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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-26) exists of draft-ietf-taps-interface-09 == Outdated reference: A later version (-18) exists of draft-ietf-taps-impl-07 -- Obsolete informational reference (is this intentional?): RFC 793 (Obsoleted by RFC 9293)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: 0 errors (**), 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: 6 May 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 2 November 2020 18 An Architecture for Transport Services 19 draft-ietf-taps-arch-09 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 6 May 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. Endpoint Objects . . . . . . . . . . . . . . . . . . 15 82 4.1.2. Connections and Related Objects . . . . . . . . . . . 15 83 4.1.3. Pre-Establishment . . . . . . . . . . . . . . . . . . 16 84 4.1.4. Establishment Actions . . . . . . . . . . . . . . . . 17 85 4.1.5. Data Transfer Objects and Actions . . . . . . . . . . 18 86 4.1.6. Event Handling . . . . . . . . . . . . . . . . . . . 19 87 4.1.7. Termination Actions . . . . . . . . . . . . . . . . . 20 88 4.1.8. Connection Groups . . . . . . . . . . . . . . . . . . 20 89 4.2. Transport Services Implementation Concepts . . . . . . . 21 90 4.2.1. Candidate Gathering . . . . . . . . . . . . . . . . . 22 91 4.2.2. Candidate Racing . . . . . . . . . . . . . . . . . . 22 92 4.2.3. Separating Connection Groups . . . . . . . . . . . . 23 93 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 94 6. Security Considerations . . . . . . . . . . . . . . . . . . . 24 95 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24 96 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 25 97 8.1. Normative References . . . . . . . . . . . . . . . . . . 25 98 8.2. Informative References . . . . . . . . . . . . . . . . . 25 99 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 101 1. Introduction 103 Many application programming interfaces (APIs) to perform transport 104 networking have been deployed, perhaps the most widely known and 105 imitated being the BSD Socket [POSIX] interface (Socket API). The 106 naming of objects and functions across these APIs is not consistent, 107 and varies depending on the protocol being used. For example, 108 sending and receiving streams of data is conceptually the same for 109 both an unencrypted Transmission Control Protocol (TCP) stream and 110 operating on an encrypted Transport Layer Security (TLS) [RFC8446] 111 stream over TCP, but applications cannot use the same socket "send()" 112 and "recv()" calls on top of both kinds of connections. Similarly, 113 terminology for the implementation of transport protocols varies 114 based on the context of the protocols themselves: terms such as 115 "flow", "stream", "message", and "connection" can take on many 116 different meanings. This variety can lead to confusion when trying 117 to understand the similarities and differences between protocols, and 118 how applications can use them effectively. 120 The goal of the Transport Services architecture is to provide a 121 common, flexible, and reusable interface for transport protocols. As 122 applications adopt this interface, they will benefit from a wide set 123 of transport features that can evolve over time, and ensure that the 124 system providing the interface can optimize its behavior based on the 125 application requirements and network conditions, without requiring 126 changes to the applications. This flexibility enables faster 127 deployment of new features and protocols. It can also support 128 applications by offering racing and fallback mechanisms, which 129 otherwise need to be implemented in each application separately. 131 This document was developed in parallel with the specification of the 132 Transport Services API [I-D.ietf-taps-interface] and Implementation 133 Guidelines [I-D.ietf-taps-impl]. Although following the Transport 134 Services Architecture does not require that all APIs and 135 implementations are identical, a common minimal set of features 136 represented in a consistent fashion will enable applications to be 137 easily ported from one system to another. 139 1.1. Background 141 The Transport Services architecture is based on the survey of 142 services provided by IETF transport protocols and congestion control 143 mechanisms [RFC8095], and the distilled minimal set of the features 144 offered by transport protocols [RFC8923]. These documents identified 145 common features and patterns across all transport protocols developed 146 thus far in the IETF. 148 Since transport security is an increasingly relevant aspect of using 149 transport protocols on the Internet, this architecture also considers 150 the impact of transport security protocols on the feature-set exposed 151 by Transport Services [RFC8922]. 153 One of the key insights to come from identifying the minimal set of 154 features provided by transport protocols [RFC8923] was that features 155 either require application interaction and guidance (referred to in 156 that document as Functional or Optimizing Features), or else can be 157 handled automatically by a system implementing Transport Services 158 (referred to as Automatable Features). Among the identified 159 Functional and Optimizing Features, some were common across all or 160 nearly all transport protocols, while others could be seen as 161 features that, if specified, would only be useful with a subset of 162 protocols, but would not harm the functionality of other protocols. 163 For example, some protocols can deliver messages faster for 164 applications that do not require messages to arrive in the order in 165 which they were sent. However, this functionality needs to be 166 explicitly allowed by the application, since reordering messages 167 would be undesirable in many cases. 169 1.2. Overview 171 This document describes the Transport Services architecture in three 172 sections: 174 * Section 2 describes how the API model of Transport Services 175 differs from traditional socket-based APIs. Specifically, it 176 offers asynchronous event-driven interaction, the use of messages 177 for data transfer, and the flexibility to use different transport 178 protocols and paths without requiring major changes to the 179 application. 181 * Section 3 explains the fundamental requirements for a Transport 182 Services API. These principles are intended to make sure that 183 transport protocols can continue to be enhanced and evolve without 184 requiring significant changes by application developers. 186 * Section 4 presents the Transport Services architecture diagram and 187 defines the concepts that are used by both the API and 188 implementation documents. The Preconnection allows applications 189 to configure Connection Properties, and the Connection represents 190 an object that can be used to send and receive Messages. 192 1.3. Specification of Requirements 194 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 195 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 196 "OPTIONAL" in this document are to be interpreted as described in BCP 197 14 [RFC2119] [RFC8174] when, and only when, they appear in all 198 capitals, as shown here. 200 2. API Model 202 The traditional model of using sockets for networking can be 203 represented as follows: 205 * Applications create connections and transfer data using the Socket 206 API. 208 * The Socket API provides the interface to the implementations of 209 TCP and UDP (typically implemented in the system's kernel). 211 * TCP and UDP in the kernel send and receive data over the available 212 network-layer interfaces. 214 * Sockets are bound directly to transport-layer and network-layer 215 addresses, obtained via a separate resolution step, usually 216 performed by a system-provided stub resolver. 218 +-----------------------------------------------------+ 219 | Application | 220 +-----------------------------------------------------+ 221 | | | 222 +------------+ +------------+ +--------------+ 223 | stub | | Stream API | | Datagram API | 224 | resolver | +------------+ +--------------+ 225 +------------+ | | 226 +---------------------------------+ 227 | TCP UDP | 228 | Kernel Networking Stack | 229 +---------------------------------+ 230 | 231 +-----------------------------------------------------+ 232 | Network Layer Interface | 233 +-----------------------------------------------------+ 234 Figure 1: Socket API Model 236 The Transport Services architecture evolves this general model of 237 interaction, aiming to both modernize the API surface presented to 238 applications by the transport layer and enrich the capabilities of 239 the Transport Services implementation. It combines interfaces for 240 multiple interaction patterns into a unified whole. By combining 241 name resolution with connection establishment and data transfer in a 242 single API, it allows for more flexible implementations to provide 243 path and transport protocol agility on the application's behalf. 245 +-----------------------------------------------------+ 246 | Application | 247 +-----------------------------------------------------+ 248 | 249 +-----------------------------------------------------+ 250 | Transport Services API | 251 +-----------------------------------------------------+ 252 | 253 +-----------------------------------------------------+ 254 | Transport Services Implementation | 255 | (Using: DNS, UDP, TCP, SCTP, DCCP, TLS, QUIC, etc) | 256 +-----------------------------------------------------+ 257 | 258 +-----------------------------------------------------+ 259 | Network Layer Interface | 260 +-----------------------------------------------------+ 262 Figure 2: Transport Services API Model 264 The Transport Services API [I-D.ietf-taps-interface] defines the 265 mechanism for an application to create network connections and 266 transfer data. The implementation [I-D.ietf-taps-impl] is 267 responsible for mapping the API to the various available transport 268 protocols and managing the available network interfaces and paths. 270 There are key differences between the architecture of the Transport 271 Services system and the architecture of the Socket API: the Transport 272 Services API is asynchronous and event-driven; it uses messages for 273 representing data transfer to applications; and it describes how 274 implementations can use multiple IP addresses, multiple protocols, 275 multiple paths, and provide multiple application streams. 277 2.1. Event-Driven API 279 Originally, sockets presented a blocking interface for establishing 280 connections and transferring data. However, most modern applications 281 interact with the network asynchronously. Emulation of an 282 asynchronous interface using sockets generally uses a try-and-fail 283 model. If the application wants to read, but data has not yet been 284 received from the peer, the call to read will fail. The application 285 then waits and can try again later. 287 In contrast to sockets, all interaction with a Transport Services 288 system is expected to be asynchronous, and use an event-driven model 289 (see Section 4.1.6). For example, if the application wants to read, 290 its call to read will not complete immediately, but will deliver an 291 event containing the received data once it is available. Error 292 handling is also asynchronous; a failure to send results in an 293 asynchronous send error as an event. 295 The Transport Services API also delivers events regarding the 296 lifetime of a connection and changes in the available network links, 297 which were not previously made explicit in sockets. 299 Using asynchronous events allows for a more natural interaction model 300 when establishing connections and transferring data. Events in time 301 more closely reflect the nature of interactions over networks, as 302 opposed to how sockets represent network resources as file system 303 objects that may be temporarily unavailable. 305 Separate from events, callbacks are also provided for asynchronous 306 interactions with the API not directly related to events on the 307 network or network interfaces. 309 2.2. Data Transfer Using Messages 311 Sockets provide a message interface for datagram protocols like UDP, 312 but provide an unstructured stream abstraction for TCP. While TCP 313 does indeed provide the ability to send and receive data as streams, 314 most applications need to interpret structure within these streams. 315 For example, HTTP/1.1 uses character delimiters to segment messages 316 over a stream [RFC7230]; TLS record headers carry a version, content 317 type, and length [RFC8446]; and HTTP/2 uses frames to segment its 318 headers and bodies [RFC7540]. 320 The Transport Services API represents data as messages, so that it 321 more closely matches the way applications use the network. Providing 322 a message-based abstraction provides many benefits, such as: 324 * the ability to associate deadlines with messages, for applications 325 that care about timing; 327 * the ability to provide control of reliability, choosing which 328 messages to retransmit when there is packet loss, and how best to 329 make use of the data that arrived; 331 * the ability to manage dependencies between messages, when the 332 Transport Services system could decide to not deliver a message, 333 either following packet loss or because it has missed a deadline. 334 In particular, this can avoid (re-)sending data that relies on a 335 previous transmission that was never received. 337 * the ability to automatically assign messages and connections to 338 underlying transport connections to utilize multi-streaming and 339 pooled connections. 341 Allowing applications to interact with messages is backwards- 342 compatible with existing protocols and APIs because it does not 343 change the wire format of any protocol. Instead, it gives the 344 protocol stack additional information to allow it to make better use 345 of modern transport services, while simplifying the application's 346 role in parsing data. For protocols which natively use a streaming 347 abstraction, framers (Section 4.1.5) bridge the gap between the two 348 abstractions. 350 2.3. Flexibile Implementation 352 Sockets, for protocols like TCP, are generally limited to connecting 353 to a single address over a single interface. They also present a 354 single stream to the application. Software layers built upon sockets 355 often propagate this limitation of a single-address single-stream 356 model. The Transport Services architecture is designed to handle 357 multiple candidate endpoints, protocols, and paths; and support 358 multipath and multistreaming protocols. 360 Transport Services implementations are meant to be flexible at 361 connection establishment time, considering many different options and 362 trying to select the most optimal combinations (Section 4.2.1 and 363 Section 4.2.2). This requires applications to provide higher-level 364 endpoints than IP addresses, such as hostnames and URLs, which are 365 used by a Transport Services implementation for resolution, path 366 selection, and racing. Transport services implementations can 367 further implement fallback mechanisms if connection establishment of 368 one protocol fails or performance is detected to be unsatisfactory. 370 Flexibility after connection establishment is also important. 371 Transport protocols that can migrate between multiple network-layer 372 interfaces need to be able to process and react to interface changes. 373 Protocols that support multiple application-layer streams need to 374 support initiating and receiving new streams using existing 375 connections. 377 3. API and Implementation Requirements 379 The goal of the Transport Services architecture is to redefine the 380 interface between applications and transports in a way that allows 381 the transport layer to evolve and improve without fundamentally 382 changing the contract with the application. This requires a careful 383 consideration of how to expose the capabilities of protocols. 385 There are several degrees in which a Transport Services system is 386 intended to offer flexibility to an application: it can provide 387 access to multiple sets of protocols and protocol features; it can 388 use these protocols across multiple paths that could have different 389 performance and functional characteristics; and it can communicate 390 with different remote systems to optimize performance, robustness to 391 failure, or some other metric. Beyond these, if the API for the 392 system remains the same over time, new protocols and features can be 393 added to the system's implementation without requiring changes in 394 applications for adoption. 396 The normative requirements described here allow Transport Services 397 APIs and Implementations to provide this functionality without 398 causing incompatibility or introducing security vulnerabilities. The 399 rest of this document describes the architecture non-normatively. 401 3.1. Provide Common APIs for Common Features 403 Any functionality that is common across multiple transport protocols 404 SHOULD be made accessible through a unified set of Transport Services 405 API calls. As a baseline, any Transport Services API MUST allow 406 access to the minimal set of features offered by transport protocols 407 [RFC8923]. 409 An application can specify constraints and preferences for the 410 protocols, features, and network interfaces it will use via 411 Properties. A Transport Services API SHOULD offer Properties that 412 are common to multiple transport protocols, which enables the system 413 to appropriately select between protocols that offer equivalent 414 features. Similarly, a Transport Services API SHOULD offer 415 Properties that are applicable to a variety of network layer 416 interfaces and paths, which permits racing of different network paths 417 without affecting the applications using the system. Each Property 418 is expected to have a default value. 420 The default values for Properties SHOULD be selected to ensure 421 correctness for the widest set of applications, while providing the 422 widest set of options for selection. For example, since both 423 applications that require reliability and those that do not require 424 reliability can function correctly when a protocol provides 425 reliability, reliability ought to be enabled by default. As another 426 example, the default value for a Property regarding the selection of 427 network interfaces ought to permit as many interfaces as possible. 429 Applications using a Transport Services system interface are REQUIRED 430 to be robust to the automated selection provided by the system, where 431 the automated selection is constrained by the requirements and 432 preferences expressed by the application. 434 3.2. Allow Access to Specialized Features 436 There are applications that will need to control fine-grained details 437 of transport protocols to optimize their behavior and ensure 438 compatibility with remote systems. A Transport Services system 439 therefore SHOULD permit more specialized protocol features to be 440 used. 442 A specialized feature could be required by an application only when 443 using a specific protocol, and not when using others. For example, 444 if an application is using TCP, it could require control over the 445 User Timeout Option for TCP; these options would not take effect for 446 other transport protocols. In such cases, the API ought to expose 447 the features in such a way that they take effect when a particular 448 protocol is selected, but do not imply that only that protocol could 449 be used. For example, if the API allows an application to specify a 450 preference to use the User Timeout Option, communication would not 451 fail when a protocol such as QUIC is selected. 453 Other specialized features, however, can be strictly required by an 454 application and thus constrain the set of protocols that can be used. 455 For example, if an application requires support for automatic 456 handover or failover for a connection, only protocol stacks that 457 provide this feature are eligible to be used, e.g., protocol stacks 458 that include a multipath protocol or a protocol that supports 459 connection migration. A Transport Services API needs to allow 460 applications to define such requirements and constrain the system's 461 options. Since such options are not part of the core/common 462 features, it will generally be simple for an application to modify 463 its set of constraints and change the set of allowable protocol 464 features without changing the core implementation. 466 3.3. Select Equivalent Protocol Stacks 468 A Transport Services implementation can select Protocol Stacks based 469 on the Properties communicated by the application. If two different 470 Protocol Stacks can be safely swapped, or raced in parallel (see 471 Section 4.2.2), then they are considered to be "equivalent". 472 Equivalent Protocol Stacks are defined as stacks that can provide the 473 same transport properties and interface expectations as requested by 474 the application. 476 The following two examples show non-equivalent Protocol Stacks: 478 * If the application requires preservation of message boundaries, a 479 Protocol Stack that runs UDP as the top-level interface to the 480 application is not equivalent to a Protocol Stack that runs TCP as 481 the top-level interface. A UDP stack would allow an application 482 to read out message boundaries based on datagrams sent from the 483 remote system, whereas TCP does not preserve message boundaries on 484 its own, but needs a framing protocol on top to determine message 485 boundaries. 487 * If the application specifies that it requires reliable 488 transmission of data, then a Protocol Stack using UDP without any 489 reliability layer on top would not be allowed to replace a 490 Protocol Stack using TCP. 492 The following example shows equivalent Protocol Stacks: 494 * If the application does not require reliable transmission of data, 495 then a Protocol Stack that adds reliability could be regarded as 496 an equivalent Protocol Stack as long as providing this would not 497 conflict with any other application-requested properties. 499 To ensure that security protocols are not incorrectly swapped, 500 Transport Services systems MUST only select Protocol Stacks that meet 501 application requirements ([RFC8922]). Systems SHOULD only race 502 Protocol Stacks where the transport security protocols within the 503 stacks are identical. Transport Services systems MUST NOT 504 automatically fall back from secure protocols to insecure protocols, 505 or to weaker versions of secure protocols. A Transport Services 506 system MAY allow applications to explicitly specify that fallback to 507 a specific other version of a protocol is allowed, e.g., to allow 508 fallback to TLS 1.2 if TLS 1.3 is not 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 4.1.2) 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 4.1.3) encompasses the properties that 600 an application can pass to describe its intent, requirements, 601 prohibitions, and preferences for its networking operations. 603 These properties apply to multiple transport protocols, unless 604 otherwise specified. Properties specified during Pre- 605 Establishment can have a large impact on the rest of the 606 interface: they modify how establishment occurs, they influence 607 the expectations around data transfer, and they determine the set 608 of events that will be supported. 610 * Establishment (Section 4.1.4) focuses on the actions that an 611 application takes on the connection objects to prepare for data 612 transfer. 614 * Data Transfer (Section 4.1.5) consists of how an application 615 represents the data to be sent and received, the functions 616 required to send and receive that data, and how the application is 617 notified of the status of its data transfer. 619 * Event Handling (Section 4.1.6) defines categories of notifications 620 which an application can receive during the lifetime of transport 621 objects. Events also provide opportunities for the application to 622 interact with the underlying transport by querying state or 623 updating maintenance options. 625 * Termination (Section 4.1.7) focuses on the methods by which data 626 transmission is stopped, and state is torn down in the transport. 628 The diagram below provides a high-level view of the actions and 629 events during the lifetime of a Connection object. Note that some 630 actions are alternatives (e.g., whether to initiate a connection or 631 to listen for incoming connections), while others are optional (e.g., 632 setting Connection and Message Properties in Pre-Establishment) or 633 have been omitted for brevity and simplicity. 635 Pre-Establishment : Established : Termination 636 ----------------- : ----------- : ----------- 637 : : 638 +-- Local Endpoint : Message : 639 +-- Remote Endpoint : Receive() | : 640 +-- Transport Properties : Send() | : 641 +-- Security Parameters : | : 642 | : | : 643 | InitiateWithSend() | Close() : 644 | +---------------+ Initiate() +-----+------+ Abort() : 645 +---+ Preconnection |------------->| Connection |-----------> Closed 646 +---------------+ Rendezvous() +------------+ : 647 Listen() | : | | : 648 | : | v : 649 v : | Connection : 650 +----------+ : | Ready : 651 | Listener |----------------------+ : 652 +----------+ Connection Received : 653 : : 655 Figure 4: The lifetime of a Connection object 657 4.1.1. Endpoint Objects 659 * Endpoint: An Endpoint represents an identifier for one side of a 660 transport connection. Endpoints can be Local Endpoints or Remote 661 Endpoints, and respectively represent an identity that the 662 application uses for the source or destination of a connection. 663 An Endpoint can be specified at various levels of abstraction, and 664 an Endpoint at a higher level of abstraction (such as a hostname) 665 can be resolved to more concrete identities (such as IP 666 addresses). 668 * Remote Endpoint: The Remote Endpoint represents the application's 669 identifier for a peer that can participate in a transport 670 connection; for example, the combination of a DNS name for the 671 peer and a service name/port. 673 * Local Endpoint: The Local Endpoint represents the application's 674 identifier for itself that it uses for transport connections; for 675 example, a local IP address and port. 677 4.1.2. Connections and Related Objects 679 * Preconnection: A Preconnection object is a representation of a 680 potential Connection. It has state that describes parameters of a 681 Connection that might exist in the future: the Local Endpoint from 682 which that Connection will be established, the Remote Endpoint 683 (Section 4.1.3) to which it will connect, and Transport Properties 684 that influence the paths and protocols a Connection will use. A 685 Preconnection can be fully specified such that it represents a 686 single possible Connection, or it can be partially specified such 687 that it represents a family of possible Connections. The Local 688 Endpoint (Section 4.1.3) is required if the Preconnection is used 689 to Listen for incoming Connections. The Local Endpoint is 690 optional if it is used to Initiate Connections. The Remote 691 Endpoint is required in the Preconnection that is used to Initiate 692 Connections. The Remote Endpoint is optional if it is used to 693 Listen for incoming Connections. The Local Endpoint and the 694 Remote Endpoint are both required if a peer-to-peer Rendezvous is 695 to occur based on the Preconnection. 697 * Transport Properties: Transport Properties allow the application 698 to express their requirements, prohibitions, and preferences and 699 configure the Transport Services system. There are three kinds of 700 Transport Properties: 702 - Selection Properties (Section 4.1.3) that can only be specified 703 on a Preconnection. 705 - Connection Properties (Section 4.1.3) that can be specified on 706 a Preconnection and changed on the Connection. 708 - Message Properties (Section 4.1.5) that can be specified as 709 defaults on a Preconnection or a Connection, and can also be 710 specified during data transfer to affect specific Messages. 712 * Connection: A Connection object represents one or more active 713 transport protocol instances that can send and/or receive Messages 714 between local and remote systems. It holds state pertaining to 715 the underlying transport protocol instances and any ongoing data 716 transfers. This represents, for example, an active Connection in 717 a connection-oriented protocol such as TCP, or a fully-specified 718 5-tuple for a connectionless protocol such as UDP. It can also 719 represent a pool of transport protocol instances, e.g., a set of 720 TCP and QUIC connections to equivalent endpoints, or a stream of a 721 multi-streaming transport protocol instance. Connections can be 722 created from a Preconnection or by a Listener. 724 * Listener: A Listener object accepts incoming transport protocol 725 connections from remote systems and generates corresponding 726 Connection objects. It is created from a Preconnection object 727 that specifies the type of incoming Connections it will accept. 729 4.1.3. Pre-Establishment 730 * Selection Properties: The Selection Properties consist of the 731 properties that an application can set to influence the selection 732 of paths between the local and remote systems, to influence the 733 selection of transport protocols, or to configure the behavior of 734 generic transport protocol features. These properties can take 735 the form of requirements, prohibitions, or preferences. Examples 736 of properties that influence path selection include the interface 737 type (such as a Wi-Fi connection, or a Cellular LTE connection), 738 requirements around the largest Message that can be sent, or 739 preferences for throughput and latency. Examples of properties 740 that influence protocol selection and configuration of transport 741 protocol features include reliability, multipath support, and fast 742 open support. 744 * Connection Properties: The Connection Properties are used to 745 configure protocol-specific options and control per-connection 746 behavior of the Transport Services system; for example, a 747 protocol-specific Connection Property can express that if TCP is 748 used, the implementation ought to use the User Timeout Option. 749 Note that the presence of such a property does not require that a 750 specific protocol will be used. In general, these properties do 751 not explicitly determine the selection of paths or protocols, but 752 can be used by an implementation during connection establishment. 753 Connection Properties are specified on a Preconnection prior to 754 Connection establishment, and can be modified on the Connection 755 later. Changes made to Connection Properties after Connection 756 establishment take effect on a best-effort basis. 758 * Security Parameters: Security Parameters define an application's 759 requirements for authentication and encryption on a Connection. 760 They are used by Transport Security protocols (such as those 761 described in [RFC8922]) to establish secure Connections. Examples 762 of parameters that can be set include local identities, private 763 keys, supported cryptographic algorithms, and requirements for 764 validating trust of remote identities. Security Parameters are 765 primarily associated with a Preconnection object, but properties 766 related to identities can be associated directly with Endpoints. 768 4.1.4. Establishment Actions 770 * Initiate: The primary action that an application can take to 771 create a Connection to a Remote Endpoint, and prepare any required 772 local or remote state to enable the transmission of Messages. For 773 some protocols, this will initiate a client-to-server style 774 handshake; for other protocols, this will just establish local 775 state (e.g., with connectionless protocols such as UDP). The 776 process of identifying options for connecting, such as resolution 777 of the Remote Endpoint, occurs in response to the Initiate call. 779 * Listen: Enables a listener to accept incoming Connections. The 780 Listener will then create Connection objects as incoming 781 connections are accepted (Section 4.1.6). Listeners by default 782 register with multiple paths, protocols, and local endpoints, 783 unless constrained by Selection Properties and/or the specified 784 Local Endpoint(s). Connections can be accepted on any of the 785 available paths or endpoints. 787 * Rendezvous: The action of establishing a peer-to-peer connection 788 with a Remote Endpoint. It simultaneously attempts to initiate a 789 connection to a Remote Endpoint while listening for an incoming 790 connection from that endpoint. The process of identifying options 791 for the connection, such as resolution of the Remote Endpoint, 792 occurs in response to the Rendezvous call. As with Listeners, the 793 set of local paths and endpoints is constrained by Selection 794 Properties. If successful, the Rendezvous call returns a 795 Connection object to represent the established peer-to-peer 796 connection. The processes by which connections are initiated 797 during a Rendezvous action will depend on the set of Local and 798 Remote Endpoints configured on the Preconnection. For example, if 799 the Local and Remote Endpoints are TCP host candidates, then a TCP 800 simultaneous open [RFC0793] will be performed. However, if the 801 set of Local Endpoints includes server reflexive candidates, such 802 as those provided by STUN, a Rendezvous action will race 803 candidates in the style of the ICE algorithm [RFC8445] to perform 804 NAT binding discovery and initiate a peer-to-peer connection. 806 4.1.5. Data Transfer Objects and Actions 808 * Message: A Message object is a unit of data that can be 809 represented as bytes that can be transferred between two systems 810 over a transport connection. The bytes within a Message are 811 assumed to be ordered. If an application does not care about the 812 order in which a peer receives two distinct spans of bytes, those 813 spans of bytes are considered independent Messages. 815 * Message Properties: Message Properties are used to specify details 816 about Message transmission. They can be specified directly on 817 individual Messages, or can be set on a Preconnection or 818 Connection as defaults. These properties might only apply to how 819 a Message is sent (such as how the transport will treat 820 prioritization and reliability), but can also include properties 821 that specific protocols encode and communicate to the Remote 822 Endpoint. When receiving Messages, Message Properties can contain 823 information about the received Message, such as metadata generated 824 at the receiver and information signalled by the remote endpoint. 825 For example, a Message can be marked with a Message Property 826 indicating that it is the final message on a connection if the 827 peer sent a TCP FIN. 829 * Send: The action to transmit a Message over a Connection to the 830 remote system. The interface to Send can accept Message 831 Properties specific to how the Message content is to be sent. The 832 status of the Send operation is delivered back to the sending 833 application in an event (Section 4.1.6). 835 * Receive: An action that indicates that the application is ready to 836 asynchronously accept a Message over a Connection from a remote 837 system, while the Message content itself will be delivered in an 838 event (Section 4.1.6). The interface to Receive can include 839 Message Properties specific to the Message that is to be delivered 840 to the application. 842 * Framer: A Framer is a data translation layer that can be added to 843 a Connection to define how application-layer Messages are 844 transmitted over a transport protocol. This is particularly 845 relevant for protocols that otherwise present unstructured 846 streams, such as TCP. 848 4.1.6. Event Handling 850 The following categories of events can be delivered to an 851 application: 853 * Connection Ready: Signals to an application that a given 854 Connection is ready to send and/or receive Messages. If the 855 Connection relies on handshakes to establish state between peers, 856 then it is assumed that these steps have been taken. 858 * Connection Closed: Signals to an application that a given 859 Connection is no longer usable for sending or receiving Messages. 860 The event delivers a reason or error to the application that 861 describes the nature of the termination. 863 * Connection Received: Signals to an application that a given 864 Listener has received a Connection. 866 * Message Received: Delivers received Message content to the 867 application, based on a Receive action. This can include an error 868 if the Receive action cannot be satisfied due to the Connection 869 being closed. 871 * Message Sent: Notifies the application of the status of its Send 872 action. This might indicate a failure if the Message cannot be 873 sent, or an indication that the Message has been processed by the 874 protocol stack. 876 * Path Properties Changed: Notifies the application that some 877 property of the Connection has changed that might influence how 878 and where data is sent and/or received. 880 4.1.7. Termination Actions 882 * Close: The action an application takes on a Connection to indicate 883 that it no longer intends to send data, is no longer willing to 884 receive data, and that the protocol should signal this state to 885 the remote system if the transport protocol allows this. (Note 886 that this is distinct from the concept of "half-closing" a 887 bidirectional connection, such as when a FIN is sent in one 888 direction of a TCP connection. Indicating the end of a stream in 889 the Transport Services architecture is possible using Message 890 Properties when sending.) 892 * Abort: The action the application takes on a Connection to 893 indicate a Close and also indicate that the Transport Services 894 system should not attempt to deliver any outstanding data. This 895 is intended for immediate termination of a connection, without 896 cleaning up state. 898 4.1.8. Connection Groups 900 A Connection Group is a set of Connections that share properties and 901 caches. For multiplexing transport protocols, only Connections 902 within the same Connection Group are allowed to be multiplexed 903 together. An application can explicitly define Connection Groups to 904 control caching boundaries, as discussed in Section 4.2.3. 906 4.2. Transport Services Implementation Concepts 908 This section defines the set of objects used internally to a system 909 or library to implement the functionality needed to provide a 910 transport service across a network, as required by the abstract 911 interface. 913 * Path: Represents an available set of properties that a local 914 system can use to communicate with a remote system, such as 915 routes, addresses, and physical and virtual network interfaces. 917 * Protocol Instance: A single instance of one protocol, including 918 any state necessary to establish connectivity or send and receive 919 Messages. 921 * Protocol Stack: A set of Protocol Instances (including relevant 922 application, security, transport, or Internet protocols) that are 923 used together to establish connectivity or send and receive 924 Messages. A single stack can be simple (a single transport 925 protocol instance over IP), or it can be complex (multiple 926 application protocol streams going through a single security and 927 transport protocol, over IP; or, a multi-path transport protocol 928 over multiple transport sub-flows). 930 * Candidate Path: One path that is available to an application and 931 conforms to the Selection Properties and System Policy, of which 932 there can be several. Candidate Paths are identified during the 933 gathering phase (Section 4.2.1) and can be used during the racing 934 phase (Section 4.2.2). 936 * Candidate Protocol Stack: One Protocol Stack that can be used by 937 an application for a connection, of which there can be several. 938 Candidate Protocol Stacks are identified during the gathering 939 phase (Section 4.2.1) and are started during the racing phase 940 (Section 4.2.2). 942 * System Policy: Represents the input from an operating system or 943 other global preferences that can constrain or influence how an 944 implementation will gather candidate paths and Protocol Stacks 945 (Section 4.2.1) and race the candidates during establishment 946 (Section 4.2.2). Specific aspects of the System Policy either 947 apply to all Connections or only certain ones, depending on the 948 runtime context and properties of the Connection. 950 * Cached State: The state and history that the implementation keeps 951 for each set of associated Endpoints that have been used 952 previously. This can include DNS results, TLS session state, 953 previous success and quality of transport protocols over certain 954 paths, as well as other information. 956 4.2.1. Candidate Gathering 958 * Candidate Path Selection: Candidate Path Selection represents the 959 act of choosing one or more paths that are available to use based 960 on the Selection Properties and any available Local and Remote 961 Endpoints provided by the application, as well as the policies and 962 heuristics of a Transport Services system. 964 * Candidate Protocol Selection: Candidate Protocol Selection 965 represents the act of choosing one or more sets of Protocol Stacks 966 that are available to use based on the Transport Properties 967 provided by the application, and the heuristics or policies within 968 the Transport Services system. 970 4.2.2. Candidate Racing 972 Connection establishment attempts for a set of candidates may be 973 performed simultaneously, synchronously, serially, or some 974 combination of all of these. We refer to this process as racing, 975 borrowing terminology from Happy Eyeballs [RFC8305]. 977 * Protocol Option Racing: Protocol Option Racing is the act of 978 attempting to establish, or scheduling attempts to establish, 979 multiple Protocol Stacks that differ based on the composition of 980 protocols or the options used for protocols. 982 * Path Racing: Path Racing is the act of attempting to establish, or 983 scheduling attempts to establish, multiple Protocol Stacks that 984 differ based on a selection from the available Paths. Since 985 different Paths will have distinct configurations for local 986 addresses and DNS servers, attempts across different Paths will 987 perform separate DNS resolution steps, which can lead to further 988 racing of the resolved Remote Endpoints. 990 * Remote Endpoint Racing: Remote Endpoint Racing is the act of 991 attempting to establish, or scheduling attempts to establish, 992 multiple Protocol Stacks that differ based on the specific 993 representation of the Remote Endpoint, such as a particular IP 994 address that was resolved from a DNS hostname. 996 4.2.3. Separating Connection Groups 998 By default, stored properties of the implementation, such as cached 999 protocol state, cached path state, and heuristics, may be shared 1000 (e.g. across multiple connections in an application). This provides 1001 efficiency and convenience for the application, since the Transport 1002 Services implementation can automatically optimize behavior. 1004 There are several reasons, however, that an application might want to 1005 explicitly isolate some Connections. These reasons include: 1007 * Privacy concerns about re-using cached protocol state that can 1008 lead to linkability. Sensitive state may include TLS session 1009 state [RFC8446] and HTTP cookies [RFC6265]. 1011 * Privacy concerns about allowing Connections to multiplex together, 1012 which can tell a Remote Endpoint that all of the Connections are 1013 coming from the same application (for example, when Connections 1014 are multiplexed HTTP/2 or QUIC streams). 1016 * Performance concerns about Connections introducing head-of-line 1017 blocking due to multiplexing or needing to share state on a single 1018 thread. 1020 The Transport Services API can allow applications to explicitly 1021 define Connection Groups that force separation of Cached State and 1022 Protocol Stacks. For example, a web browser application might use 1023 Connection Groups with separate caches for different tabs in the 1024 browser to decrease linkability. 1026 The interface to specify a Connection Group can expose fine-grained 1027 tuning for which properties and cached state is allowed to be shared 1028 with other Connections. For example, an application might want to 1029 allow sharing TCP Fast Open cookies across groups, but not TLS 1030 session state. 1032 5. IANA Considerations 1034 RFC-EDITOR: Please remove this section before publication. 1036 This document has no actions for IANA. 1038 6. Security Considerations 1040 The Transport Services architecture does not recommend use of 1041 specific security protocols or algorithms. Its goal is to offer ease 1042 of use for existing protocols by providing a generic security-related 1043 interface. Each provided interface translates to an existing 1044 protocol-specific interface provided by supported security protocols. 1045 For example, trust verification callbacks are common parts of TLS 1046 APIs. Transport Services APIs will expose similar functionality 1047 [RFC8922]. 1049 As described above in Section 3.3, if a Transport Services system 1050 races between two different Protocol Stacks, both need to use the 1051 same security protocols and options. However, a Transport Services 1052 system can race different security protocols, e.g., if the 1053 application explicitly specifies that it considers them equivalent. 1055 Applications need to ensure that they use security APIs 1056 appropriately. In cases where applications use an interface to 1057 provide sensitive keying material, e.g., access to private keys or 1058 copies of pre-shared keys (PSKs), key use needs to be validated. For 1059 example, applications ought not to use PSK material created for the 1060 Encapsulating Security Protocol (ESP, part of IPsec) [RFC4303] with 1061 QUIC, and applications ought not to use private keys intended for 1062 server authentication as keys for client authentication. 1064 Moreover, Transport Services systems must not automatically fall back 1065 from secure protocols to insecure protocols, or to weaker versions of 1066 secure protocols (see Section 3.3). For example, if an application 1067 requests a specific version of TLS, but the desired version of TLS is 1068 not available, its connection will fail. Applications are thus 1069 responsible for implementing security protocol fallback or version 1070 fallback by creating multiple Transport Services Connections, if so 1071 desired. Alternatively, a Transport Services system MAY allow 1072 applications to specify that fallback to a specific other version of 1073 a protocol is allowed. 1075 7. Acknowledgements 1077 This work has received funding from the European Union's Horizon 2020 1078 research and innovation programme under grant agreements No. 644334 1079 (NEAT) and No. 688421 (MAMI). 1081 This work has been supported by Leibniz Prize project funds of DFG - 1082 German Research Foundation: Gottfried Wilhelm Leibniz-Preis 2011 (FKZ 1083 FE 570/4-1). 1085 This work has been supported by the UK Engineering and Physical 1086 Sciences Research Council under grant EP/R04144X/1. 1088 Thanks to Theresa Enghardt, Max Franke, Mirja Kuehlewind, Jonathan 1089 Lennox, and Michael Welzl for the discussions and feedback that 1090 helped shape the architecture described here. Thanks as well to 1091 Stuart Cheshire, Josh Graessley, David Schinazi, and Eric Kinnear for 1092 their implementation and design efforts, including Happy Eyeballs, 1093 that heavily influenced this work. 1095 8. References 1097 8.1. Normative References 1099 [I-D.ietf-taps-interface] 1100 Trammell, B., Welzl, M., Enghardt, T., Fairhurst, G., 1101 Kuehlewind, M., Perkins, C., Tiesel, P., Wood, C., and T. 1102 Pauly, "An Abstract Application Layer Interface to 1103 Transport Services", Work in Progress, Internet-Draft, 1104 draft-ietf-taps-interface-09, 27 July 2020, 1105 . 1108 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1109 Requirement Levels", BCP 14, RFC 2119, 1110 DOI 10.17487/RFC2119, March 1997, 1111 . 1113 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1114 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1115 May 2017, . 1117 8.2. Informative References 1119 [I-D.ietf-taps-impl] 1120 Brunstrom, A., Pauly, T., Enghardt, T., Grinnemo, K., 1121 Jones, T., Tiesel, P., Perkins, C., and M. Welzl, 1122 "Implementing Interfaces to Transport Services", Work in 1123 Progress, Internet-Draft, draft-ietf-taps-impl-07, 13 July 1124 2020, . 1127 [POSIX] "IEEE Std. 1003.1-2008 Standard for Information Technology 1128 -- Portable Operating System Interface (POSIX). Open 1129 group Technical Standard: Base Specifications, Issue 7", 1130 2008. 1132 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 1133 RFC 793, DOI 10.17487/RFC0793, September 1981, 1134 . 1136 [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", 1137 RFC 4303, DOI 10.17487/RFC4303, December 2005, 1138 . 1140 [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, 1141 DOI 10.17487/RFC6265, April 2011, 1142 . 1144 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 1145 Protocol (HTTP/1.1): Message Syntax and Routing", 1146 RFC 7230, DOI 10.17487/RFC7230, June 2014, 1147 . 1149 [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext 1150 Transfer Protocol Version 2 (HTTP/2)", RFC 7540, 1151 DOI 10.17487/RFC7540, May 2015, 1152 . 1154 [RFC8095] Fairhurst, G., Ed., Trammell, B., Ed., and M. Kuehlewind, 1155 Ed., "Services Provided by IETF Transport Protocols and 1156 Congestion Control Mechanisms", RFC 8095, 1157 DOI 10.17487/RFC8095, March 2017, 1158 . 1160 [RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: 1161 Better Connectivity Using Concurrency", RFC 8305, 1162 DOI 10.17487/RFC8305, December 2017, 1163 . 1165 [RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive 1166 Connectivity Establishment (ICE): A Protocol for Network 1167 Address Translator (NAT) Traversal", RFC 8445, 1168 DOI 10.17487/RFC8445, July 2018, 1169 . 1171 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 1172 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 1173 . 1175 [RFC8922] Enghardt, T., Pauly, T., Perkins, C., Rose, K., and C. 1176 Wood, "A Survey of the Interaction between Security 1177 Protocols and Transport Services", RFC 8922, 1178 DOI 10.17487/RFC8922, October 2020, 1179 . 1181 [RFC8923] Welzl, M. and S. Gjessing, "A Minimal Set of Transport 1182 Services for End Systems", RFC 8923, DOI 10.17487/RFC8923, 1183 October 2020, . 1185 Authors' Addresses 1187 Tommy Pauly (editor) 1188 Apple Inc. 1189 One Apple Park Way 1190 Cupertino, California 95014, 1191 United States of America 1193 Email: tpauly@apple.com 1195 Brian Trammell (editor) 1196 Google Switzerland GmbH 1197 Gustav-Gull-Platz 1 1198 CH- 8004 Zurich 1199 Switzerland 1201 Email: ietf@trammell.ch 1203 Anna Brunstrom 1204 Karlstad University 1205 Universitetsgatan 2 1206 651 88 Karlstad 1207 Sweden 1209 Email: anna.brunstrom@kau.se 1211 Godred Fairhurst 1212 University of Aberdeen 1213 Fraser Noble Building 1214 Aberdeen, AB24 3UE 1216 Email: gorry@erg.abdn.ac.uk 1217 URI: http://www.erg.abdn.ac.uk/ 1219 Colin Perkins 1220 University of Glasgow 1221 School of Computing Science 1222 Glasgow G12 8QQ 1223 United Kingdom 1224 Email: csp@csperkins.org 1226 Philipp S. Tiesel 1227 TU Berlin 1228 Einsteinufer 25 1229 10587 Berlin 1230 Germany 1232 Email: philipp@tiesel.net 1234 Christopher A. Wood 1235 Cloudflare 1236 101 Townsend St 1237 San Francisco, 1238 United States of America 1240 Email: caw@heapingbits.net