rfc2124.txt

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   Status is set to SUCCESS in FUA messages unless an error is detected
   (see "Error Handling"). Message ID is copied from the FUN message.









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RFC 2124                          LFAP                       March 1997


   FUA messages are sent by the FAS to acknowledge a FUN message from
   the switch CCE. If a FUN message contained a multiple record IE and
   any of the updates had a error then the FUA would contain a multiple
   IE with a Flow ID and Flow Failure Code. A status of SUCCESS
   indicates that the information in the corresponding FUN message has
   been accepted and is now the responsibility of the FAS.

3.7.  Flow Change Request (FCR) Message

   Status is set to SUCCESS in FCR messages. In addition, a FCR message
   may contain the following IEs:

      Flow ID IE                    - identifier for the flow.
      Flow State IE                 - set to inactive to stop a flow.
      Optional Operating Policy IE  - possibly new policy(s) that may
                                      apply to this flow.
      Mandatory Operating Policy IE - possibly new policy(s) that must
                                      apply to this flow.

   Mandatory IE's
      Flow ID

   Optional IE's
      Flow State
      Optional Operating Policy
      Mandatory Operating Policy

   FCR messages are sent by the FAS to the CCE to provide additional (or
   change existing) operating policy information or to stop a flow.
   Flow ID is used to identify the flow to which this message applies.
   The FAS can stop a flow by setting it's flow state to inactive.  This
   will cause the CCE to generate a FUN message with the final flow
   statistics.  It will also cause the CCE to return a inactive flow
   state on the given flow.  If the FAS wishes to change operating
   policy information it merely includes the new information in the FCR
   message along with the flow id.

3.8.  Flow Change Acknowledge (FCA) Message

   Status is set to SUCCESS in FCA messages unless an error is detected
   (see "Error Handling").  Message ID is copied from the FCR message.
   FCA messages contain IEs if a error was detected in the corresponding
   FCR message (see "Error Handling").

   If an error occurs then a FCR may contain the following IE's

      Flow ID IE        - if FAS requested statistics on an
                          unknown flow.



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RFC 2124                          LFAP                       March 1997


      Flow Failure Code - for the Flow ID IE above.

   FCA messages are sent by a switch CCE in response to an FCR.

3.9.  Administrative Request (AR) Message

   Status is set to SUCCESS in AR messages. In addition, AR messages may
   contain the Command IEs:

   Mandatory IE's
      Command IE

   AR messages are sent by either the a switch CCE or the FAS when they
   seeks to perform one of the Command IE's.

3.10.  Administrative Request Acknowledge (ARA) Message

   Status reflects the result of the corresponding AR message (see Error
   Handling for details). Message ID is copied from the AR message. In
   addition, ARA messages may have the following IEs:

      Flow ID IE                 - if FAS requested statistics on an
                                   unknown flow.
      Flow Failure Code          - for the Flow ID IE above.
      Flow Identifier Prefix IE  - if the ARA is the response to a CCE
                                   Command to RETURN_FLOW_PREFIX.

   ARA messages are sent by a FAS or CCE in response to AR message
   received CCE or FAS respectively.

4.  Error Handling

   Incompatible version - Receipt of any LFAP request or notification
   message, with a version number other than that (or those) supported
   by the receiving component will result in a response (acknowledge)
   message with a Status of VERSION. The resulting message will contain
   no IEs and, as a result, may be considered a generic FAILURE message.

   Corrupted message contents - Receipt of a LFAP message which cannot
   be understood will result in a similar generic FAILURE message with
   Status set to CORRUPTED. A FAA message may contain a Flow ID IE only
   if this IE is included in the portion of the corrupt LFAP message
   that is before the point where corruption occurs. The LFAP sender
   should re-send the original message at least one time if it is still
   desired to admit the requested connection.






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RFC 2124                          LFAP                       March 1997


   With the exception of incompatible version and corrupted message
   contents, error handling is naturally related to the processing of
   response messages by both response sender and receiver. Below
   sections are thus organized around processing of FAA, FUA, FCA and
   ARA messages.

4.1.  FAA Related Error Handling

   Non-unique Flow ID - Receipt of a FAR message with a non-unique Flow
   ID may occur for two reasons: the CCE may have re-sent a FAR message
   and an error may have occurred in the ID generation function.  If the
   entire message is the same in every respect, with the possible
   exception of Message ID, as a FAR message received previously, the
   FAS will respond in the same way as it would have responded to that
   prior message.  Otherwise, the Flow ID will be returned with a Flow
   Failure Code set to AMBIGUOUS. The CCE should choose a new Flow ID
   and retry the FAR message if it is still desired to admit the
   requested connection.

   Flow is inadmissible - The FAS may determine that flow is not
   admissible for policy reasons. In this case the Flow ID is returned
   along with the Flow Failure Code of POLICY_REJECT.

4.2.  FUA Related Error Handling

   Flow Not Admitted - Receipt of Flow information for an unadmitted
   connection. Flow ID IE identifies a flow which was not admitted or
   for which admission status has been lost. The FAS will return the
   Flow ID and a Flow Failure Code of NO_SUCH_FLOW. The switch CCE
   should send an appropriate FAR message. The FAS may track occurrences
   of this error and send a FCR message to the CCE requesting dropping
   of the reported connection.

4.3.  FCA Related Error Handling

   Flow change requested for a non-existent flow - The Flow ID IE
   identifies a connection for which this CCE has no state information.
   The FCA message has the Flow ID and a Flow Failure Code set to
   NO_SUCH_FLOW and contains the Flow ID and copied from the
   corresponding FCR message.

   Policy changes requested were not supported by the CCE.  The FCA
   message has the Flow ID and a Flow Failure Code set to POLICY_REJECT
   and contains the Flow ID copied from the corresponding FCR message.







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4.4.  ARA Related Error Handling

   Flow statistics requested for a non-existent flow - The Flow ID IE
   identified a connection for which this CCE has no state information.
   The ARA message has the Flow ID and a Flow Failure Code set to
   NO_SUCH_FLOW and contains the Flow ID copied from the corresponding
   FCR message.  If there were multiple flows that were non-existent
   then the multi ie format could have the Flow Failure Code in the
   fixed information section and the individual Flow ID's in the record
   section.

5.  Security Considerations

   Security issues are not discussed in this memo.

6.  Author's Addresses

    Paul Amsden
    Phone:  [phone]
    EMail:  [e-mail]

    Jim Amweg
    Phone:  [phone]
    EMail:  [e-mail]

    Paul Calato
    Phone:  [phone]
    EMail:  [e-mail]

    Stephen Bensley
    Phone:  [phone]
    EMail:  [e-mail]

    Gregory Lyons
    Phone:  [phone]
    EMail:  [e-mail]

Cabletron Systems, Inc. is located at:

    P.O. Box 5005
    Rochester, NH, 03866-5005
    USA









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7.  References

   [363]   "B-ISDN ATM Adaptation Layer (AAL) Specification,"
           International Telecommunication Union, ITU-T Recommendation
           I.363, Mar. 1993.

   [1443]  "Textual Conventions for version 2 of the Simple Network
           Management Protocol (SNMPv2)", RFC 1443, April 1993.

   [1700]  Reynolds, J., and J. Postel, "Assigned Numbers", STD 2,
           RFC 1700, October 1994.

   [8824]  Information technology - Open Systems Interconnection -
           "Specification of Abstract Syntax Notation One (ASN.1),
           Second edition", ISO/IEC TR 8824: 1990 (E) 1990-12-15.

   [9577]  "Telecommunications and Information Exchange Between Systems
           - Protocol Identification in the Network Layer", ISO/IEC TR
           9577: 1990 (E) 1990-10-15.

   [LANE]  "LAN Emulation Over ATM Specification - Version 1.0", ATM
           Forum af-lane-021.000, January, 1995.





























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