MPLS Working Group H. van Helvoort, Ed. Internet-Draft Huawei Technologies Intended status: Standards Track J. Ryoo, Ed. Expires: April 9, 2013 ETRI October 6, 2012 MPLS-TP Ring Protection Switching (MRPS) draft-helvoort-mpls-tp-ring-protection-switching-03.txt Abstract This document describes a mechanism to address the requirements for protection of the Multi-Protocol Label Switching Transport Profile (MPLS-TP) Label Switched Paths (LSP) in a ring topology. The mechanism defined herein is designed to support point-to-point as well as point-to-multipoint LSPs. The MPLS-TP section layer OAM is used to monitor the connectivity between each two adjacent nodes using the mechanisms defined in the [RFC6371]. The Automatic Protection Switching (APS) protocol is used for coordination of protection switching actions between the ring nodes. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on April 9, 2013. Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal van Helvoort, et al. Expires April 9, 2013 [Page 1] Internet-Draft MPLS-TP Ring Protection Switching October 2012 Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Contributing authors . . . . . . . . . . . . . . . . . . . 4 2. Conventions Used in this Document . . . . . . . . . . . . . . 4 2.1. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 5 3. Ring protection schemes . . . . . . . . . . . . . . . . . . . 5 3.1. Wrapping . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1.1. Wrapping protection scheme applicability . . . . . . . 6 3.1.2. P-t-p LSP example . . . . . . . . . . . . . . . . . . 6 3.1.3. P-t-mp LSP example . . . . . . . . . . . . . . . . . . 9 3.2. Steering . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.2.1. Steering protection scheme applicability . . . . . . . 12 3.2.2. P-t-p LSP example . . . . . . . . . . . . . . . . . . 12 3.2.3. P-t-mp LSP example . . . . . . . . . . . . . . . . . . 14 4. MRPS characteristics . . . . . . . . . . . . . . . . . . . . . 17 4.1. Switching types . . . . . . . . . . . . . . . . . . . . . 18 4.2. Operation types . . . . . . . . . . . . . . . . . . . . . 18 4.3. Traffic types . . . . . . . . . . . . . . . . . . . . . . 18 4.3.1. Bandwidth sharing . . . . . . . . . . . . . . . . . . 18 4.3.2. Bandwidth and QoS considerations . . . . . . . . . . . 18 4.3.3. Point-to-point and point-to-multipoint traffic . . . . 19 5. APS protocol . . . . . . . . . . . . . . . . . . . . . . . . . 19 5.1. Transmission and acceptance of APS requests . . . . . . . 21 5.2. APS PDU structure . . . . . . . . . . . . . . . . . . . . 21 5.3. Ring node APS states . . . . . . . . . . . . . . . . . . . 22 5.3.1. Idle state . . . . . . . . . . . . . . . . . . . . . . 22 5.3.2. Switching state . . . . . . . . . . . . . . . . . . . 23 5.3.3. Pass-through state . . . . . . . . . . . . . . . . . . 23 5.3.4. APS state transitions . . . . . . . . . . . . . . . . 24 6. Protection switching triggers . . . . . . . . . . . . . . . . 26 6.1. Manual control . . . . . . . . . . . . . . . . . . . . . . 26 6.1.1. Commands not signaled on the APS protocol . . . . . . 26 6.1.2. Commands using the APS protocol . . . . . . . . . . . 27 6.2. Automatically initiated commands . . . . . . . . . . . . . 27 6.3. APS state machine . . . . . . . . . . . . . . . . . . . . 28 6.3.1. Initial states . . . . . . . . . . . . . . . . . . . . 29 6.3.2. State transitions when local request is applied . . . 30 van Helvoort, et al. Expires April 9, 2013 [Page 2] Internet-Draft MPLS-TP Ring Protection Switching October 2012 6.3.3. State transitions when remote request is applied . . . 33 6.3.4. State Transitions when request addresses to another node is received . . . . . . . . . . . . . . 36 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39 8. Security Considerations . . . . . . . . . . . . . . . . . . . 39 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 39 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39 10.1. Normative References . . . . . . . . . . . . . . . . . . . 39 10.2. Informative References . . . . . . . . . . . . . . . . . . 39 Appendix A. Ring protection requirements compliance . . . . . . . 40 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 42 van Helvoort, et al. Expires April 9, 2013 [Page 3] Internet-Draft MPLS-TP Ring Protection Switching October 2012 1. Introduction Ring topologies are well known in SDH and SONET networks and is proven to be very effective and simple in terms of protection switching. Similar to SDH networks, MPLS networks can be built over ring topologies. Such networks allow for a simple, fast recovery time, and efficient protection mechanisms similar to the protection mechanisms in SDH, as well as high bandwidth utilization achievable by using the packet switching statistical multiplexing. MPLS shared protection ring can be viewed as equivalent to SDH MS shared protection ring architecture [G.841]. The protection ring consists of two counter-rotating rings, transmitting in opposite directions relative to each other. Both rings carry working and protection traffic. The bandwidth on each ring is divided so that a part of ring capacity is dedicated for the working traffic and another part is dedicated to the protection traffic. The protection bandwidth on one ring is used to transport the working traffic from the other ring in case of failure. Part of ring bandwidth can also be dedicated to carry unprotected non-preemptable traffic (NUT). 1.1. Contributing authors Italo Busi (Alcatel-Lucent), Haiyan Zhang (Huawei Technologies), Han Li (China Mobile Communications Corporation), Ruiquan Jing (China Telecom). 2. Conventions Used in this Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. van Helvoort, et al. Expires April 9, 2013 [Page 4] Internet-Draft MPLS-TP Ring Protection Switching October 2012 2.1. Abbreviations APS Automatic Protection Switching CCW Counterclockwise EXER Exercise FS Forced Switch LP Lockout of Protection LW Lockout of Working NMS Network Management System MPLS Multi-Protocol Label Switching MPLS-TP MPLS Transport Profile MRPS MPLS-TP Ring Protection Switching MS Manual Switch NR No request NUT Non-preemptable Unprotected Traffic OAM Operation, Administration and Maintenance PDU Payload Data Unit PS Protection Switching QoS Quality of Service RR Reverse Request SF Signal Fail WTR Wait to Restore 3. Ring protection schemes 3.1. Wrapping The Wrapping technique implies that the node detecting a failure sends out an APS request to the (opposite to the failure) node adjacent to the failure. The APS request is transmitted over the APS communication protocol, as defined in [RFC6371]. When a node detects a failure or receives an APS request through APS protocol addressed to this node, the traffic of all working LSPs/tunnels transmitted towards the failed span is switched to the protection LSPs/tunnels in the opposite direction (away from the failure). This traffic travels around the ring to the other node (adjacent to the failure) where it is switched back onto the working LSPs/tunnels. The nodes that performed the protection switching revert back to the normal traffic flow when the failure or APS request is cleared. For each normal or working MPLS-TP LSP/tunnel, the protection LSP/ tunnel MUST be established in the opposite direction though all nodes in the ring. Labels assigned for the protection LSPs/tunnels MUST be associated with the labels assigned for working LSPs/tunnels to allow proper traffic switching between the working and protection LSPs/ tunnels. van Helvoort, et al. Expires April 9, 2013 [Page 5] Internet-Draft MPLS-TP Ring Protection Switching October 2012 3.1.1. Wrapping protection scheme applicability Wrapping protection scheme provides for fast and simple recovery of p-t-p and p-t-mp LSPs in case of single or multiple failures in the ring. The protection mechanism in terms of nodes behavior, data path, signaled APS protocol messages is the same in all cases. In some scenarios with large networks additional latency may be introduced during protection switching in the ring because protection traffic travels along the all the ring. 3.1.2. P-t-p LSP example +---+ [P1] +---+ | F |-------------| A | <- LSP 1 +---+ +---+ / \ [P2]/ [W1]\[P6] / \ +---+ +---+ | E | | B | +---+ +---+ \ / [P3]\ [W2]/[P5] \ / +---+ [W3] +---+ LSP 1 <-- | D |-------------| C | +---+ [P4] +---+ Figure 1: Labels allocation example for p-t-p LSP protection with wrapping protection switching Working labels: A[W1]->B[W2]->C[W3]->D Protection labels: A[P1]->F[P2]->E[P3]->D[P4]->C[P5]->B[P6]->A Working and protection labels association: [W1]<->[P6] [W2]<->[P5] [W3]<->[P4] van Helvoort, et al. Expires April 9, 2013 [Page 6] Internet-Draft MPLS-TP Ring Protection Switching October 2012 3.1.2.1. Link failure example +---+ [P1] +---+ | F |-------------| A | <- LSP 1 +---+ +---+ / \ [P2]/ [W1]\[P6] / \ +---+ +---+ | E | | B | +---+ +---+ \ / [P3]\ X \ / +---+ [W3] +---+ LSP 1 <-- | D |-------------| C | +---+ [P4] +---+ Figure 2: Wrapping protection switching operation for p-t-p LSP in case of link failure When the failure occurs between the nodes B and C, these nodes send APS request to each other around the ring. Node B switches the traffic of LSP 1 from working label [W1] to the protection label [P6] in the opposite direction (CCW). This traffic travels around the ring to the node C where it is switched from protection label [P4] to the working label [W3] and sent to the node D where it is dropped from the ring. Traffic flow and labels use when the link failure occurs: A[W1]->B[P6]->A[P1]->F[P2]->E[P3]->D[P4]->C[W3]->D van Helvoort, et al. Expires April 9, 2013 [Page 7] Internet-Draft MPLS-TP Ring Protection Switching October 2012 3.1.2.2. Node failure example +---+ [P1] +---+ | F |-------------| A | <- LSP 1 +---+ +---+ / \ [P2]/ X / \ +---+ +---+ | E | | B | +---+ +---+ \ / [P3]\ X \ / +---+ [W3] +---+ LSP 1 <-- | D |-------------| C | +---+ [P4] +---+ Figure 3: Wrapping protection switching operation for p-t-p LSP in case of node failure When node B fails or becomes isolated because of two failed links, nodes A and C send APS request to each other around the ring. Node A switches the traffic of LSP 1 to the protection label [P1] in the direction opposite to normal flow. This traffic travels around the ring to the node C where it is switched from the protection label [P4] to the working label [W3] and sent to the node D where it is dropped from the ring. Traffic flow and labels use when the node B failure occurs: A[P1]->F[P2]->E[P3]->D[P4]->C[W3]->D van Helvoort, et al. Expires April 9, 2013 [Page 8] Internet-Draft MPLS-TP Ring Protection Switching October 2012 3.1.3. P-t-mp LSP example +---+ [P1] +---+ LSP 1 <-- | F |-------------| A | <- LSP 1 +---+ +---+ / \ [P2]/[W5] [W1]\[P6] / \ +---+ +---+ | E | | B | +---+ +---+ \ / [P3]\[W4] [W2]/[P5] \ / +---+ [W3] +---+ LSP 1 <-- | D |-------------| C | --> LSP1 +---+ [P4] +---+ Figure 4: Labels allocation example for p-t-mp LSP protection with wrapping protection switching Working labels: A[W1]->B[W2]->C[W3]->D[W4]->E[W5]->F | | | v v v LSP 1 LSP 1 LSP 1 Protection labels: A[P1]->F[P2]->E[P3]->D[P4]->C[P5]->B[P6]->A Working and protection labels association: [W1]<->[P6] [W2]<->[P5] [W3]<->[P4] [W4]<->[P3] [W5]<->[P2] van Helvoort, et al. Expires April 9, 2013 [Page 9] Internet-Draft MPLS-TP Ring Protection Switching October 2012 3.1.3.1. Link failure example +---+ [P1] +---+ LSP 1 <-- | F |-------------| A | <- LSP 1 +---+ +---+ / \ [P2]/[W5] [W1]\[P6] / \ +---+ +---+ | E | | B | +---+ +---+ \ / [P3]\[W4] X \ / +---+ [W3] +---+ LSP 1 <-- | D |-------------| C | --> LSP 1 +---+ [P4] +---+ Figure 5: Wrapping protection switching operation for p-t-mp LSP in case of link failure When the failure occurs between the nodes B and C, these nodes send APS request to each other around the ring. Node B switches the traffic of LSP 1 from working label [W1] to the protection label [P6] in the opposite direction (CCW). This traffic travels around the ring to the node C where it is switched from protection label [P4] to the working label [W3] and sent to the nodes D and F where it is dropped from the ring. Traffic flow and labels use when the link failure occurs: A[W1]->B[P6]->A[P1]->F[P2]->E[P3]->D[P4]->C[W3]->D[W4]->E[W5]->F | | | v v v LSP 1 LSP 1 LSP 1 van Helvoort, et al. Expires April 9, 2013 [Page 10] Internet-Draft MPLS-TP Ring Protection Switching October 2012 3.1.3.2. Node failure example +---+ [P1] +---+ LSP 1 <-- | F |-------------| A | <- LSP 1 +---+ +---+ / \ [P2]/ X / \ +---+ +---+ | E | | B | +---+ +---+ \ / [P3]\ X \ / +---+ [W3] +---+ LSP 1 <-- | D |-------------| C | --> LSP1 +---+ [P4] +---+ Figure 6: Wrapping protection switching operation for p-t-mp LSP in case of node failure When node B fails or becomes isolated because of two failed links, nodes A and C send APS request to each other around the ring. Node A switches the traffic of LSP 1 to the protection label [P1] in the direction opposite to normal flow. This traffic travels around the ring to the node C where it is switched from the protection label [P4] to the working label [W3] and sent to the nodes D and F where it is dropped from the ring. Traffic flow and labels use when the node B failure occurs: A[P1]->F[P2]->E[P3]->D[P4]->C[W3]->D[W4]->E[W5]->F | | | v v v LSP 1 LSP 1 LSP 1 3.2. Steering The Steering technique implies that the node detecting a failure sends an APS request to the node adjacent to the failure (away from the failure). The APS request is processed by all intermediate nodes in the ring. All nodes in the ring MUST analyze which LSPs are affected by the failure or APS request. This analysis is based on the ring node maps configured at each node in the ring and LSP maps provided at each source node (that adds traffic onto the ring) and sink node (that drops the traffic from the ring). For each affected LSP the source node and the sink node switches the traffic from working LSPs/tunnels to the protection LSPs/tunnels and restore normal traffic flow when the failure or APS request is cleared. van Helvoort, et al. Expires April 9, 2013 [Page 11] Internet-Draft MPLS-TP Ring Protection Switching October 2012 3.2.1. Steering protection scheme applicability Steering protection scheme provides for recovery of p-t-p and p-t-mp LSPs in case of single or multiple failures in the ring. The protection mechanism different for p-t-p and p-t-mp LSPs in terms of nodes behavior and data path. Signaled APS protocol messages are the same. Steering mechanism introduces less latency comparing to wrapping during protection switching in the ring but it requires more complex configuration. It also may affect the protection time because of more complex operation of switching nodes. 3.2.2. P-t-p LSP example +---+ [P1] +---+ | F |-------------| A | <- LSP 1 +---+ +---+ / \ [P2]/ [W1]\ / \ +---+ +---+ | E | | B | +---+ +---+ \ / [P3]\ [W2]/ \ / +---+ [W3] +---+ LSP 1 <-- | D |-------------| C | +---+ +---+ Figure 7: Labels allocation example for p-t-p LSP protection with steering protection switching Working labels: A[W1]->B[W2]->C[W3]->D Protection labels: A[P1]->F[P2]->E[P3]->D van Helvoort, et al. Expires April 9, 2013 [Page 12] Internet-Draft MPLS-TP Ring Protection Switching October 2012 3.2.2.1. Link failure example +---+ [P1] +---+ | F |-------------| A | <- LSP 1 +---+ +---+ / \ [P2]/ \ / \ +---+ +---+ | E | | B | +---+ +---+ \ / [P3]\ X \ / +---+ +---+ LSP 1 <-- | D |-------------| C | +---+ +---+ Figure 8: Steering protection switching operation for p-t-p LSP in case of link failure When the failure occurs between the nodes B and C, these nodes send APS request to each other around the ring. Nodes A and D analyze these requests and determine that LSP 1 is affected by the failure. Node A switches the traffic of LSP 1 to the protection label [P1] in the direction opposite to normal flow. This traffic travels around the ring to the node D where it is dropped from the ring. Traffic flow and labels use when the link failure occurs: A[P1]->F[P2]->E[P3]->D 3.2.2.2. Node failure example van Helvoort, et al. Expires April 9, 2013 [Page 13] Internet-Draft MPLS-TP Ring Protection Switching October 2012 +---+ [P1] +---+ | F |-------------| A | <- LSP 1 +---+ +---+ / \ [P2]/ X / \ +---+ +---+ | E | | B | +---+ +---+ \ / [P3]\ X \ / +---+ +---+ LSP 1 <-- | D |-------------| C | +---+ +---+ Figure 9: Steering protection switching operation for p-t-p LSP in case of node failure When node B fails or becomes isolated because of two failed links, nodes A and C send APS request to each other around the ring. Nodes A and D analyze these requests and determine that LSP 1 is affected by the failure. Node A switches the traffic of LSP 1 to the protection label [P1] in the direction opposite to normal flow. This traffic travels around the ring to the node D where it is dropped from the ring. Traffic flow in case of node B failure is presented below. A[P1]->F[P2]->E[P3]->D 3.2.3. P-t-mp LSP example van Helvoort, et al. Expires April 9, 2013 [Page 14] Internet-Draft MPLS-TP Ring Protection Switching October 2012 +---+ [P1] +---+ LSP 1 <-- | F |-------------| A | <- LSP 1 +---+ +---+ / \ [P2]/[W5] [W1]\ / \ +---+ +---+ | E | | B | +---+ +---+ \ / [P3]\[W4] [W2]/ \ / +---+ [W3] +---+ LSP 1 <-- | D |-------------| C | -> LSP 1 +---+ [P4] +---+ Figure 10: Labels allocation example for p-t-mp LSP protection with steering protection switching Working labels: A[W1]->B[W2]->C[W3]->D[W4]->E[W5]->F | | | v v v LSP 1 LSP 1 LSP 1 Protection labels: A[P1]->F[P2]->E[P3]->D[P4]->C | | | v v v LSP 1 LSP 1 LSP 1 3.2.3.1. Link failure example van Helvoort, et al. Expires April 9, 2013 [Page 15] Internet-Draft MPLS-TP Ring Protection Switching October 2012 +---+ [P1] +---+ LSP 1 <-- | F |-------------| A | <- LSP 1 +---+ +---+ / \ [P2]/ [W1]\ / \ +---+ +---+ | E | | B | +---+ +---+ \ / [P3]\ [W2]/ \ / +---+ +---+ LSP 1 <-- | D |------X------| C | -> LSP 1 +---+ +---+ Figure 11: Steering protection switching operation for p-t-mp LSP in case of link failure When the failure occurs between the nodes C and D, these nodes send APS request to each other around the ring. Nodes A, C, D and F analyze these requests and determine that LSP 1 is affected by the failure. Node A duplicates the traffic of LSP 1 to the working label [W1] and the protection label [P1]. Node C detects that normal flow of LSP 1 is not affected and continues receiving working label [W2] without performing protection switching. Nodes D and F detect that normal flow of LSP 1 is affected and switch to protection labels [P3] and [P1] respectively. Traffic flow and working labels use when the link failure occurs: A[W1]->B[W2]->C->X | v LSP 1 Traffic flow and protection labels use when the link failure occurs: A[P1]->F[P2]->E[P3]->D->X | | v v LSP 1 LSP 1 van Helvoort, et al. Expires April 9, 2013 [Page 16] Internet-Draft MPLS-TP Ring Protection Switching October 2012 3.2.3.2. Node failure example +---+ [P1] +---+ LSP 1 <-- | F |-------------| A | <- LSP 1 +---+ +---+ / \ [P2]/ [W1]\ / \ +---+ +---+ | E | | B | +---+ +---+ \ / X [W2]/ \ / +---+ +---+ | D |------X------| C | -> LSP 1 +---+ +---+ Figure 12: Steering protection switching operation for p-t-mp LSP in case of node failure When node D fails or becomes isolated because of two failed links, nodes E and C send APS request to each other around the ring. Nodes A, C and F analyze these requests and determine that LSP 1 is affected by the failure. Node A duplicates the traffic of LSP 1 to the working label [W1] and the protection label [P1]. Node C detects that normal flow of LSP 1 is not affected and continues receiving working label [W2] without performing protection switching. Node F detects that normal flow of LSP 1 is affected and switch to protection label [P1]. Traffic flow and working labels use when the node failure occurs: A[W1]->B[W2]->C->X | v LSP 1 Traffic flow and protection labels use when the node failure occurs: A[P1]->F[P2]->E[P3]->X | v LSP 1 4. MRPS characteristics van Helvoort, et al. Expires April 9, 2013 [Page 17] Internet-Draft MPLS-TP Ring Protection Switching October 2012 4.1. Switching types MRPS mechanism MUST support bi-directional protection switching type. In bi-directional switching, the traffic passing in both directions the monitored MPLS-TP section layer, including the affected direction and the unaffected direction, is switched to protection LSPs/tunnels. 4.2. Operation types MRPS mechanism MUST support revertive protection operation type, which implies that the traffic will returns to (or remains on) the working LSPs/tunnels after the failure or APS request is cleared. MRPS mechanism MAY support non-revertive protection operation type, which implies that the traffic will remain on the protection LSPs/ tunnels after the failure or APS request is cleared. 4.3. Traffic types 4.3.1. Bandwidth sharing The bandwidth on each ring MUST be shared so that part of ring bandwidth capacity is guaranteed for the normal traffic and part is used for the protection traffic in case of failure on the ring. The protection part of the ring bandwidth rotating in one direction is used to carry the normal traffic from the ring rotating in other direction in case of failure. Part of ring bandwidth MAY also be dedicated to carry Non-preemptable Unprotected Traffic (NUT). 4.3.2. Bandwidth and QoS considerations The MRPS mechanism provides for the connectivity restoration of the normal traffic affected by a ring failure. The protection mechanism itself does not distinguish between different types of QoS associated with the given LSPs. It is also not aware of the bandwidth allocated or guaranteed for the protected or unprotected LSPs. In the MPLS-TP ring, in order to guarantee the bandwidth and QoS of the LSPs, normal or unprotected, traffic management and engineering measures SHOULD be taken. For example, the bandwidth and QoS parameters allocated for each protection LSP/tunnel can be equal to the bandwidth and QoS parameters of the associated working LSP/ tunnel. Bandwidth and QoS parameters calculation and allocation for the normal and protection LSPs/tunnels are out of scope of this document. van Helvoort, et al. Expires April 9, 2013 [Page 18] Internet-Draft MPLS-TP Ring Protection Switching October 2012 4.3.3. Point-to-point and point-to-multipoint traffic Both point-to-point and drop-and-continue point-to-multipoint MPLS-TP LSPs/tunnels MUST be protected by MRPS. The APS protocol functionality as well as the node's reaction on different APS requests in case of ring failure SHOULD be identical for p-t-p and p-t-mp traffic. 5. APS protocol The MRPS protection operation MUST be controlled with the help of the APS protocol. The APS processes in the each of the individual nodes that form the ring SHOULD communicate using MPLS-TP Section OAM APS PDUs. The APS protocol MUST carry the ring status information and APS requests, both automatic and externally initiated commands, between the ring nodes. Each node on the ring MUST be uniquely identified by assigning it a node ID. The maximum number of nodes on the ring supported by the APS 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 APS request. Each node SHOULD have a ring map containing information about the sequence of the nodes around the ring. The method of configuring the nodes with the ring maps is TBD. When no protection switches are active on the ring, each node MUST dispatch periodically APS requests to the two adjacent nodes, indicating No Request (NR). When a node determines that a protection switching is required, it MUST send the appropriate APS request in both directions. +---+ A->B(NR) +---+ B->C(NR) +---+ C->D(NR) -------| A |-------------| B |-------------| C |------- (NR)F<-A +---+ (NR)A<-B +---+ (NR)B<-C +---+ Figure 13: APS communication between the ring nodes in case of no failures in the ring A destination node is a node that is adjacent to a node that identified a failed span. When a node that is not the destination node receives an APS request and it has no higher priority local van Helvoort, et al. Expires April 9, 2013 [Page 19] Internet-Draft MPLS-TP Ring Protection Switching October 2012 request, it MUST transfer the APS request as received. In this way, the switching nodes can maintain direct APS protocol communication in the ring. +---+ C->B(SF) +---+ B->C(SF) +---+ C->B(SF) -------| A |-------------| B |----- X -----| C |------- (SF)C<-B +---+ (SF)C<-B +---+ (SF)B<-C +---+ Figure 14: APS communication between the ring nodes in case of failure between nodes B and C Note that in the case of a bidirectional failure such as a cable cut, two nodes detect the failure and send each other an APS request in opposite directions. o In rings utilizing the wrapping protection, when the destination node receives the APS request it MUST perform the switch from/to the working LSPs/tunnels to/from the protection LSPs/tunnels if it has no higher priority active APS request. o In rings utilizing the steering protection, when a ring switch is required, any node MUST perform the switches if its added/dropped traffic is affected by the failure. Determination of the affected traffic SHOULD be performed by examining the APS requests (indicating the nodes adjacent to the failure or failures) and the stored ring maps (indicating the relative position of the failure and the added traffic destined towards that failure). When the failure has cleared and the Wait-to-Restore (WTR) timer has expired, the nodes sourcing APS requests MUST drop their respective switches (tail end) and MUST source an APS request carrying NR code. The node receiving from both directions such APS request (head end) MUST drop its protection switches. A protection switch MUST be initiated by one of the criteria specified in Section 6. A failure of the APS protocol or controller MUST NOT trigger a protection switch. Ring switches MUST be preempted by higher priority APS requests. For example, consider a protection switch that is active due to a manual switch request on the given span, and another protection switch is required due to a failure on another span. Then a APS request MUST be generated, the former protection switch MUST be dropped, and the latter protection switch established. MRPS mechanism SHOULD support multiple protection switches in the van Helvoort, et al. Expires April 9, 2013 [Page 20] Internet-Draft MPLS-TP Ring Protection Switching October 2012 ring, resulting the ring being segmented into two or more separate segments. This may happen when several APS requests of the same priority exist in the ring due to multiple failures or external switch commands. Proper operation of the MRPS mechanism relies on all nodes having knowledge of the state of the ring (nodes and spans) so that nodes do not preempt existing APS request unless they have a higher-priority APS request. In order to accommodate ring state knowledge, during protection switch the APS requests MUST be sent in both directions. 5.1. Transmission and acceptance of APS requests A new APS request MUST be transmitted immediately when a change in the transmitted status occurs. The first three APS protocol messages carrying new APS request SHOULD be transmitted as fast as possible. For fast protection switching within 50 ms, the interval of the first three APS protocol messages SHOULD be 3.3 ms. Then APS requests SHOULD be transmitted with the interval of 5 seconds. 5.2. APS PDU structure Figure 15 depicts the format of an APS packet that is sent on the G-ACh. The Channel Type field is set to indicate that the message is an APS message. The ACH MUST NOT include the ACH TLV Header [RFC5586] meaning that no ACH TLVs can be included in the message. 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 0 0 1|0 0 0 0|0 0 0 0 0 0 0 0| APS Channel Type (0xXX) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | APS message (TBD) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 15: G-ACh APS Packet APS message structure is TBD. The following fields MUST be provided: o Destination Node ID: The destination node ID MUST always be set to value of a node ID of the adjacent node. Valid destination node ID values are 1-127. van Helvoort, et al. Expires April 9, 2013 [Page 21] Internet-Draft MPLS-TP Ring Protection Switching October 2012 o Source node ID: The source node ID MUST always be set to the value of the node ID generating the APS request. Valid source node ID values are 1-127. o APS request code: A code consisting of four bits as specified below. +-------------+-----------------------------+----------+ | Bits 4-1 | Condition, State | Priority | | (MSB - LSB) | or external Request | | +-------------------------------------------+----------+ | 1 1 1 1 | Lockout of Protection (LP) | highest | | 1 1 0 1 | Forced Switch (FS) | | | 1 0 1 1 | Signal Fail (SF) | | | 0 1 1 0 | Manual Switch (MS) | | | 0 1 0 1 | Wait-To-Restore (WTR) | | | 0 0 1 1 | Exerciser (EXER) | | | 0 0 0 1 | Reverse Request (RR) | | | 0 0 0 0 | No Request (NR) | lowest | +-------------+-----------------------------+----------+ 5.3. Ring node APS states Idle state: A node is in the idle state when it has no APS request and is sourcing and receiving NR code to/from both directions. Switching state: A node not in the idle or pass-through states is in the switching state. Pass-through state: A node is in the pass-through state when its highest priority APS request is a request not destined to or sourced by it. The pass-through is bidirectional. 5.3.1. Idle state A node in the idle state MUST source the NR request in both directions. A node in the idle state MUST terminate APS requests flow in both directions. A node in the idle state MUST block the traffic flow on protection LSPs/tunnels in both directions. van Helvoort, et al. Expires April 9, 2013 [Page 22] Internet-Draft MPLS-TP Ring Protection Switching October 2012 5.3.2. Switching state A node in the switching state MUST source APS request to adjacent node with its highest APS request code in both directions when it detects a failure or receives an external command. A node in the switching state MUST terminate APS requests flow in both directions. As soon as it receives an APS request from the short path, the node to which it is addressed MUST acknowledge the APS request by replying with the RR code on the short path, and with the received APS request code on the long path. This rule refers to the unidirectional failure detection: the RR SHOULD be issued only when the node does not detect the failure condition (i.e., the node is a head end), that is, it is not applicable when a failure is detected bidirectionally, because, in this latter case, both nodes send an APS request for the failure on both paths (short and long). The following switches MUST be allowed to coexist: o LP with LP o FS with FS o SF with SF o FS with SF When multiple MS APS requests over different spans exist at the same time, no switch SHOULD be executed and existing switches MUST be dropped. The nodes MUST signal, anyway, the MS APS request code. Multiple EXER request MUST be allowed to coexist in the ring. A node in a ring switching state that receives the external command LW for the affected span MUST drop its switch and MUST signal NR for the locked span if there is no other APS request on another span. Node still SHOULD signal relevant APS request for another span. 5.3.3. Pass-through state When a node is in a pass-through state, it MUST transmit on one side, the same APS request as it receives from the other side. When a node is in a pass-through state, it MUST allow the traffic van Helvoort, et al. Expires April 9, 2013 [Page 23] Internet-Draft MPLS-TP Ring Protection Switching October 2012 flow on protection LSPs/tunnels in both directions. 5.3.4. APS state transitions All state transitions are triggered by an incoming APS request change, a WTR expiration, an externally initiated command, or locally detected MPLS-TP section failure conditions. APS requests due to a locally detected failure, an externally initiated command, or received APS request shall pre-empt existing APS requests in the prioritized order given in Section 5.2, unless the requests are allowed to coexist. 5.3.4.1. Transitions between the idle and pass-through states The transition from the idle state to pass-through state MUST be triggered by a valid APS request change, in any direction, from the NR code to any other code, as long as the new request is not destined for the node itself. Both directions move then into a pass-through state, so that, traffic entering the node through the protection LSPs/tunnels are by-passed across the node. A node MUST revert from pass-through state to the idle state when it detects NR codes incoming from both directions. Both directions revert simultaneously from the pass-through state to the idle state. 5.3.4.2. Transitions between the idle and switching states Transition of a node from the idle state to the switching state MUST be triggered by one of the following conditions: o a valid APS request change from the NR code to any code received on either the long or the short path and destined to this node o an externally initiated command for this node o the detection of an MPLS-TP section layer failure at this node. Actions taken at a node in idle state upon transition to switching state are: o for all protection switch requests, except EXER and LP, the node MUST execute the switch o for EXER, and LP, the node MUST signal appropriate request but not execute the switch. A node MUST revert from the switching state to the idle state when it van Helvoort, et al. Expires April 9, 2013 [Page 24] Internet-Draft MPLS-TP Ring Protection Switching October 2012 detects NR codes received from both directions. o At the tail end: When a WTR time expires or an externally initiated command is cleared at a node, the node MUST drop its switch, transit to Idle state and signal the NR code in both directions. o At the head end: Upon reception of the NR code, from both directions, the head-end node MUST drop its switch, transition to Idle state and signal the NR code in both directions. 5.3.4.3. Transitions between switching states When a node that is currently executing any protection switch receives a higher priority APS request (due to a locally detected failure, an externally initiated command, or a ring protection switch request destined to it) for the same span, it MUST upgrade the priority of the switch it is executing to the priority of the received APS request. When a failure condition clears at a node, the node MUST enter WTR condition and remain in it for the appropriate time-out interval, unless: o a different APS request of higher priority than WTR is received o another failure is detected o an externally initiated command becomes active. 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 APS request (not due to a locally detected failure) receives a WTR code (unidirectional failure case), it MUST send out RR code on the short path and the WTR on the long path. 5.3.4.4. Transitions between switching and pass-through states When a node that is currently executing a switch receives an APS request for a non-adjacent span of higher priority than the switch it is executing, it MUST drop its switch immediately and enter the pass- through state. The transition of a node from pass-through to switching state MUST be triggered by: van Helvoort, et al. Expires April 9, 2013 [Page 25] Internet-Draft MPLS-TP Ring Protection Switching October 2012 o an equal, higher priority, or allowed coexisting externally initiated command o the detection of an equal, higher priority, or allowed coexisting failure o the receipt of an equal, higher priority, or allowed coexisting APS request destined to this node. 6. Protection switching triggers Protection switching action MUST be conducted when: o they are initiated by operator control (e.g., manual switch, forced switch, and lockout of protection) without a higher priority APS request being in effect on addressed span or entire ring o an MPLS-TP Section SF is declared on the associated span and without a higher priority APS request (e.g., lockout of protection, forced switch) being in effect on addressed span or entire ring and the hold-off timer has expired o the wait to restore timer expires. 6.1. Manual control Externally initiated commands are entered by the operator through the Network Management System (NMS) or the Craft interface. 6.1.1. Commands not signaled on the APS protocol The node MUST support the following commands that are not transferred by the APS protocol: o Clear: This command clears the externally initiated command and WTR timer at the node to which the command was addressed. The node-to-node signaling following removal of the externally initiated commands MUST be performed using the NR code. o Lockout of Working: This command prevents the normal traffic transported over the addressed span from being switched to the protection LSPs/tunnels by disabling the node's capability of requesting the protection switching for this span in case of failure. If any normal traffic is already switched on the protection LSPs/tunnels, the switch MUST be dropped. If no other APS requests are active on the ring, the NR code MUST be van Helvoort, et al. Expires April 9, 2013 [Page 26] Internet-Draft MPLS-TP Ring Protection Switching October 2012 transmitted. This command has no impact on any other span. If the node receives the APS request from the adjacent node from any side it MUST perform the requested switch. If the node receives the request addressed to the other node it MUST go to the pass- through state. 6.1.2. Commands using the APS protocol The node MUST support the following commands that are transferred by the APS protocol: o Lockout of Protection (LP): This command prevents any protection activity and prevents using protection switches anywhere in the ring. All existing switches in the ring MUST be dropped. o Forced Switch to protection (FS): This command performs the ring switch of normal traffic from the working LSPs/tunnels to the protection LSPs/tunnels for the span between the node at which the command is initiated and the adjacent node to which the command is directed. This switch MUST occur regardless of the state of the spans adjacent to this node unless it is satisfying a higher priority APS request. o Manual Switch to protection (MS): This command performs the ring switch of the normal traffic from the working LSPs/tunnels to the protection LSPs/tunnels for the span between the node at which the command is initiated and the adjacent node to which the command is directed. This occurs if the node is not satisfying an equal or higher priority APS request. The node MAY support the following commands that are transferred by the APS protocol: o Exercise - (EXER): This command exercises ring protection switching on the addressed span without completing the actual switch. When the command issued the RR responses are checked, but no normal traffic is affected. 6.2. Automatically initiated commands Automatically initiated commands can be initiated based on MPLS-TP section layer and equipment performance criteria and received APS requests. The node MUST support the following APS requests that are initiated automatically: van Helvoort, et al. Expires April 9, 2013 [Page 27] Internet-Draft MPLS-TP Ring Protection Switching October 2012 o Signal Fail (SF): This command is issued when the MPLS-TP section detects signal failure condition. When the tail-end detects the failure it MUST generate the APS request towards the head-end. o Wait-To-Restore (WTR): This command is issued when MPLS-TP section detects that the SF condition has cleared. It is used to maintain the state during the WTR period unless it is pre-empted by a higher priority APS request. The Wait to Restore time SHOULD be configured by the operator in 1 minute steps between 0 and 72 hours. The default value SHOULD be 5 minutes. o Reverse Request (RR): This command MUST be transmitted to the tail-end node over the short path as an acknowledgment for receiving the APS request. 6.3. APS state machine van Helvoort, et al. Expires April 9, 2013 [Page 28] Internet-Draft MPLS-TP Ring Protection Switching October 2012 6.3.1. Initial states +-----------------------------------+----------------+ | State | Signaled APS | +-----------------------------------+----------------+ | A | Idle | NR | | | Working: no switch | | | | Protection: no switch | | +-----+-----------------------------+----------------+ | B | Pass-trough | N/A | | | Working: no switch | | | | Protection: pass through | | +-----+-----------------------------+----------------+ | C | Switching - LP | LP | | | Working: no switch | | | | Protection: no switch | | +-----+-----------------------------+----------------+ | D | Idle - LW | NR | | | Working: no switch | | | | Protection: no switch | | +-----+-----------------------------+----------------+ | E | Switching - FS | FS | | | Working: switched | | | | Protection: switched | | +-----+-----------------------------+----------------+ | F | Switching - SF | SF | | | Working: switched | | | | Protection: switched | | +-----+-----------------------------+----------------+ | G | Switching - MS | MS | | | Working: switched | | | | Protection: switched | | +-----+-----------------------------+----------------+ | H | Switching - WTR | WTR | | | Working: switched | | | | Protection: switched | | +-----+-----------------------------+----------------+ | I | Switching - EXER | EXER | | | Working: no switch | | | | Protection: no switch | | +-----+-----------------------------+----------------+ van Helvoort, et al. Expires April 9, 2013 [Page 29] Internet-Draft MPLS-TP Ring Protection Switching October 2012 6.3.2. State transitions when local request is applied In the state description below 'O' means that new local request will be rejected because of exiting request. ===================================================================== Initial state New request New state ------------- ----------- --------- A (Idle) LP C (Switching - LP) LW D (Idle - LW) FS E (Switching - FS) SF F (Switching - SF) Recover from SF N/A MS G (Switching - MS) Clear N/A WTR expires N/A EXER I (Switching - EXER) ===================================================================== Initial state New request New state ------------- ----------- --------- B (Pass-trough) LP C (Switching - LP) LW B (Pass-trough) FS O - if current state is due to LP sent by another node E (Switching - FS) - otherwise SF O - if current state is due to LP sent by another node F (Switching - SF) - otherwise Recover from SF N/A MS O - if current state is due to LP, SF or FS sent by another node G (Switching - MS) - otherwise Clear N/A WTR expires N/A EXER O ===================================================================== Initial state New request New state ------------- ----------- --------- C (Switching - LP) LP N/A LW O FS O SF O Recover from SF N/A MS O Clear A (Idle) - if there is no failure in the ring van Helvoort, et al. Expires April 9, 2013 [Page 30] Internet-Draft MPLS-TP Ring Protection Switching October 2012 F (Switching - SF) - if there is a failure at this node B (Pass-trough) - if there is a failure at another node WTR expires N/A EXER O ===================================================================== Initial state New request New state ------------- ----------- --------- D (Idle - LW) LP C (Switching - LP) LW N/A - if on the same span D (Idle - LW) - if on another span FS O - if on the same span E (Switching - FS) - if on another span SF O - if on the addressed span F (Switching - SF) - if on another span Recover from SF N/A MS O - if on the same span G (Switching - MS) - if on another span Clear A (Idle) - if there is no failure on addressed span F (Switching - SF) - if there is a failure on this span WTR expires N/A EXER O ===================================================================== Initial state New request New state ------------- ----------- --------- E (Switching - FS) LP C (Switching - LP) LW O - if on another span D (Idle - LW) - if on the same span FS N/A - if on the same span E (Switching - FS) - if on another span SF O - if on the addressed span E (Switching - FS) - if on another span Recover from SF N/A MS O Clear A (Idle) - if there is no failure in the ring F (Switching - SF) - if there is a failure at this node van Helvoort, et al. Expires April 9, 2013 [Page 31] Internet-Draft MPLS-TP Ring Protection Switching October 2012 B (Pass-trough) - if there is a failure at another node WTR expires N/A EXER O ===================================================================== Initial state New request New state ------------- ----------- --------- F (Switching - SF) LP C (Switching - LP) LW O - if on another span D (Idle - LW) - if on the same span FS E (Switching - FS) SF N/A - if on the same span F (Switching - SF) - if on another span Recover from SF H (Switching - WTR) MS O Clear N/A WTR expires N/A EXER O ===================================================================== Initial state New request New state ------------- ----------- --------- G (Switching - MS) LP C (Switching - LP) LW O - if on another span D (Idle - LW) - if on the same span FS E (Switching - FS) SF F (Switching - SF) Recover from SF N/A MS N/A - if on the same span G (Switching - MS) - if on another span release the switches but signal MS Clear A WTR expires N/A EXER O ===================================================================== Initial state New request New state ------------- ----------- --------- H (Switching - WTR) LP C (Switching - LP) LW D (Idle - W) FS E (Switching - FS) SF F (Switching - SF) Recover from SF N/A MS G (Switching - MS) Clear A WTR expires A van Helvoort, et al. Expires April 9, 2013 [Page 32] Internet-Draft MPLS-TP Ring Protection Switching October 2012 EXER O ===================================================================== Initial state New request New state ------------- ----------- --------- I (Switching - EXER) LP C (Switching - LP) LW D (idle - W) FS E (Switching - FS) SF F (Switching - SF) Recover from SF N/A MS G (Switching - MS) Clear A WTR expires N/A EXER N/A - if on the same span I (Switching - EXER) ===================================================================== 6.3.3. State transitions when remote request is applied The priority of remote request does not depend on the side from which the request is received. ===================================================================== Initial state New request New state ------------- ----------- --------- A (Idle) LP C (Switching - LP) FS E (Switching - FS) SF F (Switching - SF) MS G (Switching - MS) WTR N/A EXER I (Switching - EXER) RR N/A NR A (Idle) ===================================================================== Initial state New request New state ------------- ----------- --------- B (Pass-trough) LP C (Switching - LP) FS N/A - cannot happen when there is LP request in the ring E (Switching - FS) - otherwise SF N/A - cannot happen when there is LP request in the ring F (Switching - SF) - otherwise MS N/A - cannot happen when there is LP, FS or SF request in the ring G (Switching - MS) - otherwise van Helvoort, et al. Expires April 9, 2013 [Page 33] Internet-Draft MPLS-TP Ring Protection Switching October 2012 WTR N/A - cannot happen when there is LP, FS, SF or MS request in the ring EXER N/A - cannot happen when there is LP, FS, SF, MS or WTR request in the ring I (Switching - EXER) - otherwise RR N/A NR A (Idle) - if received from both sides ===================================================================== Initial state New request New state ------------- ----------- --------- C (Switching - LP) LP C (Switching - LP) FS N/A - cannot happen when there is LP request in the ring SF N/A - cannot happen when there is LP request in the ring MS N/A - cannot happen when there is LP request in the ring WTR N/A EXER N/A - cannot happen when there is LP request in the ring RR C (Switching - LP) NR N/A ===================================================================== Initial state New request New state ------------- ----------- --------- D (Idle - LW) LP C (Switching - LP) FS E (Switching - FS) SF F (Switching - SF) MS G (Switching - MS) WTR N/A EXER I (Switching - EXER) RR N/A NR D (Idle - LW) ===================================================================== Initial state New request New state ------------- ----------- --------- E (Switching - FS) LP C (Switching - LP) FS E (Switching - FS) SF E (Switching - FS) MS N/A - cannot happen when there is FS request in the ring WTR N/A EXER N/A - cannot happen when there is FS request in the ring van Helvoort, et al. Expires April 9, 2013 [Page 34] Internet-Draft MPLS-TP Ring Protection Switching October 2012 RR E (Switching - FS) NR N/A ===================================================================== Initial state New request New state ------------- ----------- --------- F (Switching - SF) LP C (Switching - LP) FS F (Switching - SF) SF F (Switching - SF) MS N/A - cannot happen when there is SF request in the ring WTR N/A EXER N/A - cannot happen when there is SF request in the ring RR F (Switching - SF) NR N/A ===================================================================== Initial state New request New state ------------- ----------- --------- G (Switching - MS) LP C (Switching - LP) FS E (Switching - FS) SF F (Switching - SF) MS G (Switching - MS) - release the switches but signal MS WTR N/A EXER N/A - cannot happen when there is MS request in the ring RR G (Switching - MS) NR N/A ===================================================================== Initial state New request New state ------------- ----------- --------- H (Switching - WTR) LP C (Switching - LP) FS E (Switching - FS) SF F (Switching - SF) MS G (Switching - MS) WTR H (Switching - WTR) EXER N/A - cannot happen when there is WTR request in the ring RR H (Switching - WTR) NR N/A ===================================================================== Initial state New request New state ------------- ----------- --------- I (Switching - EXER) LP C (Switching - LP) FS E (Switching - FS) SF F (Switching - SF) MS G (Switching - MS) WTR N/A van Helvoort, et al. Expires April 9, 2013 [Page 35] Internet-Draft MPLS-TP Ring Protection Switching October 2012 EXER I (Switching - EXER) RR I (Switching - EXER) NR N/A ===================================================================== 6.3.4. State Transitions when request addresses to another node is received The priority of remote request does not depend on the side from which the request is received. ===================================================================== Initial state New request New state ------------- ----------- --------- A (Idle) LP B (Pass-trough) FS B (Pass-trough) SF B (Pass-trough) MS B (Pass-trough) WTR B (Pass-trough) EXER B (Pass-trough) RR N/A NR N/A ===================================================================== Initial state New request New state ------------- ----------- --------- B (Pass-trough) LP B (Pass-trough) FS N/A - cannot happen when there is LP request in the ring B (Pass-trough) - otherwise SF N/A - cannot happen when there is LP request in the ring B (Pass-trough) - otherwise MS N/A - cannot happen when there is LP, FS or SF request in the ring B (Pass-trough) - otherwise WTR N/A - cannot happen when there is LP, FS, SF or MS request in the ring B (Pass-trough) - otherwise EXER N/A - cannot happen when there is LP, FS, SF, MS or WTR request in the ring B (Pass-trough) - otherwise RR N/A van Helvoort, et al. Expires April 9, 2013 [Page 36] Internet-Draft MPLS-TP Ring Protection Switching October 2012 NR B (Pass-trough) ===================================================================== Initial state New request New state ------------- ----------- --------- C (Switching - LP) LP C (Switching - LP) FS N/A - cannot happen when there is LP request in the ring SF N/A - cannot happen when there is LP request in the ring MS N/A - cannot happen when there is LP request in the ring WTR N/A - cannot happen when there is LP in the ring EXER N/A - cannot happen when there is LP request in the ring RR N/A NR N/A ===================================================================== Initial state New request New state ------------- ----------- --------- D (Idle - LW) LP B (Pass-trough) FS B (Pass-trough) SF B (Pass-trough) MS B (Pass-trough) WTR B (Pass-trough) EXER B (Pass-trough) RR N/A NR N/A ===================================================================== Initial state New request New state ------------- ----------- --------- E (Switching - FS) LP B (Pass-trough) FS E (Switching - FS) SF E (Switching - FS) MS N/A - cannot happen when there is FS request in the ring WTR N/A - cannot happen when there is FS request in the ring EXER N/A - cannot happen when there is FS request in the ring RR N/A NR N/A ===================================================================== Initial state New request New state ------------- ----------- --------- F (Switching - SF) LP B (Pass-trough) FS F (Switching - SF) SF F (Switching - SF) van Helvoort, et al. Expires April 9, 2013 [Page 37] Internet-Draft MPLS-TP Ring Protection Switching October 2012 MS N/A - cannot happen when there is SF request in the ring WTR N/A - cannot happen when there is SF request in the ring EXER N/A - cannot happen when there is SF request in the ring RR N/A NR N/A ===================================================================== Initial state New request New state ------------- ----------- --------- G (Switching - MS) LP B (Pass-trough) FS B (Pass-trough) SF B (Pass-trough) MS G (Switching - MS) - release the switches but signal MS WTR N/A - cannot happen when there is MS request in the ring EXER N/A - cannot happen when there is MS request in the ring RR N/A NR N/A ===================================================================== Initial state New request New state ------------- ----------- --------- H (Switching - WTR) LP B (Pass-trough) FS B (Pass-trough) SF B (Pass-trough) MS B (Pass-trough) WTR N/A EXER N/A - cannot happen when there is WTR request in the ring RR N/A NR N/A ===================================================================== Initial state New request New state I (Switching - EXER) LP B (Pass-trough) FS B (Pass-trough) SF B (Pass-trough) MS B (Pass-trough) WTR N/A EXER I (Switching - EXER) RR N/A NR N/A ===================================================================== van Helvoort, et al. Expires April 9, 2013 [Page 38] Internet-Draft MPLS-TP Ring Protection Switching October 2012 7. IANA Considerations Channel Types for the Generic Associated Channel are allocated from the IANA PW Associated Channel Type registry defined in [RFC4446] and updated by [RFC5586]. IANA is requested to allocate further Channel Type as follows: o 0xXX Automatic Protection Switching (APS) Note to RFC Editor: this section may be removed on publication as an RFC. 8. Security Considerations This document does not by itself raise any particular security considerations. 9. Acknowledgements Special thanks to Igor Umansky for his contribution. 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, BCP 14, March 1997. 10.2. Informative References [RFC5654] Niven-Jenkins, B., Nadeau, T., and C. Pignataro, "Requirements for the Transport Profile of MPLS", RFC 5654, September 2009. [G.841] ITU-T, "Types and characteristics of SDH network protection architectures", Recommendation G.841, Feb 2010. [RFC6371] Busi, I. and D. Allan, "Operations, Administration, and Maintenance Framework for MPLS-Based Transport Networks", RFC 6371, September 2011. [RFC5586] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic Associated Channel", RFC 5586, June 2009. van Helvoort, et al. Expires April 9, 2013 [Page 39] Internet-Draft MPLS-TP Ring Protection Switching October 2012 [RFC4446] Martini, L., "IANA Allocations for Pseudowire Edge to Edge Emulation (PWE3)", RFC 4446, BCP 116, April 2006. Appendix A. Ring protection requirements compliance Ring protection requirements are specified in the [RFC5654] Section 2.5.6. This section summarizes the coverage of these requirements by MRPS mechanism. Generic topology-specific requirement: 91 Interoperability between the ring and mesh networks in term of protection switching is achieved by: * using a non-preemptable unprotected traffic type (NUT) in the ring for the LSPs traversing the ring that are protected with end-to-end linear protection. * implementing segmented linear protection on the ring edge nodes Optimization criteria: a. There is only one APS OAM session per ring. b. Only two network elements, which are adjacent to addressed span or node are involved in protection switching event. c. MRPS requires one protection label on each span to protect one working LSP. d. Management operations are applied per node/per span, rather than per path. Dedicated procedures for ring upgrade are supported by using operator commands, provided by the ring protection algorithm. Static provisioning of limited amount of parameters is considered. e. MRPS mechanism does not affect control plane. General criteria: 92 MRPS mechanism operates provides for recovery of protected traffic within a ring domain without affecting other parts of the network. van Helvoort, et al. Expires April 9, 2013 [Page 40] Internet-Draft MPLS-TP Ring Protection Switching October 2012 93 Current version of this draft describes protection mechanism operating in the single ring domain. Multiple rings interworking is for further study. 94 Unidirectional and bidirectional paths are protected by MRPS, due to the fact that the protection mechanism is bidirectional. 95 Unidirectional P2MP paths are protected with the same mechanism as unidirectional by wrapping scheme. Steering scheme provides different mechanisms for P2P and P2MP paths. 96 Irrelevant for this draft. 97 MRSP mechanism operates at the MPLS-TP section layer and does not depend on number of LSPs passing addressed section/span. 98.A Configuration of protection LSP is proportional to the number of working LSPs. Operation of protection switching is independent of number of working/protection path. 98.B Configuration of protection LSP is proportional to the number of nodes in the ring. Operation of protection switching is independent of number of nodes. 98.C Configuration and operation of MRPS is done per ring and is independent of number or rings interconnects. 99 MRPS mechanism operates in a ring protection domain without affecting attached networks. An MPRS ring may be connected to a general MPLS-TP network with no constraint. 100 Recovery technique of MRPS relies on standard MPLS label swapping operation. Protection algorithm relies on well established MS- SPRing/BLSR mechanism. 101 MRPS mechanism is agnostic to the server layer technology and the associated infrastructure. 102 Protection switching in MRPS is bidirectional. 103 Protection switching in MRPS is revertive in case or wrapping scheme and configurable in case of steering scheme. 104 MRPS supports operator commands and automatic evens as protection triggers. Each one is identified via dedicated code in APS protocol. van Helvoort, et al. Expires April 9, 2013 [Page 41] Internet-Draft MPLS-TP Ring Protection Switching October 2012 105 MRPS supports operator commands to lockout/disable the protection switching per span and per entire ring. 106.A MRPS supports ring protection operation in case of multiple requests in the ring. 106.B MRPS supports traffic protection in case multiple failures in the ring. 107 Supported through wait-to-restore timer. 108 Best effort traffic that can be carried in unprotected LSPs (via NUT feature) and in all of the protection bandwidth. 109 Supported through sharing the protection bandwidth of each span between all other spans in the ring. Authors' Addresses Huub van Helvoort (editor) Huawei Technologies Email: huub.van.helvoort@huawei.com Jeong-dong Ryoo (editor) ETRI Email: ryoo@etri.re.kr Italo Busi Alcatel-Lucent Email: italo.busi@alcatel-lucent.com Haiyan Zhang Huawei Technologies Email: zhanghaiyan@huawei.com van Helvoort, et al. Expires April 9, 2013 [Page 42] Internet-Draft MPLS-TP Ring Protection Switching October 2012 Han Li China Mobile Communications Corporation Email: lihan@chinamobile.com Ruiquan Jing China Telecom Email: jingrq@ctbri.com.cn van Helvoort, et al. Expires April 9, 2013 [Page 43]