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Checking references for intended status: Informational ---------------------------------------------------------------------------- No issues found here. Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group L. Geng 3 Internet-Draft China Mobile 4 Intended status: Informational L. Qiang 5 Expires: September 9, 2019 Huawei Technologies 6 T. Eckert 7 Huawei 8 March 8, 2019 10 Technical Requirements of Bounded Latency Forwarding 11 draft-geng-detnet-requirements-bounded-latency-01 13 Abstract 15 This document analyses the technical requirements that Layer 3 16 bounded latency forwarding scheme should satisfy. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at https://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on September 9, 2019. 35 Copyright Notice 37 Copyright (c) 2019 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (https://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 53 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 54 1.2. Terminology & Abbreviations . . . . . . . . . . . . . . . 3 55 2. Tolerance of Time Deviation . . . . . . . . . . . . . . . . . 3 56 3. Long Link Propagation Delay . . . . . . . . . . . . . . . . . 3 57 4. Massive Dynamic Flows . . . . . . . . . . . . . . . . . . . . 4 58 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 59 6. Security Considerations . . . . . . . . . . . . . . . . . . . 4 60 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 61 8. Normative References . . . . . . . . . . . . . . . . . . . . 5 62 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 64 1. Introduction 66 DetNet is chartered to provide deterministic forwarding over Layer 3. 67 Deterministic forwarding means packet forwarding with bounded 68 latency, loss and delay variation 69 [draft-ietf-detnet-problem-statement]. In current DetNet's 70 discussion, low packet loss is mainly achieved through PREOF (Packet 71 Replication, Elimination, and Ordering 72 Functions)[draft-ietf-detnet-architecture]. This document focuses on 73 bounded latency. 75 Common IP/MPLS forwarding has long tail effect that couldn't 76 guarantee bounded latency. DetNet has to have an approach to 77 identify DetNet flows, and divert them into a DetNet forwarding plane 78 in which some schemes are adapted to guarantee bounded latency. 79 There are several schemes are proposed for bounded latency forwarding 80 such as dedicated tunnel, light load with per-flow per-hop shaping, 81 Time Aware Shaping[IEEE802.1Qbv], Cyclic Queuing and 82 Forwarding[IEEE802.1Qch], Scalable Deterministic 83 Forwarding[draft-qiang-detnet-large-scale-detnet], and SR based 84 bounded latency[draft-chen-detnet-sr-based-bounded-latency]. This 85 document is not going to compare and analyze these schemes, but to 86 propose some factors (Layer 3 specific) worth to be considered when 87 selecting Layer 3 bounded latency forwarding scheme. 89 1.1. Requirements Language 91 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 92 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 93 "OPTIONAL" in this document are to be interpreted as described in BCP 94 14 [RFC2119][RFC8174] when, and only when, they appear in all 95 capitals, as shown here. 97 1.2. Terminology & Abbreviations 99 This document uses the terminology defined in 100 [draft-ietf-detnet-architecture]. 102 TSN: Time Sensitive Network 104 2. Tolerance of Time Deviation 106 One of DetNet's objectives is to stitch TSN domains together as shown 107 in Figure 1. We know that devices inside a TSN domain are time- 108 synchronized, and most of TSN forwarding schemes rely on precise time 109 synchronization. However two TSN domains have a high probability of 110 being asynchronous, while DetNet needs to connect them together and 111 provide end-to-end deterministic forwarding. Therefore, it is worthy 112 of have a DetNet forwarding plane which can keep the bounded latency 113 even under an unsynchronized situation. Otherwise, buffer is needed 114 to absorb the time deviation, and end-users have to bear the latency 115 and cost increase introduced by buffer. 117 Moreover, there are 119 +--------------+ +--------------+ 120 | | DetNet Forwarding | | 121 | TSN Domain I +-----------------------------+ TSN Domain II| 122 | | | | 123 +--------------+ +--------------+ 125 Figure 1: DetNet Scenario 127 3. Long Link Propagation Delay 129 In contrast to Layer 2 TSN that deployed in LAN, Layer 3 DetNet is 130 expected to be deployed in larger scale network that has longer link 131 propagation delay. Long link propagation delay can cause some 132 troubles to simple cyclic forwarding schemes, like[IEEE802.1Qch]. 133 IEEE 802.1 Qch works on the basis of time synchronization, and one 134 hop forwarding (include packet sending, packet transmission on link, 135 and packet receiving three operations) is required to be finished 136 within one cycle as shown in Figure 2. Long links whose latency 137 exceed the cycle time will make IEEE 802.1 Qch doesn't work. One 138 possible solution is to set cycle time to be a bigger value, in order 139 to absorb long link propagation delay. However, this solution will 140 lead to larger jitter. The reason is that cyclic forwarding schemes 141 only try to ensure the packet arrives at a node within a certain 142 cycle, and packet's arrival time may vary within that cycle. 144 /--\ " " 145 | | " Send " 146 \--/ " * " 147 Upstream Node " \ " 148 " \ " 149 " Short " 150 " Link\ " 151 " \ " 152 /--\ " v " 153 | | " * " 154 \--/ " Receive" 155 Downstream Node " " 156 " " 157 | | | 158 Time Line ----+-----------+-----------+----> 159 0 1 2 161 Figure 2: One Hop Forwarding in Qch 163 [Jitter on link is TBD] 165 4. Massive Dynamic Flows 167 Considering the features of TSN applications we can speculate that 168 the number of TSN flows will not dramatically change with time. 169 While DetNet targets at larger-scale deployment. There are more 170 time-sensitive applications such as VR communication, they may 171 require establishment or tear-down of the DetNet connections 172 frequently. Meanwhile, layer 3 device may serve millions of traffic 173 flows simultaneously. Hence those schemes that need complex 174 calculations may not be applicable in DetNet. More importantly, 175 forwarding schemes need to avoid impact on those in-transit flows 176 when new flows are added (or old flows are removed). 178 5. IANA Considerations 180 This document makes no request of IANA. 182 6. Security Considerations 184 This document will not introduce new security problems. 186 7. Acknowledgements 188 The Authors would like to thank David Black for his review, 189 suggestion and comments to this document. 191 8. Normative References 193 [draft-chen-detnet-sr-based-bounded-latency] 194 "SR based Bounded Latency", 195 . 198 [draft-ietf-detnet-architecture] 199 "DetNet Architecture", . 202 [draft-ietf-detnet-problem-statement] 203 "DetNet Problem Statement", 204 . 207 [draft-qiang-detnet-large-scale-detnet] 208 "Large-Scale Deterministic Network", 209 . 212 [IEEE802.1Qbv] 213 "Enhancements for Scheduled Traffic", 2016. 215 [IEEE802.1Qch] 216 "Cyclic Queuing and Forwarding", 2016. 218 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 219 Requirement Levels", BCP 14, RFC 2119, 220 DOI 10.17487/RFC2119, March 1997, 221 . 223 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 224 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 225 May 2017, . 227 Authors' Addresses 229 Liang Geng 230 China Mobile 231 Beijing 232 China 234 Email: gengliang@chinamobile.com 235 Li Qiang 236 Huawei Technologies 237 Huawei Campus, No. 156 Beiqing Rd. 238 Beijing 100095 239 China 241 Email: qiangli3@huawei.com 243 Toerless Eckert 244 Huawei USA - Futurewei Technologies Inc. 245 2330 Central Expy 246 Santa Clara 95050 247 USA 249 Email: tte+ietf@cs.fau.de