rfc3331.txt

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3.3.1.3  Establish (Request, Confirmation)

   The Establish Request message is used to establish the SS7 link or to
   indicate that the channel has been established.  The MGC controls the
   state of the SS7 link.  When the MGC desires the SS7 link to be in-
   service, it will send the Establish Request message.  Note that the
   SGP MAY already have the SS7 link established at its layer.  If so,
   upon receipt of an Establish Request, the SGP takes no action except
   to send an Establish Confirm.

   When the MGC sends an M2UA Establish Request message, the MGC MAY
   start a timer.  This timer would be stopped upon receipt of an M2UA
   Establish Confirm.  If the timer expires, the MGC would resend the
   M2UA Establish Request message and restart the timer.  In other
   words, the MGC MAY continue to request the establishment of the data
   link on a periodic basis until the desired state is achieved or some
   other action is taken (notify the Management Layer).

   The mode (Normal or Emergency) for bringing the SS7 link in service
   is defaulted to Normal.  The State Request (described in Section
   3.3.1.5 below) can be used to change the mode to Emergency.

3.3.1.4  Release (Request, Indication, Confirmation)

   This Release Request message is used to release the channel.  The
   Release Confirm and Indication messages are used to indicate that the
   channel has been released.

3.3.1.5  State Request

   The State Request message can be sent from a MGC to cause an action
   on a particular SS7 link supported by the Signalling Gateway Process.
   The SGP sends a State Confirm to the MGC if the action has been
   successfully completed.  The State Confirm reflects that state value
   received in the State Request message.





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   The State Request message contains the following parameter:

    State (mandatory)

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x302)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             State                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The valid values for State are shown in the following table.

            Define           Value        Description
      STATUS_LPO_SET          0x0      Request local processor outage
      STATUS_LPO_CLEAR        0x1      Request local processor outage
                                       recovered
      STATUS_EMER_SET         0x2      Request emergency alignment
      STATUS_EMER_CLEAR       0x3      Request normal alignment (cancel
                                       emergency)
      STATUS_FLUSH_BUFFERS    0x4      Flush or clear receive, transmit
                                       and retransmit queues
      STATUS_CONTINUE         0x5      Continue or Resume
      STATUS_CLEAR_RTB        0x6      Clear the retransmit queue
      STATUS_AUDIT            0x7      Audit state of link
      STATUS_CONG_CLEAR       0x8      Congestion cleared
      STATUS_CONG_ACCEPT      0x9      Congestion accept
      STATUS_CONG_DISCARD     0xa      Congestion discard

3.3.1.6  State Confirm

   The State Confirm message will be sent by the SGP in response to a
   State Request from the MGC.  The State Confirm reflects that state
   value received in the State Request message.

   The State Confirm message contains the following parameter:

    State (mandatory)

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x302)           |           Length = 8          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             State                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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   The valid values for State are shown in the following table.  The
   value of the State field SHOULD reflect the value received in the
   State Request message.

            Define           Value        Description
      STATUS_LPO_SET          0x0      Request local processor outage
      STATUS_LPO_CLEAR        0x1      Request local processor outage
                                       recovered
      STATUS_EMER_SET         0x2      Request emergency alignment
      STATUS_EMER_CLEAR       0x3      Request normal alignment (cancel
                                       emergency)
      STATUS_FLUSH_BUFFERS    0x4      Flush or clear receive, transmit
                                       and retransmit queues
      STATUS_CONTINUE         0x5      Continue or Resume
      STATUS_CLEAR_RTB        0x6      Clear the retransmit queue
      STATUS_AUDIT            0x7      Audit state of link
      STATUS_CONG_CLEAR       0x8      Congestion cleared
      STATUS_CONG_ACCEPT      0x9      Congestion accept
      STATUS_CONG_DISCARD     0xa      Congestion discard

3.3.1.7  State Indication

   The MTP2 State Indication message can be sent from a SGP to an ASP to
   indicate a condition on a SS7 link.

   The State Indication message contains the following parameter:

    Event (mandatory)

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x303)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Event                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The valid values for Event are shown in the following table.

          Define            Value          Description
      EVENT_RPO_ENTER        0x1      Remote entered processor outage
      EVENT_RPO_EXIT         0x2      Remote exited processor outage
      EVENT_LPO_ENTER        0x3      Link entered processor outage
      EVENT_LPO_EXIT         0x4      Link exited processor outage







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3.3.1.8  Congestion Indication

   The Congestion Indication message can be sent from a Signalling
   Gateway Process to an ASP to indicate the congestion status and
   discard status of a SS7 link.  When the MSU buffer fill increases
   above an Onset threshold or decreases below an Abatement threshold or
   crosses a Discard threshold in either direction, the SGP SHALL send a
   congestion indication message when it supports SS7 MTP2 variants that
   support multiple congestion levels.

   The SGP SHALL send the message only when there is actually a change
   in either the discard level or the congestion level to report,
   meaning it is different from the previously sent message.  In
   addition, the SGP SHALL use an implementation dependent algorithm to
   limit the frequency of congestion indication messages.

   An implementation may optionally send Congestion Indication messages
   on a "high priority" stream in order to potentially reduce delay.

   The Congestion Indication message contains the following parameters:

    Congestion Status (mandatory)
    Discard Status (optional)

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x304)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Congestion Status                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x305)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Discard Status                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The valid values for Congestion Status and Discard Status are shown
   in the following table.

            Define        Value        Description
          LEVEL_NONE       0x0       No congestion
          LEVEL_1          0x1       Congestion Level 1
          LEVEL_2          0x2       Congestion Level 2
          LEVEL_3          0x3       Congestion Level 3







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   For SS7 networks that do not support multiple levels of congestion,
   only the LEVEL_NONE and LEVEL_3 values will be used.  For SS7
   networks that support multiple levels of congestion, it is possible
   for all values to be used.  Refer to [2], [3] and [12] for more
   details on the Congestion and Discard Status of SS7 signalling links.

3.3.1.9  Retrieval Request

   The MTP2 Retrieval Request message is used during the MTP Level 3
   changeover procedure to request the BSN, to retrieve PDUs from the
   transmit and retransmit queues or to flush PDUs from the retransmit
   queue.  Examples of the use of Retrieval Request for SS7 Link
   Changeover are provided in Section 5.3.6.

   The Retrieval Request message contains the following parameters:

    Action (mandatory)
    Sequence Number (optional)

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x306)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Action                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x307)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Sequence Number                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The valid values for Action are shown in the following table.

           Define         Value       Description
      ACTION_RTRV_BSN      0x1     Retrieve the backward sequence number
      ACTION_RTRV_MSGS     0x2     Retrieve the PDUs from the transmit
                                   and retransmit queues

   In the Retrieval Request message, the Sequence Number field SHOULD
   NOT be present if the Action field is ACTION_RTRV_BSN.  The Sequence
   Number field contains the Forward Sequence Number (FSN) of the far
   end if the Action is ACTION_RTRV_MSGS.









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3.3.1.10  Retrieval Confirm

   The MTP2 Retrieval Confirm message is sent by the Signalling Gateway
   in response to a Retrieval Request message.  Examples of the use of
   the Retrieval Confirm for SS7 Link Changeover are provided in Section
   5.3.6.

   The Retrieval Confirm message contains the following parameters:

    Action (mandatory)
    Result (mandatory)
    Sequence Number (optional)

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x306)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Action                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x308)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Result                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag (0x307)           |          Length = 8           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Sequence Number                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The valid values for Action are the same as in Retrieval Request.

   The values for Result are shown below:

           Define         Value       Description
      RESULT_SUCCESS       0x0     Action successful
      RESULT_FAILURE       0x1     Action failed

   When the Signalling Gateway Process sends a Retrieval Confirm to a
   Retrieval Request, it echos the Action field.  If the Action was
   ACTION_RTRV_BSN and the SGP successfully retrieved the BSN, the SGP
   will put the Backward Sequence Number (BSN) in the Sequence Number
   field and will indicate a success in the Result field.  If the BSN
   could not be retrieved, the Sequence Number field will not be
   included and the Result field will indicate failure.







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   For a Retrieval Confirm with Action of ACTION_RTRV_MSGS, the value of
   the Result field will indicate success or failure.  A failure means
   that the buffers could not be retrieved.  The Sequence Number field
   is not used with ACTION_RTRV_MSGS.

3.3.1.11  Retrieval Indication

   The Retrieval Indication message is sent by the Signalling Gateway
   with a PDU from the transmit or retransmit queue.  The Retrieval
   Indication message does not contain the Action or Sequence Number
   fields, just a MTP3 Protocol Data Unit (PDU) from the transmit or
   retransmit queue.  Examples of the use of the Retrieval Indication
   for SS7 Link Changeover are provided in