draft-ietf-mpls-tp-shared-ring-protection-05.txt   draft-ietf-mpls-tp-shared-ring-protection-06.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: September 28, 2017 China Mobile Expires: December 14, 2017 China Mobile
H. Helvoort H. Helvoort
Hai Gaoming BV Hai Gaoming BV
J. Dong J. Dong
Huawei Technologies Huawei Technologies
March 27, 2017 June 12, 2017
Shared-Ring protection (MSRP) mechanism for ring topology Shared-Ring protection (MSRP) mechanism for ring topology
draft-ietf-mpls-tp-shared-ring-protection-05 draft-ietf-mpls-tp-shared-ring-protection-06
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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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 September 28, 2017. This Internet-Draft will expire on December 14, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 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
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Notation . . . . . . . . . . . . . . . . . . 3 2. Terminology and Notation . . . . . . . . . . . . . . . . . . 3
3. MPLS-TP Ring Protection Criteria and Requirements . . . . . . 4 3. MPLS-TP Ring Protection Criteria and Requirements . . . . . . 4
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 . . . . . . . . . . 7 4.1.2. Label Assignment and Distribution . . . . . . . . . . 8
4.1.3. Forwarding Operation . . . . . . . . . . . . . . . . 7 4.1.3. Forwarding Operation . . . . . . . . . . . . . . . . 8
4.2. Failure Detection . . . . . . . . . . . . . . . . . . . . 8 4.2. Failure Detection . . . . . . . . . . . . . . . . . . . . 9
4.3. Ring Protection . . . . . . . . . . . . . . . . . . . . . 9 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 . . . . . . . . . . . . . . . . . . . . . . 16
4.4. Interconnected Ring Protection . . . . . . . . . . . . . 17 4.4. Interconnected Ring Protection . . . . . . . . . . . . . 19
4.4.1. Interconnected Ring Topology . . . . . . . . . . . . 17 4.4.1. Interconnected Ring Topology . . . . . . . . . . . . 19
4.4.2. Interconnected Ring Protection Mechanisms . . . . . . 19 4.4.2. Interconnected Ring Protection Mechanisms . . . . . . 21
4.4.3. Ring Tunnels in Interconnected Rings . . . . . . . . 20 4.4.3. Ring Tunnels in Interconnected Rings . . . . . . . . 22
4.4.4. Interconnected Ring Switching Procedure . . . . . . . 22 4.4.4. Interconnected Ring Switching Procedure . . . . . . . 24
4.4.5. Interconnected Ring Detection Mechanism . . . . . . . 22 4.4.5. Interconnected Ring Detection Mechanism . . . . . . . 25
5. Ring Protection Coordination Protocol . . . . . . . . . . . . 23 5. Ring Protection Coordination Protocol . . . . . . . . . . . . 26
5.1. RPS Protocol . . . . . . . . . . . . . . . . . . . . . . 23 5.1. RPS and PSC Comparison on Ring Topology . . . . . . . . . 26
5.1.1. Transmission and Acceptance of RPS Requests . . . . . 25 5.2. RPS Protocol . . . . . . . . . . . . . . . . . . . . . . 27
5.1.2. RPS PDU Format . . . . . . . . . . . . . . . . . . . 26 5.2.1. Transmission and Acceptance of RPS Requests . . . . . 29
5.1.3. Ring Node RPS States . . . . . . . . . . . . . . . . 27 5.2.2. RPS PDU Format . . . . . . . . . . . . . . . . . . . 29
5.1.4. RPS State Transitions . . . . . . . . . . . . . . . . 29 5.2.3. Ring Node RPS States . . . . . . . . . . . . . . . . 31
5.2. RPS State Machine . . . . . . . . . . . . . . . . . . . . 31 5.2.4. RPS State Transitions . . . . . . . . . . . . . . . . 33
5.2.1. Switch Initiation Criteria . . . . . . . . . . . . . 31 5.3. RPS State Machine . . . . . . . . . . . . . . . . . . . . 35
5.2.2. Initial States . . . . . . . . . . . . . . . . . . . 33 5.3.1. Switch Initiation Criteria . . . . . . . . . . . . . 35
5.2.3. State transitions When Local Request is Applied . . . 34 5.3.2. Initial States . . . . . . . . . . . . . . . . . . . 37
5.2.4. State Transitions When Remote Request is Applied . . 38 5.3.3. State transitions When Local Request is Applied . . . 38
5.2.5. State Transitions When Request Addresses to Another 5.3.4. State Transitions When Remote Request is Applied . . 42
Node is Received . . . . . . . . . . . . . . . . . . 41 5.3.5. State Transitions When Request Addresses to Another
5.3. RPS and PSC Comparison on Ring Topology . . . . . . . . . 43 Node is Received . . . . . . . . . . . . . . . . . . 45
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 47
6.1. G-ACh Channel Type . . . . . . . . . . . . . . . . . . . 44 6.1. G-ACh Channel Type . . . . . . . . . . . . . . . . . . . 48
6.2. RPS Request Codes . . . . . . . . . . . . . . . . . . . . 45 6.2. RPS Request Codes . . . . . . . . . . . . . . . . . . . . 48
7. Security Considerations . . . . . . . . . . . . . . . . . . . 45 7. Operational Considerations . . . . . . . . . . . . . . . . . 48
8. Contributing Authors . . . . . . . . . . . . . . . . . . . . 45 8. Security Considerations . . . . . . . . . . . . . . . . . . . 49
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 46 9. Contributing Authors . . . . . . . . . . . . . . . . . . . . 50
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 46 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 51
10.1. Normative References . . . . . . . . . . . . . . . . . . 47 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 51
10.2. Informative References . . . . . . . . . . . . . . . . . 47 11.1. Normative References . . . . . . . . . . . . . . . . . . 52
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 48 11.2. Informative References . . . . . . . . . . . . . . . . . 52
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 53
1. Introduction 1. Introduction
As described in [RFC5654], MPLS-TP requirements, section 2.5.6.1, As described in section 2.5.6.1 of [RFC5654], several service
Ring Protection, several service providers have expressed much providers have expressed much interest in operating MPLS-TP in ring
interest in operating MPLS-TP in ring topologies and require a high- topologies and require a high- level survivability function in these
level survivability function in these topologies. In operational topologies. In operational transport network deployment, MPLS-TP
transport network deployment, MPLS-TP networks are often constructed networks are often constructed using ring topologies. This calls for
using ring topologies. This calls for an efficient and optimized an efficient and optimized ring protection mechanism to achieve
ring protection mechanism to achieve simple operation and fast, sub 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 the 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
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Terminology: Terminology:
Ring Node: All nodes in the ring topology are Ring Nodes and they Ring Node: All nodes in the ring topology are Ring Nodes and they
MUST actively participate 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
traversing the ring. The notation used for a ring tunnel is: traversing the ring. The notation used for a ring tunnel is:
R<d><p><X> where <d> = c (clockwise) or a (anticlockwise), <p> = W R<d><p><X> where <d> = c (clockwise) or a (anticlockwise), <p> = W
(working) or 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). The ring map is used by every ring ring nodes (Intact or Severed). The ring map is used by every ring
node to determine the switchover behavior of the ring tunnels. node to determine the switchover behavior of the ring tunnels.
Notation: Notation:
The following syntax will be used to describe the contents of the The following syntax will be used to describe the contents of the
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.
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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
Each ring-node requires only one instance of the RPS protocol. The Each ring node requires only one instance of the RPS protocol per
OAM of the links connected to the adjacent ring-nodes has to be ring. The OAM of the links connected to the adjacent ring-nodes has
forwarded to only this instance in order to trigger protection. to be forwarded to only this instance in order to trigger protection.
For detailed information, see section 5.2.
b. The number of elements of recovery in the ring b. The number of elements of recovery in the ring
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. For detailed
information, see section 5.2.
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. For
detailed information, see section 4.1.2.
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
means that only one maintenance operation is required per ring-node. Each ring-node requires only one instance of the RPS protocol per
ring. This means that only one maintenance operation is required per
ring-node. For detailed information, see section 5.2.
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.
For detailed information, see section 5.2.
4. Shared Ring Protection Architecture 4. Shared Ring Protection Architecture
4.1. Ring Tunnel 4.1. Ring Tunnel
This document introduces a new logical layer of the ring for shared This document introduces a new logical layer of the ring for shared
ring protection in MPLS-TP networks. As shown in Figure 1, the new ring protection in MPLS-TP networks. As shown in Figure 1, the new
logical layer consists of ring tunnels which provides a server layer logical layer consists of ring tunnels which provides a server layer
for the LSPs traverse the ring. Once a ring tunnel is established, for the LSPs traversing the ring. Once a ring tunnel is established,
the forwarding and protection switching of the ring are all performed the forwarding and protection switching of the ring are all performed
at the ring tunnel level. A port can carry multiple ring tunnels, at the ring tunnel level. A port can carry multiple ring tunnels,
and a ring tunnel can carry multiple LSPs. and a ring tunnel can carry multiple LSPs.
+------------- +-------------
+-------------| +-------------|
+-------------| | +-------------| |
===Service1===| | | ===Service1===| | |
| | Ring | Physical ===Service2===| LSP1 | |
===Service2===| LSP | Tunnel | Port +-------------| |
| | | |Ring-Tunnel1 |
===Service3===| | | +-------------| |
+-------------| | ===Service3===| | |
+-------------| ===Service4===| LSP2 | |
+------------- +-------------| |
+-------------| Physical
+-------------|
+-------------| | Port
===Service5===| | |
===Service6===| LSP3 | |
+-------------| |
|Ring-Tunnel2 |
+-------------| |
===Service7===| | |
===Service8===| LSP4 | |
+-------------| |
+-------------|
+-------------
Figure 1. The logical layers of the ring Figure 1. The logical layers of the ring
The label stack used in MPLS-TP Shared Ring Protection mechanism is The label stack used in MPLS-TP Shared Ring Protection mechanism is
[Ring Tunnel Label|LSP Label|service Label](Payload) as illustrated [Ring Tunnel Label|LSP Label|service Label](Payload) as illustrated
in figure 2. in figure 2.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ring tunnel Label | | Ring tunnel Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP Label | | LSP Label |
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[RFC3031]. The ring tunnel labels on each hop of the ring tunnel can [RFC3031]. The ring tunnel labels on each hop of the ring tunnel can
be either configured statically, provisioned by a controller, or be either configured statically, provisioned by a controller, or
distributed dynamically via a control protocol. For an LSP which distributed dynamically via a control protocol. For an LSP which
traverses the ring tunnel, the ingress ring node and the egress ring traverses the ring tunnel, the ingress ring node and the egress ring
node are considered adjacent at the LSP layer, and LSP label needs to node are considered adjacent at the LSP layer, and LSP label needs to
be allocated at these two ring nodes. The control plane for label be allocated at these two ring nodes. The control plane for label
distribution is outside the scope of this document. distribution is outside the scope of this document.
4.1.3. Forwarding Operation 4.1.3. Forwarding Operation
When an MPLS-TP transport path, such as an LSP, enters the ring, the When an MPLS-TP transport path, i.e. an LSP, enters the ring, the
ingress node on the ring pushes the working ring tunnel label which ingress node on the ring pushes the working ring tunnel label which
is used to reach the specific egress node and sends the traffic to is used to reach the specific egress node and sends the traffic to
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 service label. Figure 4 shows the label operation in the MPLS-TP and service 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.
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4.2. Failure Detection 4.2. Failure Detection
The MPLS-TP section layer OAM is used to monitor the connectivity The MPLS-TP section layer OAM is used to monitor the connectivity
between each two adjacent nodes on the ring using the mechanisms between each two adjacent nodes on the ring using the mechanisms
defined in [RFC6371]. Protection switching is triggered by the defined in [RFC6371]. Protection switching is triggered by the
failure detected on the ring by the OAM mechanisms. failure detected on the ring by the OAM mechanisms.
Two ports of a link form a Maintenance Entity Group (MEG), and an MEG Two ports of a link form a Maintenance Entity Group (MEG), and an MEG
end point (MEP) function is installed in each ring port. CC OAM end point (MEP) function is installed in each ring port. CC OAM
packets are periodically exchanged between each pair of MEPs to packets are periodically exchanged between each pair of MEPs to
monitor the link health. Three consecutive lost CC packets will be monitor the link health. Three consecutive lost CC packets MUST be
interpreted as a link failure. interpreted as a link failure.
A node failure is regarded as the failure of two links attached to A node failure is regarded as the failure of two links attached to
that node. The two nodes adjacent to the failed node detect the that node. The two nodes adjacent to the failed node detect the
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
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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). -> [RCW_D(D)| LSP1](NodeC) -> [LSP1](Payload).
Then at node D the packet will be forwarded based on the label stack Then at node D the packet will be forwarded based on the label stack
of LSP1. 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. If the RPS
protocol in any node detects RPS message with a protection switching
mode that was not provisioned in that node a failure of protocol will
be reported, and the protection mechanism will not be activated.
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
around the ring to the switching node downstream of the failure around the ring to the switching node downstream of the failure
through the protection ring tunnel, where it is switched back onto through the protection ring tunnel, where it is switched back onto
the working ring tunnel to reach the egress node. the working ring tunnel to reach the egress node.
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The following sections describe 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. Wrapping can be applicable for the protection the p2mp
LSPs on the ring, the details of which is outside the scope of this
document.
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 the OAM mechanism; if it is a uni-directional failure, one of the via the OAM mechanism; if it is an uni-directional failure, one of
two nodes would detect the failure via the OAM mechanism. In both the two nodes would detect the failure via the OAM mechanism. In
cases the node at the other side of the detected failure will be both 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 payload which enters the ring at working ring tunnel (RcW_D). The payload which enters the ring 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)
skipping to change at page 11, line 45 skipping to change at page 12, line 50
(RPS) specified in section 5. (RPS) specified in section 5.
The payload 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. The ingress node will update
location information is propagated to all the ring nodes, the its ring map according to received RPS messages and determine that
the egress node is not reachable thus it will not send traffic to
either the working or the protection tunnel. However, before the
failure 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
C detects the failure and switches the traffic from the clockwise C detects the failure and switches the traffic from the clockwise
work ring tunnel (RcW_D) to the anticlockwise protection ring tunnel work ring tunnel (RcW_D) to the anticlockwise protection ring tunnel
(RaP_D), node E also detects the failure and would switch the traffic (RaP_D), node E also detects the failure and would switch the traffic
from anticlockwise protection ring tunnel (RaP_D) back to the from anticlockwise protection ring tunnel (RaP_D) back to the
clockwise work ring tunnel (RcW_D). A possible mechanism to mitigate clockwise work ring tunnel (RcW_D). A possible mechanism to mitigate
the temporary loop problem is: the TTL of the ring tunnel label is the temporary loop problem is: the TTL of the ring tunnel label is
set to 2*N by the ingress ring node of the traffic, where N is the set to 2*N by the ingress ring node of the traffic, where N is the
number of nodes on the ring. number of nodes on the ring.
skipping to change at page 12, line 37 skipping to change at page 13, line 45
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, payload switching is executed only at With short wrapping protection, protection switching is executed only
the node upstream to the failure, and payload leaves the ring in the at the node upstream to the failure, and the packet leaves the ring
protection ring tunnel at the egress node. This scheme can reduce in the protection ring tunnel at the egress node. This scheme can
the additional latency and bandwidth consumption when traffic is reduce the additional latency and bandwidth consumption when traffic
switched to the protection path. is switched to the protection path. However the two directions of a
protected bidirectional LSP are no longer co-routed under the
protection switching conditions.
In the wrapping solution, in normal state the protection ring tunnel In the traditional wrapping solution, the protection ring tunnel is
is a closed ring, while in the short wrapping solution, the configured as a closed ring, while in the short wrapping solution,
protection ring tunnel is terminated at the egress node, which is the protection ring tunnel is configured as ended at the egress node,
similar to the working ring tunnel. Short wrapping is easy to which is similar to the working ring tunnel. Short wrapping is easy
implement in shared ring protection because both the working and to 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
skipping to change at page 13, line 52 skipping to change at page 15, line 16
For the node failure which happens on a non-egress node, the 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 an 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. The ingress node will update its ring
information is propagated to all the ring nodes using the RPS map according to received RPS messages and determine that the egress
protocol, node C switches all the traffic on the working ring tunnel node is not reachable thus it will not send traffic to either the
RcW_D to the protection ring tunnel RaP_D in the opposite direction working or the protection tunnel. However, before the failure
based on the information in the ring map. When the traffic arrives location information is propagated to all the ring nodes using the
at node E which also detects the failure of node D, the protection RPS protocol, node C switches all the traffic on the working ring
ring tunnel RaP_D cannot be used to forward traffic to node D. Since tunnel RcW_D to the protection ring tunnel RaP_D in the opposite
with short wrapping mechanism, protection switching can only be direction based on the information in the ring map. When the traffic
performed once from the working ring tunnel to the protection ring arrives at node E which also detects the failure of node D, the
tunnel, thus node E MUST NOT switch the traffic which is already protection ring tunnel RaP_D cannot be used to forward traffic to
carried on the protection ring tunnel back to the working ring tunnel node D. Since with short wrapping mechanism, protection switching
in the opposite direction. Instead, node E will discard the traffic can only be performed once from the working ring tunnel to the
received on RaP_D locally. This can avoid the temporary traffic loop protection ring tunnel, thus node E MUST NOT switch the traffic which
when the failure happens on the egress node of the ring tunnel. This is already carried on the protection ring tunnel back to the working
also illustrates one of the benefits of having separate working and ring tunnel in the opposite direction. Instead, node E will discard
protection ring tunnels in each ring direction. the traffic received on RaP_D locally. This can avoid the temporary
traffic loop when the failure happens on the egress node of the ring
tunnel. This also illustrates one of the benefits of having separate
working and 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)
#/* *\# #/* *\#
+---+ +---+ +---+ +---+
| E | | B | | E | | B |
+---+ +---+ +---+ +---+
skipping to change at page 14, line 49 skipping to change at page 16, line 34
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 the 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 the working to the traffic to the ring) perform switching from the working to the
protection ring tunnel, and at the egress node the traffic leaves the protection ring tunnel, and at the egress node the traffic leaves the
ring from 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
using the OAM mechanism sends the failure information in the opposite with OAM mechanism sends the failure information in the opposite
direction of the failure hop by hop along the ring using an RPS direction of the failure hop by hop along the ring using an RPS
request message and the ring-map information. When a ring node request message and the ring-map information. When a ring node
receives the RPS message which identifies a failure, it can determine receives the RPS message which identifies a failure, it can determine
the location of the fault by using the topology information of the the location of the fault by using the topology information of the
ring map and updates the ring map accordingly, then it can determine ring map and updates the ring map accordingly, then it can determine
whether the LSPs entering the ring locally need to switchover or not. whether the LSPs entering the ring locally need to switchover or not.
For LSPs that need to switchover, it will switch the LSPs from the For LSPs that need to switchover, it will switch the LSPs from the
working ring tunnels to their corresponding protection ring tunnels. working ring tunnels to their corresponding protection ring tunnels.
The transfer of the failure information by the RPS protocol will
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)]
#/* [RcW_D(F)] *\# #/* [RcW_D(F)] *\#
+-+-+-+-+-+-+-+ #/* *\# +-+-+-+-+-+-+-+ #/* *\#
|E|F|A|B|C|D|E| +---+ +---+ +-- LSP2 |E|F|A|B|C|D|E| +---+ +---+ +-- LSP2
skipping to change at page 17, line 45 skipping to change at page 19, line 45
If the failure occurs at the egress node of the LSP, the ingress node If the failure occurs at the egress node of the LSP, the ingress node
will update its ring map according to the received RPS messages, it will update its ring map according to the received RPS messages, it
will also determine that the egress node is not reachable after the will also determine that the egress node is not reachable after the
failure, thus it will not send traffic to either the working or the failure, thus it will not send traffic to either the working or the
protection tunnel, and a 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. For
This document will discuss two typical interconnected ring a given ring, the interconnection node acts as the egress node for
topologies: that ring, meaning that all LSPs using the interconnection node as an
egress from one specific ring to another will use the same group of
ring tunnels within the ring. 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 11 shows the topology of single-node interconnected
rings. Node C is the interconnection node between Ring1 and
Ring2.
Figure 11 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.
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
| A |------| B |----- -----| G |------| H | | A |------| B |----- -----| G |------| H |
+---+ +---+ \ / +---+ +---+ +---+ +---+ \ / +---+ +---+
| \ / | | \ / |
| \ +---+ / | | \ +---+ / |
skipping to change at page 19, line 29 skipping to change at page 21, line 29
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. A failure that happens in one ring only triggers independently. A failure that happens in one ring only triggers
protection switching in the ring itself and does not affect the other protection switching in the ring itself and does not affect the other
ring, unless the failure is on the interconnection node. In this ring, unless the failure is on the interconnection node. In this
way, protection switching on each ring is the same as the mechanisms way, protection switching on each ring is the same as the mechanisms
described in section 4.3. described in section 4.3.
The service LSPs that traverse the interconnected rings use separate The service LSPs that traverse the interconnected rings use the ring
ring tunnels on each ring, and the LSPs on different rings are tunnels in each ring, within a given ring, the tunnel is selected
stitched by the interconnection node. On the interconnection node, using normal ring selection procedures. The traversing LSPs are
stitched on the interconnection node. On the interconnection node,
the ring tunnel label of the source ring is popped, then LSP label is the ring tunnel label of the source ring is popped, then LSP label is
swapped, after that the ring tunnel label of the destination ring is swapped, after that the ring tunnel label of the destination ring is
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 node group. In interconnection nodes can be managed as a virtual node group. In
addition to the ring tunnels to each physical ring node, Each ring addition to the ring tunnels to each physical ring node, Each ring
SHOULD assign the working and protection ring tunnels to the virtual SHOULD assign the working and protection ring tunnels to the virtual
interconnection node group. In addition, on both nodes in the interconnection node group. In addition, on both nodes in the
virtual interconnection node group, the same LSP label is assigned virtual interconnection node group, the same LSP label is assigned
for each traversed LSP. This way, any interconnection node in the for each traversed LSP. This way, any interconnection node in the
virtual node group can terminate the working or protection ring virtual node group can terminate the working or protection ring
tunnels targeted to the virtual node group, and stitch the service tunnels targeted to the virtual node group, and stitch the service
LSP from the source ring tunnel to the destination ring tunnel. LSP from the source ring tunnel to the destination ring tunnel.
When the service LSP passes through the interconnected rings, the When the service LSP passes through the interconnected rings, the
direction of the working ring tunnels used on both rings SHOULD be direction of the working ring tunnels used on both rings SHOULD be
the same. For example, if the service LSP uses the clockwise working the same. In dual-node interconnected rings, this ensures that in
ring tunnel on Ring1, when the service LSP leaves Ring1 and enters normal state the traffic passes only one of the two interconnection
Ring2, the working ring tunnel used on Ring2 SHOULD also follow the nodes, and does not pass the link between the two interconnection
clockwise direction. nodes. The traffic will then only be switched to the protection path
if the interconnection node which is in working path fails. For
example, if the service LSP uses the clockwise working ring tunnel on
Ring1, when the service LSP leaves Ring1 and enters Ring2, the
working ring tunnel used on Ring2 should also follow the 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. In addition, ring tunnels to the ring of the interconnected rings. In addition, ring tunnels to the
virtual interconnection node group are established on each ring of virtual interconnection node group are established on each ring 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
skipping to change at page 23, line 27 skipping to change at page 26, line 15
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).
5. Ring Protection Coordination Protocol 5. Ring Protection Coordination Protocol
5.1. RPS Protocol 5.1. RPS and PSC Comparison on Ring Topology
The MSRP protection operation MUST be controlled with the help of the This section provides comparison between RPS and PSC [RFC6378]
Ring Protection Switch protocol (RPS). The RPS processes in each of [RFC6974] on ring topologies. This can be helpful to explain the
the individual ring nodes that form the ring MUST communicate using reason of defining a new protocol for ring protection switching.
the G-ACh channel. The RPS protocol is applicable to all the three
ring protection modes. This section takes the short-wrapping
mechanism described in section 4.3.2 as an example.
All nodes in the same ring MUST use the same protection mechanism, The PSC protocol [RFC6378] is designed for point-to-point LSPs, on
Wrapping, steering or short-wrapping. which the protection switching can only be performed on one or both
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
happen on any segment of the ring, thus RPS is capable of identifying
and handling the different failures on the ring, and coordinating the
protection switching behavior of all the nodes on the ring. As will
be specified in the following sections, this is achieved with 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
the RPS Request message.
The RPS protocol MUST carry the ring status information and RPS Taking a ring topology with N nodes as example:
requests, either automatically initiated or externally initiated,
between the ring nodes.
Each node on the ring MUST be uniquely identified by assigning it a With the mechanism specified in [RFC6974], on every ring node, a
node ID. The node ID MUST be unique on each ring. The maximum linear protection configuration has to be provisioned with every
number of nodes on the ring supported by the RPS protocol is 127. other node in the ring, i.e. with (N-1) other nodes. This means that
The node ID SHOULD be independent of the order in which the nodes on every ring node there will be (N-1) instances of the PSC protocol.
appear on the ring. The node ID is used to identity the source and And in order to detect faults and to transport the PSC message, each
destination nodes of each RPS request. instance shall have a MEP on the working path and a MEP on the
protection path respectively. This means that every node on the ring
needs to be configured with (N-1) * 2 MEPs.
With the mechanism defined in this document, on every ring node there
will only be a single instance of the RPS protocol. In order to
detect faults and to transport the RPS message, each node only needs
to have a MEP on the section to its adjacent nodes respectively. In
this way, every ring node only needs to be configured with 2 MEPs.
As shown in the above example, RPS is designed for ring topologies
and can achieve ring protection efficiently with minimum protection
instances and OAM entities, which meets the requirements on topology
specific recovery mechanisms as specified in [RFC5654].
5.2. RPS Protocol
The Ring Protection Switch (RPS) Protocol defined in this section is
used to coordinate the protection switching action of all the ring
nodes in the same ring.
The protection operation of the ring tunnels is controlled with the
help of the RPS protocol. The RPS processes in each of the
individual ring nodes that form the ring MUST communicate using the
G-ACh channel. The RPS protocol is applicable to all the three ring
protection modes. This section takes the short-wrapping mechanism
described in section 4.3.2 as an example.
The RPS protocol is used to distribute the ring status information
and RPS requests to all the ring nodes. Changes in the ring status
information and RPS requests can be initiated automatically based on
link status or caused by external commands.
Each node on the ring is uniquely identified by assigning it a 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. 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 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 exchanged between the adjacent nodes. The ring map is used message exchanged between the adjacent nodes. The ring map is used
by every ring node to determine the switchover behavior of the ring by every ring node to determine the switchover behavior of the ring
tunnels. tunnels.
As shown in Figure 14, when no protection switching is active on the As shown in Figure 14, when no protection switching is active on the
ring, each node MUST send RPS requests with No Request (NR) to its ring, each node MUST send RPS requests with No Request (NR) to its
two adjacent nodes periodically. two adjacent nodes periodically. The transmission interval of RPS
requests is specified in section 5.2.1.
+---+ 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
As shown in Figure 15, When a node detects a failure and determines As shown in Figure 15, When a node detects a failure and determines
that protection switching is required, it MUST send the appropriate that protection switching is required, it MUST send the appropriate
RPS request in both directions to the destination node. The RPS request in both directions to the destination node. The
destination node is the other node that is adjacent to the identified destination node is the other node that is adjacent to the identified
failure. When a node that is not the destination node receives an failure. When a node that is not the destination node receives an
RPS request and it has no higher priority local request, it MUST RPS request and it has no higher priority local request, it MUST
transfer in the same direction the RPS request as received. In this transfer in the same direction the RPS request as received. In this
way, the switching nodes can maintain RPS protocol communication in way, the switching nodes can maintain RPS protocol communication in
the ring. the ring. The RPS request MUST be terminated by the destination node
of the message. If an RPS request with the node itself set as the
source node is received, this message MUST be dropped and not be
forwarded to next node.
+---+ 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
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
skipping to change at page 25, line 8 skipping to change at page 28, line 43
request. request.
o In rings utilizing the short wrapping protection, each node o In rings utilizing the short wrapping protection, each node
detects the failure or receives the RPS request as the destination detects the failure or receives the RPS request as the destination
node MUST perform the switch only from the working ring tunnels to node MUST perform the switch only from the working ring tunnels to
the protection ring tunnels. the protection ring tunnels.
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 MUST 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 which generate the RPS requests MUST drop their
switches and MUST source an RPS request carrying the NR code. The respective switches and MUST generate an RPS request carrying the NR
node receiving from both directions such an RPS request MUST drop its code. The node receiving from both directions such an RPS request
protection switches. 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 5.3. 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 link, and another protection switch is switch request on the given link, and another protection switch is
required due to a failure on another link. 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 The shared ring protection mechanism supports multiple protection
ring, resulting in the ring being segmented into two or more separate switches in the ring, resulting in the ring being segmented into two
segments. This may happen when several RPS requests of the same or more separate segments. This may happen when several RPS requests
priority exist in the ring due to multiple failures or external of the same priority exist in the ring due to multiple failures or
switch commands. external switch commands.
Proper operation of the MSRP mechanism relies on all nodes using Proper operation of the MSRP mechanism relies on all nodes using
their ring map to determine the state of the ring (nodes and links). their ring map to determine the state of the ring (nodes and links).
In order to accommodate ring state knowledge, during a protection In order to accommodate ring state knowledge, during a protection
switch the RPS requests MUST be sent in both directions. switch the RPS requests MUST be sent in both directions.
5.1.1. Transmission and Acceptance of RPS Requests 5.2.1. 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 MUST
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
with the interval of 5 seconds. A ring node which is not the with the interval of 5 seconds. A ring node which is not the
destination of the received RPS message MUST forward it to the next destination of the received RPS message MUST forward it to the next
node along the ring immediately. node along the ring immediately.
5.1.2. RPS PDU Format 5.2.2. RPS PDU Format
Figure 16 depicts the format of an RPS packet that is sent on the Figure 16 depicts the format of an RPS packet that is sent on the
G-ACh. The Channel Type field is set to indicate that the message is G-ACh. The Channel Type field is set to indicate that the message is
an RPS message. an RPS 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|Version| Reserved | RPS Channel Type (TBD) | |0 0 0 1|Version| Reserved | RPS Channel Type (TBD) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 27, line 19 skipping to change at page 31, line 19
| 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 |
| 0 0 0 0 1 1 0 1 | Forced Switch (FS) | | | 0 0 0 0 1 1 0 1 | Forced Switch (FS) | |
| 0 0 0 0 1 0 1 1 | Signal Fail (SF) | | | 0 0 0 0 1 0 1 1 | Signal Fail (SF) | |
| 0 0 0 0 0 1 1 0 | Manual Switch (MS) | | | 0 0 0 0 0 1 1 0 | Manual Switch (MS) | |
| 0 0 0 0 0 1 0 1 | Wait-To-Restore (WTR) | | | 0 0 0 0 0 1 0 1 | Wait-To-Restore (WTR) | |
| 0 0 0 0 0 0 1 1 | Exercise (EXER) | | | 0 0 0 0 0 0 1 1 | Exercise (EXER) | |
| 0 0 0 0 0 0 0 1 | Reverse Request (RR) | | | 0 0 0 0 0 0 0 1 | Reverse Request (RR) | |
| 0 0 0 0 0 0 0 0 | No Request (NR) | lowest | | 0 0 0 0 0 0 0 0 | No Request (NR) | lowest |
+------------------+-----------------------------+----------+ +------------------+-----------------------------+----------+
5.1.3. Ring Node RPS States 5.2.3. Ring Node RPS States
Idle state: A node is in the idle state when it has no RPS request Idle state: A node is in the idle state when it has no RPS request
and is sourcing and receiving NR code to/from both directions. and is sending and receiving NR code to/from both directions.
Switching state: A node not in the idle or pass-through states is in Switching state: A node not in the idle or pass-through states is in
the switching state. the switching state.
Pass-through state: A node is in the pass-through state when its Pass-through state: A node is in the pass-through state when its
highest priority RPS request is a request not destined to it or highest priority RPS request is a request not destined to it or
sourced by it. The pass-through is bidirectional. generated by it. The pass-through is bidirectional.
5.1.3.1. Idle State 5.2.3.1. Idle State
A node in the idle state MUST source the NR request in both A node in the idle state MUST generate 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
ring tunnels in both directions. ring tunnels in both directions.
5.1.3.2. Switching State 5.2.3.2. Switching State
A node in the switching state MUST source RPS request to its adjacent A node in the switching state MUST generate RPS request to its
node with its highest RPS request code in both directions when it adjacent node with its highest RPS request code in both directions
detects a failure or receives an external command. when it detects a failure or receives an external command.
In bidirectional failure condition, both of the nodes adjacent to the In bidirectional failure condition, both of the nodes adjacent to the
failure detect the failure and send the RPS request in both failure detect the failure and send the RPS request in both
directions with the destination set to each other, while each node directions with the destination set to each other, while each node
can only receive the RPS request via the long path, the message sent can only receive the RPS request via the long path, the message sent
via the short path will get lost due to the bidirectional failure. via the short path will get lost due to the bidirectional failure.
Here the short path refers to the shorter path on the ring between Here the short path refers to the shorter path on the ring between
the source and destination node of the RPS request, and the long path the source and destination node of the RPS request, and the long path
refers to the longer path on the ring between the source and refers to the longer path on the ring between the source and
skipping to change at page 28, line 29 skipping to change at page 32, line 29
by replying an RPS request with the RR code on the short path, and an by replying an RPS request with the RR code on the short path, and an
RPS request with the received RPS request code on the long path. RPS request with the received RPS request code on the long path.
Accordingly, when the node which detects the failure receives RPS Accordingly, when the node which detects the failure receives RPS
request with RR code on the short path, then the RPS request received request with RR code on the short path, then the RPS request received
from the same node along the long path SHOULD be ignored. from the same node along the long path SHOULD be ignored.
A node in the switching state MUST terminate the received RPS A node in the switching state MUST terminate the received RPS
requests in both directions and not forward it further along the requests in both directions and not forward it further along the
ring. ring.
The following switches MUST be allowed to coexist: The following switches as defined in section 5.3.1 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 exist at the same time addressing When multiple MS RPS requests exist at the same time addressing
different links and there is no higher priority request on the ring, different links and there is no higher priority request on the ring,
no switch SHOULD be executed and existing switches MUST be dropped. no switch SHOULD be executed and existing switches MUST be dropped.
The nodes MUST signal, anyway, the MS RPS request code. The nodes MUST still signal RPS request with the MS 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 link 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 link if there is no other RPS request on another link. the locked link if there is no other RPS request on another link.
The node still SHOULD signal relevant RPS request for another link. The node still SHOULD signal relevant RPS request for another link.
5.1.3.3. Pass-through State 5.2.3.3. 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 unchanged 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 5.2.4. 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 preempt existing RPS initiated command, or received RPS request shall preempt existing RPS
requests in the prioritized order given in Section 5.1.2, unless the requests in the prioritized order given in Section 5.2.2, unless the
requests are allowed to coexist. requests are allowed to coexist.
5.1.4.1. Transitions Between Idle and Pass-through States 5.2.4.1. 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.
A node MUST revert from pass-through state to the idle state when it A node MUST revert from pass-through state to the idle state when RPS
detects NR codes incoming from both directions. Both directions request with NR code is received in both directions. Then both
revert simultaneously from the pass-through state to the idle state. directions revert simultaneously from the pass-through state to the
idle state.
5.1.4.2. Transitions Between Idle and Switching States 5.2.4.2. Transitions Between Idle and Switching States
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 is destined to this node on either the long or the short path and is 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 the 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
In one of the following conditions, transition from the Idle state to In one of the following conditions, transition from the Switching
the Switching state MUST be triggered: state to the Idle state MUST be triggered:
o On node which triggers the protection switching, when the WTR time o On node which triggers the protection switching, when the WTR time
expires or an externally initiated command is cleared, the node expires or an externally initiated command is cleared, the node
MUST transit from Switching state to Idle State and signal the NR MUST transit from Switching state to Idle State and signal the NR
code using RPS message in both directions. code using RPS message in both directions.
o On node which enters the switching state due to the received RPS o On node which enters the switching state due to the received RPS
request: Upon reception of the NR code from both directions, the request: Upon reception of the NR code from both directions, the
head-end node MUST drop its switch, transition to Idle State and head-end node MUST drop its switch, transition to Idle State and
signal the NR code in both directions. signal the NR code in both directions.
5.1.4.3. Transitions Between Switching States 5.2.4.3. 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 link, 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,
skipping to change at page 31, line 5 skipping to change at page 35, line 5
o An externally initiated command becomes active o An externally initiated command becomes active
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 5.2.4.4. 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 link 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
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 5.3. RPS State Machine
5.2.1. Switch Initiation Criteria 5.3.1. Switch Initiation Criteria
5.2.1.1. Administrative Commands 5.3.1.1. Administrative Commands
Administrative commands can be initiated by the network operator Administrative commands can be initiated by the network operator
through the Network Management System (NMS). The operator command through the Network Management System (NMS). The operator command
may be transmitted to the appropriate node via the MPLS-TP RPS may be transmitted to the appropriate node via the MPLS-TP RPS
message. message.
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.
skipping to change at page 32, line 17 skipping to change at page 36, line 17
o Exercise - Ring (EXER): This command exercises ring protection o Exercise - Ring (EXER): This command exercises ring protection
switching on the addressed link 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 (LW): This command prevents the normal traffic o Lockout of Working (LW): This command prevents the normal traffic
transported over the addressed link 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 link 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
link. 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 5.3.1.2. 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:
o Signal Fail (SF): This command is issued when the MPLS-TP section o Signal Fail (SF): This command is issued when the MPLS-TP section
layer OAM detects signal failure condition. layer OAM detects signal failure condition.
o Wait-To-Restore (WTR): This command is issued when MPLS-TP section 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 detects that the SF condition has cleared. It is used to maintain
the state during the WTR period unless it is preempted by a higher the state during the WTR period unless it is preempted by a higher
priority switch request. The WTR time may be configured by the priority switch request. The WTR time may be configured by the
operator in 1 minute steps between 0 and 12 minutes; the default operator in 1 minute steps between 0 and 12 minutes; the default
value is 5 minutes. value is 5 minutes.
o Reverse Request (RR): This command is transmitted to the source o Reverse Request (RR): This command is transmitted to the source
node of the received RPS message over the short path as an node of the received RPS message over the short path as an
acknowledgment for receiving the switch request. acknowledgment for receiving the switch request.
5.2.2. Initial States 5.3.2. Initial States
This section describes the possible states of a ring node, the This section describes the possible states of a ring node, the
corresponding action of the working and protection ring tunnels on corresponding action of the working and protection ring tunnels on
the node, and the RPS request which should be generated in that the node, and the RPS request which should be generated in that
state. state.
+-----------------------------------+----------------+ +-----------------------------------+----------------+
| State | Signaled RPS | | State | Signaled RPS |
+-----------------------------------+----------------+ +-----------------------------------+----------------+
| A | Idle | NR | | A | Idle | NR |
skipping to change at page 34, line 45 skipping to change at page 38, line 45
+-----+-----------------------------+----------------+ +-----+-----------------------------+----------------+
| 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 | |
+-----+-----------------------------+----------------+ +-----+-----------------------------+----------------+
5.2.3. State transitions When Local Request is Applied 5.3.3. 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 38, line 11 skipping to change at page 42, line 11
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 link EXER N/A - if on the same link
I (Switching - EXER) I (Switching - EXER)
===================================================================== =====================================================================
5.2.4. State Transitions When Remote Request is Applied 5.3.4. 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 41, line 5 skipping to change at page 45, line 5
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
===================================================================== =====================================================================
5.2.5. State Transitions When Request Addresses to Another Node is 5.3.5. 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-through) A (Idle) LP B (Pass-through)
FS B (Pass-through) FS B (Pass-through)
skipping to change at page 43, line 43 skipping to change at page 47, line 43
I (Switching - EXER) LP B (Pass-through) I (Switching - EXER) LP B (Pass-through)
FS B (Pass-through) FS B (Pass-through)
SF B (Pass-through) SF B (Pass-through)
MS B (Pass-through) MS B (Pass-through)
WTR N/A WTR N/A
EXER I (Switching - EXER) EXER I (Switching - EXER)
RR N/A RR N/A
NR N/A NR N/A
===================================================================== =====================================================================
5.3. RPS and PSC Comparison on Ring Topology
This section provides comparison between RPS and PSC [RFC6378]
[RFC6974] on ring topologies. This can be helpful to explain the
reason of defining a new protocol for ring protection switching.
The PSC protocol [RFC6378] is designed for point-to-point LSPs, on
which the protection switching can only be performed on one or both
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
happen on any segment of the ring, thus RPS SHOULD be capable of
identifying and handling the different failures on the ring, and
coordinating the protection switching behavior of all the nodes on
the ring. As specified in section 5, this is achieved with 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
the RPS Request message.
Taking a ring topology with N nodes as example:
With the mechanism specified in [RFC6974], on every ring-node, a
linear protection configuration has to be provisioned with every
other node in the ring, i.e. with (N-1) other nodes. This means that
on every ring node there will be (N-1) instances of the PSC protocol.
And in order to detect faults and to transport the PSC message, each
instance shall have a MEP on the working path and a MEP on the
protection path respectively. This means that every node on the ring
needs to be configured with (N-1) * 2 MEPs.
With the mechanism defined in this document, on every ring node there
will only be a single instance of the RPS protocol. In order to
detect faults and to transport the RPS message, each node only needs
to have a MEP on the section to its adjacent nodes respectively. In
this way, every ring-node only needs to be configured with 2 MEPs.
As shown in the above example, RPS is designed for ring topologies
and can achieve ring protection efficiently with minimum protection
instances and OAM entities, which meets the requirements on topology
specific recovery mechanisms as specified in [RFC5654].
6. IANA Considerations 6. IANA Considerations
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].
skipping to change at page 45, line 17 skipping to change at page 48, line 25
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
"Multiprotocol Label Switching (MPLS) Operations, Administration, and "Multiprotocol Label Switching (MPLS) Operations, Administration, and
Management (OAM) Parameters" registry called the "MPLS RPS Request Management (OAM) Parameters" registry called the "MPLS RPS Request
Code Registry". All code points within this registry shall be Code Registry". All code points within this registry shall be
allocated according to the "Standards Action" procedure as specified allocated according to the "Specification Required" procedure as
in [RFC5226]. specified in [RFC5226].
The RPS Request Field is 8 bits, the allocated values are as follows: The RPS Request Field is 8 bits, the allocated values are as follows:
Value Description Reference Value Description Reference
------- --------------------------- --------------- ------- --------------------------- ---------------
0 No Request (NR) this document 0 No Request (NR) this document
1 Reverse Request (RR) this document 1 Reverse Request (RR) this document
2 unassigned 2 unassigned
3 Exercise (EXER) this document 3 Exercise (EXER) this document
4 unassigned 4 unassigned
skipping to change at page 45, line 40 skipping to change at page 48, line 48
6 Manual Switch (MS) this document 6 Manual Switch (MS) this document
7-10 unassigned 7-10 unassigned
11 Signal Fail (SF) this document 11 Signal Fail (SF) this document
12 unassigned 12 unassigned
13 Forced Switch (FS) this document 13 Forced Switch (FS) this document
14 unassigned 14 unassigned
15 Lockout of Protection (LP) this document 15 Lockout of Protection (LP) this document
16-254 unassigned 16-254 unassigned
255 Reserved 255 Reserved
7. Security Considerations 7. Operational Considerations
The RPS protocol defined in this document is carried in the G-ACh This document describes three protection modes of the RPS protocol.
[RFC5586], which is a generalization of the Associated Channel Operators could choose the appropriate protection mode according to
defined in [RFC4385]. The security considerations specified in these their network and service requirement.
documents apply to the proposed RPS mechanism.
8. Contributing Authors Wrapping mode provides a ring protection mechanism in which the
protected traffic will reach every node of the ring, and is
applicable to protect both the point-to-point LSPs and LSPs which
needs to be dropped in several ring nodes, i.e. the point-to-
multipoint applications. When protection is in active, the protected
traffic is switched (wrapped) to/from the protection ring tunnel at
both sides of the defective link/node. Due to the wrapping the
additional propagation delay and bandwidth consumption of the
protection tunnel are considerable. For bidirectional LSP, the
protected traffic in both directions is co-routed.
Short wrapping mode provides a ring protection mechanism which can be
used to protect only point-to-point LSPs. When protection is in
active, the protected traffic wrapped to the protection ring tunnel
at the defective link/node and leaves the ring when the protection
ring tunnel reach the egress node. Compared with wrapping mode,
short wrapping can reduce the propagation latency and bandwidth
consumption of the protection tunnel. However the two directions of
a protected bidirectional LSP are not totally co-routed.
Steering mode provides a ring protection mechanism that can be used
to protect only point-to-point LSPs. When protection is in
active,the protected traffic is switched to the protection ring
tunnel at the ingress node and leaves the ring when the protection
ring tunnel reach the egress node. Steering mode has the least
propagation delay and bandwidth consumption of the three modes, and
the two directions of a protected bidirectional LSP can be kept co-
routed.
Note that only one protection mode can be provisioned in the whole
ring for all protected traffic.
8. Security Considerations
MPLS-TP is a subset of MPLS and so builds upon many of the aspects of
the security model of MPLS. Please refer to [RFC5920] for generic
MPLS security issues and methods for securing traffic privacy and
integrity.
The RPS message defined in this document is used for protection
coordination on the ring, if it is injected or modified by an
attacker, the ring nodes might not agree on the protection action,
and the improper protection switching action may cause temporary
break to services traversing the ring. It is important that the RPS
message is used within a trusted MPLS-TP network domain as described
in [RFC6941].
The RPS message is carried in the G-ACh [RFC5586], so it is dependent
on the security of the G-ACh itself. The G-ACh is a generalization
of the Associated Channel defined in [RFC4385]. Thus, this document
relies on the security mechanisms provided for the Associated Channel
as described in those two documents.
As described in the security considerations of [RFC6378], the G-ACh
is essentially connection oriented so injection or modification of
control messages requires the subversion of a transit node. Such
subversion is generally considered hard in connection oriented MPLS
networks and impossible to protect against at the protocol level.
Management level techniques are more appropriate. The procedures and
protocol extensions defined in this document do not affect the
security model of MPLS-TP linear protection as defined in [RFC6378].
9. Contributing Authors
Kai Liu Kai Liu
Huawei Technologies Huawei Technologies
Email: alex.liukai@huawei.com Email: alex.liukai@huawei.com
Jia He Jia He
Huawei Technologies Huawei Technologies
Email: hejia@huawei.com Email: hejia@huawei.com
Fang Li Fang Li
China Academy of Telecommunication Research MIIT., China China Academy of Telecommunication Research MIIT., China
skipping to change at page 46, line 40 skipping to change at page 51, line 40
Email: wangminxue@chinamobile.com Email: wangminxue@chinamobile.com
Sheng Liu Sheng Liu
China Mobile China Mobile
Email: liusheng@chinamobile.com Email: liusheng@chinamobile.com
Guanghui Sun Guanghui Sun
Huawei Technologies Huawei Technologies
Email: sunguanghui@huawei.com Email: sunguanghui@huawei.com
9. Acknowledgements 10. Acknowledgements
The authors would like to thank Gregory Mirsky, Yimin Shen, Eric The authors would like to thank Gregory Mirsky, Yimin Shen, Eric
Osborne, Spencer Jackson and Eric Gray for their valuable comments Osborne, Spencer Jackson and Eric Gray for their valuable comments
and suggestions. and suggestions.
10. References 11. References
10.1. Normative References 11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001, DOI 10.17487/RFC3031, January 2001,
<http://www.rfc-editor.org/info/rfc3031>. <http://www.rfc-editor.org/info/rfc3031>.
skipping to change at page 47, line 36 skipping to change at page 52, line 36
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed., [RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586, "MPLS Generic Associated Channel", RFC 5586,
DOI 10.17487/RFC5586, June 2009, DOI 10.17487/RFC5586, June 2009,
<http://www.rfc-editor.org/info/rfc5586>. <http://www.rfc-editor.org/info/rfc5586>.
[RFC5654] Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed., [RFC5654] Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
Sprecher, N., and S. Ueno, "Requirements of an MPLS Sprecher, N., and S. Ueno, "Requirements of an MPLS
Transport Profile", RFC 5654, DOI 10.17487/RFC5654, Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
September 2009, <http://www.rfc-editor.org/info/rfc5654>. September 2009, <http://www.rfc-editor.org/info/rfc5654>.
10.2. Informative References 11.2. Informative References
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008, DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>. <http://www.rfc-editor.org/info/rfc5226>.
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
<http://www.rfc-editor.org/info/rfc5920>.
[RFC6371] Busi, I., Ed. and D. Allan, Ed., "Operations, [RFC6371] Busi, I., Ed. and D. Allan, Ed., "Operations,
Administration, and Maintenance Framework for MPLS-Based Administration, and Maintenance Framework for MPLS-Based
Transport Networks", RFC 6371, DOI 10.17487/RFC6371, Transport Networks", RFC 6371, DOI 10.17487/RFC6371,
September 2011, <http://www.rfc-editor.org/info/rfc6371>. September 2011, <http://www.rfc-editor.org/info/rfc6371>.
[RFC6378] Weingarten, Y., Ed., Bryant, S., Osborne, E., Sprecher, [RFC6378] Weingarten, Y., Ed., Bryant, S., Osborne, E., Sprecher,
N., and A. Fulignoli, Ed., "MPLS Transport Profile (MPLS- N., and A. Fulignoli, Ed., "MPLS Transport Profile (MPLS-
TP) Linear Protection", RFC 6378, DOI 10.17487/RFC6378, TP) Linear Protection", RFC 6378, DOI 10.17487/RFC6378,
October 2011, <http://www.rfc-editor.org/info/rfc6378>. October 2011, <http://www.rfc-editor.org/info/rfc6378>.
[RFC6941] Fang, L., Ed., Niven-Jenkins, B., Ed., Mansfield, S., Ed.,
and R. Graveman, Ed., "MPLS Transport Profile (MPLS-TP)
Security Framework", RFC 6941, DOI 10.17487/RFC6941, April
2013, <http://www.rfc-editor.org/info/rfc6941>.
[RFC6974] Weingarten, Y., Bryant, S., Ceccarelli, D., Caviglia, D., [RFC6974] Weingarten, Y., Bryant, S., Ceccarelli, D., Caviglia, D.,
Fondelli, F., Corsi, M., Wu, B., and X. Dai, Fondelli, F., Corsi, M., Wu, B., and X. Dai,
"Applicability of MPLS Transport Profile for Ring "Applicability of MPLS Transport Profile for Ring
Topologies", RFC 6974, DOI 10.17487/RFC6974, July 2013, Topologies", RFC 6974, DOI 10.17487/RFC6974, July 2013,
<http://www.rfc-editor.org/info/rfc6974>. <http://www.rfc-editor.org/info/rfc6974>.
Authors' Addresses Authors' Addresses
Weiqiang Cheng Weiqiang Cheng
China Mobile China Mobile
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