draft-ietf-mpls-tp-shared-ring-protection-00.txt   draft-ietf-mpls-tp-shared-ring-protection-01.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 12, 2016 China Mobile Expires: September 22, 2016 China Mobile
H. Helvoort H. Helvoort
Hai Gaoming BV Hai Gaoming BV
K. Liu K. Liu
J. Dong J. Dong
J. He J. He
Huawei Technologies Huawei Technologies
F. Li F. Li
China Academy of Telecommunication Research, MIIT., China China Academy of Telecommunication Research, MIIT., China
J. Yang J. Yang
ZTE Corporation P.R.China ZTE Corporation P.R.China
J. Wang J. Wang
Fiberhome Telecommunication Technologies Co., LTD. Fiberhome Telecommunication Technologies Co., LTD.
October 10, 2015 March 21, 2016
MPLS-TP Shared-Ring protection (MSRP) mechanism for ring topology MPLS-TP Shared-Ring protection (MSRP) mechanism for ring topology
draft-ietf-mpls-tp-shared-ring-protection-00 draft-ietf-mpls-tp-shared-ring-protection-01
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 the ring topology for point- MPLS-TP Shared Ring Protection (MSRP) in the ring topology for point-
to-point (P2P) services. The mechanism of MSRP is illustrated and to-point (P2P) services. The mechanism of MSRP is illustrated and
how it satisfies the requirements for optimized ring protection in how it satisfies the requirements for optimized ring protection in
RFC 5654 is analyzed. This document also defines the Ring Protection RFC 5654 is analyzed. This document also defines the Ring Protection
Switch (RPS) Protocol which is used to coordinate the protection Switch (RPS) Protocol which is used to coordinate the protection
behavior of the nodes on MPLS ring. behavior of the nodes on MPLS ring.
skipping to change at page 2, line 10 skipping to change at page 2, line 10
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This Internet-Draft will expire on April 12, 2016. This Internet-Draft will expire on September 22, 2016.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements for MPLS-TP Ring Protection . . . . . . . . . . 4 2. Requirements for MPLS-TP Ring Protection . . . . . . . . . . 4
2.1. Recovery of Multiple Failures . . . . . . . . . . . . . . 4 2.1. Recovery of Multiple Failures . . . . . . . . . . . . . . 4
2.2. Smooth Upgrade from Linear Protection to Ring Protection 4 2.2. Smooth Upgrade from Linear Protection to Ring Protection 5
2.3. Configuration Complexity . . . . . . . . . . . . . . . . 5 2.3. Configuration Complexity . . . . . . . . . . . . . . . . 5
3. Terminology and Notation . . . . . . . . . . . . . . . . . . 5 3. Terminology and Notation . . . . . . . . . . . . . . . . . . 5
4. Shared Ring Protection Architecture . . . . . . . . . . . . . 5 4. Shared Ring Protection Architecture . . . . . . . . . . . . . 5
4.1. Ring Tunnel . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Ring Tunnel . . . . . . . . . . . . . . . . . . . . . . . 5
4.1.1. Establishment of Ring Tunnel . . . . . . . . . . . . 6 4.1.1. Establishment of Ring Tunnel . . . . . . . . . . . . 6
4.1.2. Label Assignment and Distribution . . . . . . . . . . 8 4.1.2. Label Assignment and Distribution . . . . . . . . . . 8
4.1.3. Forwarding Operation . . . . . . . . . . . . . . . . 8 4.1.3. Forwarding Operation . . . . . . . . . . . . . . . . 8
4.2. Failure Detection . . . . . . . . . . . . . . . . . . . . 9 4.2. Failure Detection . . . . . . . . . . . . . . . . . . . . 9
4.3. Ring Protection . . . . . . . . . . . . . . . . . . . . . 10 4.3. Ring Protection . . . . . . . . . . . . . . . . . . . . . 10
4.3.1. Wrapping . . . . . . . . . . . . . . . . . . . . . . 10 4.3.1. Wrapping . . . . . . . . . . . . . . . . . . . . . . 11
4.3.2. Short Wrapping . . . . . . . . . . . . . . . . . . . 12 4.3.2. Short Wrapping . . . . . . . . . . . . . . . . . . . 13
4.3.3. Steering . . . . . . . . . . . . . . . . . . . . . . 14 4.3.3. Steering . . . . . . . . . . . . . . . . . . . . . . 15
4.4. Interconnected Ring Protection . . . . . . . . . . . . . 17 4.4. Interconnected Ring Protection . . . . . . . . . . . . . 18
4.4.1. Interconnected Ring Topology . . . . . . . . . . . . 17 4.4.1. Interconnected Ring Topology . . . . . . . . . . . . 18
4.4.2. Interconnected Ring Protection Mechanisms . . . . . . 18 4.4.2. Interconnected Ring Protection Mechanisms . . . . . . 20
4.4.3. Ring Tunnels in Interconnected Rings . . . . . . . . 19 4.4.3. Ring Tunnels in Interconnected Rings . . . . . . . . 20
4.4.4. Interconnected Ring Switching Procedure . . . . . . . 21 4.4.4. Interconnected Ring Switching Procedure . . . . . . . 22
4.4.5. Interconnected Ring Detection Mechanism . . . . . . . 22 4.4.5. Interconnected Ring Detection Mechanism . . . . . . . 23
5. Ring Protection Coordination Protocol . . . . . . . . . . . . 23 5. Ring Protection Coordination Protocol . . . . . . . . . . . . 24
5.1. RPS Protocol . . . . . . . . . . . . . . . . . . . . . . 24 5.1. RPS Protocol . . . . . . . . . . . . . . . . . . . . . . 24
5.1.1. Transmission and Acceptance of RPS Requests . . . . . 26 5.1.1. Transmission and Acceptance of RPS Requests . . . . . 26
5.1.2. RPS PDU Format . . . . . . . . . . . . . . . . . . . 26 5.1.2. RPS PDU Format . . . . . . . . . . . . . . . . . . . 26
5.1.3. Ring Node RPS States . . . . . . . . . . . . . . . . 27 5.1.3. Ring Node RPS States . . . . . . . . . . . . . . . . 27
5.1.4. RPS State Transitions . . . . . . . . . . . . . . . . 29 5.1.4. RPS State Transitions . . . . . . . . . . . . . . . . 29
5.2. RPS State Machine . . . . . . . . . . . . . . . . . . . . 31 5.2. RPS State Machine . . . . . . . . . . . . . . . . . . . . 31
5.2.1. Initial States . . . . . . . . . . . . . . . . . . . 31 5.2.1. Switch Initiation Criteria . . . . . . . . . . . . . 31
5.2.2. State transitions When Local Request is Applied . . . 32 5.2.2. Initial States . . . . . . . . . . . . . . . . . . . 33
5.2.3. State Transitions When Remote Request is Applied . . 36 5.2.3. State transitions When Local Request is Applied . . . 34
5.2.4. State Transitions When Request Addresses to Another 5.2.4. State Transitions When Remote Request is Applied . . 37
Node is Received . . . . . . . . . . . . . . . . . . 39 5.2.5. State Transitions When Request Addresses to Another
5.3. RPS and PSC Comparison on Ring Topology . . . . . . . . . 41 Node is Received . . . . . . . . . . . . . . . . . . 40
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 42 5.3. RPS and PSC Comparison on Ring Topology . . . . . . . . . 43
6.1. G-ACh Channel Type . . . . . . . . . . . . . . . . . . . 42 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 43
6.2. RSP Request Codes . . . . . . . . . . . . . . . . . . . . 43 6.1. G-ACh Channel Type . . . . . . . . . . . . . . . . . . . 44
7. Security Considerations . . . . . . . . . . . . . . . . . . . 43 6.2. RSP Request Codes . . . . . . . . . . . . . . . . . . . . 44
8. Contributing Authors . . . . . . . . . . . . . . . . . . . . 43 7. Security Considerations . . . . . . . . . . . . . . . . . . . 44
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 43 8. Contributing Authors . . . . . . . . . . . . . . . . . . . . 45
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 44 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 45
10.1. Normative References . . . . . . . . . . . . . . . . . . 44 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 45
10.2. Informative References . . . . . . . . . . . . . . . . . 44 10.1. Normative References . . . . . . . . . . . . . . . . . . 45
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 45 10.2. Informative References . . . . . . . . . . . . . . . . . 46
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46
1. Introduction 1. Introduction
As described in 2.5.6.1 of [RFC5654], Ring Protection of MPLS-TP As described in 2.5.6.1 of [RFC5654], Ring Protection of MPLS-TP
requirements , several service providers have expressed much interest requirements, several service providers have expressed much interest
in operating MPLS-TP in ring topologies and require a high-level in operating MPLS-TP in ring topologies and require a high-level
survivability function in these topologies. In operational transport survivability function in these topologies. In operational transport
network deployment, MPLS-TP networks are often constructed with ring network deployment, MPLS-TP networks are often constructed with ring
topologies. It calls for an efficient and optimized ring protection topologies. It calls for an efficient and optimized ring protection
mechanism to achieve simple operation and fast, sub 50 ms, recovery mechanism to achieve simple operation and fast, sub 50 ms, recovery
performance. performance.
The requirements for MPLS-TP [RFC5654] state that recovery mechanisms The requirements for MPLS-TP [RFC5654] state that recovery mechanisms
which are optimized for ring topologies could be further developed if which are optimized for ring topologies could be further developed if
it can provide the following features: it can provide the following features:
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| LSP Label | | LSP Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW Label | | PW Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload | | Payload |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2. Label stack used in MPLS-TP Shared Ring Protection Figure 2. Label stack used in MPLS-TP Shared Ring Protection
4.1.1. Establishment of Ring Tunnel 4.1.1. Establishment of Ring Tunnel
The Ring tunnels are established based on the egress node. The The Ring tunnels are established based on the egress nodes. The
egress node is the node where traffic leaves the ring. LSPs which egress node is the node where traffic leaves the ring. LSPs which
have the same egress node on the ring share the same ring tunnels. have the same egress node on the ring share the same ring tunnels.
In other words, all the LSPs that traverse the ring and exit from the In other words, all the LSPs that traverse the ring and exit from the
same node share the same working ring tunnel and protection ring same node share the same working ring tunnel and protection ring
tunnel. For each egress node, four ring tunnels are established: tunnel. For each egress node, four ring tunnels are established:
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
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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 are determined by the
selected protection mechanism. This will be detailed in subsequent selected 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. Node A and Node B respectively, and all leave the ring at Node D. To
To protect these LSPs that traverse the ring, a clockwise working protect these LSPs that traverse the ring, a clockwise working ring
ring tunnel (RcW_D) via E->F->A->B->C->D, and its anticlockwise tunnel (RcW_D) via E->F->A->B->C->D, and its anticlockwise protection
protection ring tunnel (RaP_D) via D->C->B->A->F->E->D are ring tunnel (RaP_D) via D->C->B->A->F->E->D are established, Also, an
established, Also, an anti-clockwise working ring tunnel (RaW_D) via anti-clockwise working ring tunnel (RaW_D) via C->B->A->F->E->D, and
C->B->A->F->E->D, and its clockwise protection ring tunnel (RcP_D) its clockwise protection ring tunnel (RcP_D) via D->E->F->A->B->C->D
via D->E->F->A->B->C->D are established. For simplicity Figure 3 are established. For simplicity Figure 3 only shows RcW_D and RaP_D.
only shows RcW_D and RaP_D. A similar provisioning should be applied A similar provisioning should be applied for any other node on the
for any other node on the ring. In summary, for each node in ring. In summary, for each node in Figure 3 when acting as egress
Figure 3 when acting as egress node, the ring tunnels are created as node, the ring tunnels are created as follows:
follows:
o To Node A: RcW_A, RaW_A, RcP_A, RaP_A o To Node A: RcW_A, RaW_A, RcP_A, RaP_A
o To Node B: RcW_B, RaW_B, RcP_B, RaP_B o To Node B: RcW_B, RaW_B, RcP_B, RaP_B
o To Node C: RcW_C, RaW_C, RcP_C, RaP_C o To Node C: RcW_C, RaW_C, RcP_C, RaP_C
o To Node D: RcW_D, RaW_D, RcP_D, RaP_D o To Node D: RcW_D, RaW_D, RcP_D, RaP_D
o To Node E: RcW_E, RaW_E, RcP_E, RaP_E o To Node E: RcW_E, RaW_E, RcP_E, RaP_E
skipping to change at page 10, line 17 skipping to change at page 10, line 17
failure in the links that are connected to the failed node. failure in the links that are connected to the failed node.
4.3. Ring Protection 4.3. Ring Protection
This section specifies the ring protection mechanisms in detail. In This section specifies the ring protection mechanisms in detail. In
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 example, the corresponding anti-clockwise protection ring tunnel as example,
but the mechanism is applicable in the same way to the anti-clockwise but the mechanism is applicable in the same way to the anti-clockwise
working and clockwise protection ring tunnels. working and clockwise protection ring tunnels.
Taking the topology in Figure 4 as example, the LSP1 enters the ring In ring network, each working ring tunnel is associated with a
at Node A and leaves the ring at Node D. In normal state, LSP1 is protection ring tunnel in the opposite direction, and every node can
obtain the ring topology either by configuration or via some topology
discovery mechanism. The ring topology and the connectivity (Intact
or Severed) between the adjacent ring nodes form the ring map. Each
ring node maintains the ring map and use it to peform ring
protection.
Taking the topology in Figure 4 as example, LSP1 enters the ring at
Node A and leaves the ring at Node D. In normal state, LSP1 is
carried by clockwise working ring tunnel (RcW_D) through the path carried by 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](original data traffic carried by LSP1) -> [LSP1](original data traffic carried by LSP1) ->
[RCW_D(B)|LSP1](NodeA) -> [RCW_D(C)|LSP1](NodeB) -> [RCW_D(D)| [RCW_D(B)|LSP1](NodeA) -> [RCW_D(C)|LSP1](NodeB) -> [RCW_D(D)|
LSP1](NodeC) -> [LSP1](data traffic carried by LSP1). Then at node D LSP1](NodeC) -> [LSP1](data traffic carried by LSP1). Then at node D
the packet will be forwarded based on label stack of LSP1. the packet will be forwarded based on the label stack of LSP1.
The following sections describes the protection mechanisms used in Three typical ring protection mechanisms are specified in this
ring topology. section: wrapping, short wrapping and steering.
In wrapping ring protection, node which detects a failure or accepts
a switch request switches the traffic impacted by the failure to the
opposite direction (away from the failure). In this way, the
impacted traffic is switched to the protection ring tunnel by the
switching node upstream to the failure, then travels around the ring
to the other switching node through the protection ring tunnel, where
it is switched back onto the working ring tunnel and reach the egress
node.
Short wrapping ring protection provides some optimization to wrapping
protection, in which the impacted traffic is only switched once to
the protection ring tunnel by the switching node upstream to the
failure. At the egress node, the traffic leave the ring from the
protection ring tunnel. This can reduce the traffic detour of
wrapping protection.
Steering ring protection implies that the node that detects a failure
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
impaced traffic, the ingress node (which adds traffic to the ring)
perform switching from working to the protection ring tunnel, and at
the egress node the traffic leaves the ring from the protection ring
tunnel.
The following sections describes these protection mechanisms in
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 the link failure and closed ring protection tunnel can protect both the link failure and
the node failure. the node failure.
4.3.1.1. Wrapping for Link Failure 4.3.1.1. Wrapping for Link Failure
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 OAM mechanism; if it is a uni-directional failure, one of the two via OAM mechanism; if it is a uni-directional failure, one of the two
nodes would detect the failure and it would inform the other node via nodes would detect the failure and it would inform the other node via
the Ring Protection Switch Protocol (RPS) which is specified in the Ring Protection Switch Protocol (RPS) which is specified in
section 5. Then Node B switches the clockwise working ring tunnel section 5. Then Node B switches the clockwise working ring tunnel
(RcW_D) to the anticlockwise protection ring tunnel (RaP_D) and Node (RcW_D) to the anticlockwise protection ring tunnel (RaP_D) and Node
C switches anticlockwise protection ring tunnel(RaP_D) to the C switches anticlockwise protection ring tunnel(RaP_D) back to the
clockwise working ring tunnel(RcW_D). The data traffic which enters clockwise working ring tunnel (RcW_D). The data traffic which enters
the ring at Node A and leaves the ring at Node D follows the path the ring at 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](Original data traffic) -> [RcW_D(B)|LSP1](Node A) -> [LSP1](Original data traffic) -> [RcW_D(B)|LSP1](Node A) ->
[RaP_D(A)|LSP1](Node B) -> [RaP_D(F)|LSP1](Node A) -> [RaP_D(E)|LSP1] [RaP_D(A)|LSP1](Node B) -> [RaP_D(F)|LSP1](Node A) -> [RaP_D(E)|LSP1]
(Node F) -> [RaP_D(D)|LSP1] (Node E) -> [RaP_D(C)|LSP1] (Node D) -> (Node F) -> [RaP_D(D)|LSP1] (Node E) -> [RaP_D(C)|LSP1] (Node D) ->
[RcW_D(D)|LSP1](Node C) -> [LSP1](data traffic leaves the ring). [RcW_D(D)|LSP1](Node C) -> [LSP1](data traffic leaves the ring).
+---+#####[RaP_D(F)]######+---+ +---+#####[RaP_D(F)]######+---+
| F |---------------------| A | +-- LSP1 | F |---------------------| A | +-- LSP1
skipping to change at page 11, line 48 skipping to change at page 12, line 43
The data traffic which enters the ring at Node A and exits at Node D The data traffic 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](original data traffic carried by LSP1) -> [LSP1](original data traffic carried by LSP1) ->
[RaP_D(F)|LSP1](NodeA) -> [RaP_D(E)|LSP1](NodeF) -> [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](data traffic carried by LSP1). (NodeC) -> [LSP1](data traffic carried by LSP1).
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 is propagated to all the ring nodes, the wrapping protection location information is propagated to all the ring nodes, the
mechanism may cause temporary traffic loop: node C detects the wrapping protection mechanism may cause temporary traffic loop: node
failure and switches the traffic from the clockwise work ring tunnel C detects the failure and switches the traffic from the clockwise
(RcW_D) to the anticlockwise protection ring tunnel (RaP_D), node E work ring tunnel (RcW_D) to the anticlockwise protection ring tunnel
also detects the failure and would switch the traffic from (RaP_D), node E also detects the failure and would switch the traffic
anticlockwise protection ring tunnel (RaP_D) back to the clockwise from anticlockwise protection ring tunnel (RaP_D) back to the
work ring tunnel (RcW_D). A possible mechanism to mitigate the clockwise work ring tunnel (RcW_D). A possible mechanism to mitigate
temporary loop problem is: the TTL of the ring tunnel label is set to the temporary loop problem is: the TTL of the ring tunnel label is
2*N by the ingress ring node of the traffic, where N is the number of set to 2*N by the ingress ring node of the traffic, where N is the
nodes on the ring. number of nodes on the ring.
+---+#####[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)
#/* *\# #/* *\#
+---+ xxxxx +---+ xxxxx
| E | x B x | E | x B x
+---+ xxxxx +---+ xxxxx
skipping to change at page 12, line 33 skipping to change at page 13, line 28
LSP1 +-- | D |-------------------| C | LSP1 +-- | D |-------------------| C |
+---+#####[RaP_D(C)]####+---+ +---+#####[RaP_D(C)]####+---+
-----physical links xxxxxx Failure Node -----physical links xxxxxx Failure Node
*****RcW_D ###### RaP_D *****RcW_D ###### RaP_D
Figure 6. Wrapping for node failure Figure 6. Wrapping for node failure
4.3.2. Short Wrapping 4.3.2. Short Wrapping
With the traditional wrapping protection scheme, Protection switching With the traditional wrapping protection scheme, protection switching
is executed at both nodes detecting the failure, consequently the is executed at both nodes adjacent to the failure, consequently the
traffic will be wrapped twice. This mechanism will cause additional traffic will be wrapped twice. This mechanism will cause additional
latency and bandwidth consumption when traffic is switched to the latency and bandwidth consumption when traffic is switched to the
protection path. protection path.
With short wrapping protection, data traffic switching is executed With short wrapping protection, data traffic switching is executed
only at the upstream node detecting the failure, and data traffic only at the node upstream to the failure, and data traffic leaves the
leaves the ring in the protection ring tunnel at the egress node. ring in the protection ring tunnel at the egress node. This scheme
This scheme can reduce the additional latency and bandwidth can reduce the additional latency and bandwidth consumption when
consumption when traffic is switched to the protection path. traffic is switched to the protection path.
In the traditional wrapping solution, the protection ring tunnel is a In the traditional wrapping solution, in normal state the protection
closed ring in normal state, while in the short wrapping solution, ring tunnel is a closed ring, while in the short wrapping solution,
the protection ring tunnel is ended at the egress node, which is the protection ring tunnel is ended at the egress node, which is
similar to the working ring tunnel. Short wrapping is easy to similar to the working ring tunnel. Short wrapping is easy to
implement in shared ring protection because both the working and implement in shared ring protection because both the working and
protection ring tunnels are terminated on the egress nodes. Figure 7 protection ring tunnels are terminated on the egress nodes. Figure 7
shows the clockwise working ring tunnel and the anticlockwise shows the clockwise working ring tunnel and the anticlockwise
protection ring 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 occurs in the protection ring the opposite direction. The difference occurs in the protection ring
tunnel at egress node. In short wrapping protection, Rap_D ends in tunnel at egress node. In short wrapping protection, Rap_D ends in
Node D and then traffic will be forwarded based on the LSP labels. Node D and then traffic will be forwarded based on the LSP labels.
Thus with short wrapping mechanism, LSP1 will follow the path Thus with short wrapping mechanism, LSP1 will follow the path
A->B->A->F->E->D when link failure between Node B and Node C happens. A->B->A->F->E->D when link failure between Node B and Node C happens.
For node failure, the protection with short wrapping is similar to
the mechanism with link failure.
+---+#####[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 44 skipping to change at page 14, line 40
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 failure scenarios which happen on a non-egress node, short For the node failure which happens on a non-egress node, short
wrapping protection switching is similar to the link failure 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 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
is propagated to all the ring nodes, node C switches all the traffic information is propagated to all the ring nodes, node C switches all
on the working ring tunnel RcW_D to the protection ring tunnel RaP_D the traffic on the working ring tunnel RcW_D to the protection ring
in the opposite direction. When the traffic arrives at node E which tunnel RaP_D in the opposite direction. When the traffic arrives at
also detects the failure of node D, the protection ring tunnel RaP_D node E which also detects the failure of node D, the protection ring
cannot be used to forward traffic to node D. Since with short tunnel RaP_D cannot be used to forward traffic to node D. Since with
wrapping mechanism, protection switching can only be performed once short wrapping mechanism, protection switching can only be performed
from the working ring tunnel to the protection ring tunnel, thus node once from the working ring tunnel to the protection ring tunnel, thus
E MUST NOT switch the traffic which is already carried on the node E MUST NOT switch the traffic which is already carried on the
protection ring tunnel back to the working ring tunnel in the protection ring tunnel back to the working ring tunnel in the
opposite direction. Instead, node E will discard the traffic opposite direction. Instead, node E will discard the traffic
received on RaP_D locally. This can avoid the temporary traffic loop received on RaP_D locally. This can avoid the temporary traffic loop
when the faiulre happens on the egress node of the ring tunnel. This when the failure happens on the egress node of the ring tunnel. This
also illustrates one of the benefits of having separate working and also illustrates one of the benefits of having separate working and
protection ring tunnels in each ring direction. protection ring tunnels in each ring direction.
+---+#####[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)
#/* *\# #/* *\#
+---+ +---+ +---+ +---+
skipping to change at page 14, line 44 skipping to change at page 15, line 39
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
In ring topology, each working ring tunnel is associated with a With steering protection mechanism, the ingress node (which adds
protection ring tunnel in the opposite direction, and every node can traffic to the ring) perform switching from working to the protection
obtain the ring topology either by configuration or via some topology ring tunnel, and at the egress node the traffic leaves the ring from
discovery mechanism. The ring topology and the connectivity (Intact the protection ring tunnel.
or Severed) between the adjacent ring nodes form the ring map. Every
ring node maintains its ring map. When a failure occurs in the ring, When a failure occurs in the ring, the node which detects the failure
the nodes that detect the failure via OAM mechanism will transmit the via OAM mechanism sends the failure information in the opposite
failure information in the opposite direction of the failure hop by direction of the failure hop by hop along the ring using RPS request
hop along the ring. When a node receives the message that identifies message. When a ring node receives the RPS message which identifies
a failure, it can quickly determine the location of the fault by a failure, it can quickly determine the location of the fault by
using the topology information that is maintained by the node and using the topology information that is maintained by the node and
upate the ring map accordingly, then it can determine whether the update the ring map accordingly, then it can determine whether the
LSPs entering the ring locally need to switchover or not. For LSPs LSPs entering the ring locally need to switchover or not. For LSPs
that needs to switchover, it will switch the LSPs from the working that needs to switchover, it will switch the LSPs from the working
ring tunnels to its corresponding protection ring tunnels. ring tunnels to its corresponding protection ring tunnels.
Ring map of F +--LSPl 4.3.3.1. Steering for Link Failure
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)]
#/* [RcW_D(F)] *\# #/* [RcW_D(F)] *\#
+-+-+-+-+-+-+-+ #/* *\# +-+-+-+-+-+-+-+ #/* *\#
|E|F|A|B|C|D|E| +---+ +---+ +-- LSP2 |E|F|A|B|C|D|E| +---+ +---+ +-- LSP2
+-+-+-+-+-+-+-+ | E | | B | +-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+ | E | | B | +-+-+-+-+-+-+-+
skipping to change at page 15, line 42 skipping to change at page 16, line 39
+-+-+-+-+-+-+ +-+-+-+-+-+-+ +-+-+-+-+-+-+ +-+-+-+-+-+-+
----- physical links ***** RcW_D ##### RaP_D ----- physical links ***** RcW_D ##### RaP_D
I: Intact S: Severed I: Intact S: Severed
Figure 9. Steering operation and protection switching Figure 9. Steering operation and protection switching
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 the normal state, LSP1 is carried by the clockwise working ring In normal state, LSP1 is carried by the clockwise working ring tunnel
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]
[LSP1] -> [RcW_D(B)|LSP1](NodeA) -> [RcW_D(C)| LSP1](NodeB) -> -> [RcW_D(B)|LSP1](NodeA) -> [RcW_D(C)| LSP1](NodeB) ->
[RcW_D(D)|LSP1](NodeC) -> [LSP1] (data traffic carried by LSP1) . [RcW_D(D)|LSP1](NodeC) -> [LSP1] (data traffic carried by LSP1) .
LSP2 is carried by the clockwise working ring tunnel (RcW_D) throught LSP2 is carried by the clockwise working ring tunnel (RcW_D) throught
the path B->C->D, the label operation is: [LSP2] -> the path B->C->D, the label operation is: [LSP2] ->
[RcW_D(C)|LSP2](NodeB) -> [RcW_D(D)|LSP2](NodeC) -> [LSP2] (data [RcW_D(C)|LSP2](NodeB) -> [RcW_D(D)|LSP2](NodeC) -> [LSP2] (data
traffic carried by LSP2) . traffic carried by LSP2) .
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
skipping to change at page 16, line 28 skipping to change at page 17, line 24
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 topology, it is aware that there is a fault on the state of its ring topology, it is aware that there is a fault on the
clockwise working ring tunnel to node D (RcW_D), and LSP1 enters the clockwise working ring tunnel to node D (RcW_D), and LSP1 enters the
ring locally and is carried by this ring tunnel, thus Node A will ring locally and is carried by this ring tunnel, thus Node A will
decide to switch the LSP1 onto the anticlockwise protection ring decide to switch the LSP1 onto the anticlockwise protection ring
tunnel to node D (RaP_D). After the switchover, LSP1 will follow the tunnel to node D (RaP_D). After the switchover, LSP1 will follow the
path A->F->E->D, the label operation is: [LSP1] -> [RaP_D(F)| path A->F->E->D, the label operation is: [LSP1] -> [RaP_D(F)|
LSP1](NodeA) -> [RaP_D(E)|LSP1](NodeF) -> [RaP_D(D)|LSP1](NodeE) -> LSP1](NodeA) -> [RaP_D(E)|LSP1](NodeF) -> [RaP_D(D)|LSP1](NodeE) ->
[LSP1] (data traffic carried by LSP1). [LSP1] (data traffic carried by LSP1).
The same also apply to the operation of LSP2. When Node B updates The same procedure also applies to the operation of LSP2. When Node
the link state of its ring topology, and finds out that the working B updates the link state of its ring topology, and finds out that the
ring tunnel RcW_D has failed, it will switch the LSP2 to the working ring tunnel RcW_D has failed, it will switch the LSP2 to the
anticlockwise protection tunnel RaP_D. After the switchover, LSP2 anticlockwise protection tunnel RaP_D. After the switchover, LSP2
goes through the path B->A->F->E->D, and the label operation is: goes through the path B->A->F->E->D, and the label operation is:
[LSP2] -> [RaP_D(A)|LSP2](NodeB) -> [RaP_D(F)|LSP2](NodeA) -> [LSP2] -> [RaP_D(A)|LSP2](NodeB) -> [RaP_D(F)|LSP2](NodeA) ->
[RaP_D(E)|LSP2](NodeF) -> [RaP_D(D)|LSP2](NodeE) -> [LSP2](data [RaP_D(E)|LSP2](NodeF) -> [RaP_D(D)|LSP2](NodeE) -> [LSP2](data
traffic carried by LSP2). traffic carried by LSP2).
Then assume the link between nodes A and B breaks down, as shown in Assume the link between nodes A and B breaks down, as shown in
Figure 10. Similar to the above failure case, Node B will detect a Figure 10. Similar to the above failure case, Node B will detect a
fault in the link between A and B, and it will update the link state fault in the link between A and B, and it will update its ring map,
of its ring topology, changing the link state between A and B from changing the link state between A and B from normal to fault. The
normal to fault. The state report message is sent hop by hop in the state report message is sent hop by hop in the clockwise direction,
clockwise direction, notifying every node that there is a fault notifying every node that there is a fault between node A and B, and
between node A and B, and every node updates the link state of its every node updates the link state of its ring topology. As a result,
ring topology. As a result, Node A will detect a fault in the Node A will detect a fault in the working ring tunnel to node D, and
working ring tunnel to node D, and switch LSP1 to the protection ring switch LSP1 to the protection ring tunnel, while Node B determine
tunnel, while Node B determine that the working ring tunnel for LSP2 that the working ring tunnel for LSP2 still works fine, and will not
still works fine, and will not perform the switchover. perform the switchover.
/-- LSPl /-- 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|S|I|I|I|I| #/* x |S|I|I|I|I|I| |I|S|I|I|I|I| #/* x |S|I|I|I|I|I|
+-+-+-+-+-+-+ #/* x +-+-+-+-+-+-+ +-+-+-+-+-+-+ #/* x +-+-+-+-+-+-+
[RaP_D(E)] #/*[RcW_D(F)] [RcW_D(B)]x [RaP_D(A)] [RaP_D(E)] #/*[RcW_D(F)] [RcW_D(B)]x [RaP_D(A)]
#/* x +-- LSP2 #/* x +-- LSP2
+-+-+-+-+-+-+-+ +---+ +---++-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+ +---+ +---++-+-+-+-+-+-+-+
skipping to change at page 17, line 29 skipping to change at page 18, line 29
+-+-+-+-+-+-+-+ #\* */# +-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+ #\* */# +-+-+-+-+-+-+-+
|D|E|F|A|B|C|D| +---+ ***[RcW_D(D)]*** +---+ |C|D|E|F|A|B|C| |D|E|F|A|B|C|D| +---+ ***[RcW_D(D)]*** +---+ |C|D|E|F|A|B|C|
+-+-+-+-+-+-+-+ +-- | 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
For node failure which happens on a non-egress node, steering
protection switching is similar to the link failure case as described
in the previous section.
If the failure occurs at the egress node of the LSP, since the
ingress node can update its ring map according to the received RPS
messages, it will determine that the egress node is not reachable
after the failure, thus it will not send traffic to either the
working or protection tunnel, and 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 often used in MPLS-TP networks. This Interconnected ring topology is widely used in MPLS-TP networks.
document will discuss two typical interconnected ring topologies: This document will discuss two typical interconnected ring
topologies:
1. Single-node interconnected rings 1. Single-node interconnected rings
In single-node interconnected rings, the connection between In single-node interconnected rings, the connection between
the two rings is through a single node. Because the the two rings is through a single node. Because the
interconnection node is in fact a single point of failure, interconnection node is in fact a single point of failure,
this topology should be avoided in real transport networks. this topology should be avoided in real transport networks.
Figure 10 shows the topology of single-node interconnected Figure 11 shows the topology of single-node interconnected
rings. Node C is the interconnection node between Ring1 and rings. Node C is the interconnection node between Ring1 and
Ring2. Ring2.
2. Dual-node interconnected rings 2. Dual-node interconnected rings
In dual-node interconnected rings, the connection between the In dual-node interconnected rings, the connection between the
two rings is through two nodes. The two interconnection nodes two rings is through two nodes. The two interconnection nodes
belong to both interconnected rings. This topology can belong to both interconnected rings. This topology can
recover from one interconnection node failure. recover from one interconnection node failure.
skipping to change at page 18, line 44 skipping to change at page 20, line 9
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
| F |------| E |------| D |------| J |------| I | | F |------| E |------| D |------| J |------| I |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
Figure 12. Dual-node interconnected rings Figure 12. Dual-node interconnected rings
4.4.2. Interconnected Ring Protection Mechanisms 4.4.2. Interconnected Ring Protection Mechanisms
Interconnected rings can be treated as two independent rings. Ring Interconnected rings can be treated as two independent rings. Ring
protection switching (RPS) protocol operates on each ring protection switching (RPS) protocol operates on each ring
independently. Failure in one ring only triggers protection independently. Failure happened on one ring only triggers protection
switching on the ring itself and does not affect the other ring. switching on the ring itself and does not affect the other ring,
This way, protection switching on each ring is the same as the unless the failure is on the interconnection node. This way,
mechanisms described in section 4.3. protection switching on each ring is the same as the mechanisms
described in section 4.3.
The service LSPs that traverse the interconnected rings via the The service LSPs that traverse the interconnected rings use seperate
interconnection nodes MUST use different ring tunnels in different ring tunnels on each ring, and the LSPs on different rings are
rings, and the service LSPs traversing the interconnected rings are
stitched by the interconnection node. On the interconnection node, stitched by the interconnection node. On the interconnection node,
the ring tunnel label used in the source ring will be popped, the the ring tunnel label of the source ring is popped, then LSP label is
service LSP label will be swapped, and the ring tunnel label of the swapped, after that the ring tunnel label of the destination ring is
destination ring will be pushed. pushed.
In the dual-node interconnected ring scenario, the two In the dual-node interconnected ring scenario, the two
interconnection nodes can be managed as a virtual interconnection interconnection nodes can be managed as a virtual node group. In
node group. Each ring should assign working and protection ring addition to the ring tunnels to each physical ring node, Each ring
tunnels for the virtual interconnection node group. Both the SHOULD assign the working and protection ring tunnels to the virtual
interconnection nodes in the virtual interconnection node group can interconnection node group. In addition, on both nodes in the
terminate the working ring tunnel of each ring. The protection ring virtual interconnection node group, the same LSP label is assigned
tunnel is used to protect the working ring tunnel of each ring and for each traversed LSP. This way, any interconnection node in the
can be terminated by any node in the virtual interconnection node virtual node group can terminate the working or protection ring
group. tunnels targeted to the virtual node group, and stitch the service
LSP from the source ring tunnel to the destination ring tunnel.
On the nodes in the virtual interconnection node group of the dual-
node interconnected ring, the same label is allocated for each
service LSP. This way any interconnection node in the virtual node
group can stitch the service LSPs between the source ring tunnel and
the destination ring tunnel.
When the service traffic passes through the interconnection node, the When the service LSP passes through the interconnected rings, the
direction of the working ring tunnels in each ring for this service direction of the working ring tunnels used on both rings SHOULD be
traffic should be the same. For example, if the working ring tunnel the same. For example, if the service LSP uses the clockwise working
follows the clockwise direction in Ring1, the working ring tunnel for ring tunnel on Ring1, when the service LSP leaves Ring1 and enters
the same service traffic in Ring2 SHOULD also follow the clockwise Ring2, the working ring tunnel used on Ring2 SHOULD also follow the
direction when the service leaves Ring1 and enters Ring2. clockwise direction.
4.4.3. Ring Tunnels in Interconnected Rings 4.4.3. Ring Tunnels in Interconnected Rings
The same ring tunnels as described in section 4.1 are used in each The same ring tunnels as described in section 4.1 are used in each
ring of the interconnected rings. Note that ring tunnels to the ring of the interconnected rings. In addition, ring tunnels to the
virtual interconnection node group will be established by each ring virtual interconnection node group are established on each ring of
of the interconnected rings, i.e.: the interconnected rings, i.e.:
o one clockwise working ring tunnel to the virtual interconnection o one clockwise working ring tunnel to the virtual interconnection
node group node group
o one anticlockwise protection ring tunnel to the virtual o one anticlockwise protection ring tunnel to the virtual
interconnection node group interconnection node group
o one anticlockwise working ring tunnel to the virtual o one anticlockwise working ring tunnel to the virtual
interconnection node group interconnection node group
o one clockwise protection ring tunnel to the virtual o one clockwise protection ring tunnel to the virtual
interconnection node group interconnection node group
These ring tunnels will terminated at all nodes in the virtual These ring tunnels will terminated at any node in the virtual
interconnection node group. interconnection node group.
For example, all the ring tunnels on Ring1 of Figure 12 are For example, all the ring tunnels on Ring1 in Figure 13 are
established as follows: provisioned as follows:
o To Node A: R1cW_A, R1aW_A, R1cP_A, R1aP_A o To Node A: R1cW_A, R1aW_A, R1cP_A, R1aP_A
o To Node B: R1cW_B, R1aW_B, R1cP_B, R1aP_B o To Node B: R1cW_B, R1aW_B, R1cP_B, R1aP_B
o To Node C: R1cW_C, R1aW_C, R1cP_C, R1aP_C o To Node C: R1cW_C, R1aW_C, R1cP_C, R1aP_C
o To Node D: R1cW_D, R1aW_D, R1cP_D, R1aP_D o To Node D: R1cW_D, R1aW_D, R1cP_D, R1aP_D
o To Node E: R1cW_E, R1aW_E, R1cP_E, R1aP_E o To Node E: R1cW_E, R1aW_E, R1cP_E, R1aP_E
o To Node F: R1cW_F, R1aW_F, R1cP_F, R1aP_F o To Node F: R1cW_F, R1aW_F, R1cP_F, R1aP_F
o To the virtual interconnection node group (including Node F and o To the virtual interconnection node group (including Node F and
Node A): R1cW_F&A, R1aW_F&A, R1cP_F&A, R1aP_F&A Node A): R1cW_F&A, R1aW_F&A, R1cP_F&A, R1aP_F&A
All the ring tunnels established in Ring2 in Figure 13 are All the ring tunnels on Ring2 in Figure 13 are provisioned as
provisioned as follows: follows:
o To Node A: R2cW_A, R2aW_A, R2cP_A, R2aP_A o To Node A: R2cW_A, R2aW_A, R2cP_A, R2aP_A
o To Node F: R2cW_F, R2aW_F, R2cP_F, R2aP_F o To Node F: R2cW_F, R2aW_F, R2cP_F, R2aP_F
o To Node G: R2cW_G, R2aW_G, R2cP_G, R2aP_G o To Node G: R2cW_G, R2aW_G, R2cP_G, R2aP_G
o To Node H: R2cW_H, R2aW_H, R2cP_H, R2aP_H o To Node H: R2cW_H, R2aW_H, R2cP_H, R2aP_H
o To Node I: R2cW_I, R2aW_I, R2cP_I, R2aP_I o To Node I: R2cW_I, R2aW_I, R2cP_I, R2aP_I
o To Node J: R2cW_J, R2aW_J, R2cP_J, R2aP_J o To Node J: R2cW_J, R2aW_J, R2cP_J, R2aP_J
o To the virtual interconnection node group(including Node F and o To the virtual interconnection node group (including Node F and
Node A): R2cW_FandA, R2aW_FandA, R2cP_FandA, R2aP_FandA Node A): R2cW_F&A, R2aW_F&A, R2cP_F&A, R2aP_F&A
+---+cccccccccccc +---+ +---+cccccccccccc +---+
| H |-------------| I |--->LSP1 | H |-------------| I |--->LSP1
+---+ +---+ +---+ +---+
c/a a\ c/a a\
c/a a\ c/a a\
c/a a\ c/a a\
+---+ +---+ +---+ +---+
| G | Ring2 | J | | G | Ring2 | J |
+---+ +---+ +---+ +---+
c\a a/c c\a a/c
skipping to change at page 21, line 40 skipping to change at page 22, line 40
+---+ccccccccccccc+---+ +---+ccccccccccccc+---+
ccccccccccc R1cW_F&A ccccccccccc R1cW_F&A
aaaaaaaaaaa R1aP_F&A aaaaaaaaaaa R1aP_F&A
ccccccccccc R2cW_I ccccccccccc R2cW_I
aaaaaaaaaaa R2aP_I aaaaaaaaaaa R2aP_I
Figure 13. Ring tunnels for the interconnected rings Figure 13. Ring tunnels for the interconnected rings
4.4.4. Interconnected Ring Switching Procedure 4.4.4. Interconnected Ring Switching Procedure
As shown in Figure 13, for the service traffic LSP1 which enters As shown in Figure 13, for the service LSP1 which enters Ring1 at
Ring1 at Node D and leaves Ring1 at Node F and continues to enter Node D and leaves Ring1 at Node F and continues to enter Ring2 at
Ring2 at Node F and leaves Ring2 at Node I, the protection scheme is Node F and leaves Ring2 at Node I, the short wrapping protection
described as below. scheme is described as below.
In normal state, LSP1 follows R1cW_F&A in Ring1 and R2CW_I in Ring2. In normal state, LSP1 follows R1cW_F&A in Ring1 and R2cW_I in Ring2.
The label used for the working ring tunnel R1cW_F&A in Ring1 is At the interconnection node F, the label used for the working ring
popped and the label used for the working ring tunnel R2cW_I will be tunnel R1cW_F&A in Ring1 is popped, the LSP label is swapped, and the
pushed based the inner label lookup at the interconnection node F. label used for the working ring tunnel R2cW_I in Ring2 will be pushed
The working path that the service traffic LSP1 follows is: based the inner LSP label lookup. The working path that the service
LSP1->R1cW_F&A (D->E->F)->R2cW_I(F->G->H->I)->LSP1. LSP1 follows is: LSP1->R1cW_F&A (D->E->F)->R2cW_I(F->G->H->I)->LSP1.
In case of link failure, for example, when a failure occurs on the In case of link failure, for example, when a failure occurs on the
link between Node F and Node E, Nodes F and E will detect the failure link between Node F and Node E, Node E will detect the failure and
and execute protection switching as described in 4.3.1.1. The path execute protection switching as described in 4.3.2. The path that
that the service traffic LSP1 follows after switching change to the service LSP1 follows after switching change to: LSP1->R1cW_F&A(D-
LSP1->R1cW_F&A(D->E)->R1aP_F&A(E->D->C->B->A->F)->R1cW_F(F) >E)->R1aP_F&A(E->D->C->B->A)->R2cW_I(A->F->G->H->I)->LSP1.
->R2cW_I(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, Nodes F and D will detect the failure occurs at Node E in Ring1, Node D will detect the failure and
failure and execute protection switching as described in 4.3.1.2. execute protection switching as described in 4.3.2. The path that
The path that the service traffic LSP1 follows after switching the service LSP1 follows after switching becomes:
becomes: LSP1->R1cW_F&A(D)->R1aP_F&A(D->C->B->A->F)-> LSP1->R1cW_F&A(D)->R1aP_F&A(D->C->B->A)->R2cW_I(A->F->G->H->I)->LSP1.
R1cW_F(F)->R2cW_I(F->G->H->I).
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. Nodes E and A in Ring1 failure occurs at the interconnection Node F. Node E in Ring1 will
will detect the failure, and execute protection switching as detect the failure, and execute protection switching as described in
described in 4.3.1.2. Nodes G and A in Ring2 will also detects the 4.3.2. Node A in Ring2 will also detect the failure, and execute
failure, and execute protection switching. The path that the service protection switching as described in 4.3.2. The path that the
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)->R1cW_A(A) LSP1->R1cW_F&A(D->E)->R1aP_F&A(E->D->C->B->A)->R2aP_I(A->J->I)->LSP1.
->R2aP_I(A->J->I)->LSP1.
4.4.5. Interconnected Ring Detection Mechanism 4.4.5. Interconnected Ring Detection Mechanism
As show in Figure 14, the service traffic LSP1 traverses A->B->C in As show in Figure 13, in normal state the service traffic LSP1
Ring1 and C->G->H->I in Ring2. Node C and Node D are the traverses D->E->F in Ring1 and F->G->H->I in Ring2. Node A and F are
interconnection nodes. When both the link between Node C and Node G the interconnection nodes. When both the link between Node F and
and the link between Node C and Node D fail, the ring tunnel from Node G and the link between Node F and Node A fail, the ring tunnel
Node C to Node I in Ring2 becomes unreachable. However, Node D is from Node F to Node I in Ring2 becomes unreachable. However, the
still available, and LSP1 can still reach Node I. other interconnection node A is still available, and LSP1 can still
reach Node I via node A.
+---+ *********+---+**********+---+ +---+**********+---+
LSP1->| A |----------| B |----------| C |XXXXXXXXXX| G |----------| H |
+---+##########+---+##########+---+ +---+##########+---+
|# X #|*
|# X #|*
|# Ring1 X Ring2 #|*
|# X #|*
|# X #|*
+---+##########+---+##########+---+######### +---+##########+---+
| F |----------| E |----------| D |----------| J |----------| I | ->LSP1
+---+ +---+ +---+ +---+ +---+
*********** R1cW_C&D
########### R1aP_C&D
*********** R2cW_I
########### R2aP_I
Figure 14. Interconnected ring
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 each ring reachable. This judgment is based on the knowledge of ring map and
topology and the fault location as described in section 3.4. The the fault location as described in section 3.4. The ring map can be
ring topology can be obtained from the NMS or topology discovery obtained from the NMS or topology discovery mechanisms. The fault
mechanisms. The fault location can be obtained by transmitting the location can be obtained by transmitting the fault information around
fault information around the ring. The nodes that detect the failure the ring. The nodes that detect the failure will transmit the fault
will transmit the fault information in the opposite direction node by information in the opposite direction hop by hop using the RPS
node in the ring. When the interconnection node receives the message protocol message. When the interconnection node receives the message
that informs the failure, it will quickly calculate the location of that informs the failure, it will quickly calculate the location of
the fault by the topology information that is maintained by itself the fault according to the topology information that is maintained by
and determines whether the LSPs entering the ring at itself can reach itself and determines whether the LSPs entering the ring at itself
the destination. If the destination node is reachable, the LSP will can reach the destination. If the destination node is reachable, the
leave the source ring and enter the destination ring. If the LSP will leave the source ring and enter the destination ring. If
destination node is not reachable, the LSP will switch to the the destination node is not reachable, the LSP will switch to the
anticlockwise protection ring tunnel. anticlockwise protection ring tunnel.
In Figure 14, Node C 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 traffic LSP1 for which the destination node unreachable, the service LSP1 for which the destination node on the
on the ring tunnel is Node I should switch to the protection LSP ring2 is Node I MUST switch to the protection ring tunnel (R1aP_F&A)
(R1aP_C&D) and consequently the service traffic LSP1 traverses the and consequently the service traffic LSP1 traverses the
interconnected rings at Node D. Node D will remove the ring tunnel interconnected rings at Node A. Node A will pop the ring tunnel
label of Ring1 and add the ring tunnel label of Ring2. label of Ring1 and push the ring tunnel label of Ring2 and send the
traffic to Node I via ring tunnel (R2aW_I).
5. Ring Protection Coordination Protocol 5. Ring Protection Coordination Protocol
5.1. RPS Protocol 5.1. RPS Protocol
The MSRP protection operation MUST be controlled with the help of the The MSRP protection operation MUST be controlled with the help of the
Ring Protection Switch Protocol (RPS). The RPS processes in each of Ring Protection Switch Protocol (RPS). The RPS processes in each of
the individual ring nodes that form the ring SHOULD communicate using the individual ring nodes that form the ring SHOULD communicate using
the G-ACh channel. the G-ACh channel.
The RPS protocol MUST carry the ring status information and RPS The RPS protocol MUST carry the ring status information and RPS
requests, i.e., automatically initiated and externally initiated, requests, either automatically initiated or externally initiated,
between the ring nodes. between the ring nodes.
Each node on the ring MUST be uniquely identified by assigning it a Each node on the ring MUST be uniquely identified by assigning it a
node ID. The node ID MUST be unique on each ring. The maximum node ID. The node ID MUST be unique on each ring. The maximum
number of nodes on the ring supported by the RPS protocol is 127. number of nodes on the ring supported by the RPS protocol is 127.
The node ID SHOULD be independent of the order in which the nodes The node ID SHOULD be independent of the order in which the nodes
appear on the ring. The node ID is used to identity the source and appear on the ring. The node ID is used to identity the source and
destination nodes of each RPS request. destination nodes of each RPS request.
Every node obtains the ring topology either by configuration or via Every node obtains the ring topology either by configuration or via
some topology discovery mechanism. The ring map consists of the ring some topology discovery mechanism. The ring map consists of the ring
topology information, and connectivity status (Intact or Severed) topology information, and connectivity status (Intact or Severed)
between the adjacent ring nodes, which is determined via the OAM between the adjacent ring nodes, which is determined via the OAM
message exchange between the adjacent nodes. The ring map is used by message exchanged between the adjacent nodes. The ring map is used
every ring node to determine the switchover behavoir of the ring by every ring node to determine the switchover behavior of the ring
tunnels. tunnels.
When no protection switching is active on the ring, each node MUST When no protection switching is active on the ring, each node MUST
dispatch periodically RPS requests to the two adjacent nodes, dispatch periodically RPS requests to the two adjacent nodes,
indicating No Request (NR). When a node determines that a protection indicating No Request (NR). When a node determines that a protection
switching is required, it MUST send the appropriate RPS request in switching is required, it MUST send the appropriate RPS request in
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 15. RPS communication between the ring nodes in case of Figure 14. RPS communication between the ring nodes in case of
no failures 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 span. 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 16. RPS communication between the ring nodes in case of Figure 15. RPS communication between the ring nodes in case of
failure between nodes B and C failure between nodes B and C
Note that in the case of a bidirectional failure such as a cable cut, Note that in the case of a bidirectional failure such as a cable cut,
the two adjacent nodes detect the failure and send each other an RPS the two adjacent nodes detect the failure and send each other an RPS
request in opposite directions. request in opposite directions.
o In rings utilizing the wrapping protection. When the destination o In rings utilizing the wrapping protection. When the destination
node receives the RPS request it MUST perform the switch from/to node receives the RPS request it MUST perform the switch from/to
the working ring tunnels to/from the protection ring tunnels if it the working ring tunnels to/from the protection ring tunnels if it
has no higher priority active RPS request. has no higher priority active RPS request.
o In rings utilizing the short wrapping protection. Only the node
which is directly upstream to the failure on the working ring
tunnel perform the switch from the working ring tunnels to the
protection ring tunnels. This may be triggered by local failure
detection or the received RPS request.
o In rings utilizing the steering protection. When a ring switch is o In rings utilizing the steering protection. When a ring switch is
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 maps (indicating the relative position of the failure stored ring maps (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 RPS request (head
end) MUST drop its protection switches. 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 3.2. 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 span, 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 span. 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
skipping to change at page 26, line 36 skipping to change at page 26, line 49
an RPS message. The ACH MUST NOT include the ACH TLV Header an RPS message. The ACH MUST NOT include the ACH TLV Header
[RFC5586] meaning that no ACH TLVs can be included in the message. [RFC5586] meaning that no ACH TLVs can be included in the message.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|0 0 0 0|0 0 0 0 0 0 0 0| RPS Channel Type (TBD) | |0 0 0 1|0 0 0 0|0 0 0 0 0 0 0 0| RPS Channel Type (TBD) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Dest Node ID | Src Node ID | Request | Reserved | | Dest Node ID | Src Node ID | Request | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17. G-ACh RPS Packet Format Figure 16. G-ACh RPS Packet Format
The following fields MUST be provided: The following fields MUST be provided:
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.
skipping to change at page 27, line 40 skipping to change at page 27, line 51
5.1.3.1. Idle State 5.1.3.1. Idle State
A node in the idle state MUST source the NR request in both A node in the idle state MUST source the NR request in both
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
LSPs/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 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.
skipping to change at page 29, line 13 skipping to change at page 29, line 21
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
All state transitions are triggered by an incoming RPS request All state transitions are triggered by an incoming RPS request
change, a WTR expiration, an externally initiated command, or locally change, a WTR expiration, an externally initiated command, or locally
detected MPLS-TP section failure conditions. detected MPLS-TP section failure conditions.
RPS requests due to a locally detected failure, an externally RPS requests due to a locally detected failure, an externally
initiated command, or received RPS request shall pre-empt existing initiated command, or received RPS request shall pre-empt existing
RPS requests in the prioritized order given in Section 3.1.2, unless RPS requests in the prioritized order given in Section 5.1.2, unless
the requests are allowed to coexist. the requests are allowed to coexist.
5.1.4.1. Transitions Between Idle and Pass-through States 5.1.4.1. Transitions Between Idle and Pass-through States
The transition from the idle state to pass-through state MUST be The transition from the idle state to pass-through state MUST be
triggered by a valid RPS request change, in any direction, from the triggered by a valid RPS request change, in any direction, from the
NR code to any other code, as long as the new request is not destined NR code to any other code, as long as the new request is not destined
to the node itself. Both directions move then into a pass-through to the node itself. Both directions move then into a pass-through
state, so that, traffic entering the node through the protection Ring state, so that, traffic entering the node through the protection Ring
tunnels are transferred transparently through the node. tunnels are transferred transparently through the node.
skipping to change at page 31, line 13 skipping to change at page 31, line 26
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
allowed coexisting automatic initiated command allowed coexisting automatic initiated command
o The receipt of an equal, a higher priority, or an allowed o The receipt of an equal, a higher priority, or an allowed
coexisting RPS request destined to this node coexisting RPS request destined to this node
5.2. RPS State Machine 5.2. RPS State Machine
5.2.1. Initial States 5.2.1. Switch Initiation Criteria
5.2.1.1. Administrative Commands
Administrative commands can be initiated by the network operator
through the Network Management System (NMS). The operator command
may be transmitted to the appropriate node via the MPLS-TP RPS
message.
The following commands can be transferred by the RPS message:
o Lockout of Protection (LP): This command prevents any protection
activity and prevents using ring switches anywhere in the ring.
If any ring switches exist in the ring, this command causes the
switches to drop.
o Forced Switch to protection (FS): This command performs the ring
switch of normal traffic from the working entity to the protection
entity for the span between the node at which the command is
initiated and the adjacent node to which the command is directed.
This switch occurs regardless of the state of the MPLS-TP section
for the requested span, unless a higher priority switch request
exists.
o Manual Switch to protection (MS): This command performs the ring
switch of the normal traffic from the working entity to the
protection entity for the span between the node at which the
command is initiated and the adjacent node to which the command is
directed. This occurs if the MPLS-TP section for the requested
span is not satisfying an equal or higher priority switch request.
o Exercise - Ring (EXER): This command exercises ring protection
switching on the addressed span without completing the actual
switch. The command is issued and the responses (RR) are checked,
but no normal traffic is affected.
The following commands are not transferred by the RPS message:
o Clear: This command clears the administrative command and Wait-To-
Restore timer (WTR) at the node to which the command was
addressed. The node-to-node signaling after the removal of the
externally initiated commands is performed using the no-request
code (NR).
o Lockout of Working: This command prevents the normal traffic
transported over the addressed span from being switched to the
protection entity by disabling the node's capability of requesting
switch for this span in case of failure. If any normal traffic is
already switched on the protection entity, the switch is dropped.
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
span. If the node receives the switch request from the adjacent
node from any side it will perform the requested switch. If the
node receives the switch request addressed to the other node, it
will enter the pass-through state.
5.2.1.2. Automatically Initiated Commands
Automatically initiated commands can be initiated based on MPLS-TP
section layer OAM indication and the received switch requests.
The node can initiate the following switch requests automatically:
o Signal Fail (SF): This command is issued when the MPLS-TP section
layer OAM detects signal failure condition.
o Wait-To-Restore (WTR): This command is issued when MPLS-TP section
detects that the SF condition has cleared. It is used to maintain
the state during the WTR period unless it is pre-empted by a
higher priority switch request. The WTR time may be configured by
the operator in 1 minute steps between 0 and 12 minutes; the
default value is 5 minutes.
o Reverse Request (RR): This command is transmitted to the source
node of the received RPS message over the short path as an
acknowledgment for receiving the switch request.
5.2.2. Initial States
+-----------------------------------+----------------+ +-----------------------------------+----------------+
| State | Signaled RPS | | State | Signaled RPS |
+-----------------------------------+----------------+ +-----------------------------------+----------------+
| A | Idle | NR | | A | Idle | NR |
| | Working: no switch | | | | Working: no switch | |
| | Protection: no switch | | | | Protection: no switch | |
+-----+-----------------------------+----------------+ +-----+-----------------------------+----------------+
| B | Pass-trough | N/A | | B | Pass-trough | N/A |
| | Working: no switch | | | | Working: no switch | |
| | Protection: pass through | | | | Protection: pass through | |
skipping to change at page 32, line 44 skipping to change at page 34, line 5
+-----+-----------------------------+----------------+ +-----+-----------------------------+----------------+
| H | Switching - WTR | WTR | | H | Switching - WTR | WTR |
| | Working: switched | | | | Working: switched | |
| | Protection: switched | | | | Protection: switched | |
+-----+-----------------------------+----------------+ +-----+-----------------------------+----------------+
| I | Switching - EXER | EXER | | I | Switching - EXER | EXER |
| | Working: no switch | | | | Working: no switch | |
| | Protection: no switch | | | | Protection: no switch | |
+-----+-----------------------------+----------------+ +-----+-----------------------------+----------------+
5.2.2. State transitions When Local Request is Applied 5.2.3. State transitions When Local Request is Applied
In the state description below 'O' means that new local request will In the state description below 'O' means that new local request will
be rejected because of exiting request. be rejected because of exiting request.
===================================================================== =====================================================================
Initial state New request New state Initial state New request New state
------------- ----------- --------- ------------- ----------- ---------
A (Idle) LP C (Switching - LP) A (Idle) LP C (Switching - LP)
LW D (Idle - LW) LW D (Idle - LW)
FS E (Switching - FS) FS E (Switching - FS)
skipping to change at page 36, line 11 skipping to change at page 37, line 20
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 span
I (Switching - EXER) I (Switching - EXER)
===================================================================== =====================================================================
5.2.3. 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
------------- ----------- --------- ------------- ----------- ---------
A (Idle) LP C (Switching - LP) A (Idle) LP C (Switching - LP)
FS E (Switching - FS) FS E (Switching - FS)
SF F (Switching - SF) SF F (Switching - SF)
skipping to change at page 39, line 5 skipping to change at page 40, line 8
I (Switching - EXER) LP C (Switching - LP) I (Switching - EXER) LP C (Switching - LP)
FS E (Switching - FS) FS E (Switching - FS)
SF F (Switching - SF) SF F (Switching - SF)
MS G (Switching - MS) MS G (Switching - MS)
WTR N/A WTR N/A
EXER I (Switching - EXER) EXER I (Switching - EXER)
RR I (Switching - EXER) RR I (Switching - EXER)
NR N/A NR N/A
===================================================================== =====================================================================
5.2.4. State Transitions When Request Addresses to Another Node is 5.2.5. State Transitions When Request Addresses to Another Node is
Received Received
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
------------- ----------- --------- ------------- ----------- ---------
A (Idle) LP B (Pass-trough) A (Idle) LP B (Pass-trough)
FS B (Pass-trough) FS B (Pass-trough)
 End of changes. 68 change blocks. 
239 lines changed or deleted 348 lines changed or added

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