<pre>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


       <span class="h1">General Internet Signaling Transport (GIST) State Machine</span>

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 <a href="./rfc5741#section-2">Section&nbsp;2 of RFC 5741</a>.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   <a href="http://www.rfc-editor.org/info/rfc5972">http://www.rfc-editor.org/info/rfc5972</a>.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) 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



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   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

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













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<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>.  Introduction</span>

   The state machines described in this document are illustrative of how
   the GIST protocol defined in [<a href="#ref-1" title="&quot;GIST: General Internet Signalling Transport&quot;">1</a>] may be implemented for the GIST
   nodes in different locations of a flow path.  Where there are
   differences, [<a href="#ref-1" title="&quot;GIST: General Internet Signalling Transport&quot;">1</a>] 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:

   -  GIST querying node: GIST node that initiates the discovery of the
      next peer;

   -  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.

<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>.  Terminology</span>

   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 [<a href="#ref-2" title="&quot;Key words for use in RFCs to Indicate Requirement Levels&quot;">2</a>].

<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>.  Notational Conventions Used in State Diagrams</span>

   The following text is reused from [<a href="#ref-3" title="&quot;State Machines for Extensible Authentication Protocol (EAP) Peer and Authenticator&quot;">3</a>], and the state diagrams are
   based on the conventions specified in [<a href="#ref-4" title="&quot;Standard for Local and Metropolitan Area Networks: Port-Based Network Access Control&quot;">4</a>], Section 8.2.1.  Additional
   state machine details are taken from [<a href="#ref-5" title="&quot;State Machines for the Protocol for Carrying Authentication for Network Access (PANA)&quot;">5</a>].

   <a href="./rfc4137">RFC 4137</a> [<a href="#ref-3" title="&quot;State Machines for Extensible Authentication Protocol (EAP) Peer and Authenticator&quot;">3</a>] reproduced the following text from <a href="#section-8.2.1">Section 8.2.1</a> of IEEE
   802-1X-2004 [<a href="#ref-4" title="&quot;Standard for Local and Metropolitan Area Networks: Port-Based Network Access Control&quot;">4</a>].

      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



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      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:




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   &lt;variable&gt; = &lt;expression1&gt; | &lt;expression2&gt; | ...

      Execution of a statement of this form will result in &lt;variable&gt;
      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.

<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>.  State Machine Symbols</span>

   ( )
      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.

   &amp;&amp;
      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.





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   !=
      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.

   &gt;
      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.

   &lt;=
      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.

   &amp;
      Bitwise AND operator.

<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>.  Common Rules</span>

   Throughout the document we use terms defined in [<a href="#ref-1" title="&quot;GIST: General Internet Signalling Transport&quot;">1</a>], 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.





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   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.

<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a>.  Common Procedures</span>

   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.





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   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 (<a href="#section-5.3">Section 5.3</a>):
      Start/Restart of a certain timer.

   Install/Update/Delete UpstreamPeerInfo variable (<a href="#section-5.3">Section 5.3</a>):
      Management of upstream peer info in state machine of responding
      node.

<span class="h3"><a class="selflink" id="section-5.2" href="#section-5.2">5.2</a>.  Common Events</span>

   Rx_Query:
      Receive of Query message.

   Rx_Response:
      Receive of Response message.

   Rx_Confirm:
      Receive of Confirm message.

   Rx_Data:
      Receive of Data message.




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   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 (<a href="#section-5.3">Section 5.3</a>):
      Timeout of a certain timer.

<span class="h3"><a class="selflink" id="section-5.3" href="#section-5.3">5.3</a>.  Common Variables</span>

   Variables listed in this section are defined as:

   -  Specific information carried in the received messages.

   -  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.




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      "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) [<a href="#ref-1" title="&quot;GIST: General Internet Signalling Transport&quot;">1</a>].

   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 [<a href="#ref-1" title="&quot;GIST: General Internet Signalling Transport&quot;">1</a>].

   MAinfo:
      GIST message parameters describing the required MA or proposed MA,
      e.g., "Stack-proposal" and "Stack-Configuration-Data" [<a href="#ref-1" title="&quot;GIST: General Internet Signalling Transport&quot;">1</a>].

   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.



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   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.

<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>.  State Machines</span>

   The following section presents the state machine diagrams of GIST
   peers.  <a href="./rfc5972">RFC 5972</a> 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
   <a href="#appendix-A">Appendix A</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.














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<span class="h3"><a class="selflink" id="section-6.1" href="#section-6.1">6.1</a>.  Diagram Notations</span>

   +--------------------------------+
   |             STATE              |
   +--------------+-----------------+
                  |
                  |
                ooooo
               o  N  o   Transition N
                ooooo
                  |
                  v
   +--------------------------------+
   |             STATE              |
   +--------------------------------+

                        Figure 1: Diagram notations

<span class="h3"><a class="selflink" id="section-6.2" href="#section-6.2">6.2</a>.  State Machine for GIST Querying Node</span>

   The state machine diagram of the GIST querying node is below.
   Transition descriptions follow.

   Please refer to <a href="#appendix-A.1">Appendix A.1</a> for complete transition details
   (triggering event, action taken, and variable status).


























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   +-----------+           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






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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-14" ></span>
<span class="grey"><a href="./rfc5972">RFC 5972</a>                   GIST State Machine               October 2010</span>


   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.



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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-15" ></span>
<span class="grey"><a href="./rfc5972">RFC 5972</a>                   GIST State Machine               October 2010</span>


   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 [<a href="#ref-1" title="&quot;GIST: General Internet Signalling Transport&quot;">1</a>] for details.

   **) Depending on GIST local policy, NSLPdata might be sent as the
       payload of Query and Confirm messages (piggybacking).


















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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-16" ></span>
<span class="grey"><a href="./rfc5972">RFC 5972</a>                   GIST State Machine               October 2010</span>


<span class="h3"><a class="selflink" id="section-6.3" href="#section-6.3">6.3</a>.  State Machine for GIST Responding Node</span>

   The GIST responding node state machine diagram is below.  Transition
   descriptions follow.

   Please refer to <a href="#appendix-A.2">Appendix A.2</a> 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.



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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-17" ></span>
<span class="grey"><a href="./rfc5972">RFC 5972</a>                   GIST State Machine               October 2010</span>


   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.




<span class="grey">Tsenov, et al.                Informational                    [Page 17]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-18" ></span>
<span class="grey"><a href="./rfc5972">RFC 5972</a>                   GIST State Machine               October 2010</span>


   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.

<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>.  Security Considerations</span>

   This document does not raise new security considerations.  Security
   considerations are addressed in the GIST specification [<a href="#ref-1" title="&quot;GIST: General Internet Signalling Transport&quot;">1</a>] and in
   [<a href="#ref-6" title="&quot;Security Threats for Next Steps in Signaling (NSIS)&quot;">6</a>].

<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>.  Acknowledgments</span>

   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.

<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>.  References</span>

<span class="h3"><a class="selflink" id="section-9.1" href="#section-9.1">9.1</a>.  Normative References</span>

   [<a id="ref-1">1</a>]  Schulzrinne, H. and R. Hancock, "GIST: General Internet
        Signalling Transport", <a href="./rfc5971">RFC 5971</a>, October 2010.

   [<a id="ref-2">2</a>]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.

<span class="h3"><a class="selflink" id="section-9.2" href="#section-9.2">9.2</a>.  Informative References</span>

   [<a id="ref-3">3</a>]  Vollbrecht, J., Eronen, P., Petroni, N., and Y. Ohba, "State
        Machines for Extensible Authentication Protocol (EAP) Peer and
        Authenticator", <a href="./rfc4137">RFC 4137</a>, August 2005.






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<span class="grey"><a href="./rfc5972">RFC 5972</a>                   GIST State Machine               October 2010</span>


   [<a id="ref-4">4</a>]  Institute of Electrical and Electronics Engineers, "Standard for
        Local and Metropolitan Area Networks: Port-Based Network Access
        Control", IEEE 802-1X-2004, December 2004.

   [<a id="ref-5">5</a>]  Fajardo, V., Ed., Ohba, Y., and R. Marin-Lopez, "State Machines
        for the Protocol for Carrying Authentication for Network Access
        (PANA)", <a href="./rfc5609">RFC 5609</a>, August 2009.

   [<a id="ref-6">6</a>]  Tschofenig, H. and D. Kroeselberg, "Security Threats for Next
        Steps in Signaling (NSIS)", <a href="./rfc4081">RFC 4081</a>, June 2005.









































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<span class="grey"><a href="./rfc5972">RFC 5972</a>                   GIST State Machine               October 2010</span>


<span class="h2"><a class="selflink" id="appendix-A" href="#appendix-A">Appendix A</a>.  State Transition Tables</span>

   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.

<span class="h3"><a class="selflink" id="appendix-A.1" href="#appendix-A.1">A.1</a>.  State Transition Tables for GIST Querying Node</span>

   Please refer to the state machine diagram in Figure 2.

   -----------
   State: IDLE
   -----------

   +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   |
      |                        |                         |
   ---+------------------------+-------------------------+-----------


















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<span class="grey"><a href="./rfc5972">RFC 5972</a>                   GIST State Machine               October 2010</span>


   -----------
   State: WaitResponse
   -----------

   +Transition
   |  |Condition               |Action                   |State
   V--+------------------------+-------------------------+-----------
   2) |(timeout T_No_Response) |tg_MessageStatus         |IDLE
      |&amp;&amp;(MaxRetry)            |                         |
      |                        |                         |
   3) |(timeout T_No_Response) |Tx_Query                 |Wait
      |&amp;&amp;(!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)&amp;&amp;  |IF (RespCookie)          |Downstream
      |(MAexist))              |   tx_Confirm(RespCookie)|MRS
      |                        |tx_Data(Queued NSLP data)|
      |                        |                         |
   7) |rx_Response(MAinfo)&amp;&amp;   |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   |
      |                        |                         |
   ---+------------------------+-------------------------+-----------
















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<span class="grey"><a href="./rfc5972">RFC 5972</a>                   GIST State Machine               October 2010</span>


   -----------
   State: Established Downstream MRS
   -----------

   +Transition
   |  |Condition               |Action                   |State
   V--+------------------------+-------------------------+-----------
   4) |rx_Data                 |IF(CheckPeerInfo)        |Established
      |                        |      tg_RecvMsg to Appl.|Downstream
      |                        |                         |MRS
      |                        |                         |
   9) |((tg_SendMsg)&amp;&amp;(C-mode) |tx_Query                 |Wait
      |&amp;&amp;(!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)&amp;&amp;  |((Delete MA)||           |Wait MA
   *  |(NewPeer)&amp;&amp;(!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)&amp;&amp;         |Refresh MRS              |Established
      |(!NewPeer)              |restart T_Inactive_QNode |Downstream
     |                        |                         |MRS
      |                        |                         |
   16)|(rx_Response)||         |IF (MA is used)          |Established
      |(rx_Response(Mainfo)&amp;&amp;  |   (Delete MA)||         |Downstream
      |(MAexist)))&amp;&amp;(NewPeer)  |   (Stop using shared MA)|MRS
      |                        |Install MRS              |
      |                        |restart T_Inactive_QNode |
      |                        |IF (RespCookie)          |
      |                        |   tx_Confirm(RespCookie)|
      |                        |                         |




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   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   |
      |                        |                         |
   ---+------------------------+-------------------------+-----------


   -----------
   State: Wait MA Establishment
   -----------

   +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   |
      |                        |                         |
   ---+------------------------+-------------------------+-----------














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<span class="grey"><a href="./rfc5972">RFC 5972</a>                   GIST State Machine               October 2010</span>


<span class="h3"><a class="selflink" id="appendix-A.2" href="#appendix-A.2">A.2</a>.  State Transition Tables for GIST Responding Node</span>

   Please refer to the state machine diagram in Figure 3.

   -----------
   State: IDLE
   -----------

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


   -----------
   State: WAIT CONFIRM
   -----------

   +Transition
   |  |Condition               |Action                   |State
   v--+------------------------+-------------------------+-----------
   3) |timeout T_No_Confirm    |                         |IDLE
      |                        |                         |
   4) |rx_Query&amp;&amp;              |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
      |                        |                         |



<span class="grey">Tsenov, et al.                Informational                    [Page 24]</span></pre>
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   14)|(Tg_ERROR)||            |(Delete MRS)             |IDLE
      |(Tg_MA_Error)           |IF (MA is used)          |
      |                        |  ((Delete MA)||         |
      |                        |  (Stop using shared MA))|
      |                        |Tg_NetworkNotification   |
      |                        |                         |
   ---+------------------------+-------------------------+-----------


   -----------
   State: Established Upstream MRS
   -----------

   +Transition
   |  |Condition               |Action                   |State
   v--+------------------------+-------------------------+-----------
   7) |(rx_Query)&amp;&amp;            |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)&amp;&amp;      |Delete UpstreamPeerInfo  |Established
      |(!ConfirmRequired)      |restart T_Expire_RNode   |Upstream
      |                        |tx_Response(MAinfo)      |MRS
      |                        |                         |






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   12)|rx_Data                 |IF(UpstreamPeerInfo)     |Established
      |                        |    (tg_RecvMsg to Appl.)|Upstream
      |                        |    &amp;&amp;(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   |
      |                        |                         |
   ---+------------------------+-------------------------+-----------
































<span class="grey">Tsenov, et al.                Informational                    [Page 26]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-27" ></span>
<span class="grey"><a href="./rfc5972">RFC 5972</a>                   GIST State Machine               October 2010</span>


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]
</pre>