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Versions: (draft-wu-mpls-ldp-state) 00 01 02 03 RFC 3215

MPLS Working Group                                          Liwen Wu
Internet Draft                                       Pierrick Cheval
Expiration Date: August 1999                      Christophe Boscher
                                                         Alcatel USA

                                                           Eric Gray
                                                              Lucent

                                                       Februray 1999

                           LDP State Machine
                    draft-ietf-mpls-ldp-state-00.txt


0. Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet- Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   Distribution of this memo is unlimited.

 Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

1. Abstract

   In the current LDP draft [Ref5], there is no state machine specified
   for processing the LDP messages. We think that defining a common
   state machine is very important for interoperability between
   different ldp implementations.




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   This draft provides state machine tables for ATM switch LSRs. We
   begin in section 2 by defining a list of terminologies. Then in
   section 3, we propose two sets of state machine tables for ATM switch
   LSRs, one for non-vc merge ATM LSRs and one for the vc merge ATM
   LSRs. Finally, in section 4, we outline the possible future working
   items.

   Even though the state machines in this document are specific for
   ATM-LSR, they can be easily adapted for other types of LSRs.

2. Terminologies

   - LDP-REQUEST: LDP Label Request message

   - LDP-MAPPING: LDP Label Mapping message

   - LDP-WITHDRAW: LDP Label Withdraw message

   - LDP-RELEASE: LDP Label Release message

   - LDP-NAK: It is a LDP notifications which is used to abort a LSP
   setup or reject a LSP Label Request message.

3. State Machine

   This draft focuses on the LDP state machines and the associated
   control blocks.  It does not describe the "LDP controller" which is
   in charge of LDP session initialization, address mapping messages
   management, routing interface, etc.

   In this draft, we provide two sets of state machines: one for the ATM
   LSR which does not have VC-merge capability, and the other one for
   the ATM LSR which does have VC-merge capability.

   The state machines cover both independent LSP control and ordered LSP
   control.


   The loop detection and loop prevention message will be processed in
   the way as specified in [Ref5]. The impact of loop detection and loop
   prevention messages on a state transition is left for further study.

3.0 An LSR's Behavior in the Case of a Next Hop Change

   When there is a topology change and an LSR detects a new better next
   hop for an LSP, it may behave in 2 different ways:

   1) It tries to do a "local repair". This means that it extends the



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   LSP through the new next hop, releases the old path from this LSR
   forward and then splices into this newly extended LSP.

   2) If the LSP is created with the "pinned" option, the LSR ignores
   the new next hop change, and the LSP stays unchanged. The LSR may
   decide to send an LDP-MAPPING which contains the attribute about this
   New Next Hop (NH) change.

3.1. ATM Switch LSR with NO VC-merge

   In an MPLS domain where some ATM LSRs do not have VC-merge
   capability, downstream-on-demand mode is required for these ATM
   LSRs[Ref1]. Also, "conservative label retention mode" is required in
   this case[Ref1].

   For each LSP, there are 2 kinds of state machines involves:

   1) the LSP Control Block and its state machine which can be used to
   handle normal LSP setup. It is created when the LSR receives a new
   LDP Request and it is deleted when the LSP of this request is torn
   down.

   2) the Next Hop Trigger Control Block and its state machine which is
   used to handle switching over to a better LSP through a different
   next hop.  It is created when the LSR decides to switch over to a
   better next hop and it is deleted when the LSR finishes switching
   over to the better next hop.

3.1.1   LSP Control Block

   For each LSP, an LSP_Control_Block is defined which may contain the
   following information:

     - Upstream Label Request ID(assigned by the upstream LSR), which is
     the 'Return Message Id' in the Label Request Message received from
     the upstream LSR.

     - Downstream Label Request ID (assigned by this LSR itself), which
     is 'Return Message Id' in the Label Request Message sent to the
     downstrearm LSR.

     - Upstream LDP Session Identifier

     - Downstream LDP Session Identifier

     - State

     - FEC



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     - Upstream Label(assigned by this LSR)

     - Downstream Label(assigned by the downstream LSR)

     - Trigger Control Block Pointer, (Only used at the ingress LSR of a
     LSP)which points to the control block that triggers setting up this
     LSP or tearing down this LSP.

     - Next Hop Control Block Pointer, which points to the control block
     which is used for switching over to a better LSP.

   The following index combinations can be used to locate a unique
   LSP_Control_Block:


     - Downstream Label and Downstream LDP Session Identifier, or

     - Upstream Label and Upstream LDP Session Identifier, or

     - Upstream Label Request ID and Upstream LDP Session Identifier

   Here is the relationship between different control blocks, the detail
   definition of Next Hop Trigger Block is described in section 3.1.6.

   For example, an LSP which transit through (LSR-A, LSR-B, LSR-C,LSR-
   D):


      LSR-A ----> LSR-B ---> LSR-C ---> LSR-D

   The control blocks in LSR-A are:


      +-----------------------+
      | Trigger Control Block |
      |  (e.g, by config)     |
      +-----------------------+
                 ^
                 |(Trigger Control block pointer)
                 |
                 |
      +-----------------------+
      | LSP Control Block     |
      +-----------------------+







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   When LSR-B detects a better next hop to LSR-D through LSR-E, and it
   decides to switch over to it, so control blocks  in LSR-B are:


      +-----------------------+
      | LSP Control Block     |
      | (original LSP)        |
      +-----------------------+
   (LSP      ^  |
    Control  |  | (Next Hop Control Block Pointer)
    Block    |  |
    Pointer  |  v
      +--------------------------------+
      | Next Hop Trigger Control Block |
      +--------------------------------+
             ^  |
   (Trigger  |  | (New Next Hop LSP
     Control |  |  Control Block Pointer)
     Block   |  |
     Pointer)|  |
             |  v
      +------------------------+
      | LSP Control Block      |
      | (for LSP: LSR-B,LSR-E, |
      |   LSR-D)               |
      +------------------------+


3.1.2   States

   This section describes the various states that are used in the state
   machine for the ATM non VC-merge LSR.

   -- IDLE

   This is the initial LSP state, when the LSP_Control_Block is created.

   -- RESPONSE_AWAITED

   This state means that the LSR has received and processed an LDP-
   REQUEST from an upstream LSR, or it has received an internal set up
   request. It has sent a new LDP-REQUEST towards a downstream LSR. The
   LSR is waiting for the LDP-MAPPING message from the downstream LSR.


   -- ESTABLISHED

   This state means that the LSR has received the LDP-MAPPING message



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   from the downstream LSR and the LSP is up and operational.

   -- RELEASE_AWAITED

   This state means that the LSR has sent a LDP-WITHDRAW message
   upstream and is waiting for the LDP-RELEASE before freeing up the
   label resource.

3.1.3   Events

   -- LDP Request

   The LSR receives an LDP-REQUEST from an upstream LSR.

   -- LDP Mapping

   The LSR receives an LDP-MAPPING from a downstream LSR.

   -- LDP Release

   The LSR receives an LDP-RELEASE from an upstream LSR.

   -- LDP Withdraw

   The LSR receives an LDP-WITHDRAW from a downstream LSR.

   -- LDP Upstream Nak

   The LSR receives an LDP-NAK from an upstream LSR.

   -- LDP Downstream Nak

   The LSR receives an LDP-NAK from a downstream LSR.

   -- Upstream Lost

   The LSR loses its LDP session with an upstream LDP peer.

   -- Downstream Lost

   The LSR loses its LDP session with a downstream LDP peer.

   -- Internal SetUp

   For some reason, e.g. a configuration request of a traffic
   engineering tunnel, or recognizing a new FEC could trigger an
   Internal SetUp event to set up a new LSP from this node.




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   -- Internal Destroy

   The LSR send an Internal Destroy event to tear down an LSP.

   -- Internal Cross-Connect

   The LSR send an Internal Cross-Connect to splice two LSPs into one
   LSP.

   -- Internal New NH

   The LSR decides to switch over the better next hop.







































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3.1.4 State Transitions

   The following diagram describes briefly the state transitions.


               +-------------------+
               |                   |
     +-------->|  IDLE             |<--------------+
     |         |                   |               |
     |         +-------------------+               |(LDP Release)
     |(LDP Upstream Nak) |                         |
     |(LDP DownstreamNak)|(LDP Request)            |(LDP Upstream Nak)
     |(Downstream Lost)  |(Internal SetUp)         |
     |                   |                         |
     |(Upstream Lost)    v                         |(Upstream Lost)
     |         +-------------------+               |
     |         |                   |               |
     +---------|  RESPONSE_AWAITED |               |
               |                   |               |
               +-------------------+               |
                        |                          |
                        |(LDP Mapping)             |
                        |                          |
                        v                          |
               +-------------------+               |
               |                   |               |
               |  ESTABLISHED      |------------>--+
               |                   |               |
               +-------------------+               |
                        |                          |
                        |                          |
                        |(LDP Withdraw)            |
                        |(Downstream Lost)         |
                        |                          |
                        v                          |
               +-------------------+               |
               |                   |               |
               | RELEASE_AWAITED   |------------>--+
               |                   |
               +-------------------+



3.1.5   State Machine


3.1.5.1 State -- "IDLE"




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 State:          IDLE

 Event:          LDP Request

 New States:     Depends upon the action routine

 Actions:

   If this LSR is the LSP Egress or Proxy Egress [Ref2]

   Then:
     Choose an upstream label, connect this upstream label to the local
     IP forwarding module, allocate the resources, send the LDP-MAPPING
     message upstream with the upstream label, and go to the new state
     `ESTABLISHED'.

   else
     Obtain a next hop (or interface) with the FEC specified in the
     LDP-REQUEST message, propagate the LDP-REQUEST message towards the
     obtained next hop, and go to the new state `RESPONSE_AWAITED'.

     If the LSR uses the independent control mode[Ref2], choose an
     upstream label, connect this upstream label to the local IP
     forwarding module, and send an LDP-MAPPING message upstream with
     the upstream label.

   If unable to process the request for any reason, issue an LDP-NAK
   message to the sender with the appropriate error code and delete the
   control block.

 State:          IDLE

 Event:          LDP Mapping

 New State:      IDLE

 Actions:

   Ignore the event. It is an internal implementation error.


 State:          IDLE

 Event:          LDP Release

 New State:      IDLE

 Actions:



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   Ignore the event.  It is an internal implementation error.

 State:          IDLE

 Event:          LDP Withdraw

 New State:      IDLE

 Actions:

   Ignore the event.  It is an internal implementation error.

 State:          IDLE

 Event:          LDP Upstream Nak

 New State:      IDLE

 Actions:

   Ignore the event.  It is an internal implementation error.

 State:          IDLE

 Event:          LDP Downstream Nak

 New State:      IDLE

 Actions:

   Ignore the event.  It is an internal implementation error.

 State:         IDLE

 Event:         Upstream Lost

 New State:     IDLE

 Actions:

   Ignore the event.  It is an internal implementation error.

 State:         IDLE

 Event:         Downstream Lost

 New State:     IDLE




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 Actions:

   Ignore the event. It is an internal implementation error.

 State:         IDLE

 Event:         Internal SetUp

 New State:     RESPONSE_AWAITED

 Actions:


   Set up the Trigger Control Block pointer,

   Obtain a next hop (or interface) with the FEC specified in the
   Internal SetUp message, send a LDP-REQUEST towards the obtained next
   hop, and go to the new state 'RESPONSE_AWAITED'.

 State:         IDLE

 Event:         Internal Destroy

 New State:     IDLE

 Actions:

   Ignore. It is an internal implementation error.

 State:         IDLE

 Event:         Internal Cross-Connect

 New State:     IDLE

 Actions:

   Ignore. It is an internal implementation error.

 State:         IDLE

 Event:         Internal New NH

 New State:     IDLE

 Actions:

   Ignore. It is an internal implementaion error.



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3.1.5.2 State -- "RESPONSE_AWAITED"

 State:          RESPONSE_AWAITED

 Event:          LDP Request

 New State:            RESPONSE_AWAITED

 Actions:

   Ignore the event. It is an internal implementation error.  A non VC
   merge ATM LSR must create a new LSP control block for a new LDP
   request.

 State:          RESPONSE_AWAITED

 Event:          LDP Mapping

 New State:      ESTABLISHED

 Actions:


   1) If the LSP is triggered by the local router(Trigger Control Block
   Pointer is not zero), send event "Internal LSP UP" to the Trigger
   control block.

   2) Else If the LSR uses the ordered control mode, choose an upstream
   label.

   3) Connect the upstream label to the downstream label. Allocate the
   resources.  propagate the LDP-MAPPING message upstream with the
   upstream label.

   If unable to process the message, disconnect the upstream label from
   the downstream label, free the upstream label, release the resources,
   send an LDP-RELEASE message downstream and an LDP-Nak upstream, and
   delete the LSP_Control_Block.


 State:          RESPONSE_AWAITED

 Event:          LDP Release

 New State:      IDLE

 Actions:




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   If the LSR uses the independent control mode, free the upstream
   label.

   Send an LDP-NAK message downstream and delete the LSP_Control_Block.

 State:          RESPONSE_AWAITED

 Event:          LDP Withdraw

 New State:      RESPONSE_AWAITED

 Actions:

   Ignore the event. It's a protocol error from the downstream LSR.


 State:          RESPONSE_AWAITED

 Event:          LDP Upstream Nak

 New State:      IDLE

 Actions:

   If the LSR uses the independent control mode, free the upstream
   label.

   Send an LDP-NAK message downstream.

   Delete the LSP_Control_Block.

 State:          RESPONSE_AWAITED

 Event:          LDP Downstream Nak

 New State:      Depends on the action routine

 Actions:

   1. If the LSP is triggered by the local router(Trigger Control Block
   Pointer is not zero), send event "Internal LSP DOWN" to the Trigger
   control block.

   2. Else If the LSR uses the independent control mode, send an LDP-
   WITHDRAW message upstream and go to state 'RELEASE_AWAITED'.

   If the LSR uses the ordered control mode, send an LDP-NAK message
   upstream. Then delete the control block.



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 State:         RESPONSE_AWAITED

 Event:         Upstream Lost

 New State:     IDLE

 Actions:

   If the LSR uses the independent control mode, free the upstream
   label.

   Send an LDP-NAK downstream and delete the LSP_Control_Block.

 State:         RESPONSE_AWAITED

 Event:         Downstream Lost

 New State:     Depends on the action routine

 Actions:


   1. If the LSP is triggered by the local router(Trigger Control Block
   Pointer is not zero), send event "Internal LSP DOWN" to the trigger
   control block.

   2. Else, If the LSR uses the independent control mode, free the
   upstream label and send an LDP-WITHDRAW upstream and go to state
   'RELEASE_AWAITED'.

   If the LSR uses the ordered control mode, send an LDP-NAK upstream
   and then delete the control block.

 State:         RESPONSE_AWAITED

 Event:         Internal SetUp

 New State:     RESPONSE_AWAITED

 Actions:

   Ignore, it is an internal implementation error.

 State:         RESPONSE_AWAITED

 Event:         Internal Destroy

 New State:     IDLE



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 Actions:

   Send an LDP-NAK downstream and delete the LSP_Control_Block.

 State:         RESPONSE_AWAITED

 Event:         Internal Cross-Connect

 New State:     RESPONSE_AWAITED

 Actions:

   Ignore the event. It is an internal implementation error.

 State:         RESPONSE_AWAITED

 Event:         Internal New NH

 New State:     RESPONSE_AWAITED

 Actions:

   Send LDP-NAK to the old downstream, and send LDP-REQUEST to the new
   next hop.

3.1.5.3 State --"ESTABLISHED"

 State:          ESTABLISHED

 Event:          LDP Request

 New State:      ESTABLISHED

 Actions:

   Ignore the event. It's an internal implementation error. For non VC-
   merge ATM LSR, a new LSP control block is always created for each LDP
   request.

 State:          ESTABLISHED

 Event:          LDP Mapping

 New State:      ESTABLISHED

 Actions:

   Process the LDP-MAPPING message, which may contain the new attributes



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   of the label mapping and then propagate the LDP-MAPPING message
   upstream.

 State:          ESTABLISHED

 Event:          LDP Release

 New State:      IDLE

 Actions:

   Disconnect the upstream label from the downstream label.

   Free the upstream label.

   Free the resources.

   Send event "Internal Destroy" to the Next Hop Trigger Block if it was
   in the middle of switching over to the better next hop.

   Propagate the LDP-RELEASE message downstream if the LSR is not the
   end of LSP and delete the LSP_Control_Block.

 State:          ESTABLISHED

 Event:          LDP Withdraw

 New State:      Depends on the action routine.

 Actions:

   1) Free the resources and send LDP-RELEASE downstream.

   2) If it is independent control mode, set the state to 'IDLE', create
   a internal LDP Request with the information in the LSP_Control_Block,
   and pass event 'LDP Request' to its own state machine.

   3) Else for the ordered control mode

     3.1)If the LSP is triggerd to be setup by itself(e.g it is the
     ingress LSR of this LSP), send event "Internal LSP NAK" to the
     trigger control block and delete the control block

     3.2) else, if it is triggered by the incoming LDP Request,
     Disconnect the upstream label from the downstream label.  And
     Propagate the LDP-WITHDRAW  message upstream and go to state
     'RELEASE_AWAITED'.




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     3.3) If the LSP is in the middle of switching over to a better LSP,
     send event 'Internal Destroy' to the state machine of its New Next
     Hop LSP Control Block.

 State:          ESTABLISHED

 Event:          LDP Upstream Nak

 New State:      IDLE

 Actions:

   Disconnect the upstream label from the downstream label.

   Free the upstream label.

   Send event "Internal Destroy" if the LSR was in the middle of
   switching over to the better next hop.

   Propagate an LDP-RELEASE message downstream and delete the
   LSP_Control_Block.

 State:          ESTABLISHED

 Event:          LDP Downstream Nak

 New State:      ESTABLISHED

 Actions:

   Ignore the event. It is a protocol error from the downstream LSR.
   The downstream LSR should always LSP-WITHDRAW msg to tear down the
   LSP when the LSP is established.

 State:          ESTABLISHED

 Event:          Upstream Lost

 New State:      IDLE

 Actions:

   Disconnect the upstream label from the downstream label.

   Free the upstream label.

   Send event "Internal Destroy" to the Next Hop Trigger Control Block
   if it was in the middle of switching over to the better next hop.



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   Free the resources.

   Propagate an LDP-RELEASE message downstream and delete the
   LSP_Control_Block.

 State:          ESTABLISHED

 Event:          Downstream Lost

 New State:      Depends on the actions

 Actions:

   1) If the LSP is triggered by the local router(Trigger Control Block
   Pointer is not zero), send event "Internal LSP NAK" to the Trigger
   control block and delete the control block.

   2) Else, disconnect the upstream label from the downstream label.
   Propagate an LDP-WITHDRAW message upstream and go to state
   'RELEASE_AWAITED' state.

   3) Send event "Internal Destroy" to the Next Hop Trigger Control
   Block if it was in the middle of switching over to the better next
   hop.


 State:          ESTABLISHED

 Event:          Internal Setup

 New State:      ESTABLISHED

 Actions:

   Ignore, it is an internal implementation error.

 State:          ESTABLISHED

 Event:          Internal Destroy

 New State:      IDLE

 Actions:

   Disconnect the upstream label from the downstream label if it is not
   the ingress of the LSP.

   Free the resources.



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   Send an LDP-RELEASE message downstream and delete the
   LSP_Control_Block.

 State:          ESTABLISHED

 Event:          Internal Cross-Connect

 New State:      ESTABLISHED

 Actions:

   Connect the upstream label to the downstream label

   May need to send a new LDP-MAPPING upstream with the attributes from
   the new next hop.

   Reset Trigger Control Block Pointer to zero.

 State:          ESTABLISHED

 Event:          Internal New NH

 New State:      ESTABLISHED

 Actions:


   1) If the LSR was in the middle of switching over to a better next
   hop(Next Hop Trigger Control Block Pointer is not zero), it send
   "Internal New NH" to that control block.

   2) Else, create a new Next Hop Trigger Control Block, set Next Hop
   Trigger Control Block pointer which points this control block.  And
   then pass "Internal New NH" to this control block.

 State           RELEASE_AWAITED

 Event           LDP Request

 New State:      RELEASE_AWAITED

 Actions:

   Ignore the event. It is an internal implementation error.

 State           RELEASE_AWAITED

 Event           LDP Mapping



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 New State:      RELEASE_AWAITED

 Actions:

   Ignore the event. It is an protocol error from the downstream LDP
   peer.

 State           RELEASE_AWAITED

 Event           LDP Release

 New State:      IDLE

 Actions:


   1) Free the upstream label

   2) Delete the control block.

 State           RELEASE_AWAITED

 Event           LDP Withdraw

 New State:      IDLE

 Actions:

   Ignore the event. It is an protocol error from the downstream LDP
   peer.

 State           RELEASE_AWAITED

 Event           LDP Upstream Nak

 New State:      IDLE

 Actions:


   1) Free the upstream label

   2) Delete the control block.

 State           RELEASE_AWAITED

 Event           LDP Downstream Nak




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 New State:      RELEASE_AWAITED

 Actions:

   Ignore the event. Continue waiting for the LDP-RELEASE from upstream.

 State           RELEASE_AWAITED

 Event           Upstream Lost

 New State:      IDLE

 Actions:


   1) Free the upstream label

   2) Delete the control block.

 State           RELEASE_AWAITED

 Event           Downstream Lost

 New State:      RELEASE_AWAITED

 Actions:


   Ignore the event. Continue waiting for the LDP-RELEASE from upstream.

 State           RELEASE_AWAITED

 Event           Internal SetUp

 New State:      RELEASE_AWAITED

 Actions:

   Ignore the event. It is an internal implementation error.

 State           RELEASE_AWAITED

 Event           Internal Destroy

 New State:      RELEASE_AWAITED

 Actions:




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   Ignore the event. It is an internal implementation error.

 State           RELEASE_AWAITED

 Event           Internal Cross-Connect

 New State:      RELEASE_AWAITED

 Actions:

   Ignore the event. It is an internal implementation error.

3.1.6       Handling the Next Hop Change

   When an LSR detects a better next hop, it may decides to establish a
   new LSP through this next hop. For example, an LSR is configured as
   "local repair", or the LSR is configured as "global repair" and it is
   the ingress end of a LSP. It can then create a Next Hop Trigger
   Control Block and use the state machine of Next Hop Trigger Control
   Block to establish a new LSP through the better next hop.

3.1.6.1 Next Hop Trigger Control Block


   -- LSP Control Block Pointer, which points to the original LSP
   control block.

   -- New Next Hop LSP Control Block Pointer, which points to the LSP
   Control Block that is setting up an LSP through the new next hop.

3.1.6.2 States


   -- IDLE

   This is the initial LSP state, when the Trigger_Control_Block is
   created.

   -- NEW_NH_RETRY

   This is the state where an LSR waits for a retry timer to expire and
   then tries to establish an LSP through a new next hop.

   -- NEW_NH_RESPONSE_AWAITED

   This is the state where an LSR is in the middle of establishing a new
   LSP through a new next hop. It has triggered a LSP control block to
   send an LDP-REQUEST towards the new next hop and is waiting for the



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   LDP-MAPPING message.

3.1.6.3 Events

   -- Internal New NH

   The LSR detects there is a new next hop for a FEC.

   -- Internal Retry Timeout

   The LSP retry timer expires.

   -- Internal LSP UP

   The LSP to the new Next Hop is UP

   -- Internal LSP NAK

   The LSP through the new next hop could not get set up

   -- Internal Destroy

   This event is triggered when the LSR lost the LDP session with its
   upstream neighbor.



























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3.1.6.4 State Transition for next hop change

                   |
                   |
                   |
                   | Internal New NH
                   |
                   v
          +---------------------+
          |                     | Internal destroy
          | NEW_NH_RETRY        |--------------
          |                     |             |
          +---------------------+             |
                   |                          |
                   |                          |
                   | (Internal retry timeout) |
                   |                          |
                   v                          |
          +---------------------+             |
          |                     | Internal    |
          | NEW_NH_RESPONSE     | Destroy     |
          | _AWAITED            |-------------|
          |                     |             |
          +---------------------+             |
                   |                          |
                   | (Internal LSP UP)        |
                   | (Internal LSP NAK)       |
                   v                          v
                    the control block is deleted

3.01.3 State Machine

3.01.3.1 State -- "IDLE"

 State:          IDLE

 Event:          Internal New NH

 New States:     NEW_NH_RETRY

 Actions:

   Start the LSP retry timer and go to the 'NEW_NH_RETRY' state.

 State:          IDLE

 Event:          Internal retry timeout




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 New States:     IDLE

 Actions:

   Ignore. It is an internal implementation error.

 State:          IDLE

 Event:          Internal LSP UP

 New States:     IDLE

 Actions:

   Ignore. It is an internal implementation error.

 State:          IDLE

 Event:          Internal LSP NAK

 New States:     IDLE

 Actions:

   Ignore. It is an internal implementation error.


 State:          IDLE

 Event:          Internal destroy

 New States:     IDLE

 Actions:

   Ignore. It is an internal implementation error.

3.01.3.2 State -- "NEW_NH_RETRY"

 State:          NEW_NH_RETRY

 Event:          Internal New NH

 New States:     NEW_NH_RETRY

 Actions:

   Restart the LSP retry timer.



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 State:          NEW_NH_RETRY

 Event:          Internal retry timeout

 New States:     NEW_NH_RESPONSE_AWAITED

 Actions:

   If the new next hop is the same one as the old next hop, delete the
   control block.

   Otherwise, create an LSP control block which will try to establish a
   new LSP through the new next hop. And send event "Internal Setup" to
   its state machine.

 State:          NEW_NH_RETRY

 Event:          Internal LSP UP

 New States:     NEW_NH_RETRY

 Actions:

   Ignore. It is an internal implementation error.

 State:          NEW_NH_RETRY

 Event:          Internal LSP NAK

 New States:     NEW_NH_RETRY

 Actions:

   Ignore. It is an internal implementation error.


 State:          NEW_NH_RETRY

 Event:          Internal destroy

 New States:     IDLE

 Actions:

   Stop the timer and delete the control block.

3.01.3.3 State -- "NEW_NH_RESPONSE_AWAITED"




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 State:          NEW_NH_RESPONSE_AWAITED

 Event:          Internal New NH

 New States:     NEW_NH_RETRY

 Actions:

   Restart the LSP retry timer, send "Internal destroy" to the control
   block of the LSP for the new next hop and go to the 'NEW_NH_RETRY'
   state.

 State:          NEW_NH_RESPONSE_AWAITED

 Event:          Internal retry timeout

 New States:     NEW_NH_RESPONSE_AWAITED

 Actions:

   Ignore. It is an internal implementation error.

 State:          NEW_NH_RESPONSE_AWAITED

 Event:          Internal LSP UP

 New States:     IDLE

 Actions:

   Send event "Internal cross-connect" event to the LSP control block of
   the new next hop.

   Send event "Internal destroy" event to the original LSP control
   block.

   Then delete the control block.

   State:          NEW_NH_RESPONSE_AWAITED

   Event:          Internal LSP NAK

   New States:     IDLE

   Actions:

   Delete the control block.




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 State:          NEW_NH_RESPONSE_AWAITED

 Event:          Internal destroy

 New States:     IDLE

 Actions:

   Send event "Internal destroy" the control block for the new LSP
   through the new next hop.


3.1.7   LDP Related Message Handling

 - If an LSR receives an LDP-REQUEST from an upstream LSR:

   a) If this is a duplicate request, discard the msg. A duplicate
   request means that there is a LSP_Control_Block which has same FEC,
   same Upstream Label Request ID and same Upstream LDP Session
   Identifier.

   b) Otherwise, create a new LSP_Control_Block, store the relevant
   information from the message into the control block, then pass the
   event `LDP Request' to its state machine.

 - If an LSR receives an LDP-MAPPING from a downstream LSR:

   a) Extract the 'Label Request Message ID' field and  from the LDP-
   MAPPING message.

   b) Find an LSP_Control_Block which has the same Downstream Label
   Request ID and the same Downstream LDP Session Identifier.

   c) If an LSP_Control_Block is found, pass the event `LDP Mapping' to
   its state machine.

   d) If there is no matching LSP_Control_Block found, then try to find
   an LSP_Control_Block which has the same Downstream Lable and the same
   Downstream LDP Session Identifier.

   e) If an LSP_Control_Block is found, pass the event 'LDP Mapping' to
   its state machine.

   f) Otherwise, ignore the LDP-MAPPING message.

 -  If an LSR receives an LDP-RELEASE from an upstream LSR:

   a) Find an LSP_Control_Block which has the same Upstream Label and



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   the same Upstream LDP Session Identifier.

   b) If an LSP_Control_Block is found, pass the event 'LDP Release' to
   its state machine.

   c) Otherwise, ignore the message.

 -  If an LSR receives an LDP-WITHDRAW from a downstream LSR:

   a) Find an LSP_Control_Block which has the same Downstream Label and
   the same Downstream LDP Session Identifier.

   b) If an LSP_Control_Block is found, pass the event 'LDP Withdraw' to
   its state machine.

   c) Otherwise, ignore the LDP-WITHDRAW message.

 -  If an upstream LDP peer is lost:

   a) Find all the LSP_Control_Blocks whose upstream LDP peer is that
   LSR.

   b) Then pass the event 'Upstream Lost' to their state machines.

 -  If a downstream LDP peer is lost:

   a) Find all the LSP_Control_Blocks whose downstream LDP peer is that
   LSR.

   b) Then pass the event 'Downstream Lost' to their state machines.

 -  If the LSR detects a new next hop for an FEC:

   For each LSP which needs "local repair", or it needs "global repair"
   and it is the ingress of the LSP, pass event "Internal New NH" to its
   state machine.

 -  If an LSR receives an LDP-NAK from an upstream LSR:

   a) Extract the LDP Request ID value from the LDP-NAK message.

   b) Find an LSP_Control_Block which has the same  Upstream Label
   Request ID and the same Upstream LDP Session Identifier.

   c) If an LSP_Control_Block is found, pass the event 'LDP Upstream
   Nak' to its state machine.

   d) Otherwise, ignore the message.



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 - If the LSR receives an LDP-NAK from a downstream LSR:

   a) Extract the LDP Request ID value from the LDP-NAK.

   b) Find an LSP_Control_Block which has the same Downstream Label
   Request ID and the same Downstream LDP Session Identifier.

   c) If an LSP_Control_Block is found, pass the event


   d) Otherwise, ignore the message.

3.2.  ATM Switch LSR with VC-merge

3.2.1   VC-merge

   A VC-merge capable LSR can map multiple incoming labels(VPI/VCI) into
   one outgoing label. It is possible that this LSR can only merge a
   limited number of incoming labels into a single outgoing label. As
   described in [Ref2], suppose, for example, that due to some hardware
   limitation a node is capable of merging four incoming labels into a
   single outgoing label. Suppose however, that this particular node has
   six incoming labels arriving at it for a particular FEC. In this
   case, this node may merge these into two outgoing labels.

   When an upstream LSR has a limited merging capability, it is
   difficult for a downstream LSR to know how many labels should be
   assigned to each FEC. In this case, downstream-on-demand is
   recommended.

3.2.2   Control Block

   There are 3 types of control blocks involved:
   Upstream_LSP_Control_Block, Downstream_LSP_Control_Block, and Next
   Hop Trigger Control Block.

   There is one Upstream_LSP_Control_Block for each LDP-REQUEST
   received.

   There is one Downstream_LSP_Control_Block for each unique  LDP-
   REQUEST sent to a downstream LSR. There can be multiple
   Downstream_LSP_Control_Blocks per FEC in an LSR. This can be the
   result of an upstream LSR asking for a label of an FEC. This LSR must
   assign a unique upstream label and it can not merge this upstream
   label into an existing downstream label of this FEC.

   There is one Next Hop Trigger Control Block for each FEC which was
   detected with a better next hop and the LSR decides to switch over to



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   this better next hop. It could be the result of "local repair" or
   "global repair" if the LSR is the ingress LSR of the LSP.

   A Downstream_LSP_Control_Block contains a list of pointers to
   Upstream_LSP_Control_Blocks or the Next Hop Trigger Control Block.
   This means that this LSR has decided to map the multiple labels
   listed in the Upstream_LSP_Control_Blocks and the Next Hop Trigger
   Control Block into a single label listed in the
   Downstream_LSP_Control_Block.

   An Upstream_LSP_Control_Block may contain the following information:

          - Upstream LDP Session Identifier

          - State

          - Upstream Label(assigned by this LSR)

          - Downstream_LSP_Control_Block pointer

          - Upstream LDP Request ID (assigned by the Upstream LSR in
          downstream-on-demand mode)

          - Next_Hop_Trigger_Block pointer

   Upstream Label and Upstream LDP Session Identifier can be used to
   locate a unique Upstream_LSP_Control_Block.

   If an LSR is using downstream-on-demand mode, it can use the Upstream
   LDP Request ID and the  Upstream LDP Session Identifier to locate a
   unique Upstream_LSP_Control_Block.

   An Next_Hop_Trigger_LSP_Control_Block may contain the following
   information:

          - Upstream_LSP_Control_Block pointer, which points to the one
          which is needed to switch over to the better next hop

          - State

          - Downstream_LSP_Control_Block pointer

   A Downstream_LSP_Control_Block may contain the following information:

          - FEC

          - State




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          - Downstream LDP Session Identifier

          - list of pointers to the Upstream_LSP_Control_Blocks or the
          Trigger_Control_Blocks which are merged at this LSR for this
          FEC

          - Downstream Label(assigned by the downstream LSR)

          - Downstream Label Request ID (assigned by the LSR itself if
          it is using downstream-on-demand mode)

   Downstream Label, Downstream LDP Session Identifier can be used to
   locate a unique Downstream_LSP_Control_Block.

   If an LSR is using downstream-on-demand mode, it can also use the
   Downstream Label Request ID and the Downstream LDP Session Identifier
   to locate a unique Downstream_LSP_Control_Block.

   The following diagram details the relationship between these 2 types
   of control blocks:

   For example, the LSR has decided to merge 3 LDP-REQUESTs of a FEC
   from upstream LSR1,LSR2,LSR3 into one LDP-REQUEST and sent it to a
   downstream LSR4.



























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    +---------------------+
    |                     |
    | Upstream_LSP_Control|
    | _Block  for Upstream|-------+
    | LSR1                |       |
    +---------------------+       |
                                  |
                                  |
                                  |
                                  |
                                  |
    +---------------------+       |
    |                     |       |
    | Upstream_LSP_Control|       | (merged into)
    | _Block for Upstream |-------+
    |  LSR2               |       |
    +---------------------+       |
                                  |
                                  |
                                  |
                                  |   +------------------------------+
                                  |   |                              |
                                  +-->| Downstream_LSP_Control_Block |
                                  |   |   for Downstream LSR4        |
                                  |   |                              |
                                  |   +------------------------------+
                                  |
    +---------------------+       |
    | Next_Hop_Trigger_   |       |
    | LSP_Control_Block   |       |
    |                     |-------+
    |                     |
    +---------------------+

3.2.3   State Machines for Downstream-on-demand Mode

   The following sections describe the state machines used in
   downstream-on-demand mode.

3.2.3.1    State of the Upstream_LSP_Control_Block's State Machine
              for Downstream-on-demand Mode

   -- IDLE

   This is the initial LSP state.

   -- RESPONSE_AWAITED




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   This state means that the LSR has received and processed an LDP-
   REQUEST from an upstream LSR, and has sent a new LDP-REQUEST towards
   a downstream LSR. The LSR is waiting for the LDP-MAPPING message from
   the downstream LSR.


   -- ESTABLISHED

   This state means that the LSR has received the LDP-MAPPING message
   from the downstream LSR and the LSP is up and operational.

   -- RELEASE_AWAITED

   This state means that the LSR has sent a LDP-WITHDRAW message
   upstream and is waiting for the LDP-RELEASE before freeing up the
   label resource.


3.2.3.2    Events of the Upstream_LSP_Control_Block's State Machine
              for Downstream-on-demand Mode

   -- LDP Request

   The LSR receives an LDP-REQUEST from an upstream LSR.

   -- Internal Downstream Mapping

   This event is sent by one Downstream_LSP_Control_Block's state
   machine.  This Downstream_LSP_Control_Block is the merged
   Downstream_LSP_Control_Block of this Upstream_LSP_Control_Block. The
   event is the result of receiving an LDP-MAPPING message by the
   Downstream_LSP_Control_Block's state machine.

   -- LDP Release

   The LSR receives an LDP-RELEASE from an upstream LSR.

   -- Internal Downstream Withdraw

   This event is sent by one Downstream_LSP_Control_Block's state
   machine.  This Downstream_LSP_Control_Block is the merged
   Downstream_LSP_Control_Block of this Upstream_LSP_Control_Block. The
   event is the result of receiving an LDP-WITHDRAW message by the
   Downstream_LSP_Control_Block's state machine.

   -- LDP Upstream Nak

   The LSR receives an LDP-NAK from an upstream LSR.



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   -- Internal Downstream Nak

   This event is sent by one Downstream_LSP_Control_Block's state
   machine.  This Downstream_LSP_Control_Block is the merged
   Downstream_LSP_Control_Block of this Upstream_LSP_Control_Block. The
   event is the result of receiving an LDP-NAK message by the
   Downstream_LSP_Control_Block's state machine, or it detects an error.

   -- Upstream Lost

   The LSR loses the LDP session with its upstream LDP peer.

   -- Internal New NH

   The LSR detects there is better next hop and decides to establish the
   lsp through this better next hop

   -- Internal Re-Cross-Connect

   This event is used to trigger splicing into a different downstream
   LSP. This can happens when it is switched over to a better LSP
   through the new next hop.





























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3.2.3.3 State Transitions of the Upstream_LSP_Control_Block's State
         Machine for Downstream-on-demand Mode



               +-------------------+
               |                   |
     +-------->|  IDLE             |<------------+
     |         |                   |             |
     |         +-------------------+             |
     |(LDP Upstream Nak)|                        |
     |(Internal         |(LDP Request)           |
     | Downstream Nak)  |                        |
     |(Upstream Lost)   |                        |
     |                  v                        |
     |         +-------------------+             |
     |         |                   |             |
     +---------|  RESPONSE_AWAITED |             |
               |                   |             |(Upstream Lost)
               +-------------------+             |
                        |                        |
                        |(Internal Downstream    |
                        |  mapping)              |(LDP Release)
                        |                        |
                        v                        |
               +-------------------+             |
               |                   |             |(LDP Upstream Nak)
               |  ESTABLISHED      |------->-----+
               |                   |             |
               +-------------------+             |
                        |                        |
                        |                        |
                        |(Internal Downstream Withdraw)
                        |(Internal Downstream Nak)
                        v
               +-------------------+             |
               |                   |             |
               |RELEASE_AWAITED    |------->-----+
               |                   |
               +-------------------+



3.2.3.4 Upstream_LSP_Control_Block's State Machine
        for Downstream-on-demand Mode


3.2.3.4.1 State -- "IDLE"



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 State:          IDLE

 Event:          LDP Request

 New State:      Depends upon the action routine.

 Actions:

   If this LSR is the LSP Egress or Proxy Egress [Ref2],

   Then:

     choose an upstream label, allocate the resources, connect this
     upstream label to the local IP forwarding module, send an LDP-
     MAPPING upstream with the upstream label and go to the state
     'ESTABLISHED'.


   else

     Obtain a next hop(or interface). Find a
     Downstream_LSP_Control_Block which has the same FEC and the same
     next hop and also is able to merge more input labels. If not found,
     create a new Downstream_LSP_Control_Block with the state 'IDLE'.

     If the state of the Downstream_LSP_Control_Block is `ESTABLISHED',
     choose an upstream label, connect the upstream label with the
     downstream label and send an LDP-MAPPING message upstream with the
     upstream label, and go to the state `ESTABLISHED'.

     If the state of Downstream_LSP_Control_Block is not `ESTABLISHED',
     set the state of the Upstream_LSP_Control_Block to
     'RESPONSE_AWAITED'. If the LSR use the independent control
     mode[Ref2], choose an upstream label, and send an LDP-MAPPING
     message upstream.

     Pass the event `Internal AddUpstream' to the
     Downstream_LSP_Control_Block's state machine.

   If unable to process the request for any reason, issue an LDP-NAK
   message to the sender with the appropriate error code and delete the
   control block.

 State:          IDLE

 Event:          Internal Downstream Mapping

 New State:      IDLE



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 Actions:

   Ignore the event. It is an internal implementation error.

 State:          IDLE

 Event:          LDP Release

 New State:      IDLE

 Actions:

   Ignore the event. It is an internal implementation error.

 State:          IDLE

 Event:          Internal Downstream Withdraw

 New State:      IDLE

 Actions:

   Ignore the event. It is an internal implementation error.

 State:          IDLE

 Event:          LDP Upstream Nak

 New State:      IDLE

 Actions:

   Ignore the event. It is an internal implementation error.

 State:          IDLE

 Event:          Internal Downstream Nak

 New State:      IDLE

 Actions:

   Ignore the event. It is an internal implementation error.

 State:          IDLE

 Event:          Upstream Lost




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 New State:      IDLE

 Actions:

   Ignore the event. It is an internal implementation error.

 State:          IDLE

 Event:          Internal Re-Cross-Connect

 New State:      IDLE

 Actions:

   Ignore the event. It is an internal implementation error.

 State:          IDLE

 Event:          Internal New NH

 New State:      IDLE

 Actions:

   Ignore the event. It is an internal implementation error.

3.2.3.4.2 State -- "RESPONSE_AWAITED"


 State:          RESPONSE_AWAITED

 Event:          LDP Request

 New State:      RESPONSE_AWAITED

 Actions:

   Ignore the event. It is an internal implementation error.

 State:          RESPONSE_AWAITED

 Event:          Internal Downstream Mapping

 New State:      Depends on the action routine

 Actions:





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   If the LSR uses the ordered control mode, assign an upstream label.

   Connect the upstream label to the downstream label and allocate the
   resources.

   Send an LDP-MAPPING message upstream with the upstream label.

   Then go to the state 'ESTABLISHED'.

   If unable to process the message for any reason, issue an LDP-NAK
   message upstream and an LDP-RELEASE message downstream and delete the
   control block.

 State:          RESPONSE_AWAITED

 Event:          LDP Release

 New State:      RESPONSE_AWAITED

 Actions

   Ignore the event. It is an protocol error from the upstream peer.

 State:          RESPONSE_AWAITED

 Event:          Internal Downstream Withdraw

 New State:      RESPONSE_AWAITED

 Actions

   Ignore the event. It is an internal implementation error.

 State:          RESPONSE_AWAITED

 Event:          LDP Upstream Nak

 New State:      IDLE

 Actions

   If the LSR uses the independent control mode, free the upstream label
   and the resources.

   Send the event 'Internal DeleteUpstream' to its
   Downstream_LSP_Control_Block's state machine.

   Delete the control block.



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 State:          RESPONSE_AWAITED

 Event:          Internal Downstream Nak

 New State:      IDLE

 Actions:

   If the LSR uses the independent control mode, free the upstream label
   and the resources. Then, send an LDP-WITHDRAW message upstream.

   If the LSR uses the ordered control mode, propagate the LDP-NAK
   message upstream.

   Delete the control block.

 State:          RESPONSE_AWAITED

 Event:          Upstream Lost

 New State:      IDLE

 Actions

   If the LSR uses the independent control mode, free the upstream label
   and the resources.

   Send the event 'Internal DeleteUpstream' to its
   Downstream_LSP_Control_Block's state machine.

   Delete the control block.

 State:          RESPONSE_AWAITED

 Event:          Internal Re-Cross-Connect

 New State:      RESPONSE_AWAITED

 Actions:

   Ignore the event. It is an internal implementation error.

 State:          RESPONSE_AWAITED

 Event:          Internal New NH

 New State:      depends on the actions




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 Actions:

   Send event "Internal DeleteUpstream" to its old downstream control
   block.

   Find a Downstream_LSP_Control_Block which has the same FEC and the
   same next hop and also is able to merge more input labels. If not
   found, create a new Downstream_LSP_Control_Block with the state
   'IDLE'.

   If the state of the Downstream_LSP_Control_Block is `ESTABLISHED',
   choose an upstream label, connect the upstream label with the
   downstream label and send an LDP-MAPPING message upstream with the
   upstream label, and go to the state `ESTABLISHED'.

   If the state of Downstream_LSP_Control_Block is not `ESTABLISHED',
   set the state of the Upstream_LSP_Control_Block to
   'RESPONSE_AWAITED'.

   Pass the event `Internal AddUpstream' to the new
   Downstream_LSP_Control_Block's state machine.


3.2.3.4.3 State -- "ESTABLISHED"

 State:          ESTABLISHED

 Event:          LDP Request

 New State:      ESTABLISHED

 Actions

   Ignore the event. It is an internal implementation error.

 State:          ESTABLISHED

 Event:          Internal Downstream Mapping

 New State:      ESTABLISHED

 Actions

   Process the new attributes of the mapping and then propagate the
   LDP-MAPPING message upstream.

 State:          ESTABLISHED




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 Event:          LDP Release

 New State:      IDLE

 Actions

   Disconnect the upstream label from the downstream label, free the
   upstream label and resources.

   Send the event 'Internal DeleteUpstream' to its
   Downstream_LSP_Control_Block's state machine.

   Send the event "Internal Destroy' to the Next_Hop_Trigger_Block's
   state machine if the LSR was in the middle of switching over to the
   better next hop.

   Delete the control block.

 State:          ESTABLISHED

 Event:          Internal Downstream Withdraw

 New State:      Depends on the action routine

 Actions

   If it uses independent mode,set its state to 'IDLE' and create a
   internal 'LDP Request' and send to its own state machine.

   Else
     Disconnect the upstream label from the downstream label.

     Propagate the LDP-WITHDRAW upstream and go to state
     'RELEASE_AWAITED'.

   Send the event "Internal Destroy' to the Next_Hop_Trigger_Block's
   state machine if the LSR was in the middle of switching over to the
   better next hop.

 State:          ESTABLISHED

 Event:          LDP Upstream Nak

 New State:      IDLE

 Actions

   Disconnect the upstream label from the downstream label, free the



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   upstream label and the resources.

   Send the event 'Internal DeleteUpstream' to its
   Downstream_LSP_Control_Block's state machine.

   Send the event "Internal Destroy' to the Next_Hop_Trigger_Block's
   state machine if the LSR was in the middle of switching over to the
   better next hop.

   Delete the control block.

 State:          ESTABLISHED

 Event:          Internal Downstream Nak

 New State:      Depends on the actions

 Actions:

   If it uses independent mode,set its state to 'IDLE' and create a
   internal 'LDP Request' and send to its own state machine.

   Else
     Disconnect the upstream label from the downstream label

     Send an LDP-WITHDRAW upstream and go to state 'RELEASE_AWAITED'.

   Send the event "Internal Destroy' to the Next_Hop_Trigger_Block's
   state machine if the LSR was in the middle of switching over to the
   better next hop.

 State:          ESTABLISHED

 Event:          Upstream Lost

 New State:      IDLE

 Actions:

   Disconnect the upstream label from the downstream label, free the
   upstream label and the resources.

   Send the event 'Internal DeleteUpstream' to its
   Downstream_LSP_Control_Block's state machine.

   Send the event "Internal Destroy' to the Next_Hop_Trigger_Block's
   state machine if the LSR was in the middle of switching over to the
   better next hop.



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   Delete the control block.

 State:          ESTABLISH

 Event:          Internal Re-Cross-Connect

 New State:      ESTABLISH

 Actions:

   Reconnect the upstream lable to the new downstream lable.

   Send the event 'Internal DeleteUpstream' to its old
   Downstream_LSP_Control_Block's state machine.

 State:          ESTABLISH

 Event:          Internal New NH

 New State:      ESTABLISH

 Actions:

   Create a new Next_Hop_Trigger_Control_Block and pass event

   3.2.3.4.4 State -- "RELEASE_AWAITED"

 State:          RELEASE_AWAITED

 Event:          LDP Request

 New State:      RELEASE_AWAITED

 Actions:

   Ignore the event. It is a protocol error from the upstream LSR.

 State:          RELEASE_AWAITED

 Event:          Internal Downstream Mapping

 New State:      RELEASE_AWAITED

 Actions:

   Ignore the event. It is an internal implementatin error.

 State:          RELEASE_AWAITED



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 Event:          LDP Release

 New State:      IDLE

 Actions:

   Free the upstream lable resource. and delete the control block.

 State:          RELEASE_AWAITED

 Event:          Internal Downstream Withdraw

 New State:      RELEASE_AWAITED

 Actions:

   Ignore the event. It is a protocol error from the downstream LSR.

 State:          RELEASE_AWAITED

 Event:          LDP Upstream Nak

 New State:      IDLE

 Actions:

   Free the upstream lable resource. and delete the control block.

 State:          RELEASE_AWAITED

 Event:          Internal Downstream Nak

 New State:      RELEASE_AWAITED

 Actions:

   Ignore the event. And continue waiting for the LDP-RELEASE msg.

 State:          RELEASE_AWAITED

 Event:          Upstream Lost

 New State:      IDLE

 Actions:

   Free the upstream lable resource. and delete the control block.




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 State:          RELEASE_AWAITED

 Event:          Internal New NH

 New State:      RELEASE_AWAITED

 Actions:

   Ignore the event. And continue waiting for the LDP-RELEASE msg.

   State:          RELEASE_AWAITED

   Event:          Internal Re-Cross-Connect

   New State:      RELEASE_AWAITED

   Actions:

   Ignore the event. It is an internal implementation error.

3.2.3.5 State of the Downstream_LSP_Control_Block's State Machine
              for Downstream-on-demand Mode

   -- IDLE

   This is the initial LSP state.

   -- RESPONSE_AWAITED

   This state means that the LSR has received an LDP-REQUEST from an
   upstream LSR, has processed the LDP-REQUEST, and has sent a new LDP-
   REQUEST towards a downstream LSR. The LSR is waiting for the LDP-
   MAPPING message from the downstream LSR.


   -- ESTABLISHED

   This state means that the LSR has received the LDP-MAPPING message
   from the downstream LSR and the LSP is up and operational.

3.2.3.6 Events of the Downstream_LSP_Control_Block's State Machine
         for Downstream-on-demand Mode

   -- Internal AddUpstream

   This event is sent by an Upstream_LSP_Control_Block's state machine
   when it is created.




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   -- Internal DeleteUpstream

   This event is sent by an Upstream_LSP_Control_Block's state machine
   when it is deleted.

   -- LDP Mapping

   The LSR receives an LDP-MAPPING message from a downstream LSR.

   -- LDP Withdraw

   The LSR receives an LDP-WITHDRAW message from a downstream LSR.


   -- LDP Downstream Nak

   The LSR receives an LDP-NAK from a downstream LSR.

   -- Downstream Lost

   The LSR loses the LDP session with its downstream LSR.






























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3.2.3.7  State Transitions of the Downstream_LSP_Control_Block'S
       State Machine for Downstream-on-demand mode



               +-------------------+
               |                   |
               |  IDLE             |<--------------+
               |                   |               |(last Internal
               +-------------------+               | DeleteUpstream)
                        |                          |(LDP Withdraw)
                        |(1st Internal AddUpstream)|
                        |                          |(LDP Downstream
                        v                          | Nak)
               +-------------------+               |(Downstream
               |                   |               |   Lost)
               |  RESPONSE_AWAITED |---------->----^
               |                   |               |
               +-------------------+               |
                        |                          |
                        |(LDP Mapping)             |
                        |                          |
                        v                          |
               +-------------------+               |
               |                   |               |
               |  ESTABLISHED      |-------->------^
               |                   |
               +-------------------+


3.2.3.8  Downstream_LSP_Control_Block'S State Machine for
         Downstream-on-demand Mode.

3.2.3.8.1 State -- "IDLE"

 State:          IDLE

 Event:          Internal AddUpstream

 New State:      RESPONSE_AWAITED

 Actions

   Initialize the list of pointers in the Upstream_LSP_Control_Block to
   contain the newly added upstream pointer.

   Send a new LDP-REQUEST downstream and go to the state
   'RESPONSE_AWAITED'.



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 State:          IDLE

 Event:          Internal DeleteUpstream

 New State:      IDLE

 Actions

   Ignore the event. It is an internal implementation error.

 State:          IDLE

 Event:          LDP Mapping

 New State:      IDLE

 Actions

   Ignore the event. It is an internal implementation error.

 State:          IDLE

 Event:          LDP Withdraw

 New State:      IDLE

 Actions

   Ignore the event.It is an internal implementation error.

 State:          IDLE

 Event:          LDP Downstream Nak

 New State:      IDLE

 Actions

   Ignore the event. It is an internal implementation error.

 State:          IDLE

 Event:          Downstream Lost

 New State:     IDLE

 Actions




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   Ignore the event. It is an internal implementation error.

3.2.3.8.2 State -- "RESPONSE_AWAITED"

 State:          RESPONSE_AWAITED

 Event:          Internal AddUpstream

 New State:      RESPONSE_AWAITED

 Actions

   Add the pointer to new Upstream_LSP_Control_Block to the
   Upstream_LSP_Control_Blocks pointer list.

 State:          RESPONSE_AWAITED

 Event:          Internal DeleteUpstream

 New State:      Depend on the action routine

 Actions

   Delete the Upstream_LSP_Control_Block pointer from the
   Upstream_LSP_Control_Block pointers list.

   If the list becomes empty, release the resources, send an LDP-NAK
   downstream, and then delete the control block.

 State:          RESPONSE_AWAITED

 Event:          LDP Mapping

 New State:      ESTABLISHED

 Actions

   For each Upstream_LSP_Control_Block in the Upstream_LSP_Control_Block
   pointers list, pass the event 'Internal Downstream Mapping' to its
   state machine.

 State:          RESPONSE_AWAITED

 Event:          LDP Withdraw

 New State:      RESPONSE_AWAITED

 Actions



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   Ignore the event. It is a protocol error from the downstream LDP
   peer.

 State:          RESPONSE_AWAITED

 Event:          LDP Downstream Nak

 New State:      IDLE

 Actions

   For each Upstream_LSP_Control_Block in the Upstream_LSP_Control_Block
   pointers list, pass the event 'Internal Downstream Nak' to its state
   machine.

   Release the resources, and delete the control block.

 State:          RESPONSE_AWAITED

 Event:          Downstream Lost

 New State:      IDLE

 Actions

   For each Upstream_LSP_Control_Block in the
   Upstream_LSP_Control_Block pointers list, pass the event 'Internal
   Downstream Nak' to its state machine.

   Release the resources, and delete the control block.

3.2.3.8.3 State -- "ESTABLISHED"

 State:          ESTABLISHED

 Event:          Internal AddUpstream

 New State:      ESTABLISHED

 Actions

   Add the pointer to new Upstream_LSP_Control_Block to the
   Upstream_LSP_Control_Block pointers list.

 State:          ESTABLISHED

 Event:          Internal DeleteUpstream




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 New State:      Depends on the action routine

 Actions

   Delete the pointer of Upstream_LSP_Control_Block from its
   Upstream_LSP_Control_Block pointers list.

   If the list becomes empty, release the resources, send an LDP-RELEASE
   downstream, and then delete the control block.

 State:          ESTABLISHED

 Event:          LDP Mapping

 New State:      ESTABLISHED

 Actions

   For each Upstream_LSP_Control_Block in the Upstream_LSP_Control_Block
   pointers list, pass the event 'Internal Downstream mapping' to its
   state machine.

 State:          ESTABLISHED

 Event:          LDP Withdraw

 New State:      IDLE

 Actions

   For each Upstream_LSP_Control_Block in the Upstream_LSP_Control_Block
   pointers list, pass the event 'Internal Downstream withdraw' to its
   state machine.

   Release the resources, and delete the control block.

 State:          ESTABLISHED

 Event:          LDP Downstream Nak

 New State:      ESTABLISHED

 Actions

   It is a protocol error from the downstream LDP peer.

3.2.3.9 State of the Next_Hop_Trigger_Control_Block's State Machine
              for Downstream-on-demand Mode



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   -- IDLE

   This is the initial LSP state.

   -- NEW_NH_RETRY

   This is the state where an LSR waits for a retry timer to expire and
   then tries to establish an LSP through a new next hop.

   -- NEW_NH_RESPONSE_AWAITED

   This state means that the LSR has sent a new LDP-REQUEST towards a
   downstream LSR. The LSR is waiting for the LDP-MAPPING message from
   the downstream LSR.

3.2.3.10    Events of the Next_Hop_Trigger_Control_Block's State Machine
              for Downstream-on-demand Mode

   -- Internal New NH

   Trigger to setup an LSP through a better next hop.

   -- Internal Downstream Mapping

   This event is sent by one Downstream_LSP_Control_Block's state
   machine.  This Downstream_LSP_Control_Block is the merged
   Downstream_LSP_Control_Block of this Upstream_LSP_Control_Block. The
   event is the result of receiving an LDP-MAPPING message by the
   Downstream_LSP_Control_Block's state machine.

   -- Internal Downstream Nak

   This event is sent by one Downstream_LSP_Control_Block's state
   machine.  This Downstream_LSP_Control_Block is the merged
   Downstream_LSP_Control_Block of this Upstream_LSP_Control_Block. The
   event is the result of receiving an LDP-NAK message by the
   Downstream_LSP_Control_Block's state machine, or it detects an error.

   -- Internal Destroy This event is used to stop the procedure of
   switching over to the better next hop.











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3.2.3.11 State Transitions of the Next_Hop_Trigger_Control_Block's State
         Machine for Downstream-on-demand Mode


                   |
                   |
                   |
                   | Internal New NH
                   |
                   v
          +---------------------+
          |                     | Internal destroy
          | NEW_NH_RETRY        |--------------
          |                     |             |
          +---------------------+             |
                   |                          |
                   |                          |
                   | (Internal retry timeout) |
                   |                          |
                   v                          |
          +---------------------+             |
          |                     | Internal    |
          | NEW_NH_RESPONSE     | Destroy     |
          | _AWAITED            |-------------|
          |                     |             |
          +---------------------+             |
                   |                          |
                   | (Internal Downstream     |
                   |   Mapping                |
                   | (Internal Downstream     |
                   |    Nak)                  |
                   v                          v
                    the control block is deleted

3.2.3.12 State Machine

3.2.3.12.1 State -- "IDLE"

 State:          IDLE

 Event:          Internal New NH

 New States:     NEW_NH_RETRY

 Actions:

   Start the LSP retry timer and go to the 'NEW_NH_RETRY' state.




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 State:          IDLE

 Event:          Internal retry timeout

 New States:     IDLE

 Actions:

   Ignore. It is an internal implementation error.

 State:          IDLE

 Event:          Internal Downstream Mapping

 New States:     IDLE

 Actions:

   Ignore. It is an internal implementation error.

 State:          IDLE

 Event:          Internal Downstream Nak

 New States:     IDLE

 Actions:

   Ignore. It is an internal implementation error.


 State:          IDLE

 Event:          Internal destroy

 New States:     IDLE

 Actions:

   Ignore. It is an internal implementation error.

3.2.3.12.2 State -- "NEW_NH_RETRY"

 State:          NEW_NH_RETRY

 Event:          Internal New NH

 New States:     NEW_NH_RETRY



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 Actions:

   Restart the LSP retry timer.

 State:          NEW_NH_RETRY

 Event:          Internal retry timeout

 New States:     NEW_NH_RESPONSE_AWAITED

 Actions:

   If the new next hop is the same one as the old next hop, delete the
   control block.

   Otherwise, find an downstream LSP control block which go through the
   same next hop for the same FEC, if there is no one, create one, and
   pass "Internal AddUpstream'event to its state machine.

 State:          NEW_NH_RETRY

 Event:          Internal Downstream Mapping

 New States:     NEW_NH_RETRY

 Actions:

   Ignore. It is an internal implementation error.

 State:          NEW_NH_RETRY

 Event:          Internal Downstream NAK

 New States:     NEW_NH_RETRY

 Actions:

   Ignore. It is an internal implementation error.


 State:          NEW_NH_RETRY

 Event:          Internal destroy

 New States:     IDLE

 Actions:




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   Stop the timer and delete the control block.

3.2.3.12.3 State -- "NEW_NH_RESPONSE_AWAITED"

 State:          NEW_NH_RESPONSE_AWAITED

 Event:          Internal New NH

 New States:     NEW_NH_RETRY

 Actions:

   Restart the LSP retry timer, send "Internal destroy" to the control
   block of the LSP for the new next hop and go to the 'NEW_NH_RETRY'
   state.

 State:          NEW_NH_RESPONSE_AWAITED

 Event:          Internal retry timeout

 New States:     NEW_NH_RESPONSE_AWAITED

 Actions:

   Ignore. It is an internal implementation error.

 State:          NEW_NH_RESPONSE_AWAITED

 Event:          Internal Downstream Mapping

 New States:     IDLE

 Actions:

   Send event "Internal Re-cross-connect" event to the Upstream LSP
   control block of the new next hop.

   Send event "DeleteUpstream" event to the downstream LSP control block
   of the the new next hop, since the upstream has spliced into the new
   next hop.

   Then delete the control block.

   State:          NEW_NH_RESPONSE_AWAITED

   Event:          Internal Downstream NAK

   New States:     IDLE



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   Actions:

   Delete the control block.


 State:          NEW_NH_RESPONSE_AWAITED

 Event:          Internal destroy

 New States:     IDLE

 Actions:

   Send event "Internal DeleteUpstream" the control block for the new
   LSP through the new next hop.

   3.2.4   LDP Related Message Processing

 - If an LSR receives an LDP-REQUEST message:

   a) If this is a duplicate request, discard the msg. A duplicate
   request means that there is a LSP_Control_Block which has same FEC,
   same Upstream Label Request ID and same Upstream LDP Session
   Identifier.

   b) Otherwise, create a new  Upstream_LSP_Control_Block. Then pass the
   event `LDP Request' to this Upstream_LSP_Control_Block's state
   machine.

 - If an LSR receives an LDP-MAPPING message:

   Locate a Downstream_LSP_Control_Block which has the same FEC, the
   same Downstream LDP Session Identifier and the same Downstream Label.
   If a Downstream_LSP_Control_Block is found, pass the event `LDP
   Mapping' to its state table. This could mean that the attributes of
   label binding have changed.

   Otherwise, use the Downstream LDP request ID(the 'Lable Request
   Message ID' field in the LDP-MAPPING MSG) and Downstream LDP Session
   Identifier to locate the Downstream_LSP_Control_Block and  pass the
   event `LDP Mapping' to its state machine. If no
   Downstream_LSP_Control_Block is found, ignore the message.

 -  If an LSR receives an LDP-RELEASE message:

   Locate an Upstream_LSP_Control_Block which has the same FEC, the same
   Upstream Label, the same Upstream LDP Session Identifier. If no
   Upstream_LSP_Control_Block is found, ignore the message. If an



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   Upstream_LSP_Control_Block is found, send the event `LDP Release' to
   its state machine.


 -  If an LSR receives an LDP-WITHDRAW message:

   Find a Downstream_LSP_Control_Block which has the same FEC, the same
   Downstream LDP Session Identifier and the same Downstream Label. Pass
   the event `LDP Withdraw' to its state machines.

 -  If an Upstream LDP peer is lost:

   Pass the event `Upstream Lost' to the state machines of all the
   Upstream_LSP_Control_Blocks whose upstream LDP peer is that LSR.

 -  If a Downstream LDP peer is lost:

   Pass the event `Downstream Lost' to the state machines of all the
   Downstream_LSP_Control_Blocks whose the downstream LDP peer is that
   LSR.

 -  If a next hop of an FEC is changed:

   For all the Upstream_LSP_Control_Blocks which are infected by this
   change, pass the event 'Internal New NH' to their state machines.

 - If an LSR receives an LDP-NAK from an  Upstream LSR:

   Use the Upstream LDP Request ID and Upstream LDP Session Identifier
   to locate the Upstream_LSP_Control_Block and pass the event `LDP
   Upstream Nak' to its state machine.

 -  If an LSR receives an LDP-NAK from a downstream LSR:

   Use the Downstream LDP Request ID and Downstream Session Identifier
   to locate a Downstream_LSP_control_block and pass the event `LDP
   Downstream Nak' to its state machine.

3.2.4  Downstream Unsolicited

   The following sections describe the state machines for the ATM-LSR
   which uses downstream unsolicited mode.

   While both independent LSP control and ordered LSP control modes are
   possible, only the ordered mode is taken into account, because the
   independant LSP control mode uses the liberal label retention mode
   and so is considered burning too many ATM resources.




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   In downstream unsolicited mode, multiple path is not allowed in this
   version and will be For Further Study(FFS). We suspect with multiple
   next hops and Downstream mode, it is easy to get into loop condition.

3.2.4.0   Control Block

   There are 2 types of control blocks involved:
   Upstream_LSP_Control_Block, Downstream_LSP_Control_Block.

   There is a list of Upstream_LSP_Control_Blocks for each FEC in the
   routing table, with each one correspondng to a LDP peer. A
   Upstream_LSP_Control_Block is created for each FEC when there is a
   label ready to be distributed to that upstream.  It is deleted when
   the FEC is deleted from the FEC table, or the LDP peer disappears, or
   the downstream label is withdrawed.

   There is one Downstream_LSP_Control_Blocks for each FEC in the
   routing table. It is created when the FEC is inserted into the
   forwarding table and deleted when the FEC is removed from the
   forwarding table.

   An Upstream_LSP_Control_Block may contain the following information:

          - Upstream LDP Session Identifier

          - State

          - Upstream Label(assigned by this LSR)

          - FEC

   Upstream Label and Upstream LDP Session Identifier, or FEC and
   Upstream LDP Session Identifier can be used to locate a unique
   Upstream_LSP_Control_Block.

   A Downstream_LSP_Control_Block may contain the following information:

          - FEC

          - State

          - Downstream LDP Session Identifier

          - Downstream Label(assigned by the downstream LSR)

          - Downstream Label Request ID (assigned by the LSR itself)

   Downstream Label and Downstream LDP Session Identifier, or FEC and



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   Downsteam LDP Session Identifier can be used to locate a unique
   Downstream_LSP_Control_Block.

3.2.4.1    States of the Upstream_LSP_Control_Block's State Machine
              for Downstream Mode

   -- IDLE

   This is the initial LSP state.

   -- ESTABLISHED

   This state means that the LSR has received the LDP-MAPPING message
   from the downstream LSR and the LSP is up and operational.

   -- RELEASE_AWAITED

   This state means that the LSR is waiting for the LDP-RELEASE msg in
   respond to the LDP-WITHDRAW sent by this LSR.

   -- RESOUCES_AWAITED

   This state means that the LSR is waiting for the label resources.

3.2.4.2   Events of the Upstream_LSP_Control_Block's State Machine
             for Downstream Mode

   -- Internal Downstream Mapping

   This event is sent by one Downstream_LSP_Control_Block's state
   machine. The event is the result of receiving an LDP-MAPPING message
   by the Downstream_LSP_Control_Block's state machine. Or when the LDP
   peer is discovered and there is a downstream Label available for this
   FEC.

   -- LDP Release

   The LSR receives an LDP-RELEASE from an upstream LSR.

   -- Internal Withdraw

   This event is sent by Downstream_LSP_Control_Block's state machine.
   The event is the result of receiving an LDP-WITHDRAW message by the
   Downstream_LSP_Control_Block's state machine.

   -- Resource Available

   This event means the local resource(such as label) becomes available.



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   -- Delete FEC

   This event means that either the FEC is removed from the forwarding
   table.

   -- Upstream Lost

   This event means that the upstream LDP peer is lost.











































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3.2.4.3   State Transitions of Upstream_LSP_Control_Block's State
           Machine for Downstream Mode

                            |
                            |(created when
                            |a label is to be distributed
                            | to the LDP peer)
                            v
                  +-------------------+
                  |                   |
                  |  IDLE             |<--------------+
                  |                   |               |
                  +-------------------+               |
                           |                          |(LDP Release)
                           |                          |
                           |                          |
                           |                          |
                           |(Internal Downstream      |
       +-------------------|  Mapping)                |
       |                   |                          |
       |(no label resource)v                          |
       |          +-------------------+               |
       |          |                   |               |
       |    +-----|  ESTABLISHED      |---------------+
       |    |     |                   |               ^
       |    |     +-------------------+               |
       |    |(delete FEC)   ^                         |
       |    |(Internal      |(Resource Available)     | (LDP Release)
       |    |  Withdraw)    |                         | (Internal
       |    |               |                         |  Downstraem
       |    |               |                         |    Withdraw)
       |    |     +-------------------+               |
       +--------->|                   |               |
            |     |RESOURCES_AWAITED  |---------------+
            |     |                   |               |
            |     +-------------------+               |
            |                                         |
            | (Internal Downstream Withdraw)          |(LDP Release)
            |     +-------------------+               |
            |     |                   |               |
            +---->|  RELEASE_AWAITED  |---------------+
                  |                   |
                  +-------------------+


3.2.4.4   Upstream_LSP_Control_Block's State Machine for
             Downstream Mode




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3.2.4.4.1 : State -- "IDLE"

 State:          IDLE

 Event:          Internal Downstream mapping

 New State:      Depends on the action.

 Actions

   Choose an upstream label, connect the upstream label with the
   downstream label. And go to state 'ESTABLISHED'

   Propagate the LDP-MAPPING upstream.

   If there is no resource for the upstream label, go to state
   'RESOURCE_AWAITED'.

 State:          IDLE

 Event:          LDP Release

 New State:      IDLE

 Actions

   Ignore the event. It is an internal implementation error.

 State:          IDLE

 Event:          Internal Downstream Withdraw

 New State:      IDLE

 Actions

   Ignore the event. It is an internal implementation error.

 State:          IDLE

 Event:          Resource Available

 New State:      IDLE

 Actions

   Ignore the event. It is an internal implementation error.




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 State:          IDLE

 Event:          Delete FEC

 New State:      IDLE

 Actions

   Delete the control block.

 State:          IDLE

 Event:          Upstream Lost

 New State:      IDLE

 Actions

   Delete the control block.

3.2.4.4.2 : State -- "ESTABLISHED"

 State:          ESTABLISHED

 Event:          Internal Downstream Mapping

 New State:      ESTABLISHED

 Actions

   Process the new attributes of the new mapping msg.

   Propagate the LDP-MAPPING upstream.

 State:          ESTABLISHED

 Event:          LDP Release

 New State:      IDLE

 Actions

   Disconnect upstream label from downstream label.

   Release the upstream label resource

   Delete the control block.




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 State:          ESTABLISHED

 Event:          Internal Downstream Withdraw

 New State:      RELEASE_AWAITED

 Actions

   Disconnect upstream label from downstream label.

   Propagate the LDP-WITHDRAW upstream.

 State:          ESTABLISHED

 Event:          Resource Available

 New State:      ESTABLISHED

 Actions

   Ignore the event. It is an internal implementation error.

 State:          ESTABLISHED

 Event:          Delete FEC

 New State:      RELEASE_AWAITED

 Actions

   Send a LDP-WITHDRAW upstream.

 State:          ESTABLISHED

 Event:          Upstream Lost

 New State:      IDLE

 Actions

   Release the upstream label and delete the control block.

3.2.4.4.2 : State -- "RELEASE_AWAITED"

 State:          RELEASE_AWAITED

 Event:          Internal Downstream Mapping




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 New State:      RELEASE_AWAITED

 Actions

   Ignore the msg.

 State:          RELEASE_AWAITED

 Event:          LDP Release

 New State:      IDLE

 Actions

   Release the upstream label and delete the control block.

 State:          RELEASE_AWAITED

 Event:          Internal Downstream Withdraw

 New State:      RELEASE_AWAITED

 Actions

   Ignore the event.

 State:          RELEASE_AWAITED

 Event:          Resource Available

 New State:      RELEASE_AWAITED

 Actions

   Ignore the event. It is an internal implementation error.

 State:          RELEASE_AWAITED

 Event:          Delete FEC

 New State:      RELEASE_AWAITED

 Actions

   Do nothing.

 State:          RELEASE_AWAITED




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 Event:          Upstream Lost

 New State:      IDLE

 Actions

   Release the upstream label and delete the control block.

3.2.4.4.2 : State -- "RESOURCE_AWAITED"

 State:          RESOURCE_AWAITED

 Event:          Internal Downstream Mapping

 New State:      RESOURCE_AWAITED

 Actions

   Ignore the msg.

 State:          RESOURCE_AWAITED

 Event:          LDP Release

 New State:      RESOURCE_AWAITED

 Actions

   Ignore the msg. It is an internal implementation error.

 State:          RESOURCE_AWAITED

 Event:          Internal Downstream Withdraw

 New State:      IDLE

 Actions

   Delete the control block.

 State:          RESOURCE_AWAITED

 Event:          Resource Available

 New State:      ESTABLISHED

 Actions




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   Allocate an upstream label, connect the upstream label with the
   downstream label, and send LDP-MAPPING upstream.

 State:          RESOURCE_AWAITED

 Event:          Delete FEC

 New State:      IDLE

 Actions

   Delete the control block.

 State:          RESOURCE_AWAITED

 Event:          Upstream Lost

 New State:      IDLE

 Actions

   Delete the control block.


3.2.4.5  State of the Downstream_LSP_Control_Block's State Machine
              for Downstream Mode

   -- IDLE

   This is the initial LSP state.


   -- ESTABLISHED

   This state means that the LSR has received the LDP-MAPPING msg from
   the downstream LSR.

3.2.4.6 Events of the Downstream_LSP_Control_Block's State Machine
             for Downstream Mode

   -- LDP Mapping

   The LSR receives an LDP-MAPPING msg from a downstream LSR.

   -- LDP Withdraw

   The LSR receives an LDP-WITHDRAW msg from a downstream LSR.




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   -- Delete FEC

   The FEC is deleted from the forwarding table.

   -- Next Hop Change

   The next hop for this FEC is change to different LSR.

   -- Downstream Lost

   The downstream peer is gone.








































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3.2.4.7 State Transitions of Downstream_LSP_Control_Block's State
          Machine for Downstream Mode

                           |
                           |(FEC is being added into the forwarding
   table)
                           v
                  +-------------------+
                  |                   |
                  |  IDLE             |<--------------+
                  |                   |               |
                  +-------------------+               |
                           |                          |
                           |                          |(LDP Withdraw)
                           |                          |(Internal New NH)
                           |                          |(Downstream Lost)
                           |  (LDP Mapping)           |
                           |                          |
                           v                          |
                  +-------------------+               |
                  |                   |               |
                  |  ESTABLISHED      |---------------+
                  |                   |
                  +-------------------+
                           |
                           |(FEC is deleted from the forwarding table)
                           v

3.2.4.8 Downstream_LSP_Control_Block's State Machine
           for Downstream Mode

3.2.4.8.1 : State -- "IDLE"

 State:          IDLE

 Event:          LDP mapping

 New State:      ESTABLISHED

 Actions

   For all the LDP peers except the downstream LSR which assigned the
   label, create an Upstream_LSP_Control_Block, and pass the event
   `Internal Downstream Mapping' to each of the
   Upstream_LSP_Control_Block's state machines.

 State:          IDLE




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 Event:          LDP withdraw

 New State:      IDLE

 Actions
   Ignore the event. It is an internal implementation error.

 State:          IDLE

 Event:          Delete FEC

 New State:      IDLE

 Actions

   Delete the control block.

 State:          IDLE

 Event:          Next Hop Change

 New State:      IDLE

 Actions

   Ignore the event.

 State:          IDLE

 Event:          Downstream Lost

 New State:      IDLE

 Actions

   Ignore the event.

3.2.4.8.1 : State -- "ESTABLISHED"

 State:          ESTABLISHED

 Event:          LDP mapping

 New State:      ESTABLISHED

 Actions

 For each Upstream_LSP_control_block of this FEC, pass event `Internal



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 downstream mapping' to its state machine.

 State:          ESTABLISHED

 Event:          LDP withdraw

 New State:      IDLE

 Actions

   For each Upstream_LSP_control_block for this FEC, pass event
   `Internal downstream Withdraw' to its state machine.

   Send a LDP Withdraw downstream.

 State:          ESTABLISHED

 Event:          Delete FEC

 New State:      IDLE

 Actions

   Send LDP-RELEASE downstream and delete the control block.

   State:          ESTABLISHED

   Event:          Next Hop Change

   New State:      IDLE

   Actions

   For each Upstream_LSP_control_block for this FEC, pass event
   `Internal downstream Withdraw' to its state machine.

   Send LDP-REQUEST to the new next hop.

 State:          ESTABLISHED

 Event:          Downstream Lost

 New State:      IDLE

 Actions

   Send LDP-WITHDRAW to all Upstream_Control_Block's state machine of
   this FEC.



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3.2.4.5         LDP Related Message Processing for downstream mode.

 - If an LSR receives an LDP-REQUEST message:

   If there is a next hop for this FEC and there is a
   Downstream_Control_Block for this FEC whose state is 'ESTABLISHED',
   create a new Upstream_Control_Block and pass 'internal Mapping' event
   to its state machine.

 - If an LSR receives an LDP-MAPPING message:

   Locate a Downstream_LSP_Control_Block which has the same FEC, the
   same Downstream LDP Session Identifier and the same Downstream Label.
   If a Downstream_LSP_Control_Block is found, pass the event `LDP
   Mapping' to its state table. This could mean that the attributes of
   label binding have changed.

   Otherwise, if there is no matching Downstream_LSP_Control_Block
   found, find a Downstream_LSP_Control_Block of this FEC and its next
   hop is the this downstream peer, pass the event `LDP Mapping' to its
   state machine.

 -  If an LSR receives an LDP-RELEASE message:

   Locate an Upstream_LSP_Control_Block which has the same FEC, the same
   Upstream Label, the same Upstream LDP Session Identifier. If no
   Upstream_LSP_Control_Block is found, ignore the message. If an
   Upstream_LSP_Control_Block is found, send the event `LDP Release' to
   its state machine.


 -  If an LSR receives an LDP-WITHDRAW message:

   Find a Downstream_LSP_Control_Block which has the same FEC, the same
   Downstream LDP Session Identifier and the same Downstream Label. Pass
   the event `LDP Withdraw' to its state machines.

 -  If an Upstream LDP peer is lost:

   Pass the event `Upstream Lost' to the state machines of all the
   Upstream_LSP_Control_Blocks whose upstream LDP peer is that LSR.

 -  If a Downstream LDP peer is lost:

   Pass the event `Label Withdraw' to the state machines of all the
   Downstream_LSP_Control_Blocks whose the downstream LDP peer is that
   LSR.




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 -  If a next hop of an FEC is changed:

   Find all the Downstream_LSP_Control_Blocks which has the same FEC and
   the same next hop and pass the event `Next Hop Change' to their state
   machine

 - If there is a FEC being added to the forwarding table

   Create a new Downstream_LSP_Control_Block with state 'IDLE'

 - If the FEC is deleted from the forwarding table

   Send the 'Delete FEC' event to the its control block.

 - If an LSR receives an LDP-NAK from an  Upstream LSR:

   Ignore the msg. An LDP-NAK should never appear in the downstream-mode
   LSR

 -  If an LSR receives an LDP-NAK from a downstream LSR:

   Ignore the msg. It is an protocol error from the downstream LSR.

4. The Possible Future Works

   The following is a list of items that might need to be worked on in
   the future:

   1) Support senario such that: in a downstream-on-demand mode, a Label
   request contains multiple FEC items, whereas the corresponding Label
   Withdraw only withdraw one FEC item.

   2) The impact of loop detection, loop recovery and loop prevention

   3)Once the LSP is operational, whether the LSR can receive an LDP-NAK
   message is also debatable.

   4)In this draft, for the VC-merge case, the LDP-REQUEST message only
   goes up to the merge point. Whether the LDP-REQUEST need to go all
   the way to the egress and back in order for the path to be setup
   (brute force way) is debatable.

   5) Define all the necessary information for the control block.  For
   example, the ER-HOP list information used to re-build a Label Request
   in case of "local repair".

5. Security Considerations




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   Security considerations will be addressed in a future revision of
   this document.

6. Acknowledgements

   The authors would like to acknowledge the helpful comments and
   suggestions of the following people:

7. Authors's Address

   Liwen Wu

     Alcatel
     44983 Knoll Square
     Ashburn, VA. 20147
     U.S.A
     Phone: 703-724-2619
     Email:liwen.wu@adn.alcatel.com

   Pierrick Cheval

     Alcatel
     44983 Knoll Square
     Ashburn, VA. 20147
     U.S.A
     Phone: 703-724-2080
     Email: pierrick.cheval@adn.alcatel.com

   Christophe Boscher

     Alcatel CIT
     Le Mail
     44700 Nantes-Orvault
     France
     Phone: (33) 251781828
     Email: christophe.boscher@or.cit.alcatel.fr

   Eric Gray

     Lucent Technologies, Inc.
     1600 Osgood Street
     North Andover, MA 01845
     Email: ewgray@lucent.com


8. References

 1."Use of Label Switching With ATM", Bruce Davie, Jeremy Lawrence,



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 Keith McCloghrie, Yakov Rekhter, Eric Rosen, George Swallow, Paul
 Doolan, work in progress, Internet Draft, <draft-ietf-mpls-atm-01.txt>

 2."Multiprotocol Label Switching Architecture", Eric C Rosen, Arun
 Viswanathan, Ross Callon, work in progress, Internet Draft, <draft-
 ietf-mpls-arch-02.txt>

 3."Definition of Managed Objects for the Multiprotocol Label Switching,
 Label Distribution Protocol (LDP)", Joan Cucchiara, Hans Sjostrand,
 James V. Luciani, work in progress, Internet Draft, <draft-ietf-mpls-
 ldp-mib-00.txt>

 4."Requirements for Traffic Engineering Over MPLS", Daniel O.Awduche,
 Joe Malcolm, Johnson Agogbua, Mike O'Dell, Jim McMaus, work in
 progress,Internet Draft, <draft-ietf-mpls-traffic-eng-00.txt>

 5. "LDP Specification", Loa Andersson, Paul Doolan,Nancy Feldman, Andre
 Fredette, Bob Thomas, work in progress, Internet Draft, <draft-ietf-
 mpls-ldp-03.txt>

 6. "MPLS Loop Prevention Mechanism", Yoshihiro Ohba, Yasuhiro Katsube,
 Eric Rosen, Paul Doolan, work in progress, Internet Draft, <draft-
 ohba-mpls-loop-prevention-02.txt>




























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