idnits 2.17.00 (12 Aug 2021) /tmp/idnits2687/draft-pthubert-raw-problem-statement-01.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack a Security Considerations section. ** The document seems to lack an IANA Considerations section. (See Section 2.2 of https://www.ietf.org/id-info/checklist for how to handle the case when there are no actions for IANA.) Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (September 23, 2019) is 971 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Unused Reference: 'CCAMP' is defined on line 309, but no explicit reference was found in the text == Unused Reference: 'PCE' is defined on line 318, but no explicit reference was found in the text == Unused Reference: 'TEAS' is defined on line 321, but no explicit reference was found in the text == Outdated reference: A later version (-04) exists of draft-bernardos-raw-use-cases-00 == Outdated reference: draft-ietf-6tisch-architecture has been published as RFC 9030 == Outdated reference: draft-ietf-detnet-architecture has been published as RFC 8655 == Outdated reference: A later version (-05) exists of draft-thubert-raw-technologies-03 Summary: 2 errors (**), 0 flaws (~~), 8 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 RAW P. Thubert, Ed. 3 Internet-Draft Cisco Systems 4 Intended status: Informational September 23, 2019 5 Expires: March 26, 2020 7 Reliable and Available Wireless Problem Statement 8 draft-pthubert-raw-problem-statement-01 10 Abstract 12 Due to uncontrolled interferences, including the self-induced 13 multipath fading, deterministic networking can only be approached on 14 wireless links. The radio conditions may change -way- faster than a 15 centralized routing can adapt and reprogram, in particular when the 16 controller is distant and connectivity is slow and limited. RAW 17 separates the routing time scale at which a complex path is 18 recomputed from the forwarding time scale at which the forwarding 19 decision is taken for an individual packet. RAW operates at the 20 forwarded time scale. The RAW problem is to decide, within the 21 redundant solutions that are proposed by the routing, which will be 22 used for each individual packet to provide a DetNet service while 23 minimizing the waste of resources. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at https://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on March 26, 2020. 42 Copyright Notice 44 Copyright (c) 2019 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (https://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 2. Use Cases and Requirements Served . . . . . . . . . . . . . . 4 61 3. Routing Scale vs. Forwarding Scale . . . . . . . . . . . . . 4 62 4. Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . 5 63 5. Functional Gaps . . . . . . . . . . . . . . . . . . . . . . . 5 64 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 65 6.1. Normative References . . . . . . . . . . . . . . . . . . 6 66 6.2. Informative References . . . . . . . . . . . . . . . . . 7 67 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 69 1. Introduction 71 Bringing determinism in a packet network means eliminating the 72 statistical effects of multiplexing that result in probabilistic 73 jitter and loss. This can be approached with a tight control of the 74 physical resources to maintain the amount of traffic within a 75 budgetted volume of data per unit of time that fits the physical 76 capabilities of the underlying technology, and the use of time-shared 77 resources (bandwidth and buffers) per circuit, and/or by shaping and/ 78 or scheduling the packets at every hop. 80 Wireless networks operate on a shared medium where uncontrolled 81 interference, including the self-induced multipath fading, adds 82 another dimension to the statistical effects that affect the 83 delivery. Scheduling transmissions can alleviate those effects by 84 leveraging diversity in the spatial, time, code, and frequency 85 domains, and provide a Reliable and Available service while 86 preserving energy and optimizing the use of the shared spectrum. 88 Deterministic Networking is an attempt to mostly eliminate packet 89 loss for a committed bandwidth with a guaranteed worst-case end-to- 90 end latency, even when co-existing with best-effort traffic in a 91 shared network. This innovation is enabled by recent developments in 92 technologies including IEEE 802.1 TSN (for Ethernet LANs) and IETF 93 DetNet (for wired IP networks). It is getting traction in various 94 industries including manufacturing, online gaming, professional A/V, 95 cellular radio and others, making possible many cost and performance 96 optimizations. 98 Reliable and Available Wireless (RAW) networking services extend 99 DetNet to approach end-to-end deterministic performances in a network 100 with scheduled wireless segments, possibly combined with wired 101 segments, and possibly sharing physical resources with non- 102 deterministic traffic. The wireless and wired media are 103 fundamentally different at the physical level, and while the generic 104 Problem Statement for DetNet applies to the wired as well as the 105 wireless medium, the methods to achieve RAW will differ from those 106 used to support time-sensitive networking over wires, as a RAW 107 solution will need to address less consistent transmissions, energy 108 conservation and shared spectrum efficiency. 110 The development of RAW technologies has been lagging behind 111 deterministic efforts for wired systems both at the IEEE and the 112 IETF. But recent efforts at the IEEE and 3GPP indicate that wireless 113 is finally catching up at the lower layer and that it is now possible 114 for the IETF to extend DetNet for wireless segments that are capable 115 of scheduled wireless transmissions. 117 The intent for RAW is to provide DetNet elements that are specialized 118 for short range radios. From this inheritance, RAW stays agnostic to 119 the radio layer underneath though the capability to schedule 120 transmissions is assumed. How the PHY is programmed to do so, and 121 whether the radio is single-hop or meshed, are unknown at the IP 122 layer and not part of the RAW abstraction. 124 Still, in order to focus on real-worlds issues and assert the 125 feasibility of the proposed capabilities, RAW will focus on selected 126 technologies that can be scheduled at the lower layers: IEEE Std. 127 802.15.4 timeslotted channel hopping (TSCH), 3GPP 5G ultra-reliable 128 low latency communications (URLLC), IEEE 802.11ax/be where 802.11be 129 is extreme high throughput (EHT), and L-band Digital Aeronautical 130 Communications System (LDACS). See [I-D.thubert-raw-technologies] 131 for more. 133 The establishment of a path is not in-scope for RAW. It may be the 134 product of a centralized Controller Plane as described for DetNet. 135 As opposed to wired networks, the action of installing a path over a 136 set of wireless links may be very slow relative to the speed at which 137 the radio conditions vary, and it makes sense in the wireless case to 138 provide redundant forwarding solutions along a complex path and to 139 leave it to the RAW Network Plane to select which of those forwarding 140 solutions are to be used for a given packet based on the current 141 conditions. 143 RAW distinguishes the longer time scale at which routes are computed 144 from the the shorter forwarding time scale where per-packet decisions 145 are made. RAW operates at the forwarding time scale on one DetNet 146 flow over one path that is preestablished and installed by means 147 outside of the scope of RAW. The scope of the RAW WG comprises 148 Network plane protocol elements such as OAM and in-band control to 149 improve the RAW operation at the Service and at the forwarding sub- 150 layers, e.g., controlling whether to use packet replication, Hybrid 151 ARQ and coding, with a constraint to limit the use of redundancy when 152 it is really needed, e.g., when a spike of loss is observed. This is 153 discussed in more details in Section 3 and the next sections. 155 2. Use Cases and Requirements Served 157 [RFC8578] presents a number of wireless use cases including Wireless 158 for Industrial Applications. [I-D.bernardos-raw-use-cases] adds a 159 number of use cases that demonstrate the need for RAW capabilities in 160 Pro-Audio, gaming and robotics. 162 3. Routing Scale vs. Forwarding Scale 164 RAW extends DetNet to focus on issues that are mostly a concern on 165 wireless links. See [I-D.ietf-detnet-architecture] for more on 166 DetNet. With DetNet, the end-to-end routing can be centralized and 167 can reside outside the network. In wireless, and in particular in a 168 wireless mesh, the path to the controller that performs the route 169 computation and maintenance may be slow and expensive in terms of 170 critical resources such as air time and energy. 172 Reaching to the routing computation can be slow in regards to the 173 speed of events that affect the forwarding operation at the radio 174 layer. Due to the cost and latency to perform a route computation, 175 routing is not expected to be sensitive/reactive to transient 176 changes. The abstraction of a link at the routing level is expected 177 to use statistical operational metrics that aggregate the behavior of 178 a link over long periods of time, and represent its availability as a 179 shade of gray as opposed to either up or down. 181 In the case of wireless, the changes that affect the forwarding 182 decision can happen frequently and often for shot durations, e.g., a 183 mobile object moves between a transmitter and a receiver, and will 184 cancel the line of sight transmission for a few seconds, or a radar 185 measures the depth of a pool and interferes on a particular channel 186 for a split second. 188 There is thus a desire to separate the long term computation of the 189 route and the short term forwarding decision. In such a model, the 190 routing operation computes a complex Track that enables multiple non- 191 equal cost multipath (N-ECMP) forwarding solutions, and leaves it to 192 the forwarding plane to make the per-packet decision of which of 193 these possibilities should be used. 195 In the case of wires, the concept is known in traffic engineering 196 where an alternate path can be used upon the detection of a failure 197 in the main path, e.g., using OAM in MPLS-TP or BFD over a collection 198 of SD-WAN tunnels. RAW formalizes a routing time scale that is order 199 of magnitude longer than the forwarding time scale, and separates the 200 protocols and metrics that are used at both scales. Routing can 201 operate on long term statistics such as delivery ratio over minutes 202 to hours, but as a first approximation can ignore flapping. On the 203 other hand, the RAW forwarding decision is made at packet speed, and 204 uses information that must be pertinent at the present time for the 205 current transmission. 207 4. Prerequisites 209 A prerequisite to the RAW work is that an end-to-end routing function 210 computes a complex sub-topology along which forwarding can happen 211 between a source and one or more destinations. For 6TiSCH, this is a 212 Track. The concept of Track is specified in the 213 [I-D.ietf-6tisch-architecture]. Tracks provide a high degree of 214 redundancy and diversity and enable DetNet PREOF, end-to-end network 215 coding, and possibly radio-specific abstracted techniques such as 216 ARQ, overhearing, frequency diversity, time slotting, and possibly 217 others. 219 How the routing operation computes the Track is out of scope for RAW. 220 The scope of the RAW operation is one Track, and the goal of the RAW 221 operation is to optimize the use of the Track at the forwarding 222 timescale to maintain the expected service while optimizing the usage 223 of constrained resources such as energy and spectrum. 225 Another prerequisite is that an IP link can be established over the 226 radio with some guarantees in terms of service reliability, e.g., it 227 can be relied upon to transmit a packet within a bounded latency and 228 provides a guaranteed BER/PDR outside rare but existing transient 229 outage windows that can last from split seconds to minutes. The 230 radio layer can be programmed with abstract parameters, and can 231 return an abstract view of the state of the Link to help forwarding 232 decision (think DLEP from MANET). In the layered approach, how the 233 radio manages its PHY layer is out of control and out of scope. 234 Whether it is single hop or meshed is also unknown and out of scope. 236 5. Functional Gaps 238 Within a large routed topology, the routing operation builds a 239 particular complex Track with one source and one or more 240 destinations; within the Track, packets may follows different paths 241 and may be subject to RAW forwarding operations that include 242 replication, elimination, retries, overhearing and reordering. 244 The RAW forwarding decisions include the selection of points of 245 replication and elimination, how many retries can take place, and a 246 limit of validity for the packet beyond which the packet should be 247 destroyed rather than forwarded uselessly further down the Track. 249 The decision to apply the RAW techniques must be done quickly, and 250 depends on a very recent and precise knowledge of the forwarding 251 conditions withing the complex Track. There is a need for an 252 observation method to provide the RAW forwarding plane with the 253 specific knowledge of the state of the Track for the type of flow of 254 interest (e.g., for a QoS level of interest). To observe the whole 255 Track in quasi real time, RAW will consider existing tools such as 256 L2-triggers, DLEP, BFD and in-band and out-of-band OAM. 258 One possible way of making the RAW forwarding decisions is to make 259 them all at the ingress and express them in-band in the packet, which 260 requires new loose or strict Hop-by-hop signaling. To control the 261 RAW forwarding operation along a Track for the individual packets, 262 RAW may leverage and extend known techniques such as Segment Routing 263 (SRv6) or BIER-TE such as done with 264 [I-D.thubert-bier-replication-elimination]. 266 An alternate way is to enable each forwarding node to make the RAW 267 forwarding decisions for a packet on its own, based on its knowledge 268 of the expectation (timeliness and reliability) for that packet and a 269 recent observation of the rest of the way across the possible paths 270 within the Track. Information about the service should be placed in 271 the packet and matched with the forwarding node's capabilities and 272 policies. 274 In either case, a per-flow state is installed in all intermediate 275 nodes to recognize the flow and determine the forwarding policy to be 276 applied. 278 6. References 280 6.1. Normative References 282 [I-D.bernardos-raw-use-cases] 283 Papadopoulos, G., Thubert, P., Theoleyre, F., and C. 284 Bernardos, "RAW use cases", draft-bernardos-raw-use- 285 cases-00 (work in progress), July 2019. 287 [I-D.ietf-6tisch-architecture] 288 Thubert, P., "An Architecture for IPv6 over the TSCH mode 289 of IEEE 802.15.4", draft-ietf-6tisch-architecture-26 (work 290 in progress), August 2019. 292 [I-D.ietf-detnet-architecture] 293 Finn, N., Thubert, P., Varga, B., and J. Farkas, 294 "Deterministic Networking Architecture", draft-ietf- 295 detnet-architecture-13 (work in progress), May 2019. 297 [I-D.thubert-raw-technologies] 298 Thubert, P., Cavalcanti, D., Vilajosana, X., and C. 299 Schmitt, "Reliable and Available Wireless Technologies", 300 draft-thubert-raw-technologies-03 (work in progress), July 301 2019. 303 [RFC8578] Grossman, E., Ed., "Deterministic Networking Use Cases", 304 RFC 8578, DOI 10.17487/RFC8578, May 2019, 305 . 307 6.2. Informative References 309 [CCAMP] IETF, "Common Control and Measurement Plane", 310 . 312 [I-D.thubert-bier-replication-elimination] 313 Thubert, P., Eckert, T., Brodard, Z., and H. Jiang, "BIER- 314 TE extensions for Packet Replication and Elimination 315 Function (PREF) and OAM", draft-thubert-bier-replication- 316 elimination-03 (work in progress), March 2018. 318 [PCE] IETF, "Path Computation Element", 319 . 321 [TEAS] IETF, "Traffic Engineering Architecture and Signaling", 322 . 324 Author's Address 326 Pascal Thubert (editor) 327 Cisco Systems, Inc 328 Building D 329 45 Allee des Ormes - BP1200 330 MOUGINS - Sophia Antipolis 06254 331 FRANCE 333 Phone: +33 497 23 26 34 334 Email: pthubert@cisco.com