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IEEE 802.21 MEDIA INDEPENDENT HANDOVER DCN: 21-07-0302-00-0000Title: MIH State Machines RepresentationDate Submitted: October 2007Presented at IEEE 802.21 ad-hoc meeting, Murray Hill, NJ

Authors or Source(s):  Yoshihiro Ohba, Miriam Tauil

Abstract: This document propose resolution to SB comments related to the MIH state Machines.

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IEEE 802.21 presentation release statementsThis document has been prepared to assist the IEEE 802.21 Working Group. It is

offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

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The contributor is familiar with IEEE patent policy, as outlined in Section 6.3 of the IEEE-SA Standards Board Operations Manual <http://standards.ieee.org/guides/opman/sect6.html#6.3> and in Understanding Patent Issues During IEEE Standards Development http://standards.ieee.org/board/pat/guide.html> 

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State Machine SB Comments This contribution is mainly driven by SB comment 11 and its

suggested remedy.Comment 11: The MIH protocol is inadequately specified. In particular, the state

machine is overly simplified, and none of the state variables are rigorously or formally defined.

Comment 11 Suggested Remedy:Include a formal specification of the MIH protocol, either as a

completely defined state machine (in the manner of IEEE 802.3), a reference code specification (in the manner of IEEE 802.1), or a formalized language (in the manner of IEEE 802.11).

Also addresses the following comments ..

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Additional SB Comments:Retransmission in the state machines diagrams

Comments 568, 569 Figure 22/24: The state diagram in Figure does not match the

description in the text. More specifically, the state diagram does not show that retransmission shall happen only twice. Note that the IEEE SA has ruled that state diagrams are normative, which means that the state diagram must be correct.

Comments 56, 57, 58- p. 145, l. 34 , 8.2.2.1/2/3The text states a transition from SENDING to INIT after two

(unsuccessful) retransmission but the state machine does not reflect this.

Text states that max. 2 retransmissions are allowed but the state machine does reflect this

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Additional SB Comments:Retransmission – why 2 times?

Comment 231: There seems to be arbitrary decisions made regarding the MIH Protocol Acknowledgement operation. For example, why re-transmit only 2 times? Such variables are usually expressed in a MIB. What about the possibility of aggregated Ack messages?

Suggested Remedy: Restrict description of MIH Acknowledgement operation to the messages exchange. Implementation details should be left out or else in the Annex

Comment 2 : "The source MIH node may at most make two retransmission attempts in addition to the first attempt for an MIH protocol message with the same Message-ID and the same Transaction-ID.“ What's special about "two"? Why this embedded magic number?

This depends on the properties of the link, and couples the protocol to assumptions about the medium.

Suggested Remedy: Make this number a property of the link type.

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Additional SB comments

Error condition transitions in the state machines- Comment 336- p145 What if a source node can not receive any answer even it sent a REQ? and also what if

a destination node can not give any response even if it receives a REQ? Therefore, I suggest all states except INIT should have transition to INIT when the transaction time expires.

Make transition to INIT in all states when the transaction time expires, page 145-146.Capability DiscoverComment 193: page 154 line 5The broadcasting of this message cannot be consumed by any of the state diagrams in

8.2. New state machines need to be added to permit transmission and reception of this very special case. None of the current state diagrams can be used because they all include the ack/rep bit behavior, which cannot be used in these cases.

Add new state diagrams, or remove this capability and any associated material from the entire draft.

Comment 338:There is no transaction state diagram for broadcast MIH_Capability_Discover

message.Refer to contribution, 21-07-0316-00-0000-MIH_Capability_Discovery

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State Machines

Transaction Source State Machine

Transaction DestinationState Machine

ACK-requestorState Machine

ACK-responderState Machine

ACK-requestorState Machine

ACK-responderState Machine

ACK/Retransmission Handling

OpCode specific Handling

Remote Interaction via MIH protocolLocal Interaction via global variables

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Variable Types

Name AttributesMessage Attributes Type Range Description

ACK-Req Integer:1 [0,1] ACK request bit. Initialized to 0.ACK-Rsp Integer:1 [0,1] ACK response bit. Initialized to 0MID Message-

IDN/A Message Identifier

TID Integer:16 [0,2^16-1] Transaction IdentifierVariable-Part

String N/A Variable Part (optional)

Name AttributesMessage-ID

Name Type Range DescriptionSID Integer:4 [1,4] Service IdentifierOpcode Integer:2 [1,3] Operation AID Integer:10 [1,1023] Action Identifier

Name Type Range DescriptionBoolean Enumerate {TRUE,FALSE} Logical 1 (TRUE) or 0 (FALSE)

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Global Variables Name Type Read/

Write/Export

Description

MsgIn Message R/E Incoming MessageMsgInAvail Boolean R/W/E Indicates if there is an incoming message for

the transaction. Initialized to FALSE.MsgOut Message R/E Outgoing MessageMsgOutAvail Boolean R/E Indicates if there is an outgoing message for

the transaction. Initialized to FALSE.Opcode Integer R/W An OpcodeTID Integer R/W A transaction identifierMID Integer R/W A message identifierStartACKRequestor Boolean R/W Indicates if ACK requester state machine is

started.StartACKResponder Boolean R/W Indicates if ACK responder state machine is

started.AckFailure Boolean R/W Indicates if ACK operation failedTransactionTimeout Boolean R/W A timer to cancel transaction

Exported variables are writable from entities that use the state machines defined in this document.

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Local Variables Name Type Within DescriptionBroadcast Boolean Tr. Src/Dst Indicates whether a message has a

broadcast destination address.DUP Message ACK

ResponderA message which has already been sent

ACK Message A message with a null variable load and ACK-Rsp bit set

DelayedAckTimeout Boolean A timer to delay ACKRetransmissionTimeout Boolean ACK

RequestorA timer to retransmit a message

RetransmissionInterval Integer The delay value for delayed ACKRtxCtr Integer Retransmission CounterRtxCtrMax Integer Maximum number of retransmission

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Functions

Name Input Output DescriptionNewTID() Void Integer Output a new Transaction IdentifierStartTimer() Boolean Void Start a timer associated with the boolean input

variable. The boolean input variable is initialized to false. After a time period specified in the integer input variable, the boolean input variable is set to True.

Integer

StopTimer() Boolean Void Stop a timer corresponding to the input variable.

Process() Message Void Process an incoming messageTransmit() Message Void Transmit a message.BroadcastMsg() Message Boolean Output TRUE if the input message has a

broadcast destination MIHF ID. Otherwise output FALSE.

GetAckDelay() Integer Integer Compute the time duration for delaying an ACK using MID of a message. Especially the output value is always zero (0) if MID.Opcode==indication or MID.Opcode==response. If MID.opcode==request, the time duration for delaying the ACK may depend on MID.SID and MID.AID.

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Conventions

• State machine conventions defined in IEEE 802.1X are used in this document

• State transitions occur upon a change in values of variables

• UCT (Unconditional Transition) is a special boolean variable which always has a TRUE value

• The action specified inside each state box is executed when entering the box (not when exiting the box)

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Transaction Source State Machine

INIT

MsgOutAvail=MsgInAvail=FALSE;StartAckRequestor=StartAckResponder=FALSE;AckFailure=FALSE;StartTimer(TransactionTimeout, TransactionLifetime);Opcode=MsgOut.MID.Opcode;MsgOut.TID=NewTID();Transmit(MsgOut);StartAckRequestor=(MsgOut.ACK-Req==1?TRUE:FALSE);Broadcast=BroadcastMsg(MsgOut);MsgOutAvail=FALSE;

WAIT_RESPONSE_MSG

SUCCESSFAILURE

TransactionTimeout || AckFailure

MsgOutAvail

MsgInAvail&&MsgIn.TID==MsgOut.TID

PROCESS_MSG

StartAckResponder= (MsgIn.ACK-Req == 1 ? TRUE : FALSE);Process(MsgIn);MsgInAvail=FALSE;

! Broadcast || TransactionTimeout

Opcode==RequestOpcode==Indication ||( Opcode==Response && Broadcast )

MsgInAvail&& MsgIn.TID==MsgOut.TID&&Broadcast

Send unsolicited

broadcasted responses

Receive responses to broadcasted

request

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Receive unsolicited

broadcasted responses

Transaction Destination State Machine

INIT

StartAckResponder=StartACKRequestor=FALSE;(Opcode,MID,TID)=MsgIn.(Opcode,MID,TID);StartTimer(TransactionTimeout, TransactionLifetime);Process(MsgIn);StartAckResponder=(Msg.ACK-Req==1 ? TRUE : FALSE);Broadcast=BroadcastMsg(MsgIn);MsgInAvail=FALSE;

SUCCESS

MsgInAvail

FAILURETransactionTimeout

SEND_RESPONSE

StartAckRequestor=(MsgOut.ACK-Req==1 ? TRUE : FALSE);MsgOut.TID=MsgIn.TID;Transmit(MsgOut);

WAIT_RESPONSE_PRM

MsgOutAvail&&(!StartAckResponder ||MsgOut.ACK-Rsp==1)

Opcode==Indication ||(Broadcast &&Opcode ==Response)

Opcode==Request

UCT

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ACK Requestor State Machine

INIT

RtxCtr=0;

WAIT_ACK

StartTimer(RetransactionTimeout, RetransmissionInterval);

SUCCESS FAILURE

AckFailure=TRUE;

MsgInAvail&&MsgIn.ACK-Rsp==1&&MsgIn.TID==MsgOut.TID

RetransmissionTimeout&&RtxCtr==RtxCtrMax

StartAckRequestor

RETRANSMIT

Transmit(MsgOut);RtxCtr++

RetransmissionTimeout&&RtxCtr<RtxCtrMax

UCT

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ACK Responder State Machine

RETURN_ACK

Transmit(ACK);MsgInAvail=FALSE;

DELAYING_ACK

StartTimer(DelayedAckTimeout, AckDelayTime);

AckDelayTime>0

MsgOutAvailDelayedAckTimeout

PIGGYBACKING

DUP=MsgOut;MsgOut.ACK-Rsp=1;

AckDelayTime==0

INIT

ACK.ACK-Req=0; ACK.ACK-Rsp=1;ACK.(Opcode, MID, TID)=(Opcode,MID,TID);AckDelayTime=GetAckDelay(MID);

StartAckResponder

MsgInAvail

MsgOutAvail

MsgInAvailRETURN_DUPLICATE

Transmit(DUP);MsgInAvail=FALSE;

MsgInAvail

SUCCESS TransactionTimeout

TransactionTimeout

TransactionTimeout

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References

1. IEEE Std 802.1X™-2004 – Port-Based Network Access Control