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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) -- Possible downref: Non-RFC (?) normative reference: ref. 'CRC16' ** Obsolete normative reference: RFC 4960 (Obsoleted by RFC 9260) ** Obsolete normative reference: RFC 7049 (Obsoleted by RFC 8949) -- Possible downref: Non-RFC (?) normative reference: ref. 'SABR' -- Possible downref: Non-RFC (?) normative reference: ref. 'UTC' Summary: 2 errors (**), 0 flaws (~~), 2 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Delay-Tolerant Networking Working Group S. Burleigh 2 Internet Draft JPL, Calif. Inst. Of Technology 3 Intended status: Standards Track K. Fall 4 Expires: January 29, 2021 Roland Computing Services 5 E. Birrane 6 APL, Johns Hopkins University 7 July 28, 2020 9 Bundle Protocol Version 7 10 draft-ietf-dtn-bpbis-26.txt 12 Status of this Memo 14 This Internet-Draft is submitted in full conformance with the 15 provisions of BCP 78 and BCP 79. 17 Internet-Drafts are working documents of the Internet Engineering 18 Task Force (IETF), its areas, and its working groups. Note that 19 other groups may also distribute working documents as Internet- 20 Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six 23 months and may be updated, replaced, or obsoleted by other documents 24 at any time. It is inappropriate to use Internet-Drafts as 25 reference material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/ietf/1id-abstracts.txt 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html 33 This Internet-Draft will expire on January 29, 2021. 35 Copyright Notice 37 Copyright (c) 2020 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with 45 respect to this document. Code Components extracted from this 46 document must include Simplified BSD License text as described in 47 Section 4.e of the Trust Legal Provisions and are provided without 48 warranty as described in the Simplified BSD License. 50 Abstract 52 This Internet Draft presents a specification for the Bundle 53 Protocol, adapted from the experimental Bundle Protocol 54 specification developed by the Delay-Tolerant Networking Research 55 group of the Internet Research Task Force and documented in RFC 56 5050. 58 Table of Contents 60 1. Introduction...................................................3 61 2. Conventions used in this document..............................5 62 3. Service Description............................................5 63 3.1. Definitions...............................................5 64 3.2. Discussion of BP concepts.................................9 65 3.3. Services Offered by Bundle Protocol Agents...............12 66 4. Bundle Format.................................................13 67 4.1. BP Fundamental Data Structures...........................13 68 4.1.1. CRC Type............................................13 69 4.1.2. CRC.................................................14 70 4.1.3. Bundle Processing Control Flags.....................14 71 4.1.4. Block Processing Control Flags......................16 72 4.1.5. Identifiers.........................................17 73 4.1.5.1. Endpoint ID....................................17 74 4.1.5.1.1. The "dtn" URI scheme......................18 75 4.1.5.1.2. The "ipn" URI scheme......................19 76 4.1.5.2. Node ID........................................21 77 4.1.6. DTN Time............................................21 78 4.1.7. Creation Timestamp..................................22 79 4.1.8. Block-type-specific Data............................22 80 4.2. Bundle Representation....................................22 81 4.2.1. Bundle..............................................23 82 4.2.2. Primary Bundle Block................................23 83 4.2.3. Canonical Bundle Block Format.......................26 84 4.3. Extension Blocks.........................................27 85 4.3.1. Previous Node.......................................27 86 4.3.2. Bundle Age..........................................27 87 4.3.3. Hop Count...........................................28 88 5. Bundle Processing.............................................28 89 5.1. Generation of Administrative Records.....................28 90 5.2. Bundle Transmission......................................29 91 5.3. Bundle Dispatching.......................................30 92 5.4. Bundle Forwarding........................................30 93 5.4.1. Forwarding Contraindicated..........................32 94 5.4.2. Forwarding Failed...................................33 95 5.5. Bundle Expiration........................................33 96 5.6. Bundle Reception.........................................33 97 5.7. Local Bundle Delivery....................................34 98 5.8. Bundle Fragmentation.....................................35 99 5.9. Application Data Unit Reassembly.........................37 100 5.10. Bundle Deletion.........................................37 101 5.11. Discarding a Bundle.....................................37 102 5.12. Canceling a Transmission................................38 103 6. Administrative Record Processing..............................38 104 6.1. Administrative Records...................................38 105 6.1.1. Bundle Status Reports...............................39 106 6.2. Generation of Administrative Records.....................42 107 7. Services Required of the Convergence Layer....................42 108 7.1. The Convergence Layer....................................42 109 7.2. Summary of Convergence Layer Services....................42 110 8. Implementation Status.........................................43 111 9. Security Considerations.......................................45 112 10. IANA Considerations..........................................46 113 10.1. Bundle Block Types......................................46 114 10.2. Primary Bundle Protocol Version.........................47 115 10.3. Bundle Processing Control Flags.........................47 116 10.4. Block Processing Control Flags..........................50 117 10.5. Bundle Status Report Reason Codes.......................51 118 10.6. Bundle Protocol URI scheme types........................52 119 10.7. URI scheme "dtn"........................................54 120 10.8. URI scheme "ipn"........................................54 121 11. References...................................................55 122 11.1. Normative References....................................55 123 11.2. Informative References..................................56 124 12. Acknowledgments..............................................57 125 13. Significant Changes from RFC 5050............................57 126 Appendix A. For More Information.................................58 127 Appendix B. CDDL expression......................................59 129 1. Introduction 131 Since the publication of the Bundle Protocol Specification 132 (Experimental RFC 5050 [RFC5050]) in 2007, the Delay-Tolerant 133 Networking (DTN) Bundle Protocol has been implemented in multiple 134 programming languages and deployed to a wide variety of computing 135 platforms. This implementation and deployment experience has 136 identified opportunities for making the protocol simpler, more 137 capable, and easier to use. The present document, standardizing the 138 Bundle Protocol (BP), is adapted from RFC 5050 in that context, 139 reflecting lessons learned. Significant changes from the Bundle 140 Protocol specification defined in RFC 5050 are listed in section 13. 142 This document describes version 7 of BP. 144 Delay Tolerant Networking is a network architecture providing 145 communications in and/or through highly stressed environments. 146 Stressed networking environments include those with intermittent 147 connectivity, large and/or variable delays, and high bit error 148 rates. To provide its services, BP may be viewed as sitting at the 149 application layer of some number of constituent networks, forming a 150 store-carry-forward overlay network. Key capabilities of BP 151 include: 153 . Ability to use physical motility for the movement of data 154 . Ability to move the responsibility for error control from one 155 node to another 156 . Ability to cope with intermittent connectivity, including cases 157 where the sender and receiver are not concurrently present in 158 the network 159 . Ability to take advantage of scheduled, predicted, and 160 opportunistic connectivity, whether bidirectional or 161 unidirectional, in addition to continuous connectivity 162 . Late binding of overlay network endpoint identifiers to 163 underlying constituent network addresses 165 For descriptions of these capabilities and the rationale for the DTN 166 architecture, see [ARCH] and [SIGC]. 168 BP's location within the standard protocol stack is as shown in 169 Figure 1. BP uses underlying "native" transport and/or network 170 protocols for communications within a given constituent network. 171 The layer at which those underlying protocols are located is here 172 termed the "convergence layer" and the interface between the bundle 173 protocol and a specific underlying protocol is termed a "convergence 174 layer adapter". 176 Figure 1 shows three distinct transport and network protocols 177 (denoted T1/N1, T2/N2, and T3/N3). 179 +-----------+ +-----------+ 180 | BP app | | BP app | 181 +---------v-| +->>>>>>>>>>v-+ +->>>>>>>>>>v-+ +-^---------+ 182 | BP v | | ^ BP v | | ^ BP v | | ^ BP | 183 +---------v-+ +-^---------v-+ +-^---------v-+ +-^---------+ 184 | T1 v | + ^ T1/T2 v | + ^ T2/T3 v | | ^ T3 | 185 +---------v-+ +-^---------v-+ +-^---------v + +-^---------+ 186 | N1 v | | ^ N1/N2 v | | ^ N2/N3 v | | ^ N3 | 187 +---------v-+ +-^---------v + +-^---------v-+ +-^---------+ 188 | >>>>>>>>^ >>>>>>>>>>^ >>>>>>>>^ | 189 +-----------+ +-------------+ +-------------+ +-----------+ 190 | | | | 191 |<---- A network ---->| |<---- A network ---->| 192 | | | | 194 Figure 1: The Bundle Protocol in the Protocol Stack Model 196 This document describes the format of the protocol data units 197 (called "bundles") passed between entities participating in BP 198 communications. 200 The entities are referred to as "bundle nodes". This document does 201 not address: 203 . Operations in the convergence layer adapters that bundle nodes 204 use to transport data through specific types of internets. 205 (However, the document does discuss the services that must be 206 provided by each adapter at the convergence layer.) 207 . The bundle route computation algorithm. 208 . Mechanisms for populating the routing or forwarding information 209 bases of bundle nodes. 210 . The mechanisms for securing bundles en route. 211 . The mechanisms for managing bundle nodes. 213 Note that implementations of the specification presented in this 214 document will not be interoperable with implementations of RFC 5050. 216 2. Conventions used in this document 218 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 219 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 220 "OPTIONAL" in this document are to be interpreted as described in 221 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 222 capitals, as shown here. 224 3. Service Description 226 3.1. Definitions 228 Bundle - A bundle is a protocol data unit of BP, so named because 229 negotiation of the parameters of a data exchange may be impractical 230 in a delay-tolerant network: it is often better practice to "bundle" 231 with a unit of application data all metadata that might be needed in 232 order to make the data immediately usable when delivered to the 233 application. Each bundle comprises a sequence of two or more 234 "blocks" of protocol data, which serve various purposes. 236 Block - A bundle protocol block is one of the protocol data 237 structures that together constitute a well-formed bundle. 239 Application Data Unit (ADU) - An application data unit is the unit 240 of data whose conveyance to the bundle's destination is the purpose 241 for the transmission of some bundle that is not a fragment (as 242 defined below). 244 Bundle payload - A bundle payload (or simply "payload") is the 245 content of the bundle's payload block. The terms "bundle content", 246 "bundle payload", and "payload" are used interchangeably in this 247 document. For a bundle that is not a fragment (as defined below), 248 the payload is an application data unit. 250 Partial payload - A partial payload is a payload that comprises 251 either the first N bytes or the last N bytes of some other payload 252 of length M, such that 0 < N < M. Note that every partial payload 253 is a payload and therefore can be further subdivided into partial 254 payloads. 256 Fragment - A fragment is a bundle whose payload block contains a 257 partial payload. 259 Bundle node - A bundle node (or, in the context of this document, 260 simply a "node") is any entity that can send and/or receive bundles. 261 Each bundle node has three conceptual components, defined below, as 262 shown in Figure 2: a "bundle protocol agent", a set of zero or more 263 "convergence layer adapters", and an "application agent". ("CL1 264 PDUs" are the PDUs of the convergence-layer protocol used in network 265 1.) 267 +-----------------------------------------------------------+ 268 |Node | 269 | | 270 | +-------------------------------------------------------+ | 271 | |Application Agent | | 272 | | | | 273 | | +--------------------------+ +----------------------+ | | 274 | | |Administrative element | |Application-specific | | | 275 | | | | |element | | | 276 | | | | | | | | 277 | | +--------------------------+ +----------------------+ | | 278 | | ^ ^ | | 279 | | Admin|records Application|data | | 280 | | | | | | 281 | +----------------v--------------------------v-----------+ | 282 | ^ | 283 | | ADUs | 284 | | | 285 | +-----------------------------v-------------------------+ | 286 | |Bundle Protocol Agent | | 287 | | | | 288 | | | | 289 | +-------------------------------------------------------+ | 290 | ^ ^ ^ | 291 | | Bundles | Bundles Bundles | | 292 | | | | | 293 | +------v-----+ +-----v------+ +-----v-----+ | 294 | |CLA 1 | |CLA 2 | |CLA n | | 295 | | | | | . . . | | | 296 | | | | | | | | 297 +-+------------+-----+------------+-----------+-----------+-+ 298 ^ ^ ^ 299 CL1|PDUs CL2|PDUs CLn|PDUs 300 | | | 301 +------v-----+ +-----v------+ +-----v-----+ 302 Network 1 Network 2 Network n 304 Figure 2: Components of a Bundle Node 306 Bundle protocol agent - The bundle protocol agent (BPA) of a node is 307 the node component that offers the BP services and executes the 308 procedures of the bundle protocol. 310 Convergence layer adapter - A convergence layer adapter (CLA) is a 311 node component that sends and receives bundles on behalf of the BPA, 312 utilizing the services of some 'native' protocol stack that is 313 supported in one of the networks within which the node is 314 functionally located. 316 Application agent - The application agent (AA) of a node is the node 317 component that utilizes the BP services to effect communication for 318 some user purpose. The application agent in turn has two elements, 319 an administrative element and an application-specific element. 321 Application-specific element - The application-specific element of 322 an AA is the node component that constructs, requests transmission 323 of, accepts delivery of, and processes units of user application 324 data. 326 Administrative element - The administrative element of an AA is the 327 node component that constructs and requests transmission of 328 administrative records (defined below), including status reports, 329 and accepts delivery of and processes any administrative records 330 that the node receives. 332 Administrative record - A BP administrative record is an application 333 data unit that is exchanged between the administrative elements of 334 nodes' application agents for some BP administrative purpose. The 335 only administrative record defined in this specification is the 336 status report, discussed later. 338 Bundle endpoint - A bundle endpoint (or simply "endpoint") is a set 339 of zero or more bundle nodes that all identify themselves for BP 340 purposes by some common identifier, called a "bundle endpoint ID" 341 (or, in this document, simply "endpoint ID"; endpoint IDs are 342 described in detail in Section 4.5.5.1 below. 344 Singleton endpoint - A singleton endpoint is an endpoint that always 345 contains exactly one member. 347 Registration - A registration is the state machine characterizing a 348 given node's membership in a given endpoint. Any single 349 registration has an associated delivery failure action as defined 350 below and must at any time be in one of two states: Active or 351 Passive. Registrations are local; information about a node's 352 registrations is not expected to be available at other nodes, and 353 the Bundle Protocol does not include a mechanism for distributing 354 information about registrations. 356 Delivery - A bundle is considered to have been delivered at a node 357 subject to a registration as soon as the application data unit that 358 is the payload of the bundle, together with any relevant metadata 359 (an implementation matter), has been presented to the node's 360 application agent in a manner consistent with the state of that 361 registration. 363 Deliverability - A bundle is considered "deliverable" subject to a 364 registration if and only if (a) the bundle's destination endpoint is 365 the endpoint with which the registration is associated, (b) the 366 bundle has not yet been delivered subject to this registration, and 367 (c) the bundle has not yet been "abandoned" (as defined below) 368 subject to this registration. 370 Abandonment - To abandon a bundle subject to some registration is to 371 assert that the bundle is not deliverable subject to that 372 registration. 374 Delivery failure action - The delivery failure action of a 375 registration is the action that is to be taken when a bundle that is 376 "deliverable" subject to that registration is received at a time 377 when the registration is in the Passive state. 379 Destination - The destination of a bundle is the endpoint comprising 380 the node(s) at which the bundle is to be delivered (as defined 381 above). 383 Transmission - A transmission is an attempt by a node's BPA to cause 384 copies of a bundle to be delivered to one or more of the nodes that 385 are members of some endpoint (the bundle's destination) in response 386 to a transmission request issued by the node's application agent. 388 Forwarding - To forward a bundle to a node is to invoke the services 389 of one or more CLAs in a sustained effort to cause a copy of the 390 bundle to be received by that node. 392 Discarding - To discard a bundle is to cease all operations on the 393 bundle and functionally erase all references to it. The specific 394 procedures by which this is accomplished are an implementation 395 matter. 397 Retention constraint - A retention constraint is an element of the 398 state of a bundle that prevents the bundle from being discarded. 399 That is, a bundle cannot be discarded while it has any retention 400 constraints. 402 Deletion - To delete a bundle is to remove unconditionally all of 403 the bundle's retention constraints, enabling the bundle to be 404 discarded. 406 3.2. Discussion of BP concepts 408 Multiple instances of the same bundle (the same unit of DTN protocol 409 data) might exist concurrently in different parts of a network -- 410 possibly differing in some blocks -- in the memory local to one or 411 more bundle nodes and/or in transit between nodes. In the context of 412 the operation of a bundle node, a bundle is an instance (copy), in 413 that node's local memory, of some bundle that is in the network. 415 The payload for a bundle forwarded in response to a bundle 416 transmission request is the application data unit whose location is 417 provided as a parameter to that request. The payload for a bundle 418 forwarded in response to reception of a bundle is the payload of the 419 received bundle. 421 In the most familiar case, a bundle node is instantiated as a single 422 process running on a general-purpose computer, but in general the 423 definition is meant to be broader: a bundle node might alternatively 424 be a thread, an object in an object-oriented operating system, a 425 special-purpose hardware device, etc. 427 The manner in which the functions of the BPA are performed is wholly 428 an implementation matter. For example, BPA functionality might be 429 coded into each node individually; it might be implemented as a 430 shared library that is used in common by any number of bundle nodes 431 on a single computer; it might be implemented as a daemon whose 432 services are invoked via inter-process or network communication by 433 any number of bundle nodes on one or more computers; it might be 434 implemented in hardware. 436 Every CLA implements its own thin layer of protocol, interposed 437 between BP and the (usually "top") protocol(s) of the underlying 438 native protocol stack; this "CL protocol" may only serve to 439 multiplex and de-multiplex bundles to and from the underlying native 440 protocol, or it may offer additional CL-specific functionality. The 441 manner in which a CLA sends and receives bundles, as well as the 442 definitions of CLAs and CL protocols, are beyond the scope of this 443 specification. 445 Note that the administrative element of a node's application agent 446 may itself, in some cases, function as a convergence-layer adapter. 447 That is, outgoing bundles may be "tunneled" through encapsulating 448 bundles: 450 . An outgoing bundle constitutes a byte array. This byte array 451 may, like any other, be presented to the bundle protocol agent 452 as an application data unit that is to be transmitted to some 453 endpoint. 454 . The original bundle thus forms the payload of an encapsulating 455 bundle that is forwarded using some other convergence-layer 456 protocol(s). 457 . When the encapsulating bundle is received, its payload is 458 delivered to the peer application agent administrative element, 459 which then instructs the bundle protocol agent to dispatch that 460 original bundle in the usual way. 462 The purposes for which this technique may be useful (such as cross- 463 domain security) are beyond the scope of this specification. 465 The only interface between the BPA and the application-specific 466 element of the AA is the BP service interface. But between the BPA 467 and the administrative element of the AA there is a (conceptual) 468 private control interface in addition to the BP service interface. 469 This private control interface enables the BPA and the 470 administrative element of the AA to direct each other to take action 471 under specific circumstances. 473 In the case of a node that serves simply as a BP "router", the AA 474 may have no application-specific element at all. The application- 475 specific elements of other nodes' AAs may perform arbitrarily 476 complex application functions, perhaps even offering multiplexed DTN 477 communication services to a number of other applications. As with 478 the BPA, the manner in which the AA performs its functions is wholly 479 an implementation matter. 481 Singletons are the most familiar sort of endpoint, but in general 482 the endpoint notion is meant to be broader. For example, the nodes 483 in a sensor network might constitute a set of bundle nodes that are 484 all registered in a single common endpoint and will all receive any 485 data delivered at that endpoint. *Note* too that any given bundle 486 node might be registered in multiple bundle endpoints and receive 487 all data delivered at each of those endpoints. 489 Recall that every node, by definition, includes an application agent 490 which in turn includes an administrative element, which exchanges 491 administrative records with the administrative elements of other 492 nodes. As such, every node is permanently, structurally registered 493 in the singleton endpoint at which administrative records received 494 from other nodes are delivered. Registration in no other endpoint 495 can ever be assumed to be permanent. This endpoint, termed the 496 node's "administrative endpoint", is therefore uniquely and 497 permanently associated with the node, and for this reason the ID of 498 a node's administrative endpoint additionally serves as the "node 499 ID" (see 4.1.5.2 below) of the node. 501 The destination of every bundle is an endpoint, which may or may not 502 be singleton. The source of every bundle is a node, identified by 503 node ID. Note, though, that the source node ID asserted in a given 504 bundle may be the null endpoint ID (as described later) rather than 505 the ID of the source node; bundles for which the asserted source 506 node ID is the null endpoint ID are termed "anonymous" bundles. 508 Any number of transmissions may be concurrently undertaken by the 509 bundle protocol agent of a given node. 511 When the bundle protocol agent of a node determines that a bundle 512 must be forwarded to a node (either to a node that is a member of 513 the bundle's destination endpoint or to some intermediate forwarding 514 node) in the course of completing the successful transmission of 515 that bundle, the bundle protocol agent invokes the services of one 516 or more CLAs in a sustained effort to cause a copy of the bundle to 517 be received by that node. 519 Upon reception, the processing of a bundle that has been received by 520 a given node depends on whether or not the receiving node is 521 registered in the bundle's destination endpoint. If it is, and if 522 the payload of the bundle is non-fragmentary (possibly as a result 523 of successful payload reassembly from fragmentary payloads, 524 including the original payload of the newly received bundle), then 525 the bundle is normally delivered to the node's application agent 526 subject to the registration characterizing the node's membership in 527 the destination endpoint. 529 The bundle protocol does not natively ensure delivery of a bundle to 530 its destination. Data loss along the path to the destination node 531 can be minimized by utilizing reliable convergence-layer protocols 532 between neighbors on all segments of the end-to-end path, but for 533 end-to-end bundle delivery assurance it will be necessary to develop 534 extensions to the bundle protocol and/or application-layer 535 mechanisms. 537 The bundle protocol is designed for extensibility. Bundle protocol 538 extensions, documented elsewhere, may extend this specification by: 540 . defining additional blocks; 541 . defining additional administrative records; 542 . defining additional bundle processing flags; 543 . defining additional block processing flags; 544 . defining additional types of bundle status reports; 545 . defining additional bundle status report reason codes; 546 . defining additional mandates and constraints on processing 547 that conformant bundle protocol agents must perform at 548 specified points in the inbound and outbound bundle processing 549 cycles. 551 3.3. Services Offered by Bundle Protocol Agents 553 The BPA of each node is expected to provide the following services 554 to the node's application agent: 556 . commencing a registration (registering the node in an 557 endpoint); 558 . terminating a registration; 559 . switching a registration between Active and Passive states; 560 . transmitting a bundle to an identified bundle endpoint; 561 . canceling a transmission; 562 . polling a registration that is in the Passive state; 563 . delivering a received bundle. 565 Note that the details of registration functionality are an 566 implementation matter and are beyond the scope of this 567 specification. 569 4. Bundle Format 571 The format of bundles SHALL conform to the Concise Binary Object 572 Representation (CBOR [RFC7049]). 574 Each bundle SHALL be a concatenated sequence of at least two blocks, 575 represented as a CBOR indefinite-length array. The first block in 576 the sequence (the first item of the array) MUST be a primary bundle 577 block in CBOR representation as described below; the bundle MUST 578 have exactly one primary bundle block. The primary block MUST be 579 followed by one or more canonical bundle blocks (additional array 580 items) in CBOR representation as described in 4.2.3 below. The last 581 such block MUST be a payload block; the bundle MUST have exactly one 582 payload block. The payload block SHALL be followed by a CBOR 583 "break" stop code, terminating the array. 585 (Note that, while CBOR permits considerable flexibility in the 586 encoding of bundles, this flexibility must not be interpreted as 587 inviting increased complexity in protocol data unit structure.) 589 An implementation of the Bundle Protocol MAY discard any sequence of 590 bytes that does not conform to the Bundle Protocol specification. 592 An implementation of the Bundle Protocol MAY accept a sequence of 593 bytes that does not conform to the Bundle Protocol specification 594 (e.g., one that represents data elements in fixed-length arrays 595 rather than indefinite-length arrays) and transform it into 596 conformant BP structure before processing it. Procedures for 597 accomplishing such a transformation are beyond the scope of this 598 specification. 600 4.1. BP Fundamental Data Structures 602 4.1.1. CRC Type 604 CRC type is an unsigned integer type code for which the following 605 values (and no others) are valid: 607 . 0 indicates "no CRC is present." 608 . 1 indicates "a standard X-25 CRC-16 is present." [CRC16] 609 . 2 indicates "a standard CRC32C (Castagnoli) CRC-32 is present." 610 [RFC4960] 612 CRC type SHALL be represented as a CBOR unsigned integer. 614 For examples of CRC32C CRCs, see Appendix A.4 of [RFC7143]. 616 Note that more robust protection of BP data integrity, as needed, 617 may be provided by means of Block Integrity Blocks as defined in the 618 Bundle Security Protocol [BPSEC]). 620 4.1.2. CRC 622 CRC SHALL be omitted from a block if and only if the block's CRC 623 type code is zero. 625 When not omitted, the CRC SHALL be represented as a CBOR byte string 626 of two bytes (that is, CBOR additional information 2, if CRC type is 627 1) or of four bytes (that is, CBOR additional information 4, if CRC 628 type is 2); in each case the sequence of bytes SHALL constitute an 629 unsigned integer value (of 16 or 32 bits, respectively) in network 630 byte order. 632 4.1.3. Bundle Processing Control Flags 634 Bundle processing control flags assert properties of the bundle as a 635 whole rather than of any particular block of the bundle. They are 636 conveyed in the primary block of the bundle. 638 The following properties are asserted by the bundle processing 639 control flags: 641 . The bundle is a fragment. (Boolean) 643 . The bundle's payload is an administrative record. (Boolean) 645 . The bundle must not be fragmented. (Boolean) 647 . Acknowledgment by the user application is requested. (Boolean) 649 . Status time is requested in all status reports. (Boolean) 651 . Flags requesting types of status reports (all Boolean): 653 o Request reporting of bundle reception. 655 o Request reporting of bundle forwarding. 657 o Request reporting of bundle delivery. 659 o Request reporting of bundle deletion. 661 If the bundle processing control flags indicate that the bundle's 662 application data unit is an administrative record, then all status 663 report request flag values MUST be zero. 665 If the bundle's source node is omitted (i.e., the source node ID is 666 the ID of the null endpoint, which has no members as discussed 667 below; this option enables anonymous bundle transmission), then the 668 bundle is not uniquely identifiable and all bundle protocol features 669 that rely on bundle identity must therefore be disabled: the "Bundle 670 must not be fragmented" flag value MUST be 1 and all status report 671 request flag values MUST be zero. 673 Bundle processing control flags that are unrecognized MUST be 674 ignored, as future definitions of additional flags might not be 675 integrated simultaneously into the Bundle Protocol implementations 676 operating at all nodes. 678 The bundle processing control flags SHALL be represented as a CBOR 679 unsigned integer item, the value of which SHALL be processed as a 680 bit field indicating the control flag values as follows (note that 681 bit numbering in this instance is reversed from the usual practice, 682 beginning with the low-order bit instead of the high-order bit, in 683 recognition of the potential definition of additional control flag 684 values in the future): 686 . Bit 0 (the low-order bit, 0x000001): bundle is a fragment. 687 . Bit 1 (0x000002): payload is an administrative record. 688 . Bit 2 (0x000004): bundle must not be fragmented. 689 . Bit 3 (0x000008): reserved. 690 . Bit 4 (0x000010): reserved. 691 . Bit 5 (0x000020): user application acknowledgement is 692 requested. 693 . Bit 6 (0x000040): status time is requested in all status 694 reports. 695 . Bit 7 (0x000080): reserved. 696 . Bit 8 (0x000100): reserved. 697 . Bit 9 (0x000200): reserved. 698 . Bit 10(0x000400): reserved. 699 . Bit 11(0x000800): reserved. 700 . Bit 12(0x001000): reserved. 701 . Bit 13(0x002000): reserved. 702 . Bit 14(0x004000): bundle reception status reports are 703 requested. 705 . Bit 15(0x008000): reserved. 706 . Bit 16(0x010000): bundle forwarding status reports are 707 requested. 708 . Bit 17(0x020000): bundle delivery status reports are requested. 709 . Bit 18(0x040000): bundle deletion status reports are requested. 710 . Bits 19-20 are reserved. 711 . Bits 21-63 are unassigned. 713 4.1.4. Block Processing Control Flags 715 The block processing control flags assert properties of canonical 716 bundle blocks. They are conveyed in the header of the block to 717 which they pertain. 719 Block processing control flags that are unrecognized MUST be 720 ignored, as future definitions of additional flags might not be 721 integrated simultaneously into the Bundle Protocol implementations 722 operating at all nodes. 724 The block processing control flags SHALL be represented as a CBOR 725 unsigned integer item, the value of which SHALL be processed as a 726 bit field indicating the control flag values as follows (note that 727 bit numbering in this instance is reversed from the usual practice, 728 beginning with the low-order bit instead of the high-order bit, for 729 agreement with the bit numbering of the bundle processing control 730 flags): 732 . Bit 0(the low-order bit, 0x01): block must be replicated in 733 every fragment. 734 . Bit 1(0x02): transmission of a status report is requested if 735 block can't be processed. 736 . Bit 2(0x04): bundle must be deleted if block can't be 737 processed. 738 . Bit 3(0x08): reserved. 739 . Bit 4(0x10): block must be removed from bundle if it can't be 740 processed. 741 . Bit 5(0x20): reserved. 742 . Bit 6 (0x40): reserved. 743 . Bits 7-63 are unassigned. 745 For each bundle whose bundle processing control flags indicate that 746 the bundle's application data unit is an administrative record, or 747 whose source node ID is the null endpoint ID as defined below, the 748 value of the "Transmit status report if block can't be processed" 749 flag in every canonical block of the bundle MUST be zero. 751 4.1.5. Identifiers 753 4.1.5.1. Endpoint ID 755 The destinations of bundles are bundle endpoints, identified by text 756 strings termed "endpoint IDs" (see Section 3.1). Each endpoint ID 757 (EID) is a Uniform Resource Identifier (URI; [URI]). As such, each 758 endpoint ID can be characterized as having this general structure: 760 < scheme name > : < scheme-specific part, or "SSP" > 762 The scheme identified by the < scheme name > in an endpoint ID is a 763 set of syntactic and semantic rules that fully explain how to parse 764 and interpret the SSP. Each scheme that may be used to form a BP 765 endpoint ID must be added to the registry of URI scheme code numbers 766 for Bundle Protocol maintained by IANA as described in Section 10; 767 association of a unique URI scheme code number with each scheme name 768 in this registry helps to enable compact representation of endpoint 769 IDs in bundle blocks. Note that the set of allowable schemes is 770 effectively unlimited. Any scheme conforming to [URIREG] may be 771 added to the URI scheme code number registry and thereupon used in a 772 bundle protocol endpoint ID. 774 Each entry in the URI scheme code number registry MUST contain a 775 reference to a scheme code number definition document, which defines 776 the manner in which the scheme-specific part of any URI formed in 777 that scheme is parsed and interpreted and MUST be encoded, in CBOR 778 representation, for transmission as a BP endpoint ID. The scheme 779 code number definition document may also contain information as to 780 (a) which convergence-layer protocol(s) may be used to forward a 781 bundle to a BP destination endpoint identified by such an ID, and 782 (b) how the ID of the convergence-layer protocol endpoint to use for 783 that purpose can be inferred from that destination endpoint ID. 785 Note that, although endpoint IDs are URIs, implementations of the BP 786 service interface may support expression of endpoint IDs in some 787 internationalized manner (e.g., Internationalized Resource 788 Identifiers (IRIs); see [RFC3987]). 790 Each BP endpoint ID (EID) SHALL be represented as a CBOR array 791 comprising two items. 793 The first item of the array SHALL be the code number identifying the 794 endpoint ID's URI scheme, as defined in the registry of URI scheme 795 code numbers for Bundle Protocol. Each URI scheme code number SHALL 796 be represented as a CBOR unsigned integer. 798 The second item of the array SHALL be the applicable CBOR 799 representation of the scheme-specific part (SSP) of the EID, defined 800 as noted in the specification for the EID's URI scheme. 802 4.1.5.1.1. The "dtn" URI scheme 804 The "dtn" scheme supports the identification of BP endpoints by 805 arbitrarily expressive character strings. It is specified as 806 follows: 808 Scheme syntax: This specification uses the Augmented Backus-Naur 809 Form (ABNF) notation of [RFC5234]. 811 dtn-uri = "dtn:" dtn-hier-part 813 dtn-hier-part = "//" node-name name-delim demux ; a path-rootless 815 node-name = 1*VCHAR 817 name-delim = "/" 819 demux = *VCHAR 821 Scheme semantics: URIs of the DTN scheme are used as endpoint 822 identifiers in the Delay-Tolerant Networking (DTN) Bundle Protocol 823 (BP) as described in the present document. 825 The endpoint ID "dtn:none" identifies the "null endpoint", the 826 endpoint that by definition never has any members. 828 All BP endpoints identified by all other dtn-scheme endpoint IDs for 829 which the first character of demux is a character other than '~' 830 (tilde) are singleton endpoints. All BP endpoints identified by dtn- 831 scheme endpoint IDs for which the first character *is* '~' (tilde) 832 are *not* singleton endpoints. 834 A dtn-scheme endpoint ID for which the demux is of length zero MAY 835 identify the administrative endpoint for the node identified by 836 node-name, and as such may serve as a node ID. No dtn-scheme 837 endpoint ID for which the demux is of non-zero length may do so. 839 Encoding considerations: For transmission as a BP endpoint ID, the 840 scheme-specific part of a URI of the dtn scheme SHALL be represented 841 as a CBOR text string unless the EID's SSP is "none", in which case 842 the SSP SHALL be represented as a CBOR unsigned integer with the 843 value zero. For all other purposes, URIs of the dtn scheme are 844 encoded exclusively in US-ASCII characters. 846 Interoperability considerations: none. 848 Security considerations: 850 . Reliability and consistency: none of the BP endpoints 851 identified by the URIs of the DTN scheme are guaranteed to be 852 reachable at any time, and the identity of the processing 853 entities operating on those endpoints is never guaranteed by 854 the Bundle Protocol itself. Bundle authentication as defined by 855 the Bundle Security Protocol is required for this purpose. 856 . Malicious construction: malicious construction of a conformant 857 DTN-scheme URI is limited to the malicious selection of node 858 names and the malicious selection of demux strings. That is, a 859 maliciously constructed DTN-scheme URI could be used to direct 860 a bundle to an endpoint that might be damaged by the arrival of 861 that bundle or, alternatively, to declare a false source for a 862 bundle and thereby cause incorrect processing at a node that 863 receives the bundle. In both cases (and indeed in all bundle 864 processing), the node that receives a bundle should verify its 865 authenticity and validity before operating on it in any way. 866 . Back-end transcoding: the limited expressiveness of URIs of the 867 DTN scheme effectively eliminates the possibility of threat due 868 to errors in back-end transcoding. 869 . Rare IP address formats: not relevant, as IP addresses do not 870 appear anywhere in conformant DTN-scheme URIs. 871 . Sensitive information: because DTN-scheme URIs are used only to 872 represent the identities of Bundle Protocol endpoints, the risk 873 of disclosure of sensitive information due to interception of 874 these URIs is minimal. Examination of DTN-scheme URIs could be 875 used to support traffic analysis; where traffic analysis is a 876 plausible danger, bundles should be conveyed by secure 877 convergence-layer protocols that do not expose endpoint IDs. 878 . Semantic attacks: the simplicity of DTN-scheme URI syntax 879 minimizes the possibility of misinterpretation of a URI by a 880 human user. 882 4.1.5.1.2. The "ipn" URI scheme 884 The "ipn" scheme supports the identification of BP endpoints by 885 pairs of unsigned integers, for compact representation in bundle 886 blocks. It is specified as follows: 888 Scheme syntax: This specification uses the Augmented Backus-Naur 889 Form (ABNF) notation of [RFC5234], including the core ABNF syntax 890 rule for DIGIT defined by that specification. 892 ipn-uri = "ipn:" ipn-hier-part 893 ipn-hier-part = node-nbr nbr-delim service-nbr ; a path-rootless 895 node-nbr = 1*DIGIT 897 nbr-delim = "." 899 service-nbr = 1*DIGIT 901 Scheme semantics: URIs of the ipn scheme are used as endpoint 902 identifiers in the Delay-Tolerant Networking (DTN) Bundle Protocol 903 (BP) as described in the present document. 905 All BP endpoints identified by ipn-scheme endpoint IDs are singleton 906 endpoints. 908 An ipn-scheme endpoint ID for which service-nbr is zero MAY identify 909 the administrative endpoint for the node identified by node-nbr, and 910 as such may serve as a node ID. No ipn-scheme endpoint ID for which 911 service-nbr is non-zero may do so. 913 Encoding considerations: For transmission as a BP endpoint ID, the 914 scheme-specific part of a URI of the dtn scheme the SSP SHALL be 915 represented as a CBOR array comprising two items. The first item of 916 this array SHALL be the EID's node number (a number that identifies 917 the node) represented as a CBOR unsigned integer. The second item 918 of this array SHALL be the EID's service number (a number that 919 identifies some application service) represented as a CBOR unsigned 920 integer. For all other purposes, URIs of the IPN scheme are encoded 921 exclusively in US-ASCII characters. 923 Interoperability considerations: none. 925 Security considerations: 927 . Reliability and consistency: none of the BP endpoints 928 identified by the URIs of the IPN scheme are guaranteed to be 929 reachable at any time, and the identity of the processing 930 entities operating on those endpoints is never guaranteed by 931 the Bundle Protocol itself. Bundle authentication as defined by 932 the Bundle Security Protocol [BPSEC] is required for this 933 purpose. 934 . Malicious construction: malicious construction of a conformant 935 IPN-scheme URI is limited to the malicious selection of node 936 numbers and the malicious selection of service numbers. That 937 is, a maliciously constructed IPN-scheme URI could be used to 938 direct a bundle to an endpoint that might be damaged by the 939 arrival of that bundle or, alternatively, to declare a false 940 source for a bundle and thereby cause incorrect processing at a 941 node that receives the bundle. In both cases (and indeed in 942 all bundle processing), the node that receives a bundle should 943 verify its authenticity and validity before operating on it in 944 any way. 945 . Back-end transcoding: the limited expressiveness of URIs of the 946 IPN scheme effectively eliminates the possibility of threat due 947 to errors in back-end transcoding. 948 . Rare IP address formats: not relevant, as IP addresses do not 949 appear anywhere in conformant IPN-scheme URIs. 950 . Sensitive information: because IPN-scheme URIs are used only to 951 represent the identities of Bundle Protocol endpoints, the risk 952 of disclosure of sensitive information due to interception of 953 these URIs is minimal. Examination of IPN-scheme URIs could be 954 used to support traffic analysis; where traffic analysis is a 955 plausible danger, bundles should be conveyed by secure 956 convergence-layer protocols that do not expose endpoint IDs. 957 . Semantic attacks: the simplicity of IPN-scheme URI syntax 958 minimizes the possibility of misinterpretation of a URI by a 959 human user. 961 4.1.5.2. Node ID 963 For many purposes of the Bundle Protocol it is important to identify 964 the node that is operative in some context. 966 As discussed in 3.1 above, nodes are distinct from endpoints; 967 specifically, an endpoint is a set of zero or more nodes. But 968 rather than define a separate namespace for node identifiers, we 969 instead use endpoint identifiers to identify nodes as discussed in 970 3.2 above. Formally: 972 . Every node is, by definition, permanently registered in the 973 singleton endpoint at which administrative records are 974 delivered to its application agent's administrative element, 975 termed the node's "administrative endpoint". 976 . As such, the EID of a node's administrative endpoint SHALL 977 uniquely identify that node. 978 . A "node ID" is an EID that identifies the administrative 979 endpoint of a node. 981 4.1.6. DTN Time 983 A DTN time is an unsigned integer indicating the number of 984 milliseconds that have elapsed since the start of the year 2000 on 985 the Coordinated Universal Time (UTC) scale [UTC]. Each DTN time 986 SHALL be represented as a CBOR unsigned integer item. 988 Implementers need to be aware that DTN time values conveyed in CBOR 989 representation in bundles will nearly always exceed (2**32 - 1). 991 4.1.7. Creation Timestamp 993 Each bundle's creation timestamp SHALL be represented as a CBOR 994 array comprising two items. 996 The first item of the array, termed "bundle creation time", SHALL be 997 the DTN time at which the transmission request was received that 998 resulted in the creation of the bundle, represented as a CBOR 999 unsigned integer. 1001 The second item of the array, termed the creation timestamp's 1002 "sequence number", SHALL be the latest value (as of the time at 1003 which the transmission request was received) of a monotonically 1004 increasing positive integer counter managed by the source node's 1005 bundle protocol agent, represented as a CBOR unsigned integer. The 1006 sequence counter MAY be reset to zero whenever the current time 1007 advances by one millisecond. 1009 For nodes that lack accurate clocks, it is recommended that bundle 1010 creation time be set to zero and that the counter used as the source 1011 of the bundle sequence count never be reset to zero. 1013 Note that, in general, the creation of two distinct bundles with the 1014 same source node ID and bundle creation timestamp may result in 1015 unexpected network behavior and/or suboptimal performance. The 1016 combination of source node ID and bundle creation timestamp serves 1017 to identify a single transmission request, enabling it to be 1018 acknowledged by the receiving application (provided the source node 1019 ID is not the null endpoint ID). 1021 4.1.8. Block-type-specific Data 1023 Block-type-specific data in each block (other than the primary 1024 block) SHALL be the applicable CBOR representation of the content of 1025 the block. Details of this representation are included in the 1026 specification defining the block type. 1028 4.2. Bundle Representation 1030 This section describes the primary block in detail and non-primary 1031 blocks in general. Rules for processing these blocks appear in 1032 Section 5 of this document. 1034 Note that supplementary DTN protocol specifications (including, but 1035 not restricted to, the Bundle Security Protocol [BPSEC]) may require 1036 that BP implementations conforming to those protocols construct and 1037 process additional blocks. 1039 4.2.1. Bundle 1041 Each bundle SHALL be represented as a CBOR indefinite-length array. 1042 The first item of this array SHALL be the CBOR representation of a 1043 Primary Block. Every other item of the array SHALL be the CBOR 1044 representation of a Canonical Block. The last block of the bundle 1045 SHALL be followed by a CBOR "break" stop code, terminating the 1046 array. 1048 Associated with each block of a bundle is a block number. The block 1049 number uniquely identifies the block within the bundle, enabling 1050 blocks (notably bundle security protocol blocks) to reference other 1051 blocks in the same bundle without ambiguity. The block number of 1052 the primary block is implicitly zero; the block numbers of all other 1053 blocks are explicitly stated in block headers as noted below. Block 1054 numbering is unrelated to the order in which blocks are sequenced in 1055 the bundle. The block number of the payload block is always 1. 1057 4.2.2. Primary Bundle Block 1059 The primary bundle block contains the basic information needed to 1060 forward bundles to their destinations. 1062 Each primary block SHALL be represented as a CBOR array; the number 1063 of elements in the array SHALL be 8 (if the bundle is not a fragment 1064 and the block has no CRC), 9 (if the block has a CRC and the bundle 1065 is not a fragment), 10 (if the bundle is a fragment and the block 1066 has no CRC), or 11 (if the bundle is a fragment and the block has a 1067 CRC). 1069 The primary block of each bundle SHALL be immutable. The values of 1070 all fields in the primary block must remain unchanged from the time 1071 the block is created to the time it is delivered. 1073 The fields of the primary bundle block SHALL be as follows, listed 1074 in the order in which they MUST appear: 1076 Version: An unsigned integer value indicating the version of the 1077 bundle protocol that constructed this block. The present document 1078 describes version 7 of the bundle protocol. Version number SHALL be 1079 represented as a CBOR unsigned integer item. 1081 Bundle Processing Control Flags: The Bundle Processing Control Flags 1082 are discussed in Section 4.1.3. above. 1084 CRC Type: CRC Type codes are discussed in Section 4.1.1. above. The 1085 CRC Type code for the primary block MAY be zero if the bundle 1086 contains a BPsec [BPSEC] Block Integrity Block whose target is the 1087 primary block; otherwise the CRC Type code for the primary block 1088 MUST be non-zero. 1090 Destination EID: The Destination EID field identifies the bundle 1091 endpoint that is the bundle's destination, i.e., the endpoint that 1092 contains the node(s) at which the bundle is to be delivered. 1094 Source node ID: The Source node ID field identifies the bundle node 1095 at which the bundle was initially transmitted, except that Source 1096 node ID may be the null endpoint ID in the event that the bundle's 1097 source chooses to remain anonymous. 1099 Report-to EID: The Report-to EID field identifies the bundle 1100 endpoint to which status reports pertaining to the forwarding and 1101 delivery of this bundle are to be transmitted. 1103 Creation Timestamp: The creation timestamp (discussed in 4.1.7 1104 above) comprises two unsigned integers that, together with the 1105 source node ID and (if the bundle is a fragment) the fragment offset 1106 and payload length, serve to identify the bundle. The first of these 1107 integers is the bundle's creation time, while the second is the 1108 bundle's creation timestamp sequence number. Bundle creation time 1109 SHALL be the DTN time at which the transmission request was received 1110 that resulted in the creation of the bundle. Sequence count SHALL be 1111 the latest value (as of the time at which that transmission request 1112 was received) of a monotonically increasing positive integer counter 1113 managed by the source node's bundle protocol agent that MAY be reset 1114 to zero whenever the current time advances by one millisecond. For 1115 nodes that lack accurate clocks, it is recommended that bundle 1116 creation time be set to zero and that the counter used as the source 1117 of the bundle sequence count never be reset to zero. Note that, in 1118 general, the creation of two distinct bundles with the same source 1119 node ID and bundle creation timestamp may result in unexpected 1120 network behavior and/or suboptimal performance. The combination of 1121 source node ID and bundle creation timestamp serves to identify a 1122 single transmission request, enabling it to be acknowledged by the 1123 receiving application (provided the source node ID is not the null 1124 endpoint ID). 1126 Lifetime: The lifetime field is an unsigned integer that indicates 1127 the time at which the bundle's payload will no longer be useful, 1128 encoded as a number of milliseconds past the creation time. (For 1129 high-rate deployments with very brief disruptions, fine-grained 1130 expression of bundle lifetime may be useful.) When a bundle's age 1131 exceeds its lifetime, bundle nodes need no longer retain or forward 1132 the bundle; the bundle SHOULD be deleted from the network. 1134 If the asserted lifetime for a received bundle is so lengthy that 1135 retention of the bundle until its expiration time might degrade 1136 operation of the node at which the bundle is received, or if the 1137 bundle protocol agent of that node determines that the bundle must 1138 be deleted in order to prevent network performance degradation 1139 (e.g., the bundle appears to be part of a denial-of-service attack), 1140 then that bundle protocol agent MAY impose a temporary overriding 1141 lifetime of shorter duration; such overriding lifetime SHALL NOT 1142 replace the lifetime asserted in the bundle but SHALL serve as the 1143 bundle's effective lifetime while the bundle resides at that node. 1144 Procedures for imposing lifetime overrides are beyond the scope of 1145 this specification. 1147 For bundles originating at nodes that lack accurate clocks, it is 1148 recommended that bundle age be obtained from the Bundle Age 1149 extension block (see 4.3.2 below) rather than from the difference 1150 between current time and bundle creation time. Bundle lifetime 1151 SHALL be represented as a CBOR unsigned integer item. 1153 Fragment offset: If and only if the Bundle Processing Control Flags 1154 of this Primary block indicate that the bundle is a fragment, 1155 fragment offset SHALL be present in the primary block. Fragment 1156 offset SHALL be represented as a CBOR unsigned integer indicating 1157 the offset from the start of the original application data unit at 1158 which the bytes comprising the payload of this bundle were located. 1160 Total Application Data Unit Length: If and only if the Bundle 1161 Processing Control Flags of this Primary block indicate that the 1162 bundle is a fragment, total application data unit length SHALL be 1163 present in the primary block. Total application data unit length 1164 SHALL be represented as a CBOR unsigned integer indicating the total 1165 length of the original application data unit of which this bundle's 1166 payload is a part. 1168 CRC: A CRC SHALL be present in the primary block unless the bundle 1169 includes a BPsec [BPSEC] Block Integrity Block whose target is the 1170 primary block, in which case a CRC MAY be present in the primary 1171 block. The length and nature of the CRC SHALL be as indicated by 1172 the CRC type. The CRC SHALL be computed over the concatenation of 1173 all bytes (including CBOR "break" characters) of the primary block 1174 including the CRC field itself, which for this purpose SHALL be 1175 temporarily populated with all bytes set to zero. 1177 4.2.3. Canonical Bundle Block Format 1179 Every block other than the primary block (all such blocks are termed 1180 "canonical" blocks) SHALL be represented as a CBOR array; the number 1181 of elements in the array SHALL be 5 (if CRC type is zero) or 6 1182 (otherwise). 1184 The fields of every canonical block SHALL be as follows, listed in 1185 the order in which they MUST appear: 1187 . Block type code, an unsigned integer. Bundle block type code 1 1188 indicates that the block is a bundle payload block. Block type 1189 codes 2 through 9 are explicitly reserved as noted later in 1190 this specification. Block type codes 192 through 255 are not 1191 reserved and are available for private and/or experimental use. 1192 All other block type code values are reserved for future use. 1193 . Block number, an unsigned integer as discussed in 4.2.1 above. 1194 Block number SHALL be represented as a CBOR unsigned integer. 1195 . Block processing control flags as discussed in Section 4.1.4 1196 above. 1197 . CRC type as discussed in Section 4.1.1 above. 1198 . Block-type-specific data represented as a single definite- 1199 length CBOR byte string, i.e., a CBOR byte string that is not 1200 of indefinite length. For each type of block, the block-type- 1201 specific data byte string is the serialization, in a block- 1202 type-specific manner, of the data conveyed by that type of 1203 block; definitions of blocks are required to define the manner 1204 in which block-type-specific data are serialized within the 1205 block-type-specific data field. For the Payload Block in 1206 particular (block type 1), the block-type-specific data field, 1207 termed the "payload", SHALL be an application data unit, or 1208 some contiguous extent thereof, represented as a definite- 1209 length CBOR byte string. 1210 . If and only if the value of the CRC type field of this block is 1211 non-zero, a CRC. If present, the length and nature of the CRC 1212 SHALL be as indicated by the CRC type and the CRC SHALL be 1213 computed over the concatenation of all bytes of the block 1214 (including CBOR "break" characters) including the CRC field 1215 itself, which for this purpose SHALL be temporarily populated 1216 with all bytes set to zero. 1218 4.3. Extension Blocks 1220 "Extension blocks" are all blocks other than the primary and payload 1221 blocks. Because not all extension blocks are defined in the Bundle 1222 Protocol specification (the present document), not all nodes 1223 conforming to this specification will necessarily instantiate Bundle 1224 Protocol implementations that include procedures for processing 1225 (that is, recognizing, parsing, acting on, and/or producing) all 1226 extension blocks. It is therefore possible for a node to receive a 1227 bundle that includes extension blocks that the node cannot process. 1228 The values of the block processing control flags indicate the action 1229 to be taken by the bundle protocol agent when this is the case. 1231 The following extension blocks are defined in the current document. 1233 4.3.1. Previous Node 1235 The Previous Node block, block type 6, identifies the node that 1236 forwarded this bundle to the local node (i.e., to the node at which 1237 the bundle currently resides); its block-type-specific data is the 1238 node ID of that forwarder node which SHALL take the form of a node 1239 ID represented as described in Section 4.1.5.2. above. If the local 1240 node is the source of the bundle, then the bundle MUST NOT contain 1241 any Previous Node block. Otherwise the bundle SHOULD contain one 1242 (1) occurrence of this type of block and MUST NOT contain more than 1243 one. 1245 4.3.2. Bundle Age 1247 The Bundle Age block, block type 7, contains the number of 1248 milliseconds that have elapsed between the time the bundle was 1249 created and time at which it was most recently forwarded. It is 1250 intended for use by nodes lacking access to an accurate clock, to 1251 aid in determining the time at which a bundle's lifetime expires. 1252 The block-type-specific data of this block is an unsigned integer 1253 containing the age of the bundle in milliseconds, which SHALL be 1254 represented as a CBOR unsigned integer item. (The age of the bundle 1255 is the sum of all known intervals of the bundle's residence at 1256 forwarding nodes, up to the time at which the bundle was most 1257 recently forwarded, plus the summation of signal propagation time 1258 over all episodes of transmission between forwarding nodes. 1259 Determination of these values is an implementation matter.) If the 1260 bundle's creation time is zero, then the bundle MUST contain exactly 1261 one (1) occurrence of this type of block; otherwise, the bundle MAY 1262 contain at most one (1) occurrence of this type of block. A bundle 1263 MUST NOT contain multiple occurrences of the bundle age block, as 1264 this could result in processing anomalies. 1266 4.3.3. Hop Count 1268 The Hop Count block, block type 10, contains two unsigned integers, 1269 hop limit and hop count. A "hop" is here defined as an occasion on 1270 which a bundle was forwarded from one node to another node. Hop 1271 limit MUST be in the range 1 through 255. The hop limit value SHOULD 1272 NOT be changed at any time after creation of the Hop Count block; 1273 the hop count value SHOULD initially be zero and SHOULD be increased 1274 by 1 on each hop. 1276 The hop count block is mainly intended as a safety mechanism, a 1277 means of identifying bundles for removal from the network that can 1278 never be delivered due to a persistent forwarding error. Hop count 1279 is particularly valuable as a defense against routing anomalies that 1280 might cause a bundle to be forwarded in a cyclical "ping-pong" 1281 fashion between two nodes. When a bundle's hop count exceeds its 1282 hop limit, the bundle SHOULD be deleted for the reason "hop limit 1283 exceeded", following the bundle deletion procedure defined in 1284 Section 5.10. 1286 Procedures for determining the appropriate hop limit for a bundle 1287 are beyond the scope of this specification. 1289 The block-type-specific data in a hop count block SHALL be 1290 represented as a CBOR array comprising two items. The first item of 1291 this array SHALL be the bundle's hop limit, represented as a CBOR 1292 unsigned integer. The second item of this array SHALL be the 1293 bundle's hop count, represented as a CBOR unsigned integer. A bundle 1294 MAY contain one occurrence of this type of block but MUST NOT 1295 contain more than one. 1297 5. Bundle Processing 1299 The bundle processing procedures mandated in this section and in 1300 Section 6 govern the operation of the Bundle Protocol Agent and the 1301 Application Agent administrative element of each bundle node. They 1302 are neither exhaustive nor exclusive. Supplementary DTN protocol 1303 specifications (including, but not restricted to, the Bundle 1304 Security Protocol [BPSEC]) may augment, override, or supersede the 1305 mandates of this document. 1307 5.1. Generation of Administrative Records 1309 All transmission of bundles is in response to bundle transmission 1310 requests presented by nodes' application agents. When required to 1311 "generate" an administrative record (such as a bundle status 1312 report), the bundle protocol agent itself is responsible for causing 1313 a new bundle to be transmitted, conveying that record. In concept, 1314 the bundle protocol agent discharges this responsibility by 1315 directing the administrative element of the node's application agent 1316 to construct the record and request its transmission as detailed in 1317 Section 6 below. In practice, the manner in which administrative 1318 record generation is accomplished is an implementation matter, 1319 provided the constraints noted in Section 6 are observed. 1321 Status reports are relatively small bundles. Moreover, even when 1322 the generation of status reports is enabled the decision on whether 1323 or not to generate a requested status report is left to the 1324 discretion of the bundle protocol agent. Nonetheless, note that 1325 requesting status reports for any single bundle might easily result 1326 in the generation of (1 + (2 *(N-1))) status report bundles, where N 1327 is the number of nodes on the path from the bundle's source to its 1328 destination, inclusive. That is, the requesting of status reports 1329 for large numbers of bundles could result in an unacceptable 1330 increase in the bundle traffic in the network. For this reason, the 1331 generation of status reports MUST be disabled by default and enabled 1332 only when the risk of excessive network traffic is deemed 1333 acceptable. Mechanisms that could assist in assessing and 1334 mitigating this risk, such as pre-placed agreements authorizing the 1335 generation of status reports under specified circumstances, are 1336 beyond the scope of this specification. 1338 Notes on administrative record terminology: 1340 . A "bundle reception status report" is a bundle status report 1341 with the "reporting node received bundle" flag set to 1. 1342 . A "bundle forwarding status report" is a bundle status report 1343 with the "reporting node forwarded the bundle" flag set to 1. 1344 . A "bundle delivery status report" is a bundle status report 1345 with the "reporting node delivered the bundle" flag set to 1. 1346 . A "bundle deletion status report" is a bundle status report 1347 with the "reporting node deleted the bundle" flag set to 1. 1349 5.2. Bundle Transmission 1351 The steps in processing a bundle transmission request are: 1353 Step 1: Transmission of the bundle is initiated. An outbound bundle 1354 MUST be created per the parameters of the bundle transmission 1355 request, with the retention constraint "Dispatch pending". The 1356 source node ID of the bundle MUST be either the null endpoint ID, 1357 indicating that the source of the bundle is anonymous, or else the 1358 EID of a singleton endpoint whose only member is the node of which 1359 the BPA is a component. 1361 Step 2: Processing proceeds from Step 1 of Section 5.4. 1363 5.3. Bundle Dispatching 1365 The steps in dispatching a bundle are: 1367 Step 1: If the bundle's destination endpoint is an endpoint of which 1368 the node is a member, the bundle delivery procedure defined in 1369 Section 5.7 MUST be followed and for the purposes of all subsequent 1370 processing of this bundle at this node the node's membership in the 1371 bundle's destination endpoint SHALL be disavowed; specifically, even 1372 though the node is a member of the bundle's destination endpoint, 1373 the node SHALL NOT undertake to forward the bundle to itself in the 1374 course of performing the procedure described in Section 5.4. 1376 Step 2: Processing proceeds from Step 1 of Section 5.4. 1378 5.4. Bundle Forwarding 1380 The steps in forwarding a bundle are: 1382 Step 1: The retention constraint "Forward pending" MUST be added to 1383 the bundle, and the bundle's "Dispatch pending" retention constraint 1384 MUST be removed. 1386 Step 2: The bundle protocol agent MUST determine whether or not 1387 forwarding is contraindicated (that is, rendered inadvisable) for 1388 any of the reasons listed in the IANA registry of Bundle Status 1389 Report Reason Codes (see section 10.5 below), whose initial contents 1390 are listed in Figure 4. In particular: 1392 . The bundle protocol agent MAY choose either to forward the 1393 bundle directly to its destination node(s) (if possible) or to 1394 forward the bundle to some other node(s) for further 1395 forwarding. The manner in which this decision is made may 1396 depend on the scheme name in the destination endpoint ID and/or 1397 on other state but in any case is beyond the scope of this 1398 document; one possible mechanism is described in [SABR]. If the 1399 BPA elects to forward the bundle to some other node(s) for 1400 further forwarding but finds it impossible to select any 1401 node(s) to forward the bundle to, then forwarding is 1402 contraindicated. 1403 . Provided the bundle protocol agent succeeded in selecting the 1404 node(s) to forward the bundle to, the bundle protocol agent 1405 MUST subsequently select the convergence layer adapter(s) whose 1406 services will enable the node to send the bundle to those 1407 nodes. The manner in which specific appropriate convergence 1408 layer adapters are selected is beyond the scope of this 1409 document; the TCP convergence-layer adapter [TCPCL] MUST be 1410 implemented when some or all of the bundles forwarded by the 1411 bundle protocol agent must be forwarded via the Internet but 1412 may not be appropriate for the forwarding of any particular 1413 bundle. If the agent finds it impossible to select any 1414 appropriate convergence layer adapter(s) to use in forwarding 1415 this bundle, then forwarding is contraindicated. 1417 Step 3: If forwarding of the bundle is determined to be 1418 contraindicated for any of the reasons listed in the IANA registry 1419 of Bundle Status Report Reason Codes (see section 10.5 below), then 1420 the Forwarding Contraindicated procedure defined in Section 5.4.1 1421 MUST be followed; the remaining steps of Section 5.4 are skipped at 1422 this time. 1424 Step 4: For each node selected for forwarding, the bundle protocol 1425 agent MUST invoke the services of the selected convergence layer 1426 adapter(s) in order to effect the sending of the bundle to that 1427 node. Determining the time at which the bundle protocol agent 1428 invokes convergence layer adapter services is a BPA implementation 1429 matter. Determining the time at which each convergence layer 1430 adapter subsequently responds to this service invocation by sending 1431 the bundle is a convergence-layer adapter implementation matter. 1432 Note that: 1434 . If the bundle has a Previous Node block, as defined in 4.3.1 1435 above, then that block MUST be removed from the bundle before 1436 the bundle is forwarded. 1437 . If the bundle protocol agent is configured to attach Previous 1438 Node blocks to forwarded bundles, then a Previous Node block 1439 containing the node ID of the forwarding node MUST be inserted 1440 into the bundle before the bundle is forwarded. 1441 . If the bundle has a bundle age block, as defined in 4.3.2. 1442 above, then at the last possible moment before the CLA 1443 initiates conveyance of the bundle via the CL protocol the 1444 bundle age value MUST be increased by the difference between 1445 the current time and the time at which the bundle was received 1446 (or, if the local node is the source of the bundle, created). 1448 Step 5: When all selected convergence layer adapters have informed 1449 the bundle protocol agent that they have concluded their data 1450 sending procedures with regard to this bundle, processing may depend 1451 on the results of those procedures. 1453 If completion of the data sending procedures by all selected 1454 convergence layer adapters has not resulted in successful forwarding 1455 of the bundle (an implementation-specific determination that is 1456 beyond the scope of this specification), then the bundle protocol 1457 agent MAY choose (in an implementation-specific manner, again beyond 1458 the scope of this specification) to initiate another attempt to 1459 forward the bundle. In that event, processing proceeds from Step 4 1460 of Section 5.4. The minimum number of times a given node will 1461 initiate another forwarding attempt for any single bundle in this 1462 event (a number which may be zero) is a node configuration parameter 1463 that MUST be exposed to other nodes in the network to the extent 1464 that this is required by the operating environment. 1466 If completion of the data sending procedures by all selected 1467 convergence layer adapters HAS resulted in successful forwarding of 1468 the bundle, or if it has not but the bundle protocol agent does not 1469 choose to initiate another attempt to forward the bundle, then: 1471 . If the "request reporting of bundle forwarding" flag in the 1472 bundle's status report request field is set to 1, and status 1473 reporting is enabled, then a bundle forwarding status report 1474 SHOULD be generated, destined for the bundle's report-to 1475 endpoint ID. The reason code on this bundle forwarding status 1476 report MUST be "no additional information". 1477 . If any applicable bundle protocol extensions mandate generation 1478 of status reports upon conclusion of convergence-layer data 1479 sending procedures, all such status reports SHOULD be generated 1480 with extension-mandated reason codes. 1481 . The bundle's "Forward pending" retention constraint MUST be 1482 removed. 1484 5.4.1. Forwarding Contraindicated 1486 The steps in responding to contraindication of forwarding are: 1488 Step 1: The bundle protocol agent MUST determine whether or not to 1489 declare failure in forwarding the bundle. Note: this decision is 1490 likely to be influenced by the reason for which forwarding is 1491 contraindicated. 1493 Step 2: If forwarding failure is declared, then the Forwarding 1494 Failed procedure defined in Section 5.4.2 MUST be followed. 1496 Otherwise, when - at some future time - the forwarding of this 1497 bundle ceases to be contraindicated, processing proceeds from Step 4 1498 of Section 5.4. 1500 5.4.2. Forwarding Failed 1502 The steps in responding to a declaration of forwarding failure are: 1504 Step 1: The bundle protocol agent MAY forward the bundle back to the 1505 node that sent it, as identified by the Previous Node block, if 1506 present. This forwarding, if performed, SHALL be accomplished by 1507 performing Step 4 and Step 5 of section 5.4 where the sole node 1508 selected for forwarding SHALL be the node that sent the bundle. 1510 Step 2: If the bundle's destination endpoint is an endpoint of which 1511 the node is a member, then the bundle's "Forward pending" retention 1512 constraint MUST be removed. Otherwise, the bundle MUST be deleted: 1513 the bundle deletion procedure defined in Section 5.10 MUST be 1514 followed, citing the reason for which forwarding was determined to 1515 be contraindicated. 1517 5.5. Bundle Expiration 1519 A bundle expires when the bundle's age exceeds its lifetime as 1520 specified in the primary bundle block or as overridden by the bundle 1521 protocol agent. Bundle age MAY be determined by subtracting the 1522 bundle's creation timestamp time from the current time if (a) that 1523 timestamp time is not zero and (b) the local node's clock is known 1524 to be accurate; otherwise bundle age MUST be obtained from the 1525 Bundle Age extension block. Bundle expiration MAY occur at any 1526 point in the processing of a bundle. When a bundle expires, the 1527 bundle protocol agent MUST delete the bundle for the reason 1528 "lifetime expired" (when the expired lifetime is the lifetime as 1529 specified in the primary block) or "traffic pared" (when the expired 1530 lifetime is a lifetime override as imposed by the bundle protocol 1531 agent): the bundle deletion procedure defined in Section 5.10 MUST 1532 be followed. 1534 5.6. Bundle Reception 1536 The steps in processing a bundle that has been received from another 1537 node are: 1539 Step 1: The retention constraint "Dispatch pending" MUST be added to 1540 the bundle. 1542 Step 2: If the "request reporting of bundle reception" flag in the 1543 bundle's status report request field is set to 1, and status 1544 reporting is enabled, then a bundle reception status report with 1545 reason code "No additional information" SHOULD be generated, 1546 destined for the bundle's report-to endpoint ID. 1548 Step 3: CRCs SHOULD be computed for every block of the bundle that 1549 has an attached CRC. If any block of the bundle is malformed 1550 according to this specification (including syntactically invalid 1551 CBOR), or if any block has an attached CRC and the CRC computed for 1552 this block upon reception differs from that attached CRC, then the 1553 bundle protocol agent MUST delete the bundle for the reason "Block 1554 unintelligible". The bundle deletion procedure defined in Section 1555 5.10 MUST be followed and all remaining steps of the bundle 1556 reception procedure MUST be skipped. 1558 Step 4: For each block in the bundle that is an extension block that 1559 the bundle protocol agent cannot process: 1561 . If the block processing flags in that block indicate that a 1562 status report is requested in this event, and status reporting 1563 is enabled, then a bundle reception status report with reason 1564 code "Block unintelligible" SHOULD be generated, destined for 1565 the bundle's report-to endpoint ID. 1566 . If the block processing flags in that block indicate that the 1567 bundle must be deleted in this event, then the bundle protocol 1568 agent MUST delete the bundle for the reason "Block 1569 unintelligible"; the bundle deletion procedure defined in 1570 Section 5.10 MUST be followed and all remaining steps of the 1571 bundle reception procedure MUST be skipped. 1572 . If the block processing flags in that block do NOT indicate 1573 that the bundle must be deleted in this event but do indicate 1574 that the block must be discarded, then the bundle protocol 1575 agent MUST remove this block from the bundle. 1576 . If the block processing flags in that block indicate neither 1577 that the bundle must be deleted nor that that the block must be 1578 discarded, then processing continues with the next extension 1579 block that the bundle protocol agent cannot process, if any; 1580 otherwise, processing proceeds from step 5. 1582 Step 5: Processing proceeds from Step 1 of Section 5.3. 1584 5.7. Local Bundle Delivery 1586 The steps in processing a bundle that is destined for an endpoint of 1587 which this node is a member are: 1589 Step 1: If the received bundle is a fragment, the application data 1590 unit reassembly procedure described in Section 5.9 MUST be followed. 1591 If this procedure results in reassembly of the entire original 1592 application data unit, processing of the fragmentary bundle whose 1593 payload has been replaced by the reassembled application data unit 1594 (whether this bundle or a previously received fragment) proceeds 1595 from Step 2; otherwise, the retention constraint "Reassembly 1596 pending" MUST be added to the bundle and all remaining steps of this 1597 procedure MUST be skipped. 1599 Step 2: Delivery depends on the state of the registration whose 1600 endpoint ID matches that of the destination of the bundle: 1602 . An additional implementation-specific delivery deferral 1603 procedure MAY optionally be associated with the registration. 1604 . If the registration is in the Active state, then the bundle 1605 MUST be delivered automatically as soon as it is the next 1606 bundle that is due for delivery according to the BPA's bundle 1607 delivery scheduling policy, an implementation matter. 1608 . If the registration is in the Passive state, or if delivery of 1609 the bundle fails for some implementation-specific reason, then 1610 the registration's delivery failure action MUST be taken. 1611 Delivery failure action MUST be one of the following: 1613 o defer delivery of the bundle subject to this registration 1614 until (a) this bundle is the least recently received of 1615 all bundles currently deliverable subject to this 1616 registration and (b) either the registration is polled or 1617 else the registration is in the Active state, and also 1618 perform any additional delivery deferral procedure 1619 associated with the registration; or 1621 o abandon delivery of the bundle subject to this registration 1622 (as defined in 3.1. ). 1624 Step 3: As soon as the bundle has been delivered, if the "request 1625 reporting of bundle delivery" flag in the bundle's status report 1626 request field is set to 1 and bundle status reporting is enabled, 1627 then a bundle delivery status report SHOULD be generated, destined 1628 for the bundle's report-to endpoint ID. Note that this status report 1629 only states that the payload has been delivered to the application 1630 agent, not that the application agent has processed that payload. 1632 5.8. Bundle Fragmentation 1634 It may at times be advantageous for bundle protocol agents to reduce 1635 the sizes of bundles in order to forward them. This might be the 1636 case, for example, if a node to which a bundle is to be forwarded is 1637 accessible only via intermittent contacts and no upcoming contact is 1638 long enough to enable the forwarding of the entire bundle. 1640 The size of a bundle can be reduced by "fragmenting" the bundle. To 1641 fragment a bundle whose payload is of size M is to replace it with 1642 two "fragments" - new bundles with the same source node ID and 1643 creation timestamp as the original bundle, a.k.a. "fragmentary 1644 bundles" - whose payloads are the first N and the last (M - N) bytes 1645 of the original bundle's payload, where 0 < N < M. 1647 Note that fragments are bundles and therefore may themselves be 1648 fragmented, so multiple episodes of fragmentation may in effect 1649 replace the original bundle with more than two fragments. (However, 1650 there is only one 'level' of fragmentation, as in IP fragmentation.) 1652 Any bundle whose primary block's bundle processing flags do NOT 1653 indicate that it must not be fragmented MAY be fragmented at any 1654 time, for any purpose, at the discretion of the bundle protocol 1655 agent. NOTE, however, that some combinations of bundle 1656 fragmentation, replication, and routing might result in unexpected 1657 traffic patterns. 1659 Fragmentation SHALL be constrained as follows: 1661 . The concatenation of the payloads of all fragments produced by 1662 fragmentation MUST always be identical to the payload of the 1663 fragmented bundle (that is, the bundle that is being 1664 fragmented). Note that the payloads of fragments resulting from 1665 different fragmentation episodes, in different parts of the 1666 network, may be overlapping subsets of the fragmented bundle's 1667 payload. 1668 . The primary block of each fragment MUST differ from that of the 1669 fragmented bundle, in that the bundle processing flags of the 1670 fragment MUST indicate that the bundle is a fragment and both 1671 fragment offset and total application data unit length must be 1672 provided. Additionally, the CRC of the primary block of the 1673 fragmented bundle, if any, MUST be replaced in each fragment by 1674 a new CRC computed for the primary block of that fragment. 1675 . The payload blocks of fragments will differ from that of the 1676 fragmented bundle as noted above. 1677 . If the fragmented bundle is not a fragment or is the fragment 1678 with offset zero, then all extension blocks of the fragmented 1679 bundle MUST be replicated in the fragment whose offset is zero. 1680 . Each of the fragmented bundle's extension blocks whose "Block 1681 must be replicated in every fragment" flag is set to 1 MUST be 1682 replicated in every fragment. 1683 . Beyond these rules, rules for the replication of extension 1684 blocks in the fragments must be defined in the specifications 1685 for those extension block types. 1687 5.9. Application Data Unit Reassembly 1689 Note that the bundle fragmentation procedure described in 5.8 above 1690 may result in the replacement of a single original bundle with an 1691 arbitrarily large number of fragmentary bundles. In order to be 1692 delivered at a destination node, the original bundle's payload must 1693 be reassembled from the payloads of those fragments. 1695 If the concatenation - as informed by fragment offsets and payload 1696 lengths - of the non-overlapping portions of the payloads of all 1697 previously received fragments with the same source node ID and 1698 creation timestamp as this fragment, together with the non- 1699 overlapping portion of the payload of this fragment, forms a 1700 continuous byte array whose length is equal to the total application 1701 data unit length in the fragment's primary block, then: 1703 . This byte array -- the reassembled application data unit -- 1704 MUST replace the payload of that fragment whose payload is a 1705 subset, starting at offset zero, of the reassembled application 1706 data unit. Note that this will enable delivery of the 1707 reconstituted original bundle as described in Step 1 of 5.7. 1708 . The "Reassembly pending" retention constraint MUST be removed 1709 from every previously received fragment whose payload is a 1710 subset of the reassembled application data unit. 1712 Note: reassembly of application data units from fragments occurs at 1713 the nodes that are members of destination endpoints as necessary; an 1714 application data unit MAY also be reassembled at some other node on 1715 the path to the destination. 1717 5.10. Bundle Deletion 1719 The steps in deleting a bundle are: 1721 Step 1: If the "request reporting of bundle deletion" flag in the 1722 bundle's status report request field is set to 1, and if status 1723 reporting is enabled, then a bundle deletion status report citing 1724 the reason for deletion SHOULD be generated, destined for the 1725 bundle's report-to endpoint ID. 1727 Step 2: All of the bundle's retention constraints MUST be removed. 1729 5.11. Discarding a Bundle 1731 As soon as a bundle has no remaining retention constraints it MAY be 1732 discarded, thereby releasing any persistent storage that may have 1733 been allocated to it. 1735 5.12. Canceling a Transmission 1737 When requested to cancel a specified transmission, where the bundle 1738 created upon initiation of the indicated transmission has not yet 1739 been discarded, the bundle protocol agent MUST delete that bundle 1740 for the reason "transmission cancelled". For this purpose, the 1741 procedure defined in Section 5.10 MUST be followed. 1743 6. Administrative Record Processing 1745 6.1. Administrative Records 1747 Administrative records are standard application data units that are 1748 used in providing some of the features of the Bundle Protocol. One 1749 type of administrative record has been defined to date: bundle 1750 status reports. Note that additional types of administrative 1751 records may be defined by supplementary DTN protocol specification 1752 documents. 1754 Every administrative record consists of: 1756 . Record type code (an unsigned integer for which valid values 1757 are as defined below). 1758 . Record content in type-specific format. 1760 Valid administrative record type codes are defined as follows: 1762 +---------+--------------------------------------------+ 1764 | Value | Meaning | 1766 +=========+============================================+ 1768 | 1 | Bundle status report. | 1770 +---------+--------------------------------------------+ 1772 | (other) | Reserved for future use. | 1774 +---------+--------------------------------------------+ 1776 Figure 3: Administrative Record Type Codes 1778 Each BP administrative record SHALL be represented as a CBOR array 1779 comprising two items. 1781 The first item of the array SHALL be a record type code, which SHALL 1782 be represented as a CBOR unsigned integer. 1784 The second element of this array SHALL be the applicable CBOR 1785 representation of the content of the record. Details of the CBOR 1786 representation of administrative record type 1 are provided below. 1787 Details of the CBOR representation of other types of administrative 1788 record type are included in the specifications defining those 1789 records. 1791 6.1.1. Bundle Status Reports 1793 The transmission of "bundle status reports" under specified 1794 conditions is an option that can be invoked when transmission of a 1795 bundle is requested. These reports are intended to provide 1796 information about how bundles are progressing through the system, 1797 including notices of receipt, forwarding, final delivery, and 1798 deletion. They are transmitted to the Report-to endpoints of 1799 bundles. 1801 Each bundle status report SHALL be represented as a CBOR array. The 1802 number of elements in the array SHALL be either 6 (if the subject 1803 bundle is a fragment) or 4 (otherwise). 1805 The first item of the bundle status report array SHALL be bundle 1806 status information represented as a CBOR array of at least 4 1807 elements. The first four items of the bundle status information 1808 array shall provide information on the following four status 1809 assertions, in this order: 1811 . Reporting node received bundle. 1812 . Reporting node forwarded the bundle. 1813 . Reporting node delivered the bundle. 1814 . Reporting node deleted the bundle. 1816 Each item of the bundle status information array SHALL be a bundle 1817 status item represented as a CBOR array; the number of elements in 1818 each such array SHALL be either 2 (if the value of the first item of 1819 this bundle status item is 1 AND the "Report status time" flag was 1820 set to 1 in the bundle processing flags of the bundle whose status 1821 is being reported) or 1 (otherwise). The first item of the bundle 1822 status item array SHALL be a status indicator, a Boolean value 1823 indicating whether or not the corresponding bundle status is 1824 asserted, represented as a CBOR Boolean value. The second item of 1825 the bundle status item array, if present, SHALL indicate the time 1826 (as reported by the local system clock, an implementation matter) at 1827 which the indicated status was asserted for this bundle, represented 1828 as a DTN time as described in Section 4.1.6. above. 1830 The second item of the bundle status report array SHALL be the 1831 bundle status report reason code explaining the value of the status 1832 indicator, represented as a CBOR unsigned integer. Valid status 1833 report reason codes are registered in the IANA Bundle Status Report 1834 Reason Codes registry in the Bundle Protocol Namespace (see 10.5 1835 below). The initial contents of that registry are listed in Figure 1836 4 below but the list of status report reason codes provided here is 1837 neither exhaustive nor exclusive; supplementary DTN protocol 1838 specifications (including, but not restricted to, the Bundle 1839 Security Protocol [BPSEC]) may define additional reason codes. 1841 +---------+--------------------------------------------+ 1843 | Value | Meaning | 1845 +=========+============================================+ 1847 | 0 | No additional information. | 1849 +---------+--------------------------------------------+ 1851 | 1 | Lifetime expired. | 1853 +---------+--------------------------------------------+ 1855 | 2 | Forwarded over unidirectional link. | 1857 +---------+--------------------------------------------+ 1859 | 3 | Transmission canceled. | 1861 +---------+--------------------------------------------+ 1863 | 4 | Depleted storage. | 1865 +---------+--------------------------------------------+ 1867 | 5 | Destination endpoint ID unavailable. | 1869 +---------+--------------------------------------------+ 1871 | 6 | No known route to destination from here. | 1873 +---------+--------------------------------------------+ 1874 | 7 | No timely contact with next node on route. | 1876 +---------+--------------------------------------------+ 1878 | 8 | Block unintelligible. | 1880 +---------+--------------------------------------------+ 1882 | 9 | Hop limit exceeded. | 1884 +---------+--------------------------------------------+ 1886 | 10 | Traffic pared (e.g., status reports). | 1888 +---------+--------------------------------------------+ 1890 | (other) | Reserved for future use. | 1892 +---------+--------------------------------------------+ 1894 Figure 4: Status Report Reason Codes 1896 The third item of the bundle status report array SHALL be the source 1897 node ID identifying the source of the bundle whose status is being 1898 reported, represented as described in Section 4.1.5.1.1. above. 1900 The fourth item of the bundle status report array SHALL be the 1901 creation timestamp of the bundle whose status is being reported, 1902 represented as described in Section 4.1.7. above. 1904 The fifth item of the bundle status report array SHALL be present if 1905 and only if the bundle whose status is being reported contained a 1906 fragment offset. If present, it SHALL be the subject bundle's 1907 fragment offset represented as a CBOR unsigned integer item. 1909 The sixth item of the bundle status report array SHALL be present if 1910 and only if the bundle whose status is being reported contained a 1911 fragment offset. If present, it SHALL be the length of the subject 1912 bundle's payload represented as a CBOR unsigned integer item. 1914 Note that the forwarding parameters (such as lifetime, applicable 1915 security measures, etc.) of the bundle whose status is being 1916 reported MAY be reflected in the parameters governing the forwarding 1917 of the bundle that conveys a status report, but this is an 1918 implementation matter. Bundle protocol deployment experience to 1919 date has not been sufficient to suggest any clear guidance on this 1920 topic. 1922 6.2. Generation of Administrative Records 1924 Whenever the application agent's administrative element is directed 1925 by the bundle protocol agent to generate an administrative record, 1926 the following procedure must be followed: 1928 Step 1: The administrative record must be constructed. If the 1929 administrative record references a bundle and the referenced bundle 1930 is a fragment, the administrative record MUST contain the fragment 1931 offset and fragment length. 1933 Step 2: A request for transmission of a bundle whose payload is this 1934 administrative record MUST be presented to the bundle protocol 1935 agent. 1937 7. Services Required of the Convergence Layer 1939 7.1. The Convergence Layer 1941 The successful operation of the end-to-end bundle protocol depends 1942 on the operation of underlying protocols at what is termed the 1943 "convergence layer"; these protocols accomplish communication 1944 between nodes. A wide variety of protocols may serve this purpose, 1945 so long as each convergence layer protocol adapter provides a 1946 defined minimal set of services to the bundle protocol agent. This 1947 convergence layer service specification enumerates those services. 1949 7.2. Summary of Convergence Layer Services 1951 Each convergence layer protocol adapter is expected to provide the 1952 following services to the bundle protocol agent: 1954 . sending a bundle to a bundle node that is reachable via the 1955 convergence layer protocol; 1956 . notifying the bundle protocol agent of the disposition of its 1957 data sending procedures with regard to a bundle, upon 1958 concluding those procedures; 1959 . delivering to the bundle protocol agent a bundle that was sent 1960 by a bundle node via the convergence layer protocol. 1962 The convergence layer service interface specified here is neither 1963 exhaustive nor exclusive. That is, supplementary DTN protocol 1964 specifications (including, but not restricted to, the Bundle 1965 Security Protocol [BPSEC]) may expect convergence layer adapters 1966 that serve BP implementations conforming to those protocols to 1967 provide additional services such as reporting on the transmission 1968 and/or reception progress of individual bundles (at completion 1969 and/or incrementally), retransmitting data that were lost in 1970 transit, discarding bundle-conveying data units that the convergence 1971 layer protocol determines are corrupt or inauthentic, or reporting 1972 on the integrity and/or authenticity of delivered bundles. 1974 In addition, bundle protocol relies on the capabilities of protocols 1975 at the convergence layer to minimize congestion in the store-carry- 1976 forward overlay network. The potentially long round-trip times 1977 characterizing delay-tolerant networks are incompatible with end-to- 1978 end reactive congestion control mechanisms, so convergence-layer 1979 protocols MUST provide rate limiting or congestion control. 1981 8. Implementation Status 1983 [NOTE to the RFC Editor: please remove this section before 1984 publication, as well as the reference to RFC 7942.] 1986 This section records the status of known implementations of the 1987 protocol defined by this specification at the time of posting of 1988 this Internet-Draft, and is based on a proposal described in RFC 1989 7942. The description of implementations in this section is 1990 intended to assist the IETF in its decision processes in progressing 1991 drafts to RFCs. Please note that the listing of any individual 1992 implementation here does not imply endorsement by the IETF. 1993 Furthermore, no effort has been spent to verify the information 1994 presented here that was supplied by IETF contributors. This is not 1995 intended as, and must not be construed to be, a catalog of available 1996 implementations or their features. Readers are advised to note that 1997 other implementations may exist. 1999 According to RFC 7942, "this will allow reviewers and working groups 2000 to assign due consideration to documents that have the benefit of 2001 running code, which may serve as evidence of valuable 2002 experimentation and feedback that have made the implemented 2003 protocols more mature. It is up to the individual working groups to 2004 use this information as they see fit". 2006 At the time of this writing, there are six known implementations of 2007 the current document. 2009 The first known implementation is microPCN (https://upcn.eu/). 2010 According to the developers: 2012 The Micro Planetary Communication Network (uPCN) is a free 2013 software project intended to offer an implementation of Delay- 2014 tolerant Networking protocols for POSIX operating systems (well, 2015 and for Linux) plus for the ARM Cortex STM32F4 microcontroller 2016 series. More precisely it currently provides an implementation of 2018 . the Bundle Protocol (BP, RFC 5050), 2019 . version 6 of the Bundle Protocol version 7 specification 2020 draft, 2021 . the DTN IP Neighbor Discovery (IPND) protocol, and 2022 . a routing approach optimized for message-ferry micro LEO 2023 satellites. 2025 uPCN is written in C and is built upon the real-time operating 2026 system FreeRTOS. The source code of uPCN is released under the 2027 "BSD 3-Clause License". 2029 The project depends on an execution environment offering link 2030 layer protocols such as AX.25. The source code uses the USB 2031 subsystem to interact with the environment. 2033 The second known implementation is PyDTN, developed by X-works, 2034 s.r.o (https://x-works.sk/). The final third of the implementation 2035 was developed during the IETF 101 Hackathon. According to the 2036 developers, PyDTN implements bundle coding/decoding and neighbor 2037 discovery. PyDTN is written in Python and has been shown to be 2038 interoperable with uPCN. 2040 The third known implementation is "Terra" 2041 (https://github.com/RightMesh/Terra/), a Java implementation 2042 developed in the context of terrestrial DTN. It includes an 2043 implementation of a "minimal TCP" convergence layer adapter. 2045 The fourth and fifth known implementations are products of 2046 cooperating groups at two German universities: 2048 . An implementation written in Go, licensed under GPLv3, is 2049 focused on being easily extensible suitable for research. It 2050 is maintained at the University of Marburg and can be accessed 2051 from https://github.com/dtn7/dtn7-go. 2052 . An implementation written in Rust, licensed under the 2053 MIT/Apache license, is intended for environments with limited 2054 resources or demanding safety and/or performance requirements. 2055 It is maintained at the Technical University of Darmstadt and 2056 can be accessed at https://github.com/dtn7/dtn7-rs/. 2058 The sixth known implementation is the "bpv7" module in version 4.0.0 2059 of the Interplanetary Overlay Network (ION) software maintained at 2060 the Jet Propulsion Laboratory, California Institute of Technology, 2061 for the U.S. National Aeronautics and Space Administration (NASA). 2063 9. Security Considerations 2065 The bundle protocol security architecture and the available security 2066 services are specified in an accompanying document, the Bundle 2067 Security Protocol (BPsec) specification [BPSEC]. Whenever Bundle 2068 Protocol security services (as opposed to the security services 2069 provided by overlying application protocols or underlying 2070 convergence-layer protocols) are required, those services SHALL be 2071 provided by BPsec rather than by some other mechanism with the same 2072 or similar scope. 2074 The BPsec extensions to Bundle Protocol enable each block of a 2075 bundle (other than a BPsec extension block) to be individually 2076 authenticated by a signature block (Block Integrity Block, or BIB) 2077 and also enable each block of a bundle other than the primary block 2078 (and the BPsec extension blocks themselves) to be individually 2079 encrypted by a Block Confidentiality Bock (BCB). 2081 Because the security mechanisms are extension blocks that are 2082 themselves inserted into the bundle, the protections they afford 2083 apply while the bundle is at rest, awaiting transmission at the next 2084 forwarding opportunity, as well as in transit. 2086 Additionally, convergence-layer protocols that ensure authenticity 2087 of communication between adjacent nodes in BP network topology 2088 SHOULD be used where available, to minimize the ability of 2089 unauthenticated nodes to introduce inauthentic traffic into the 2090 network. Convergence-layer protocols that ensure confidentiality of 2091 communication between adjacent nodes in BP network topology SHOULD 2092 also be used where available, to minimize exposure of the bundle's 2093 primary block and other clear-text blocks, thereby offering some 2094 defense against traffic analysis. 2096 Note that, while the primary block must remain in the clear for 2097 routing purposes, the Bundle Protocol could be protected against 2098 traffic analysis to some extent by using bundle-in-bundle 2099 encapsulation [BIBE] to tunnel bundles to a safe forward 2100 distribution point: the encapsulated bundle could form the payload 2101 of an encapsulating bundle, and that payload block could be 2102 encrypted by a BCB. 2104 Note that the generation of bundle status reports is disabled by 2105 default because malicious initiation of bundle status reporting 2106 could result in the transmission of extremely large numbers of 2107 bundles, effecting a denial of service attack. Imposing bundle 2108 lifetime overrides would constitute one defense against such an 2109 attack. 2111 Note also that the reception of large numbers of fragmentary bundles 2112 with very long lifetimes could constitute a denial of service 2113 attack, occupying storage while pending reassembly that will never 2114 occur. Imposing bundle lifetime overrides would, again, constitute 2115 one defense against such an attack. 2117 10. IANA Considerations 2119 The Bundle Protocol includes fields requiring registries managed by 2120 IANA. 2122 10.1. Bundle Block Types 2124 The current Bundle Block Types registry in the Bundle Protocol 2125 Namespace is augmented by adding a column identifying the version of 2126 the Bundle protocol (Bundle Protocol Version) that applies to the 2127 new values. IANA is requested to add the following values, as 2128 described in section 4.3.1, to the Bundle Block Types registry. The 2129 current values in the Bundle Block Types registry should have the 2130 Bundle Protocol Version set to the value "6", as shown below. 2132 +----------+-------+-----------------------------+---------------+ 2134 | Bundle | Value | Description | Reference | 2136 | Protocol | | | | 2138 | Version | | | | 2140 +----------+-------+-----------------------------+---------------+ 2142 | none | 0 | Reserved | [RFC6255] | 2144 | 6,7 | 1 | Bundle Payload Block | [RFC5050] | 2146 | | | | RFC-to-be | 2148 | 6 | 2 | Bundle Authentication Block | [RFC6257] | 2150 | 6 | 3 | Payload Integrity Block | [RFC6257] | 2152 | 6 | 4 | Payload Confidentiality | [RFC6257] | 2154 | | | Block | RFC-to-be | 2156 | 6 | 5 | Previous-Hop Insertion Block| [RFC6259] | 2157 | 7 | 6 | Previous node (proximate | RFC-to-be | 2159 | | | sender) | | 2161 | 7 | 7 | Bundle age (in milliseconds)| RFC-to-be | 2163 | 6 | 8 | Metadata Extension Block | [RFC6258] | 2165 | 6 | 9 | Extension Security Block | [RFC6257] | 2167 | 7 | 10 | Hop count (#prior xmit | RFC-to-be | 2169 | | | attempts) | | 2171 | 7 | 11-191| Unassigned | | 2173 | 6 |192-255| Reserved for Private and/or | [RFC5050], | 2175 | | | Experimental Use | RFC-to-be | 2177 +----------+-------+-----------------------------+---------------+ 2179 10.2. Primary Bundle Protocol Version 2181 IANA is requested to add the following value to the Primary Bundle 2182 Protocol Version registry in the Bundle Protocol Namespace. 2184 +-------+-------------+---------------+ 2186 | Value | Description | Reference | 2188 +-------+-------------+---------------+ 2190 | 7 | Assigned | RFC-to-be | 2192 +-------+-------------+---------------+ 2194 Values 8-255 (rather than 7-255) are now Unassigned. 2196 10.3. Bundle Processing Control Flags 2198 The current Bundle Processing Control Flags registry in the Bundle 2199 Protocol Namespace is augmented by adding a column identifying the 2200 version of the Bundle protocol (Bundle Protocol Version) that 2201 applies to the new values. IANA is requested to add the following 2202 values, as described in section 4.1.3, to the Bundle Processing 2203 Control Flags registry. The current values in the Bundle Processing 2204 Control Flags registry should have the Bundle Protocol Version set 2205 to the value 6 or "6, 7", as shown below. 2207 Bundle Processing Control Flags Registry 2209 +--------------------+----------------------------------+----------+ 2211 | Bundle | Bit | Description | Reference| 2213 | Protocol| Position | | | 2215 | Version | (right | | | 2217 | | to left) | | | 2219 +--------------------+----------------------------------+----------+ 2221 | 6,7 | 0 | Bundle is a fragment |[RFC5050],| 2223 | | | |RFC-to-be | 2225 | 6,7 | 1 | Application data unit is an |[RFC5050],| 2227 | | | administrative record |RFC-to-be | 2229 | 6,7 | 2 | Bundle must not be fragmented |[RFC5050],| 2231 | | | |RFC-to-be | 2233 | 6 | 3 | Custody transfer is requested |[RFC5050] | 2235 | 6 | 4 | Destination endpoint is singleton|[RFC5050] | 2237 | 6,7 | 5 | Acknowledgement by application |[RFC5050],| 2239 | | | is requested |RFC-to-be | 2241 | 7 | 6 | Status time requested in reports |RFC-to-be | 2243 | 6 | 7 | Class of service, priority |[RFC5050],| 2245 | | | |RFC-to-be | 2247 | 6 | 8 | Class of service, priority |[RFC5050],| 2249 | | | |RFC-to-be | 2250 | 6 | 9 | Class of service, reserved |[RFC5050],| 2252 | | | |RFC-to-be | 2254 | 6 | 10 | Class of service, reserved |[RFC5050],| 2256 | | | |RFC-to-be | 2258 | 6 | 11 | Class of service, reserved |[RFC5050],| 2260 | | | |RFC-to-be | 2262 | 6 | 12 | Class of service, reserved |[RFC5050],| 2264 | | | |RFC-to-be | 2266 | 6 | 13 | Class of service, reserved |[RFC5050],| 2268 | | | |RFC-to-be | 2270 | 6,7 | 14 | Request reporting of bundle |[RFC5050],| 2272 | | | reception |RFC-to-be | 2274 | 6,7 | 16 | Request reporting of bundle |[RFC5050],| 2276 | | | forwarding |RFC-to-be | 2278 | 6,7 | 17 | Request reporting of bundle |[RFC5050],| 2280 | | | delivery |RFC-to-be | 2282 | 6,7 | 18 | Request reporting of bundle |[RFC5050],| 2284 | | | deletion |RFC-to-be | 2286 | 6 | 19 | Reserved |[RFC5050],| 2288 | | | |RFC-to-be | 2290 | 6 | 20 | Reserved |[RFC5050],| 2292 | | | |RFC-to-be | 2294 | | 21-63 | Unassigned | | 2296 +--------------------+----------------------------------+----------+ 2297 The registration policy for this registry is changed to "Standards 2298 Action". Given the limited number of bits available, the allocation 2299 should only be granted for a standards-track RFC approved by the 2300 IESG. 2302 10.4. Block Processing Control Flags 2304 The current Block Processing Control Flags registry in the Bundle 2305 Protocol Namespace is augmented by adding a column identifying the 2306 version of the Bundle protocol (Bundle Protocol Version) that 2307 applies to the related BP version. The current values in the Block 2308 Processing Control Flags registry should have the Bundle Protocol 2309 Version set to the value 6 or "6, 7", as shown below. 2311 Block Processing Control Flags Registry 2313 +--------------------+----------------------------------+----------+ 2315 | Bundle | Bit | Description | Reference| 2317 | Protocol| Position | | | 2319 | Version | (right | | | 2321 | | to left) | | | 2323 +--------------------+----------------------------------+----------+ 2325 | 6,7 | 0 | Block must be replicated in |[RFC5050],| 2327 | | | every fragment |RFC-to-be | 2329 | 6,7 | 1 | Transmit status report if block |[RFC5050],| 2331 | | | can't be processed |RFC-to-be | 2333 | 6,7 | 2 | Delete bundle if block can't be |[RFC5050],| 2335 | | | processed |RFC-to-be | 2337 | 6 | 3 | Last block |[RFC5050] | 2339 | 6,7 | 4 | Discard block if it can't be |[RFC5050],| 2341 | | | processed |RFC-to-be | 2343 | 6 | 5 | Block was forwarded without |[RFC5050] | 2344 | | | being processed | | 2346 | 6 | 6 | Block contains an EID reference |[RFC5050] | 2348 | | | field | | 2350 | | 7-63 | Unassigned | | 2352 +--------------------+----------------------------------+----------+ 2354 The registration policy for this registry is changed to "Standards 2355 Action". Given the limited number of bits available, the allocation 2356 should only be granted for a standards-track RFC approved by the 2357 IESG. 2359 10.5. Bundle Status Report Reason Codes 2361 The current Bundle Status Report Reason Codes registry in the Bundle 2362 Protocol Namespace is augmented by adding a column identifying the 2363 version of the Bundle protocol (Bundle Protocol Version) that 2364 applies to the new values. IANA is requested to add the following 2365 values, as described in section 6.1.1, to the Bundle Status Report 2366 Reason Codes registry. The current values in the Bundle Status 2367 Report Reason Codes registry should have the Bundle Protocol Version 2368 set to the value 6 or 7 or "6, 7", as shown below. 2370 Bundle Status Report Reason Codes Registry 2372 +--------------------+----------------------------------+----------+ 2374 | Bundle | Value | Description | Reference| 2376 | Protocol| | | | 2378 | Version | | | | 2380 | | | | | 2382 +--------------------+----------------------------------+----------+ 2384 | 6,7 | 0 | No additional information |[RFC5050],| 2386 | | | |RFC-to-be | 2388 | 6,7 | 1 | Lifetime expired |[RFC5050],| 2390 | | | |RFC-to-be | 2391 | 6,7 | 2 | Forwarded over unidirectional |[RFC5050],| 2393 | | | link |RFC-to-be | 2395 | 6,7 | 3 | Transmission canceled |[RFC5050],| 2397 | | | |RFC-to-be | 2399 | 6,7 | 4 | Depleted storage |[RFC5050],| 2401 | | | |RFC-to-be | 2403 | 6,7 | 5 | Destination endpoint ID |[RFC5050],| 2405 | | | unavailable |RFC-to-be | 2407 | 6,7 | 6 | No known route to destination |[RFC5050],| 2409 | | | from here |RFC-to-be | 2411 | 6,7 | 7 | No timely contact with next node |[RFC5050],| 2413 | | | on route |RFC-to-be | 2415 | 6,7 | 8 | Block unintelligible |[RFC5050],| 2417 | | | |RFC-to-be | 2419 | 7 | 9 | Hop limit exceeded |RFC-to-be | 2421 | 7 | 10 | Traffic pared |RFC-to-be | 2423 | | 11-254 | Unassigned | | 2425 | 6 | 255 | Reserved |[RFC6255],| 2427 | | | |RFC-to-be | 2429 +-------+-----------------------------------------------+----------+ 2431 10.6. Bundle Protocol URI scheme types 2433 The Bundle Protocol has a URI scheme type field - an unsigned 2434 integer of indefinite length - for which IANA is requested to create 2435 and maintain a new "Bundle Protocol URI Scheme Type" registry in the 2436 Bundle Protocol Namespace. The "Bundle Protocol URI Scheme Type" 2437 registry governs an unsigned integer namespace. Initial values for 2438 the Bundle Protocol URI Scheme Type registry are given below. 2440 The registration policy for this registry is: Standards Action. The 2441 allocation should only be granted for a standards-track RFC approved 2442 by the IESG. 2444 The value range is: unsigned integer. 2446 Each assignment consists of a URI scheme type name and its 2447 associated description, a reference to the document that defines the 2448 URI scheme, and a reference to the document that defines the use of 2449 this URI scheme in BP endpoint IDs (including the CBOR 2450 representation of those endpoint IDs in transmitted bundles). 2452 Bundle Protocol URI Scheme Type Registry 2454 +---------+-------------+----------------+------------------+ 2456 | | | BP Utilization | URI Definition | 2458 | Value | Description | Reference | Reference | 2460 +---------+-------------+----------------+------------------+ 2462 | 0 | Reserved | n/a | | 2464 | 1 | dtn | RFC-to-be | RFC-to-be | 2466 | 2 | ipn | RFC-to-be | [RFC6260], | 2468 | | | | RFC-to-be | 2470 | 3-254 | Unassigned | n/a | | 2472 |255-65535| reserved | n/a | | 2474 | >65535 | open for | n/a | | 2476 | | private use | n/a | | 2478 +---------+-------------+----------------+------------------+ 2480 10.7. URI scheme "dtn" 2482 In the Uniform Resource Identifier (URI) Schemes (uri-schemes) 2483 registry, IANA is requested to update the registration of the URI 2484 scheme with the string "dtn" as the scheme name, as follows: 2486 URI scheme name: "dtn" 2488 Status: permanent 2490 Applications and/or protocols that use this URI scheme name: the 2491 Delay-Tolerant Networking (DTN) Bundle Protocol (BP). 2493 Contact: 2495 Scott Burleigh 2497 Jet Propulsion Laboratory, 2499 California Institute of Technology 2501 scott.c.burleigh@jpl.nasa.gov 2503 +1 (800) 393-3353 2505 Change controller: 2507 IETF, iesg@ietf.org 2509 10.8. URI scheme "ipn" 2511 In the Uniform Resource Identifier (URI) Schemes (uri-schemes) 2512 registry, IANA is requested to update the registration of the URI 2513 scheme with the string "ipn" as the scheme name, originally 2514 documented in RFC 6260 [RFC6260], as follows. 2516 URI scheme name: "ipn" 2518 Status: permanent 2520 Applications and/or protocols that use this URI scheme name: the 2521 Delay-Tolerant Networking (DTN) Bundle Protocol (BP). 2523 Contact: 2525 Scott Burleigh 2526 Jet Propulsion Laboratory, 2528 California Institute of Technology 2530 scott.c.burleigh@jpl.nasa.gov 2532 +1 (800) 393-3353 2534 Change controller: 2536 IETF, iesg@ietf.org 2538 11. References 2540 11.1. Normative References 2542 [BPSEC] Birrane, E., "Bundle Security Protocol Specification", 2543 draft-ietf-dtn-bpsec, January 2020. 2545 [CRC16] ITU-T Recommendation X.25, p. 9, section 2.2.7.4, 2546 International Telecommunications Union, October 1996. 2548 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2549 Requirement Levels", BCP 14, RFC 2119, March 1997. 2551 [RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC 2552 4960, September 2007. 2554 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 2555 Specifications: ABNF", STD 68, RFC 5234, January 2008. 2557 [RFC7049] Borman, C. and P. Hoffman, "Concise Binary Object 2558 Representation (CBOR)", RFC 7049, October 2013. 2560 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2561 2119 Key Words", BCP 14, RFC 8174, May 2017. 2563 [SABR] "Schedule-Aware Bundle Routing", CCSDS Recommended Standard 2564 734.3-B-1, Consultative Committee for Space Data Systems, July 2019. 2566 [TCPCL] Sipos, B., Demmer, M., Ott, J., and S. Perreault, "Delay- 2567 Tolerant Networking TCP Convergence Layer Protocol Version 4", 2568 draft-ietf-dtn-tcpclv4, January 2020. 2570 [URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 2571 Resource Identifier (URI): Generic Syntax", RFC 3986, STD 66, 2572 January 2005. 2574 [URIREG] Thaler, D., Hansen, T., and T. Hardie, "Guidelines and 2575 Registration Procedures for URI Schemes", RFC 7595, BCP 35, June 2576 2015. 2578 [UTC] Arias, E. and B. Guinot, "Coordinated universal time UTC: 2579 historical background and perspectives" in "Journees systemes de 2580 reference spatio-temporels", 2004. 2582 11.2. Informative References 2584 [ARCH] V. Cerf et al., "Delay-Tolerant Network Architecture", RFC 2585 4838, April 2007. 2587 [BIBE] Burleigh, S., "Bundle-in-Bundle Encapsulation", draft-ietf- 2588 dtn-bibect, August 2019. 2590 [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource 2591 Identifiers (IRIs)", RFC 3987, January 2005. 2593 [RFC5050] Scott, K. and S. Burleigh, "Bundle Protocol 2594 Specification", RFC 5050, November 2007. 2596 [RFC6255] Blanchet, M., "Delay-Tolerant Networking Bundle Protocol 2597 IANA Registries", RFC 6255, May 2011. 2599 [RFC6257] Symington, S., Farrell, S., Weiss, H., and P. Lovell, 2600 "Bundle Security Protocol Specification", RFC 6257, May 2011. 2602 [RFC6258] Symington, S., "Delay-Tolerant Networking Metadata 2603 Extension Block", RFC 6258, May 2011. 2605 [RFC6259] Symington, S., "Delay-Tolerant Networking Previous-Hop 2606 Insertion Block", RFC 6259, May 2011. 2608 [RFC6260] Burleigh, S., "Compressed Bundle Header Encoding (CBHE)", 2609 RFC 6260, May 2011. 2611 [RFC7143] Chadalapaka, M., Satran, J., Meth, K., and D. Black, 2612 "Internet Small Computer System Interface (iSCSI) Protocol 2613 (Consolidated)", RFC 7143, April 2014. 2615 [SIGC] Fall, K., "A Delay-Tolerant Network Architecture for 2616 Challenged Internets", SIGCOMM 2003. 2618 12. Acknowledgments 2620 This work is freely adapted from RFC 5050, which was an effort of 2621 the Delay Tolerant Networking Research Group. The following DTNRG 2622 participants contributed significant technical material and/or 2623 inputs to that document: Dr. Vinton Cerf of Google, Scott Burleigh, 2624 Adrian Hooke, and Leigh Torgerson of the Jet Propulsion Laboratory, 2625 Michael Demmer of the University of California at Berkeley, Robert 2626 Durst, Keith Scott, and Susan Symington of The MITRE Corporation, 2627 Kevin Fall of Carnegie Mellon University, Stephen Farrell of Trinity 2628 College Dublin, Howard Weiss and Peter Lovell of SPARTA, Inc., and 2629 Manikantan Ramadas of Ohio University. 2631 This document was prepared using 2-Word-v2.0.template.dot. 2633 13. Significant Changes from RFC 5050 2635 Points on which this draft significantly differs from RFC 5050 2636 include the following: 2638 . Clarify the difference between transmission and forwarding. 2639 . Migrate custody transfer to the bundle-in-bundle encapsulation 2640 specification [BIBE]. 2641 . Introduce the concept of "node ID" as functionally distinct 2642 from endpoint ID, while having the same syntax. 2643 . Restructure primary block, making it immutable. Add optional 2644 CRC. 2645 . Add optional CRCs to non-primary blocks. 2646 . Add block ID number to canonical block format (to support 2647 BPsec). 2648 . Add definition of bundle age extension block. 2649 . Add definition of previous node extension block. 2650 . Add definition of hop count extension block. 2651 . Remove Quality of Service markings. 2652 . Change from SDNVs to CBOR representation. 2653 . Add lifetime overrides. 2655 Appendix A. For More Information 2657 Copyright (c) 2020 IETF Trust and the persons identified as authors 2658 of the code. All rights reserved. 2660 Redistribution and use in source and binary forms, with or without 2661 modification, is permitted pursuant to, and subject to the license 2662 terms contained in, the Simplified BSD License set forth in Section 2663 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents 2664 (http://trustee.ietf.org/license-info). 2666 Appendix B. CDDL expression 2668 For informational purposes, Carsten Bormann and Brian Sipos have 2669 kindly provided an expression of the Bundle Protocol specification 2670 in the Concise Data Definition Language (CDDL). That CDDL 2671 expression is presented below. Note that wherever the CDDL 2672 expression is in disagreement with the textual representation of the 2673 BP specification presented in the earlier sections of this document, 2674 the textual representation rules. 2676 start = bundle / #6.55799(bundle) 2678 ; Times before 2000 are invalid 2680 dtn-time = uint 2682 ; CRC enumerated type 2684 crc-type = &( 2686 crc-none: 0, 2688 crc-16bit: 1, 2690 crc-32bit: 2 2692 ) 2694 ; Either 16-bit or 32-bit 2696 crc-value = (bstr .size 2) / (bstr .size 4) 2698 creation-timestamp = [ 2700 dtn-time, ; absolute time of creation 2702 sequence: uint ; sequence within the time 2704 ] 2706 eid = $eid .within eid-structure 2708 eid-structure = [ 2710 uri-code: uint, 2711 SSP: any 2713 ] 2715 $eid /= [ 2717 uri-code: 1, 2719 SSP: (tstr / 0) 2721 ] 2723 $eid /= [ 2725 uri-code: 2, 2727 SSP: [ 2729 nodenum: uint, 2731 servicenum: uint 2733 ] 2735 ] 2737 ; The root bundle array 2739 bundle = [primary-block, *extension-block, payload-block] 2741 primary-block = [ 2743 version: 7, 2745 bundle-control-flags, 2747 crc-type, 2749 destination: eid, 2751 source-node: eid, 2753 report-to: eid, 2755 creation-timestamp, 2757 lifetime: uint, 2758 ? ( 2760 fragment-offset: uint, 2762 total-application-data-length: uint 2764 ), 2766 ? crc-value, 2768 ] 2770 bundle-control-flags = uint .bits bundleflagbits 2772 bundleflagbits = &( 2774 reserved: 21, 2776 reserved: 20, 2778 reserved: 19, 2780 bundle-deletion-status-reports-are-requested: 18, 2782 bundle-delivery-status-reports-are-requested: 17, 2784 bundle-forwarding-status-reports-are-requested: 16, 2786 reserved: 15, 2788 bundle-reception-status-reports-are-requested: 14, 2790 reserved: 13, 2792 reserved: 12, 2794 reserved: 11, 2796 reserved: 10, 2798 reserved: 9, 2800 reserved: 8, 2802 reserved: 7, 2803 status-time-is-requested-in-all-status-reports: 6, 2805 user-application-acknowledgement-is-requested: 5, 2807 reserved: 4, 2809 reserved: 3, 2811 bundle-must-not-be-fragmented: 2, 2813 payload-is-an-administrative-record: 1, 2815 bundle-is-a-fragment: 0 2817 ) 2819 ; Abstract shared structure of all non-primary blocks 2821 canonical-block-structure = [ 2823 block-type-code: uint, 2825 block-number: uint, 2827 block-control-flags, 2829 crc-type, 2831 ; Each block type defines the content within the bytestring 2833 block-type-specific-data, 2835 ? crc-value 2837 ] 2839 block-control-flags = uint .bits blockflagbits 2841 blockflagbits = &( 2843 reserved: 7, 2845 reserved: 6, 2847 reserved: 5, 2849 block-must-be-removed-from-bundle-if-it-cannot-be-processed: 4, 2850 reserved: 3, 2852 bundle-must-be-deleted-if-block-cannot-be-processed: 2, 2854 status-report-must-be-transmitted-if-block-cannot-be-processed: 1, 2856 block-must-be-replicated-in-every-fragment: 0 2858 ) 2860 block-type-specific-data = bstr / #6.24(bstr) 2862 ; Actual CBOR data embedded in a bytestring, with optional tag to 2863 indicate so 2865 embedded-cbor = (bstr .cbor Item) / #6.24(bstr .cbor Item) 2867 ; Extension block type, which does not specialize other than the 2868 code/number 2870 extension-block = $extension-block-structure .within canonical- 2871 block-structure 2873 ; Generic shared structure of all non-primary blocks 2875 extension-block-use = [ 2877 block-type-code: CodeValue, 2879 block-number: (uint .gt 1), 2881 block-control-flags, 2883 crc-type, 2885 BlockData, 2887 ? crc-value 2889 ] 2891 ; Payload block type 2893 payload-block = payload-block-structure .within canonical-block- 2894 structure 2895 payload-block-structure = [ 2897 block-type-code: 1, 2899 block-number: 1, 2901 block-control-flags, 2903 crc-type, 2905 $payload-block-data, 2907 ? crc-value 2909 ] 2911 ; Arbitrary payload data, including non-CBOR bytestring 2913 $payload-block-data /= block-type-specific-data 2915 ; Administrative record as a payload data specialization 2917 $payload-block-data /= embedded-cbor 2919 admin-record = $admin-record .within admin-record-structure 2921 admin-record-structure = [ 2923 record-type-code: uint, 2925 record-content: any 2927 ] 2929 ; Only one defined record type 2931 $admin-record /= [1, status-record-content] 2933 status-record-content = [ 2935 bundle-status-information, 2937 status-report-reason-code: uint, 2939 source-node-eid: eid, 2941 subject-creation-timestamp: creation-timestamp, 2942 ? ( 2944 subject-payload-offset: uint, 2946 subject-payload-length: uint 2948 ) 2950 ] 2952 bundle-status-information = [ 2954 reporting-node-received-bundle: status-info-content, 2956 reporting-node-forwarded-bundle: status-info-content, 2958 reporting-node-delivered-bundle: status-info-content, 2960 reporting-node-deleted-bundle: status-info-content 2962 ] 2964 status-info-content = [ 2966 status-indicator: bool, 2968 ? timestamp: dtn-time 2970 ] 2972 ; Previous Node extension block 2974 $extension-block-structure /= 2976 extension-block-use<6, embedded-cbor> 2978 ext-data-previous-node = eid 2980 ; Bundle Age extension block 2982 $extension-block-structure /= 2984 extension-block-use<7, embedded-cbor> 2986 ext-data-bundle-age = uint 2988 ; Hop Count extension block 2989 $extension-block-structure /= 2991 extension-block-use<10, embedded-cbor> 2993 ext-data-hop-count = [ 2995 hop-limit: uint, 2997 hop-count: uint 2999 ] 3001 Authors' Addresses 3003 Scott Burleigh 3004 Jet Propulsion Laboratory, California Institute of Technology 3005 4800 Oak Grove Dr. 3006 Pasadena, CA 91109-8099 3007 US 3008 Phone: +1 818 393 3353 3009 Email: Scott.C.Burleigh@jpl.nasa.gov 3011 Kevin Fall 3012 Roland Computing Services 3013 3871 Piedmont Ave. Suite 8 3014 Oakland, CA 94611 3015 US 3016 Email: kfall+rcs@kfall.com 3018 Edward J. Birrane 3019 Johns Hopkins University Applied Physics Laboratory 3020 11100 Johns Hopkins Rd 3021 Laurel, MD 20723 3022 US 3023 Phone: +1 443 778 7423 3024 Email: Edward.Birrane@jhuapl.edu