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Versions: (draft-fu-nsis-ntlp-statemachine) 00 01 02 03 04 05 06 07 08 09 10 RFC 5972

NSIS                                                           T. Tsenov
Internet-Draft                                             H. Tschofenig
Expires: January 6, 2005                                         Siemens
                                                                   X. Fu
                                                        Univ. Goettingen
                                                                 C. Aoun
                                                                  Nortel
                                                               E. Davies
                                                        Folly Consulting
                                                            July 5, 2005

                          GIMPS State Machine
                draft-ietf-nsis-ntlp-statemachine-00.txt

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Copyright Notice

   Copyright (C) The Internet Society (2005).  All Rights Reserved.

Abstract

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






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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 Variables . . . . . . . . . . . . . . . . . . . . .   9
     5.3  Constants  . . . . . . . . . . . . . . . . . . . . . . . .  11
   6.   State machines . . . . . . . . . . . . . . . . . . . . . . .  12
     6.1  Diagram notations  . . . . . . . . . . . . . . . . . . . .  12
     6.2  State machine for GIMPS querying node  . . . . . . . . . .  12
     6.3  State machine for GIMPS responding node  . . . . . . . . .  13
   7.   Security Considerations  . . . . . . . . . . . . . . . . . .  14
   8.   Open Issues  . . . . . . . . . . . . . . . . . . . . . . . .  14
   9.   Contributors . . . . . . . . . . . . . . . . . . . . . . . .  15
   10.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . .  15
   11.  References . . . . . . . . . . . . . . . . . . . . . . . . .  16
     11.1   Normative References . . . . . . . . . . . . . . . . . .  16
     11.2   Informative References . . . . . . . . . . . . . . . . .  16
   Appendix A.  ASCII versions of the state diagrams . . . . . . . .  17
     A.1    State machine for GIMPS querying node (Figure 2) . . . .  17
     A.2    State Machine for GIMPS responding node (Figure 3) . . .  20
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  23
        Intellectual Property and Copyright Statements . . . . . . .  24

























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1.  Introduction

   This document describes the state machines for GIMPS [1], trying to
   show how GIMPS can be implemented to support its deployment.  The
   state machines described in this document are illustrative of how the
   GIMPS protocol defined in [1] may be implemented for the GIMPS nodes
   in different locations of a flow path.  Where there are differences
   [1] are authoritative.  The state machines are informative only.
   Implementations may achieve the same results using different methods.

   There are two types of possible entities for GIMPS signaling:

   - GIMPS querying node - GIMPS node that initiates the discovery of
   the next peer;

   - GIMPS responding node - GIMPS node that is the discovered next
   peer;

   We describe a set of state machines for these entities to illustrate
   how GIMPS 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].

   The complete text is reproduced here:

   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 evaluates to TRUE).  A
   transition that is global in nature (i.e., a transition that occurs



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   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 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 of 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, i.e., 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 of 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:

   <variable> = <expression1> | <expression2> | ...

      Execution of a statement of this form will result in <variable>



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      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

   MA
      Messaging Association

   Upstream/Downstream MRS
      Message Routing State with upstream/downstream peer state info

   ( )
      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.



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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.

   >
      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 the [1], such as
   Query, Response, Confirm.

   State machine represents handling of GIMPS messages that match a
   Message Routing State's MRI and NSLPID and with no protocol errors.
   Separate parallel instances of the state machines should handle
   messages for different Message Routing States.

   The state machine states represent the upstream/downstream peers
   states 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.

   Presented in this document state machines do not cover all functions
   of a GIMPS node.  Functionality of message forwarding, ROA
   processing, transmission of NSLP data without MRS establishment and



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   providing of the received messages to the appropriate MRS, we refer
   as "Lower level pre-processing" step.  The interaction of this step
   with the presented here state machines is defined as follows:

   Pre-processing provides to the appropriate MRS FSM only the messages
   which are matched against waiting Query/Response cookies, or
   established MRS MRI+NSLPID primary key.  This is presented by "rx_*"
   events in the state machines.

5.1  Common Procedures

   Tg_SendMsg:
      NSLP/GIMPS API message that request transmission of a NSLP
      message.

   Tg_SetStateLifetime(time_period):
      NSLP/GIMPS API message providing info for the Lifetime of an RS,
      required by the application. "Time_period = 0" represents the
      cancellation of established RSs/MAs (invoked by NSLP application).

   Tg_MessageDeliveryError:
      NSLP/GIMPS API message informing NSLP application of unsuccessful
      delivery of a message

   Tg_RecvMsg:
      NSLP/GIMPS API message that provides received message to the NSLP

   Tg_NetworkNotification:
      NSLP/GIMPS API message that informs NSLP for change in MRS

   Tx_Query:
      Transmit of Query message in Dmode

   Tx_Response_Dmode:
      Transmit of Response message in Dmode

   Tx_Confirm_Dmode:
      Transmit of Confirm message in Dmode

   Rx_Query_Dmode:
      Receive of Query message in Dmode

   Rx_Response_Dmode:
      Receive of Response message in Dmode

   Rx_Confirm_Cmode:
      Receive of Confirm message in Dmode




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   Tx_Response_Cmode:
      Transmit of Response message in Cmode (via MA)

   Tx_Confirm_Cmode:
      Transmit of Confirm message in Cmode (via MA)

   Rx_Response_Cmode:
      Receive of Response message in Cmode (via MA)

   Rx_Confirm_Cmode:
      Receive of Confirm message in Cmode (via MA)

   Queue NSLP msg info:
      Save NLSP messages in a queue until a required MA association is
      established

   Tx_Msg_Cmode:
      Transmit message in Cmode (via MA)

   Rx_Msg_Cmode:
      Receive message in Cmode (via MA)

   Tx_Msg_Dmode:
      Transmit message in Dmode

   Rx_Msg_Dmode:
      Receive message in Dmode

   TIMEOUT_MRSlifetime:
      Expiration of the lifetime timer of the upstream/downstream peer
      state info of the Message Routing State.

   TIMEOUT_Refresh:
      Refresh interval timer expiration

   TIMEOUT_WaitResponse:
      Expiration of Timer for the waiting period for Response message.

   TIMEOUT_WaitConfirm:
      Expiration of Timer for the waiting period for Confirm message.

   Install downstream/upstream MRS:
      Install new Message Routing State and save the corespoding peer
      state info (IP address and UDP port or pointer to the used MA) for
      the current Message Routing State or update the coresponding peer
      state info.

   DELETE MRS:



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      Delete installed downstream/upstream peer's info for the current
      Message Routing State and delete the Message Routing State if
      required.

   Establish MA:
      Establish Message Association (MA) between current node and its
      downstream peer

   Established MA:
      A Message Association (MA) is established between the current node
      and its upstream peer.  The initiator for the establishment is the
      upstream peer.  Re-use existing MA: An existing MA between the
      current node and its peer is re-used.

   DELETE MA:
      Delete/disconnect used MA.

   Stop using shared MA:
      Stop using shared MA. If the shared MA is no more used by any
      other MRSs, it depends on the local policy whether it is deleted
      or kept.

   REFRESH MRS:
      Refreshes installed MRS.

   Tg_MA_Error:
      Error event with used MA.

   Tg_PathChange:
      External event for Path change detected.

   Tg_Establish_MA:
      Trigers establishment of MA.

   Tg_MA_Established:
      MA has been successfully established.

   Tg_ERROR:
      General Error event / system level error.

   No_MRS_Installed:
      Error response, send by the Responding node indicating lost
      Confirm message.

5.2  Common Variables

   It is assumed that the type of mode and destination info (which need
   to be taken from the application parameters and local GIMPS policy)is



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   provided.  This is represented by the common variables Dmode, Cmode,
   MAinfo, MApresent and Refresh.

   Dmode:
      The message MUST be transmitted in Dmode.  This is specified by
      "Message transfer attributes" set to the following values:

      "Reliability" is set to FALSE.

      "Security" is set to values that do not request special security
         handling of a message.

      "Local processing" is set to values that do not require services
         offered by Cmode [1]

   Cmode:
      The message MUST be transmitted in Cmode.  This is specified by
      "Message transfer attributes" set to any of the following values:

      "Reliability" is set to TRUE.

      "Security" is set to values that request secure handling of a
      message.

      "Local processing" is set to values that require services offered
      by Cmode (e.g., congestion control). [1]

   MAinfo:
      GIMPS message parameters describing the required MA or proposed MA
      e.g. "Stack-proposal" and "Node-addressing". This list of GIMPS
      parameters is not complete.  A full mapping is left for future
      version of the document.

   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.

   Refresh:
      This variable specifies that the message is for refresh purposes.

   ConfirmRequired:
      TConfirm message is required by the local policy rule for
      installation of the new MRS.




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   NewPeer:
      Response message is received from new responding peer.

   MAexist:
      Existing MA will be reused.

   CheckPeerInfo:
      The sender of the received data message is matched against the
      installed peer info in the MRS.

   UpstreamPeerInstalled:
      Upstream peer info is installed in the MRS.


5.3  Constants




































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6.  State machines

   The following section presents the state machine diagrams of GIMPS
   peers.

6.1  Diagram notations

              (see the .pdf version for missing diagram or
            refer to Appendix A if reading the .txt version)

                      Figure 1: Diagram notations

6.2  State machine for GIMPS querying node

   The following is a diagram of the GIMPS querying node state machine.
   Also included is clarification of notation.

              (see the .pdf version for missing diagram or
           refer to Appendix A.1 if reading the .txt version)

              Figure 1: GIMPS Querying Node State Machine


   *) Response and Confirm messages might be send either in Dmode or
      Cmode, before or after MA establishment depending on node's local
      3-way handshake policy and the availability of MAs to be reused.
      See draft for details.
   **) Depending on the local policy NSLPdata might be send as payload
      of Query and Confirm messages. (piggybacking)
   1) Initial request from NSLP are received, which triggers Query
      messages requesting either D_mode or C_mode.  Dependign on local
      policy of the node, NSLP data might be piggybacked in the Query
      requesting D_mode.
   2) Response message is received.  If C_mode connections must be
      established and there is no available MA to be reused, MA
      establishment is initiated and waited to be completed.  If D_mode
      connection is requested or available MA can be reused if C_mode is
      requested the MRS is established.
   3) New MA is successfully established and MRS, which will use it, is
      installed.
   4) Path change detected events - local recovery procedure, where new
      MA must be established for requested C_mode  connection. THIS IS
      VALID ONLY IF THE NODE IS CROSSOVER NODE.
   5) Path change detected events - local recovery procedure, where
      D_mode or C_mode with available MA must be established.  THIS IS
      VALID ONLY IF THE NODE IS CROSSOVER NODE.
   6) NSLP data is queued, because downstream peer is not discovered or
      required MA is still not established.



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   7) Received Data messages are checked if their sender matches the
      installed downstream peer info in the MRS and then processed.
   8) Received Data messages are checked if their sender matches the
      installed downstream peer info in the MRS and then processed. In
      WaitResponse state, this event might happen in the process of MA
      upgrade, when the downstream peer is still not aware of
      establishment of the new MA.
   9) Depending on the requested transport from NSLP and currently
      established D_mode or C_mode, NSLP message is sent D_mode if
      D_mode is requested and C_mode if the features of the used MA
      covers the required transport. ( e.g. used MA is reliable and NSLP
      request reliable but not secure transport)
   10) External event notifies for Path Change and discovery procedures
      is restarted. THIS IS VALID ONLY IF THE NODE IS CROSSOVER NODE OR
      NSLP requests C_mode transport that is not covered by currently
      used D_mode or MA (case of MA upgrade) and discovery procedure is
      restared but current downstream peer info is kept in order to be
      able to receive messages from it during the upgrade process.

6.3  State machine for GIMPS responding node

   The following is a diagram of the GIMPS responding node state
   machine. Also included is clarification of notation.

              (see the .pdf version for missing diagram or
           refer to Appendix A.2 if reading the .txt version)

             Figure 3: GIMPS Responding Node State Machine

   *) Response and Confirm messages might be send either in Dmode or
      Cmode depending on node's local 3-way handshake policy and the
      availability of MAs to be reused. See draft for details.
   **) Differentiation between WaitConfirm timer expiration of initial
      MRS event or MA_upgrade event is based on the presence of
      installed peer info in the MRS. If no peer info is installed this
      is initial MRS establishment.
   1) Initial Query messages requesting either D_mode or C_mode
      connection.  In both cases, explicit Confirm message is required
      for MRS installation, based on the local policy. Query requesting
      D_mode might carry piggybacked NSLP data.
   2) Initial Query messages requesting either D_mode or C_mode
      connection.  In both cases, MRS is installed immediately, based on
      the local policy.  Query requesting D_mode might carry piggybacked
      NSLP data.  In the case of C_mode request, Confirm message is
      required to confirm the establishment of the used MA.
   3) In case of lost Confirm message, data messages might be received
      from the upstream node (it is unaware of the lost Confirm
      message).  Response indicating the loss of the Confirm is sent



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      back to the upstream node.
   4) Event of change of the upstream peer (e.g., path change) with
      request of D_mode and non-paranoid local policy.
   5) Event of request of change of the used connection mode (from
      D_mode/C_mode to better C_mode),  event of change of the upstream
      peer (e.g., path change) with request for C_mode or D_mode
      connection and paranoid local policy.
   6) Confirm message is received which causes installation of the
      complete MRS or just installation of the used MA as a upstream
      peer info.
   7) Differentiation between WaitConfirm timer expiration of initial
      MRS event or MA upgrade/change event is based on the presence of
      installed peer info in the MRS.  If no peer info is installed this
      is initial MRS establishment and installed MRS must be deleted.
   8) Data messages are accepted only if complete MRS is installed,
      e.g., there is installed upstream peer info.  If not then Confirm
      message is expected and data message will not be accepted but
      Response indicating the loss of the Confirm is sent back to the
      upstream node.
   9) NSLP message can't be sent upstream if Confirm message is not
      received and MA is not installed as upstream peer info.  They are
      queued.

8.  Security Considerations

   This document does not raise new security considerations. Any
   security concerns with GIMPS are likely reflected in security related
   NSIS work already (such as [1] or [6]).

   For the time being, the state machines described in this document do
   not consider the security aspect of GMIPS protocol itself. A future
   versions of this document will add security relevant states and state
   transitions.

9.  Open Issues

   We have left for further version of the document the following
   issues:

   1. The FSM that handles the management of a MA is considered in the
      document (e.g., tg_Establish_MA, tg_MA_established events), but it
      is not currently explicitely presented.  It is left for future
      version of the document.
   2. Functionality of, as referred in the document "Lower level pre-
      processing" (Section 5), namely message forwarding, RAO
      processing, transmission of NSLP data without MRS establishment
      and providing of the received messages to the appropriate MRS is
      left for future version of the document.



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   3. Currently we use WaitConfirm state in the Responding node FSM, but
      following the DoS prevention approaches for no state installation
      in the Responding node before receiving of Confirm message, we
      consider possible removing of this state.  This issue requires
      further investigations.

10.  Contributors

   Christian Dickmann contributed to refining of the state machine since
   01 version.

11.  Acknowledgments

   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.



































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12.  References

12.1.  Normative References

   [1]         Schulzrinne, H., "GIMPS: General Internet Messaging
               Protocol for Signaling", draft-ietf-nsis-ntlp-05 (work in
               progress), February
                2005.

   [2]         Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

11.2.  Informative References

   [3]         Vollbrecht, J., Eronen, P., Petroni, N., and Y. Ohba,
               "State Machines for Extensible Authentication Protocol
               (EAP) Peer and Authenticator", draft-ietf-eap-
               statemachine-06 (work in progress), December 2004.

   [4]         Institute of Electrical and Electronics Engineers, "DRAFT
                Standard for Local and Metropolitan Area Networks: Port-
               Based
                Network Access Control (Revision)", IEEE 802-1X-REV/D11,
               July 2004.

   [5]         Ohba, Y., "State Machines for Protocol for Carrying
               Authentication for Network Access  (PANA)",
                draft-ohba-pana-statemachine-01 (work in progress),
               February 2005.

   [6]         Tschofenig, H. and D. Kroeselberg, "Security Threats for
               NSIS", draft-ietf-nsis-threats-06 (work in progress),
               October 2004.


















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Appendix A. ASCII versions of state diagrams

   This appendix contains the state diagrams in ASCII format.  Please
   use the PDF version whenever possible: it is much easier to
   understand.

   The notation is as follows: 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 machine for GIMPS querying node (Figure 2)

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

Condition                Action                    State      Note
------------------------+-------------------------+-----------+---
(tg_SendMsg)&&(Dmode)   |Tx_Query                 |Wait       |1)
                        |Queue_NSLP_msg_data      |Response   |**
                        |                         |           |
(tg_SendMsg)&&(Cmode)   |Tx_Query(MAinfo)         |Wait       |1)
                        |Queue_NSLP_msg_data      |Response   |
                        |                         |           |
------------------------+-------------------------+-----------+---



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

Condition                Action                    State      Note
------------------------+-------------------------+-----------+---
(rx_Response_Dmode)||   |Install MRS              |Established|**
((rx_Response_?mode(    |If (RespCookie)          |Downstream |2)
     MAinfo)&&(MAexist))|  tx_Confirm_?mode(Resp  |MRS        |
                        |                  Cookie)|           |
                        |Tx_queued_Msg_?mode      |           |
                        |                         |           |
(rx_Response_?mode(     |Tg_Establish_MA          |Wait MA    |*
   MAinfo)&&(!MA_exist))|(Tx_Confirm_?mode)       |Establish. |2)
                        |                         |           |
rx_Msg_?mode            |IF(CheckPeerInfo)        |Wait       |8)
                        |      Tg_RecvMsg to Appl.|Response   |
                        |                         |           |



Tsenov, et al.                                                 [Page 17]

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tg_SendMsg              |Queue NSLP msg data      |Wait       |6)
                        |                         |Response   |
                        |                         |           |
Timeout_WaitResponse    |(Tx_Query(MAinfo)) ||    |Wait       |
                        |(Tx_Query(NSLPdata))||   |Response   |
                        |(Tx_Query)               |           |
                        |                         |           |
(Timeout_WaitResponse)  |Tg_MessageDeliveryError  |IDLE       |
&&(MaxRetry)            |                         |           |
                        |                         |           |
Tg_ERROR                |(Delete MRS)             |IDLE       |
                        |IF (MA is used)          |           |
                        |  ((Delete MA)||         |           |
                        |  (Stop using shared MA))|           |
                        |Tg_NetworkNotification   |           |
                        |                         |           |
------------------------+-------------------------+-----------+---





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

Condition                Action                    State      Note
------------------------+-------------------------+-----------+---
rx_Msg_?mode            |IF(CheckPeerInfo)        |Established|7)
                        |      Tg_RecvMsg to Appl.|Downstream |
                        |                         |MRS        |
                        |                         |           |
tg_SendMsg_?mode        |IF(Cmode)&&(MAexist)     |Established|9)
                        |           Tx_Msg_Cmode  |Downstream |
                        |IF(Dmode)  Tx_Msg_Dmode  |MRS        |
                        |                         |           |
((tg_SendMsg)&&(Cmode)&&|Tx_Query(MAinfo)         |Wait       |10)
(!MAexist))||           |Queue NSLP msg data      |Response   |
(tg_MA_error)||         |                         |           |
(tg_Path_Change)        |                         |           |
                        |                         |           |
Timeout_refresh         |Tx_Query(Refresh)        |Established|
                        |                         |Downstream |
                        |                         |MRS        |
                        |                         |           |
rx_Response(No_MRS      |tx_Confirm(RespCookie)   |Established|
             _installed)|Tx_queued_Msg_Cmode      |Downstream |
                        |                         |MRS        |



Tsenov, et al.                                                 [Page 18]

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                        |                         |           |
(Timeout_MRSlifetime)|| |(Delete MRS)             |IDLE       |
(tg_SetStateLifetime(0))|                         |           |
||(Tg_ERROR)            |                         |           |
                        |                         |           |
                        |Tg_NetworkNotification   |           |
                        |                         |           |
(rx_Response_Dmode)||   |IF (MA is used)          |Established|5)
(rx_Response_?mode(     |  ((Delete MA)||         |Downstream |
    Mainfo)&&(NewPeer)&&|  (Stop using shared MA))|MRS        |
(MAexist)               |Install MRS              |           |
                        |If (RespCookie)          |           |
                        |  tx_Confirm_?mode(Resp  |           |
                        |                  Cookie)|           |
                        |                         |           |
(rx_Response_?mode(     |((Delete MA)||           |Wait MA    |*
    MAinfo)&&(NewPeer)&&|(Stop using shared MA))  |Establish. |4)
(!MA_exist)             |Tg_Establish_MA          |           |
                        |(Tx_Confirm_?mode)       |           |
                        |                         |           |
                        |                         |           |
                        |                         |           |
                        |                         |           |
                        |                         |           |
------------------------+-------------------------+-----------+---



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

Condition                Action                    State      Note
------------------------+-------------------------+-----------+---
tg_SendMsg              |Queue NSLP msg data      |Wait MA    |6)
                        |                         |Establish. |
                        |                         |           |
Tg_MA_Established       |Install MRS              |Established|3)
                        |(Tx_Confirm_?mode)       |Downstream |*
                        |(Tx_queued_Msg_Cmode)    |MRS        |**
                        |                         |           |
Tg_MA_error             |Delete MRS               |IDLE       |
                        |Tg_NetworkNotification   |           |
                        |                         |           |
Tg_ERROR                |(Delete MRS)             |IDLE       |
                        |IF (MA is used)          |           |
                        |  ((Delete MA)||         |           |
                        |  (Stop using shared MA))|           |



Tsenov, et al.                                                 [Page 19]

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                        |Tg_NetworkNotification   |           |
                        |                         |           |
------------------------+-------------------------+-----------+---

                                Figure 4

A.2.  State Machine for GIMPS responding node (Figure 3)

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

Condition                Action                    State      Note
------------------------+-------------------------+-----------+---
rx_Query(?)             |Tx_Response_Dmode(Resp   |Wait       |1)
&&(ConfirmRequired)     |                  Cookie)|Confirm    |
                        |IF(NSLPdata)             |           |
                        |Tg_RecvMsg(NSLPdata)     |           |
                        |                 to Appl.|           |
                        |                         |           |
rx_Query(?)             |Tx_Response_Dmode        |Established|2)
&&(!ConfirmRequired)    |Install MRS              |Upstream   |
                        |IF(NSLPdata)             |MRS        |
                        |Tg_RecvMsg(NSLPdata)     |           |
                        |                 to Appl.|           |
                        |                         |           |
rx_Query(MAinfo)        |Tx_Response_?mode(Resp   |Wait       |*
&&(ConfirmRequired)     |          Cookie, MAinfo)|Confirm    |1)
                        |                         |           |
rx_Query(Mainfo)        |Tx_Response_?mode(Resp   |Established|*
&&(!ConfirmRequired)    |          Cookie, MAinfo)|Upstream   |2)
                        |Set WaitConfirm timer    |MRS        |
                        |Install MRS              |           |
                        |                         |           |
------------------------+-------------------------+-----------+---



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

Condition                Action                    State      Note
------------------------+-------------------------+-----------+---
rx_Msg_?mode            |Tx_Response(No_MRS_      |Wait       |3)
                        |               installed)|Confirm    |
                        |                         |           |
Rx_Confirm_?mode        |Install Upstream MRS     |Established|*



Tsenov, et al.                                                 [Page 20]

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                        |                         |Upstream   |6)
                        |                         |MRS        |
                        |                         |           |
Timeout_WaitConfirm     |                         |IDLE       |
                        |                         |           |
------------------------+-------------------------+-----------+---



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

Condition                Action                    State      Note
------------------------+-------------------------+-----------+---
Rx_Confirm_?mode        |Stop WaitConfirm timer   |Established|6)
                        |Install MRS              |Upstream   |
                        |Tx_queued_Msg_Cmode      |MRS        |
                        |                         |           |
(Timeout_WaitConfirm)&& |(Delete MRS)             |IDLE       |7)
(!UpstreamPeerInstalled)|IF (MA is used)          |           |**
                        |   ((Delete MA)||        |           |
                        |  (Stop using shared MA))|           |
                        |Tg_NetworkNotification   |           |
                        |                         |           |
rx_Msg_?mode            |IF(CheckPeerInfo)        |Established|8)
                        |      Tg_RecvMsg to Appl.|Upstream   |
                        |ELSE                     |MRS        |
                        |Tx_Response(No_MRS_      |           |
                        |               installed)|           |
                        |                         |           |
tg_SendMsg              |IF(WaitConfirm timer set)|Established|9)
                        |      Queue NSLP msg data|Upstream   |
                        |ELSE Tx_Msg_?mode        |MRS        |
                        |                         |           |
(Timeout_MRSlifetime)|| |(Delete MRS)&&           |IDLE       |
(tg_SetStateLifetime(0))|IF (MA is used)          |           |
                        |   ((Delete MA)||        |           |
                        |  (Stop using shared MA))|           |
                        |Tg_NetworkNotification   |           |
                        |                         |           |
rx_Query(Refresh)       |Refresh MRS              |Established|
                        |Tx_Response(Refresh)     |Upstream   |
                        |                         |MRS        |
                        |                         |           |
(rx_Query(MAinfo))||    |Tx_Response_?mode(Resp   |Established|*
((rx_Query)&&(!MAinfo)&&|          Cookie, MAinfo)|Upstream   |5)
      (ConfirmRequired))|Set WaitConfirm timer    |MRS        |



Tsenov, et al.                                                 [Page 21]

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                        |                         |           |
(rx_Query)&&(!MAinfo)&& |Install MRS              |Established|4)
(!ConfirmRequired)      |tx_Response              |Upstream   |
                        |IF (MA is used)          |MRS        |
                        |   ((Delete MA)||        |           |
                        |  (Stop using shared MA))|           |
                        |IF(NSLPdata)             |           |
                        |Tg_RecvMsg(NSLPdata)     |           |
                        |                 to Appl.|           |
                        |                         |           |
Tg_ERROR                |(Delete MRS)             |IDLE       |
                        |IF (MA is used)          |           |
                        |  ((Delete MA)||         |           |
                        |  (Stop using shared MA))|           |
                        |Tg_NetworkNotification   |           |
                        |                         |           |
------------------------+-------------------------+-----------+---

                                Figure 5
































Tsenov, et al.                                                 [Page 22]

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Authors' Addresses

   Tseno Tsenov
   Siemens
   Otto-Hahn-Ring 6
   Munich, Bayern  81739
   Germany

   Email: tseno.tsenov@mytum.de


   Hannes Tschofenig
   Siemens
   Otto-Hahn-Ring 6
   Munich, Bayern  81739
   Germany

   Email: Hannes.Tschofenig@siemens.com


   Xiaoming Fu
   University of Goettingen
   Telematics Group
   Lotzestr. 16-18
   Goettingen  37083
   Germany

   Email: fu@cs.uni-goettingen.de


   Cedric Aoun
   Nortel
   France

   Email: cedric.aoun@nortel.com


   Elwyn B. Davies
   Folly Consulting
   Soham, Cambs
   UK

   Phone: +44 7889 488 335
   Email: elwynd@dial.pipex.com







Tsenov, et al.                                                 [Page 23]

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Tsenov, et al.                                                 [Page 24]


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