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Cui 3 Internet-Draft R. Winter 4 Intended status: Informational NEC 5 Expires: July 9, 2016 H. Shah 6 Ciena 7 S. Aldrin 8 Huawei Technologies 9 M. Daikoku 10 KDDI 11 January 6, 2016 13 Use Cases and Requirements for MPLS-TP multi-failure protection 14 draft-cui-mpls-tp-mfp-use-case-and-requirements-06 16 Abstract 18 For the Multiprotocol Label Switching Transport Profile (MPLS-TP) 19 linear protection capable of 1+1 and 1:1 protection has already been 20 defined. That linear protection mechanism has not been designed for 21 handling multiple, simultaneously occuring failures, i.e. multiple 22 failures that affect the working and the protection entity during the 23 same time period. In these situations currently defined protection 24 mechanisms would fail. 26 This document introduces use cases and requirements for mechanisms 27 that are capable of protecting against such failures. It does not 28 specify a multi-failure protection mechanism itself. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on July 9, 2016. 47 Copyright Notice 49 Copyright (c) 2016 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (http://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 65 1.1. Document scope . . . . . . . . . . . . . . . . . . . . . 3 66 1.2. Requirements notation . . . . . . . . . . . . . . . . . . 3 67 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 68 2. General m:n protection scenario . . . . . . . . . . . . . . . 4 69 3. Use cases . . . . . . . . . . . . . . . . . . . . . . . . . . 5 70 3.1. m:1 (m > 1) protection . . . . . . . . . . . . . . . . . 5 71 3.1.1. Pre-configuration . . . . . . . . . . . . . . . . . . 5 72 3.1.2. On-demand configuration . . . . . . . . . . . . . . . 6 73 3.2. m:n (m, n > 1, n >= m > 1) protection . . . . . . . . . . 6 74 4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 6 75 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 76 6. Normative References . . . . . . . . . . . . . . . . . . . . 7 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 79 1. Introduction 81 Today's packet optical transport networks concentrate large volumes 82 of traffic onto a relatively small number of nodes and links. As a 83 result, the failure of a single network element can potentially 84 interrupt a large amount of traffic. For this reason, ensuring 85 survivability through careful network design and appropriate 86 technical means is important. 88 In MPLS-TP networks, a basic survivability technique is available as 89 specified in [RFC6378], [RFC7271] and [RFC7324]. That protocol 90 however is limited to 1+1 and 1:1 protection and not designed to 91 handle multiple failures that affect both the working and protection 92 entity at the same time. 94 There are various scenarios where multi-failure protection is an 95 important requirement for network survivability. E.g for disaster 96 recovery, after catastrophic events such as earthquakes or tsunamis. 97 During the period after such events, network availability is crucial, 98 in particular for high-priority services such as emergency telephone 99 calls. Existing 1+1 or 1:n protection however is limited to cover 100 single failures which has proven as not sufficient during past 101 events. 103 Beyond the natural disaster use case above, multi-failure protection 104 is also beneficial in situations where the network is particularly 105 vulnerable, e.g., when a working entity or protection entity was 106 closed for maintenance or construction work. During this time, the 107 network service becomes vulnerable to single failures since one 108 entity is already down. If a failure occurs during this time, an 109 operator might not be able to meet service level agreements (SLA). 110 Thus, a technical means for multi-failure protection could take 111 pressure off network operations. 113 1.1. Document scope 115 This document describes use cases and requirements for m:1 and m:n 116 protection in MPLS-TP networks without the use of control plane 117 protocols. Existing solutions based on a control plane such as GMPLS 118 may be able to restore user traffic when multiple failures occur. 119 Some networks however do not use full control plane operation for 120 reasons such as service provider preferences, certain limitations or 121 the requirement for fast service restoration (faster than achievable 122 with control plane mechanisms). These networks are the focus of this 123 document which defines a set of requirements for m:1 and m:n 124 protection not based on control plane support. This document imposes 125 no formal time constraints on detection times. 127 1.2. Requirements notation 129 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 130 "SHOULD","SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 131 document are to be interpreted as described in [RFC2119]. 133 1.3. Terminology 135 The terminology used in this document is based on the terminology 136 defined in the MPLS-TP Survivability Framework document [RFC6372], 137 which in turn is based on [RFC4427]. 139 In particular, the following protection schemes are defined in 140 [RFC4427] and used as terms in this document: 142 o 1+1 protection 144 o 1:n (n >= 1) protection 146 o m:n (m, n > 1, n >= m > 1) protection 148 o Further, the following additional terminology is from [RFC4427] is 149 used: 151 o "broadcast bridge" 153 o "selector bridge" 155 o "working entity" 157 o "protection entity" 159 This document defines a new protection type: 161 o m:1 (m > 1) protection: A set of m protection entities protecting 162 a single working entity 164 2. General m:n protection scenario 166 The general underlying assumption of this work is that an m:n 167 relationship between protection entity and working entity exists, 168 i.e. there is no artificial limitation on the ratio between 169 protection and working entities. 171 This general scenario is illustrated in Figure 1 which shows a 172 protection domain with n working entities and m protection entities 173 between Node A and Node Z. 175 At Node A, traffic is transported over its respective working entity 176 and may be simultaneously transported over one of its protection 177 entities (in case of a broadcast bridge), or it is transported over 178 its working entity and only in case of failure over one of the 179 protection entities (in case of a selector bridge). At Node Z, the 180 traffic is selected from either its working entity or one of the 181 protection entities. Note that any of the n working entities and m 182 protection entities should follow a disjoint path through the network 183 from Node A to Node Z. 185 +------+ +------+ 186 |Node A| working entity #1 |Node Z| 187 | |=============================| | 188 | | .... | | 189 | | working entity #n | | 190 | |=============================| | 191 | | | | 192 | | | | 193 | | protection entity #1 | | 194 | |*****************************| | 195 | | .... | | 196 | | protection entity #m | | 197 | |*****************************| | 198 +------+ +------+ 199 |--------Protection Domain--------| 201 Figure 1: m:n protection domain 203 3. Use cases 205 3.1. m:1 (m > 1) protection 207 With MPLS-TP linear protection such as 1+1/1:1 protection, when a 208 single failure is detected on the working entity, the service can be 209 restored using the protection entity. However, during the time the 210 protection is active the traffic is unprotected until the working 211 entity is restored. 213 m:1 protection can increase service availability and reduce 214 operational pressure since multiple protection entities are 215 available. For any m > 1, m - 1 protection entities may fail and the 216 service still would have a protection entity available. 218 There are different ways to provision these alternative protection 219 entities which are outlined in the following sub-sections. 221 3.1.1. Pre-configuration 223 The relationship between the working entity and the protection 224 entities is part of the system configuration and needs to be 225 configured before the working entity is being used. The same applies 226 to additional protection entities. 228 Unprotected traffic can be transported over the m protection entities 229 as long as these entities do not carry protected traffic. 231 3.1.2. On-demand configuration 233 The protection relationship between a working entity and a protection 234 entity is configured while the system is in operation. 236 Additional protection entities are configured by either a control 237 plane protocol or static configuration using a management system 238 directly after failure detection and/or notification of either the 239 working entity or the protection entities. In case a management 240 system is used, there is no need for a standardized solution. 242 3.2. m:n (m, n > 1, n >= m > 1) protection 244 In order to reduce the cost of protection entities, in the m:n 245 scenario, m dedicated protection transport entities are sharing 246 protection resources for n working transport entities. 248 The bandwidth of each protection entity should be allocated in such a 249 way that it may be possible to protect any of the n working entities 250 in case at least one of the m protection entities is available. When 251 a working entity is determined to be impaired, its traffic first must 252 be assigned to an available protection transport entity followed by a 253 transition from the working to the assigned protection entity at both 254 Node A and Node Z of the protected domain. It is noted that when 255 more than m working entities are impaired, only m working entities 256 can be protected. 258 4. Requirements 260 A number of recovery requirements are defined in [RFC5654]. These 261 requirements however are limited to cover single failure case and not 262 multiple, simultaneously occuring failures. This section extends the 263 list of requirements to support multiple failures scenarios. 265 R1. MPLS-TP SHOULD support m:1 (m > 1) protection. 267 1. An m:1 protection mechanism MUST protect against multiple 268 failures that are detected on both the working entity and one or 269 more protection entities. 271 2. Pre-configuration of protection entities SHOULD be supported. 273 3. On-demand protection entity configuration MAY be supported. 275 4. On-demand protection resource activation MAY be supported. 277 5. A priority scheme MUST be provided, since a protection entity has 278 to be chosen out of two or more protection entities. 280 R2. MPLS-TP SHOULD support m:n (m, n > 1, n >= m > 1) protection. 282 1. An m:n protection mechanism MUST protect against multiple 283 failures that are simultaneously detected on both a working 284 entity and a protection entity or multiple working entities. 286 2. A priority scheme MUST be provided, since protection resources 287 are shared by multiple working entities dynamically. 289 If a solution is designed based on an existing mechanism such as PSC, 290 then this solution MUST be backward compatible and not break such 291 mechanisms. 293 5. Security Considerations 295 General security considerations for MPLS-TP are covered in [RFC5921]. 296 The security considerations for the generic associated control 297 channel are described in [RFC5586]. The requirements described in 298 this document are extensions to the requirements presented in 299 [RFC5654] and does not introduce any new security risks. 301 6. Normative References 303 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 304 Requirement Levels", BCP 14, RFC 2119, March 1997. 306 [RFC4427] Mannie, E. and D. Papadimitriou, "Recovery (Protection and 307 Restoration) Terminology for Generalized Multi-Protocol 308 Label Switching (GMPLS)", RFC 4427, March 2006. 310 [RFC5586] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic 311 Associated Channel", RFC 5586, June 2009. 313 [RFC5654] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., 314 and S. Ueno, "Requirements of an MPLS Transport Profile", 315 RFC 5654, September 2009. 317 [RFC5921] Bocci, M., Bryant, S., Frost, D., Levrau, L., and L. 318 Berger, "A Framework for MPLS in Transport Networks", RFC 319 5921, July 2010. 321 [RFC6372] Sprecher, N. and A. Farrel, "MPLS Transport Profile (MPLS- 322 TP) Survivability Framework", RFC 6372, September 2011. 324 [RFC6378] Weingarten, Y., Bryant, S., Osborne, E., Sprecher, N., and 325 A. Fulignoli, "MPLS Transport Profile (MPLS-TP) Linear 326 Protection", RFC 6378, October 2011. 328 [RFC7271] Ryoo, J., Gray, E., van Helvoort, H., D'Alessandro, A., 329 Cheung, T., and E. Osborne, "MPLS Transport Profile (MPLS- 330 TP) Linear Protection to Match the Operational 331 Expectations of Synchronous Digital Hierarchy, Optical 332 Transport Network, and Ethernet Transport Network 333 Operators", RFC 7271, June 2014. 335 [RFC7324] Osborne, E., "Updates to MPLS Transport Profile Linear 336 Protection", RFC 7324, July 2014. 338 Authors' Addresses 340 Zhenlong Cui 341 NEC 343 Email: c-sai@bx.jp.nec.com 345 Rolf Winter 346 NEC 348 Email: Rolf.Winter@neclab.eu 350 Himanshu Shah 351 Ciena 353 Email: hshah@ciena.com 355 Sam Aldrin 356 Huawei Technologies 358 Email: aldrin.ietf@gmail.com 360 Masahiro Daikoku 361 KDDI 363 Email: ms-daikoku@kddi.com