Network Working Group Igor Umansky, Ed. Internet-Draft Alcatel-Lucent Intended status: Standard Track Huub van Helvoort, Ed. Expires: April 22, 2010 Huawei Technologies October 19, 2009 MPLS-TP Ring Protection Switching (MRPS) draft-umansky-mpls-tp-ring-protection-switching-00.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 22, 2010. Copyright Notice Copyright (c) 2009 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 Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Umansky, et al. Expires April 22, 2010 [Page 1] Internet-Draft MPLS-TP Ring Protection Switching October 2009 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 [MPLS-TP OAM]. The Automatic Protection Switching (APS) protocol is used for coordination of protection switching actions between the ring nodes. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions used in this document . . . . . . . . . . . . . . . 3 2.1. Abbreviations . . . . . . . . . . . . . . . . . . . . . . . 3 3. Ring protection schemes . . . . . . . . . . . . . . . . . . . . 5 3.1. Wrapping . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.2. Steering . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. MRPS characteristics. . . . . . . . . . . . . . . . . . . . . . 7 4.1. Switching types . . . . . . . . . . . . . . . . . . . . . . 7 4.2. Operation types . . . . . . . . . . . . . . . . . . . . . . 7 4.3. Traffic types . . . . . . . . . . . . . . . . . . . . . . . 7 4.3.1 Bandwidth sharing. . . . . . . . . . . . . . . . . . . . 7 4.3.2 Bandwidth and QoS considerations . . . . . . . . . . . . 7 4.3.3 Point-to-point and point-to-multipoint traffic . . . . . 8 5 APS protocol. . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.1. Transmission and acceptance of APS requests . . . . . . . .10 5.2. APS PDU structure . . . . . . . . . . . . . . . . . . . . .10 5.3. Ring node APS states. . . . . . . . . . . . . . . . . . . .11 5.3.1. Idle state. . . . . . . . . . . . . . . . . . . . . . .11 5.3.2. Switching state . . . . . . . . . . . . . . . . . . . .12 5.3.3. Pass-through state . . . . . . . . . . . . . . . . . . 12 5.3.4. APS state transitions. . . . . . . . . . . . . . . . . 13 6. Protection switching triggers. . . . . . . . . . . . . . . . . 15 6.1. Manual control . . . . . . . . . . . . . . . . . . . . . . 15 6.1.1. Commands not signaled on the APS protocol. . . . . . . 15 6.1.2. Commands using the APS protocol. . . . . . . . . . . . 16 6.2. Automatically initiated commands. .. . . . . . . . . . . . 16 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . .18 8. Security Considerations . . . . . . . . . . . . . . . . . . . .18 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .18 10. Informative References . . . . . . . . . . . . . . . . . . . .18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .19 Umansky, et al. Expires April 22, 2010 [Page 2] Internet-Draft MPLS-TP Ring Protection Switching October 2009 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). 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 RFC-2119. 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 Umansky, et al. Expires April 22, 2010 [Page 3] Internet-Draft MPLS-TP Ring Protection Switching October 2009 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 Umansky, et al. Expires April 22, 2010 [Page 4] Internet-Draft MPLS-TP Ring Protection Switching October 2009 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 [OAM framework]. 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 forming a closed loop. 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. LSP 1 LSP 2 | v +---+& & & & & & &+---+ LSP 2 <-- * *| F |-------------| A | +---+* * * * * * *+---+ &/ @\& &/ @\& &/ @\& +---+ +---+ | E | | B | +---+ +---+ &\ / &\ X &\ / +---+@ @ @ @ @ @ @+---+ LSP 1 <-- @ @| D |-------------| C | +---+& & & & & & &+---+ Figure 1: MPLS-TP Ring Protection Switching - Wrapping Figure 1 provides an example of wrapping ring protection scheme. LSP 1 and LSP 2 are added to the ring at node A and dropped from the ring at nodes D and F respectively. Umansky, et al. Expires April 22, 2010 [Page 5] Internet-Draft MPLS-TP Ring Protection Switching October 2009 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 working LSP 1 (@)to the protection LSP 1 (&) in the opposite direction (CCW). This traffic travels around the ring to the node C where it is switched back to the working LSP 1 and sent to the node D where it is dropped from the ring. Working LSP 1: A->B->C->D Protection LSP 1: A->F->E->D->C->B->A Traffic flow when the failure occurs: A->B->A->F->E->D->C->D 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. For each affected LSP the source node (that adds traffic onto the ring) and the sink node (that drops the traffic from the ring) 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. LSP 1 LSP 2 | v +---+& & & & & & &+---+ LSP 2 <-- * *| F |-------------| A | +---+* * * * * * *+---+ &/ \ &/ \ &/ \ +---+ +---+ | E | | B | +---+ +---+ &\ / &\ X &\ / +---+ +---+ LSP 1 <-- @ @| D |-------------| C | +---+ +---+ Figure 2: MPLS-TP Ring Protection Switching - Steering In the example above when the failure occurs between the nodes B and C, these nodes send APS request to each other around the ring. Node A analyzes these requests and determines that LSP 1 is affected by the failure and switches the traffic of working LSP 1 (@) to the protection LSP 1 (&) in the opposite direction (CCW). This Umansky, et al. Expires April 22, 2010 [Page 6] Internet-Draft MPLS-TP Ring Protection Switching October 2009 traffic travels around the ring to the node D where it is switched back to the working LSP 1 and dropped from the ring. Working LSP 1: A->B->C->D Protection LSP 1: A->F->E->D Traffic flow when the failure occurs: A->F->E->D 4. MRPS characteristics 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. Umansky, et al. Expires April 22, 2010 [Page 7] Internet-Draft MPLS-TP Ring Protection Switching October 2009 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. 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. Umansky, et al. Expires April 22, 2010 [Page 8] Internet-Draft MPLS-TP Ring Protection Switching October 2009 +---+ A->B(NR) +---+ B->C(NR) +---+ C->D(NR) -------| A |-------------| B |-------------| C |------- (NR)F<-A +---+ (NR)A<-B +---+ (NR)B<-C +---+ Figure 3: 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 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 4: 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. - 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. - 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 clause 6. A failure of the APS protocol or controller MUST NOT trigger a protection switch. Umansky, et al. Expires April 22, 2010 [Page 9] Internet-Draft MPLS-TP Ring Protection Switching October 2009 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 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 5 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 [RFC 5586] 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 5: G-ACh APS Packet APS message structure is TBD. Umansky, et al. Expires April 22, 2010 [Page 10] Internet-Draft MPLS-TP Ring Protection Switching October 2009 The following fields MUST be provided: 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. 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. 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. Umansky, et al. Expires April 22, 2010 [Page 11] Internet-Draft MPLS-TP Ring Protection Switching October 2009 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: - LP with LP - FS with FS - SF with SF - 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 flow on protection LSPs/tunnels in both directions. Umansky, et al. Expires April 22, 2010 [Page 12] Internet-Draft MPLS-TP Ring Protection Switching October 2009 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 Clause 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. 5.2.4.2. 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: - 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 - an externally initiated command for this node - 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: - for all protection switch requests, except EXER and LP, the node MUST execute the switch - for EXER, and LP, the node MUST signal appropriate request but not execute the switch. Umansky, et al. Expires April 22, 2010 [Page 13] Internet-Draft MPLS-TP Ring Protection Switching October 2009 A node MUST revert from the switching state to the idle state when it detects NR codes received from both directions. - 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. - 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: - a different APS request of higher priority than WTR is received - another failure is detected - 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. Umansky, et al. Expires April 22, 2010 [Page 14] Internet-Draft MPLS-TP Ring Protection Switching October 2009 The transition of a node from pass-through to switching state MUST be triggered by: - an equal, higher priority, or allowed coexisting externally initiated command - the detection of an equal, higher priority, or allowed coexisting failure - 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: - 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 - 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 - 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: - 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. - 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 transmitted. This command has no impact on any other span. If the Umansky, et al. Expires April 22, 2010 [Page 15] Internet-Draft MPLS-TP Ring Protection Switching October 2009 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: - 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. - 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. - 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: - 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: - 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. Umansky, et al. Expires April 22, 2010 [Page 16] Internet-Draft MPLS-TP Ring Protection Switching October 2009 - 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. - 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. Umansky, et al. Expires April 22, 2010 [Page 17] Internet-Draft MPLS-TP Ring Protection Switching October 2009 7. IANA Considerations Channel Types for the Generic Associated Channel are allocated from the IANA PW Associated Channel Type registry defined in [RFC 4446] and updated by [RFC 5586]. IANA is requested to allocate two further Channel Types as follows: - 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 8. References 8.1. Normative References [RFC 2119] Bradner, S., Editor, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC2119, April 2297. 8.2. Informative References [MPLS-TP Reqs] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and S. Ueno, "Requirements for the Trasport Profile of MPLS", ID draft-ietf-mpls-tp-requirements-09, June 2009. [G.841] ITU-T Recommendation G.841 (1998), Types and characteristics of SDH network protection architectures. [MPLS-TP OAM] Busi,I., Niven-Jenkins, B., "MPLS-TP OAM Framework and Overview", draft-ietf-mpls-tp-oam-framework-01 (work in progress), July 2009. [RFC 5586] M. Bocci, M. Vigoureux, S. Bryant," MPLS Generic Associated Channel", RFC 5586, June 2009. Umansky, et al. Expires April 22, 2010 [Page 18] Internet-Draft MPLS-TP Ring Protection Switching October 2009 [RFC 4446] L. Martini, IANA Allocations for Pseudowire Edge to Edge Emulation (PWE3), RFC 4446, April 2006. Authors' Addresses Igor Umansky Alcatel-Lucent Email: igor.umansky@alcatel-lucent.com Huub van Helvoort Huawei Technologies Co., Ltd. Email: hhelvoort@huawei.com Umansky, et al. Expires April 22, 2010 [Page 19]