idnits 2.17.1 draft-ietf-netconf-restconf-notif-03.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack an IANA Considerations section. (See Section 2.2 of https://www.ietf.org/id-info/checklist for how to handle the case when there are no actions for IANA.) Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (August 4, 2017) is 2428 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 6536 (Obsoleted by RFC 8341) ** Obsolete normative reference: RFC 7540 (Obsoleted by RFC 9113) Summary: 3 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 NETCONF E. Voit 3 Internet-Draft A. Tripathy 4 Intended status: Standards Track E. Nilsen-Nygaard 5 Expires: February 5, 2018 Cisco Systems 6 A. Clemm 7 Huawei 8 A. Gonzalez Prieto 9 VMWare 10 A. Bierman 11 YumaWorks 12 August 4, 2017 14 Restconf and HTTP Transport for Event Notifications 15 draft-ietf-netconf-restconf-notif-03 17 Abstract 19 This document defines Restconf, HTTP2, and HTTP1.1 bindings for the 20 transport of Subscription requests and corresponding push updates. 21 Being subscribed may be either publisher defined event streams or 22 nodes/subtrees of YANG Datastores. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at http://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on February 5, 2018. 41 Copyright Notice 43 Copyright (c) 2017 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 59 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 60 3. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 3 61 3.1. Dynamic YANG Subscription with RESTCONF control . . . . . 3 62 3.2. Subscription Multiplexing . . . . . . . . . . . . . . . . 6 63 4. Encoded Subscription and Notification Message Examples . . . 7 64 4.1. Restconf Subscription and Events over HTTP1.1 . . . . . . 7 65 4.2. Event Notification over HTTP2 . . . . . . . . . . . . . . 12 66 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12 67 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13 68 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 69 7.1. Normative References . . . . . . . . . . . . . . . . . . 13 70 7.2. Informative References . . . . . . . . . . . . . . . . . 14 71 Appendix A. End-to-End Deployment Guidance . . . . . . . . . . . 14 72 A.1. Call Home . . . . . . . . . . . . . . . . . . . . . . . . 14 73 A.2. TLS Heartbeat . . . . . . . . . . . . . . . . . . . . . . 15 74 Appendix B. RESTCONF over GRPC . . . . . . . . . . . . . . . . . 15 75 Appendix C. Changes between revisions . . . . . . . . . . . . . 15 76 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 78 1. Introduction 80 Mechanisms to support Event subscription and push are defined in 81 [sn]. Enhancements to [sn] which enable YANG Datastore subscription 82 and push are defined in [yang-push]. This document provides a 83 transport specification for these protocols over Restconf and HTTP. 84 Driving these requirements is [RFC7923]. 86 The streaming of notifications encapsulating the resulting 87 information push can be done with either HTTP1.1 and HTTP2. When 88 using HTTP2 [RFC7540] benefits which can be realized include: 90 o Elimination of head-of-line blocking 92 o Weighting and proportional dequeuing of Events from different 93 subscriptions 95 o Explicit precedence in subscriptions so that events from one 96 subscription must be sent before another dequeues 98 2. Terminology 100 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 101 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 102 document are to be interpreted as described in RFC 2119 [RFC2119]. 104 The following terms use the defintions from [sn]: configured 105 subscription, dynamic subscription, event notification, publisher, 106 receiver, subscriber, and subscription. 108 3. Solution 110 Subscribing to event streams is defined in [sn], YANG Datastore 111 subscription is defined in [yang-push]. This section specifies 112 transport mechanisms applicable to both. 114 3.1. Dynamic YANG Subscription with RESTCONF control 116 Dynamic Subscriptions for both [sn] and its [yang-push] augmentations 117 are configured and managed via signaling messages transported over 118 [RFC8040]. These interactions will be accomplished via a Restconf 119 POST into RPCs located on the Publisher. HTTP responses codes will 120 indicate the results of the interaction with the Publisher. An HTTP 121 status code of 200 is the proper response to a successful RPC call. The successful will 123 result in a HTTP message with returned subscription URI on a 124 logically separate mechanism than was used for the original Restconf 125 POST. This mechanism is via a parallel TCP connection in the case of 126 HTTP 1.x, or in the case of HTTP2 via a separate HTTP stream within 127 the HTTP connection. When a being returned by the Publisher, failure 128 will be indicated by error codes transported in payload. 130 Once established, the resulting stream of notification messages are 131 then delivered via SSE for HTTP1.1 and via HTTP Data for HTTP2. 133 3.1.1. Call Flow for HTTP2 135 Requests to [sn] or [yang-push] augmented RPCs are sent on one or 136 more HTTP2 streams indicated by (a) in Figure 2. Notification 137 messages related to a single subscription are pushed on a unique 138 logical channel (b). In the case below, a newly established 139 subscription has its associated messages pushed over HTTP2 stream 140 (7). 142 +------------+ +------------+ 143 | Subscriber | | Publisher | 144 |HTTP2 Stream| |HTTP2 Stream| 145 | (a) (b) | | (a) (b) | 146 +------------+ +------------+ 147 | Restconf POST (RPC:establish-subscription) | 148 |--------------------------------------------->| 149 | HTTP 200 OK (URI)| 150 |<---------------------------------------------| 151 | (7)HTTP POST (URI) (7) 152 | |--------------------------------------------->| 153 | | HTTP 200 OK| 154 | |<---------------------------------------------| 155 | | HTTP Data (event-notif)| 156 | |<---------------------------------------------| 157 | Restconf POST (RPC:modify-subscription) | | 158 |--------------------------------------------->| | 159 | | HTTP 200 OK| | 160 |<---------------------------------------------| | 161 | | HTTP Data (subscription-modified)| 162 | |<---------------------------------------------| 163 | | HTTP Data (event-notif)| 164 | |<---------------------------------------------| 165 | Restconf POST (RPC:delete-subscription) | | 166 |--------------------------------------------->| | 167 | | HTTP 200 OK| | 168 |<---------------------------------------------| | 169 | | HTTP Headers (end of stream)| 170 | (/7)<-----------------------------------------(/7) 171 | 173 Figure 1: Dynamic with HTTP2 175 3.1.2. Call flow for HTTP1.1 177 Requests to [yang-push] RPCs are sent on the TCP connection indicated 178 by (a). Notification messages are pushed on a separate connection 179 (b). This connection (b) will be used for all notification messages 180 across all subscriptions. 182 +--------------+ +--------------+ 183 | Subscriber | | Publisher | 184 |TCP connection| |TCP connection| 185 | (a) (b) | | (a) (b) | 186 +--------------+ +--------------+ 187 | Restconf POST (RPC:establish-subscription) | 188 |--------------------------------------------->| 189 | HTTP 200 OK (URI)| 190 |<---------------------------------------------| 191 | |HTTP GET (URI) | 192 | |--------------------------------------------->| 193 | | HTTP 200 OK| 194 | |<---------------------------------------------| 195 | | SSE (event-notif)| 196 | |<---------------------------------------------| 197 | Restconf POST (RPC:modify-subscription) | | 198 |--------------------------------------------->| | 199 | | HTTP 200 OK| | 200 |<---------------------------------------------| | 201 | | SSE (subscription-modified)| 202 | |<---------------------------------------------| 203 | | SSE (event-notif)| 204 | |<---------------------------------------------| 205 | Restconf POST (RPC:delete-subscription) | | 206 |--------------------------------------------->| | 207 | | HTTP 200 OK| | 208 |<---------------------------------------------| | 209 | | | 210 | | 212 Figure 2: Dynamic with HTTP1.1 214 3.1.3. Configured Subscription over HTTP2 216 With a Configured Subscription, all information needed to establish a 217 secure relationship with that Receiver is available on the Publisher. 218 With this information, the Publisher will establish a secure 219 transport connection with the Receiver and then begin pushing 220 notification messages to the Receiver. Since Restconf might not 221 exist on the Receiver, it is not desirable to require that subscribed 222 content be pushed with any dependency on Restconf. Nor is there 223 value which Restconf provides on top of HTTP. Therefore in place of 224 Restconf, a TLS secured HTTP2 Client connection must be established 225 with an HTTP2 Server located on the Receiver. Notification messages 226 will then be sent as part of an extended HTTP POST to the Receiver. 228 POST messages will be addressed to HTTP augmentation code on the 229 Receiver capable of accepting and responding to state change 230 notifications and subscribed content notification messages. The 231 first POST message must be a subscription-started notification. 232 Notifications which include any subscribed content must not be sent 233 until the receipt of an HTTP 200 OK for this initial notification. 234 The 200 OK will indicate that the Receiver is ready for the delivery 235 of subscribed content. At this point a Subscription must be 236 allocated its own HTTP2 stream. Figure 4 depicts this message flow. 238 +------------+ +------------+ 239 | Receiver | | Publisher | 240 |HTTP2 Stream| |HTTP2 Stream| 241 | (a) (b) | | (a) (b) | 242 +------------+ +------------+ 243 | HTTP Post Headers, Data (sub-start, SubID)| 244 |<---------------------------------------------| 245 | HTTP 200 OK | 246 |--------------------------------------------->| 247 | | HTTP Post Headers, Data (event-notif)| 248 | |<---------------------------------------------| 249 | | HTTP Data (event-notif)| 250 | |<---------------------------------------------| 251 | | HTTP Data (sub-terminate)| 252 | |<---------------------------------------------| 253 | |HTTP 200 OK | 254 | |--------------------------------------------->| 256 Figure 3: Configured over HTTP2 258 As the HTTP2 transport is available to the Receiver, the Publisher 259 should: 261 o take any subscription-priority and copy it into the HTTP2 stream 262 priority, and 264 o take a subscription-dependency if it has been provided and map the 265 HTTP2 stream for the parent subscription into the HTTP2 stream 266 dependency. 268 3.2. Subscription Multiplexing 270 It is possible that updates across subscriptions might be delivered 271 in a different sequence than the encapsulated records were generated. 272 Reasons for this might include (but are not limited to): 274 o generation of event records on different line cards 276 o replay of pushed information, and 277 o temporary loss of transport connectivity, with update buffering 278 and different dequeuing priorities per Subscription 280 o population, marshalling and bundling across independent 281 Subscription Updates, and 283 Therefore each notification message will include a timestamp to 284 provide a Receiver with its best information indicating when a 285 particular record was generated. Use of this timestamp can give an 286 indication of the state of objects at a Publisher. This is 287 especially important when state-entangled information is received 288 across different subscriptions. Note that use of notification 289 message timestamps may not indicate a the exact time of occurrence. 290 So when state-entangled updates have inconsistent object values and 291 temporally close timestamps, a Receiver might consider performing a 292 GET to validate the current state of a Publisher. 294 4. Encoded Subscription and Notification Message Examples 296 4.1. Restconf Subscription and Events over HTTP1.1 298 Subscribers can dynamically learn whether a RESTCONF server supports 299 various types of Event or Yang datastore subscription capabilities. 300 This is done by issuing an HTTP request OPTIONS, HEAD, or GET on the 301 stream. Some examples building upon the Call flow for HTTP1.1 from 302 Section 3.2.2 are: 304 GET /restconf/data/ietf-restconf-monitoring:restconf-state/ 305 streams/stream=yang-push HTTP/1.1 306 Host: example.com 307 Accept: application/yang.data+xml 309 If the server supports it, it may respond 310 HTTP/1.1 200 OK 311 Content-Type: application/yang.api+xml 312 313 yang-push 314 Yang push stream 315 316 xml 317 https://example.com/streams/yang-push-xml 318 319 320 321 json 322 https://example.com/streams/yang-push-json 323 324 325 327 If the server does not support any form of subscription, it may 328 respond 330 HTTP/1.1 404 Not Found 331 Date: Mon, 25 Apr 2012 11:10:30 GMT 332 Server: example-server 334 Subscribers can determine the URL to receive updates by sending an 335 HTTP GET as a request for the "location" leaf with the stream list 336 entry. The stream to use for may be selected from the Event Stream 337 list provided in the capabilities exchange. Note that different 338 encodings are supporting using different Event Stream locations. For 339 example, the Subscriber might send the following request: 341 GET /restconf/data/ietf-restconf-monitoring:restconf-state/ 342 streams/stream=yang-push/access=xml/location HTTP/1.1 343 Host: example.com 344 Accept: application/yang.data+xml 346 The Publisher might send the following response: 348 HTTP/1.1 200 OK 349 Content-Type: application/yang.api+xml 350 352 https://example.com/streams/yang-push-xml 353 355 To subscribe and start receiving updates, the subscriber can then 356 send an HTTP GET request for the URL returned by the Publisher in the 357 request above. The accept header must be "text/event-stream". The 358 Publisher uses the Server Sent Events [W3C-20150203] transport 359 strategy to push filtered events from the event stream. 361 The Publisher MUST support individual parameters within the POST 362 request body for all the parameters of a subscription. The only 363 exception is the encoding, which is embedded in the URI. An example 364 of this is: 366 // subtree filter = /foo 367 // periodic updates, every 5 seconds 368 POST /restconf/operations/ietf-event-notifications: 369 establish-subscription HTTP/1.1 370 Host: example.com 371 Content-Type: application/yang-data+json 373 { 374 "ietf-event-notifications:input" : { 375 "stream": "push-data" 376 "period" : 5, 377 "xpath-filter" : "/ex:foo[starts-with('bar'.'some']" 378 } 379 } 381 Should the publisher not support the requested subscription, it may 382 reply: 384 HTTP/1.1 501 Not Implemented 385 Date: Mon, 23 Apr 2012 17:11:00 GMT 386 Server: example-server 387 Content-Type: application/yang.errors+xml 388 389 390 application 391 operation-not-supported 392 error 393 Xpath filters not supported 394 395 397 398 399 400 401 403 with an equivalent JSON encoding representation of: 405 HTTP/1.1 501 Not Implemented 406 Date: Mon, 23 Apr 2012 17:11:00 GMT 407 Server: example-server 408 Content-Type: application/yang.errors+json 409 { 410 "ietf-restconf:errors": { 411 "error": { 412 "error-type": "protocol", 413 "error-tag": "operation-not-supported", 414 "error-message": "Xpath filters not supported." 415 "error-info": { 416 "datastore-push:supported-subscription": { 417 "subtree-filter": [null] 418 } 419 } 420 } 421 } 422 } 424 The following is an example of a pushed content for the Subscription 425 above. It contains a subtree with root foo that contains a leaf 426 called bar: 428 XML encoding representation: 429 430 431 433 my-sub 434 435 2015-03-09T19:14:56.233Z 436 438 439 some_string 440 441 442 444 Or with the equivalent YANG over JSON encoding representation as 445 defined in [RFC7951]: 447 { 448 "ietf-restconf:notification": { 449 "datastore-push:subscription-id": "my-sub", 450 "eventTime": "2015-03-09T19:14:56.233Z", 451 "datastore-push:datastore-contents": { 452 "example-mod:foo": { "bar": "some_string" } 453 } 454 } 455 } 457 To modify a Subscription, the subscriber issues another POST request 458 on the provided URI using the same subscription-id as in the original 459 request. For example, to modify the update period to 10 seconds, the 460 subscriber may send: 462 POST /restconf/operations/ietf-event-notifications: 463 modify-subscription HTTP/1.1 464 Host: example.com 465 Content-Type: application/yang-data+json 467 { 468 "ietf-event-notifications:input" : { 469 "subscription-id": 100, 470 "period" : 10 471 } 472 } 474 To delete a Subscription, the Subscriber issues a DELETE request on 475 the provided URI using the same subscription-id as in the original 476 request 478 4.2. Event Notification over HTTP2 480 The basic encoding will look as below. It will consists of a JSON 481 representation wrapped in an HTTP2 header. 483 HyperText Transfer Protocol 2 484 Stream: HEADERS, Stream ID: 5 485 Header: :method: POST 486 Stream: HEADERS, Stream ID: 5 488 { 489 "ietf-yangpush:notification": { 490 "datastore-push:subscription-id": "my-sub", 491 "eventTime": "2015-03-09T19:14:56.233Z", 492 "datastore-push:datastore-contents": { 493 "foo": { "bar": "some_string" } 494 } 495 } 496 } 498 5. Security Considerations 500 Subscriptions could be used to intentionally or accidentally overload 501 the resources of a Publisher. For this reason, it is important that 502 the Publisher has the ability to prioritize the establishment and 503 push of notification messages where there is the potential for 504 resource exhaust. In addition, a server needs to be able to suspend 505 existing Subscriptions when needed. When this occurs, the 506 subscription status must be updated accordingly and the Receivers 507 notified. 509 A Subscription could be used to attempt retrieve information for 510 which a Receiver has no authorized access. Therefore it is important 511 that data pushed via a Subscription is authorized equivalently with 512 regular data retrieval operations. Data being pushed to a Receiver 513 needs therefore to be filtered accordingly, just like if the data 514 were being retrieved on-demand. The Netconf Authorization Control 515 Model [RFC6536] applies even though the transport is not NETCONF. 517 One or more Publishers of Configured Subscriptions could be used to 518 overwhelm a Receiver which doesn't even support Subscriptions. There 519 are two protections here. First, notification messages for 520 Configured Subscriptions MUST only be transmittable over encrypted 521 transports. Clients which do not want pushed content need only 522 terminate or refuse any transport sessions from the Publisher. 523 Second, the HTTP transport augmentation on the Receiver must send an 524 HTTP 200 OK to a subscription started notification before the 525 Publisher starts streaming any subscribed content. 527 One or more Publishers could overwhelm a Receiver which is unable to 528 control or handle the volume of Event Notifications received. In 529 deployments where this might be a concern, HTTP2 transport such as 530 HTTP2) should be selected. 532 6. Acknowledgments 534 We wish to acknowledge the helpful contributions, comments, and 535 suggestions that were received from: Susan Hares, Tim Jenkins, Balazs 536 Lengyel, Kent Watsen, Michael Scharf, and Guangying Zheng. 538 7. References 540 7.1. Normative References 542 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 543 Requirement Levels", BCP 14, RFC 2119, 544 DOI 10.17487/RFC2119, March 1997, 545 . 547 [RFC6520] Seggelmann, R., Tuexen, M., and M. Williams, "Transport 548 Layer Security (TLS) and Datagram Transport Layer Security 549 (DTLS) Heartbeat Extension", RFC 6520, 550 DOI 10.17487/RFC6520, February 2012, 551 . 553 [RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration 554 Protocol (NETCONF) Access Control Model", RFC 6536, 555 DOI 10.17487/RFC6536, March 2012, 556 . 558 [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext 559 Transfer Protocol Version 2 (HTTP/2)", RFC 7540, 560 DOI 10.17487/RFC7540, May 2015, 561 . 563 [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF 564 Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, 565 . 567 [sn] Voit, E., Clemm, A., Gonzalez Prieto, A., Prasad Tripathy, 568 A., and E. Nilsen-Nygaard, "Subscribing to Event 569 Notifications", February 2017, 570 . 573 7.2. Informative References 575 [GRPC] "RPC framework that runs over HTTP2", August 2017, 576 . 578 [RFC7923] Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements 579 for Subscription to YANG Datastores", RFC 7923, 580 DOI 10.17487/RFC7923, June 2016, 581 . 583 [RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG", 584 RFC 7951, DOI 10.17487/RFC7951, August 2016, 585 . 587 [RFC8071] Watsen, K., "NETCONF Call Home and RESTCONF Call Home", 588 RFC 8071, DOI 10.17487/RFC8071, February 2017, 589 . 591 [W3C-20150203] 592 "Server-Sent Events, World Wide Web Consortium CR CR- 593 eventsource-20121211", February 2015, 594 . 596 [yang-push] 597 Clemm, A., Voit, E., Gonzalez Prieto, A., Prasad Tripathy, 598 A., Nilsen-Nygaard, E., Bierman, A., and B. Lengyel, 599 "Subscribing to YANG datastore push updates", March 2017, 600 . 603 Appendix A. End-to-End Deployment Guidance 605 Several technologies are expected to be seen within a deployment to 606 achieve security and ease-of-use requirements. These are not 607 necessary for an implementation of this specification, but will be 608 useful to consider when considering the operational context. 610 A.1. Call Home 612 Implementations should include the ability to transparently 613 incorporate 'call home' [RFC8071] so that secure TLS connections can 614 originate from the desired device. 616 A.2. TLS Heartbeat 618 HTTP sessions might not quickly allow a Subscriber to recognize when 619 the communication path has been lost from the Publisher. To 620 recognize this, it is possible for a Receiver to establish a TLS 621 heartbeat [RFC6520]. In the case where a TLS heartbeat is included, 622 it should be sent just from Receiver to Publisher. Loss of the 623 heartbeat should result in any Subscription related TCP sessions 624 between those endpoints being torn down. The subscription can then 625 attempt to re-establish. 627 Appendix B. RESTCONF over GRPC 629 An initial goal for this document was to support [GRPC] transport 630 seamlessly without any mapping or extra layering. However there is 631 an incompatibility of RESTCONF and GRPC. RESTCONF uses HTTP GET, and 632 GRPC uses HTTP2's POST rather than GET. As GET is used across 633 RESTCONF for things like capabilities exchange, a seamless mapping 634 depends on specification changes outside the scope of this document. 635 If/when GRPC supports GET, or RESTCONF is updated to support POST, 636 this should be revisited. It is hoped that the resulting fix will be 637 transparent to this document. 639 Appendix C. Changes between revisions 641 (To be removed by RFC editor prior to publication) 643 v01 - v03 645 o Terminoology aligned with draft-voit-netconf-notification- 646 messages. 648 o Tweaks to wording/capitalization/format. 650 v01 - v02 652 o Removed sections now redundant with [sn] and [yang-push] such as: 653 mechanisms for subscription maintenance, terminology definitions, 654 stream discovery. 656 o 3rd party subscriptions are out-of-scope. 658 o SSE only used with Restconf and HTTP1.1 Dynamic Subscriptions 660 o Timeframes for event tagging are self-defined. 662 o Clean-up of wording, references to terminology, section numbers. 664 v00 - v01 666 o Removed the ability for more than one subscription to go to a 667 single HTTP2 stream. 669 o Updated call flows. Extensively. 671 o SSE only used with Restconf and HTTP1.1 Dynamic Subscriptions 673 o HTTP is not used to determine that a Receiver has gone silent and 674 is not Receiving Event Notifications 676 o Many clean-ups of wording and terminology 678 Authors' Addresses 680 Eric Voit 681 Cisco Systems 683 Email: evoit@cisco.com 685 Ambika Prasad Tripathy 686 Cisco Systems 688 Email: ambtripa@cisco.com 690 Einar Nilsen-Nygaard 691 Cisco Systems 693 Email: einarnn@cisco.com 695 Alexander Clemm 696 Huawei 698 Email: ludwig@clemm.org 700 Alberto Gonzalez Prieto 701 VMWare 703 Email: agonzalezpri@vmware.com 704 Andy Bierman 705 YumaWorks 707 Email: andy@yumaworks.com