
D0: recv 00 f1 01 0b