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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-26) exists of draft-ietf-taps-interface-06 == Outdated reference: A later version (-18) exists of draft-ietf-taps-impl-06 -- Obsolete informational reference (is this intentional?): RFC 793 (Obsoleted by RFC 9293) -- Obsolete informational reference (is this intentional?): RFC 7230 (Obsoleted by RFC 9110, RFC 9112) -- Obsolete informational reference (is this intentional?): RFC 7540 (Obsoleted by RFC 9113) Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 TAPS Working Group T. Pauly, Ed. 3 Internet-Draft Apple Inc. 4 Intended status: Standards Track B. Trammell, Ed. 5 Expires: 14 January 2021 Google Switzerland GmbH 6 A. Brunstrom 7 Karlstad University 8 G. Fairhurst 9 University of Aberdeen 10 C. Perkins 11 University of Glasgow 12 P. Tiesel 13 TU Berlin 14 C.A. Wood 15 Cloudflare 16 13 July 2020 18 An Architecture for Transport Services 19 draft-ietf-taps-arch-08 21 Abstract 23 This document describes an architecture for exposing transport 24 protocol features to applications for network communication, the 25 Transport Services architecture. The Transport Services Application 26 Programming Interface (API) is based on an asynchronous, event-driven 27 interaction pattern. It uses messages for representing data transfer 28 to applications, and it describes how implementations can use 29 multiple IP addresses, multiple protocols, and multiple paths, and 30 provide multiple application streams. This document further defines 31 common terminology and concepts to be used in definitions of 32 Transport Services APIs and implementations. 34 Status of This Memo 36 This Internet-Draft is submitted in full conformance with the 37 provisions of BCP 78 and BCP 79. 39 Internet-Drafts are working documents of the Internet Engineering 40 Task Force (IETF). Note that other groups may also distribute 41 working documents as Internet-Drafts. The list of current Internet- 42 Drafts is at https://datatracker.ietf.org/drafts/current/. 44 Internet-Drafts are draft documents valid for a maximum of six months 45 and may be updated, replaced, or obsoleted by other documents at any 46 time. It is inappropriate to use Internet-Drafts as reference 47 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on 14 January 2021. 50 Copyright Notice 52 Copyright (c) 2020 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 57 license-info) in effect on the date of publication of this document. 58 Please review these documents carefully, as they describe your rights 59 and restrictions with respect to this document. Code Components 60 extracted from this document must include Simplified BSD License text 61 as described in Section 4.e of the Trust Legal Provisions and are 62 provided without warranty as described in the Simplified BSD License. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 67 1.1. Background . . . . . . . . . . . . . . . . . . . . . . . 4 68 1.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4 69 1.3. Specification of Requirements . . . . . . . . . . . . . . 5 70 2. API Model . . . . . . . . . . . . . . . . . . . . . . . . . . 5 71 2.1. Event-Driven API . . . . . . . . . . . . . . . . . . . . 7 72 2.2. Data Transfer Using Messages . . . . . . . . . . . . . . 7 73 2.3. Flexibile Implementation . . . . . . . . . . . . . . . . 8 74 3. API and Implementation Requirements . . . . . . . . . . . . . 9 75 3.1. Provide Common APIs for Common Features . . . . . . . . . 9 76 3.2. Allow Access to Specialized Features . . . . . . . . . . 10 77 3.3. Select Equivalent Protocol Stacks . . . . . . . . . . . . 11 78 3.4. Maintain Interoperability . . . . . . . . . . . . . . . . 12 79 4. Transport Services Architecture and Concepts . . . . . . . . 12 80 4.1. Transport Services API Concepts . . . . . . . . . . . . . 13 81 4.1.1. Connections and Related Objects . . . . . . . . . . . 15 82 4.1.2. Pre-Establishment . . . . . . . . . . . . . . . . . . 16 83 4.1.3. Establishment Actions . . . . . . . . . . . . . . . . 17 84 4.1.4. Data Transfer Objects and Actions . . . . . . . . . . 18 85 4.1.5. Event Handling . . . . . . . . . . . . . . . . . . . 19 86 4.1.6. Termination Actions . . . . . . . . . . . . . . . . . 20 87 4.1.7. Connection Groups . . . . . . . . . . . . . . . . . . 20 88 4.2. Transport Services Implementation Concepts . . . . . . . 20 89 4.2.1. Candidate Gathering . . . . . . . . . . . . . . . . . 21 90 4.2.2. Candidate Racing . . . . . . . . . . . . . . . . . . 22 91 4.2.3. Separating Connection Groups . . . . . . . . . . . . 22 92 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 93 6. Security Considerations . . . . . . . . . . . . . . . . . . . 23 94 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24 95 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 96 8.1. Normative References . . . . . . . . . . . . . . . . . . 24 97 8.2. Informative References . . . . . . . . . . . . . . . . . 25 98 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 100 1. Introduction 102 Many application programming interfaces (APIs) to perform transport 103 networking have been deployed, perhaps the most widely known and 104 imitated being the BSD Socket [POSIX] interface (Socket API). The 105 naming of objects and functions across these APIs is not consistent, 106 and varies depending on the protocol being used. For example, 107 sending and receiving streams of data is conceptually the same for 108 both an unencrypted Transmission Control Protocol (TCP) stream and 109 operating on an encrypted Transport Layer Security (TLS) [RFC8446] 110 stream over TCP, but applications cannot use the same socket "send()" 111 and "recv()" calls on top of both kinds of connections. Similarly, 112 terminology for the implementation of transport protocols varies 113 based on the context of the protocols themselves: terms such as 114 "flow", "stream", "message", and "connection" can take on many 115 different meanings. This variety can lead to confusion when trying 116 to understand the similarities and differences between protocols, and 117 how applications can use them effectively. 119 The goal of the Transport Services architecture is to provide a 120 common, flexible, and reusable interface for transport protocols. As 121 applications adopt this interface, they will benefit from a wide set 122 of transport features that can evolve over time, and ensure that the 123 system providing the interface can optimize its behavior based on the 124 application requirements and network conditions, without requiring 125 changes to the applications. This flexibility enables faster 126 deployment of new features and protocols. It can also support 127 applications by offering racing and fallback mechanisms, which 128 otherwise need to be implemented in each application separately. 130 This document was developed in parallel with the specification of the 131 Transport Services API [I-D.ietf-taps-interface] and Implementation 132 Guidelines [I-D.ietf-taps-impl]. Although following the Transport 133 Services Architecture does not require that all APIs and 134 implementations are identical, a common minimal set of features 135 represented in a consistent fashion will enable applications to be 136 easily ported from one system to another. 138 1.1. Background 140 The Transport Services architecture is based on the survey of 141 services provided by IETF transport protocols and congestion control 142 mechanisms [RFC8095], and the distilled minimal set of the features 143 offered by transport protocols [I-D.ietf-taps-minset]. These 144 documents identified common features and patterns across all 145 transport protocols developed thus far in the IETF. 147 Since transport security is an increasingly relevant aspect of using 148 transport protocols on the Internet, this architecture also considers 149 the impact of transport security protocols on the feature-set exposed 150 by Transport Services [I-D.ietf-taps-transport-security]. 152 One of the key insights to come from identifying the minimal set of 153 features provided by transport protocols [I-D.ietf-taps-minset] was 154 that features either require application interaction and guidance 155 (referred to in that document as Functional or Optimizing Features), 156 or else can be handled automatically by a system implementing 157 Transport Services (referred to as Automatable Features). Among the 158 Functional and Optimizing Features, some were common across all or 159 nearly all transport protocols, while others could be seen as 160 features that, if specified, would only be useful with a subset of 161 protocols, but would not harm the functionality of other protocols. 162 For example, some protocols can deliver messages faster for 163 applications that do not require messages to arrive in the order in 164 which they were sent. However, this functionality needs to be 165 explicitly allowed by the application, since reordering messages 166 would be undesirable in many cases. 168 1.2. Overview 170 This document describes the Transport Services architecture in three 171 sections: 173 * Section 2 describes how the API model of Transport Services 174 differs from traditional socket-based APIs. Specifically, it 175 offers asynchronous event-driven interaction, the use of messages 176 for data transfer, and the flexibility to use different transport 177 protocols and paths without requiring major changes to the 178 application. 180 * Section 3 explains the fundamental requirements for a Transport 181 Services API. These principles are intended to make sure that 182 transport protocols can continue to be enhanced and evolve without 183 requiring significant changes by application developers. 185 * Section 4 presents the Transport Services architecture diagram and 186 defines the concepts that are used by both the API and 187 implementation documents. The Preconnection allows applications 188 to configure Connection Properties, and the Connection represents 189 an object that can be used to send and receive Messages. 191 1.3. Specification of Requirements 193 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 194 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 195 "OPTIONAL" in this document are to be interpreted as described in BCP 196 14 [RFC2119] [RFC8174] when, and only when, they appear in all 197 capitals, as shown here. 199 2. API Model 201 The traditional model of using sockets for networking can be 202 represented as follows: 204 * Applications create connections and transfer data using the Socket 205 API. 207 * The Socket API provides the interface to the implementations of 208 TCP and UDP (typically implemented in the system's kernel). 210 * TCP and UDP in the kernel send and receive data over the available 211 network-layer interfaces. 213 * Sockets are bound directly to transport-layer and network-layer 214 addresses, obtained via a separate resolution step, usually 215 performed by a system-provided stub resolver. 217 +-----------------------------------------------------+ 218 | Application | 219 +-----------------------------------------------------+ 220 | | | 221 +------------+ +------------+ +--------------+ 222 | stub | | Stream API | | Datagram API | 223 | resolver | +------------+ +--------------+ 224 +------------+ | | 225 +---------------------------------+ 226 | TCP UDP | 227 | Kernel Networking Stack | 228 +---------------------------------+ 229 | 230 +-----------------------------------------------------+ 231 | Network Layer Interface | 232 +-----------------------------------------------------+ 233 Figure 1: Socket API Model 235 The Transport Services architecture evolves this general model of 236 interaction, aiming to both modernize the API surface presented to 237 applications by the transport layer and enrich the capabilities of 238 the Transport Services implementation. It combines interfaces for 239 multiple interaction patterns into a unified whole. By combining 240 name resolution with connection establishment and data transfer in a 241 single API, it allows for more flexible implementations to provide 242 path and transport protocol agility on the application's behalf. 244 +-----------------------------------------------------+ 245 | Application | 246 +-----------------------------------------------------+ 247 | 248 +-----------------------------------------------------+ 249 | Transport Services API | 250 +-----------------------------------------------------+ 251 | 252 +-----------------------------------------------------+ 253 | Transport Services Implementation | 254 | (Using: DNS, UDP, TCP, SCTP, DCCP, TLS, QUIC, etc) | 255 +-----------------------------------------------------+ 256 | 257 +-----------------------------------------------------+ 258 | Network Layer Interface | 259 +-----------------------------------------------------+ 261 Figure 2: Transport Services API Model 263 The Transport Services API [I-D.ietf-taps-interface] defines the 264 mechanism for an application to create network connections and 265 transfer data. The implementation [I-D.ietf-taps-impl] is 266 responsible for mapping the API to the various available transport 267 protocols and managing the available network interfaces and paths. 269 There are key differences between the architecture of the Transport 270 Services system and the architecture of the Socket API: the Transport 271 Services API is asynchronous and event-driven; it uses messages for 272 representing data transfer to applications; and it describes how 273 implementations can use multiple IP addresses, multiple protocols, 274 multiple paths, and provide multiple application streams. 276 2.1. Event-Driven API 278 Originally, sockets presented a blocking interface for establishing 279 connections and transferring data. However, most modern applications 280 interact with the network asynchronously. Emulation of an 281 asynchronous interface using sockets generally uses a try-and-fail 282 model. If the application wants to read, but data has not yet been 283 received from the peer, the call to read will fail. The application 284 then waits and can try again later. 286 In contrast to sockets, all interaction with a Transport Services 287 system is expected to be asynchronous, and use an event-driven model 288 (see Section 4.1.5). For example, if the application wants to read, 289 its call to read will not complete immediately, but will deliver an 290 event containing the received data once it is available. Error 291 handling is also asynchronous; a failure to send results in an 292 asynchronous send error as an event. 294 The Transport Services API also delivers events regarding the 295 lifetime of a connection and changes in the available network links, 296 which were not previously made explicit in sockets. 298 Using asynchronous events allows for a more natural interaction model 299 when establishing connections and transferring data. Events in time 300 more closely reflect the nature of interactions over networks, as 301 opposed to how sockets represent network resources as file system 302 objects that may be temporarily unavailable. 304 Separate from events, callbacks are also provided for asynchronous 305 interactions with the API not directly related to events on the 306 network or network interfaces. 308 2.2. Data Transfer Using Messages 310 Sockets provide a message interface for datagram protocols like UDP, 311 but provide an unstructured stream abstraction for TCP. While TCP 312 does indeed provide the ability to send and receive data as streams, 313 most applications need to interpret structure within these streams. 314 For example, HTTP/1.1 uses character delimiters to segment messages 315 over a stream [RFC7230]; TLS record headers carry a version, content 316 type, and length [RFC8446]; and HTTP/2 uses frames to segment its 317 headers and bodies [RFC7540]. 319 The Transport Services API represents data as messages, so that it 320 more closely matches the way applications use the network. Providing 321 a message-based abstraction provides many benefits, such as: 323 * the ability to associate deadlines with messages, for applications 324 that care about timing; 326 * the ability to provide control of reliability, choosing which 327 messages to retransmit when there is packet loss, and how best to 328 make use of the data that arrived; 330 * the ability to manage dependencies between messages, when the 331 Transport Services system could decide to not deliver a message, 332 either following packet loss or because it has missed a deadline. 333 In particular, this can avoid (re-)sending data that relies on a 334 previous transmission that was never received. 336 * the ability to automatically assign messages and connections to 337 underlying transport connections to utilize multi-streaming and 338 pooled connections. 340 Allowing applications to interact with messages is backwards- 341 compatible with existings protocols and APIs, as it does not change 342 the wire format of any protocol. Instead, it gives the protocol 343 stack additional information to allow it to make better use of modern 344 transport services, while simplifying the application's role in 345 parsing data. For protocols which natively use a streaming 346 abstraction, framers (Section 4.1.4) bridge the gap between the two 347 abstractions. 349 2.3. Flexibile Implementation 351 Sockets, for protocols like TCP, are generally limited to connecting 352 to a single address over a single interface. They also present a 353 single stream to the application. Software layers built upon sockets 354 often propagate this limitation of a single-address single-stream 355 model. The Transport Services architecture is designed to handle 356 multiple candidate endpoints, protocols, and paths; and support 357 multipath and multistreaming protocols. 359 Transport Services implementations are meant to be flexible at 360 connection establishment time, considering many different options and 361 trying to select the most optimal combinations (Section 4.2.1 and 362 Section 4.2.2). This requires applications to provide higher-level 363 endpoints than IP addresses, such as hostnames and URLs, which are 364 used by a Transport Services implementation for resolution, path 365 selection, and racing. Transport services implementations can 366 further implement fallback mechanisms if connection establishment of 367 one protocol fails or performance is detected to be unsatisfactory. 369 Flexibility after connection establishment is also important. 370 Transport protocols that can migrate between multiple network-layer 371 interfaces need to be able to process and react to interface changes. 372 Protocols that support multiple application-layer streams need to 373 support initiating and receiving new streams using existing 374 connections. 376 3. API and Implementation Requirements 378 The goal of the Transport Services architecture is to redefine the 379 interface between applications and transports in a way that allows 380 the transport layer to evolve and improve without fundamentally 381 changing the contract with the application. This requires a careful 382 consideration of how to expose the capabilities of protocols. 384 There are several degrees in which a Transport Services system is 385 intended to offer flexibility to an application: it can provide 386 access to multiple sets of protocols and protocol features; it can 387 use these protocols across multiple paths that could have different 388 performance and functional characteristics; and it can communicate 389 with different remote systems to optimize performance, robustness to 390 failure, or some other metric. Beyond these, if the API for the 391 system remains the same over time, new protocols and features can be 392 added to the system's implementation without requiring changes in 393 applications for adoption. 395 The normative requirements described here allow Transport Services 396 APIs and Implementations to provide this functionlity without causing 397 incompatibility or introducing security vulnerabilities. The rest of 398 this document describes the architecture non-normatively. 400 3.1. Provide Common APIs for Common Features 402 Any functionality that is common across multiple transport protocols 403 SHOULD be made accessible through a unified set of Transport Services 404 API calls. As a baseline, any Transport Services API MUST allow 405 access to the minimal set of features offered by transport protocols 406 [I-D.ietf-taps-minset]. 408 An application can specify constraints and preferences for the 409 protocols, features, and network interfaces it will use via 410 Properties. A Transport Services API SHOULD offer Properties that 411 are common to multiple transport protocols, in order to enable the 412 system to appropriately select between protocols that offer 413 equivalent features. Similarly, a Transport Services API SHOULD 414 offer Properties that are applicable to a variety of network layer 415 interfaces and paths, in order to permit racing of different network 416 paths without affecting the applications using the system. Each 417 Property is expected to have a default value. 419 The default values for Properties SHOULD be selected to ensure 420 correctness for the widest set of applications, while providing the 421 widest set of options for selection. For example, since both 422 applications that require reliability and those that do not require 423 reliability can function correctly when a protocol provides 424 reliability, reliability ought to be enabled by default. As another 425 example, the default value for a Property regarding the selection of 426 network interfaces ought to permit as many interfaces as possible. 428 Applications using a Transport Services system interface are REQUIRED 429 to be robust to the automated selection provided by the system, where 430 the automated selection is constrained by the requirements and 431 preferences expressed by the application. 433 3.2. Allow Access to Specialized Features 435 There are applications that will need to control fine-grained details 436 of transport protocols to optimize their behavior and ensure 437 compatibility with remote systems. A Transport Services system 438 therefore SHOULD permit more specialized protocol features to be 439 used. 441 A specialized feature could be required by an application only when 442 using a specific protocol, and not when using others. For example, 443 if an application is using TCP, it could require control over the 444 User Timeout Option for TCP; these options would not take effect for 445 other transport protocols. In such cases, the API ought to expose 446 the features in such a way that they take effect when a particular 447 protocol is selected, but do not imply that only that protocol could 448 be used. For example, if the API allows an application to specify a 449 preference to use the User Timeout Option, communication would not 450 fail when a protocol such as QUIC is selected. 452 Other specialized features, however, can be strictly required by an 453 application and thus constrain the set of protocols that can be used. 454 For example, if an application requires support for automatic 455 handover or failover for a connection, only protocol stacks that 456 provide this feature are eligible to be used, e.g., protocol stacks 457 that include a multipath protocol or a protocol that supports 458 connection migration. A Transport Services API needs to allow 459 applications to define such requirements and constrain the system's 460 options. Since such options are not part of the core/common 461 features, it will generally be simple for an application to modify 462 its set of constraints and change the set of allowable protocol 463 features without changing the core implementation. 465 3.3. Select Equivalent Protocol Stacks 467 A Transport Services implementation can select Protocol Stacks based 468 on the Properties communicated by the application. If two different 469 Protocol Stacks can be safely swapped, or raced in parallel (see 470 Section 4.2.2), then they are considered to be "equivalent". 471 Equivalent Protocol Stacks are defined as stacks that can provide the 472 same transport properties and interface expectations as requested by 473 the application. 475 The following two examples show non-equivalent Protocol Stacks: 477 * If the application requires preservation of message boundaries, a 478 Protocol Stack that runs UDP as the top-level interface to the 479 application is not equivalent to a Protocol Stack that runs TCP as 480 the top-level interface. A UDP stack would allow an application 481 to read out message boundaries based on datagrams sent from the 482 remote system, whereas TCP does not preserve message boundaries on 483 its own, but needs a framing protocol on top to determine message 484 boundaries. 486 * If the application specifies that it requires reliable 487 transmission of data, then a Protocol Stack using UDP without any 488 reliability layer on top would not be allowed to replace a 489 Protocol Stack using TCP. 491 The following example shows equivalent Protocol Stacks: 493 * If the application does not require reliable transmission of data, 494 then a Protocol Stack that adds reliability could be regarded as 495 an equivalent Protocol Stack as long as providing this would not 496 conflict with any other application-requested properties. 498 To ensure that security protocols are not incorrectly swapped, 499 Transport Services systems MUST only select Protocol Stacks that meet 500 application requirements ([I-D.ietf-taps-transport-security]). 501 Systems SHOULD only race Protocol Stacks where the transport security 502 protocols within the stacks are identical. Transport Services 503 systems MUST NOT automatically fall back from secure protocols to 504 insecure protocols, or to weaker versions of secure protocols. A 505 Transport Services system MAY allow applications to explicitly 506 specify that fallback to a specific other version of a protocol is 507 allowed, e.g., to allow fallback to TLS 1.2 if TLS 1.3 is not 508 available. 510 3.4. Maintain Interoperability 512 It is important to note that neither the Transport Services API 513 [I-D.ietf-taps-interface] nor the Implementation document 514 [I-D.ietf-taps-impl] define new protocols or protocol capabilities 515 that affect what is communicated across the network. Use of a 516 Transport Services system MUST NOT require that a peer on the other 517 side of a connection uses the same API or implementation. A 518 Transport Services system acting as a connection initiator is able to 519 communicate with any existing system that implements the transport 520 protocol(s) and all the required properties selected by the Transport 521 Services system. Similarly, a Transport Services system acting as a 522 listener can receive connections for any protocol that is supported 523 by the system from existing initiators that implement the protocol, 524 independent of whether the initiator uses a Transport Services system 525 or not. 527 In normal use, a Transport Services system SHOULD result in 528 consistent protocol and interface selection decisions for the same 529 network conditions given the same set of Properties. This is 530 intended to provide predictable outcomes to the application using the 531 API. 533 4. Transport Services Architecture and Concepts 535 The concepts defined in this document are intended primarily for use 536 in the documents and specifications that describe the Transport 537 Services architecture and API. While the specific terminology can be 538 used in some implementations, it is expected that there will remain a 539 variety of terms used by running code. 541 The architecture divides the concepts for Transport Services into two 542 categories: 544 1. API concepts, which are intended to be exposed to applications; 545 and 547 2. System-implementation concepts, which are intended to be 548 internally used when building systems that implement Transport 549 Services. 551 The following diagram summarizes the top-level concepts in the 552 architecture and how they relate to one another. 554 +-----------------------------------------------------+ 555 | Application | 556 +-+----------------+------^-------+--------^----------+ 557 | | | | | 558 pre- | data | events 559 establishment | transfer | | 560 | establishment | termination | 561 | | | | | 562 | +--v------v-------v+ | 563 +-v-------------+ Connection(s) +-------+----------+ 564 | Transport +--------+---------+ | 565 | Services | | 566 | API | +-------------+ | 567 +------------------------+--+ Framer(s) |-----------+ 568 | +-------------+ 569 +------------------------|----------------------------+ 570 | Transport | | 571 | System | +-----------------+ | 572 | Implementation | | Cached | | 573 | | | State | | 574 | (Candidate Gathering) | +-----------------+ | 575 | | | 576 | (Candidate Racing) | +-----------------+ | 577 | | | System | | 578 | | | Policy | | 579 | +----------v-----+ +-----------------+ | 580 | | Protocol | | 581 +-------------+ Stack(s) +----------------------+ 582 +-------+--------+ 583 V 584 Network Layer Interface 586 Figure 3: Concepts and Relationships in the Transport Services 587 Architecture 589 4.1. Transport Services API Concepts 591 Fundamentally, a Transport Services API needs to provide connection 592 objects (Section 4.1.1) that allow applications to establish 593 communication, and then send and receive data. These could be 594 exposed as handles or referenced objects, depending on the language. 596 Beyond the connection objects, there are several high-level groups of 597 actions that any Transport Services API needs to provide: 599 * Pre-Establishment (Section 4.1.2) encompasses the properties that 600 an application can pass to describe its intent, requirements, 601 prohibitions, and preferences for its networking operations. 602 These properties apply to multiple transport protocols, unless 603 otherwise specified. Properties specified during Pre- 604 Establishment can have a large impact on the rest of the 605 interface: they modify how establishment occurs, they influence 606 the expectations around data transfer, and they determine the set 607 of events that will be supported. 609 * Establishment (Section 4.1.3) focuses on the actions that an 610 application takes on the connection objects to prepare for data 611 transfer. 613 * Data Transfer (Section 4.1.4) consists of how an application 614 represents the data to be sent and received, the functions 615 required to send and receive that data, and how the application is 616 notified of the status of its data transfer. 618 * Event Handling (Section 4.1.5) defines categories of notifications 619 which an application can receive during the lifetime of transport 620 objects. Events also provide opportunities for the application to 621 interact with the underlying transport by querying state or 622 updating maintenance options. 624 * Termination (Section 4.1.6) focuses on the methods by which data 625 transmission is stopped, and state is torn down in the transport. 627 The diagram below provides a high-level view of the actions and 628 events during the lifetime of a Connection object. Note that some 629 actions are alternatives (e.g., whether to initiate a connection or 630 to listen for incoming connections), while others are optional (e.g., 631 setting Connection and Message Properties in Pre-Establishment) or 632 have been omitted for brevity and simplicity. 634 Pre-Establishment : Established : Termination 635 ----------------- : ----------- : ----------- 636 : : 637 +-- Local Endpoint : Message : 638 +-- Remote Endpoint : Receive() | : 639 +-- Transport Properties : Send() | : 640 +-- Security Parameters : | : 641 | : | : 642 | InitiateWithSend() | Close() : 643 | +---------------+ Initiate() +-----+------+ Abort() : 644 +---+ Preconnection |------------->| Connection |-----------> Closed 645 +---------------+ Rendezvous() +------------+ : 646 Listen() | : | | : 647 | : | v : 648 v : | Connection : 649 +----------+ : | Ready : 650 | Listener |----------------------+ : 651 +----------+ Connection Received : 652 : : 654 Figure 4: The lifetime of a Connection object 656 4.1.1. Connections and Related Objects 658 * Preconnection: A Preconnection object is a representation of a 659 potential Connection. It has state that describes parameters of a 660 Connection that might exist in the future: the Local Endpoint from 661 which that Connection will be established, the Remote Endpoint 662 (Section 4.1.2) to which it will connect, and Transport Properties 663 that influence the paths and protocols a Connection will use. A 664 Preconnection can be fully specified such that it represents a 665 single possible Connection, or it can be partially specified such 666 that it represents a family of possible Connections. The Local 667 Endpoint (Section 4.1.2) is required if the Preconnection is used 668 to Listen for incoming Connections. The Local Endpoint is 669 optional if it is used to Initiate Connections. The Remote 670 Endpoint is required in the Preconnection that is used to Initiate 671 Connections. The Remote Endpoint is optional if it is used to 672 Listen for incoming Connections. The Local Endpoint and the 673 Remote Endpoint are both required if a peer-to-peer Rendezvous is 674 to occur based on the Preconnection. 676 * Transport Properties: Transport Properties allow the application 677 to express their requirements, prohibitions, and preferences and 678 configure the Transport Services system. There are three kinds of 679 Transport Properties: 681 - Selection Properties (Section 4.1.2) that can only be specified 682 on a Preconnection. 684 - Connection Properties (Section 4.1.2) that can be specified on 685 a Preconnection and changed on the Connection. 687 - Message Properties (Section 4.1.4) that can be specified as 688 defaults on a Preconnection or a Connection, and can also be 689 specified during data transfer to affect specific Messages. 691 * Connection: A Connection object represents one or more active 692 transport protocol instances that can send and/or receive Messages 693 between local and remote systems. It holds state pertaining to 694 the underlying transport protocol instances and any ongoing data 695 transfers. This represents, for example, an active Connection in 696 a connection-oriented protocol such as TCP, or a fully-specified 697 5-tuple for a connectionless protocol such as UDP. It can also 698 represent a pool of transport protocol instances, e.g., a set of 699 TCP and QUIC connections to equivalent endpoints, or a stream of a 700 multi-streaming transport protocol instance. Connections can be 701 created from a Preconnection or by a Listener. 703 * Listener: A Listener object accepts incoming transport protocol 704 connections from remote systems and generates corresponding 705 Connection objects. It is created from a Preconnection object 706 that specifies the type of incoming Connections it will accept. 708 4.1.2. Pre-Establishment 710 * Endpoint: An Endpoint represents an identifier for one side of a 711 transport connection. Endpoints can be Local Endpoints or Remote 712 Endpoints, and respectively represent an identity that the 713 application uses for the source or destination of a connection. 714 An Endpoint can be specified at various levels of abstraction, and 715 an Endpoint at a higher level of abstraction (such as a hostname) 716 can be resolved to more concrete identities (such as IP 717 addresses). 719 * Remote Endpoint: The Remote Endpoint represents the application's 720 identifier for a peer that can participate in a transport 721 connection; for example, the combination of a DNS name for the 722 peer and a service name/port. 724 * Local Endpoint: The Local Endpoint represents the application's 725 identifier for itself that it uses for transport connections; for 726 example, a local IP address and port. 728 * Selection Properties: The Selection Properties consist of the 729 options that an application can set to influence the selection of 730 paths between the local and remote systems, to influence the 731 selection of transport protocols, or to configure the behavior of 732 generic transport protocol features. These options can take the 733 form of requirements, prohibitions, or preferences. Examples of 734 options that influence path selection include the interface type 735 (such as a Wi-Fi connection, or a Cellular LTE connection), 736 requirements around the largest Message that can be sent, or 737 preferences for throughput and latency properties. Examples of 738 options that influence protocol selection and configuration of 739 transport protocol features include reliability, multipath 740 support, and fast open support. 742 * Connection Properties: The Connection Properties are used to 743 configure protocol-specific options and control per-connection 744 behavior of the Transport Services system; for example, a 745 protocol-specific Connection Property can express that if TCP is 746 used, the implementation ought to use the User Timeout Option. 747 Note that the presence of such a property does not require that a 748 specific protocol will be used. In general, these properties do 749 not explicitly determine the selection of paths or protocols, but 750 can be used in this way by an implementation during connection 751 establishment. Connection Properties are specified on a 752 Preconnection prior to Connection establishment, and can be 753 modified on the Connection later. Changes made to Connection 754 Properties after Connection establishment take effect on a best- 755 effort basis. 757 * Security Parameters: Security Parameters define an application's 758 requirements for authentication and encryption on a Connection. 759 They are used by Transport Security protocols (such as those 760 described in [I-D.ietf-taps-transport-security]) to establish 761 secure Connections. Examples of parameters that can be set 762 include local identities, private keys, supported cryptographic 763 algorithms, and requirements for validating trust of remote 764 identities. Security Parameters are primarily associated with a 765 Preconnection object, but properties related to identities can be 766 associated directly with Endpoints. 768 4.1.3. Establishment Actions 769 * Initiate: The primary action that an application can take to 770 create a Connection to a Remote Endpoint, and prepare any required 771 local or remote state to enable the transmission of Messages. For 772 some protocols, this will initiate a client-to-server style 773 handshake; for other protocols, this will just establish local 774 state (e.g., with connectionless protocols such as UDP). The 775 process of identifying options for connecting, such as resolution 776 of the Remote Endpoint, occurs in response to the Initiate call. 778 * Listen: Enables a listener to accept incoming Connections. The 779 Listener will then create Connection objects as incoming 780 connections are accepted (Section 4.1.5). Listeners by default 781 register with multiple paths, protocols, and local endpoints, 782 unless constrained by Selection Properties and/or the specified 783 Local Endpoint(s). Connections can be accepted on any of the 784 available paths or endpoints. 786 * Rendezvous: The action of establishing a peer-to-peer connection 787 with a Remote Endpoint. It simultaneously attempts to initiate a 788 connection to a Remote Endpoint while listening for an incoming 789 connection from that endpoint. The process of identifying options 790 for the connection, such as resolution of the Remote Endpoint, 791 occurs in response to the Rendezvous call. As with Listeners, the 792 set of local paths and endpoints is constrained by Selection 793 Properties. If successful, the Rendezvous call returns a 794 Connection object to represent the established peer-to-peer 795 connection. The processes by which connections are initiated 796 during a Rendezvous action will depend on the set of Local and 797 Remote Endpoints configured on the Preconnection. For example, if 798 the Local and Remote Endpoints are TCP host candidates, then a TCP 799 simultaneous open [RFC0793] will be performed. However, if the 800 set of Local Endpoints includes server reflexive candidates, such 801 as those provided by STUN, a Rendezvous action will race 802 candidates in the style of the ICE algorithm [RFC8445] to perform 803 NAT binding discovery and initiate a peer-to-peer connection. 805 4.1.4. Data Transfer Objects and Actions 807 * Message: A Message object is a unit of data that can be 808 represented as bytes that can be transferred between two systems 809 over a transport connection. The bytes within a Message are 810 assumed to be ordered. If an application does not care about the 811 order in which a peer receives two distinct spans of bytes, those 812 spans of bytes are considered independent Messages. 814 * Message Properties: Message Properties are used to specify details 815 about Message transmission. They can be specified directly on 816 individual Messages, or can be set on a Preconnection or 817 Connection as defaults. These properties might only apply to how 818 a Message is sent (such as how the transport will treat 819 prioritization and reliability), but can also include properties 820 that specific protocols encode and communicate to the Remote 821 Endpoint. When receiving Messages, Message Properties can contain 822 information about the received Message, such as metadata generated 823 at the receiver and information signalled by the remote endpoint. 824 For example, a Message can be marked with a Message Property 825 indicating that it is the final message on a connection if the 826 peer sent a TCP FIN. 828 * Send: The action to transmit a Message over a Connection to the 829 remote system. The interface to Send can accept Message 830 Properties specific to how the Message content is to be sent. The 831 status of the Send operation is delivered back to the sending 832 application in an event (Section 4.1.5). 834 * Receive: An action that indicates that the application is ready to 835 asynchronously accept a Message over a Connection from a remote 836 system, while the Message content itself will be delivered in an 837 event (Section 4.1.5). The interface to Receive can include 838 Message Properties specific to the Message that is to be delivered 839 to the application. 841 * Framer: A Framer is a data translation layer that can be added to 842 a Connection to define how application-layer Messages are 843 transmitted over a transport protocol. This is particularly 844 relevant for protocols that otherwise present unstructured 845 streams, such as TCP. 847 4.1.5. Event Handling 849 The following categories of events can be delivered to an 850 application: 852 * Connection Ready: Signals to an application that a given 853 Connection is ready to send and/or receive Messages. If the 854 Connection relies on handshakes to establish state between peers, 855 then it is assumed that these steps have been taken. 857 * Connection Closed: Signals to an application that a given 858 Connection is no longer usable for sending or receiving Messages. 859 The event delivers a reason or error to the application that 860 describes the nature of the termination. 862 * Connection Received: Signals to an application that a given 863 Listener has received a Connection. 865 * Message Received: Delivers received Message content to the 866 application, based on a Receive action. This can include an error 867 if the Receive action cannot be satisfied due to the Connection 868 being closed. 870 * Message Sent: Notifies the application of the status of its Send 871 action. This might indicate a failure if the Message cannot be 872 sent, or an indication that the Message has been processed by the 873 protocol stack. 875 * Path Properties Changed: Notifies the application that some 876 property of the Connection has changed that might influence how 877 and where data is sent and/or received. 879 4.1.6. Termination Actions 881 * Close: The action an application takes on a Connection to indicate 882 that it no longer intends to send data, is no longer willing to 883 receive data, and that the protocol should signal this state to 884 the remote system if the transport protocol allows this. (Note 885 that this is distinct from the concept of "half-closing" a 886 bidirectional connection, such as when a FIN is sent in one 887 direction of a TCP connection. Indicating the end of a stream in 888 the Transport Services architecture is possible using Message 889 Properties when sending.) 891 * Abort: The action the application takes on a Connection to 892 indicate a Close and also indicate that the Transport Services 893 system should not attempt to deliver any outstanding data. This 894 is intended for immediate termination of a connection, without 895 cleaning up state. 897 4.1.7. Connection Groups 899 A Connection Group is a set of Connections that share properties and 900 caches. For multiplexing transport protocols, only Connections 901 within the same Connection Group are allowed to be multiplexed 902 together. An application can explicitly define Connection Groups to 903 control caching boundaries, as discussed in Section 4.2.3. 905 4.2. Transport Services Implementation Concepts 907 This section defines the set of objects used internally to a system 908 or library to implement the functionality needed to provide a 909 transport service across a network, as required by the abstract 910 interface. 912 * Path: Represents an available set of properties that a local 913 system can use to communicate with a remote system, such as 914 routes, addresses, and physical and virtual network interfaces. 916 * Protocol Instance: A single instance of one protocol, including 917 any state necessary to establish connectivity or send and receive 918 Messages. 920 * Protocol Stack: A set of Protocol Instances (including relevant 921 application, security, transport, or Internet protocols) that are 922 used together to establish connectivity or send and receive 923 Messages. A single stack can be simple (a single transport 924 protocol instance over IP), or it can be complex (multiple 925 application protocol streams going through a single security and 926 transport protocol, over IP; or, a multi-path transport protocol 927 over multiple transport sub-flows). 929 * Candidate Path: One path that is available to an application and 930 conforms to the Selection Properties and System Policy, of which 931 there can be several. Candidate Paths are identified during the 932 gathering phase (Section 4.2.1) and can be used during the racing 933 phase (Section 4.2.2). 935 * Candidate Protocol Stack: One Protocol Stack that can be used by 936 an application for a connection, of which there can be several. 937 Candidate Protocol Stacks are identified during the gathering 938 phase (Section 4.2.1) and are started during the racing phase 939 (Section 4.2.2). 941 * System Policy: Represents the input from an operating system or 942 other global preferences that can constrain or influence how an 943 implementation will gather candidate paths and Protocol Stacks 944 (Section 4.2.1) and race the candidates during establishment 945 (Section 4.2.2). Specific aspects of the System Policy either 946 apply to all Connections or only certain ones, depending on the 947 runtime context and properties of the Connection. 949 * Cached State: The state and history that the implementation keeps 950 for each set of associated Endpoints that have been used 951 previously. This can include DNS results, TLS session state, 952 previous success and quality of transport protocols over certain 953 paths, as well as other information. 955 4.2.1. Candidate Gathering 956 * Candidate Path Selection: Candidate Path Selection represents the 957 act of choosing one or more paths that are available to use based 958 on the Selection Properties and any available Local and Remote 959 Endpoints provided by the application, as well as the policies and 960 heuristics of a Transport Services system. 962 * Candidate Protocol Selection: Candidate Protocol Selection 963 represents the act of choosing one or more sets of Protocol Stacks 964 that are available to use based on the Transport Properties 965 provided by the application, and the heuristics or policies within 966 the Transport Services system. 968 4.2.2. Candidate Racing 970 Connection establishment attempts for a set of candidates may be 971 performed simultaneously, synchronously, serially, or some 972 combination of all of these. We refer to this process as racing, 973 borrowing terminology from Happy Eyeballs [RFC8305]. 975 * Protocol Option Racing: Protocol Option Racing is the act of 976 attempting to establish, or scheduling attempts to establish, 977 multiple Protocol Stacks that differ based on the composition of 978 protocols or the options used for protocols. 980 * Path Racing: Path Racing is the act of attempting to establish, or 981 scheduling attempts to establish, multiple Protocol Stacks that 982 differ based on a selection from the available Paths. Since 983 different Paths will have distinct configurations for local 984 addresses and DNS servers, attempts across different Paths will 985 perform separate DNS resolution steps, which can lead to further 986 racing of the resolved Remote Endpoints. 988 * Remote Endpoint Racing: Remote Endpoint Racing is the act of 989 attempting to establish, or scheduling attempts to establish, 990 multiple Protocol Stacks that differ based on the specific 991 representation of the Remote Endpoint, such as a particular IP 992 address that was resolved from a DNS hostname. 994 4.2.3. Separating Connection Groups 996 By default, stored properties of the implementation, such as cached 997 protocol state, cached path state, and heuristics, may be shared 998 (e.g. across multiple connections in an application). This provides 999 efficiency and convenience for the application, since the Transport 1000 Services implementation can automatically optimize behavior. 1002 There are several reasons, however, that an application might want to 1003 explicitly isolate some Connections. These reasons include: 1005 * Privacy concerns about re-using cached protocol state that can 1006 lead to linkability. Sensitive state may include TLS session 1007 state [RFC8446] and HTTP cookies [RFC6265]. 1009 * Privacy concerns about allowing Connections to multiplex together, 1010 which can tell a Remote Endpoint that all of the Connections are 1011 coming from the same application (for example, when Connections 1012 are multiplexed HTTP/2 or QUIC streams). 1014 * Performance concerns about Connections introducing head-of-line 1015 blocking due to multiplexing or needing to share state on a single 1016 thread. 1018 The Transport Services API can allow applications to explicitly 1019 define Connection Groups that force separation of Cached State and 1020 Protocol Stacks. For example, a web browser application might use 1021 Connection Groups with separate caches for different tabs in the 1022 browser to decrease linkability. 1024 The interface to specify a Connection Group can expose fine-grained 1025 tuning for which properties and cached state is allowed to be shared 1026 with other Connections. For example, an application might want to 1027 allow sharing TCP Fast Open cookies across groups, but not TLS 1028 session state. 1030 5. IANA Considerations 1032 RFC-EDITOR: Please remove this section before publication. 1034 This document has no actions for IANA. 1036 6. Security Considerations 1038 The Transport Services architecture does not recommend use of 1039 specific security protocols or algorithms. Its goal is to offer ease 1040 of use for existing protocols by providing a generic security-related 1041 interface. Each provided interface translates to an existing 1042 protocol-specific interface provided by supported security protocols. 1043 For example, trust verification callbacks are common parts of TLS 1044 APIs. Transport Services APIs will expose similar functionality 1045 [I-D.ietf-taps-transport-security]. 1047 As described above in Section 3.3, if a Transport Services system 1048 races between two different Protocol Stacks, both need to use the 1049 same security protocols and options. However, a Transport Services 1050 system can race different security protocols, e.g., if the 1051 application explicitly specifies that it considers them equivalent. 1053 Applications need to ensure that they use security APIs 1054 appropriately. In cases where applications use an interface to 1055 provide sensitive keying material, e.g., access to private keys or 1056 copies of pre-shared keys (PSKs), key use needs to be validated. For 1057 example, applications ought not to use PSK material created for the 1058 Encapsulating Security Protocol (ESP, part of IPsec) [RFC4303] with 1059 QUIC, and applications ought not to use private keys intended for 1060 server authentication as keys for client authentication. 1062 Moreover, Transport Services systems must not automatically fall back 1063 from secure protocols to insecure protocols, or to weaker versions of 1064 secure protocols (see Section 3.3). For example, if an application 1065 requests a specific version of TLS, but the desired version of TLS is 1066 not available, its connection will fail. Applications are thus 1067 responsible for implementing security protocol fallback or version 1068 fallback by creating multiple Transport Services Connections, if so 1069 desired. Alternatively, a Transport Services system MAY allow 1070 applications to specify that fallback to a specific other version of 1071 a protocol is allowed. 1073 7. Acknowledgements 1075 This work has received funding from the European Union's Horizon 2020 1076 research and innovation programme under grant agreements No. 644334 1077 (NEAT) and No. 688421 (MAMI). 1079 This work has been supported by Leibniz Prize project funds of DFG - 1080 German Research Foundation: Gottfried Wilhelm Leibniz-Preis 2011 (FKZ 1081 FE 570/4-1). 1083 This work has been supported by the UK Engineering and Physical 1084 Sciences Research Council under grant EP/R04144X/1. 1086 Thanks to Theresa Enghardt, Max Franke, Mirja Kuehlewind, Jonathan 1087 Lennox, and Michael Welzl for the discussions and feedback that 1088 helped shape the architecture described here. Thanks as well to 1089 Stuart Cheshire, Josh Graessley, David Schinazi, and Eric Kinnear for 1090 their implementation and design efforts, including Happy Eyeballs, 1091 that heavily influenced this work. 1093 8. References 1095 8.1. Normative References 1097 [I-D.ietf-taps-interface] 1098 Trammell, B., Welzl, M., Enghardt, T., Fairhurst, G., 1099 Kuehlewind, M., Perkins, C., Tiesel, P., Wood, C., and T. 1100 Pauly, "An Abstract Application Layer Interface to 1101 Transport Services", Work in Progress, Internet-Draft, 1102 draft-ietf-taps-interface-06, 9 March 2020, 1103 . 1106 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1107 Requirement Levels", BCP 14, RFC 2119, 1108 DOI 10.17487/RFC2119, March 1997, 1109 . 1111 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1112 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1113 May 2017, . 1115 8.2. Informative References 1117 [I-D.ietf-taps-impl] 1118 Brunstrom, A., Pauly, T., Enghardt, T., Grinnemo, K., 1119 Jones, T., Tiesel, P., Perkins, C., and M. Welzl, 1120 "Implementing Interfaces to Transport Services", Work in 1121 Progress, Internet-Draft, draft-ietf-taps-impl-06, 9 March 1122 2020, . 1125 [I-D.ietf-taps-minset] 1126 Welzl, M. and S. Gjessing, "A Minimal Set of Transport 1127 Services for End Systems", Work in Progress, Internet- 1128 Draft, draft-ietf-taps-minset-11, 27 September 2018, 1129 . 1132 [I-D.ietf-taps-transport-security] 1133 Enghardt, T., Pauly, T., Perkins, C., Rose, K., and C. 1134 Wood, "A Survey of the Interaction Between Security 1135 Protocols and Transport Services", Work in Progress, 1136 Internet-Draft, draft-ietf-taps-transport-security-12, 23 1137 April 2020, . 1140 [POSIX] "IEEE Std. 1003.1-2008 Standard for Information Technology 1141 -- Portable Operating System Interface (POSIX). Open 1142 group Technical Standard: Base Specifications, Issue 7", 1143 2008. 1145 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 1146 RFC 793, DOI 10.17487/RFC0793, September 1981, 1147 . 1149 [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", 1150 RFC 4303, DOI 10.17487/RFC4303, December 2005, 1151 . 1153 [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, 1154 DOI 10.17487/RFC6265, April 2011, 1155 . 1157 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 1158 Protocol (HTTP/1.1): Message Syntax and Routing", 1159 RFC 7230, DOI 10.17487/RFC7230, June 2014, 1160 . 1162 [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext 1163 Transfer Protocol Version 2 (HTTP/2)", RFC 7540, 1164 DOI 10.17487/RFC7540, May 2015, 1165 . 1167 [RFC8095] Fairhurst, G., Ed., Trammell, B., Ed., and M. Kuehlewind, 1168 Ed., "Services Provided by IETF Transport Protocols and 1169 Congestion Control Mechanisms", RFC 8095, 1170 DOI 10.17487/RFC8095, March 2017, 1171 . 1173 [RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: 1174 Better Connectivity Using Concurrency", RFC 8305, 1175 DOI 10.17487/RFC8305, December 2017, 1176 . 1178 [RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive 1179 Connectivity Establishment (ICE): A Protocol for Network 1180 Address Translator (NAT) Traversal", RFC 8445, 1181 DOI 10.17487/RFC8445, July 2018, 1182 . 1184 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 1185 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 1186 . 1188 Authors' Addresses 1190 Tommy Pauly (editor) 1191 Apple Inc. 1192 One Apple Park Way 1193 Cupertino, California 95014, 1194 United States of America 1196 Email: tpauly@apple.com 1197 Brian Trammell (editor) 1198 Google Switzerland GmbH 1199 Gustav-Gull-Platz 1 1200 CH- 8004 Zurich 1201 Switzerland 1203 Email: ietf@trammell.ch 1205 Anna Brunstrom 1206 Karlstad University 1207 Universitetsgatan 2 1208 651 88 Karlstad 1209 Sweden 1211 Email: anna.brunstrom@kau.se 1213 Godred Fairhurst 1214 University of Aberdeen 1215 Fraser Noble Building 1216 Aberdeen, AB24 3UE 1218 Email: gorry@erg.abdn.ac.uk 1219 URI: http://www.erg.abdn.ac.uk/ 1221 Colin Perkins 1222 University of Glasgow 1223 School of Computing Science 1224 Glasgow G12 8QQ 1225 United Kingdom 1227 Email: csp@csperkins.org 1229 Philipp S. Tiesel 1230 TU Berlin 1231 Einsteinufer 25 1232 10587 Berlin 1233 Germany 1235 Email: philipp@tiesel.net 1237 Christopher A. Wood 1238 Cloudflare 1239 101 Townsend St 1240 San Francisco, 1241 United States of America 1243 Email: caw@heapingbits.net