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  • How to Determine the Reason for Disconnect from ISDN PRI

    ANSWER
    If a call disconnects for a reason beyond a standard hangup by either party, you can find the reason by capturing the call in real time via a PRI trace and decoding the disconnect message.

    First, log in to the ISDN switch and run the commands:

    pri_trace=4
    pri_log=4


    From here, data will display for all inbound or outbound calls on the Telco PRI circuit connected to the switch. You will want to identify all the pertinent information about your call, so ensure that your console/
    telnet session has a large enough screen buffer to capture everything. (If from a standard Windows
    telnet page, right-click on the window, select "Properties->Layout" and then adjust the screen buffer height to 999 lines, or set up your
    Telnet/SSH client, such as Putty, to log all output to a file.)

    You may want to mark a location in the switch output by typing in something identifiable and unique before you place the test call (i.e. "
    xxxxxxxxx_call_started_here_xxxxxxxxxxxxxx"). This will give you a starting point to search for when reviewing the trace output.
    The information will scroll rapidly across the screen as the call progresses. It is virtually impossible to read it as it occurs in real-time, so gather the call trace data when it
    is completed.

    You may want to type in another identifier at the end (i.e. "
    call_ended_here"), or
    simply turn the logging off by entering the commands "pri_trace=0" and "pri_log=0"
    ).
    Capture
    all of the data on the buffer and copy it into a text editor, or open the log file where you captured the output. Search for your identifier and try to find the test call origination. To find for the particular call, search for the phone number that
    was dialed
    as follows:
    38 30 30 37 32 34 32 33 34 38 (the number dialed in this example is 8007242348
    -- note the second digit in each pair matches the phone number)
    The digits are in ASCII format, in which the ASCII characters 0-9
    are conveniently encoded as Hexadecimal 30-39, so 1 = 31, 4 = 34, 8 = 38
    etc.

    NOTE 1:
    The number could be broken across multiple lines, so if you can't find the whole string, try searching for the last 4 digits, first 4, etc.

    NOTE 2: If searching for an inbound call,
    you should only search for the amount of digits being sent from the carrier!

    The first occurrence of this after your identifier in the text file should be the start of your call. Look for the SETUP message (the example below is for an outbound call):
    CC -> L3 00 NL_DATA_REQ 001 8603 0000 CC_SETUP_REQ
    400 300 00 340 00 00 00 00 08 02 00 00 80 04 03 80 90 a3 18 03 a9 83 85 6c
    0c 00 80 35 31 32 34 38 36 38 34 36 39 70 0b 80 38 30 30 37 32 34 32 33 34 38
    L3 -> L2 00 DL_DATA_REQ 001 8603 0603 SETUP
    300 20a 00 240 00 00 00 00 08 02 06 03 05 04 03 80 90 a3 18 03 a9 83 85 6c
    0c 00 80 35 31 32 34 38 36 38 34 36 39 70 0b 80 38 30 30 37 32 34 32 33 34 38

    If the called number is not easy to identify, you can also try to search for the caller ID in the same manner. In this example, the caller ID is 5124868469, again in ASCII Hex format.
    The number "603" seen before the SETUP is the identifier for this call, so you can track it throughout the trace. To find the disconnect reason, open your search window again and search for:


    603 DISCONNECT

    This will bring up the disconnect portion of the call, and from here we can determine the reason.
    L3 -> L2 02 DL_DATA_REQ 001 8603 0603 DISCONNECT
    300 20a 02 240 00 00 00 00 08 02 06 03 45 08 02 80 90

    Disconnect codes are captured as a hex value and are written after the code "45 08". The next hex value indicates the number of codes in the disconnect reason, which in this example is 2. Immediately after this value is code indicating the actual reason(s) for the disconnect.
    In the above PRI trace, we see codes 80 and 90. In the additional information included below, these are listed as "0x80 - Normal Disconnect" and "0x90 Normal Call Clearing", which generally indicates that one party hung up the phone.
    Lance Paddock
    BTX | Business Telephone eXchange
    1(800) 289-0299

  • #2
    There are many
    possible codes that can
    be used;
    the most common ones are listed below.
    NOTE: At the beginning of each call segment is information
    indicating the direction the PRI messages are being sent. You can determine this by comparing to the OSI model, where the carrier switch is CC (Layer 4) and proceeds down towards the physical layer.
    The order
    (from switch to physical layer/carrier) is CC->L3->L2->L2D. For instance, a DISCONNECT message that starts with L2 -> L3 is a message sent from the carrier to the switch, and one that starts with L3 -> L2 is from the switch to the carrier.

    Disconnect Cause codes:

    0x80 Normal Disconnect
    The call disconnects normally.

    0x81
    Unallocated or unassigned number
    The switch receives the ISDN number in the correct format. However, the number does
    not belong to destination equipment.

    0x82 No route to
    specified network
    The ISDN exchange receives a request to route the call through an unrecognized
    intermediate network.
    This cause
    indicates that the equipment receives a request to route the call through a

    particular transit network. However, the equipment does not recognize the network.
    The equipment that sends this cause does not recognize the transit network
    due to one of
    these reasons:
    The transit network does not exist.
    The transit network exists, but does not serve the equipment that sends this cause.

    This cause is supported on a network-dependent basis.

    0x83 No route to destination
    The call routes through an intermediate network that does not serve the destination
    address.
    This cause
    indicates that the called user is not reachable. A user is not reachable when the
    network used to route the call does not serve the required destination.

    This cause is supported on a network-dependent basis.

    0x84 Send special information tone
    The remote number you dialed is not reachable.
    Check the number you dial. Verify if you need any prefixes to access the network. For

    example, you need to dial 9 for outbound calls through a PBX. Contact your
    telco/PBX
    administrator for details.

    0x85
    Misdialled trunk prefix.
    The remote number you dialed is not reachable.
    Check the number you dial. Verify if you need any prefixes to access the network. For

    example, you need to dial 9 for outbound calls through a PBX. Contact your
    telco/PBX
    administrator for details.

    0x86 Channel unacceptable
    The service quality of the specified channel
    is insufficient to accept the connection. The
    call attempt fails because the channel is unusable.
    If you use a PBX, check the configuration of the PBX. For a PRI, find out how many
    channels your
    telco provides.

    0x87 Call awarded and delivered in established channel
    The user assigns an incoming call that connects to an already established call channel.
    This cause
    indicates that the user receives an incoming call, which connects to a channel
    already in use for similar calls (for example, packet-mode X.25 virtual calls).

    0x88 Preemption

    Your call is blocked. Calls
    are sometimes blocked if another call has a higher priority
    than your call. This situation is common with voice calls. Wait and call again later.
    If you use a PBX (or the remote site to which you connect uses a PBX), check the
    configuration of the PBX. If the condition persists, contact your telco.

    0x89 Preemption, circuit reserved for re-use
    Your call is blocked. Calls are sometimes blocked if another call has a higher priority
    than your call. This situation is common with voice calls. Wait and call again later.
    If either side uses a PBX, check the configuration of the PBX. If the condition persists,
    contact your telco.

    0x90 Normal call clearing
    Normal call clearing occurs. You do not need to perform any action.
    This cause indicates that the call disconnects because one of the users involved in the call
    has made a request to clear the call. Under normal situations, the network is not the
    source of this cause.
    If the call fails with this Disconnect Cause Code, the call most likely fails at a higher
    layer protocol such as PPP, authentication or idle timeout related issues. Verify the router
    configuration.
    Also, if you have requested a callback, the remote device disconnects the call, generates
    this code, and then calls you back.

    0x91 User busy
    The called system acknowledges the connection request. However, the system cannot
    accept the call because all B-channels are in use. The user equipment is compatible with
    the call in this situation.
    Note: If you have multiple ISDN circuits, the telco can configure them in a "hunt-group",
    in which calls switch to the next available circuit.

    0x92 No user response
    The connection fails because the destination does not respond to the call.
    This cause indicates that a user does not respond to a call establishment message within
    the prescribed period. The user must respond with either an alert or connect indication
    according to ITU-T Q.931, when either timer T303 or T310 expires.

    0x93 No answer from user
    The destination responds to the connection request but fails to complete the connection
    within the prescribed time. This cause indicates that a user has provided an alert
    indication, but has not provided a connect indication within a prescribed period. Q.931
    procedures do not necessarily generate this cause. Internal network timers sometimes
    generate this cause.
    The problem is at the remote end of the connection.

    0x94 Subscriber absent
    The remote device you attempt to reach is unavailable and is disconnected from the ISDN
    network.
    Contact the person responsible for that device.

    0x95 Call rejected
    The destination is able to accept the call but rejects the call for an unknown reason.
    This cause indicates that the equipment that sends this cause does not want to accept this
    call.
    Note: The equipment is able to accept the call because the equipment that sends this
    cause is neither busy nor incompatible. However, the equipment rejects the call.

    0x96 Number changed
    The ISDN number used to set up the call does not belong to a system.
    A caller receives this cause when the called party number is no longer assigned. You can
    optionally include the new called party number in the diagnostic field. If a network does
    not support this capability, the caller receives cause No. 81, unassigned (unallocated)
    number.
    Lance Paddock
    BTX | Business Telephone eXchange
    1(800) 289-0299

    Comment


    • #3
      0x97 Redirection to new destination
      Your call is routed to a different ISDN number.
      Check the number you call. Also verify the PBX configuration (if you use PBX).

      0x99 Exchange routing error
      Your call cannot be successfully routed to the remote party.
      Check the number you call. Also verify the PBX configuration (if you use PBX).

      0x9A Non-selected user clearing
      The destination is able to accept the call. However, the destination rejects the call because
      the call is not assigned to a user.

      0x9B Destination out of order
      The destination is not reachable because of an interface malfunction. In addition, a
      signaling message cannot be delivered. This condition can be temporary. However, the
      condition can last for an extended period in some cases.
      This cause indicates that a signaling message could not be delivered to the remote user.
      For example, a physical layer or data link layer fails at the remote user end, and the user
      equipment is off-line (turned off).

      0x9C Invalid number format
      The connection fails because the destination address is in an unrecognizable format, or is
      incomplete.
      Verify whether the format of the number is correct. This includes any appropriate digits
      for a PBX, and long distance.

      0x9D Facility rejected
      The network cannot provide the facility that the user requests.

      0x9E Response to STATUS ENQUIRY
      The status message appears in direct response to the receipt of a status inquiry message.

      0x9F Normal, unspecified
      This message reports the occurrence of a normal event when no standard cause applies.
      No action is required.

      0xA1 Circuit out of order
      The call cannot go through due to some problem in the ISDN network.

      0xA2 No channel available
      The connection fails because no appropriate channel is available to take the call.

      0xA3 Destination unattainable
      The destination is not reachable through the Telco network. Contact the Telco.

      0xA4 Out of order
      Some part of the network necessary to route the call is out of order.
      The destination is not reachable because of a network malfunction. The condition can last
      for an extended period. An immediate attempt to reconnect will probably fail.
      If you use a long distance carrier, try to use a Presubscribed Inter-exchange Carrier (PIC).
      For example, you can use a 10-10-xyz carrier. A PIC enables you to verify whether the
      problem lies with the long distance carrier.

      0xA6 Network out of order
      The destination is not reachable because of a network malfunction. The condition can last
      for an extended period. An immediate attempt to reconnect will probably fail.
      If you use a long distance carrier, try to use a Presubscribed Inter-exchange Carrier (PIC).
      For example, you can use a 10-10-xyz carrier. A PIC enables you to verify whether the
      problem lies with the long distance carrier.

      0xA7 Permanent frame mode connection out of service
      This message indicates that equipment failure probably terminates the permanent
      connection.
      If the problem persists, contact your telco

      0xA8 Permanent frame mode connection operational
      This message occurs when the permanent connection is fully operational again after a
      termination. Equipment failure probably terminated the connection previously.

      0xA9 Temporary failure
      An error occurs because of a network malfunction. Contact the telco if the problem
      persists.

      0xAA Switching equipment congestion
      The destination is not reachable because of a temporary overload on the network
      switching equipment. Try again later.

      0xAB Access information discarded
      The network cannot provide the access information that the user requests.
      This cause indicates that the network is unable to deliver access information to the remote
      user. For example, user-to-user information, low layer compatibility, high layer
      compatibility, or a sub-address as the diagnostic indicates.
      Note: You have the option to include the particular type of discarded access information
      in the diagnostic.

      0xAC Requested channel not available
      The remote equipment cannot provide the channel that the user requests, due to an
      unknown reason. This problem is usually temporary.

      0xAF Resources unavailable, unspecified
      The channel or service that the user requests is unavailable for an unknown reason. This
      problem is usually temporary.

      0xB1 Quality of service (QoS) unavailable
      The network cannot provide the quality of service that the user requests. This issue can
      occur due to a subscription problem.
      This cause reports that the network cannot provide the QoS as defined in
      Recommendation X.213. For example, this cause code appears when the network cannot
      support throughput or transit delay.
      Lance Paddock
      BTX | Business Telephone eXchange
      1(800) 289-0299

      Comment

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