draft-ietf-mpls-tp-shared-ring-protection-03.txt   draft-ietf-mpls-tp-shared-ring-protection-04.txt 
Network Working Group W. Cheng Network Working Group W. Cheng
Internet-Draft L. Wang Internet-Draft L. Wang
Intended status: Standards Track H. Li Intended status: Standards Track H. Li
Expires: April 2, 2017 China Mobile Expires: June 16, 2017 China Mobile
H. Helvoort H. Helvoort
Hai Gaoming BV Hai Gaoming BV
J. Dong J. Dong
Huawei Technologies Huawei Technologies
September 29, 2016 December 13, 2016
Shared-Ring protection (MSRP) mechanism for ring topology Shared-Ring protection (MSRP) mechanism for ring topology
draft-ietf-mpls-tp-shared-ring-protection-03 draft-ietf-mpls-tp-shared-ring-protection-04
Abstract Abstract
This document describes requirements, architecture and solutions for This document describes requirements, architecture and solutions for
MPLS-TP Shared Ring Protection (MSRP) in a ring topology for point- MPLS-TP Shared Ring Protection (MSRP) in a ring topology for point-
to-point (P2P) services. The MSRP mechanism is described to meet the to-point (P2P) services. The MSRP mechanism is described to meet the
ring protection requirements as described in RFC 5654. This document ring protection requirements as described in RFC 5654. This document
defines the Ring Protection Switch (RPS) Protocol that is used to defines the Ring Protection Switch (RPS) Protocol that is used to
coordinate the protection behavior of the nodes on MPLS ring. coordinate the protection behavior of the nodes on MPLS ring.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 2, 2017. This Internet-Draft will expire on June 16, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
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level survivability function in these topologies. In operational level survivability function in these topologies. In operational
transport network deployment, MPLS-TP networks are often constructed transport network deployment, MPLS-TP networks are often constructed
using ring topologies. This calls for an efficient and optimized using ring topologies. This calls for an efficient and optimized
ring protection mechanism to achieve simple operation and fast, sub ring protection mechanism to achieve simple operation and fast, sub
50 ms, recovery performance. 50 ms, recovery performance.
This document specifies an MPLS-TP Shared-Ring Protection mechanisms This document specifies an MPLS-TP Shared-Ring Protection mechanisms
that meets the criteria for ring protection and the ring protection that meets the criteria for ring protection and the ring protection
requirements described in section 2.5.6.1 of [RFC5654]. requirements described in section 2.5.6.1 of [RFC5654].
The basic concept and architecture of Shared-Ring protection The basic concept and architecture of the Shared-Ring protection
mechanism are specified in this document. This document describes mechanism are specified in this document. This document describes
the solutions for point-to-point transport paths. While the basic the solutions for point-to-point transport paths. While the basic
concept may also apply to point-to-multipoint transport paths, the concept may also apply to point-to-multipoint transport paths, the
solution for point-to-multipoint transport paths is out of the scope solution for point-to-multipoint transport paths is out of the scope
of this document. of this document.
2. Terminology and Notation 2. Terminology and Notation
Terminology: Terminology:
Ring Node: A ring node is a node in the ring topology that actively Ring Node: All nodes in the ring topology are Ring Nodes and they
participates in the ring protection. MUST actively participate in the ring protection.
Ring tunnel: A ring tunnel provides a server layer for the LSPs Ring tunnel: A ring tunnel provides a server layer for the LSPs
traverse the ring. The notation for ring tunnel is: xxxx R<d><P>_<x> traversing the ring. The notation used for a ring tunnel is:
where <d> = c (clockwise) or a (anticlockwise), <P> = W (working) or R<d><p><X> where <d> = c (clockwise) or a (anticlockwise), <p> = W
P (protecting), and <x> the node name. (working) or P (protecting), and <X> = the node name.
Ring map: A ring map is present in each ring-node. The ring-map Ring map: A ring map is present in each ring-node. The ring-map
contains the ring topology information, i.e. the nodes in the ring, contains the ring topology information, i.e. the nodes in the ring,
the adjacency of the ring-nodes and the status of the links between the adjacency of the ring-nodes and the status of the links between
ring-nodes (Intact or Severed) and for each protected LSP at which ring-nodes (Intact or Severed) and for each protected LSP at which
node it enters and leaves the ring. The ring map is used by every node it enters and leaves the ring. The ring map is used by every
ring node to determine the switchover behavior of the ring tunnels. ring node to determine the switchover behavior of the ring tunnels.
Notation: Notation:
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label stack: label stack:
1. The label stack will be enclosed in square brackets ("[]"). 1. The label stack will be enclosed in square brackets ("[]").
2. Each level in the stack will be separated by the '|' character. 2. Each level in the stack will be separated by the '|' character.
It should be noted that the label stack may contain additional It should be noted that the label stack may contain additional
layers. However, we only present the layers that are related to the layers. However, we only present the layers that are related to the
protection mechanism. protection mechanism.
3. If the Label is assigned by Node X, the Node Name is enclosed in 3. If the Label is assigned by Node X, the Node Name is enclosed in
bracket ("()") parentheses ("()").
3. MPLS-TP Ring Protection Criteria and Requirements 3. MPLS-TP Ring Protection Criteria and Requirements
The generic requirements for MPLS-TP protection are specified in The generic requirements for MPLS-TP protection are specified in
[RFC5654]. The requirements specific for ring protection are [RFC5654]. The requirements specific for ring protection are
specified in section 2.5.6.1 of [RFC5654]. This section describes specified in section 2.5.6.1 of [RFC5654]. This section describes
how the criteria for ring protection are met: how the criteria for ring protection are met:
a. The number of OAM entities needed to trigger protection a. The number of OAM entities needed to trigger protection
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Each ring-node requires only one instance of the RPS protocol and is Each ring-node requires only one instance of the RPS protocol and is
independent of the number of LSPs that are protected. independent of the number of LSPs that are protected.
c. The required number of labels required for the protection paths c. The required number of labels required for the protection paths
The RPS protocol uses ring tunnels and each tunnel has a set of The RPS protocol uses ring tunnels and each tunnel has a set of
labels. The number of ring tunnel labels is related to the number of labels. The number of ring tunnel labels is related to the number of
ring-nodes and is independent of the number of protected LSPs. ring-nodes and is independent of the number of protected LSPs.
d. The amount of control and management-plane transactions d. The amount of control and management-plane transactions
Each ring-node requires only one instance of the RPS protocol this Each ring-node requires only one instance of the RPS protocol. This
means that only one maintenance operation is required per ring-node. means that only one maintenance operation is required per ring-node.
e. Minimize the signaling and routing information exchange during e. Minimize the signaling and routing information exchange during
protection protection
Information exchange during a protection switch is using the in-band Information exchange during a protection switch is using the in-band
RPS and OAM messages. No control plane interactions are required. RPS and OAM messages. No control plane interactions are required.
4. Shared Ring Protection Architecture 4. Shared Ring Protection Architecture
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o one clockwise working ring tunnel, which is protected by the o one clockwise working ring tunnel, which is protected by the
anticlockwise protection ring tunnel anticlockwise protection ring tunnel
o one anticlockwise protection ring tunnel o one anticlockwise protection ring tunnel
o one anticlockwise working ring tunnel, which is protected by the o one anticlockwise working ring tunnel, which is protected by the
clockwise protection ring tunnel clockwise protection ring tunnel
o one clockwise protection ring tunnel o one clockwise protection ring tunnel
The structure of the protection tunnels are determined by the The structure of the protection tunnels is determined by the selected
selected protection mechanism. This will be detailed in subsequent protection mechanism. This will be detailed in subsequent sections.
sections.
As shown in Figure 3, LSP1, LSP2 and LSP3 enter the ring from Node E, As shown in Figure 3, LSP1, LSP2 and LSP3 enter the ring from Node E,
Node A and Node B respectively, and all leave the ring at Node D. To Node A and Node B respectively, and all leave the ring at Node D. To
protect these LSPs that traverse the ring, a clockwise working ring protect these LSPs that traverse the ring, a clockwise working ring
tunnel (RcW_D) via E->F->A->B->C->D, and its anticlockwise protection tunnel (RcW_D) via E->F->A->B->C->D, and its anticlockwise protection
ring tunnel (RaP_D) via D->C->B->A->F->E->D are established, Also, an ring tunnel (RaP_D) via D->C->B->A->F->E->D are established, Also, an
anti-clockwise working ring tunnel (RaW_D) via C->B->A->F->E->D, and anti-clockwise working ring tunnel (RaW_D) via C->B->A->F->E->D, and
its clockwise protection ring tunnel (RcP_D) via D->E->F->A->B->C->D its clockwise protection ring tunnel (RcP_D) via D->E->F->A->B->C->D
are established. For simplicity Figure 3 only shows RcW_D and RaP_D. are established. For simplicity Figure 3 only shows RcW_D and RaP_D.
A similar provisioning should be applied for any other node on the A similar provisioning should be applied for any other node on the
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the next hop. The transit nodes on the working ring tunnel swap the the next hop. The transit nodes on the working ring tunnel swap the
ring tunnel labels and forward the packets to the next hop. When the ring tunnel labels and forward the packets to the next hop. When the
packet arrives at the egress node, the egress node pops the ring packet arrives at the egress node, the egress node pops the ring
tunnel label and forwards the packets based on the inner LSP label tunnel label and forwards the packets based on the inner LSP label
and PW label. Figure 4 shows the label operation in the MPLS-TP and PW label. Figure 4 shows the label operation in the MPLS-TP
shared ring protection mechanism. Assume that LSP1 enters the ring shared ring protection mechanism. Assume that LSP1 enters the ring
at Node A and exits from Node D, and the following label operations at Node A and exits from Node D, and the following label operations
are executed. are executed.
1. Ingress node: Packets of LSP1 arrive at Node A with a label stack 1. Ingress node: Packets of LSP1 arrive at Node A with a label stack
[LSP1] and is supposed to be forwarded in the clockwise direction [LSP1] and are supposed to be forwarded in the clockwise
of the ring. The clockwise working ring tunnel label RcW_D will direction of the ring. The clockwise working ring tunnel label
be pushed at Node A, the label stack for the forwarded packet at RcW_D will be pushed at Node A, the label stack for the forwarded
Node A is changed to [RcW_D(B)|LSP1]. packet at Node A is changed to [RcW_D(B)|LSP1].
2. Transit nodes: In this case, Node B and Node C forward the 2. Transit nodes: In this case, Node B and Node C forward the
packets by swapping the working ring tunnel labels. For example, packets by swapping the working ring tunnel labels. For example,
the label [RcW_D(B)|LSP1] is swapped to [RcW_D(C)|LSP1] at Node the label [RcW_D(B)|LSP1] is swapped to [RcW_D(C)|LSP1] at Node
B. B.
3. Egress node: When the packet arrives at Node D (i.e. the egress 3. Egress node: When the packet arrives at Node D (i.e. the egress
node) with label stack [RcW_D(D)|LSP1], Node D pops RcW_D(D), and node) with label stack [RcW_D(D)|LSP1], Node D pops RcW_D(D), and
subsequently deals with the inner labels of LSP1. subsequently deals with the inner labels of LSP1.
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general, the description uses the clockwise working ring tunnel and general, the description uses the clockwise working ring tunnel and
the corresponding anti-clockwise protection ring tunnel as an the corresponding anti-clockwise protection ring tunnel as an
example, but the mechanism is applicable in the same way to the anti- example, but the mechanism is applicable in the same way to the anti-
clockwise working and clockwise protection ring tunnels. clockwise working and clockwise protection ring tunnels.
In a ring network, each working ring tunnel is associated with a In a ring network, each working ring tunnel is associated with a
protection ring tunnel in the opposite direction, and every node MUST protection ring tunnel in the opposite direction, and every node MUST
obtain the ring topology either by configuration or via a topology obtain the ring topology either by configuration or via a topology
discovery mechanism. The ring topology and the connectivity (Intact discovery mechanism. The ring topology and the connectivity (Intact
or Severed) between two adjacent ring nodes form the ring map. Each or Severed) between two adjacent ring nodes form the ring map. Each
ring node maintains the ring map and use it to perform ring ring node maintains the ring map and uses it to perform ring
protection. protection switching.
Taking the topology in Figure 4 as an example, LSP1 enters the ring Taking the topology in Figure 4 as an example, LSP1 enters the ring
at Node A and leaves the ring at Node D. In normal state, LSP1 is at Node A and leaves the ring at Node D. In normal state, LSP1 is
carried by the clockwise working ring tunnel (RcW_D) through the path carried by the clockwise working ring tunnel (RcW_D) through the path
A->B->C->D. The label operation is: A->B->C->D. The label operation is:
[LSP1](Payload) -> [RCW_D(B)|LSP1](NodeA) -> [RCW_D(C)|LSP1](NodeB) [LSP1](Payload) -> [RCW_D(B)|LSP1](NodeA) -> [RCW_D(C)|LSP1](NodeB)
-> [RCW_D(D)| LSP1](NodeC) -> [LSP1](Payload). Then at node D the -> [RCW_D(D)| LSP1](NodeC) -> [LSP1](Payload).
packet will be forwarded based on the label stack of LSP1.
Then at node D the packet will be forwarded based on the label stack
of LSP1.
Three typical ring protection mechanisms are described in this Three typical ring protection mechanisms are described in this
section: wrapping, short wrapping and steering. All nodes on the section: wrapping, short wrapping and steering. All nodes on the
same ring MUST use the same protection mechanism. same ring MUST use the same protection mechanism.
Wrapping ring protection: the node which detects a failure or accepts Wrapping ring protection: the node which detects a failure or accepts
a switch request switches the traffic impacted by the failure or the a switch request switches the traffic impacted by the failure or the
switch request to the opposite direction (away from the failure). In switch request to the opposite direction (away from the failure). In
this way, the impacted traffic is switched to the protection ring this way, the impacted traffic is switched to the protection ring
tunnel by the switching node upstream of the failure, then travels tunnel by the switching node upstream of the failure, then travels
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Short wrapping ring protection provides some optimization to wrapping Short wrapping ring protection provides some optimization to wrapping
protection, in which the impacted traffic is only switched once to protection, in which the impacted traffic is only switched once to
the protection ring tunnel by the switching node upstream to the the protection ring tunnel by the switching node upstream to the
failure. At the egress node, the traffic leave the ring from the failure. At the egress node, the traffic leave the ring from the
protection ring tunnel. This can reduce the traffic detour of protection ring tunnel. This can reduce the traffic detour of
wrapping protection. wrapping protection.
Steering ring protection implies that the node that detects a failure Steering ring protection implies that the node that detects a failure
sends a request along the ring to the other node adjacent to the sends a request along the ring to the other node adjacent to the
failure, and all nodes in the ring process this information. For the failure, and all nodes in the ring process this information. For the
impaced traffic, the ingress node (which adds traffic to the ring) impacted traffic, the ingress node (which adds traffic to the ring)
perform switching of the traffic from working to the protection ring performs switching of the traffic from working to the protection ring
tunnel, and the egress node will drop the traffic received from the tunnel, and the egress node will drop the traffic received from the
protection ring tunnel. protection ring tunnel.
The following sections describes these protection mechanisms in The following sections describe these protection mechanisms in
detail. detail.
4.3.1. Wrapping 4.3.1. Wrapping
With the wrapping mechanism, the protection ring tunnel is a closed With the wrapping mechanism, the protection ring tunnel is a closed
ring identified by the egress node. As shown in Figure 4, the RaP_D ring identified by the egress node. As shown in Figure 4, the RaP_D
is the anticlockwise protection ring tunnel for the clockwise working is the anticlockwise protection ring tunnel for the clockwise working
ring tunnel RcW_D. As specified in the following sections, the ring tunnel RcW_D. As specified in the following sections, the
closed ring protection tunnel can protect both link failures and node closed ring protection tunnel can protect both link failures and node
failures. failures.
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When a link failure between Node B and Node C occurs, if it is a bi- When a link failure between Node B and Node C occurs, if it is a bi-
directional failure, both Node B and Node C can detect the failure directional failure, both Node B and Node C can detect the failure
via the OAM mechanism; if it is a uni-directional failure, one of the via the OAM mechanism; if it is a uni-directional failure, one of the
two nodes would detect the failure via the OAM mechanism. In both two nodes would detect the failure via the OAM mechanism. In both
cases the node at the other side of the detected failure will be cases the node at the other side of the detected failure will be
determined by the ring-map and informed using the Ring Protection determined by the ring-map and informed using the Ring Protection
Switch Protocol (RPS) which is specified in section 5. Then Node B Switch Protocol (RPS) which is specified in section 5. Then Node B
switches the clockwise working ring tunnel (RcW_D) to the switches the clockwise working ring tunnel (RcW_D) to the
anticlockwise protection ring tunnel (RaP_D) and Node C switches anticlockwise protection ring tunnel (RaP_D) and Node C switches
anticlockwise protection ring tunnel(RaP_D) back to the clockwise anticlockwise protection ring tunnel(RaP_D) back to the clockwise
working ring tunnel (RcW_D). The data traffic which enters the ring working ring tunnel (RcW_D). The payload which enters the ring at
at Node A and leaves the ring at Node D follows the path Node A and leaves the ring at Node D follows the path
A->B->A->F->E->D->C->D. The label operation is: A->B->A->F->E->D->C->D. The label operation is:
[LSP1](Payload) -> [RcW_D(B)|LSP1](Node A) -> [RaP_D(A)|LSP1](Node B) [LSP1](Payload) -> [RcW_D(B)|LSP1](Node A) -> [RaP_D(A)|LSP1](Node B)
-> [RaP_D(F)|LSP1](Node A) -> [RaP_D(E)|LSP1] (Node F) -> -> [RaP_D(F)|LSP1](Node A) -> [RaP_D(E)|LSP1] (Node F) ->
[RaP_D(D)|LSP1] (Node E) -> [RaP_D(C)|LSP1] (Node D) -> [RaP_D(D)|LSP1] (Node E) -> [RaP_D(C)|LSP1] (Node D) ->
[RcW_D(D)|LSP1](Node C) -> [LSP1](Payload). [RcW_D(D)|LSP1](Node C) -> [LSP1](Payload).
+---+#####[RaP_D(F)]######+---+ +---+#####[RaP_D(F)]######+---+
| F |---------------------| A | +-- LSP1 | F |---------------------| A | +-- LSP1
+---+*****[RcW_D(A)]******+---+ +---+*****[RcW_D(A)]******+---+
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As shown in Figure 6, when Node B fails, Node A detects the failure As shown in Figure 6, when Node B fails, Node A detects the failure
between A and B and switches the clockwise work ring tunnel (RcW_D) between A and B and switches the clockwise work ring tunnel (RcW_D)
to the anticlockwise protection ring tunnel (RaP_D), Node C detects to the anticlockwise protection ring tunnel (RaP_D), Node C detects
the failure between C and B and switches the anticlockwise protection the failure between C and B and switches the anticlockwise protection
ring tunnel (RaP_D) to the clockwise working ring tunnel (RcW_D). ring tunnel (RaP_D) to the clockwise working ring tunnel (RcW_D).
The node at the other side of the failed node will be determined by The node at the other side of the failed node will be determined by
the ring-map and informed using the Ring Protection Switch Protocol the ring-map and informed using the Ring Protection Switch Protocol
(RPS) specified in section 5. (RPS) specified in section 5.
The data traffic which enters the ring at Node A and exits at Node D The payload which enters the ring at Node A and exits at Node D
follows the path A->F->E->D->C->D. The label operation is: follows the path A->F->E->D->C->D. The label operation is:
[LSP1](Payload)-> [RaP_D(F)|LSP1](NodeA) -> [RaP_D(E)|LSP1](NodeF) -> [LSP1](Payload)-> [RaP_D(F)|LSP1](NodeA) -> [RaP_D(E)|LSP1](NodeF) ->
[RaP_D(D)|LSP1](NodeE) -> [RaP_D(C)|LSP1] (NodeD) -> [RcW_D(D)|LSP1] [RaP_D(D)|LSP1](NodeE) -> [RaP_D(C)|LSP1] (NodeD) -> [RcW_D(D)|LSP1]
(NodeC) -> [LSP1](Payload). (NodeC) -> [LSP1](Payload).
In one special case where node D fails, all the ring tunnels with In one special case where node D fails, all the ring tunnels with
node D as egress will become unusable. However, before the failure node D as egress will become unusable. However, before the failure
location information is propagated to all the ring nodes, the location information is propagated to all the ring nodes, the
wrapping protection mechanism may cause temporary traffic loop: node wrapping protection mechanism may cause temporary traffic loop: node
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Figure 6. Wrapping for node failure Figure 6. Wrapping for node failure
4.3.2. Short Wrapping 4.3.2. Short Wrapping
With the wrapping protection scheme, protection switching is executed With the wrapping protection scheme, protection switching is executed
at both nodes adjacent to the failure, consequently the traffic will at both nodes adjacent to the failure, consequently the traffic will
be wrapped twice. This mechanism will cause additional latency and be wrapped twice. This mechanism will cause additional latency and
bandwidth consumption when traffic is switched to the protection bandwidth consumption when traffic is switched to the protection
path. path.
With short wrapping protection, data traffic switching is executed With short wrapping protection, payload switching is executed only at
only at the node upstream to the failure, and data traffic leaves the the node upstream to the failure, and payload leaves the ring in the
ring in the protection ring tunnel at the egress node. This scheme protection ring tunnel at the egress node. This scheme can reduce
can reduce the additional latency and bandwidth consumption when the additional latency and bandwidth consumption when traffic is
traffic is switched to the protection path. switched to the protection path.
In the wrapping solution, in normal state the protection ring tunnel In the wrapping solution, in normal state the protection ring tunnel
is a closed ring, while in the short wrapping solution, the is a closed ring, while in the short wrapping solution, the
protection ring tunnel is ended at the egress node, which is similar protection ring tunnel is terminated at the egress node, which is
to the working ring tunnel. Short wrapping is easy to implement in similar to the working ring tunnel. Short wrapping is easy to
shared ring protection because both the working and protection ring implement in shared ring protection because both the working and
tunnels are terminated on the egress nodes. Figure 7 shows the protection ring tunnels are terminated on the egress nodes. Figure 7
clockwise working ring tunnel and the anticlockwise protection ring shows the clockwise working ring tunnel and the anticlockwise
tunnel with node D as the egress node. protection ring tunnel with node D as the egress node.
4.3.2.1. Short Wrapping for Link Failure 4.3.2.1. Short Wrapping for Link Failure
As shown in Figure 7, in normal state, LSP1 is carried by the As shown in Figure 7, in normal state, LSP1 is carried by the
clockwise working ring tunnel (RcW_D) through the path A->B->C->D. clockwise working ring tunnel (RcW_D) through the path A->B->C->D.
When a link failure between Node B and Node C occurs, Node B switches When a link failure between Node B and Node C occurs, Node B switches
the working ring tunnel RcW_D to the protection ring tunnel RaP_D in the working ring tunnel RcW_D to the protection ring tunnel RaP_D in
the opposite direction. The difference with wrapping occurs in the the opposite direction. The difference with wrapping occurs in the
protection ring tunnel at egress node. In short wrapping protection, protection ring tunnel at the egress node. In short wrapping
Rap_D ends in Node D and then traffic will be forwarded based on the protection, Rap_D ends in Node D and then traffic will be forwarded
LSP labels. Thus with short wrapping mechanism, LSP1 will follow the based on the LSP labels. Thus with the short wrapping mechanism,
path A->B->A->F->E->D when link failure between Node B and Node C LSP1 will follow the path A->B->A->F->E->D when a link failure
happens. The protection switch at node D is based on the information between Node B and Node C happens. The protection switch at node D
from its ring map and the information received via the RPS protocol. is based on the information from its ring map and the information
received via the RPS protocol.
+---+#####[RaP_D(F)]######+---+ +---+#####[RaP_D(F)]######+---+
| F |---------------------| A | +-- LSP1 | F |---------------------| A | +-- LSP1
+---+*****[RcW_D(A)]******+---+ +---+*****[RcW_D(A)]******+---+
#/* *\# #/* *\#
[RaP_D(E)]#/*[RcW_D(F)] [RcW_D(B)]*\#RaP_D(A) [RaP_D(E)]#/*[RcW_D(F)] [RcW_D(B)]*\#RaP_D(A)
#/* *\# #/* *\#
+---+ +---+ +---+ +---+
| E | | B | | E | | B |
+---+ +---+ +---+ +---+
skipping to change at page 13, line 42 skipping to change at page 13, line 43
LSP1 +-- | D |-------------------| C | LSP1 +-- | D |-------------------| C |
+---+ +---+ +---+ +---+
----- physical links xxxxx Failure Link ----- physical links xxxxx Failure Link
****** RcW_D ###### RaP_D ****** RcW_D ###### RaP_D
Figure 7. Short wrapping for link failure Figure 7. Short wrapping for link failure
4.3.2.2. Short Wrapping for Node Failure 4.3.2.2. Short Wrapping for Node Failure
For the node failure which happens on a non-egress node, short For the node failure which happens on a non-egress node, the short
wrapping protection switching is similar to the link failure case as wrapping protection switching is similar to the link failure case as
described in the previous section. This section specifies the described in the previous section. This section specifies the
scenario of egress node failure. scenario of an egress node failure.
As shown in Figure 8, LSP1 enters the ring on node A, and leaves the As shown in Figure 8, LSP1 enters the ring on node A, and leaves the
ring on node D. In normal state, LSP1 is carried by the clockwise ring on node D. In normal state, LSP1 is carried by the clockwise
working ring tunnel (RcW_D) through the path A->B->C->D. When node D working ring tunnel (RcW_D) through the path A->B->C->D. When node D
fails, traffic of LSP1 cannot be protected by any ring tunnels which fails, traffic of LSP1 cannot be protected by any ring tunnels which
use node D as the egress node. However, before the failure location use node D as the egress node. However, before the failure location
information is propagated to all the ring nodes using the RPS information is propagated to all the ring nodes using the RPS
protocol, node C switches all the traffic on the working ring tunnel protocol, node C switches all the traffic on the working ring tunnel
RcW_D to the protection ring tunnel RaP_D in the opposite direction RcW_D to the protection ring tunnel RaP_D in the opposite direction
based on the information in the ring map. When the traffic arrives based on the information in the ring map. When the traffic arrives
skipping to change at page 14, line 42 skipping to change at page 14, line 43
LSP1 +-- x D x-------------------| C | LSP1 +-- x D x-------------------| C |
xxxxx +---+ xxxxx +---+
-----physical links xxxxxx Failure Node -----physical links xxxxxx Failure Node
*****RcW_D ###### RaP_D *****RcW_D ###### RaP_D
Figure 8. Short Wrapping for egress node failure Figure 8. Short Wrapping for egress node failure
4.3.3. Steering 4.3.3. Steering
With steering protection mechanism, the ingress node (which adds With the steering protection mechanism, the ingress node (which adds
traffic to the ring) perform switching from working to the protection traffic to the ring) perform switching from the working to the
ring tunnel, and at the egress node the traffic leaves the ring from protection ring tunnel, and at the egress node the traffic leaves the
the protection ring tunnel. ring from the protection ring tunnel.
When a failure occurs in the ring, the node which detects the failure When a failure occurs in the ring, the node which detects the failure
via OAM mechanism sends the failure information in the opposite using the OAM mechanism sends the failure information in the opposite
direction of the failure hop by hop along the ring using RPS request direction of the failure hop by hop along the ring using an RPS
message and the ring-map information. When a ring node receives the request message and the ring-map information. When a ring node
RPS message which identifies a failure, it can determine the location receives the RPS message which identifies a failure, it can determine
of the fault by using the topology information of the ring map and the location of the fault by using the topology information of the
update the ring map accordingly, then it can determine whether the ring map and updates the ring map accordingly, then it can determine
LSPs entering the ring locally need to switchover or not. For LSPs whether the LSPs entering the ring locally need to switchover or not.
that need to switchover, it will switch the LSPs from the working For LSPs that need to switchover, it will switch the LSPs from the
ring tunnels to its corresponding protection ring tunnels. The working ring tunnels to their corresponding protection ring tunnels.
transfer of the failure information by the RPS protocol will increase The transfer of the failure information by the RPS protocol will
the protection switch time. increase the protection switch time.
4.3.3.1. Steering for Link Failure 4.3.3.1. Steering for Link Failure
Ring map of F +--LSPl Ring map of F +--LSPl
+-+-+-+-+-+-+-+ +---+ ###[RaP_D(F)]### +---/ +-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+ +---+ ###[RaP_D(F)]### +---/ +-+-+-+-+-+-+-+
|F|A|B|C|D|E|F| | F | ---------------- | A | |A|B|C|D|E|F|A| |F|A|B|C|D|E|F| | F | ---------------- | A | |A|B|C|D|E|F|A|
+-+-+-+-+-+-+-+ +---+ ***[RcW_D(A)]*** +---+ +-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+ +---+ ***[RcW_D(A)]*** +---+ +-+-+-+-+-+-+-+
|I|I|I|S|I|I| |I|I|S|I|I|I| |I|I|I|S|I|I| |I|I|S|I|I|I|
+-+-+-+-+-+-+ #/* *\# +-+-+-+-+-+-+ +-+-+-+-+-+-+ #/* *\# +-+-+-+-+-+-+
[RaP_D(E)] #/* [RcW_D(B)] *\# [RaP_D(A)] [RaP_D(E)] #/* [RcW_D(B)] *\# [RaP_D(A)]
skipping to change at page 15, line 49 skipping to change at page 16, line 5
As shown in Figure 9, LSP1 enters the ring from Node A while LSP2 As shown in Figure 9, LSP1 enters the ring from Node A while LSP2
enters the ring from Node B, and both of them have the same enters the ring from Node B, and both of them have the same
destination node D. destination node D.
In normal state, LSP1 is carried by the clockwise working ring tunnel In normal state, LSP1 is carried by the clockwise working ring tunnel
(RcW_D) through the path A->B->C->D, the label operation is: (RcW_D) through the path A->B->C->D, the label operation is:
[LSP1](Payload) -> [RcW_D(B)|LSP1](NodeA) -> [RcW_D(C)| LSP1](NodeB) [LSP1](Payload) -> [RcW_D(B)|LSP1](NodeA) -> [RcW_D(C)| LSP1](NodeB)
-> [RcW_D(D)|LSP1](NodeC) -> [LSP1](Payload) . -> [RcW_D(D)|LSP1](NodeC) -> [LSP1](Payload) .
LSP2 is carried by the clockwise working ring tunnel (RcW_D) throught LSP2 is carried by the clockwise working ring tunnel (RcW_D) through
the path B->C->D, the label operation is: [LSP2](Payload) -> the path B->C->D, the label operation is: [LSP2](Payload) ->
[RcW_D(C)|LSP2](NodeB) -> [RcW_D(D)|LSP2](NodeC) -> [LSP2](Payload) . [RcW_D(C)|LSP2](NodeB) -> [RcW_D(D)|LSP2](NodeC) -> [LSP2](Payload) .
If the link between nodes C and D fails, according to the fault If the link between nodes C and D fails, according to the fault
detection and distribution mechanisms, Node D will find out that detection and distribution mechanisms, Node D will find out that
there is a failure in the link between C and D, and it will update there is a failure in the link between C and D, and it will update
the link state of its ring topology, changing the link between C and the link state of its ring topology, changing the link between C and
D from normal to fault. In the direction that opposite to the D from normal to fault. In the direction that is opposite to the
failure position, Node D will send the state report message to Node failure position, Node D will send the state report message to Node
E, informing Node E of the fault between C and D, and E will update E, informing Node E of the fault between C and D, and E will update
the link state of its ring topology accordingly, changing the link the link state of its ring topology accordingly, changing the link
between C and D from normal to fault. In this way, the state report between C and D from normal to fault. In this way, the state report
message is sent hop by hop in the clockwise direction. Similar to message is sent hop by hop in the clockwise direction. Similar to
Node D, Node C will send the failure information in the anti- Node D, Node C will send the failure information in the anti-
clockwise direction. clockwise direction.
When Node A receives the failure report message and updates the link When Node A receives the failure report message and updates the link
state of its ring map, it is aware that there is a fault on the state of its ring map, it is aware that there is a fault on the
skipping to change at page 17, line 31 skipping to change at page 17, line 31
+-+-+-+-+-+-+-+ +-- | D | ---------------- | C | +-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+ +-- | D | ---------------- | C | +-+-+-+-+-+-+-+
|I|I|I|S|I|I| LSP1 +---+ ###[RaP_D(C)]### +---+ |I|I|I|I|S|I| |I|I|I|S|I|I| LSP1 +---+ ###[RaP_D(C)]### +---+ |I|I|I|I|S|I|
+-+-+-+-+-+-+ LSP2 +-+-+-+-+-+-+ +-+-+-+-+-+-+ LSP2 +-+-+-+-+-+-+
----- physical links ***** RcW_D ##### RaP_D ----- physical links ***** RcW_D ##### RaP_D
Figure 10. Steering operation and protection switching (2) Figure 10. Steering operation and protection switching (2)
4.3.3.2. Steering for Node Failure 4.3.3.2. Steering for Node Failure
For node failure which happens on a non-egress node, steering For a node failure which happens on a non-egress node, steering
protection switching is similar to the link failure case as described protection switching is similar to the link failure case as described
in the previous section. in the previous section.
If the failure occurs at the egress node of the LSP, since the If the failure occurs at the egress node of the LSP, the ingress node
ingress node can update its ring map according to the received RPS will update its ring map according to the received RPS messages, it
messages, it will determine that the egress node is not reachable will also determine that the egress node is not reachable after the
after the failure, thus it will not send traffic to either the failure, thus it will not send traffic to either the working or the
working or protection tunnel, and traffic loop can be avoided. protection tunnel, and a traffic loop can be avoided.
4.4. Interconnected Ring Protection 4.4. Interconnected Ring Protection
4.4.1. Interconnected Ring Topology 4.4.1. Interconnected Ring Topology
Interconnected ring topology is widely used in MPLS-TP networks. Interconnected ring topology is widely used in MPLS-TP networks.
This document will discuss two typical interconnected ring This document will discuss two typical interconnected ring
topologies: topologies:
1. Single-node interconnected rings 1. Single-node interconnected rings
skipping to change at page 22, line 18 skipping to change at page 22, line 18
the service LSP1 follows after switching change to: LSP1->R1cW_F&A(D- the service LSP1 follows after switching change to: LSP1->R1cW_F&A(D-
>E)->R1aP_F&A(E->D->C->B->A)->R2cW_I(A->F->G->H->I)->LSP1. >E)->R1aP_F&A(E->D->C->B->A)->R2cW_I(A->F->G->H->I)->LSP1.
In case of a non-interconnection node failure, for example, when the In case of a non-interconnection node failure, for example, when the
failure occurs at Node E in Ring1, Node D will detect the failure and failure occurs at Node E in Ring1, Node D will detect the failure and
execute protection switching as described in 4.3.2. The path that execute protection switching as described in 4.3.2. The path that
the service LSP1 follows after switching becomes: the service LSP1 follows after switching becomes:
LSP1->R1cW_F&A(D)->R1aP_F&A(D->C->B->A)->R2cW_I(A->F->G->H->I)->LSP1. LSP1->R1cW_F&A(D)->R1aP_F&A(D->C->B->A)->R2cW_I(A->F->G->H->I)->LSP1.
In case of an interconnection node failure, for example, when the In case of an interconnection node failure, for example, when the
failure occurs at the interconnection Node F. Node E in Ring1 will failure occurs at the interconnection Node F, Node E in Ring1 will
detect the failure, and execute protection switching as described in detect the failure, and execute protection switching as described in
4.3.2. Node A in Ring2 will also detect the failure, and execute 4.3.2. Node A in Ring2 will also detect the failure, and execute
protection switching as described in 4.3.2. The path that the protection switching as described in 4.3.2. The path that the
service traffic LSP1 follows after switching is: service traffic LSP1 follows after switching is:
LSP1->R1cW_F&A(D->E)->R1aP_F&A(E->D->C->B->A)->R2aP_I(A->J->I)->LSP1. LSP1->R1cW_F&A(D->E)->R1aP_F&A(E->D->C->B->A)->R2aP_I(A->J->I)->LSP1.
4.4.5. Interconnected Ring Detection Mechanism 4.4.5. Interconnected Ring Detection Mechanism
As show in Figure 13, in normal state the service traffic LSP1 As shown in Figure 13, in normal state the service traffic LSP1
traverses D->E->F in Ring1 and F->G->H->I in Ring2. Node A and F are traverses D->E->F in Ring1 and F->G->H->I in Ring2. Node A and F are
the interconnection nodes. When both the link between Node F and the interconnection nodes. When both the link between Node F and
Node G and the link between Node F and Node A fail, the ring tunnel Node G and the link between Node F and Node A fail, the ring tunnel
from Node F to Node I in Ring2 becomes unreachable. However, the from Node F to Node I in Ring2 becomes unreachable. However, the
other interconnection node A is still available, and LSP1 can still other interconnection node A is still available, and LSP1 can still
reach Node I via node A. reach Node I via node A.
In order to achieve this, the interconnection nodes need to know the In order to achieve this, the interconnection nodes need to know the
ring topology of each ring so that they can judge whether a node is ring topology of each ring so that they can judge whether a node is
reachable. This judgment is based on the knowledge of ring map and reachable. This judgment is based on the knowledge of ring map and
the fault location as described in section 3.4. The ring map can be the fault location. The ring map can be obtained from the NMS or
obtained from the NMS or topology discovery mechanisms. The fault topology discovery mechanisms. The fault location can be obtained by
location can be obtained by transmitting the fault information around transmitting the fault information around the ring. The nodes that
the ring. The nodes that detect the failure will transmit the fault detect the failure will transmit the fault information in the
information in the opposite direction hop by hop using the RPS opposite direction hop by hop using the RPS protocol message. When
protocol message. When the interconnection node receives the message the interconnection node receives the message that informs the
that informs the failure, it will quickly calculate the location of failure, it will calculate the location of the fault according to the
the fault according to the topology information that is maintained by topology information that is maintained by itself and determines
itself and determines whether the LSPs entering the ring at itself whether the LSPs entering the ring at itself can reach the
can reach the destination. If the destination node is reachable, the destination. If the destination node is reachable, the LSP will
LSP will leave the source ring and enter the destination ring. If leave the source ring and enter the destination ring. If the
the destination node is not reachable, the LSP will switch to the destination node is not reachable, the LSP will switch to the
anticlockwise protection ring tunnel. anticlockwise protection ring tunnel.
In Figure 13, Node F determines that the ring tunnel to Node I is In Figure 13, Node F determines that the ring tunnel to Node I is
unreachable, the service LSP1 for which the destination node on the unreachable, the service LSP1 for which the destination node on the
ring2 is Node I MUST switch to the protection ring tunnel (R1aP_F&A) ring2 is Node I MUST switch to the protection ring tunnel (R1aP_F&A)
and consequently the service traffic LSP1 traverses the and consequently the service traffic LSP1 traverses the
interconnected rings at Node A. Node A will pop the ring tunnel interconnected rings at Node A. Node A will pop the ring tunnel
label of Ring1 and push the ring tunnel label of Ring2 and send the label of Ring1 and push the ring tunnel label of Ring2 and send the
traffic to Node I via ring tunnel (R2aW_I). traffic to Node I via ring tunnel (R2aW_I).
skipping to change at page 24, line 13 skipping to change at page 24, line 13
both directions. both directions.
+---+ A->B(NR) +---+ B->C(NR) +---+ C->D(NR) +---+ A->B(NR) +---+ B->C(NR) +---+ C->D(NR)
-------| A |-------------| B |-------------| C |------- -------| A |-------------| B |-------------| C |-------
(NR)F<-A +---+ (NR)A<-B +---+ (NR)B<-C +---+ (NR)F<-A +---+ (NR)A<-B +---+ (NR)B<-C +---+
Figure 14. RPS communication between the ring nodes in case of Figure 14. RPS communication between the ring nodes in case of
no failure in the ring no failure in the ring
A destination node is a node that is adjacent to a node that A destination node is a node that is adjacent to a node that
identified a failed span. When a node that is not the destination identified a failed link. When a node that is not the destination
node receives an RPS request and it has no higher priority local node receives an RPS request and it has no higher priority local
request, it MUST transfer in the same direction the RPS request as request, it MUST transfer in the same direction the RPS request as
received. In this way, the switching nodes can maintain direct RPS received. In this way, the switching nodes can maintain direct RPS
protocol communication in the ring. protocol communication in the ring.
+---+ C->B(SF) +---+ B->C(SF) +---+ C->B(SF) +---+ C->B(SF) +---+ B->C(SF) +---+ C->B(SF)
-------| A |-------------| B |----- X -----| C |------- -------| A |-------------| B |----- X -----| C |-------
(SF)C<-B +---+ (SF)C<-B +---+ (SF)B<-C +---+ (SF)C<-B +---+ (SF)C<-B +---+ (SF)B<-C +---+
Figure 15. RPS communication between the ring nodes in case of Figure 15. RPS communication between the ring nodes in case of
skipping to change at page 25, line 4 skipping to change at page 25, line 4
required, any node MUST perform the switches if its added/dropped required, any node MUST perform the switches if its added/dropped
traffic is affected by the failure. Determination of the affected traffic is affected by the failure. Determination of the affected
traffic SHOULD be performed by examining the RPS requests traffic SHOULD be performed by examining the RPS requests
(indicating the nodes adjacent to the failure or failures) and the (indicating the nodes adjacent to the failure or failures) and the
stored ring map (indicating the relative position of the failure stored ring map (indicating the relative position of the failure
and the added traffic destined towards that failure). and the added traffic destined towards that failure).
When the failure has cleared and the Wait-to-Restore (WTR) timer has When the failure has cleared and the Wait-to-Restore (WTR) timer has
expired, the nodes sourcing RPS requests MUST drop their respective expired, the nodes sourcing RPS requests MUST drop their respective
switches (tail end) and MUST source an RPS request carrying the NR switches (tail end) and MUST source an RPS request carrying the NR
code. The node receiving from both directions such RPS request (head code. The node receiving from both directions such an RPS request
end) MUST drop its protection switches. (head end) MUST drop its protection switches.
A protection switch MUST be initiated by one of the criteria A protection switch MUST be initiated by one of the criteria
specified in Section 5.2. A failure of the RPS protocol or specified in Section 5.2. A failure of the RPS protocol or
controller MUST NOT trigger a protection switch. controller MUST NOT trigger a protection switch.
Ring switches MUST be preempted by higher priority RPS requests. For Ring switches MUST be preempted by higher priority RPS requests. For
example, consider a protection switch that is active due to a manual example, consider a protection switch that is active due to a manual
switch request on the given span, and another protection switch is switch request on the given link, and another protection switch is
required due to a failure on another span. Then an RPS request MUST required due to a failure on another link. Then an RPS request MUST
be generated, the former protection switch MUST be dropped, and the be generated, the former protection switch MUST be dropped, and the
latter protection switch established. latter protection switch established.
MSRP mechanism SHOULD support multiple protection switches in the MSRP mechanism SHOULD support multiple protection switches in the
ring, resulting the ring being segmented into two or more separate ring, resulting in the ring being segmented into two or more separate
segments. This may happen when several RPS requests of the same segments. This may happen when several RPS requests of the same
priority exist in the ring due to multiple failures or external priority exist in the ring due to multiple failures or external
switch commands. switch commands.
Proper operation of the MSRP mechanism relies on all nodes having Proper operation of the MSRP mechanism relies on all nodes using
knowledge of the state of the ring (nodes and spans) so that nodes do their ring map to determine the state of the ring (nodes and links).
not preempt existing RPS request unless they have a higher-priority In order to accommodate ring state knowledge, during a protection
RPS request. In order to accommodate ring state knowledge, during a switch the RPS requests MUST be sent in both directions.
protection switch the RPS requests MUST be sent in both directions.
5.1.1. Transmission and Acceptance of RPS Requests 5.1.1. Transmission and Acceptance of RPS Requests
A new RPS request MUST be transmitted immediately when a change in A new RPS request MUST be transmitted immediately when a change in
the transmitted status occurs. the transmitted status occurs.
The first three RPS protocol messages carrying new RPS request SHOULD The first three RPS protocol messages carrying new RPS request SHOULD
be transmitted as fast as possible. For fast protection switching be transmitted as fast as possible. For fast protection switching
within 50 ms, the interval of the first three RPS protocol messages within 50 ms, the interval of the first three RPS protocol messages
SHOULD be 3.3 ms. The successive RPS requests SHOULD be transmitted SHOULD be 3.3 ms. The successive RPS requests SHOULD be transmitted
skipping to change at page 26, line 25 skipping to change at page 26, line 25
o Destination Node ID: The destination node ID MUST always be set to o Destination Node ID: The destination node ID MUST always be set to
value of the node ID of the adjacent node. The Node ID MUST be value of the node ID of the adjacent node. The Node ID MUST be
unique on each ring. Valid destination node ID values are 1-127. unique on each ring. Valid destination node ID values are 1-127.
o Source Node ID: The source node ID MUST always be set to the ID o Source Node ID: The source node ID MUST always be set to the ID
value of the node generating the RPS request. The Node ID MUST be value of the node generating the RPS request. The Node ID MUST be
unique on each ring. Valid source node ID values are 1-127. unique on each ring. Valid source node ID values are 1-127.
o Protection Switching Mode (M): This 2-bit field indicates the o Protection Switching Mode (M): This 2-bit field indicates the
protection swithcing mode used by the sending node of the RPS protection switching mode used by the sending node of the RPS
message. This can be used to check that the ring nodes on the message. This can be used to check that the ring nodes on the
same ring use the same protecion switching mechanism. The defined sane ring use the same protection switching mechanism. The
values of the M field are listed as below: defined values of the M field are listed as below:
+------------------+-----------------------------+ +------------------+-----------------------------+
| Bits (MSB-LSB) | Protecton Switching Mode | | Bits (MSB-LSB) | Protecton Switching Mode |
+------------------+-----------------------------+ +------------------+-----------------------------+
| 0 0 | Wrapping | | 0 0 | Reserved |
| 0 1 | Short Wrapping | | 0 1 | Wrapping |
| 1 0 | Steering | | 1 0 | Short Wrapping |
| 1 1 | Reserved | | 1 1 | Steering |
+------------------+-----------------------------+ +------------------+-----------------------------+
o RPS request code: A code consisting of eight bits as specified o RPS request code: A code consisting of eight bits as specified
below: below:
+------------------+-----------------------------+----------+ +------------------+-----------------------------+----------+
| Bits | Condition, State | Priority | | Bits | Condition, State | Priority |
| (MSB - LSB) | or external Request | | | (MSB - LSB) | or external Request | |
+------------------+-----------------------------+----------+ +------------------+-----------------------------+----------+
| 0 0 0 0 1 1 1 1 | Lockout of Protection (LP) | highest | | 0 0 0 0 1 1 1 1 | Lockout of Protection (LP) | highest |
skipping to change at page 27, line 44 skipping to change at page 27, line 44
directions. directions.
A node in the idle state MUST terminate RPS requests flow in both A node in the idle state MUST terminate RPS requests flow in both
directions. directions.
A node in the idle state MUST block the traffic flow on protection A node in the idle state MUST block the traffic flow on protection
ring tunnels in both directions. ring tunnels in both directions.
5.1.3.2. Switching State 5.1.3.2. Switching State
A node in the switching state MUST source RPS request to adjacent A node in the switching state MUST source RPS request to its adjacent
node with its highest RPS request code in both directions when it node with its highest RPS request code in both directions when it
detects a failure or receives an external command. detects a failure or receives an external command.
A node in the switching state MUST terminate RPS requests flow in A node in the switching state MUST terminate RPS requests flow in
both directions. both directions.
As soon as it receives an RPS request from the short path, the node As soon as it receives an RPS request from the short path, the node
to which it is addressed MUST acknowledge the RPS request by replying to which it is addressed MUST acknowledge the RPS request by replying
with the RR code on the short path, and with the received RPS request with the RR code on the short path, and with the received RPS request
code on the long path. Accordingly, if RR code is received from the code on the long path. Accordingly, if RR code is received from the
short path, then the RPS request sent by the same node over the long short path, then the RPS request sent by the same node over the long
path SHOULD be ignored. Here the short path refers to the shorter path SHOULD be ignored. Here the short path refers to the shorter
span on the ring between the source and destination node of the RPS path on the ring between the source and destination node of the RPS
request, and the long path refers to the longer span on the ring request, and the long path refers to the longer path on the ring
between the source and destination node of the RPS request. between the source and destination node of the RPS request.
This rule refers to the unidirectional failure detection: the RR This rule refers to the unidirectional failure detection: the RR
SHOULD be issued only when the node does not detect the failure SHOULD be issued only when the node does not detect the failure
condition (i.e., the node is a head end), that is, it is not condition (i.e., the node is a head end), that is, it is not
applicable when a bidirectional failure is detected, because, in this applicable when a bidirectional failure is detected, because, in this
case, both nodes adjacent to the failure will send an RPS request for case, both nodes adjacent to the failure will send an RPS request for
the failure on both paths (short and long). the failure on both paths (short and long).
The following switches MUST be allowed to coexist: The following switches MUST be allowed to coexist:
o LP and LP o LP and LP
o FS and FS o FS and FS
o SF and SF o SF and SF
o FS and SF o FS and SF
When multiple MS RPS requests over different spans exist at the same When multiple MS RPS requests exist at the same time addressing
time, no switch SHOULD be executed and existing switches MUST be different links and there is no higher priority request on the ring,
dropped. The nodes MUST signal, anyway, the MS RPS request code. no switch SHOULD be executed and existing switches MUST be dropped.
The nodes MUST signal, anyway, the MS RPS request code.
Multiple EXER requests MUST be allowed to coexist in the ring. Multiple EXER requests MUST be allowed to coexist in the ring.
A node in a ring switching state that receives the external command A node in a ring switching state that receives the external command
LP for the affected span MUST drop its switch and MUST signal NR for LP for the affected link MUST drop its switch and MUST signal NR for
the locked span if there is no other RPS request on another span. the locked link if there is no other RPS request on another link.
Node still SHOULD signal relevant RPS request for another span. The node still SHOULD signal relevant RPS request for another link.
5.1.3.3. Pass-through State 5.1.3.3. Pass-through State
When a node is in a pass-through state, it MUST transfer the received When a node is in a pass-through state, it MUST transfer the received
RPS Request in the same direction. RPS Request in the same direction.
When a node is in a pass-through state, it MUST enable the traffic When a node is in a pass-through state, it MUST enable the traffic
flow on protection ring tunnels in both directions. flow on protection ring tunnels in both directions.
5.1.4. RPS State Transitions 5.1.4. RPS State Transitions
skipping to change at page 29, line 41 skipping to change at page 29, line 41
Transition of a node from the idle state to the switching state MUST Transition of a node from the idle state to the switching state MUST
be triggered by one of the following conditions: be triggered by one of the following conditions:
o A valid RPS request change from the NR code to any code received o A valid RPS request change from the NR code to any code received
on either the long or the short path and destined to this node on either the long or the short path and destined to this node
o An externally initiated command for this node o An externally initiated command for this node
o The detection of an MPLS-TP section layer failure at this node o The detection of an MPLS-TP section layer failure at this node
Actions taken at a node in the idle state upon transition to Actions taken at a node in the idle state upon transition to the
switching state are: switching state are:
o For all protection switch requests, except EXER and LP, the node o For all protection switch requests, except EXER and LP, the node
MUST execute the switch MUST execute the switch
o For EXER, and LP, the node MUST signal appropriate request but not o For EXER, and LP, the node MUST signal appropriate request but not
execute the switch execute the switch
A node MUST revert from the switching state to the idle state when it A node MUST revert from the switching state to the idle state when it
detects NR codes received from both directions. detects NR codes received from both directions.
skipping to change at page 30, line 19 skipping to change at page 30, line 19
o At the head end: Upon reception of the NR code, from both o At the head end: Upon reception of the NR code, from both
directions, the head-end node MUST drop its switch, transition to directions, the head-end node MUST drop its switch, transition to
Idle State and signal the NR code in both directions. Idle State and signal the NR code in both directions.
5.1.4.3. Transitions Between Switching States 5.1.4.3. Transitions Between Switching States
When a node that is currently executing any protection switch When a node that is currently executing any protection switch
receives a higher priority RPS request (due to a locally detected receives a higher priority RPS request (due to a locally detected
failure, an externally initiated command, or a ring protection switch failure, an externally initiated command, or a ring protection switch
request destined to it) for the same span, it MUST update the request destined to it) for the same link, it MUST update the
priority of the switch it is executing to the priority of the priority of the switch it is executing to the priority of the
received RPS request. received RPS request.
When a failure condition clears at a node, the node MUST enter WTR When a failure condition clears at a node, the node MUST enter WTR
condition and remain in it for the appropriate time-out interval, condition and remain in it for the appropriate time-out interval,
unless: unless:
o A different RPS request with a higher priority than WTR is o A different RPS request with a higher priority than WTR is
received received
skipping to change at page 30, line 44 skipping to change at page 30, line 44
The node MUST send out a WTR code on both the long and short paths. The node MUST send out a WTR code on both the long and short paths.
When a node that is executing a switch in response to incoming SF RPS When a node that is executing a switch in response to incoming SF RPS
request (not due to a locally detected failure) receives a WTR code request (not due to a locally detected failure) receives a WTR code
(unidirectional failure case), it MUST send out RR code on the short (unidirectional failure case), it MUST send out RR code on the short
path and the WTR on the long path. path and the WTR on the long path.
5.1.4.4. Transitions Between Switching and Pass-through States 5.1.4.4. Transitions Between Switching and Pass-through States
When a node that is currently executing a switch receives an RPS When a node that is currently executing a switch receives an RPS
request for a non-adjacent span of higher priority than the switch it request for a non-adjacent link of higher priority than the switch it
is executing, it MUST drop its switch immediately and enter the pass- is executing, it MUST drop its switch immediately and enter the pass-
through state. through state.
The transition of a node from pass-through to switching state MUST be The transition of a node from pass-through to switching state MUST be
triggered by: triggered by:
o An equal priority, a higher priority, or an allowed coexisting o An equal priority, a higher priority, or an allowed coexisting
externally initiated command externally initiated command
o The detection of an equal priority, a higher priority, or an o The detection of an equal priority, a higher priority, or an
skipping to change at page 31, line 31 skipping to change at page 31, line 31
The following commands can be transferred by the RPS message: The following commands can be transferred by the RPS message:
o Lockout of Protection (LP): This command prevents any protection o Lockout of Protection (LP): This command prevents any protection
activity and prevents using ring switches anywhere in the ring. activity and prevents using ring switches anywhere in the ring.
If any ring switches exist in the ring, this command causes the If any ring switches exist in the ring, this command causes the
switches to drop. switches to drop.
o Forced Switch to protection (FS): This command performs the ring o Forced Switch to protection (FS): This command performs the ring
switch of normal traffic from the working entity to the protection switch of normal traffic from the working entity to the protection
entity for the span between the node at which the command is entity for the link between the node at which the command is
initiated and the adjacent node to which the command is directed. initiated and the adjacent node to which the command is directed.
This switch occurs regardless of the state of the MPLS-TP section This switch occurs regardless of the state of the MPLS-TP section
for the requested span, unless a higher priority switch request for the requested link, unless a higher priority switch request
exists. exists.
o Manual Switch to protection (MS): This command performs the ring o Manual Switch to protection (MS): This command performs the ring
switch of the normal traffic from the working entity to the switch of the normal traffic from the working entity to the
protection entity for the span between the node at which the protection entity for the link between the node at which the
command is initiated and the adjacent node to which the command is command is initiated and the adjacent node to which the command is
directed. This occurs if the MPLS-TP section for the requested directed. This occurs if the MPLS-TP section for the requested
span is not satisfying an equal or higher priority switch request. link is not satisfying an equal or higher priority switch request.
o Exercise - Ring (EXER): This command exercises ring protection o Exercise - Ring (EXER): This command exercises ring protection
switching on the addressed span without completing the actual switching on the addressed link without completing the actual
switch. The command is issued and the responses (RR) are checked, switch. The command is issued and the responses (RR) are checked,
but no normal traffic is affected. but no normal traffic is affected.
The following commands are not transferred by the RPS message: The following commands are not transferred by the RPS message:
o Clear: This command clears the administrative command and Wait-To- o Clear: This command clears the administrative command and Wait-To-
Restore timer (WTR) at the node to which the command was Restore timer (WTR) at the node to which the command was
addressed. The node-to-node signaling after the removal of the addressed. The node-to-node signaling after the removal of the
externally initiated commands is performed using the no-request externally initiated commands is performed using the no-request
code (NR). code (NR).
o Lockout of Working: This command prevents the normal traffic o Lockout of Working: This command prevents the normal traffic
transported over the addressed span from being switched to the transported over the addressed link from being switched to the
protection entity by disabling the node's capability of requesting protection entity by disabling the node's capability of requesting
switch for this span in case of failure. If any normal traffic is switch for this link in case of failure. If any normal traffic is
already switched on the protection entity, the switch is dropped. already switched on the protection entity, the switch is dropped.
If no other switch requests are active on the ring, the no-request If no other switch requests are active on the ring, the no-request
code (NR) is transmitted. This command has no impact on any other code (NR) is transmitted. This command has no impact on any other
span. If the node receives the switch request from the adjacent link. If the node receives the switch request from the adjacent
node from any side it will perform the requested switch. If the node from any side it will perform the requested switch. If the
node receives the switch request addressed to the other node, it node receives the switch request addressed to the other node, it
will enter the pass-through state. will enter the pass-through state.
5.2.1.2. Automatically Initiated Commands 5.2.1.2. Automatically Initiated Commands
Automatically initiated commands can be initiated based on MPLS-TP Automatically initiated commands can be initiated based on MPLS-TP
section layer OAM indication and the received switch requests. section layer OAM indication and the received switch requests.
The node can initiate the following switch requests automatically: The node can initiate the following switch requests automatically:
skipping to change at page 35, line 5 skipping to change at page 35, line 5
F (Switching - SF) - if there F (Switching - SF) - if there
is a failure at this node is a failure at this node
B (Pass-through) - if there is B (Pass-through) - if there is
a failure at another node a failure at another node
WTR expires N/A WTR expires N/A
EXER O EXER O
===================================================================== =====================================================================
Initial state New request New state Initial state New request New state
------------- ----------- --------- ------------- ----------- ---------
D (Idle - LW) LP C (Switching - LP) D (Idle - LW) LP C (Switching - LP)
LW N/A - if on the same span LW N/A - if on the same link
D (Idle - LW) - if on another D (Idle - LW) - if on another
span link
FS O - if on the same span FS O - if on the same link
E (Switching - FS) - if on E (Switching - FS) - if on
another span another link
SF O - if on the addressed span SF O - if on the addressed link
F (Switching - SF) - if on F (Switching - SF) - if on
another span another link
Recover from SF N/A Recover from SF N/A
MS O - if on the same span MS O - if on the same link
G (Switching - MS) - if on G (Switching - MS) - if on
another span another link
Clear A (Idle) - if there is no Clear A (Idle) - if there is no
failure on addressed span failure on addressed link
F (Switching - SF) - if there F (Switching - SF) - if there
is a failure on this span is a failure on this link
WTR expires N/A WTR expires N/A
EXER O EXER O
===================================================================== =====================================================================
Initial state New request New state Initial state New request New state
------------- ----------- --------- ------------- ----------- ---------
E (Switching - FS) LP C (Switching - LP) E (Switching - FS) LP C (Switching - LP)
LW O - if on another span LW O - if on another link
D (Idle - LW) - if on the same D (Idle - LW) - if on the same
span link
FS N/A - if on the same span FS N/A - if on the same link
E (Switching - FS) - if on E (Switching - FS) - if on
another span another link
SF O - if on the addressed span SF O - if on the addressed link
E (Switching - FS) - if on E (Switching - FS) - if on
another span another link
Recover from SF N/A Recover from SF N/A
MS O MS O
Clear A (Idle) - if there is no Clear A (Idle) - if there is no
failure in the ring failure in the ring
F (Switching - SF) - if there F (Switching - SF) - if there
is a failure at this node is a failure at this node
B (Pass-through) - if there is B (Pass-through) - if there is
a failure at another node a failure at another node
WTR expires N/A WTR expires N/A
EXER O EXER O
===================================================================== =====================================================================
Initial state New request New state Initial state New request New state
------------- ----------- --------- ------------- ----------- ---------
F (Switching - SF) LP C (Switching - LP) F (Switching - SF) LP C (Switching - LP)
LW O - if on another span LW O - if on another link
D (Idle - LW) - if on the same D (Idle - LW) - if on the same
span link
FS E (Switching - FS) FS E (Switching - FS)
SF N/A - if on the same span SF N/A - if on the same link
F (Switching - SF) - if on F (Switching - SF) - if on
another span another link
Recover from SF H (Switching - WTR) Recover from SF H (Switching - WTR)
MS O MS O
Clear N/A Clear N/A
WTR expires N/A WTR expires N/A
EXER O EXER O
===================================================================== =====================================================================
Initial state New request New state Initial state New request New state
------------- ----------- --------- ------------- ----------- ---------
G (Switching - MS) LP C (Switching - LP) G (Switching - MS) LP C (Switching - LP)
LW O - if on another span LW O - if on another link
D (Idle - LW) - if on the same D (Idle - LW) - if on the same
span link
FS E (Switching - FS) FS E (Switching - FS)
SF F (Switching - SF) SF F (Switching - SF)
Recover from SF N/A Recover from SF N/A
MS N/A - if on the same span MS N/A - if on the same link
G (Switching - MS) - if on G (Switching - MS) - if on
another span release the another link release the
switches but signal MS switches but signal MS
Clear A Clear A
WTR expires N/A WTR expires N/A
EXER O EXER O
===================================================================== =====================================================================
Initial state New request New state Initial state New request New state
------------- ----------- --------- ------------- ----------- ---------
H (Switching - WTR) LP C (Switching - LP) H (Switching - WTR) LP C (Switching - LP)
LW D (Idle - W) LW D (Idle - W)
FS E (Switching - FS) FS E (Switching - FS)
skipping to change at page 37, line 7 skipping to change at page 37, line 7
Initial state New request New state Initial state New request New state
------------- ----------- --------- ------------- ----------- ---------
I (Switching - EXER) LP C (Switching - LP) I (Switching - EXER) LP C (Switching - LP)
LW D (idle - W) LW D (idle - W)
FS E (Switching - FS) FS E (Switching - FS)
SF F (Switching - SF) SF F (Switching - SF)
Recover from SF N/A Recover from SF N/A
MS G (Switching - MS) MS G (Switching - MS)
Clear A Clear A
WTR expires N/A WTR expires N/A
EXER N/A - if on the same span EXER N/A - if on the same link
I (Switching - EXER) I (Switching - EXER)
===================================================================== =====================================================================
5.2.4. State Transitions When Remote Request is Applied 5.2.4. State Transitions When Remote Request is Applied
The priority of a remote request does not depend on the side from The priority of a remote request does not depend on the side from
which the request is received. which the request is received.
===================================================================== =====================================================================
Initial state New request New state Initial state New request New state
skipping to change at page 42, line 51 skipping to change at page 42, line 51
===================================================================== =====================================================================
5.3. RPS and PSC Comparison on Ring Topology 5.3. RPS and PSC Comparison on Ring Topology
This section provides comparison between RPS and PSC [RFC6378] This section provides comparison between RPS and PSC [RFC6378]
[RFC6974] on ring topologies. This can be helpful to explain the [RFC6974] on ring topologies. This can be helpful to explain the
reason of defining a new protocol for ring protection switching. reason of defining a new protocol for ring protection switching.
The PSC protocol [RFC6378] is designed for point-to-point LSPs, on The PSC protocol [RFC6378] is designed for point-to-point LSPs, on
which the protection switching can only be performed on one or both which the protection switching can only be performed on one or both
of the end points of the LSP. While RPS is designed for ring of the end points of the LSP. The RPS protocol is designed for ring
tunnels, which consist of multiple ring nodes, and the failure could tunnels, which consist of multiple ring nodes, and the failure could
happen on any segment of the ring, thus RPS SHOULD be capable of happen on any segment of the ring, thus RPS SHOULD be capable of
identifying and handling the different failures on the ring, and identifying and handling the different failures on the ring, and
coordinating the protection switching behavior of all the nodes on coordinating the protection switching behavior of all the nodes on
the ring. As specified in section 5, this is achieved with the the ring. As specified in section 5, this is achieved with the
introduction of the "Pass-Through" state for the ring nodes, and the introduction of the "Pass-Through" state for the ring nodes, and the
location of the protection request is identified via the Node IDs in location of the protection request is identified via the Node IDs in
the RPS Request message. the RPS Request message.
Taking a ring topology with N nodes as example: Taking a ring topology with N nodes as example:
skipping to change at page 43, line 46 skipping to change at page 43, line 46
IANA is requested to administer the assignment of new values defined IANA is requested to administer the assignment of new values defined
in this document and listed in the sections below. in this document and listed in the sections below.
6.1. G-ACh Channel Type 6.1. G-ACh Channel Type
The Channel Types for the Generic Associated channel (GACh) are The Channel Types for the Generic Associated channel (GACh) are
allocated from the IANA PW Associated Channel Type registry defined allocated from the IANA PW Associated Channel Type registry defined
in [RFC4446] and updated by [RFC5586]. in [RFC4446] and updated by [RFC5586].
IANA is requested to allocate a new GACH Channel Type as follows: IANA is requested to allocate a new GACh Channel Type as follows:
Value| Description | Reference Value| Description | Reference
------+---------------------------+-------------- ------+---------------------------+--------------
TBD | Ring Protection Switching |this document TBD | Ring Protection Switching |this document
| Protocol (RPS) | | Protocol (RPS) |
------+---------------------------+-------------- ------+---------------------------+--------------
6.2. RPS Request Codes 6.2. RPS Request Codes
IANA is requested to create a new sub-registry under the IANA is requested to create a new sub-registry under the
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