One document matched: draft-wu-mpls-ldp-state-00.txt-83172.txt
MPLS Working Group Liwen Wu
Internet Draft Pierrick Cheval
Expiration Date: March 1999 Christophe Boscher
Alcatel USA
October 1998
LDP State Machine
draft-wu-mpls-ldp-state-00.txt
0. Status of this Memo
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1. Abstract
In the current LDP draft [Ref5], there is no state machine specified
for processing the hop-by-hop routed LDP messages. We think that
defining a common state machine is very important for
interoperability between different ldp implementations.
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 the state machine tables for ATM switch 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
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- LDP-MAPPING: LDP Label Mapping message
- LDP-WITHDRAW: LDP Label Withdraw message
- LDP-RELEASE: LDP Label Release message
- LDP-NAK: LDP notifications which related to Label mapping.
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.
As of today, there are two proposals for handling loop detection and
loop prevention, path vector[Ref5] and color scheme[Ref6], but there
has been no decision made on which one will be adopted as the
standard option. So the impact of loop detection and loop prevention
messages on a state machine 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 3 different ways:
1) It tries to do a "local repair". This means that it extends the
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) The LSR may also decide to tear down the whole LSP ("global
repair") in the case of next hop change. It sends an LDP-WITHDRAW
message upstream and an LDP-RELEASE message downstream.
3.1. ATM Switch LSR with NO VC-merge
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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].
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)
- Downstream Label Request ID (assigned by this LSR itself)
- Upstream LDP Session Identifier
- Downstream LDP Session Identifier
- State
- FEC
- Upstream Label(assigned by this LSR)
- Downstream Label(assigned by the downstream LSR)
- New Next Hop(NH) Behavior Flag, which can be:
-- "local repair" or
-- "pinned" or
-- "global repair"(which means
tear down the whole LSP)
- New NH Downstream LDP Session Identifier(used while
waiting for the new next hop label)
- New NH Downstream Label Request ID(used while
waiting for the new next hop label)
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, or
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- Downstream Label Request ID and Downstream LDP Session
Identifier
- New NH Downstream LDP Session Identifier and New
NH Downstream Label Request ID
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 an LDP-REQUEST from an
upstream LSR, has processed the LDP-REQUEST, and has sent a new LDP-
REQUEST towards a downstream LSR. And 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.
-- 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 sent an LDP-REQUEST towards the
new next hop and is waiting for the LDP-MAPPING message.
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.
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-- LDP Release
The LSR receives an LDP-RELEASE from an upstream LSR.
-- LDP Withdraw
The LSR receives an LDP-WITHDRAW from a downstream LSR.
-- Internal New NH
The LSR detects there is a new next hop for a FEC.
-- 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.
-- Internal Retry Timeout
The LSP retry timer expires.
-- 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.
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3.1.4 State Transitions
+-------------------+
| |
+-------->| IDLE |<--------------+
| | | |
| +-------------------+ |(LDP Release)
|(LDP Upstream Nak) | |(LDP Withdraw)
|(LDP DownstreamNak)|(LDP Request) |(LDP Upstream Nak?)
|(Downstream Lost) | |(LDP Downstream
| | | Nak?)
|(Upstream Lost) v |(Upstream Lost)
| +-------------------+ |(Downstream Lost)
| | | |
+---------| RESPONSE_AWAITED | |
| | |
+-------------------+ |
| |
|(LDP Mapping) |
| |
v |
+-------------------+ |
| | |
| ESTABLISHED |------------>--+
| |<--------------|---+
+-------------------+ | |
| | |
|(Internal New NH) | |
| | |
v | |
+-------------------+ | |
| | | |
|NEW_NH_RETRY | | |
| | | |
+-------------------+ | |
| | |
|(Internal retry timeout) | |
| ^ |
v | |
+-------------------+ | |
| |------------>--+ |
|NEW_NH_RESPONSE |-------------------+
| _AWAITED | (LDP Mapping)
+-------------------+
3.1.5 State Machine
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3.1.5.1 State -- "IDLE"
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.
State: IDLE
Event: LDP Release
New State: IDLE
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Actions:
Ignore the event.
State: IDLE
Event: LDP Withdraw
New State: IDLE
Actions:
Ignore the event.
State: IDLE
Event: Internal New NH
New State: IDLE
Actions:
Ignore the event.
State: IDLE
Event: LDP Upstream Nak
New State: IDLE
Actions:
Ignore the event.
State: IDLE
Event: LDP Downstream Nak
New State: IDLE
Actions:
Ignore the event.
State: IDLE
Event: Internal Retry Timeout
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New State: IDLE
Actions:
Ignore the event.
State: IDLE
Event: Upstream Lost
New State: IDLE
Actions:
Ignore the event.
State: IDLE
Event: Downstream Lost
New State: IDLE
Actions:
Ignore the event.
3.1.5.2 State -- "RESPONSE_AWAITED"
State: RESPONSE_AWAITED
Event: LDP Request
New State: RESPONSE_AWAITED
Actions:
Ignore the event.
State: RESPONSE_AWAITED
Event: LDP Mapping
New State: ESTABLISHED
Actions:
If the LSR uses the ordered control mode, choose an upstream label.
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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:
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.
State: RESPONSE_AWAITED
Event: Internal New Next Hop
New State: Depends on the action routine
Actions:
If the LSP is "pinned", ignore the event.
If a "local repair" is desired, send an LDP-REQUEST to the new next
hop, send an LDP-NAK to the old next hop and stay in
'RESPONSE_AWAITED' state.
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If a "global repair" is desired:
If the LSR uses the independent mode, send an LDP-WITHDRAW message
upstream.
If the LSR uses the ordered control mode, send an LDP-NAK message
upstream.
Send an LDP-NAK message downstream.
Delete the control block.
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: IDLE
Actions:
If the LSR uses the independent control mode, free the upstream label
and send an LDP-WITHDRAW message upstream.
If the LSR uses the ordered control mode, send an LDP-NAK message
upstream.
Then, delete the LSP_Control_Block.
State: RESPONSE_AWAITED
Event: Internal Retry Timeout
New State: RESPONSE_AWAITED
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Actions:
Ignore the event.
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: IDLE
Actions:
If the LSR uses the independent control mode, free the upstream label
and send an LDP-WITHDRAW upstream.
If the LSR uses the ordered control mode, send an LDP-NAK upstream.
Delete the LSP_Control_Block.
3.1.5.3 State --"ESTABLISHED"
State: ESTABLISHED
Event: LDP Request
New State: ESTABLISHED
Actions:
Ignore the event.
State: ESTABLISHED
Event: LDP Mapping
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New State: ESTABLISHED
Actions:
Process the LDP-MAPPING message, which may contain the new attributes
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.
Propagate the LDP-RELEASE message downstream and delete the
LSP_Control_Block.
State: ESTABLISHED
Event: LDP Withdraw
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Free the resources.
Propagate the LDP-WITHDRAW message upstream and delete the
LSP_Control_Block.
State: ESTABLISHED
Event: Internal New NH
New State: Depend on the action routine
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Actions:
If the LSP is "pinned", ignore the event.
Start the LSP retry timer and go to the 'NEW_NH_RETRY' state.
State: ESTABLISHED
Event: LDP Upstream Nak
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Propagate an LDP-RELEASE message downstream and delete the
LSP_Control_Block.
State: ESTABLISHED
Event: LDP Downstream Nak
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Free the resources.
Propagate an LDP-WITHDRAW message upstream and delete the
LSP_Control_Block.
State: ESTABLISHED
Event: Internal Retry Timeout
New State: ESTABLISHED
Actions:
Ignore the event.
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State: ESTABLISHED
Event: Upstream Lost
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Free the resources.
Propagate an LDP-RELEASE message downstream and delete the
LSP_Control_Block.
State: ESTABLISHED
Event: Downstream Lost
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Free the resources.
Propagate an LDP-WITHDRAW message upstream and delete the
LSP_Control_Block.
3.1.5.4 State -- "NEW_NH_RETRY"
State: NEW_NH_RETRY
Event: LDP Request
New State: NEW_NH_RETRY
Actions:
Ignore the event.
State: NEW_NH_RETRY
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Event: LDP Mapping
New State: NEW_NH_RETRY
Actions:
Process the LDP-MAPPING message, which may contain the new attributes
of the label binding and then propagate the LDP-MAPPING message
upstream.
State: NEW_NH_RETRY
Event: LDP Release
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Free the resources.
Propagate an LDP-RELEASE message to the old downstream next hop LSR.
Delete the LSP_Control_Block.
State: NEW_NH_RETRY
Event: LDP Withdraw
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Free the resources.
Propagate an LDP-WITHDRAW message upstream.
Delete the LSP_Control_Block.
State: NEW_NH_RETRY
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Event: Internal New NH
New State: NEW_NH_RETRY
Actions:
Restart the LSP retry timer.
State: NEW_NH_RETRY
Event: LDP Upstream Nak
New State: NEW_NH_RETRY
Actions:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Free the resources.
Propagate an LDP-RELEASE message to the old downstream next hop LSR.
Delete the LSP_Control_Block.
State: NEW_NH_RETRY
Event: LDP Downstream Nak
New State: NEW_NH_RETRY
Actions:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Free the resources.
Propagate an LDP-WITHDRAW message upstream.
Delete the LSP_Control_Block.
State: NEW_NH_RETRY
Event: Internal Retry Timeout
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New State: Depends on the action routine
Actions:
If the new next hop is the same one as the old next hop, go to the
state 'ESTABLISHED'.
Otherwise, if the new next hop is different than the old next hop:
If a "local repair" is desired, send an LDP-REQUEST to the new next
hop and go to the state 'NEW_NH_RESPONSE_AWAITED'.
If a "global repair" is desired, send an LDP-WITHDRAW upstream and
an LDP-RELEASE downstream, then delete the control block.
State: NEW_NH_RETRY
Event: Upstream Lost
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Free the resources.
Propagate an LDP-RELEASE message to the old downstream next hop LSR.
Delete the LSP_Control_Block.
State: NEW_NH_RETRY
Event: Downstream Lost
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Free the resources.
Propagate an LDP-WITHDRAW message upstream.
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Delete the LSP_Control_Block.
3.1.5.4 State -- "NEW_NH_RESPONSE_AWAITED"
State: NEW_NH_RESPONSE_AWAITED
Event: LDP Request
New State: NEW_NH_RESPONSE_AWAITED
Actions:
Ignore the event.
State: NEW_NH_RESPONSE_AWAITED
Event: LDP Mapping
New State: Depends on the action routine
Actions:
If the LDP-MAPPING message comes from the new next hop LSR:
Connect the upstream label to the new next hop downstream label.
Propagate the new LDP-MAPPING message upstream.
Send an LDP-RELEASE to the old next hop LSR and go to the state
'ESTABLISHED'.
If unable to process the message, send an LDP-NAK downstream,
restart the LSP retry timer,and go to the state 'NEW_NH_RETRY'.
If the LDP-MAPPING comes from the old next hop LSR,
Process the LDP-MAPPING message.
Propagate the LDP-MAPPING message upstream.
State: NEW_NH_RESPONSE_AWAITED
Event: LDP Release
New State: IDLE
Actions:
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Disconnect the upstream label from the downstream label.
Free the upstream label.
Release the resources.
Propagate an LDP-RELEASE message to the old next hop downstream LSR.
Send an LDP-NAK to the new next hop downstream LSR.
Delete the LSP_Control_Block.
State: NEW_NH_RESPONSE_AWAITED
Event: LDP Withdraw
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Propagate an LDP-WITHDRAW message upstream.
Send an LDP-NAK to the new next hop downstream LSR.
Delete the LSP_Control_Block.
State: NEW_NH_RESPONSE_AWAITED
Event: Internal New Next Hop
New State: NEW_NH_RETRY
Actions:
To avoid route flapping, send an LDP-NAK to the previous new next hop
LSR, restart the LSP retry timer, and go to the state 'NEW_NH_RETRY'.
State: NEW_NH_RESPONSE_AWAITED
Event: LDP Upstream Nak
New State: IDLE
Actions:
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Disconnect the upstream label from the downstream label.
Free the upstream label.
Free the resources.
Propagate an LDP-RELEASE message to the old next hop downstream LSR.
Send an LDP-NAK to the new next hop downstream LSR.
Delete the LSP_Control_Block.
State: NEW_NH_RESPONSE_AWAITED
Event: LDP Downstream Nak
New State: Depends on the action routine
Actions:
If the LDP-NAK comes from the old next hop LSR:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Free the resources.
Propagate an LDP-WITHDRAW message upstream.
Send an LDP-NAK to the new next hop downstream LSR.
Delete the LSP_Control_Block.
If the LDP-NAK comes from the new next hop LSR:
restart the LSP retry timer, and go to the state 'NEW_NH_RETRY'.
State: NEW_NH_RESPONSE_AWAITED
Event: Internal Retry Timeout
New State: NEW_NH_RESPONSE_AWAITED
Actions:
Ignore the event.
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State: NEW_NH_RESPONSE_AWAITED
Event: Upstream Lost
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Free the resources.
Propagate an LDP-RELEASE message to the old next hop downstream LSR.
Send an LDP-NAK to the new next hop downstream LSR.
Delete the LSP_Control_Block.
State: NEW_NH_RESPONSE_AWAITED
Event: Downstream Lost
New State: Depends on the action routine
Actions:
If the old next hop downstream LSR is lost:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Free the resources.
Propagate an LDP-WITHDRAW message upstream.
Send an LDP-NAK to the new next hop downstream LSR.
Delete the LSP_Control_Block.
If the new next hop downstream LSR is lost:
Restart the LSP retry timer, and go to the state 'NEW_NH_RETRY'.
3.1.6 LDP Related Message Handling
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- If an LSR receives an LDP-REQUEST from an upstream LSR:
a) 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 LDP Request ID value from the LDP-MAPPING message.
b) Find an LSP_Control_Block with the same Downstream Label Request
ID and the same Downstream LDP Session Identifier, or with the same
New NH Downstream Label Request ID and the same New NH Downstream LDP
Session Identifier.
c) If an LSP_Control_Block is found, pass the event `LDP Mapping' to
its state machine.
d) 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
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, or the same New NH
Downstream Label Request ID and the same New NH 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.
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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:
a) Find all the LSP_Control_Blocks which are affected by this next
hop change.
b) Pass the event `Internal New NH' to their state machines.
- 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.
- 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, or the
same New NH 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.
- If an LSP retry timer expires:
a) Pass the event 'Internal Retry Timeout' to its corresponding
LSP_Control_Block.
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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 2 types of control blocks involved:
Upstream_LSP_Control_Block, Downstream_LSP_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.
A Downstream_LSP_Control_Block contains a list of pointers to
Upstream_LSP_Control_Blocks. This means that this LSR has decided to
map the multiple labels listed in the Upstream_LSP_Control_Blocks
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
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- Upstream LDP Request ID (assigned by the Upstream LSR in
downstream-on-demand mode)
- New Next Hop Behavior Flag, which can be:
-- "local repair" or,
-- "pinned" or,
-- "global repair"
- New Next Hop Downstream_LSP_Control_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.
A Downstream_LSP_Control_Block may contain the following information:
- FEC
- State
- Downstream LDP Session Identifier
- list of pointers to the Upstream_LSP_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 |
| | |
| +------------------------------+
|
+---------------------+ |
| | |
| Upstream_LSP_Control| |
|_Block for Upstream |-------+
| LSR3 |
+---------------------+
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 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.
-- NEW_NH_RETRY
This is the state where an LSR waits for a retry timer to expire and
then tries to reestablish an LSP through a new next hop.
-- NEW_NH_RESPONSE_AWAITED
This is the state where an LSR is in middle of extending the LSP
through a new next hop. It has sent an LDP-REQUEST towards the new
next hop and is waiting for the LDP-MAPPING message.
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.
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-- Internal New NH
The LSR detects there is a new next hop for a FEC.
-- LDP Upstream Nak
The LSR receives an LDP-NAK from an upstream LSR.
-- Internal Retry Timeout
The LSP retry timer expires.
-- 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.
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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
| | Nak ??)
|(Internal Downstream |
| mapping) |(LDP Release)
| |(Internal Downstream
v | Withdraw)
+-------------------+ |
| | |(LDP Upstream Nak?)
| ESTABLISHED |------->-----^
| |<--------- |
+-------------------+ | |
| | |
|(Internal New NH) | |
| | |
v | |
+-------------------+ | |
| | | |
| NEW_NH_RETRY |----->---|---^
| | | |
+-------------------+ | |
| | |
|(Internal Retry | |
| Timeout) | |
| | |
v | |
+-------------------+ | |
| |----->---|---^
|NEW_NH_RESPONSE |---------+
| _AWAITED | (LDP mapping)
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+-------------------+
3.2.3.4 Upstream_LSP_Control_Block's State Machine
for Downstream-on-demand Mode
3.2.3.4.1 State -- "IDLE"
State: IDLE
Event: LDP Request
New State: Depends upon the action routine.
Actions:
If this LSR is the LSP Egress or Proxy Egress [Ref2], 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'.
Otherwise, choose a next hop. 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
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New State: IDLE
Actions:
Ignore the event.
State: IDLE
Event: LDP Release
New State: IDLE
Actions:
Ignore the event.
State: IDLE
Event: Internal Downstream Withdraw
New State: IDLE
Actions:
Ignore the event.
State: IDLE
Event: Internal New NH
New State: IDLE
Actions:
Ignore the event.
State: IDLE
Event: LDP Upstream Nak
New State: IDLE
Actions:
Ignore the event.
State: IDLE
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Event: Internal Retry Timeout
New State: IDLE
Actions:
Ignore the event.
State: IDLE
Event: Internal Downstream Nak
New State: IDLE
Actions:
Ignore the event
State: IDLE
Event: Upstream Lost
New State: IDLE
Actions:
Ignore the event.
3.2.3.4.2 State -- "RESPONSE_AWAITED"
State: RESPONSE_AWAITED
Event: LDP Request
New State: RESPONSE_AWAITED
Actions:
Ignore the event.
State: RESPONSE_AWAITED
Event: Internal Downstream Mapping
New State: Depends on the action routine
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Actions:
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: IDLE
Actions
If the LSR uses the independent control mode, release the upstream
label and other resources.
Send the event "DeleteUpstream" to the state machine of its
Downstream_LSP_Control_Block.
State: RESPONSE_AWAITED
Event: Internal Downstream Withdraw
New State: IDLE
Actions
Ignore the event.
State: RESPONSE_AWAITED
Event: Internal New NH
New State: Depends on the action routine
Actions
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If the LSP is "pinned", ignore the event.
If a "local repair" is desired, send an LDP-REQUEST to the new next
hop, send an LDP-NAK to the old next hop and stay in
'RESPONSE_AWAITED' state.
Otherwise, if a "global repair" is desired, send an LDP-RELEASE
downstream. Pass the event `Internal DeleteUpstream' to the state
machine of its Downstream_LSP_Control_Block. Then delete the control
block.
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.
State: RESPONSE_AWAITED
Event: Internal Retry Timeout
New State: RESPONSE_AWAITED
Actions
Ignore the event.
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.
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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.
3.2.3.4.3 State -- "ESTABLISHED"
State: ESTABLISHED
Event: LDP Request
New State: ESTABLISHED
Actions
Ignore the event.
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
Event: LDP Release
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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.
Delete the control block.
State: ESTABLISHED
Event: Internal Downstream Withdraw
New State: IDLE
Actions
Disconnect the upstream label from the downstream label, free the
upstream label and resources.
Propagate the LDP-WITHDRAW upstream.
Delete the control block.
State: ESTABLISHED
Event: Internal New NH
New State: Depends on the action routine
Actions
If the LSP is "pinned", ignore the event.
Otherwise, start the LSP retry timer and go to the state
'NEW_NH_RETRY'.
State: ESTABLISHED
Event: LDP Upstream Nak
New State: IDLE
Actions
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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.
Delete the control block.
State: ESTABLISHED
Event: Internal Retry Timeout
New State: IDLE
Actions
Ignore the event.
State: ESTABLISHED
Event: Internal Downstream Nak
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label, free the
upstream label and the resources.
Send an LDP-WITHDRAW upstream.
Delete the control block.
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.
Delete the control block.
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3.2.3.4.1 State -- "NEW_NH_RETRY"
State: NEW_NH_RETRY
Event: LDP Request
New State: NEW_NH_RETRY
Actions
Ignore the event.
State: NEW_NH_RETRY
Event: Internal Downstream Mapping
New State: NEW_NH_RETRY
Actions
Process the new attributes of the mapping and then propagate the
LDP-MAPPING message upstream.
State: NEW_NH_RETRY
Event: LDP Release
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 old next hop's
Downstream_LSP_Control_Block's state machine.
Delete the control block.
State: NEW_NH_RETRY
Event: Internal Downstream Withdraw
New State: IDLE
Actions
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Disconnect the upstream label from the downstream label, free the
upstream label and the resources.
Delete the control block.
State: NEW_NH_RETRY
Event: Internal New NH
New State: NEW_NH_RETRY
Actions
Ignore the event.
State: NEW_NH_RETRY
Event: LDP Upstream NAK
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 old(actual) next
hop's Downstream_LSP_Control_Block's state machine.
Delete the control block.
State: NEW_NH_RETRY
Event: Internal Retry Timeout
New State: NEW_NH_RESPONSE_AWAITED
Actions
If a "local repair" is desired:
Choose a next hop. Find a Downstream_LSP_Control_Block which has
the same FEC and the same next hop and which is able to merge more
input labels. If not found, create a new
Downstream_LSP_Control_Block and set its state to 'IDLE'.
If the state of the Downstream_LSP_Control_Block is `ESTABLISHED',
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connect the old upstream lable with the new downstream label, send
an LDP-RELEASE message to the old next hop downstream LSR and go to
the State `ESTABLISHED. Otherwise, go to the State
'NEW_NH_RESPONSE_AWAITED'.
Pass the event `Internal AddUpstream' to the new next hop's
Downstream_LSP_Control_Block's state machine.
Set the new next hop Downstream_LSP_Control_Block pointer with the
correct value.
If a "global repair" is desired:
Send an LDP-WITHDRAW message upstream and an LDP-RELEASE message
downstream.
Delete the control block.
State: NEW_NH_RETRY
Event: Internal Downstream Nak
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label, free the
upstream label and the resources.
Delete the control block.
State: NEW_NH_RETRY
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 old next hop's
Downstream_LSP_Control_Block's state machine.
Delete the control block.
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3.2.3.4.1 State -- "NEW_NH_RESPONSE_AWAITED"
State: NEW_NH_RESPONSE_AWAITED
Event: LDP Request
New State: NEW_NH_RESPONSE_AWAITED
Actions:
Ignore the event.
State: NEW_NH_RESPONSE_AWAITED
Event: Internal Downstream Mapping
New State: ESTABLISHED
Actions:
If the LDP-MAPPING comes from the new next hop LSR, then:
Connect the old upstream label to the new downstream label.
Send the LDP-MAPPING message upstream.
Send the event 'Internal DeleteUpstream' to its old next hop's
Downstream_LSP_Control_Block's state machine.
Set the Downstream_LSP_Control_Block pointer to the new next hop's
Downstream_LSP_Control_Block.
else if the LDP-MAPPING message comes from the old next hop LSR:
Process the new attributes of the LDP-MAPPING message.
Propagate the LDP-MAPPING upstream
State: NEW_NH_RESPONSE_AWAITED
Event: LDP Release
New State: IDLE
Actions
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Disconnect the upstream label from the downstream label and free the
upstream label and the resources.
Send the event 'Internal DeleteUpstream' to both old and new next
hop's Downstream_LSP_Control_Block's state machine.
Delete the control block.
State: NEW_NH_RESPONSE_AWAITED
Event: Internal Downstream Withdraw
New State: IDLE
Actions
If the LDP-WITHDRAW messages comes from the old next hop LSR:
Disconnect the upstream label from the downstream label and free
the upstream label and the resources.
Send the event 'Internal DeleteUpstream' to both the new next hop's
Downstream_LSP_Control_Block's state machine
Delete the control block.
If the LDP-WITHDRAW messages comes from the new next hop LSR:
Restart the LSP retry timer, and go to the state 'NEW_NH_RETRY'.
State: NEW_NH_RESPONSE_AWAITED
Event: Internal New NH
New State: NEW_NH_RETRY
Actions
Send the event 'Internal DeleteUpstream' to its new next hop's
Downstream_LSP_Control_Block's state machine.
Retart the LSP retry timer and go to the state 'NEW_NH_RETRY'
State: NEW_NH_RESPONSE_AWAITED
Event: LDP Upstream Nak
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New State: IDLE
Actions
Disconnect the upstream label from the downstream label and free the
upstream label and the resources.
Send the event 'Internal DeleteUpstream' to both old and new next
hop's Downstream_LSP_Control_Block's state machine.
Delete the control block.
State: NEW_NH_RESPONSE_AWAITED
Event: Internal retry timeout
New State: NEW_NH_RESPONSE_AWAITED
Actions
Ignore the event.
State: NEW_NH_RESPONSE_AWAITED
Event: Internal Downstream Nak
New State: Depends on the action routine
Actions:
If the message is caused by the old next hop LSR:
Disconnect the upstream label from the downstream label and free
the upstream label and the resources.
Send the event 'Internal DeleteUpstream' to both old and new next
hop's Downstream_LSP_Control_Block's state machine.
Delete the control block.
If the message is caused by the new next hop LSR:
Restart the LSP retry timer, and go to the state 'NEW_NH_RETRY'.
State: NEW_NH_RESPONSE_AWAITED
Event: Upstream Lost
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New State: IDLE
Actions
Disconnect the upstream label from the downstream label and free the
upstream label and the resources.
Send the event 'Internal DeleteUpstream' to both old and new next
hop's Downstream_LSP_Control_Block's state machine.
Delete the control block.
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.
-- Internal DeleteUpstream
This event is sent by an Upstream_LSP_Control_Block's state machine
when it is deleted.
-- LDP Mapping
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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.
State: IDLE
Event: LDP Mapping
New State: IDLE
Actions
Ignore the event.
State: IDLE
Event: LDP Withdraw
New State: IDLE
Actions
Ignore the event.
State: IDLE
Event: LDP Downstream Nak
New State: IDLE
Actions
Ignore the event.
State: IDLE
Event: Downstream Lost
New State: IDLE
Actions
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Ignore the event.
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.
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
New State: Depends on the action routine
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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: 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.
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3.2.4 Downstream
The following sections describe the state machines for the ATM-LSR
which uses downstream 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.
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.
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. 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.
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3.2.4.3 State Transitions of Upstream_LSP_Control_Block's State
Machine for Downstream Mode
+-------------------+
| |
| IDLE |<--------------+
| | |
+-------------------+ |
| |(LDP Release)
| |(LDP Downstream
| | Withdraw)
| |
|(Internal Downstream |
| Mapping) |
| |
v |
+-------------------+ |
| | |
| ESTABLISHED |---------------+
| |
+-------------------+
3.2.4.4 Upstream_LSP_Control_Block's State Machine for
Downstream Mode
3.2.4.4.1 : State -- "IDLE"
State: IDLE
Event: Internal Downstream mapping
New State: ESTABLISHED
Actions
Choose an upstream label, connect the upstream label with the
downstream label.
Propagate the LDP-MAPPING upstream.
State: IDLE
Event: LDP Release
New State: IDLE
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Actions
Ignore the event.
State: IDLE
Event: Internal Downstream Withdraw
New State: IDLE
Actions
Ignore the event.
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.
Get Downstream_LSP_control_block from UPstream_LSP_control_block,
pass the event `Internal DeleteUpstream' to its state machine.
State: ESTABLISHED
Event: Internal Downstream Withdraw
New State: IDLE
Actions
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Disconnect upstream label from downstream label.
Propagate the LDP-WITHDRAW upstream.
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 and the LSP is up and operational.
3.2.4.6 Events of the Downstream_LSP_Control_Block's State Machine
for Downstream Mode
-- Internal DeleteUpstream
This event is sent by an Upstream_LSP_Control_Block's state machine
when it is created.
-- 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.
-- Internal New NH
The LSR detects there is a new next hop for an FEC.
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3.2.4.7 State Transitions of Downstream_LSP_Control_Block's State
Machine for Downstream Mode
+-------------------+
| |
| IDLE |<--------------+
| | |
+-------------------+ |(last Internal
| | DeleteUpstream)
| |(LDP Withdraw)
| |(Internal New NH)
| |
| (LDP Mapping) |
| |
v |
+-------------------+ |
| | |
| ESTABLISHED |---------------+
| |
+-------------------+
3.2.4.8 Downstream_LSP_Control_Block's State Machine
for Downstream Mode
3.2.4.8.1 : State -- "IDLE"
State: IDLE
Event: Internal DeleteUpstream
New State: IDLE
Actions
Ignore the event.
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, chain them together into
the Upstream_LSP_Control_Block pointer list of the
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Downstream_LSP_Control_Block and pass the event `Internal Downstream
Mapping' to each of the Upstream_LSP_Control_Block's state machines.
State: IDLE
Event: LDP withdraw
New State: IDLE
Actions
ignore the event.
State: IDLE
Event: Internal New NH
New State: IDLE
Actions
ignore the event.
3.2.4.8.1 : State -- "ESTABLISHED"
State: ESTABLISHED
Event: Internal DeleteUpstream
New State: depend on the action routine
Actions
Delete the Upstream LSP_control_block from the
Upstream_LSP_control_block pointer list.
If the list becomes empty, propagate LDP-RELEASE to downstream LSR
and delete the control block.
State: ESTABLISHED
Event: LDP mapping
New State: ESTABLISHED
Actions
For each Upstream_LSP_control_block in UPstream_LSP_control_block
pointer list, pass event `Internal downstream mapping' to its state
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machine.
State: ESTABLISHED
Event: LDP withdraw
New State: IDLE
Actions
For each Upstream_LSP_control_block in UPstream_LSP_control_block
pointer list, pass event `Internal downstream Withdraw' to its state
machine.
delete the control block.
State: ESTABLISHED
Event: Internal New NH
New State: IDLE
Actions
For each Upstream_LSP_control_block in UPstream_LSP_control_block
pointer list, pass event `Internal downstream Withdraw' to its state
machine.
Send LDP-REQUEST to downstream LSR (RequestWhenNeeded behavior).
delete control block.
3.2.5 LDP Related Message Processing
- If an LSR receives an LDP-REQUEST message:
If the LSR uses the downstream mode, ignore the message.
If the LSR uses the downstream-on-demand, 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
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label binding have changed.
Otherwise, if it is downstream mode, and if there is no matching
Downstream_LSP_Control_Block found, and the downstream LSR is the
next hop of the FEC listed in the LDP-MAPPING message (ordered mode),
create a new Downstream_LSP_Control_Block and pass the event `LDP
Mapping' to its state machine.
If it is downstream-on-demand mode, use the Downstream LDP request ID
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
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:
If it is downstream mode, find all the Downstream_LSP_Control_Blocks
which has the same FEC and the same next hop and pass the event
`Internal New NH' to their state machine
If it is downstream-on-demand mode, find all the
Upstream_LSP_Control_Blocks which are infected by this change, pass
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the event 'Internal New NH' to their state machines.
- If an LSR receives an LDP-NAK from an Upstream LSR:
If it is downstream mode, ignore the msg. An LDP-NAK should never
appear in the downstream-mode LSR
If it is downstream-on-demand mode, 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:
If it is using downstream mode, ignore the msg.
If it is downstream-on-demand mode, 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.
4. The Possible Future Works
The following is a list of items that might need to be worked on in
the future:
1)Throughout the state machines in this document, the action 'ignore
the event' needs to be further classified whether it is 1) a protocol
error, or 2) an internal implementation error, or 3) other for
interworking purpose.
2)In the Downstream-on-Demand and Ordered LSP Control mode, some
timers may be needed to protect the lost of LDP messages. For
example, if an LSR has sent an LDP-REQUEST downstream, but the LDP-
MAPPING is lost (??is it possible) on its way back, in this case, the
LSR may want to use a timer to recover from this situation.
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.
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5. Security Considerations
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: Mary Sue Mangan, Steve
Silverman, Gerard Gobillard.
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
8. References
1."Use of Label Switching With ATM", Bruce Davie, Jeremy Lawrence,
Keith McCloghrie, Yokov Rekhter, Eric Rosen, George Swallow, Paul
Doolan, work in progress, Internet Draft, <draft-davie-mpls-atm-01.txt>
2."Multiprotocol Label Switching Architecture", Eric C Rosen, Arun
Viswanathan, Ross Callon, work in progress, Internet Draft, <draft-
Wu, Cheval, Boscher [Page 61]
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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-awduche-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-01.txt>
6. "MPLS Loop Prevention Mechanism", Yoshihiro Ohba, Yasuhiro Katsube,
Eric Rosen, Paul Doolan, work in progress, Internet Draft, <draft-
ohba-mpls-loop-prevention-01.txt>
Wu, Cheval, Boscher [Page 62]
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