rfc2297.txt

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             used, and the field is not present, in the adjacency
             protocol.

   The following fields are frequently found in GSMP messages. They are
   defined here to avoid repetition.




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   Port
             Gives the port number of the switch port to which the
             message applies.

   Port Session Number
             Each switch port maintains a Port Session Number assigned
             by the switch. The port session number of a port remains
             unchanged while the port is continuously in the Available
             state and the link status is continuously Up. When a port
             returns to the Available state after it has been
             Unavailable or in any of the Loopback states, or when the
             line status returns to the Up state after it has been Down
             or in Test, or after a power cycle, a new Port Session
             Number must be generated.  Port session numbers should be
             assigned using some form of random number.

             If the Port Session Number in a request message does not
             match the current Port Session Number for the specified
             port, a failure response message must be returned with the
             Code field indicating, "Invalid port session number."  The
             current port session number for a port may be obtained
             using a Port Configuration or an All Ports Configuration
             message.

   Any field in a GSMP message that is unused or defined as "reserved"
   must be set to zero by the sender and ignored by the receiver.

   It is not an error for a GSMP message to contain additional data
   after the end of the Message Body. This is to support development and
   experimental purposes. However, the maximum transmission unit of the
   GSMP message, as defined by the data link layer encapsulation, must
   not be exceeded.

   A success response message must not be sent until the requested
   operation has been successfully completed.

3.2 Failure Response Messages

   A failure response message is formed by returning the request message
   that caused the failure with the Result field in the header
   indicating failure (Result = 4) and the Code field giving the failure
   code. The failure code specifies the reason for the switch being
   unable to satisfy the request message.

   If the switch issues a failure response in reply to a request
   message, no change should be made to the state of the switch as a
   result of the message causing the failure. (For request messages that
   contain multiple requests, such as the Delete Branches message, the



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   failure response message will specify which requests were successful
   and which failed. The successful requests may result in changed
   state.)

   If the switch issues a failure response it must choose the most
   specific failure code according to the following precedence:

       Invalid Message

       Failure specific to the particular message type (failure code
           16). (The meaning of this failure is dependent upon the
           particular message type and is specified in the text defining
           the message.)

       A failure response specified in the text defining the message
           type.

       Connection Failures

       Virtual Path Connection Failures

       Multicast Failures

       QoS Failures (QoS failures are specified in Section 9.7.)

       General Failures

   If multiple failures match in any of the following categories, the
   one that is listed first should be returned. The following failure
   response messages and failure codes are defined:

   Invalid Message

       3:  The specified request is not implemented on this switch.
               The Message Type field specifies a message that is not
               implemented on the switch or contains a value that is not
               defined in the version of the protocol running in this
               session of GSMP.

       5:  One or more of the specified ports does not exist.
               At least one of the ports specified in the message is
               invalid. A port is invalid if it does not exist or if it
               has been removed from the switch.

       4:  Invalid Port Session Number.
               The value given in the Port Session Number field does not
               match the current Port Session Number for the specified
               port.



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   Connection Failures

       8:  The specified connection does not exist.
               An operation that expects a connection to be specified,
               either a virtual channel or a virtual path connection,
               cannot locate the specified connection. A virtual channel
               connection is specified by the input port, input VPI, and
               input VCI on which it arrives. A virtual path connection
               is specified by the input port and input VPI on which it
               arrives.

       9:  The specified branch does not exist.
               An operation that expects a branch of an existing
               connection to be specified, either a virtual channel or a
               virtual path connection, cannot locate the specified
               branch.  A branch of a virtual channel connection is
               specified by the virtual channel connection it belongs to
               and the output port, output VPI, and output VCI on which
               it departs. A branch of a virtual path connection is
               specified by the virtual path connection it belongs to
               and the output port and output VPI on which it departs.

       18: One or more of the specified input VPIs is invalid.

       19: One or more of the specified input VCIs is invalid.

       20: One or more of the specified output VPIs is invalid.

       21: One or more of the specified output VCIs is invalid.

       22: Invalid Class of Service field in a Connection Management
               message.
               The value of the Class of Service field is invalid.

       23: Insufficient resources for QoS Profile.
               The resources requested by the QoS Profile in the Class
               of service field are not available.

   Virtual Path Connections

       24: Virtual path switching is not supported on this input port.

       25: Point-to-multipoint virtual path connections are not
               supported on either the requested input port or the
               requested output port.
               One or both of the requested input and output ports is
               unable to support point-to-multipoint virtual path
               connections.



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       26: Attempt to add a virtual path connection branch to an
               existing virtual channel connection.
               It is invalid to mix branches switched as virtual channel
               connections with branches switched as virtual path
               connections on the same point-to-multipoint connection.

       27: Attempt to add a virtual channel connection branch to an
               existing virtual path connection.
               It is invalid to mix branches switched as virtual channel
               connections with branches switched as virtual path
               connections on the same point-to-multipoint connection.

   Multicast Failures

       10: A branch belonging to the specified point-to-multipoint
               connection is already established on the specified output
               port and the switch cannot support more than a single
               branch of any point-to-multipoint connection on the same
               output port.

       11: The limit on the maximum number of point-to-multipoint
               connections that the switch can support has been reached.

       12: The limit on the maximum number of branches that the
               specified point-to-multipoint connection can support has
               been reached.

       17: Cannot label each output branch of a point-to-multipoint tree
               with a different label.
               Some early designs, and some low-cost ATM switch designs,
               require all output branches of a multicast connection to
               use the same value of VPI/VCI.

       28: Only point-to-point bidirectional connections may be
               established.
               It is an error to attempt to add an additional output
               branch to an existing connection with the bidirectional
               flag set.

       13: Unable to assign the requested VPI/VCI value to the requested
               branch on the specified point-to-multipoint connection.
               Although the requested VPI and VCI are valid, the switch
               is unable to support the request using the specified
               values of VPI and VCI for some reason not covered by the
               above failure responses. This message implies that a
               valid value of VPI or VCI exists that the switch could





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               support. For example, some switch designs restrict the
               number of distinct VPI/VCI values available to a point-
               to-multipoint connection. (Most switch designs will not
               require this message.)

       14: General problem related to the manner in which point-to-
               multipoint is supported by the switch.
               Use this message if none of the more specific multicast
               failure messages apply.  (Most switch designs will not
               require this message.)

   General Failures

       2:  Invalid request message.
               There is an error in one of the fields of the message not
               covered by a more specific failure message.

       6:  One or more of the specified ports is down.
               A port is down if its Port Status is Unavailable.
               Connection Management, Connection State, Port Management,
               and Configuration operations are permitted on a port that
               is Unavailable. Connection Activity and Statistics
               operations are not permitted on a port that is
               Unavailable and will generate this failure response. A
               Port Management message specifying a Take Down function
               on a port already in the Unavailable state will also
               generate this failure response.

       15: Out of resources.
               The switch has exhausted a resource not covered by a more
               specific failure message, for example, running out of
               memory.

       1:  Unspecified reason not covered by other failure codes.
               The failure message of last resort.

   The following failure response messages are only used by the Label
               Range message.