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Copyright Notice

Copyright (C) The Internet Society (2004).

Abstract

This document describes the state machines for the NSIS Signaling Layer Protocol for Quality-of-Service signaling (QoS NSLP). A set of state machines for QoS NSLP entities at different locations of a flow path are presented in order to illustrate how QoS NSLP may be implemented.

Table of Contents

1.  Introduction
2.  Terminology
3.  Notational conventions used in state diagrams
4.  State Machine Symbols
5.  Common Rules
    5.1  Common Procedures
    5.2  Common Variables
    5.3  Constants
6.  State machine for first QoS NSLP node in the flow path
7.  State machine for intermediate QoS NSLP nodes
8.  State machine for last QoS NSLP node in the flow path
9.  Security Considerations
10.  Open Issues
11.  Acknowledgments
12.  References
12.1  Normative References
12.2  Informative References
§  Authors' Addresses
§  Intellectual Property and Copyright Statements

1. Introduction

This document describes the state machines for QoS NSLP [1]Bosch, S., Karagiannis, G. and A. McDonald, NSLP for Quality-of-Service signaling, October 2004., trying to show how QoS NSLP can be implemented to support its deployment. The state machines described in this document are illustrative of how the QoS NSLP protocol defined in [1]Bosch, S., Karagiannis, G. and A. McDonald, NSLP for Quality-of-Service signaling, July 2004. may be implemented for the first QoS NSLP node in the flow path, intermediate QoS NSLP nodes, and the last QoS NSLP node in the flow path. Where there are differences [1]Bosch, S., Karagiannis, G. and A. McDonald, NSLP for Quality-of-Service signaling, July 2004. are authoritative. The state machines are informative only. Implementations may achieve the same results using different methods.

According to [1]Bosch, S., Karagiannis, G. and A. McDonald, NSLP for Quality-of-Service signaling, July 2004., there are several possibilities for QoS NSLP signaling, at least including the following:

end-to-end signaling vs. scoped signaling

sender-initiated signaling vs. receiver-initiated signaling

(which need to be incorporated into use scenarios when describing state machine. Note they are represented by way of certain objects/flags in Reserve and Query messages.)

The messages used in the QoS NSLP protocol can be summarized as follows:

               
   Requesting message       Responding message
   ------------------------+---------------------------
   RESERVE                 |None or RESERVE or RESPONSE
   QUERY                   |RESERVE or RESPONSE
   RESPONSE                |NONE
   NOTIFY                  |NONE
   ------------------------+---------------------------
                   

We describe a set of state machines for different roles of entities running QoS NSLP to illustrate how QoS NSLP 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]Bradner, S., Key words for use in RFCs to Indicate Requirement Levels, March 1997..

3. Notational conventions used in state diagrams

The following text is reused from [3]Vollbrecht, J., Eronen, P., Petroni, N. and Y. Ohba, State Machines for Extensible Authentication Protocol (EAP) Peer and Authenticator, September 2004. and the state diagrams are based on the conventions specified in [4]Institute of Electrical and Electronics Engineers, DRAFT Standard for Local and Metropolitan Area Networks: Port-Based Network Access Control (Revision), January 2004., Section 8.2.1. Additional state machine details are taken from [5]Ohba, Y., State Machines for Protocol for Carrying Authentication for Network Access (PANA), July 2004..

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 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> having a value of exactly one of the expressions. The logic for which of those expressions gets executed is outside of the state machine and could be environmental, configurable, or based on another state machine such as that of the method.

4. State Machine Symbols

( )

Used to force the precedence of operators in Boolean expressions and to delimit the argument(s) of actions within state boxes.

;

Used as a terminating delimiter for actions within state boxes. Where a state box contains multiple actions, the order of execution follows the normal 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.

!=

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.

5. Common Rules

Throughout the document we use terms defined in the [1]Bosch, S., Karagiannis, G. and A. McDonald, NSLP for Quality-of-Service signaling, July 2004., such as flow sender, flow receiver, QUERY, RESERVE or RESPONSE.

5.1 Common Procedures

tx_RESERVE(Toff):

Transmit RESERVE message with 'Teardown' bit off

tx_RESERVE(Ton):

Transmit RESERVE message with 'Teardown' bit on

tx_RESPONSE():

Transmit RESPONSE message

tx_QUERY(w/RII):

Transmit QUERY message with Request Identification Information (RII) object

tx_QUERY(w/oRII):

Transmit QUERY message without RII object

rx_RESPONSE():

Receive RESPONSE message

rx_QUERY():

Receive QUERY message

rx_RESERVE():

Receive RESERVE message

TIMEOUT_State:

State lifetime timer expiration

TIMEOUT_Refresh:

Refresh interval timer expiration

tg_QUERY:

External trigger to send a QUERY message (typically triggered by the application).

tg_RESERVE:

External trigger to send a RESERVE message.

tg_TEARDOWN:

External trigger to clear previously established QoS state (typically triggered by the application). It is translated to a tx_RESERVE(Ton) message.

Set QoS state:

establish the local QoS state.

Refresh QoS state:

refresh the local QoS state.

Clear QoS state:

delete the local QoS state.

Send info to Application:

report information to the application.

RMF:

Performs Resource Management Function and returns the following values{AVAIL, NO_AVAIL}.

SetRII:

Sets the RII object of the messages e.g. the node requests explicit response to the message being sent. Returns values {0,1}.

CheckRII:

Checks the RII object of received RESPONSE message if it is requested by current node or other upstream node. Returns values {LOCAL, NO_LOCAL}.

Result:

Processes the information of the RESPONSE messages and provides information. It tells whether the reservation is successful or not (if it is a response to a reserve message), or the information carried in the response message (if it is a response to a query message), or an error has occurred. Returns values {INFO, SUCCESSFUL, ERROR}.

5.2 Common Variables

RII:

Request Identification Information (RII) object. Logical variable representing if the RII is set or not. Takes values {0,1}.

SCOPING:

Scoping flag of common message header. Takes values {"Next_hop","Whole_path"}.

5.3 Constants

6. State machine for first QoS NSLP node in the flow path

   -----------
   State: INIT
   -----------

   Condition                Action                    State
   ------------------------+-------------------------+------------
   UCT                     | initialize variables    |IDLE
   ------------------------+-------------------------+------------
                

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

   Condition                Action                    State      Note
   ------------------------+-------------------------+-----------+---
   (rx_QUERY) && (!RII) && |tx_NOTIFY(ERROR)         |IDLE       |1)
      (RMF="NO_AVAIL")     |                         |           |2)
                           |                         |           |
   (rx_QUERY) && (RII)     |tx_RESPONSE(w/RII)       |IDLE       | 
                           |                         |           |
   (tg_RESERVE) &&         |Send info to Application |IDLE       | 
      (RMF="NO_AVAIL")     |                         |           |
                           |                         |           |
   (tg_QUERY) && (setRII)  |tx_QUERY(w/RII)          |WAITRESP1  | 
                           |                         |           |
   (tg_RESERVE) && (RII) &&|tx_RESERVE(w/RII)        |WAITRESP2  | 
      (RMF="AVAIL")        |                         |           |
                           |                         |           |
   (rx_QUERY) && (!RII) && |tx_RESERVE(w/RII)        |WAITRESP2  |2) 
      (setRII) &&          |                         |           |
      (RMF="AVAIL")        |                         |           |
                           |                         |           |
   (rx_QUERY) && (!RII) && |tx_RESERVE(w/oRII),      |ESTABLISHED|2) 
      (!setRII) &&         | Set QoS state,          |           |
      (RMF="AVAIL")        | Send info to Application|           |
                           |                         |           |
   (tg_RESERVE) &&         |tx_RESERVE(w/oRII),      |ESTABLISHED| 
      (!setRII) &&         | Set QoS state,          |           |
      (RMF="AVAIL")        | Send info to Application|           |
   ------------------------+-------------------------+-----------+---

   Note: 1) tx_NOTIFY(ERROR) is transmitted when an ERROR event must 
      be announced to other downstream nodes which do not expect 
      a RESPONSE message for this action. E.g., there is no provided 
      RII which will be included in a RESPONSE message;
         2) Relevant for Receiver-initiated reservation.
               

   ----------------
   State: WAITRESP1
   ----------------

   Condition                Action                    State
   ------------------------+-------------------------+------------
   (TIMEOUT_Refresh) &&    |tx_RESERVE(w/RII)        |WAITRESP1
      (!MaxRetry)          |                         |           
                           |                         |           
   (TIMEOUT_Refresh) &&    |Send info to Application |IDLE
      (MaxRetry)           |                         |           
                           |                         |           
   rx_RESPONSE             |Send info to Application |IDLE        
   ------------------------+-------------------------+------------
                

   ------------------
   State: ESTABLISHED
   ------------------

   Condition                Action                    State
   ------------------------+-------------------------+------------
   TIMEOUT_Refresh         |tx_RESERVE               |ESTABLISHED
                           |                         |
   tg_TEARDOWN             |tx_RESERVE(Ton),         |IDLE
                           | Clear QoS state         |
   ------------------------+-------------------------+------------
                

   ----------------
   State: WAITRESP2
   ----------------

   Condition                Action                    State
   ------------------------+-------------------------+------------
   (TIMEOUT_Refresh) &&    |tx_RESERVE(w/RII)        |WAITRESP2
      (!MaxRetry)          |                         |           
                           |                         |
   (TIMEOUT_Refresh) &&    |Send info to Application |IDLE 
      (MaxRetry)           |                         |        
                           |                         |
   (rx_RESPONSE) &&        |Send info to Application |IDLE 
      (Result="ERROR")     |                         |   
                           |                         |   
   (rx_RESPONSE) &&        |Set QoS state,           |ESTABLISHED 
      (Result="SUCCESS")&& | Send info to Application|  
      (RMF="AVAIL")        |                         |   
   ------------------------+-------------------------+------------
              

7. State machine for intermediate QoS NSLP nodes

   -----------
   State: INIT
   -----------

   Condition                Action                    State
   ------------------------+-------------------------+------------
   UCT                     | initialize variables    |IDLE
   ------------------------+-------------------------+------------
                

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

   Condition                Action                    State      Note
   ------------------------+-------------------------+-----------+---
   (rx_RESERVE)&& !((RII)&&|Set QoS state,           |ESTABLISHED|1a)
      (setRII)) &&         | tx_RESERVE(w/oRII)      |           |
      (RMF="AVAIL")        |                         |           |
                           |                         |           |
   (rx_RESERVE) && (RII) &&|Set QoS state,           |ESTABLISHED|1b)
      (RMF="AVAIL") &&     | tx_RESPONSE(w/RII)      |           |
      (SCOPING="Next_hop") |                         |           |
                           |                         |           |
   (rx_RESERVE) && (!RII)&&|Set QoS state            |ESTABLISHED|1b)
      (RMF="AVAIL") &&     |                         |           |
      (SCOPING="Next_hop") |                         |           |
                           |                         |           |
   (rx_QUERY) && (!RII)    |tx_QUERY(w/oRII)         |IDLE       |2)
                           |                         |           |
   (rx_QUERY) &&           |tx_QUERY(w/RII)          |IDLE       | 
      (SCOPING="Next_hop") |                         |           |
                           |                         |           |
   (rx_RESERVE) && (RII)&& |tx_RESPONSE(RII, ERROR)  |IDLE       |3)
      (RMF="NO_AVAIL")     |                         |           |
                           |                         |           |
   (rx_RESERVE) && (!RII)&&|tx_NOTIFY(ERROR)         |IDLE       |3)
      (RMF="NO_AVAIL")     |                         |           |
                           |                         |           |
   (rx_RESERVE) && ((RII)|||tx_RESERVE(w/RII)        |WAITRESP1  |4)
      (setRII)) &&         |                         |           |
      (RMF="AVAIL")        |                         |           |
                           |                         |           |
   (rx_QUERY) && (RII)     |tx_QUERY(w/RII)          |WAITRESP2  |5)
                           |                         |           |
   (tg_QUERY) && (setRII)  |tx_QUERY(w/RII)          |WAITRESP2  |5)
   ------------------------+-------------------------+-----------+---
               

   ------------------
   State: ESTABLISHED
   ------------------

   Condition                Action                    State
   ------------------------+-------------------------+------------
   rx_RESERVE(Ton)         |tx_RESERVE(Ton),         |IDLE
                           |  clear QoS state        |    
                           |                         |    
   TIMEOUT_Refresh         |Refresh QoS state;       |ESTABLISHED
                           |  if state changes,      |    
                           |  tx_RESERVE(w/RII)      |    
                           |                         |    
   TIMEOUT_State           |Clear QoS state          |IDLE
   ------------------------+-------------------------+------------
                

   ----------------
   State: WAITRESP1
   ----------------

   Condition                Action                    State      
   ------------------------+-------------------------+------------
   (TIMEOUT_Refresh) &&    |tx_RESERVE(w/RII)        |WAITRESP1  
      (!MaxRetry)          | Send info to Application|           
                           |                         |           
   (TIMEOUT_Refresh) &&    |tx_NOTIFY(ERROR),        |           
      (MaxRetry) &&        | Send info to Application|IDLE       
      (CheckRII="LOCAL")   |                         |           
                           |                         |           
   (TIMEOUT_Refresh) &&    |tx_RESPONSE(w/RII,Result=|           
      (MaxRetry) &&        |  "ERROR")               |IDLE       
      (CheckRII="NO_LOCAL")|                         |           
                           |                         |           
   (rx_RESPONSE) &&        |Set QoS state            |ESTABLISHED 
      (CheckRII="LOCAL")&& |                         |           
      (Result="SUCCESS")   |                         |           
                           |                         |           
   (rx_RESPONSE) &&        |Set QoS state,           |ESTABLISHED 
      (CheckRII="NO_LOCAL")|  tx_RESPONSE(RII)       |           
      &&(Result="SUCCESS") |                         |           
                           |                         |           
   (rx_RESPONSE) &&        |tx_NOTIFY(ERROR),        |IDLE       
      (CheckRII="LOCAL")&& | send info to Application|           
      (Result="ERROR")     |                         |           
                           |                         |           
   (rx_RESPONSE) &&        |tx_RESPONSE(w/RII)       |IDLE        
      (CheckRII="NO_LOCAL")|                         |           
      &&(Result="ERROR")   |                         |           
   ------------------------+-------------------------+-------------
               

   ----------------
   State: WAITRESP2
   ----------------

   Condition                Action                    State       
   ------------------------+-------------------------+------------
   (TIMEOUT_Refresh) &&    |tx_QUERY(w/RII)          |WAITRESP2  
      (!MaxRetry)          |                         |           
                           |                         |           
   (TIMEOUT_Refresh) &&    |Send info to Application |IDLE       
      (MaxRetry) &&        |                         |  
      (CheckRII="LOCAL")   |                         |           
                           |                         |           
   (TIMEOUT_Refresh) &&    |tx_RESPONSE(Result=      |IDLE       
      (MaxRetry) &&        |  "ERROR")               |  
      (CheckRII="NO_LOCAL")|                         |           
                           |                         |           
   (rx_RESPONSE) &&        |Send info to Application |IDLE 
      (CheckRII="LOCAL")   |                         |           
                           |                         |           
   (rx_RESPONSE) &&        |tx_RESPONSE(w/RII)       |IDLE  
      (CheckRII="NO_LOCAL")|                         |           
   ------------------------+-------------------------+-------------

   Note: 1) Successful reservation with response request (1a) and 
     with Scoping (1b);
         2) Processing of Query msg for Receiver initiated 
     reservation;
         3) Unsuccessful reservation for Receiver initiated 
     reservation, with/without request for response from the flow
     sender side.  Tx_NOTIFY(ERROR) is sent to the upstream nodes to
     indicate failure of the reservation in the case when no RESPONSE
     is required by them;
         4) Reservation requests with RII set in the upstream nodes 
     or in this node;
         5) Processing of Query message received from a neighboring 
     node or triggered by the application layer.
               

8. State machine for last QoS NSLP node in the flow path

   -----------
   State: INIT
   -----------

   Condition                Action                    State
   ------------------------+-------------------------+------------
   UCT                     | initialize variables    |IDLE
   ------------------------+-------------------------+------------
                

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

   Condition                Action                    State      Note
   ------------------------+-------------------------+-----------+---
   (tg_QUERY) &&           |tx_QUERY(w/RII)          |WAITRESV   |1)
      (!setRII)            |                         |           |
                           |                         |           |
   (rx_RESERVE) && (RII) &&|Set QoS state,           |ESTABLISHED|2a)
      (RMF="AVAIL")        |  tx_RESPONSE(w/RII)     |           |
                           |                         |           |
   (rx_RESERVE) && (!RII)&&|Set QoS state            |ESTABLISHED|2b)
      (RMF="AVAIL")        |                         |           |
                           |                         |           |
   (tg_RESERVE) &&         |Send info to Application |IDLE       |3)
      (RMF="NO_AVAIL")     |                         |           |
                           |                         |           |
   (rx_RESPONSE) && (RII)&&|tx_RESPONSE(RII, ERROR)  |IDLE       | 
      (RMF="NO_AVAIL")     |                         |           |
                           |                         |           |
   (rx_QUERY) && (RII) &&  |tx_QUERY(w/RII)          |IDLE       | 
   ------------------------+-------------------------+-----------+---
               

   ------------------
   State: ESTABLISHED
   ------------------

   Condition                Action                    State
   ------------------------+-------------------------+------------
   rx_RESERVE              |Refresh QoS state        |ESTABLISHED
                           |                         |    
   TIMEOUT_State           |Clear QoS state          |IDLE
   ------------------------+-------------------------+------------
                

   ---------------
   State: WAITRESV
   ---------------

   Condition                Action                    State      Note
   ------------------------+-------------------------+-----------+---
   (rx_RESPONSE) &&        |Send info to Application |IDLE       | 
      (Result="ERROR")     |                         |           |
                           |                         |           |
   (rx_RESERVE) && (!RII)&&|Set QoS state            |ESTABLISHED|2) 
      (RMF="AVAIL")        |                         |           |
                           |                         |           |
   (rx_RESERVE) && (RII)&& |Set QoS state,           |ESTABLISHED|2) 
      (RMF="AVAIL")        | tx_RESPONSE(w/RII)      |           |
   (rx_RESERVE) && (RII) &&|tx_NOTIFY(ERROR),        |IDLE       |4)
      (RMF="NO_AVAIL")     | Send info to Application|           |
                           |                         |           |
   (rx_RESERVE) && (!RII)&&|tx_RESPONSE(RII,ERROR),  |IDLE       |4)
      (RMF="NO_AVAIL")     | Send info to Application|           |
   ------------------------+-------------------------+-----------+---

   Note: 1) Initiation of receiver-side reservation;
         2) Successful reservation with&without response request from 
     sender side;
         3) In case of no response requested (RII not present in 
     RESERVE message), NOTIFY(ERROR) message is sent back to the 
     upstream nodes in order to clear already established QoS state;
         4) Unsuccessful reservation with&without response request 
     from sender side;
               

9. Security Considerations

This document does not raise new security considerations. Any security concerns with the QoS NSLP are likely reflected in security related NSIS work already (such as [1]Bosch, S., Karagiannis, G. and A. McDonald, NSLP for Quality-of-Service signaling, July 2004. or [6]Tschofenig, H. and D. Kroeselberg, Security Threats for NSIS, October 2004.).

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

10. Open Issues

This document tries to describe possible states and transitions for QoS NSLP according to its current specification [1]Bosch, S., Karagiannis, G. and A. McDonald, NSLP for Quality-of-Service signaling, July 2004., Section 5. We found some issues during the development of the state machines. For example, for receiver-initiated reservation, it is unclear who triggers a teardown; bi-directional reservation is difficult to support as the state machine becomes quite complex (note at one particular point in time the protocol state engine can be only in one state). Another example is, it is often ignored for the functionality of abort operation after a defined MaxRetry number of retries. Results of this type of transitions are dependent on the parameter RII (e.g., if it is locally set or not).

There are further unclear issues with processing rules and message definition, e.g., soft state handling and how to process notification messages, which will be described in more detail in a future version of this document.

To avoid confusions in state machines, instead of QNI, QNE and QNR, in this document we use the notations of "first QoS NSLP node in the flow path" (the closest one to the flow sender or the flow sender itself), "intermediate QoS NSLP nodes" and "last QoS NSLP node in the flow path" (the closest one to the flow receiver or the flow receiver itself).

Default rules and common state transitions in case of reception of certain messages as Notify, and Query(w/RII), will be described in a future version of this document.

11. Acknowledgments

The authors would like to thank Sven Van den Bosch for his feedback.

12. References

12.1 Normative References

12.2 Informative References

Authors' Addresses

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