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rfc:rfc5972

Internet Engineering Task Force (IETF) T. Tsenov Request for Comments: 5972 H. Tschofenig Category: Informational Nokia Siemens Network ISSN: 2070-1721 X. Fu, Ed.

                                                      Univ. Goettingen
                                                               C. Aoun
                                                            Consultant
                                                             E. Davies
                                                      Folly Consulting
                                                          October 2010
     General Internet Signaling Transport (GIST) State Machine

Abstract

 This document describes state machines for the General Internet
 Signaling Transport (GIST).  The states of GIST nodes for a given
 flow and their transitions are presented in order to illustrate how
 GIST may be implemented.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc5972.

Copyright Notice

 Copyright (c) 2010 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must

Tsenov, et al. Informational [Page 1] RFC 5972 GIST State Machine October 2010

 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Table of Contents

 1. Introduction ....................................................3
 2. Terminology .....................................................3
 3. Notational Conventions Used in State Diagrams ...................3
 4. State Machine Symbols ...........................................5
 5. Common Rules ....................................................6
    5.1. Common Procedures ..........................................7
    5.2. Common Events ..............................................8
    5.3. Common Variables ...........................................9
 6. State Machines .................................................11
    6.1. Diagram Notations .........................................12
    6.2. State Machine for GIST Querying Node ......................12
    6.3. State Machine for GIST Responding Node ....................16
 7. Security Considerations ........................................18
 8. Acknowledgments ................................................18
 9. References .....................................................18
    9.1. Normative References ......................................18
    9.2. Informative References ....................................18
 Appendix A. State Transition Tables ...............................20
    A.1. State Transition Tables for GIST Querying Node ............20
    A.2. State Transition Tables for GIST Responding Node ..........24

Tsenov, et al. Informational [Page 2] RFC 5972 GIST State Machine October 2010

1. Introduction

 The state machines described in this document are illustrative of how
 the GIST protocol defined in [1] may be implemented for the GIST
 nodes in different locations of a flow path.  Where there are
 differences, [1] is authoritative.  The state machines are
 informative only.  Implementations may achieve the same results using
 different methods.
 There are two types of possible entities for GIST signaling:
  1. GIST querying node: GIST node that initiates the discovery of the

next peer;

  1. GIST responding node: GIST node that is the discovered next peer.
 We describe a set of state machines for these entities to illustrate
 how GIST may be implemented.

2. Terminology

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [2].

3. Notational Conventions Used in State Diagrams

 The following text is reused from [3], and the state diagrams are
 based on the conventions specified in [4], Section 8.2.1.  Additional
 state machine details are taken from [5].
 RFC 4137 [3] reproduced the following text from Section 8.2.1 of IEEE
 802-1X-2004 [4].
    State diagrams are used to represent the operation of the protocol
    by a number of cooperating state machines, each comprising a group
    of connected, mutually exclusive states.  Only one state of each
    machine can be active at any given time.
    . . .
    All permissible transitions between states are represented by
    arrows, the arrowhead denoting the direction of the possible
    transition.  Labels attached to arrows denote the condition(s)
    that must be met in order for the transition to take place.  All
    conditions are expressions that evaluate to TRUE or FALSE; if a
    condition evaluates to TRUE, then the condition is met.  The label
    UCT denotes an unconditional transition (i.e., UCT always

Tsenov, et al. Informational [Page 3] RFC 5972 GIST State Machine October 2010

    evaluates to TRUE).  A transition that is global in nature (i.e.,
    a transition that occurs from any of the possible states if the
    condition attached to the arrow is met) is denoted by an open
    arrow; i.e., no specific state is identified as the origin of the
    transition.  When the condition associated with a global
    transition is met, it supersedes all other exit conditions
    including UCT.  The special global condition BEGIN supersedes all
    other global conditions, and once asserted it remains asserted
    until all state blocks have executed to the point that variable
    assignments and other consequences of their execution remain
    unchanged.
    On entry to a state, the procedures defined for the state (if any)
    are executed exactly once, in the order that they appear on the
    page.  Each action is deemed to be atomic; i.e., execution of a
    procedure completes before the next sequential procedure starts to
    execute.  No procedures execute outside a state block.  The
    procedures in only one state block execute at a time, even if the
    conditions for execution of state blocks in different state
    machines are satisfied, and all procedures in an executing state
    block complete execution before the transition to and execution of
    any other state block occurs.  That is, the execution of any state
    block appears to be atomic with respect to the execution of any
    other state block, and the transition condition to that state from
    the previous state is TRUE when execution commences.  The order of
    execution of state blocks in different state machines is undefined
    except as constrained by their transition conditions.  A variable
    that is set to a particular value in a state block retains this
    value until a subsequent state block executes a procedure that
    modifies the value.
    On completion of all the procedures within a state, all exit
    conditions for the state (including all conditions associated with
    global transitions) are evaluated continuously until one of the
    conditions is met.  The label ELSE denotes a transition that
    occurs if none of the other conditions for transitions from the
    state are met (i.e., ELSE evaluates to TRUE if all other possible
    exit conditions from the state evaluate to FALSE).  Where two or
    more exit conditions with the same level of precedence become TRUE
    simultaneously, the choice as to which exit condition causes the
    state transition to take place is arbitrary.
 In addition to the above notation, there are a couple of
 clarifications specific to this document.  First, all boolean
 variables are initialized to FALSE before the state machine execution
 begins.  Second, the following notational shorthand is specific to
 this document:

Tsenov, et al. Informational [Page 4] RFC 5972 GIST State Machine October 2010

 <variable> = <expression1> | <expression2> | ...
    Execution of a statement of this form will result in <variable>
    having a value of exactly one of the expressions.  The logic for
    which of those expressions gets executed is outside of the state
    machine and could be environmental, configurable, or based on
    another state machine such as that of the method.

4. State Machine Symbols

 ( )
    Used to force the precedence of operators in boolean expressions
    and to delimit the argument(s) of actions within state boxes.
 ;
    Used as a terminating delimiter for actions within state boxes.
    Where a state box contains multiple actions, the order of
    execution follows the normal English language conventions for
    reading text.
 =
    Assignment action.  The value of the expression to the right of
    the operator is assigned to the variable to the left of the
    operator.  Where this operator is used to define multiple
    assignments, e.g., a = b = X, the action causes the value of the
    expression following the right-most assignment operator to be
    assigned to all of the variables that appear to the left of the
    right-most assignment operator.
 !
    Logical NOT operator.
 &&
    Logical AND operator.
 ||
    Logical OR operator.
 if...then...
    Conditional action.  If the boolean expression following the "if"
    evaluates to TRUE, then the action following the "then" is
    executed.
 { statement 1, ... statement N }
    Compound statement.  Braces are used to group statements that are
    executed together as if they were a single statement.

Tsenov, et al. Informational [Page 5] RFC 5972 GIST State Machine October 2010

 !=
    Inequality.  Evaluates to TRUE if the expression to the left of
    the operator is not equal in value to the expression to the right.
 ==
    Equality.  Evaluates to TRUE if the expression to the left of the
    operator is equal in value to the expression to the right.
 >
    Greater than.  Evaluates to TRUE if the value of the expression to
    the left of the operator is greater than the value of the
    expression to the right.
 <=
    Less than or equal to.  Evaluates to TRUE if the value of the
    expression to the left of the operator is either less than or
    equal to the value of the expression to the right.
 ++
    Increment the preceding integer operator by 1.
 +
    Arithmetic addition operator.
 &
    Bitwise AND operator.

5. Common Rules

 Throughout the document we use terms defined in [1], such as Query,
 Response, and Confirm.
 The state machine represents the handling of GIST messages that match
 a Message Routing State's Message Routing Information (MRI), NSIS
 Signaling Layer Protocol identifier (NSLPID), and session identifier
 (SID) and with no protocol errors.  Separate parallel instances of
 the state machines should handle messages for different Message
 Routing States (MRSs).
 The state machine represents the states and transitions of the
 upstream and downstream peers of the Message Routing State.
 For simplification, not all objects included in a message are shown.
 Only those that are significant for the case are shown.  State
 machines do not present handling of messages that are not significant
 for management of the states.

Tsenov, et al. Informational [Page 6] RFC 5972 GIST State Machine October 2010

 The state machines presented in this document do not cover all
 functions of a GIST node.  Functionality of message forwarding,
 transmission of NSLP data without MRS establishment, and providing of
 the received messages to the appropriate MRS, we refer to as "lower-
 level pre-processing" step.  Pre-processing provides to the
 appropriate MRS state machine only the messages that are matched
 against waiting Query/Response cookies, or the triplet (MRI, NSLPID,
 SID) of the established MRS.  This is represented by "rx_*" events in
 the state machines.
 Management of messaging associations (MAs) is considered in the
 document via procedures, events, and variables, which describe MA
 interaction with the MRS state machines.  A state machine for MA
 management is not explicitly presented.

5.1. Common Procedures

 Tx_Query:
    Transmit of Query message.
 Tx_Response:
    Transmit of Response message.
 Tx_Confirm:
    Transmit of Confirm message.
 Tx_Data:
    Transmit of Data message.
 Tg_MessageStatus:
    NSLP/GIST API message informing NSLP application of unsuccessful
    delivery of a message
 Tg_RecvMsg:
    NSLP/GIST API message that provides received message to NSLP
    application.
 Tg_NetworkNotification:
    NSLP/GIST API message that informs NSLP application of change in
    MRS.
 Install downstream/upstream MRS:
    Install new Message Routing State and save the corresponding peer
    state info (IP address and UDP port, or pointer to the used MA)
    for the current Message Routing State or update the corresponding
    peer state info.

Tsenov, et al. Informational [Page 7] RFC 5972 GIST State Machine October 2010

 Delete MRS:
    Delete installed downstream/upstream peer's info for the current
    Message Routing State, and delete the Message Routing State if
    required.
 Refresh MRS:
    Refreshes installed MRS.
 Queue NSLP info:
    Save NSLP messages in a queue until conditions for their sending
    are present, e.g., a required MA association is established.
 CheckPeerInfo:
    The sender of the received data message is matched against the
    installed peer info in the MRS.
 Delete MA:
    Delete/disconnect used MA.
 Stop using shared MA:
    Stop using shared MA.  If the shared MA is no longer being used by
    any other MRSs, it depends on the local policy whether it is
    deleted or kept.
 Tg_Establish_MA:
    Triggers establishment of a new MA.
 Start/Restart a timer variable (Section 5.3):
    Start/Restart of a certain timer.
 Install/Update/Delete UpstreamPeerInfo variable (Section 5.3):
    Management of upstream peer info in state machine of responding
    node.

5.2. Common Events

 Rx_Query:
    Receive of Query message.
 Rx_Response:
    Receive of Response message.
 Rx_Confirm:
    Receive of Confirm message.
 Rx_Data:
    Receive of Data message.

Tsenov, et al. Informational [Page 8] RFC 5972 GIST State Machine October 2010

 Tg_SendMsg:
    NSLP/GIST API message from NSLP application that requests
    transmission of a NSLP message.
 Tg_SetStateLifetime(time_period):
    NSLP/GIST API message providing info for the lifetime of a Routing
    State (RS), required by the application.  "Time_period = 0"
    represents the cancellation of established RSs/MAs, invoked by the
    NSLP application.
 Tg_InvalidRoutingState:
    NSLP/GIST API notification from NSLP application for path change.
 Tg_ERROR:
    General Error event / system level error.
 Tg_MA_Established:
    A new MA has been successfully established.
 Tg_MA_Error:
    Error event with used MA.
 Timeout a timer variable (Section 5.3):
    Timeout of a certain timer.

5.3. Common Variables

 Variables listed in this section are defined as:
  1. Specific information carried in the received messages.
  1. Conditions that are results of processes not defined in the state

machine model.

 State machine logic is based on these general conditions and message
 parameters.
 The type of mode and destination info is determined by NSLP
 application parameters and local GIST policy.  Here it is represented
 by the common variables D-mode, C-mode, and MAinfo.
 C-mode:
    The message MUST be transmitted in C-mode.  This is specified by
    "Message transfer attributes" set by NSLP application to any of
    the following values:
    "Reliability" is set to TRUE.

Tsenov, et al. Informational [Page 9] RFC 5972 GIST State Machine October 2010

    "Security" is set to values that request secure handling of a
    message.
    "Local processing" is set to values that require services offered
    by C-mode (e.g., congestion control) [1].
 D-mode:
    The message MUST be transmitted in D-mode.  This is specified by
    local policy rules.  If the "Message transfer attributes" are not
    set by NSLP application to any of the following values, then:
    "Reliability" is set to TRUE.
    "Security" is set to values that request special security handling
    of a message.
    "Local processing" is set to values that require services offered
    by C-mode [1].
 MAinfo:
    GIST message parameters describing the required MA or proposed MA,
    e.g., "Stack-proposal" and "Stack-Configuration-Data" [1].
 NSLPdata:
    NSLP application data.
 RespCookie:
    Responder Cookie that is being sent by the responding node with
    the Response message in case that its local policy requires a
    confirmation from the querying node.
 ConfirmRequired:
    Indicator that a Confirm message is required by the local policy
    rule for installation of a new MRS.
 NewPeer:
    Indicator that a Response message is received from a new
    responding peer.
 MAexist:
    Indicator that an existing MA will be reused in data transfer
    between peers.
 UpstreamPeerInfo:
    Upstream peer info that is saved in an established MRS.
 T_Inactive_QNode:
    Message Routing State lifetime timer in querying node.

Tsenov, et al. Informational [Page 10] RFC 5972 GIST State Machine October 2010

 T_Expired_RNode:
    Message Routing State lifetime timer in responding node.
 T_Refresh_QNode:
    Message Routing State refresh timer in querying node.
 T_No_Response:
    Timer for the waiting period for Response message in querying
    node.
 T_No_Confirm:
    Timer for the waiting period for Confirm message in responding
    node.
 No_MRS_Installed:
    Data sent by responding node via a Response message that indicates
    loss of Confirm message.

6. State Machines

 The following section presents the state machine diagrams of GIST
 peers.  RFC 5972 is published as a .txt file.  A supplementary .pdf
 is being published as well.
 In the .pdf document, the state machine diagrams are depicted in
 detail.  All state machine information (triggering event, action
 taken, and variable status) is represented in the diagrams.
 In the .txt document, state machine diagrams depict only transition
 numbers.  Following each diagram is a list of state transition
 descriptions.  Complete transition details (triggering event, action
 taken, and variable status) are given in state transition tables in
 Appendix A.
 Please use the .pdf version whenever possible.  It is the clearer
 representation of the state machine.  In case of a difference between
 the two documents, please refer to the .pdf version.

Tsenov, et al. Informational [Page 11] RFC 5972 GIST State Machine October 2010

6.1. Diagram Notations

 +--------------------------------+
 |             STATE              |
 +--------------+-----------------+
                |
                |
              ooooo
             o  N  o   Transition N
              ooooo
                |
                v
 +--------------------------------+
 |             STATE              |
 +--------------------------------+
                      Figure 1: Diagram notations

6.2. State Machine for GIST Querying Node

 The state machine diagram of the GIST querying node is below.
 Transition descriptions follow.
 Please refer to Appendix A.1 for complete transition details
 (triggering event, action taken, and variable status).

Tsenov, et al. Informational [Page 12] RFC 5972 GIST State Machine October 2010

 +-----------+           ooooo
 | Any State +----------o  18 o
 +-----------+           ooooo
                           |
                           v
 +-----------------------------------------------------------------+
 |                             IDLE                                |
 +--+--------------------------------------------------------------+
    |        ^                                        ^        ^
    |        |                                        |        |
  ooooo    ooooo     ooooo      ooooo      ooooo      |        |
 o  1  o  o  2  o  +o  3  o+  +o  4  o+  +o  5  o+    |        |
  ooooo    ooooo   | ooooo |  | ooooo |  | ooooo |    |        |
    |        |     |       |  |       |  |       |    |        |
    v        |     |       v  |       v  |       v    |        |
 +-----------+-----+----------+----------+--------+   |        |
 |                 Wait Response                  |   |        |
 +--+-------------------------------------+-------+   |        |
    |       ^                             |           |        |
    |       |                             |           |        |
  ooooo     |           ooooo           ooooo       ooooo      |
 o  6  o    |         +o  5  o+        o  7  o     o  8  o     |
  ooooo     |         | ooooo |         ooooo       ooooo      |
    |       |         |       |           |           |        |
    |       |         |       v           v           |        |
    |       |    +----+-------------------------------+---+    |
    |       |    |         Wait MA Establishment          |    |
    |       |    +------------------------------+---------+    |
    |       |          ^                        |              |
    |       |          |                        |              |
    |     ooooo      ooooo        ooooo       ooooo          ooooo
    |    o  9  o    o  11 o     +o  13 o+    o  12 o        o  10 o
    |     ooooo      ooooo      | ooooo |     ooooo          ooooo
    |       |          |        |       |       |              |
    v       |          |        |       v       v              |
 +----------+----------+--------+------------------------------+---+
 |                  Established Downstream MRS                     |
 +--+-----------+-----------+-----------+-----------+--------------+
    |       ^   |       ^   |       ^   |       ^   |       ^
    |       |   |       |   |       |   |       |   |       |
    | ooooo |   | ooooo |   | ooooo |   | ooooo |   | ooooo |
    +o  16 o+   +o  14 o+   +o  15 o+   +o  4  o+   +o  17 o+
      ooooo       ooooo       ooooo       ooooo       ooooo
            Figure 2: State Machine for GIST Querying Node

Tsenov, et al. Informational [Page 13] RFC 5972 GIST State Machine October 2010

 1**) An initial request from the NSLP application is received, which
      triggers Query messages requesting either D-mode or C-mode.
      Depending on the node's local policy, the NSLP data might be
      piggybacked in the Query requesting D-mode.  The Query may carry
      MAinfo if C-mode transport is needed.
 2)   T_No_Response timer expires, and the maximum number of retries
      has been reached.  The NSLP application is notified of the GIST
      peer discovery failure.
 3)   T_No_Response timer expires.  The Query is resent.
 4)   A Data message is received.  It is checked to see whether its
      sender matches the installed downstream peer info in the MRS; if
      so, it is processed.  In WaitResponse state, this event might
      happen in the process of an MA upgrade, when the downstream peer
      is still not aware of establishment of the new MA.
 5)   The NSLP application provides data for sending.  NSLP data is
      queued because the downstream peer is not discovered or the
      required MA is still not established.
 6)   A Response message is received.  If a D-mode connection is
      requested or the available MA can be reused for the requested
      C-mode, the MRS is established.
 7*)  Response message is received.  If a C-mode connection must be
      established, and there is no available MA to be reused, MA
      establishment is initiated and the system waits for it to be
      completed.
 8)   MA establishment fails.  NSLP application is notified for
      unsuccessful message delivery.
 9)   The NSLP application provides data for sending, and the
      requested transport parameters require an upgrade of the
      established MRS from D-mode/C-mode to C-mode.  Or, the NSLP
      application notifies the GIST instance of the path change.  As a
      result, downstream GIST peer discovery is initiated.
 10)  The MRS lifetime expires or the NSLP application notifies that
      the MRS is no longer needed.  The MRS is deleted.  If not
      needed, the MA is deleted, too.  The NSLP application is
      notified of the MRS change.
 11*) The path change is detected as a Response message from a new
      downstream GIST peer is received.  A new MA must be established
      for the requested C-mode.

Tsenov, et al. Informational [Page 14] RFC 5972 GIST State Machine October 2010

 12*) A new MA is established.  The MRS is installed.  The queued NSLP
      data is sent.
 13)  T_Refresh_QNode timer expires.  The Query message is sent.
 14)  The NSLP application provides data for sending.  It is sent via
      Data message towards the downstream GIST peer.
 15)  The Response message from the downstream GIST peer is received.
      The peer is not changed.  The MRS is refreshed (T_Refresh_QNode
      timer is restarted).
 16)  The path change is detected as a Response message from a new
      downstream GIST peer is received.  D-mode is requested, or the
      existing MA can be reused for the requested C-mode.
 17)  The responding peer indicates that it has not received a Confirm
      message and it has no established upstream MRS.  The Confirm
      message is resent.
 18)  A general error or system-level error occurs.  The MRS is
      deleted.  If not needed, the MA is deleted, too.  The NSLP
      application is notified of the MRS change.
 Remarks:
  • ) Response and Confirm messages might be sent either in D-mode or

C-mode, before or after MA establishment, depending on the node's

     local three-way handshake policy and the availability of the MAs
     to be reused.  See [1] for details.
  • *) Depending on GIST local policy, NSLPdata might be sent as the

payload of Query and Confirm messages (piggybacking).

Tsenov, et al. Informational [Page 15] RFC 5972 GIST State Machine October 2010

6.3. State Machine for GIST Responding Node

 The GIST responding node state machine diagram is below.  Transition
 descriptions follow.
 Please refer to Appendix A.2 for complete transition details
 (triggering event, action taken, and variable status).
 +-----------+           ooooo
 | Any State +----------o  14 o
 +-----------+           ooooo
                           |
                           v
 +-----------------------------------------------------------------+
 |                             IDLE                                |
 +--+-------------------------------+------------------------------+
    |                 ^             |                          ^
    |                 |             |                          |
  ooooo               |           ooooo          ooooo       ooooo
 o  1  o              |          o  2  o       +o  4  o+    o  3  o
  ooooo               |           ooooo        | ooooo |     ooooo
    |                 |             |          |       |       |
    |                 |             v          |       v       |
    |                 |   +--------------------+---------------+---+
    |                 |   |             Wait Confirm               |
    |                 |   +---------+------------------+-----------+
    |                 |             |          ^       |       ^
    |                 |             |          |       |       |
    |     ooooo     ooooo         ooooo      ooooo     | ooooo |
    |   +o  13 o+  o  8  o       o  5  o    o  7  o    +o  6  o+
    |   | ooooo |   ooooo         ooooo      ooooo       ooooo
    |   |       |     |             |          |
    v   |       v     |             v          |
  +------+-------------+------------------------+-------------------+
  |                  Established Upstream MRS                       |
  +------+-------------+-------------+------------+-----------------+
         |       ^     |       ^     |       ^     |       ^
         |       |     |       |     |       |     |       |
         | ooooo |     | ooooo |     | ooooo |     | ooooo |
         +o  9  o+     +o  11 o+     +o  12 o+     +o  10 o+
           ooooo         ooooo         ooooo         ooooo
           Figure 3: State Machine for GIST Responding Node
 1) A Query message is received.  The MRS is installed immediately
    because local policy permits it.  The Query message might carry
    piggybacked NSLP data that will be provided to the NSLP
    application.

Tsenov, et al. Informational [Page 16] RFC 5972 GIST State Machine October 2010

 2) A Query message is received.  Local policy requires an explicit
    Confirm message for MRS installation.  The Query message might
    carry piggybacked NSLP data that will be provided to the NSLP
    application.
 3) T_No_Confirm timer expires.  Note that all cases of lost handshake
    GIST messages are handled only by the GIST querying node via
    resend of the Query message.
 4) A Query message is received again.  This means that the sent
    Response message has not been received by the upstream GIST peer.
    The Response message is resent.
 5) A Confirm message is received that causes installation of the
    upstream MRS.
 6) In case of a lost Confirm message, data messages might be received
    from the upstream GIST node (it is unaware of the lost Confirm
    message).  A Response message indicating the loss of the Confirm
    is sent back to the upstream GIST node.
 7) A Query message is received (from either an existing upstream GIST
    node or a new upstream GIST node) with a request to change the
    used GIST operation mode (from D-mode/C-mode to C-mode, if
    available; otherwise, it stays the same).  Local policy requires
    an explicit Confirm message for MRS installation.
 8) The MRS lifetime expires or the NSLP application notifies that the
    MRS is no longer needed.  The MRS is deleted.  If used and not
    needed, the MA is deleted, too.  The NSLP application is notified
    of the MRS change.
 9) The NSLP application provides data for sending.  NSLP data is sent
    if the discovery process is successfully accomplished, or it is
    queued if a Confirm message is still expected to confirm
    establishment of an MA.
 10) A Query message is received.  If it is sent from a new upstream
     GIST node, then there is a path change.  Local policy does not
     need an explicit Confirm message for MRS installation.  The MRS
     data is updated.
 11) A Query message is received with a request to change the used
     GIST operation mode (from D-mode/C-mode to C-mode, if available;
     otherwise, it stays the same).  Local policy does not need an
     explicit Confirm message for MRS installation.  The MRS data is
     updated.

Tsenov, et al. Informational [Page 17] RFC 5972 GIST State Machine October 2010

 12) A Data message is received.  Data messages are accepted only if
     the complete MRS is installed, e.g., the upstream peer info is
     installed.  If not, then a Confirm message is expected and the
     Data message is not accepted.  A Response message indicating the
     loss of the Confirm is sent back to the upstream GIST node.
 13) A Confirm message is received.  It accomplishes assignment of an
     existing MA (or establishment of a new MA) needed for data
     transfer between peers.  The information for the used MA is
     installed as the upstream peer info.
 14) A general error or system-level error occurs.  The MRS is
     deleted.  If not needed, the MA is deleted, too.  The NSLP
     application is notified of the MRS change.

7. Security Considerations

 This document does not raise new security considerations.  Security
 considerations are addressed in the GIST specification [1] and in
 [6].

8. Acknowledgments

 The authors would like to thank Christian Dickmann who contributed to
 refining of the state machine.
 The authors would like to thank Robert Hancock, Ingo Juchem, Andreas
 Westermaier, Alexander Zrim, Julien Abeille Youssef Abidi, and Bernd
 Schloer for their insightful comments.

9. References

9.1. Normative References

 [1]  Schulzrinne, H. and R. Hancock, "GIST: General Internet
      Signalling Transport", RFC 5971, October 2010.
 [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.

9.2. Informative References

 [3]  Vollbrecht, J., Eronen, P., Petroni, N., and Y. Ohba, "State
      Machines for Extensible Authentication Protocol (EAP) Peer and
      Authenticator", RFC 4137, August 2005.

Tsenov, et al. Informational [Page 18] RFC 5972 GIST State Machine October 2010

 [4]  Institute of Electrical and Electronics Engineers, "Standard for
      Local and Metropolitan Area Networks: Port-Based Network Access
      Control", IEEE 802-1X-2004, December 2004.
 [5]  Fajardo, V., Ed., Ohba, Y., and R. Marin-Lopez, "State Machines
      for the Protocol for Carrying Authentication for Network Access
      (PANA)", RFC 5609, August 2009.
 [6]  Tschofenig, H. and D. Kroeselberg, "Security Threats for Next
      Steps in Signaling (NSIS)", RFC 4081, June 2005.

Tsenov, et al. Informational [Page 19] RFC 5972 GIST State Machine October 2010

Appendix A. State Transition Tables

 The state transition tables below represent the state diagrams in
 ASCII format.  Please use the .pdf version whenever possible.  It is
 the clearer representation of the state machine.
 For each state there is a separate table that lists in each row:
 - an event that triggers a transition,
 - actions taken as a result of the incoming event,
 - and the new state at which the transitions ends.

A.1. State Transition Tables for GIST Querying Node

 Please refer to the state machine diagram in Figure 2.
  1. ———-

State: IDLE

  1. ———-
 +Transition
 |  |Condition               |Action                   |State
 V--+------------------------+-------------------------+-----------
 1) |tg_SendMsg              |tx_Query                 |Wait
 ** |                        |start T_No_Response      |Response
    |                        |Queue NSLP data          |
    |                        |                         |
 18)|Tg_ERROR                |Delete MRS               |IDLE
    |                        |IF (MA is used)          |
    |                        |  ((Delete MA)||         |
    |                        |  (Stop using shared MA))|
    |                        |Tg_NetworkNotification   |
    |                        |                         |
 ---+------------------------+-------------------------+-----------

Tsenov, et al. Informational [Page 20] RFC 5972 GIST State Machine October 2010

  1. ———-

State: WaitResponse

  1. ———-
 +Transition
 |  |Condition               |Action                   |State
 V--+------------------------+-------------------------+-----------
 2) |(timeout T_No_Response) |tg_MessageStatus         |IDLE
    |&&(MaxRetry)            |                         |
    |                        |                         |
 3) |(timeout T_No_Response) |Tx_Query                 |Wait
    |&&(!MaxRetry)           |restart T_No_Response    |Response
    |                        |                         |
 4) |rx_Data                 |IF(CheckPeerInfo)        |Wait
    |                        |      tg_RecvMsg to Appl.|Response
    |                        |                         |
 5) |tg_SendMsg              |Queue NSLP data          |Wait
    |                        |                         |Response
    |                        |                         |
 6) |rx_Response)||          |Install MRS              |Established
    |(rx_Response(MAinfo)&&  |IF (RespCookie)          |Downstream
    |(MAexist))              |   tx_Confirm(RespCookie)|MRS
    |                        |tx_Data(Queued NSLP data)|
    |                        |                         |
 7) |rx_Response(MAinfo)&&   |tg_Establish_MA          |Wait MA
 *  |(!MAexist)              |(tx_Confirm)             |Establish.
    |                        |                         |
    |                        |                         |
 18)|Tg_ERROR                |(Delete MRS)             |IDLE
    |                        |IF (MA is used)          |
    |                        |  ((Delete MA)||         |
    |                        |  (Stop using shared MA))|
    |                        |Tg_NetworkNotification   |
    |                        |                         |
 ---+------------------------+-------------------------+-----------

Tsenov, et al. Informational [Page 21] RFC 5972 GIST State Machine October 2010

  1. ———-

State: Established Downstream MRS

  1. ———-
 +Transition
 |  |Condition               |Action                   |State
 V--+------------------------+-------------------------+-----------
 4) |rx_Data                 |IF(CheckPeerInfo)        |Established
    |                        |      tg_RecvMsg to Appl.|Downstream
    |                        |                         |MRS
    |                        |                         |
 9) |((tg_SendMsg)&&(C-mode) |tx_Query                 |Wait
    |&&(!MAexist))||         |Queue NSLP data          |Response
    |(tg_MA_error)||         |                         |
    |(tg_InvalidRoutingState)|                         |
    |                        |                         |
 10)|(timeout T_Inactive_    |Delete MRS               |IDLE
    |                QNode)|||IF (MA is used)          |
    |(tg_SetStateLifetime(0))|   (Delete MA)||         |
    |                        |   (Stop using shared MA)|
    |                        |Tg_NetworkNotification   |
    |                        |                         |
 11)|(rx_Response(MAinfo)&&  |((Delete MA)||           |Wait MA
 *  |(NewPeer)&&(!MA_exist)) |(Stop using shared MA))  |Establish.
    |                        |tg_Establish_MA          |
    |                        |(tx_Confirm)             |
    |                        |                         |
 13)|timeout T_Refresh_QNode |tx_Query                 |Established
    |                        |                         |Downstream
    |                        |                         |MRS
    |                        |                         |
 14)|tg_SendMsg              |tx_Data                  |Established
    |                        |restart T_Inactive_QNode |Downstream
    |                        |                         |MRS
    |                        |                         |
 15)|(rx_Response)&&         |Refresh MRS              |Established
    |(!NewPeer)              |restart T_Inactive_QNode |Downstream
   |                        |                         |MRS
    |                        |                         |
 16)|(rx_Response)||         |IF (MA is used)          |Established
    |(rx_Response(Mainfo)&&  |   (Delete MA)||         |Downstream
    |(MAexist)))&&(NewPeer)  |   (Stop using shared MA)|MRS
    |                        |Install MRS              |
    |                        |restart T_Inactive_QNode |
    |                        |IF (RespCookie)          |
    |                        |   tx_Confirm(RespCookie)|
    |                        |                         |

Tsenov, et al. Informational [Page 22] RFC 5972 GIST State Machine October 2010

 17)|rx_Response(No_MRS_     |tx_Confirm(RespCookie)   |Established
    |              installed)|tx_Data(Queued NSLP data)|Downstream
    |                        |                         |MRS
    |                        |                         |
 18)|Tg_ERROR                |(Delete MRS)             |IDLE
    |                        |IF (MA is used)          |
    |                        |  ((Delete MA)||         |
    |                        |  (Stop using shared MA))|
    |                        |Tg_NetworkNotification   |
    |                        |                         |
 ---+------------------------+-------------------------+-----------
  1. ———-

State: Wait MA Establishment

  1. ———-
 +Transition
 |  |Condition               |Action                   |State
 V--+------------------------+-------------------------+-----------
 5) |tg_SendMsg              |Queue NSLP data          |Wait MA
    |                        |                         |Establish.
    |                        |                         |
 8) |tg_MA_error             |Delete MRS               |IDLE
    |                        |tg_MessageStatus         |
    |                        |                         |
 12)|tg_MA_Established       |Install MRS              |Established
 *  |                        |(tx_Confirm)             |Downstream
    |                        |tx_Data(Queued NSLP data)|MRS
    |                        |                         |
 18)|Tg_ERROR                |Delete MRS               |IDLE
    |                        |IF (MA is used)          |
    |                        |  ((Delete MA)||         |
    |                        |  (Stop using shared MA))|
    |                        |Tg_NetworkNotification   |
    |                        |                         |
 ---+------------------------+-------------------------+-----------

Tsenov, et al. Informational [Page 23] RFC 5972 GIST State Machine October 2010

A.2. State Transition Tables for GIST Responding Node

 Please refer to the state machine diagram in Figure 3.
  1. ———-

State: IDLE

  1. ———-
 +Transition
 |  |Condition               |Action                   |State
 v--+------------------------+-------------------------+-----------
 1) |rx_Query&&              |tx_Response              |Established
    |(!ConfirmRequired)      |Install MRS              |Upstream
    |                        |IF(NSLPdata)             |MRS
    |                        |     tg_RecvMsg(NSLPdata)|
    |                        |                 to Appl.|
    |                        |                         |
 2) |rx_Query&&              |tx_Response              |Wait
    |(ConfirmRequired)       |start T_No_Confirm       |Confirm
    |                        |IF(NSLPdata)             |
    |                        |     tg_RecvMsg(NSLPdata)|
    |                        |                 to Appl.|
    |                        |                         |
 ---+------------------------+-------------------------+-----------
  1. ———-

State: WAIT CONFIRM

  1. ———-
 +Transition
 |  |Condition               |Action                   |State
 v--+------------------------+-------------------------+-----------
 3) |timeout T_No_Confirm    |                         |IDLE
    |                        |                         |
 4) |rx_Query&&              |tx_Response              |Wait
    |(ConfirmRequired)       |start T_No_Confirm       |Confirm
    |                        |IF(NSLPdata)             |
    |                        |     tg_RecvMsg(NSLPdata)|
    |                        |                 to Appl.|
    |                        |                         |
 5) |rx_Confirm              |Install Upstream MRS     |Established
    |                        |                         |Upstream
    |                        |                         |MRS
    |                        |                         |
 6) |rx_Data                 |tx_Response(No_MRS_      |Wait
    |                        |               installed)|Confirm
    |                        |                         |

Tsenov, et al. Informational [Page 24] RFC 5972 GIST State Machine October 2010

 14)|(Tg_ERROR)||            |(Delete MRS)             |IDLE
    |(Tg_MA_Error)           |IF (MA is used)          |
    |                        |  ((Delete MA)||         |
    |                        |  (Stop using shared MA))|
    |                        |Tg_NetworkNotification   |
    |                        |                         |
 ---+------------------------+-------------------------+-----------
  1. ———-

State: Established Upstream MRS

  1. ———-
 +Transition
 |  |Condition               |Action                   |State
 v--+------------------------+-------------------------+-----------
 7) |(rx_Query)&&            |Delete MRS               |Wait
    |(ConfirmRequired)       |tx_Response              |Confirm
    |                        |start T_No_Confirm       |
    |                        |IF(MA is used)           |
    |                        |   (Delete MA)||         |
    |                        |   (Stop using shared MA)|
    |                        |IF(NSLPdata)             |
    |                        |   tg_RecvMsg(NSLPdata)  |
    |                        |                 to Appl.|
    |                        |                         |
 8) |(timeout T_Expire_RNode)|Delete MRS               |IDLE
    |||                      |tg_NetworkNotification   |
    |(tg_SetStateLifetime(0))|IF(MA is used)           |
    |                        |   (Delete MA)||         |
    |                        |   (Stop using shared MA)|
    |                        |                         |
 9) |tg_SendMsg              |IF(!UpstreamPeerInfo)    |Established
    |                        |    Queue NSLP data      |Upstream
    |                        |ELSE tx_Data             |MRS
    |                        |                         |
 10)|rx_Query                |IF (NewPeer)             |Established
    |                        |  Update UpstreamPeerInfo|Upstream
    |                        |tx_Response              |MRS
    |                        |restart T_Expire_RNode   |
    |                        |                         |
 11)|rx_Query(MAinfo)&&      |Delete UpstreamPeerInfo  |Established
    |(!ConfirmRequired)      |restart T_Expire_RNode   |Upstream
    |                        |tx_Response(MAinfo)      |MRS
    |                        |                         |

Tsenov, et al. Informational [Page 25] RFC 5972 GIST State Machine October 2010

 12)|rx_Data                 |IF(UpstreamPeerInfo)     |Established
    |                        |    (tg_RecvMsg to Appl.)|Upstream
    |                        |    &&(restart_T_Expire_ |MRS
    |                        |                   RNode)|
    |                        |ELSE                     |
    |                        |    tx_Error(No_MRS_     |
    |                        |               installed)|
    |                        |                         |
 13)|rx_Confirm              |Install UpstreamPeerInfo |Established
    |                        |tx_Data(queued_NSLP_data)|Upstream
    |                        |                         |MRS
    |                        |                         |
 14)|(Tg_ERROR)||            |(Delete MRS)             |IDLE
    |(Tg_MA_Error)           |IF (MA is used)          |
    |                        |  ((Delete MA)||         |
    |                        |  (Stop using shared MA))|
    |                        |Tg_NetworkNotification   |
    |                        |                         |
 ---+------------------------+-------------------------+-----------

Tsenov, et al. Informational [Page 26] RFC 5972 GIST State Machine October 2010

Authors' Addresses

 Tseno Tsenov
 Sofia, Bulgaria
 EMail: tseno.tsenov@mytum.de
 Hannes Tschofenig
 Nokia Siemens Networks
 Linnoitustie 6
 Espoo  02600
 Finland
 EMail: Hannes.Tschofenig@nsn.com
 Xiaoming Fu (editor)
 University of Goettingen
 Computer Networks Group
 Goldschmidtstr. 7
 Goettingen 37077
 Germany
 EMail: fu@cs.uni-goettingen.de
 Cedric Aoun
 Consultant
 Paris, France
 EMail: cedaoun@yahoo.fr
 Elwyn B. Davies
 Folly Consulting
 Soham, Cambs, UK
 Phone: +44 7889 488 335
 EMail: elwynd@dial.pipex.com

Tsenov, et al. Informational [Page 27]

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