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Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- 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: April 30, 2021 Roland Computing Services 5 E. Birrane 6 APL, Johns Hopkins University 7 October 27, 2020 9 Bundle Protocol Version 7 10 draft-ietf-dtn-bpbis-27.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 April 30, 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...........................14 68 4.1.1. CRC Type............................................14 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......................20 76 4.1.5.2. Node ID........................................21 77 4.1.6. DTN Time............................................22 78 4.1.7. Creation Timestamp..................................22 79 4.1.8. Block-type-specific Data............................23 80 4.2. Bundle Representation....................................23 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.....................29 90 5.2. Bundle Transmission......................................30 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.........................................34 97 5.7. Local Bundle Delivery....................................35 98 5.8. Bundle Fragmentation.....................................36 99 5.9. Application Data Unit Reassembly.........................37 100 5.10. Bundle Deletion.........................................37 101 5.11. Discarding a Bundle.....................................38 102 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.........................48 115 10.3. Bundle Processing Control Flags.........................48 116 10.4. Block Processing Control Flags..........................50 117 10.5. Bundle Status Report Reason Codes.......................51 118 10.6. Bundle Protocol URI scheme types........................53 119 10.7. URI scheme "dtn"........................................54 120 10.8. URI scheme "ipn"........................................55 121 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.................................59 127 Appendix B. CDDL expression......................................60 129 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, a.k.a. "fragmentary bundle", is a bundle 257 whose payload block contains a 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 Cryptographic verification of a block is possible only if the 575 sequence of octets on which the verifying node computes its hash - 576 the canonicalized representation of the block - is identical to the 577 sequence of octets on which the hash declared for that block was 578 computed. To ensure that blocks are always in canonical 579 representation when they are transmitted and received, the CBOR 580 representation of every integer in every block SHALL be of minimum 581 length; that is, no CBOR integer representation may contain any 582 leading octet whose value is 0x00. 584 Each bundle SHALL be a concatenated sequence of at least two blocks, 585 represented as a CBOR indefinite-length array. The first block in 586 the sequence (the first item of the array) MUST be a primary bundle 587 block in CBOR representation as described below; the bundle MUST 588 have exactly one primary bundle block. The primary block MUST be 589 followed by one or more canonical bundle blocks (additional array 590 items) in CBOR representation as described in 4.2.3 below. The last 591 such block MUST be a payload block; the bundle MUST have exactly one 592 payload block. The payload block SHALL be followed by a CBOR 593 "break" stop code, terminating the array. 595 (Note that, while CBOR permits considerable flexibility in the 596 encoding of bundles, this flexibility must not be interpreted as 597 inviting increased complexity in protocol data unit structure.) 599 An implementation of the Bundle Protocol MAY discard any sequence of 600 bytes that does not conform to the Bundle Protocol specification. 602 An implementation of the Bundle Protocol MAY accept a sequence of 603 bytes that does not conform to the Bundle Protocol specification 604 (e.g., one that represents data elements in fixed-length arrays 605 rather than indefinite-length arrays) and transform it into 606 conformant BP structure before processing it. Procedures for 607 accomplishing such a transformation are beyond the scope of this 608 specification. 610 4.1. BP Fundamental Data Structures 612 4.1.1. CRC Type 614 CRC type is an unsigned integer type code for which the following 615 values (and no others) are valid: 617 . 0 indicates "no CRC is present." 618 . 1 indicates "a standard X-25 CRC-16 is present." [CRC16] 619 . 2 indicates "a standard CRC32C (Castagnoli) CRC-32 is present." 620 [RFC4960] 622 CRC type SHALL be represented as a CBOR unsigned integer. 624 For examples of CRC32C CRCs, see Appendix A.4 of [RFC7143]. 626 Note that more robust protection of BP data integrity, as needed, 627 may be provided by means of Block Integrity Blocks as defined in the 628 Bundle Security Protocol [BPSEC]). 630 4.1.2. CRC 632 CRC SHALL be omitted from a block if and only if the block's CRC 633 type code is zero. 635 When not omitted, the CRC SHALL be represented as a CBOR byte string 636 of two bytes (that is, CBOR additional information 2, if CRC type is 637 1) or of four bytes (that is, CBOR additional information 4, if CRC 638 type is 2); in each case the sequence of bytes SHALL constitute an 639 unsigned integer value (of 16 or 32 bits, respectively) in network 640 byte order. 642 4.1.3. Bundle Processing Control Flags 644 Bundle processing control flags assert properties of the bundle as a 645 whole rather than of any particular block of the bundle. They are 646 conveyed in the primary block of the bundle. 648 The following properties are asserted by the bundle processing 649 control flags: 651 . The bundle is a fragment. (Boolean) 653 . The bundle's payload is an administrative record. (Boolean) 655 . The bundle must not be fragmented. (Boolean) 656 . Acknowledgment by the user application is requested. (Boolean) 658 . Status time is requested in all status reports. (Boolean) 660 . Flags requesting types of status reports (all Boolean): 662 o Request reporting of bundle reception. 664 o Request reporting of bundle forwarding. 666 o Request reporting of bundle delivery. 668 o Request reporting of bundle deletion. 670 If the bundle processing control flags indicate that the bundle's 671 application data unit is an administrative record, then all status 672 report request flag values MUST be zero. 674 If the bundle's source node is omitted (i.e., the source node ID is 675 the ID of the null endpoint, which has no members as discussed 676 below; this option enables anonymous bundle transmission), then the 677 bundle is not uniquely identifiable and all bundle protocol features 678 that rely on bundle identity must therefore be disabled: the "Bundle 679 must not be fragmented" flag value MUST be 1 and all status report 680 request flag values MUST be zero. 682 Bundle processing control flags that are unrecognized MUST be 683 ignored, as future definitions of additional flags might not be 684 integrated simultaneously into the Bundle Protocol implementations 685 operating at all nodes. 687 The bundle processing control flags SHALL be represented as a CBOR 688 unsigned integer item, the value of which SHALL be processed as a 689 bit field indicating the control flag values as follows (note that 690 bit numbering in this instance is reversed from the usual practice, 691 beginning with the low-order bit instead of the high-order bit, in 692 recognition of the potential definition of additional control flag 693 values in the future): 695 . Bit 0 (the low-order bit, 0x000001): bundle is a fragment. 696 . Bit 1 (0x000002): payload is an administrative record. 697 . Bit 2 (0x000004): bundle must not be fragmented. 698 . Bit 3 (0x000008): reserved. 699 . Bit 4 (0x000010): reserved. 700 . Bit 5 (0x000020): user application acknowledgement is 701 requested. 703 . Bit 6 (0x000040): status time is requested in all status 704 reports. 705 . Bit 7 (0x000080): reserved. 706 . Bit 8 (0x000100): reserved. 707 . Bit 9 (0x000200): reserved. 708 . Bit 10(0x000400): reserved. 709 . Bit 11(0x000800): reserved. 710 . Bit 12(0x001000): reserved. 711 . Bit 13(0x002000): reserved. 712 . Bit 14(0x004000): bundle reception status reports are 713 requested. 714 . Bit 15(0x008000): reserved. 715 . Bit 16(0x010000): bundle forwarding status reports are 716 requested. 717 . Bit 17(0x020000): bundle delivery status reports are requested. 718 . Bit 18(0x040000): bundle deletion status reports are requested. 719 . Bits 19-20 are reserved. 720 . Bits 21-63 are unassigned. 722 4.1.4. Block Processing Control Flags 724 The block processing control flags assert properties of canonical 725 bundle blocks. They are conveyed in the header of the block to 726 which they pertain. 728 Block processing control flags that are unrecognized MUST be 729 ignored, as future definitions of additional flags might not be 730 integrated simultaneously into the Bundle Protocol implementations 731 operating at all nodes. 733 The block processing control flags SHALL be represented as a CBOR 734 unsigned integer item, the value of which SHALL be processed as a 735 bit field indicating the control flag values as follows (note that 736 bit numbering in this instance is reversed from the usual practice, 737 beginning with the low-order bit instead of the high-order bit, for 738 agreement with the bit numbering of the bundle processing control 739 flags): 741 . Bit 0(the low-order bit, 0x01): block must be replicated in 742 every fragment. 743 . Bit 1(0x02): transmission of a status report is requested if 744 block can't be processed. 745 . Bit 2(0x04): bundle must be deleted if block can't be 746 processed. 747 . Bit 3(0x08): reserved. 748 . Bit 4(0x10): block must be removed from bundle if it can't be 749 processed. 751 . Bit 5(0x20): reserved. 752 . Bit 6 (0x40): reserved. 753 . Bits 7-63 are unassigned. 755 For each bundle whose bundle processing control flags indicate that 756 the bundle's application data unit is an administrative record, or 757 whose source node ID is the null endpoint ID as defined below, the 758 value of the "Transmit status report if block can't be processed" 759 flag in every canonical block of the bundle MUST be zero. 761 4.1.5. Identifiers 763 4.1.5.1. Endpoint ID 765 The destinations of bundles are bundle endpoints, identified by text 766 strings termed "endpoint IDs" (see Section 3.1). Each endpoint ID 767 (EID) is a Uniform Resource Identifier (URI; [URI]). As such, each 768 endpoint ID can be characterized as having this general structure: 770 < scheme name > : < scheme-specific part, or "SSP" > 772 The scheme identified by the < scheme name > in an endpoint ID is a 773 set of syntactic and semantic rules that fully explain how to parse 774 and interpret the SSP. Each scheme that may be used to form a BP 775 endpoint ID must be added to the registry of URI scheme code numbers 776 for Bundle Protocol maintained by IANA as described in Section 10; 777 association of a unique URI scheme code number with each scheme name 778 in this registry helps to enable compact representation of endpoint 779 IDs in bundle blocks. Note that the set of allowable schemes is 780 effectively unlimited. Any scheme conforming to [URIREG] may be 781 added to the URI scheme code number registry and thereupon used in a 782 bundle protocol endpoint ID. 784 Each entry in the URI scheme code number registry MUST contain a 785 reference to a scheme code number definition document, which defines 786 the manner in which the scheme-specific part of any URI formed in 787 that scheme is parsed and interpreted and MUST be encoded, in CBOR 788 representation, for transmission as a BP endpoint ID. The scheme 789 code number definition document may also contain information as to 790 (a) which convergence-layer protocol(s) may be used to forward a 791 bundle to a BP destination endpoint identified by such an ID, and 792 (b) how the ID of the convergence-layer protocol endpoint to use for 793 that purpose can be inferred from that destination endpoint ID. 795 Note that, although endpoint IDs are URIs, implementations of the BP 796 service interface may support expression of endpoint IDs in some 797 internationalized manner (e.g., Internationalized Resource 798 Identifiers (IRIs); see [RFC3987]). 800 Each BP endpoint ID (EID) SHALL be represented as a CBOR array 801 comprising two items. 803 The first item of the array SHALL be the code number identifying the 804 endpoint ID's URI scheme, as defined in the registry of URI scheme 805 code numbers for Bundle Protocol. Each URI scheme code number SHALL 806 be represented as a CBOR unsigned integer. 808 The second item of the array SHALL be the applicable CBOR 809 representation of the scheme-specific part (SSP) of the EID, defined 810 as noted in the URI scheme code number registry entry for the EID's 811 URI scheme. 813 4.1.5.1.1. The "dtn" URI scheme 815 The "dtn" scheme supports the identification of BP endpoints by 816 arbitrarily expressive character strings. It is specified as 817 follows: 819 Scheme syntax: This specification uses the Augmented Backus-Naur 820 Form (ABNF) notation of [RFC5234]. 822 dtn-uri = "dtn:" ("none"/dtn-hier-part) 824 dtn-hier-part = "//" node-name name-delim demux ; a path-rootless 826 node-name = 1*(ALPHA/DIGIT/"-"/"."/"_") reg-name 828 name-delim = "/" 830 demux = *VCHAR 832 Scheme semantics: URIs of the DTN scheme are used as endpoint 833 identifiers in the Delay-Tolerant Networking (DTN) Bundle Protocol 834 (BP) as described in the present document. 836 The endpoint ID "dtn:none" identifies the "null endpoint", the 837 endpoint that by definition never has any members. 839 All BP endpoints identified by all other dtn-scheme endpoint IDs for 840 which the first character of demux is a character other than '~' 841 (tilde) are singleton endpoints. All BP endpoints identified by dtn- 842 scheme endpoint IDs for which the first character *is* '~' (tilde) 843 are *not* singleton endpoints. 845 A dtn-scheme endpoint ID for which the demux is of length zero MAY 846 identify the administrative endpoint for the node identified by 847 node-name, and as such may serve as a node ID. No dtn-scheme 848 endpoint ID for which the demux is of non-zero length may do so. 850 Encoding considerations: For transmission as a BP endpoint ID, the 851 scheme-specific part of a URI of the dtn scheme SHALL be represented 852 as a CBOR text string unless the EID's SSP is "none", in which case 853 the SSP SHALL be represented as a CBOR unsigned integer with the 854 value zero. For all other purposes, URIs of the dtn scheme are 855 encoded exclusively in US-ASCII characters. 857 Interoperability considerations: none. 859 Security considerations: 861 . Reliability and consistency: none of the BP endpoints 862 identified by the URIs of the DTN scheme are guaranteed to be 863 reachable at any time, and the identity of the processing 864 entities operating on those endpoints is never guaranteed by 865 the Bundle Protocol itself. Bundle authentication as defined by 866 the Bundle Security Protocol is required for this purpose. 867 . Malicious construction: malicious construction of a conformant 868 DTN-scheme URI is limited to the malicious selection of node 869 names and the malicious selection of demux strings. That is, a 870 maliciously constructed DTN-scheme URI could be used to direct 871 a bundle to an endpoint that might be damaged by the arrival of 872 that bundle or, alternatively, to declare a false source for a 873 bundle and thereby cause incorrect processing at a node that 874 receives the bundle. In both cases (and indeed in all bundle 875 processing), the node that receives a bundle should verify its 876 authenticity and validity before operating on it in any way. 877 . Back-end transcoding: the limited expressiveness of URIs of the 878 DTN scheme effectively eliminates the possibility of threat due 879 to errors in back-end transcoding. 880 . Rare IP address formats: not relevant, as IP addresses do not 881 appear anywhere in conformant DTN-scheme URIs. 882 . Sensitive information: because DTN-scheme URIs are used only to 883 represent the identities of Bundle Protocol endpoints, the risk 884 of disclosure of sensitive information due to interception of 885 these URIs is minimal. Examination of DTN-scheme URIs could be 886 used to support traffic analysis; where traffic analysis is a 887 plausible danger, bundles should be conveyed by secure 888 convergence-layer protocols that do not expose endpoint IDs. 889 . Semantic attacks: the simplicity of DTN-scheme URI syntax 890 minimizes the possibility of misinterpretation of a URI by a 891 human user. 893 4.1.5.1.2. The "ipn" URI scheme 895 The "ipn" scheme supports the identification of BP endpoints by 896 pairs of unsigned integers, for compact representation in bundle 897 blocks. It is specified as follows: 899 Scheme syntax: This specification uses the Augmented Backus-Naur 900 Form (ABNF) notation of [RFC5234], including the core ABNF syntax 901 rule for DIGIT defined by that specification. 903 ipn-uri = "ipn:" ipn-hier-part 905 ipn-hier-part = node-nbr nbr-delim service-nbr ; a path-rootless 907 node-nbr = 1*DIGIT 909 nbr-delim = "." 911 service-nbr = 1*DIGIT 913 Scheme semantics: URIs of the ipn scheme are used as endpoint 914 identifiers in the Delay-Tolerant Networking (DTN) Bundle Protocol 915 (BP) as described in the present document. 917 All BP endpoints identified by ipn-scheme endpoint IDs are singleton 918 endpoints. 920 An ipn-scheme endpoint ID for which service-nbr is zero MAY identify 921 the administrative endpoint for the node identified by node-nbr, and 922 as such may serve as a node ID. No ipn-scheme endpoint ID for which 923 service-nbr is non-zero may do so. 925 Encoding considerations: For transmission as a BP endpoint ID, the 926 scheme-specific part of a URI of the dtn scheme the SSP SHALL be 927 represented as a CBOR array comprising two items. The first item of 928 this array SHALL be the EID's node number (a number that identifies 929 the node) represented as a CBOR unsigned integer. The second item 930 of this array SHALL be the EID's service number (a number that 931 identifies some application service) represented as a CBOR unsigned 932 integer. For all other purposes, URIs of the IPN scheme are encoded 933 exclusively in US-ASCII characters. 935 Interoperability considerations: none. 937 Security considerations: 939 . Reliability and consistency: none of the BP endpoints 940 identified by the URIs of the IPN scheme are guaranteed to be 941 reachable at any time, and the identity of the processing 942 entities operating on those endpoints is never guaranteed by 943 the Bundle Protocol itself. Bundle authentication as defined by 944 the Bundle Security Protocol [BPSEC] is required for this 945 purpose. 946 . Malicious construction: malicious construction of a conformant 947 IPN-scheme URI is limited to the malicious selection of node 948 numbers and the malicious selection of service numbers. That 949 is, a maliciously constructed IPN-scheme URI could be used to 950 direct a bundle to an endpoint that might be damaged by the 951 arrival of that bundle or, alternatively, to declare a false 952 source for a bundle and thereby cause incorrect processing at a 953 node that receives the bundle. In both cases (and indeed in 954 all bundle processing), the node that receives a bundle should 955 verify its authenticity and validity before operating on it in 956 any way. 957 . Back-end transcoding: the limited expressiveness of URIs of the 958 IPN scheme effectively eliminates the possibility of threat due 959 to errors in back-end transcoding. 960 . Rare IP address formats: not relevant, as IP addresses do not 961 appear anywhere in conformant IPN-scheme URIs. 962 . Sensitive information: because IPN-scheme URIs are used only to 963 represent the identities of Bundle Protocol endpoints, the risk 964 of disclosure of sensitive information due to interception of 965 these URIs is minimal. Examination of IPN-scheme URIs could be 966 used to support traffic analysis; where traffic analysis is a 967 plausible danger, bundles should be conveyed by secure 968 convergence-layer protocols that do not expose endpoint IDs. 969 . Semantic attacks: the simplicity of IPN-scheme URI syntax 970 minimizes the possibility of misinterpretation of a URI by a 971 human user. 973 4.1.5.2. Node ID 975 For many purposes of the Bundle Protocol it is important to identify 976 the node that is operative in some context. 978 As discussed in 3.1 above, nodes are distinct from endpoints; 979 specifically, an endpoint is a set of zero or more nodes. But 980 rather than define a separate namespace for node identifiers, we 981 instead use endpoint identifiers to identify nodes as discussed in 982 3.2 above. Formally: 984 . Every node is, by definition, permanently registered in the 985 singleton endpoint at which administrative records are 986 delivered to its application agent's administrative element, 987 termed the node's "administrative endpoint". 988 . As such, the EID of a node's administrative endpoint SHALL 989 uniquely identify that node. 990 . A "node ID" is an EID that identifies the administrative 991 endpoint of a node. 993 4.1.6. DTN Time 995 A DTN time is an unsigned integer indicating the number of 996 milliseconds that have elapsed since the start of the year 2000 on 997 the Coordinated Universal Time (UTC) scale [UTC]. Each DTN time 998 SHALL be represented as a CBOR unsigned integer item. 1000 Implementers need to be aware that DTN time values conveyed in CBOR 1001 representation in bundles will nearly always exceed (2**32 - 1). 1003 4.1.7. Creation Timestamp 1005 Each bundle's creation timestamp SHALL be represented as a CBOR 1006 array comprising two items. 1008 The first item of the array, termed "bundle creation time", SHALL be 1009 the DTN time at which the transmission request was received that 1010 resulted in the creation of the bundle, represented as a CBOR 1011 unsigned integer. 1013 The second item of the array, termed the creation timestamp's 1014 "sequence number", SHALL be the latest value (as of the time at 1015 which the transmission request was received) of a monotonically 1016 increasing positive integer counter managed by the source node's 1017 bundle protocol agent, represented as a CBOR unsigned integer. The 1018 sequence counter MAY be reset to zero whenever the current time 1019 advances by one millisecond. 1021 For nodes that lack accurate clocks, it is recommended that bundle 1022 creation time be set to zero and that the counter used as the source 1023 of the bundle sequence count never be reset to zero. 1025 Note that, in general, the creation of two distinct bundles with the 1026 same source node ID and bundle creation timestamp may result in 1027 unexpected network behavior and/or suboptimal performance. The 1028 combination of source node ID and bundle creation timestamp serves 1029 to identify a single transmission request, enabling it to be 1030 acknowledged by the receiving application (provided the source node 1031 ID is not the null endpoint ID). 1033 4.1.8. Block-type-specific Data 1035 Block-type-specific data in each block (other than the primary 1036 block) SHALL be the applicable CBOR representation of the content of 1037 the block. Details of this representation are included in the 1038 specification defining the block type. 1040 4.2. Bundle Representation 1042 This section describes the primary block in detail and non-primary 1043 blocks in general. Rules for processing these blocks appear in 1044 Section 5 of this document. 1046 Note that supplementary DTN protocol specifications (including, but 1047 not restricted to, the Bundle Security Protocol [BPSEC]) may require 1048 that BP implementations conforming to those protocols construct and 1049 process additional blocks. 1051 4.2.1. Bundle 1053 Each bundle SHALL be represented as a CBOR indefinite-length array. 1054 The first item of this array SHALL be the CBOR representation of a 1055 Primary Block. Every other item of the array SHALL be the CBOR 1056 representation of a Canonical Block. The last block of the bundle 1057 SHALL be followed by a CBOR "break" stop code, terminating the 1058 array. 1060 Associated with each block of a bundle is a block number. The block 1061 number uniquely identifies the block within the bundle, enabling 1062 blocks (notably bundle security protocol blocks) to reference other 1063 blocks in the same bundle without ambiguity. The block number of 1064 the primary block is implicitly zero; the block numbers of all other 1065 blocks are explicitly stated in block headers as noted below. Block 1066 numbering is unrelated to the order in which blocks are sequenced in 1067 the bundle. The block number of the payload block is always 1. 1069 4.2.2. Primary Bundle Block 1071 The primary bundle block contains the basic information needed to 1072 forward bundles to their destinations. 1074 Each primary block SHALL be represented as a CBOR array; the number 1075 of elements in the array SHALL be 8 (if the bundle is not a fragment 1076 and the block has no CRC), 9 (if the block has a CRC and the bundle 1077 is not a fragment), 10 (if the bundle is a fragment and the block 1078 has no CRC), or 11 (if the bundle is a fragment and the block has a 1079 CRC). 1081 The primary block of each bundle SHALL be immutable. The CBOR- 1082 encoded values of all fields in the primary block MUST remain 1083 unchanged from the time the block is created to the time it is 1084 delivered. 1086 The fields of the primary bundle block SHALL be as follows, listed 1087 in the order in which they MUST appear: 1089 Version: An unsigned integer value indicating the version of the 1090 bundle protocol that constructed this block. The present document 1091 describes version 7 of the bundle protocol. Version number SHALL be 1092 represented as a CBOR unsigned integer item. 1094 Bundle Processing Control Flags: The Bundle Processing Control Flags 1095 are discussed in Section 4.1.3. above. 1097 CRC Type: CRC Type codes are discussed in Section 4.1.1. above. The 1098 CRC Type code for the primary block MAY be zero if the bundle 1099 contains a BPsec [BPSEC] Block Integrity Block whose target is the 1100 primary block; otherwise the CRC Type code for the primary block 1101 MUST be non-zero. 1103 Destination EID: The Destination EID field identifies the bundle 1104 endpoint that is the bundle's destination, i.e., the endpoint that 1105 contains the node(s) at which the bundle is to be delivered. 1107 Source node ID: The Source node ID field identifies the bundle node 1108 at which the bundle was initially transmitted, except that Source 1109 node ID may be the null endpoint ID in the event that the bundle's 1110 source chooses to remain anonymous. 1112 Report-to EID: The Report-to EID field identifies the bundle 1113 endpoint to which status reports pertaining to the forwarding and 1114 delivery of this bundle are to be transmitted. 1116 Creation Timestamp: The creation timestamp (discussed in 4.1.7 1117 above) comprises two unsigned integers that, together with the 1118 source node ID and (if the bundle is a fragment) the fragment offset 1119 and payload length, serve to identify the bundle. The first of these 1120 integers is the bundle's creation time, while the second is the 1121 bundle's creation timestamp sequence number. Bundle creation time 1122 SHALL be the DTN time at which the transmission request was received 1123 that resulted in the creation of the bundle. Sequence count SHALL be 1124 the latest value (as of the time at which that transmission request 1125 was received) of a monotonically increasing positive integer counter 1126 managed by the source node's bundle protocol agent that MAY be reset 1127 to zero whenever the current time advances by one millisecond. For 1128 nodes that lack accurate clocks, it is recommended that bundle 1129 creation time be set to zero and that the counter used as the source 1130 of the bundle sequence count never be reset to zero. Note that, in 1131 general, the creation of two distinct bundles with the same source 1132 node ID and bundle creation timestamp may result in unexpected 1133 network behavior and/or suboptimal performance. The combination of 1134 source node ID and bundle creation timestamp serves to identify a 1135 single transmission request, enabling it to be acknowledged by the 1136 receiving application (provided the source node ID is not the null 1137 endpoint ID). 1139 Lifetime: The lifetime field is an unsigned integer that indicates 1140 the time at which the bundle's payload will no longer be useful, 1141 encoded as a number of milliseconds past the creation time. (For 1142 high-rate deployments with very brief disruptions, fine-grained 1143 expression of bundle lifetime may be useful.) When a bundle's age 1144 exceeds its lifetime, bundle nodes need no longer retain or forward 1145 the bundle; the bundle SHOULD be deleted from the network. 1147 If the asserted lifetime for a received bundle is so lengthy that 1148 retention of the bundle until its expiration time might degrade 1149 operation of the node at which the bundle is received, or if the 1150 bundle protocol agent of that node determines that the bundle must 1151 be deleted in order to prevent network performance degradation 1152 (e.g., the bundle appears to be part of a denial-of-service attack), 1153 then that bundle protocol agent MAY impose a temporary overriding 1154 lifetime of shorter duration; such overriding lifetime SHALL NOT 1155 replace the lifetime asserted in the bundle but SHALL serve as the 1156 bundle's effective lifetime while the bundle resides at that node. 1157 Procedures for imposing lifetime overrides are beyond the scope of 1158 this specification. 1160 For bundles originating at nodes that lack accurate clocks, it is 1161 recommended that bundle age be obtained from the Bundle Age 1162 extension block (see 4.3.2 below) rather than from the difference 1163 between current time and bundle creation time. Bundle lifetime 1164 SHALL be represented as a CBOR unsigned integer item. 1166 Fragment offset: If and only if the Bundle Processing Control Flags 1167 of this Primary block indicate that the bundle is a fragment, 1168 fragment offset SHALL be present in the primary block. Fragment 1169 offset SHALL be represented as a CBOR unsigned integer indicating 1170 the offset from the start of the original application data unit at 1171 which the bytes comprising the payload of this bundle were located. 1173 Total Application Data Unit Length: If and only if the Bundle 1174 Processing Control Flags of this Primary block indicate that the 1175 bundle is a fragment, total application data unit length SHALL be 1176 present in the primary block. Total application data unit length 1177 SHALL be represented as a CBOR unsigned integer indicating the total 1178 length of the original application data unit of which this bundle's 1179 payload is a part. 1181 CRC: A CRC SHALL be present in the primary block unless the bundle 1182 includes a BPsec [BPSEC] Block Integrity Block whose target is the 1183 primary block, in which case a CRC MAY be present in the primary 1184 block. The length and nature of the CRC SHALL be as indicated by 1185 the CRC type. The CRC SHALL be computed over the concatenation of 1186 all bytes (including CBOR "break" characters) of the primary block 1187 including the CRC field itself, which for this purpose SHALL be 1188 temporarily populated with all bytes set to zero. 1190 4.2.3. Canonical Bundle Block Format 1192 Every block other than the primary block (all such blocks are termed 1193 "canonical" blocks) SHALL be represented as a CBOR array; the number 1194 of elements in the array SHALL be 5 (if CRC type is zero) or 6 1195 (otherwise). 1197 The fields of every canonical block SHALL be as follows, listed in 1198 the order in which they MUST appear: 1200 . Block type code, an unsigned integer. Bundle block type code 1 1201 indicates that the block is a bundle payload block. Block type 1202 codes 2 through 9 are explicitly reserved as noted later in 1203 this specification. Block type codes 192 through 255 are not 1204 reserved and are available for private and/or experimental use. 1205 All other block type code values are reserved for future use. 1206 . Block number, an unsigned integer as discussed in 4.2.1 above. 1207 Block number SHALL be represented as a CBOR unsigned integer. 1208 . Block processing control flags as discussed in Section 4.1.4 1209 above. 1210 . CRC type as discussed in Section 4.1.1 above. 1211 . Block-type-specific data represented as a single definite- 1212 length CBOR byte string, i.e., a CBOR byte string that is not 1213 of indefinite length. For each type of block, the block-type- 1214 specific data byte string is the serialization, in a block- 1215 type-specific manner, of the data conveyed by that type of 1216 block; definitions of blocks are required to define the manner 1217 in which block-type-specific data are serialized within the 1218 block-type-specific data field. For the Payload Block in 1219 particular (block type 1), the block-type-specific data field, 1220 termed the "payload", SHALL be an application data unit, or 1221 some contiguous extent thereof, represented as a definite- 1222 length CBOR byte string. 1223 . If and only if the value of the CRC type field of this block is 1224 non-zero, a CRC. If present, the length and nature of the CRC 1225 SHALL be as indicated by the CRC type and the CRC SHALL be 1226 computed over the concatenation of all bytes of the block 1227 (including CBOR "break" characters) including the CRC field 1228 itself, which for this purpose SHALL be temporarily populated 1229 with all bytes set to zero. 1231 4.3. Extension Blocks 1233 "Extension blocks" are all blocks other than the primary and payload 1234 blocks. Because not all extension blocks are defined in the Bundle 1235 Protocol specification (the present document), not all nodes 1236 conforming to this specification will necessarily instantiate Bundle 1237 Protocol implementations that include procedures for processing 1238 (that is, recognizing, parsing, acting on, and/or producing) all 1239 extension blocks. It is therefore possible for a node to receive a 1240 bundle that includes extension blocks that the node cannot process. 1241 The values of the block processing control flags indicate the action 1242 to be taken by the bundle protocol agent when this is the case. 1244 The following extension blocks are defined in the current document. 1246 4.3.1. Previous Node 1248 The Previous Node block, block type 6, identifies the node that 1249 forwarded this bundle to the local node (i.e., to the node at which 1250 the bundle currently resides); its block-type-specific data is the 1251 node ID of that forwarder node which SHALL take the form of a node 1252 ID represented as described in Section 4.1.5.2. above. If the local 1253 node is the source of the bundle, then the bundle MUST NOT contain 1254 any Previous Node block. Otherwise the bundle SHOULD contain one 1255 (1) occurrence of this type of block and MUST NOT contain more than 1256 one. 1258 4.3.2. Bundle Age 1260 The Bundle Age block, block type 7, contains the number of 1261 milliseconds that have elapsed between the time the bundle was 1262 created and time at which it was most recently forwarded. It is 1263 intended for use by nodes lacking access to an accurate clock, to 1264 aid in determining the time at which a bundle's lifetime expires. 1265 The block-type-specific data of this block is an unsigned integer 1266 containing the age of the bundle in milliseconds, which SHALL be 1267 represented as a CBOR unsigned integer item. (The age of the bundle 1268 is the sum of all known intervals of the bundle's residence at 1269 forwarding nodes, up to the time at which the bundle was most 1270 recently forwarded, plus the summation of signal propagation time 1271 over all episodes of transmission between forwarding nodes. 1272 Determination of these values is an implementation matter.) If the 1273 bundle's creation time is zero, then the bundle MUST contain exactly 1274 one (1) occurrence of this type of block; otherwise, the bundle MAY 1275 contain at most one (1) occurrence of this type of block. A bundle 1276 MUST NOT contain multiple occurrences of the bundle age block, as 1277 this could result in processing anomalies. 1279 4.3.3. Hop Count 1281 The Hop Count block, block type 10, contains two unsigned integers, 1282 hop limit and hop count. A "hop" is here defined as an occasion on 1283 which a bundle was forwarded from one node to another node. Hop 1284 limit MUST be in the range 1 through 255. The hop limit value SHOULD 1285 NOT be changed at any time after creation of the Hop Count block; 1286 the hop count value SHOULD initially be zero and SHOULD be increased 1287 by 1 on each hop. 1289 The hop count block is mainly intended as a safety mechanism, a 1290 means of identifying bundles for removal from the network that can 1291 never be delivered due to a persistent forwarding error. Hop count 1292 is particularly valuable as a defense against routing anomalies that 1293 might cause a bundle to be forwarded in a cyclical "ping-pong" 1294 fashion between two nodes. When a bundle's hop count exceeds its 1295 hop limit, the bundle SHOULD be deleted for the reason "hop limit 1296 exceeded", following the bundle deletion procedure defined in 1297 Section 5.10. 1299 Procedures for determining the appropriate hop limit for a bundle 1300 are beyond the scope of this specification. 1302 The block-type-specific data in a hop count block SHALL be 1303 represented as a CBOR array comprising two items. The first item of 1304 this array SHALL be the bundle's hop limit, represented as a CBOR 1305 unsigned integer. The second item of this array SHALL be the 1306 bundle's hop count, represented as a CBOR unsigned integer. A bundle 1307 MAY contain one occurrence of this type of block but MUST NOT 1308 contain more than one. 1310 5. Bundle Processing 1312 The bundle processing procedures mandated in this section and in 1313 Section 6 govern the operation of the Bundle Protocol Agent and the 1314 Application Agent administrative element of each bundle node. They 1315 are neither exhaustive nor exclusive. Supplementary DTN protocol 1316 specifications (including, but not restricted to, the Bundle 1317 Security Protocol [BPSEC]) may augment, override, or supersede the 1318 mandates of this document. 1320 5.1. Generation of Administrative Records 1322 All transmission of bundles is in response to bundle transmission 1323 requests presented by nodes' application agents. When required to 1324 "generate" an administrative record (such as a bundle status 1325 report), the bundle protocol agent itself is responsible for causing 1326 a new bundle to be transmitted, conveying that record. In concept, 1327 the bundle protocol agent discharges this responsibility by 1328 directing the administrative element of the node's application agent 1329 to construct the record and request its transmission as detailed in 1330 Section 6 below. In practice, the manner in which administrative 1331 record generation is accomplished is an implementation matter, 1332 provided the constraints noted in Section 6 are observed. 1334 Status reports are relatively small bundles. Moreover, even when 1335 the generation of status reports is enabled the decision on whether 1336 or not to generate a requested status report is left to the 1337 discretion of the bundle protocol agent. Nonetheless, note that 1338 requesting status reports for any single bundle might easily result 1339 in the generation of (1 + (2 *(N-1))) status report bundles, where N 1340 is the number of nodes on the path from the bundle's source to its 1341 destination, inclusive. That is, the requesting of status reports 1342 for large numbers of bundles could result in an unacceptable 1343 increase in the bundle traffic in the network. For this reason, the 1344 generation of status reports MUST be disabled by default and enabled 1345 only when the risk of excessive network traffic is deemed 1346 acceptable. Mechanisms that could assist in assessing and 1347 mitigating this risk, such as pre-placed agreements authorizing the 1348 generation of status reports under specified circumstances, are 1349 beyond the scope of this specification. 1351 Notes on administrative record terminology: 1353 . A "bundle reception status report" is a bundle status report 1354 with the "reporting node received bundle" flag set to 1. 1355 . A "bundle forwarding status report" is a bundle status report 1356 with the "reporting node forwarded the bundle" flag set to 1. 1357 . A "bundle delivery status report" is a bundle status report 1358 with the "reporting node delivered the bundle" flag set to 1. 1359 . A "bundle deletion status report" is a bundle status report 1360 with the "reporting node deleted the bundle" flag set to 1. 1362 5.2. Bundle Transmission 1364 The steps in processing a bundle transmission request are: 1366 Step 1: Transmission of the bundle is initiated. An outbound bundle 1367 MUST be created per the parameters of the bundle transmission 1368 request, with the retention constraint "Dispatch pending". The 1369 source node ID of the bundle MUST be either the null endpoint ID, 1370 indicating that the source of the bundle is anonymous, or else the 1371 EID of a singleton endpoint whose only member is the node of which 1372 the BPA is a component. 1374 Step 2: Processing proceeds from Step 1 of Section 5.4. 1376 5.3. Bundle Dispatching 1378 The steps in dispatching a bundle are: 1380 Step 1: If the bundle's destination endpoint is an endpoint of which 1381 the node is a member, the bundle delivery procedure defined in 1382 Section 5.7 MUST be followed and for the purposes of all subsequent 1383 processing of this bundle at this node the node's membership in the 1384 bundle's destination endpoint SHALL be disavowed; specifically, even 1385 though the node is a member of the bundle's destination endpoint, 1386 the node SHALL NOT undertake to forward the bundle to itself in the 1387 course of performing the procedure described in Section 5.4. 1389 Step 2: Processing proceeds from Step 1 of Section 5.4. 1391 5.4. Bundle Forwarding 1393 The steps in forwarding a bundle are: 1395 Step 1: The retention constraint "Forward pending" MUST be added to 1396 the bundle, and the bundle's "Dispatch pending" retention constraint 1397 MUST be removed. 1399 Step 2: The bundle protocol agent MUST determine whether or not 1400 forwarding is contraindicated (that is, rendered inadvisable) for 1401 any of the reasons listed in the IANA registry of Bundle Status 1402 Report Reason Codes (see section 10.5 below), whose initial contents 1403 are listed in Figure 4. In particular: 1405 . The bundle protocol agent MAY choose either to forward the 1406 bundle directly to its destination node(s) (if possible) or to 1407 forward the bundle to some other node(s) for further 1408 forwarding. The manner in which this decision is made may 1409 depend on the scheme name in the destination endpoint ID and/or 1410 on other state but in any case is beyond the scope of this 1411 document; one possible mechanism is described in [SABR]. If the 1412 BPA elects to forward the bundle to some other node(s) for 1413 further forwarding but finds it impossible to select any 1414 node(s) to forward the bundle to, then forwarding is 1415 contraindicated. 1416 . Provided the bundle protocol agent succeeded in selecting the 1417 node(s) to forward the bundle to, the bundle protocol agent 1418 MUST subsequently select the convergence layer adapter(s) whose 1419 services will enable the node to send the bundle to those 1420 nodes. The manner in which specific appropriate convergence 1421 layer adapters are selected is beyond the scope of this 1422 document; the TCP convergence-layer adapter [TCPCL] MUST be 1423 implemented when some or all of the bundles forwarded by the 1424 bundle protocol agent must be forwarded via the Internet but 1425 may not be appropriate for the forwarding of any particular 1426 bundle. If the agent finds it impossible to select any 1427 appropriate convergence layer adapter(s) to use in forwarding 1428 this bundle, then forwarding is contraindicated. 1430 Step 3: If forwarding of the bundle is determined to be 1431 contraindicated for any of the reasons listed in the IANA registry 1432 of Bundle Status Report Reason Codes (see section 10.5 below), then 1433 the Forwarding Contraindicated procedure defined in Section 5.4.1 1434 MUST be followed; the remaining steps of Section 5.4 are skipped at 1435 this time. 1437 Step 4: For each node selected for forwarding, the bundle protocol 1438 agent MUST invoke the services of the selected convergence layer 1439 adapter(s) in order to effect the sending of the bundle to that 1440 node. Determining the time at which the bundle protocol agent 1441 invokes convergence layer adapter services is a BPA implementation 1442 matter. Determining the time at which each convergence layer 1443 adapter subsequently responds to this service invocation by sending 1444 the bundle is a convergence-layer adapter implementation matter. 1445 Note that: 1447 . If the bundle has a Previous Node block, as defined in 4.3.1 1448 above, then that block MUST be removed from the bundle before 1449 the bundle is forwarded. 1450 . If the bundle protocol agent is configured to attach Previous 1451 Node blocks to forwarded bundles, then a Previous Node block 1452 containing the node ID of the forwarding node MUST be inserted 1453 into the bundle before the bundle is forwarded. 1454 . If the bundle has a bundle age block, as defined in 4.3.2. 1455 above, then at the last possible moment before the CLA 1456 initiates conveyance of the bundle via the CL protocol the 1457 bundle age value MUST be increased by the difference between 1458 the current time and the time at which the bundle was received 1459 (or, if the local node is the source of the bundle, created). 1461 Step 5: When all selected convergence layer adapters have informed 1462 the bundle protocol agent that they have concluded their data 1463 sending procedures with regard to this bundle, processing may depend 1464 on the results of those procedures. 1466 If completion of the data sending procedures by all selected 1467 convergence layer adapters has not resulted in successful forwarding 1468 of the bundle (an implementation-specific determination that is 1469 beyond the scope of this specification), then the bundle protocol 1470 agent MAY choose (in an implementation-specific manner, again beyond 1471 the scope of this specification) to initiate another attempt to 1472 forward the bundle. In that event, processing proceeds from Step 4. 1473 The minimum number of times a given node will initiate another 1474 forwarding attempt for any single bundle in this event (a number 1475 which may be zero) is a node configuration parameter that must be 1476 exposed to other nodes in the network to the extent that this is 1477 required by the operating environment. 1479 If completion of the data sending procedures by all selected 1480 convergence layer adapters HAS resulted in successful forwarding of 1481 the bundle, or if it has not but the bundle protocol agent does not 1482 choose to initiate another attempt to forward the bundle, then: 1484 . If the "request reporting of bundle forwarding" flag in the 1485 bundle's status report request field is set to 1, and status 1486 reporting is enabled, then a bundle forwarding status report 1487 SHOULD be generated, destined for the bundle's report-to 1488 endpoint ID. The reason code on this bundle forwarding status 1489 report MUST be "no additional information". 1490 . If any applicable bundle protocol extensions mandate generation 1491 of status reports upon conclusion of convergence-layer data 1492 sending procedures, all such status reports SHOULD be generated 1493 with extension-mandated reason codes. 1494 . The bundle's "Forward pending" retention constraint MUST be 1495 removed. 1497 5.4.1. Forwarding Contraindicated 1499 The steps in responding to contraindication of forwarding are: 1501 Step 1: The bundle protocol agent MUST determine whether or not to 1502 declare failure in forwarding the bundle. Note: this decision is 1503 likely to be influenced by the reason for which forwarding is 1504 contraindicated. 1506 Step 2: If forwarding failure is declared, then the Forwarding 1507 Failed procedure defined in Section 5.4.2 MUST be followed. 1509 Otherwise, when - at some future time - the forwarding of this 1510 bundle ceases to be contraindicated, processing proceeds from Step 4 1511 of Section 5.4. 1513 5.4.2. Forwarding Failed 1515 The steps in responding to a declaration of forwarding failure are: 1517 Step 1: The bundle protocol agent MAY forward the bundle back to the 1518 node that sent it, as identified by the Previous Node block, if 1519 present. This forwarding, if performed, SHALL be accomplished by 1520 performing Step 4 and Step 5 of section 5.4 where the sole node 1521 selected for forwarding SHALL be the node that sent the bundle. 1523 Step 2: If the bundle's destination endpoint is an endpoint of which 1524 the node is a member, then the bundle's "Forward pending" retention 1525 constraint MUST be removed. Otherwise, the bundle MUST be deleted: 1526 the bundle deletion procedure defined in Section 5.10 MUST be 1527 followed, citing the reason for which forwarding was determined to 1528 be contraindicated. 1530 5.5. Bundle Expiration 1532 A bundle expires when the bundle's age exceeds its lifetime as 1533 specified in the primary bundle block or as overridden by the bundle 1534 protocol agent. Bundle age MAY be determined by subtracting the 1535 bundle's creation timestamp time from the current time if (a) that 1536 timestamp time is not zero and (b) the local node's clock is known 1537 to be accurate; otherwise bundle age MUST be obtained from the 1538 Bundle Age extension block. Bundle expiration MAY occur at any 1539 point in the processing of a bundle. When a bundle expires, the 1540 bundle protocol agent MUST delete the bundle for the reason 1541 "lifetime expired" (when the expired lifetime is the lifetime as 1542 specified in the primary block) or "traffic pared" (when the expired 1543 lifetime is a lifetime override as imposed by the bundle protocol 1544 agent): the bundle deletion procedure defined in Section 5.10 MUST 1545 be followed. 1547 5.6. Bundle Reception 1549 The steps in processing a bundle that has been received from another 1550 node are: 1552 Step 1: The retention constraint "Dispatch pending" MUST be added to 1553 the bundle. 1555 Step 2: If the "request reporting of bundle reception" flag in the 1556 bundle's status report request field is set to 1, and status 1557 reporting is enabled, then a bundle reception status report with 1558 reason code "No additional information" SHOULD be generated, 1559 destined for the bundle's report-to endpoint ID. 1561 Step 3: CRCs SHOULD be computed for every block of the bundle that 1562 has an attached CRC. If any block of the bundle is malformed 1563 according to this specification (including syntactically invalid 1564 CBOR), or if any block has an attached CRC and the CRC computed for 1565 this block upon reception differs from that attached CRC, then the 1566 bundle protocol agent MUST delete the bundle for the reason "Block 1567 unintelligible". The bundle deletion procedure defined in Section 1568 5.10 MUST be followed and all remaining steps of the bundle 1569 reception procedure MUST be skipped. 1571 Step 4: For each block in the bundle that is an extension block that 1572 the bundle protocol agent cannot process: 1574 . If the block processing flags in that block indicate that a 1575 status report is requested in this event, and status reporting 1576 is enabled, then a bundle reception status report with reason 1577 code "Block unintelligible" SHOULD be generated, destined for 1578 the bundle's report-to endpoint ID. 1579 . If the block processing flags in that block indicate that the 1580 bundle must be deleted in this event, then the bundle protocol 1581 agent MUST delete the bundle for the reason "Block 1582 unintelligible"; the bundle deletion procedure defined in 1583 Section 5.10 MUST be followed and all remaining steps of the 1584 bundle reception procedure MUST be skipped. 1585 . If the block processing flags in that block do NOT indicate 1586 that the bundle must be deleted in this event but do indicate 1587 that the block must be discarded, then the bundle protocol 1588 agent MUST remove this block from the bundle. 1589 . If the block processing flags in that block indicate neither 1590 that the bundle must be deleted nor that that the block must be 1591 discarded, then processing continues with the next extension 1592 block that the bundle protocol agent cannot process, if any; 1593 otherwise, processing proceeds from step 5. 1595 Step 5: Processing proceeds from Step 1 of Section 5.3. 1597 5.7. Local Bundle Delivery 1599 The steps in processing a bundle that is destined for an endpoint of 1600 which this node is a member are: 1602 Step 1: If the received bundle is a fragment, the application data 1603 unit reassembly procedure described in Section 5.9 MUST be followed. 1604 If this procedure results in reassembly of the entire original 1605 application data unit, processing of the fragmentary bundle whose 1606 payload has been replaced by the reassembled application data unit 1607 (whether this bundle or a previously received fragment) proceeds 1608 from Step 2; otherwise, the retention constraint "Reassembly 1609 pending" MUST be added to the bundle and all remaining steps of this 1610 procedure MUST be skipped. 1612 Step 2: Delivery depends on the state of the registration whose 1613 endpoint ID matches that of the destination of the bundle: 1615 . An additional implementation-specific delivery deferral 1616 procedure MAY optionally be associated with the registration. 1617 . If the registration is in the Active state, then the bundle 1618 MUST be delivered automatically as soon as it is the next 1619 bundle that is due for delivery according to the BPA's bundle 1620 delivery scheduling policy, an implementation matter. 1621 . If the registration is in the Passive state, or if delivery of 1622 the bundle fails for some implementation-specific reason, then 1623 the registration's delivery failure action MUST be taken. 1624 Delivery failure action MUST be one of the following: 1626 o defer delivery of the bundle subject to this registration 1627 until (a) this bundle is the least recently received of 1628 all bundles currently deliverable subject to this 1629 registration and (b) either the registration is polled or 1630 else the registration is in the Active state, and also 1631 perform any additional delivery deferral procedure 1632 associated with the registration; or 1634 o abandon delivery of the bundle subject to this registration 1635 (as defined in 3.1. ). 1637 Step 3: As soon as the bundle has been delivered, if the "request 1638 reporting of bundle delivery" flag in the bundle's status report 1639 request field is set to 1 and bundle status reporting is enabled, 1640 then a bundle delivery status report SHOULD be generated, destined 1641 for the bundle's report-to endpoint ID. Note that this status report 1642 only states that the payload has been delivered to the application 1643 agent, not that the application agent has processed that payload. 1645 5.8. Bundle Fragmentation 1647 It may at times be advantageous for bundle protocol agents to reduce 1648 the sizes of bundles in order to forward them. This might be the 1649 case, for example, if a node to which a bundle is to be forwarded is 1650 accessible only via intermittent contacts and no upcoming contact is 1651 long enough to enable the forwarding of the entire bundle. 1653 The size of a bundle can be reduced by "fragmenting" the bundle. To 1654 fragment a bundle whose payload is of size M is to replace it with 1655 two "fragments" - new bundles with the same source node ID and 1656 creation timestamp as the original bundle - whose payloads are the 1657 first N and the last (M - N) bytes of the original bundle's payload, 1658 where 0 < N < M. 1660 Note that fragments are bundles and therefore may themselves be 1661 fragmented, so multiple episodes of fragmentation may in effect 1662 replace the original bundle with more than two fragments. (However, 1663 there is only one 'level' of fragmentation, as in IP fragmentation.) 1665 Any bundle whose primary block's bundle processing flags do NOT 1666 indicate that it must not be fragmented MAY be fragmented at any 1667 time, for any purpose, at the discretion of the bundle protocol 1668 agent. NOTE, however, that some combinations of bundle 1669 fragmentation, replication, and routing might result in unexpected 1670 traffic patterns. 1672 Fragmentation SHALL be constrained as follows: 1674 . The concatenation of the payloads of all fragments produced by 1675 fragmentation MUST always be identical to the payload of the 1676 fragmented bundle (that is, the bundle that is being 1677 fragmented). Note that the payloads of fragments resulting from 1678 different fragmentation episodes, in different parts of the 1679 network, may be overlapping subsets of the fragmented bundle's 1680 payload. 1681 . The primary block of each fragment MUST differ from that of the 1682 fragmented bundle, in that the bundle processing flags of the 1683 fragment MUST indicate that the bundle is a fragment and both 1684 fragment offset and total application data unit length must be 1685 provided. Additionally, the CRC of the primary block of the 1686 fragmented bundle, if any, MUST be replaced in each fragment by 1687 a new CRC computed for the primary block of that fragment. 1689 . The payload blocks of fragments will differ from that of the 1690 fragmented bundle as noted above. 1691 . If the fragmented bundle is not a fragment or is the fragment 1692 with offset zero, then all extension blocks of the fragmented 1693 bundle MUST be replicated in the fragment whose offset is zero. 1694 . Each of the fragmented bundle's extension blocks whose "Block 1695 must be replicated in every fragment" flag is set to 1 MUST be 1696 replicated in every fragment. 1697 . Beyond these rules, rules for the replication of extension 1698 blocks in the fragments must be defined in the specifications 1699 for those extension block types. 1701 5.9. Application Data Unit Reassembly 1703 Note that the bundle fragmentation procedure described in 5.8 above 1704 may result in the replacement of a single original bundle with an 1705 arbitrarily large number of fragmentary bundles. In order to be 1706 delivered at a destination node, the original bundle's payload must 1707 be reassembled from the payloads of those fragments. 1709 If the concatenation - as informed by fragment offsets and payload 1710 lengths - of the non-overlapping portions of the payloads of all 1711 previously received fragments with the same source node ID and 1712 creation timestamp as this fragment, together with the non- 1713 overlapping portion of the payload of this fragment, forms a 1714 continuous byte array whose length is equal to the total application 1715 data unit length in the fragment's primary block, then: 1717 . This byte array -- the reassembled application data unit -- 1718 MUST replace the payload of that fragment whose payload is a 1719 subset, starting at offset zero, of the reassembled application 1720 data unit. Note that this will enable delivery of the 1721 reconstituted original bundle as described in Step 1 of 5.7. 1722 . The "Reassembly pending" retention constraint MUST be removed 1723 from every previously received fragment whose payload is a 1724 subset of the reassembled application data unit. 1726 Note: reassembly of application data units from fragments occurs at 1727 the nodes that are members of destination endpoints as necessary; an 1728 application data unit MAY also be reassembled at some other node on 1729 the path to the destination. 1731 5.10. Bundle Deletion 1733 The steps in deleting a bundle are: 1735 Step 1: If the "request reporting of bundle deletion" flag in the 1736 bundle's status report request field is set to 1, and if status 1737 reporting is enabled, then a bundle deletion status report citing 1738 the reason for deletion SHOULD be generated, destined for the 1739 bundle's report-to endpoint ID. 1741 Step 2: All of the bundle's retention constraints MUST be removed. 1743 5.11. Discarding a Bundle 1745 As soon as a bundle has no remaining retention constraints it MAY be 1746 discarded, thereby releasing any persistent storage that may have 1747 been allocated to it. 1749 5.12. Canceling a Transmission 1751 When requested to cancel a specified transmission, where the bundle 1752 created upon initiation of the indicated transmission has not yet 1753 been discarded, the bundle protocol agent MUST delete that bundle 1754 for the reason "transmission cancelled". For this purpose, the 1755 procedure defined in Section 5.10 MUST be followed. 1757 6. Administrative Record Processing 1759 6.1. Administrative Records 1761 Administrative records are standard application data units that are 1762 used in providing some of the features of the Bundle Protocol. One 1763 type of administrative record has been defined to date: bundle 1764 status reports. Note that additional types of administrative 1765 records may be defined by supplementary DTN protocol specification 1766 documents. 1768 Every administrative record consists of: 1770 . Record type code (an unsigned integer for which valid values 1771 are as defined below). 1772 . Record content in type-specific format. 1774 Valid administrative record type codes are defined as follows: 1776 +---------+--------------------------------------------+ 1778 | Value | Meaning | 1780 +=========+============================================+ 1781 | 1 | Bundle status report. | 1783 +---------+--------------------------------------------+ 1785 | (other) | Reserved for future use. | 1787 +---------+--------------------------------------------+ 1789 Figure 3: Administrative Record Type Codes 1791 Each BP administrative record SHALL be represented as a CBOR array 1792 comprising two items. 1794 The first item of the array SHALL be a record type code, which SHALL 1795 be represented as a CBOR unsigned integer. 1797 The second element of this array SHALL be the applicable CBOR 1798 representation of the content of the record. Details of the CBOR 1799 representation of administrative record type 1 are provided below. 1800 Details of the CBOR representation of other types of administrative 1801 record type are included in the specifications defining those 1802 records. 1804 6.1.1. Bundle Status Reports 1806 The transmission of "bundle status reports" under specified 1807 conditions is an option that can be invoked when transmission of a 1808 bundle is requested. These reports are intended to provide 1809 information about how bundles are progressing through the system, 1810 including notices of receipt, forwarding, final delivery, and 1811 deletion. They are transmitted to the Report-to endpoints of 1812 bundles. 1814 Each bundle status report SHALL be represented as a CBOR array. The 1815 number of elements in the array SHALL be either 6 (if the subject 1816 bundle is a fragment) or 4 (otherwise). 1818 The first item of the bundle status report array SHALL be bundle 1819 status information represented as a CBOR array of at least 4 1820 elements. The first four items of the bundle status information 1821 array shall provide information on the following four status 1822 assertions, in this order: 1824 . Reporting node received bundle. 1825 . Reporting node forwarded the bundle. 1826 . Reporting node delivered the bundle. 1827 . Reporting node deleted the bundle. 1829 Each item of the bundle status information array SHALL be a bundle 1830 status item represented as a CBOR array; the number of elements in 1831 each such array SHALL be either 2 (if the value of the first item of 1832 this bundle status item is 1 AND the "Report status time" flag was 1833 set to 1 in the bundle processing flags of the bundle whose status 1834 is being reported) or 1 (otherwise). The first item of the bundle 1835 status item array SHALL be a status indicator, a Boolean value 1836 indicating whether or not the corresponding bundle status is 1837 asserted, represented as a CBOR Boolean value. The second item of 1838 the bundle status item array, if present, SHALL indicate the time 1839 (as reported by the local system clock, an implementation matter) at 1840 which the indicated status was asserted for this bundle, represented 1841 as a DTN time as described in Section 4.1.6. above. 1843 The second item of the bundle status report array SHALL be the 1844 bundle status report reason code explaining the value of the status 1845 indicator, represented as a CBOR unsigned integer. Valid status 1846 report reason codes are registered in the IANA Bundle Status Report 1847 Reason Codes registry in the Bundle Protocol Namespace (see 10.5 1848 below). The initial contents of that registry are listed in Figure 1849 4 below but the list of status report reason codes provided here is 1850 neither exhaustive nor exclusive; supplementary DTN protocol 1851 specifications (including, but not restricted to, the Bundle 1852 Security Protocol [BPSEC]) may define additional reason codes. 1854 +---------+--------------------------------------------+ 1856 | Value | Meaning | 1858 +=========+============================================+ 1860 | 0 | No additional information. | 1862 +---------+--------------------------------------------+ 1864 | 1 | Lifetime expired. | 1866 +---------+--------------------------------------------+ 1868 | 2 | Forwarded over unidirectional link. | 1870 +---------+--------------------------------------------+ 1872 | 3 | Transmission canceled. | 1874 +---------+--------------------------------------------+ 1875 | 4 | Depleted storage. | 1877 +---------+--------------------------------------------+ 1879 | 5 | Destination endpoint ID unavailable. | 1881 +---------+--------------------------------------------+ 1883 | 6 | No known route to destination from here. | 1885 +---------+--------------------------------------------+ 1887 | 7 | No timely contact with next node on route. | 1889 +---------+--------------------------------------------+ 1891 | 8 | Block unintelligible. | 1893 +---------+--------------------------------------------+ 1895 | 9 | Hop limit exceeded. | 1897 +---------+--------------------------------------------+ 1899 | 10 | Traffic pared (e.g., status reports). | 1901 +---------+--------------------------------------------+ 1903 | (other) | Reserved for future use. | 1905 +---------+--------------------------------------------+ 1907 Figure 4: Status Report Reason Codes 1909 The third item of the bundle status report array SHALL be the source 1910 node ID identifying the source of the bundle whose status is being 1911 reported, represented as described in Section 4.1.5.1.1. above. 1913 The fourth item of the bundle status report array SHALL be the 1914 creation timestamp of the bundle whose status is being reported, 1915 represented as described in Section 4.1.7. above. 1917 The fifth item of the bundle status report array SHALL be present if 1918 and only if the bundle whose status is being reported contained a 1919 fragment offset. If present, it SHALL be the subject bundle's 1920 fragment offset represented as a CBOR unsigned integer item. 1922 The sixth item of the bundle status report array SHALL be present if 1923 and only if the bundle whose status is being reported contained a 1924 fragment offset. If present, it SHALL be the length of the subject 1925 bundle's payload represented as a CBOR unsigned integer item. 1927 Note that the forwarding parameters (such as lifetime, applicable 1928 security measures, etc.) of the bundle whose status is being 1929 reported MAY be reflected in the parameters governing the forwarding 1930 of the bundle that conveys a status report, but this is an 1931 implementation matter. Bundle protocol deployment experience to 1932 date has not been sufficient to suggest any clear guidance on this 1933 topic. 1935 6.2. Generation of Administrative Records 1937 Whenever the application agent's administrative element is directed 1938 by the bundle protocol agent to generate an administrative record, 1939 the following procedure must be followed: 1941 Step 1: The administrative record must be constructed. If the 1942 administrative record references a bundle and the referenced bundle 1943 is a fragment, the administrative record MUST contain the fragment 1944 offset and fragment length. 1946 Step 2: A request for transmission of a bundle whose payload is this 1947 administrative record MUST be presented to the bundle protocol 1948 agent. 1950 7. Services Required of the Convergence Layer 1952 7.1. The Convergence Layer 1954 The successful operation of the end-to-end bundle protocol depends 1955 on the operation of underlying protocols at what is termed the 1956 "convergence layer"; these protocols accomplish communication 1957 between nodes. A wide variety of protocols may serve this purpose, 1958 so long as each convergence layer protocol adapter provides a 1959 defined minimal set of services to the bundle protocol agent. This 1960 convergence layer service specification enumerates those services. 1962 7.2. Summary of Convergence Layer Services 1964 Each convergence layer protocol adapter is expected to provide the 1965 following services to the bundle protocol agent: 1967 . sending a bundle to a bundle node that is reachable via the 1968 convergence layer protocol; 1970 . notifying the bundle protocol agent of the disposition of its 1971 data sending procedures with regard to a bundle, upon 1972 concluding those procedures; 1973 . delivering to the bundle protocol agent a bundle that was sent 1974 by a bundle node via the convergence layer protocol. 1976 The convergence layer service interface specified here is neither 1977 exhaustive nor exclusive. That is, supplementary DTN protocol 1978 specifications (including, but not restricted to, the Bundle 1979 Security Protocol [BPSEC]) may expect convergence layer adapters 1980 that serve BP implementations conforming to those protocols to 1981 provide additional services such as reporting on the transmission 1982 and/or reception progress of individual bundles (at completion 1983 and/or incrementally), retransmitting data that were lost in 1984 transit, discarding bundle-conveying data units that the convergence 1985 layer protocol determines are corrupt or inauthentic, or reporting 1986 on the integrity and/or authenticity of delivered bundles. 1988 In addition, bundle protocol relies on the capabilities of protocols 1989 at the convergence layer to minimize congestion in the store-carry- 1990 forward overlay network. The potentially long round-trip times 1991 characterizing delay-tolerant networks are incompatible with end-to- 1992 end reactive congestion control mechanisms, so convergence-layer 1993 protocols MUST provide rate limiting or congestion control. 1995 8. Implementation Status 1997 [NOTE to the RFC Editor: please remove this section before 1998 publication, as well as the reference to RFC 7942.] 2000 This section records the status of known implementations of the 2001 protocol defined by this specification at the time of posting of 2002 this Internet-Draft, and is based on a proposal described in RFC 2003 7942. The description of implementations in this section is 2004 intended to assist the IETF in its decision processes in progressing 2005 drafts to RFCs. Please note that the listing of any individual 2006 implementation here does not imply endorsement by the IETF. 2007 Furthermore, no effort has been spent to verify the information 2008 presented here that was supplied by IETF contributors. This is not 2009 intended as, and must not be construed to be, a catalog of available 2010 implementations or their features. Readers are advised to note that 2011 other implementations may exist. 2013 According to RFC 7942, "this will allow reviewers and working groups 2014 to assign due consideration to documents that have the benefit of 2015 running code, which may serve as evidence of valuable 2016 experimentation and feedback that have made the implemented 2017 protocols more mature. It is up to the individual working groups to 2018 use this information as they see fit". 2020 At the time of this writing, there are six known implementations of 2021 the current document. 2023 The first known implementation is microPCN (https://upcn.eu/). 2024 According to the developers: 2026 The Micro Planetary Communication Network (uPCN) is a free 2027 software project intended to offer an implementation of Delay- 2028 tolerant Networking protocols for POSIX operating systems (well, 2029 and for Linux) plus for the ARM Cortex STM32F4 microcontroller 2030 series. More precisely it currently provides an implementation of 2032 . the Bundle Protocol (BP, RFC 5050), 2033 . version 6 of the Bundle Protocol version 7 specification 2034 draft, 2035 . the DTN IP Neighbor Discovery (IPND) protocol, and 2036 . a routing approach optimized for message-ferry micro LEO 2037 satellites. 2039 uPCN is written in C and is built upon the real-time operating 2040 system FreeRTOS. The source code of uPCN is released under the 2041 "BSD 3-Clause License". 2043 The project depends on an execution environment offering link 2044 layer protocols such as AX.25. The source code uses the USB 2045 subsystem to interact with the environment. 2047 The second known implementation is PyDTN, developed by X-works, 2048 s.r.o (https://x-works.sk/). The final third of the implementation 2049 was developed during the IETF 101 Hackathon. According to the 2050 developers, PyDTN implements bundle coding/decoding and neighbor 2051 discovery. PyDTN is written in Python and has been shown to be 2052 interoperable with uPCN. 2054 The third known implementation is "Terra" 2055 (https://github.com/RightMesh/Terra/), a Java implementation 2056 developed in the context of terrestrial DTN. It includes an 2057 implementation of a "minimal TCP" convergence layer adapter. 2059 The fourth and fifth known implementations are products of 2060 cooperating groups at two German universities: 2062 . An implementation written in Go, licensed under GPLv3, is 2063 focused on being easily extensible suitable for research. It 2064 is maintained at the University of Marburg and can be accessed 2065 from https://github.com/dtn7/dtn7-go. 2066 . An implementation written in Rust, licensed under the 2067 MIT/Apache license, is intended for environments with limited 2068 resources or demanding safety and/or performance requirements. 2069 It is maintained at the Technical University of Darmstadt and 2070 can be accessed at https://github.com/dtn7/dtn7-rs/. 2072 The sixth known implementation is the "bpv7" module in version 4.0.0 2073 of the Interplanetary Overlay Network (ION) software maintained at 2074 the Jet Propulsion Laboratory, California Institute of Technology, 2075 for the U.S. National Aeronautics and Space Administration (NASA). 2077 9. Security Considerations 2079 The bundle protocol security architecture and the available security 2080 services are specified in an accompanying document, the Bundle 2081 Security Protocol (BPsec) specification [BPSEC]. Whenever Bundle 2082 Protocol security services (as opposed to the security services 2083 provided by overlying application protocols or underlying 2084 convergence-layer protocols) are required, those services SHALL be 2085 provided by BPsec rather than by some other mechanism with the same 2086 or similar scope. 2088 A Bundle Protocol Agent (BPA) which sources, cryptographically 2089 verifies, and/or accepts a bundle MUST implement support for BPsec. 2090 Use of BPsec for a particular Bundle Protocol session is optional. 2092 The BPsec extensions to Bundle Protocol enable each block of a 2093 bundle (other than a BPsec extension block) to be individually 2094 authenticated by a signature block (Block Integrity Block, or BIB) 2095 and also enable each block of a bundle other than the primary block 2096 (and the BPsec extension blocks themselves) to be individually 2097 encrypted by a Block Confidentiality Block (BCB). 2099 Because the security mechanisms are extension blocks that are 2100 themselves inserted into the bundle, the protections they afford 2101 apply while the bundle is at rest, awaiting transmission at the next 2102 forwarding opportunity, as well as in transit. 2104 Additionally, convergence-layer protocols that ensure authenticity 2105 of communication between adjacent nodes in BP network topology 2106 SHOULD be used where available, to minimize the ability of 2107 unauthenticated nodes to introduce inauthentic traffic into the 2108 network. Convergence-layer protocols that ensure confidentiality of 2109 communication between adjacent nodes in BP network topology SHOULD 2110 also be used where available, to minimize exposure of the bundle's 2111 primary block and other clear-text blocks, thereby offering some 2112 defense against traffic analysis. 2114 Note that, while the primary block must remain in the clear for 2115 routing purposes, the Bundle Protocol could be protected against 2116 traffic analysis to some extent by using bundle-in-bundle 2117 encapsulation [BIBE] to tunnel bundles to a safe forward 2118 distribution point: the encapsulated bundle could form the payload 2119 of an encapsulating bundle, and that payload block could be 2120 encrypted by a BCB. 2122 Note that the generation of bundle status reports is disabled by 2123 default because malicious initiation of bundle status reporting 2124 could result in the transmission of extremely large numbers of 2125 bundles, effecting a denial of service attack. Imposing bundle 2126 lifetime overrides would constitute one defense against such an 2127 attack. 2129 Note also that the reception of large numbers of fragmentary bundles 2130 with very long lifetimes could constitute a denial of service 2131 attack, occupying storage while pending reassembly that will never 2132 occur. Imposing bundle lifetime overrides would, again, constitute 2133 one defense against such an attack. 2135 This protocol makes use of absolute timestamps for several purposes. 2136 Provisions are included for nodes without accurate clocks to retain 2137 most of the protocol functionality, but nodes that are unaware that 2138 their clock is inaccurate may exhibit unexpected behavior. 2140 10. IANA Considerations 2142 The Bundle Protocol includes fields requiring registries managed by 2143 IANA. 2145 10.1. Bundle Block Types 2147 The current Bundle Block Types registry in the Bundle Protocol 2148 Namespace is augmented by adding a column identifying the version of 2149 the Bundle protocol (Bundle Protocol Version) that applies to the 2150 new values. IANA is requested to add the following values, as 2151 described in section 4.3.1, to the Bundle Block Types registry. The 2152 current values in the Bundle Block Types registry should have the 2153 Bundle Protocol Version set to the value "6", as shown below. 2155 +----------+-------+-----------------------------+---------------+ 2157 | Bundle | Value | Description | Reference | 2158 | Protocol | | | | 2160 | Version | | | | 2162 +----------+-------+-----------------------------+---------------+ 2164 | none | 0 | Reserved | [RFC6255] | 2166 | 6,7 | 1 | Bundle Payload Block | [RFC5050] | 2168 | | | | RFC-to-be | 2170 | 6 | 2 | Bundle Authentication Block | [RFC6257] | 2172 | 6 | 3 | Payload Integrity Block | [RFC6257] | 2174 | 6 | 4 | Payload Confidentiality | [RFC6257] | 2176 | | | Block | RFC-to-be | 2178 | 6 | 5 | Previous-Hop Insertion Block| [RFC6259] | 2180 | 7 | 6 | Previous node (proximate | RFC-to-be | 2182 | | | sender) | | 2184 | 7 | 7 | Bundle age (in milliseconds)| RFC-to-be | 2186 | 6 | 8 | Metadata Extension Block | [RFC6258] | 2188 | 6 | 9 | Extension Security Block | [RFC6257] | 2190 | 7 | 10 | Hop count (#prior xmit | RFC-to-be | 2192 | | | attempts) | | 2194 | 7 | 11-191| Unassigned | | 2196 | 6 |192-255| Reserved for Private and/or | [RFC5050], | 2198 | | | Experimental Use | RFC-to-be | 2200 +----------+-------+-----------------------------+---------------+ 2202 10.2. Primary Bundle Protocol Version 2204 IANA is requested to add the following value to the Primary Bundle 2205 Protocol Version registry in the Bundle Protocol Namespace. 2207 +-------+-------------+---------------+ 2209 | Value | Description | Reference | 2211 +-------+-------------+---------------+ 2213 | 7 | Assigned | RFC-to-be | 2215 +-------+-------------+---------------+ 2217 Values 8-255 (rather than 7-255) are now Unassigned. 2219 10.3. Bundle Processing Control Flags 2221 The current Bundle Processing Control Flags registry in the Bundle 2222 Protocol Namespace is augmented by adding a column identifying the 2223 version of the Bundle protocol (Bundle Protocol Version) that 2224 applies to the new values. IANA is requested to add the following 2225 values, as described in section 4.1.3, to the Bundle Processing 2226 Control Flags registry. The current values in the Bundle Processing 2227 Control Flags registry should have the Bundle Protocol Version set 2228 to the value 6 or "6, 7", as shown below. 2230 Bundle Processing Control Flags Registry 2232 +--------------------+----------------------------------+----------+ 2234 | Bundle | Bit | Description | Reference| 2236 | Protocol| Position | | | 2238 | Version | (right | | | 2240 | | to left) | | | 2242 +--------------------+----------------------------------+----------+ 2244 | 6,7 | 0 | Bundle is a fragment |[RFC5050],| 2246 | | | |RFC-to-be | 2248 | 6,7 | 1 | Application data unit is an |[RFC5050],| 2249 | | | administrative record |RFC-to-be | 2251 | 6,7 | 2 | Bundle must not be fragmented |[RFC5050],| 2253 | | | |RFC-to-be | 2255 | 6 | 3 | Custody transfer is requested |[RFC5050] | 2257 | 6 | 4 | Destination endpoint is singleton|[RFC5050] | 2259 | 6,7 | 5 | Acknowledgement by application |[RFC5050],| 2261 | | | is requested |RFC-to-be | 2263 | 7 | 6 | Status time requested in reports |RFC-to-be | 2265 | 6 | 7 | Class of service, priority |[RFC5050],| 2267 | | | |RFC-to-be | 2269 | 6 | 8 | Class of service, priority |[RFC5050],| 2271 | | | |RFC-to-be | 2273 | 6 | 9 | Class of service, reserved |[RFC5050],| 2275 | | | |RFC-to-be | 2277 | 6 | 10 | Class of service, reserved |[RFC5050],| 2279 | | | |RFC-to-be | 2281 | 6 | 11 | Class of service, reserved |[RFC5050],| 2283 | | | |RFC-to-be | 2285 | 6 | 12 | Class of service, reserved |[RFC5050],| 2287 | | | |RFC-to-be | 2289 | 6 | 13 | Class of service, reserved |[RFC5050],| 2291 | | | |RFC-to-be | 2293 | 6,7 | 14 | Request reporting of bundle |[RFC5050],| 2295 | | | reception |RFC-to-be | 2296 | 6,7 | 16 | Request reporting of bundle |[RFC5050],| 2298 | | | forwarding |RFC-to-be | 2300 | 6,7 | 17 | Request reporting of bundle |[RFC5050],| 2302 | | | delivery |RFC-to-be | 2304 | 6,7 | 18 | Request reporting of bundle |[RFC5050],| 2306 | | | deletion |RFC-to-be | 2308 | 6 | 19 | Reserved |[RFC5050],| 2310 | | | |RFC-to-be | 2312 | 6 | 20 | Reserved |[RFC5050],| 2314 | | | |RFC-to-be | 2316 | | 21-63 | Unassigned | | 2318 +--------------------+----------------------------------+----------+ 2320 The registration policy for this registry is changed to "Standards 2321 Action". Given the limited number of bits available, the allocation 2322 should only be granted for a standards-track RFC approved by the 2323 IESG. 2325 10.4. Block Processing Control Flags 2327 The current Block Processing Control Flags registry in the Bundle 2328 Protocol Namespace is augmented by adding a column identifying the 2329 version of the Bundle protocol (Bundle Protocol Version) that 2330 applies to the related BP version. The current values in the Block 2331 Processing Control Flags registry should have the Bundle Protocol 2332 Version set to the value 6 or "6, 7", as shown below. 2334 Block Processing Control Flags Registry 2336 +--------------------+----------------------------------+----------+ 2338 | Bundle | Bit | Description | Reference| 2340 | Protocol| Position | | | 2342 | Version | (right | | | 2343 | | to left) | | | 2345 +--------------------+----------------------------------+----------+ 2347 | 6,7 | 0 | Block must be replicated in |[RFC5050],| 2349 | | | every fragment |RFC-to-be | 2351 | 6,7 | 1 | Transmit status report if block |[RFC5050],| 2353 | | | can't be processed |RFC-to-be | 2355 | 6,7 | 2 | Delete bundle if block can't be |[RFC5050],| 2357 | | | processed |RFC-to-be | 2359 | 6 | 3 | Last block |[RFC5050] | 2361 | 6,7 | 4 | Discard block if it can't be |[RFC5050],| 2363 | | | processed |RFC-to-be | 2365 | 6 | 5 | Block was forwarded without |[RFC5050] | 2367 | | | being processed | | 2369 | 6 | 6 | Block contains an EID reference |[RFC5050] | 2371 | | | field | | 2373 | | 7-63 | Unassigned | | 2375 +--------------------+----------------------------------+----------+ 2377 The registration policy for this registry is changed to "Standards 2378 Action". Given the limited number of bits available, the allocation 2379 should only be granted for a standards-track RFC approved by the 2380 IESG. 2382 10.5. Bundle Status Report Reason Codes 2384 The current Bundle Status Report Reason Codes registry in the Bundle 2385 Protocol Namespace is augmented by adding a column identifying the 2386 version of the Bundle protocol (Bundle Protocol Version) that 2387 applies to the new values. IANA is requested to add the following 2388 values, as described in section 6.1.1, to the Bundle Status Report 2389 Reason Codes registry. The current values in the Bundle Status 2390 Report Reason Codes registry should have the Bundle Protocol Version 2391 set to the value 6 or 7 or "6, 7", as shown below. 2393 Bundle Status Report Reason Codes Registry 2395 +--------------------+----------------------------------+----------+ 2397 | Bundle | Value | Description | Reference| 2399 | Protocol| | | | 2401 | Version | | | | 2403 | | | | | 2405 +--------------------+----------------------------------+----------+ 2407 | 6,7 | 0 | No additional information |[RFC5050],| 2409 | | | |RFC-to-be | 2411 | 6,7 | 1 | Lifetime expired |[RFC5050],| 2413 | | | |RFC-to-be | 2415 | 6,7 | 2 | Forwarded over unidirectional |[RFC5050],| 2417 | | | link |RFC-to-be | 2419 | 6,7 | 3 | Transmission canceled |[RFC5050],| 2421 | | | |RFC-to-be | 2423 | 6,7 | 4 | Depleted storage |[RFC5050],| 2425 | | | |RFC-to-be | 2427 | 6,7 | 5 | Destination endpoint ID |[RFC5050],| 2429 | | | unavailable |RFC-to-be | 2431 | 6,7 | 6 | No known route to destination |[RFC5050],| 2433 | | | from here |RFC-to-be | 2435 | 6,7 | 7 | No timely contact with next node |[RFC5050],| 2436 | | | on route |RFC-to-be | 2438 | 6,7 | 8 | Block unintelligible |[RFC5050],| 2440 | | | |RFC-to-be | 2442 | 7 | 9 | Hop limit exceeded |RFC-to-be | 2444 | 7 | 10 | Traffic pared |RFC-to-be | 2446 | | 11-254 | Unassigned | | 2448 | 6 | 255 | Reserved |[RFC6255],| 2450 | | | |RFC-to-be | 2452 +-------+-----------------------------------------------+----------+ 2454 10.6. Bundle Protocol URI scheme types 2456 The Bundle Protocol has a URI scheme type field - an unsigned 2457 integer of indefinite length - for which IANA is requested to create 2458 and maintain a new "Bundle Protocol URI Scheme Type" registry in the 2459 Bundle Protocol Namespace. The "Bundle Protocol URI Scheme Type" 2460 registry governs an unsigned integer namespace. Initial values for 2461 the Bundle Protocol URI Scheme Type registry are given below. 2463 The registration policy for this registry is: Standards Action. The 2464 allocation should only be granted for a standards-track RFC approved 2465 by the IESG. 2467 The value range is: unsigned integer. 2469 Each assignment consists of a URI scheme type name and its 2470 associated description, a reference to the document that defines the 2471 URI scheme, and a reference to the document that defines the use of 2472 this URI scheme in BP endpoint IDs (including the CBOR 2473 representation of those endpoint IDs in transmitted bundles). 2475 Bundle Protocol URI Scheme Type Registry 2477 +---------+-------------+----------------+------------------+ 2479 | | | BP Utilization | URI Definition | 2481 | Value | Description | Reference | Reference | 2482 +---------+-------------+----------------+------------------+ 2484 | 0 | Reserved | n/a | | 2486 | 1 | dtn | RFC-to-be | RFC-to-be | 2488 | 2 | ipn | RFC-to-be | [RFC6260], | 2490 | | | | RFC-to-be | 2492 | 3-254 | Unassigned | n/a | | 2494 |255-65535| reserved | n/a | | 2496 | >65535 | open for | n/a | | 2498 | | private use | n/a | | 2500 +---------+-------------+----------------+------------------+ 2502 10.7. URI scheme "dtn" 2504 In the Uniform Resource Identifier (URI) Schemes (uri-schemes) 2505 registry, IANA is requested to update the registration of the URI 2506 scheme with the string "dtn" as the scheme name, as follows: 2508 URI scheme name: "dtn" 2510 Status: permanent 2512 Applications and/or protocols that use this URI scheme name: the 2513 Delay-Tolerant Networking (DTN) Bundle Protocol (BP). 2515 Contact: 2517 Scott Burleigh 2519 Jet Propulsion Laboratory, 2521 California Institute of Technology 2523 scott.c.burleigh@jpl.nasa.gov 2524 +1 (800) 393-3353 2526 Change controller: 2528 IETF, iesg@ietf.org 2530 10.8. URI scheme "ipn" 2532 In the Uniform Resource Identifier (URI) Schemes (uri-schemes) 2533 registry, IANA is requested to update the registration of the URI 2534 scheme with the string "ipn" as the scheme name, originally 2535 documented in RFC 6260 [RFC6260], as follows. 2537 URI scheme name: "ipn" 2539 Status: permanent 2541 Applications and/or protocols that use this URI scheme name: the 2542 Delay-Tolerant Networking (DTN) Bundle Protocol (BP). 2544 Contact: 2546 Scott Burleigh 2548 Jet Propulsion Laboratory, 2550 California Institute of Technology 2552 scott.c.burleigh@jpl.nasa.gov 2554 +1 (800) 393-3353 2556 Change controller: 2558 IETF, iesg@ietf.org 2560 11. References 2562 11.1. Normative References 2564 [BPSEC] Birrane, E., "Bundle Security Protocol Specification", 2565 draft-ietf-dtn-bpsec, January 2020. 2567 [CRC16] ITU-T Recommendation X.25, p. 9, section 2.2.7.4, 2568 International Telecommunications Union, October 1996. 2570 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2571 Requirement Levels", BCP 14, RFC 2119, March 1997. 2573 [RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC 2574 4960, September 2007. 2576 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 2577 Specifications: ABNF", STD 68, RFC 5234, January 2008. 2579 [RFC7049] Borman, C. and P. Hoffman, "Concise Binary Object 2580 Representation (CBOR)", RFC 7049, October 2013. 2582 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2583 2119 Key Words", BCP 14, RFC 8174, May 2017. 2585 [SABR] "Schedule-Aware Bundle Routing", CCSDS Recommended Standard 2586 734.3-B-1, Consultative Committee for Space Data Systems, July 2019. 2588 [TCPCL] Sipos, B., Demmer, M., Ott, J., and S. Perreault, "Delay- 2589 Tolerant Networking TCP Convergence Layer Protocol Version 4", 2590 draft-ietf-dtn-tcpclv4, January 2020. 2592 [URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 2593 Resource Identifier (URI): Generic Syntax", RFC 3986, STD 66, 2594 January 2005. 2596 [URIREG] Thaler, D., Hansen, T., and T. Hardie, "Guidelines and 2597 Registration Procedures for URI Schemes", RFC 7595, BCP 35, June 2598 2015. 2600 [UTC] Arias, E. and B. Guinot, "Coordinated universal time UTC: 2601 historical background and perspectives" in "Journees systemes de 2602 reference spatio-temporels", 2004. 2604 11.2. Informative References 2606 [ARCH] V. Cerf et al., "Delay-Tolerant Network Architecture", RFC 2607 4838, April 2007. 2609 [BIBE] Burleigh, S., "Bundle-in-Bundle Encapsulation", draft-ietf- 2610 dtn-bibect, August 2019. 2612 [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource 2613 Identifiers (IRIs)", RFC 3987, January 2005. 2615 [RFC5050] Scott, K. and S. Burleigh, "Bundle Protocol 2616 Specification", RFC 5050, November 2007. 2618 [RFC6255] Blanchet, M., "Delay-Tolerant Networking Bundle Protocol 2619 IANA Registries", RFC 6255, May 2011. 2621 [RFC6257] Symington, S., Farrell, S., Weiss, H., and P. Lovell, 2622 "Bundle Security Protocol Specification", RFC 6257, May 2011. 2624 [RFC6258] Symington, S., "Delay-Tolerant Networking Metadata 2625 Extension Block", RFC 6258, May 2011. 2627 [RFC6259] Symington, S., "Delay-Tolerant Networking Previous-Hop 2628 Insertion Block", RFC 6259, May 2011. 2630 [RFC6260] Burleigh, S., "Compressed Bundle Header Encoding (CBHE)", 2631 RFC 6260, May 2011. 2633 [RFC7143] Chadalapaka, M., Satran, J., Meth, K., and D. Black, 2634 "Internet Small Computer System Interface (iSCSI) Protocol 2635 (Consolidated)", RFC 7143, April 2014. 2637 [SIGC] Fall, K., "A Delay-Tolerant Network Architecture for 2638 Challenged Internets", SIGCOMM 2003. 2640 12. Acknowledgments 2642 This work is freely adapted from RFC 5050, which was an effort of 2643 the Delay Tolerant Networking Research Group. The following DTNRG 2644 participants contributed significant technical material and/or 2645 inputs to that document: Dr. Vinton Cerf of Google, Scott Burleigh, 2646 Adrian Hooke, and Leigh Torgerson of the Jet Propulsion Laboratory, 2647 Michael Demmer of the University of California at Berkeley, Robert 2648 Durst, Keith Scott, and Susan Symington of The MITRE Corporation, 2649 Kevin Fall of Carnegie Mellon University, Stephen Farrell of Trinity 2650 College Dublin, Howard Weiss and Peter Lovell of SPARTA, Inc., and 2651 Manikantan Ramadas of Ohio University. 2653 This document was prepared using 2-Word-v2.0.template.dot. 2655 13. Significant Changes from RFC 5050 2657 Points on which this draft significantly differs from RFC 5050 2658 include the following: 2660 . Clarify the difference between transmission and forwarding. 2661 . Migrate custody transfer to the bundle-in-bundle encapsulation 2662 specification [BIBE]. 2663 . Introduce the concept of "node ID" as functionally distinct 2664 from endpoint ID, while having the same syntax. 2666 . Restructure primary block, making it immutable. Add optional 2667 CRC. 2668 . Add optional CRCs to non-primary blocks. 2669 . Add block ID number to canonical block format (to support 2670 BPsec). 2671 . Add definition of bundle age extension block. 2672 . Add definition of previous node extension block. 2673 . Add definition of hop count extension block. 2674 . Remove Quality of Service markings. 2675 . Change from SDNVs to CBOR representation. 2676 . Add lifetime overrides. 2678 Appendix A. For More Information 2680 Copyright (c) 2020 IETF Trust and the persons identified as authors 2681 of the code. All rights reserved. 2683 Redistribution and use in source and binary forms, with or without 2684 modification, is permitted pursuant to, and subject to the license 2685 terms contained in, the Simplified BSD License set forth in Section 2686 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents 2687 (http://trustee.ietf.org/license-info). 2689 Appendix B. CDDL expression 2691 For informational purposes, Carsten Bormann and Brian Sipos have 2692 kindly provided an expression of the Bundle Protocol specification 2693 in the Concise Data Definition Language (CDDL). That CDDL 2694 expression is presented below. Note that wherever the CDDL 2695 expression is in disagreement with the textual representation of the 2696 BP specification presented in the earlier sections of this document, 2697 the textual representation rules. 2699 start = bundle / #6.55799(bundle) 2701 ; Times before 2000 are invalid 2703 dtn-time = uint 2705 ; CRC enumerated type 2707 crc-type = &( 2709 crc-none: 0, 2711 crc-16bit: 1, 2713 crc-32bit: 2 2715 ) 2717 ; Either 16-bit or 32-bit 2719 crc-value = (bstr .size 2) / (bstr .size 4) 2721 creation-timestamp = [ 2723 dtn-time, ; absolute time of creation 2725 sequence: uint ; sequence within the time 2727 ] 2729 eid = $eid .within eid-structure 2731 eid-structure = [ 2733 uri-code: uint, 2734 SSP: any 2736 ] 2738 $eid /= [ 2740 uri-code: 1, 2742 SSP: (tstr / 0) 2744 ] 2746 $eid /= [ 2748 uri-code: 2, 2750 SSP: [ 2752 nodenum: uint, 2754 servicenum: uint 2756 ] 2758 ] 2760 ; The root bundle array 2762 bundle = [primary-block, *extension-block, payload-block] 2764 primary-block = [ 2766 version: 7, 2768 bundle-control-flags, 2770 crc-type, 2772 destination: eid, 2774 source-node: eid, 2776 report-to: eid, 2778 creation-timestamp, 2780 lifetime: uint, 2781 ? ( 2783 fragment-offset: uint, 2785 total-application-data-length: uint 2787 ), 2789 ? crc-value, 2791 ] 2793 bundle-control-flags = uint .bits bundleflagbits 2795 bundleflagbits = &( 2797 reserved: 21, 2799 reserved: 20, 2801 reserved: 19, 2803 bundle-deletion-status-reports-are-requested: 18, 2805 bundle-delivery-status-reports-are-requested: 17, 2807 bundle-forwarding-status-reports-are-requested: 16, 2809 reserved: 15, 2811 bundle-reception-status-reports-are-requested: 14, 2813 reserved: 13, 2815 reserved: 12, 2817 reserved: 11, 2819 reserved: 10, 2821 reserved: 9, 2823 reserved: 8, 2825 reserved: 7, 2826 status-time-is-requested-in-all-status-reports: 6, 2828 user-application-acknowledgement-is-requested: 5, 2830 reserved: 4, 2832 reserved: 3, 2834 bundle-must-not-be-fragmented: 2, 2836 payload-is-an-administrative-record: 1, 2838 bundle-is-a-fragment: 0 2840 ) 2842 ; Abstract shared structure of all non-primary blocks 2844 canonical-block-structure = [ 2846 block-type-code: uint, 2848 block-number: uint, 2850 block-control-flags, 2852 crc-type, 2854 ; Each block type defines the content within the bytestring 2856 block-type-specific-data, 2858 ? crc-value 2860 ] 2862 block-control-flags = uint .bits blockflagbits 2864 blockflagbits = &( 2866 reserved: 7, 2868 reserved: 6, 2870 reserved: 5, 2872 block-must-be-removed-from-bundle-if-it-cannot-be-processed: 4, 2873 reserved: 3, 2875 bundle-must-be-deleted-if-block-cannot-be-processed: 2, 2877 status-report-must-be-transmitted-if-block-cannot-be-processed: 1, 2879 block-must-be-replicated-in-every-fragment: 0 2881 ) 2883 block-type-specific-data = bstr / #6.24(bstr) 2885 ; Actual CBOR data embedded in a bytestring, with optional tag to 2886 indicate so 2888 embedded-cbor = (bstr .cbor Item) / #6.24(bstr .cbor Item) 2890 ; Extension block type, which does not specialize other than the 2891 code/number 2893 extension-block = $extension-block-structure .within canonical- 2894 block-structure 2896 ; Generic shared structure of all non-primary blocks 2898 extension-block-use = [ 2900 block-type-code: CodeValue, 2902 block-number: (uint .gt 1), 2904 block-control-flags, 2906 crc-type, 2908 BlockData, 2910 ? crc-value 2912 ] 2914 ; Payload block type 2916 payload-block = payload-block-structure .within canonical-block- 2917 structure 2918 payload-block-structure = [ 2920 block-type-code: 1, 2922 block-number: 1, 2924 block-control-flags, 2926 crc-type, 2928 $payload-block-data, 2930 ? crc-value 2932 ] 2934 ; Arbitrary payload data, including non-CBOR bytestring 2936 $payload-block-data /= block-type-specific-data 2938 ; Administrative record as a payload data specialization 2940 $payload-block-data /= embedded-cbor 2942 admin-record = $admin-record .within admin-record-structure 2944 admin-record-structure = [ 2946 record-type-code: uint, 2948 record-content: any 2950 ] 2952 ; Only one defined record type 2954 $admin-record /= [1, status-record-content] 2956 status-record-content = [ 2958 bundle-status-information, 2960 status-report-reason-code: uint, 2962 source-node-eid: eid, 2964 subject-creation-timestamp: creation-timestamp, 2965 ? ( 2967 subject-payload-offset: uint, 2969 subject-payload-length: uint 2971 ) 2973 ] 2975 bundle-status-information = [ 2977 reporting-node-received-bundle: status-info-content, 2979 reporting-node-forwarded-bundle: status-info-content, 2981 reporting-node-delivered-bundle: status-info-content, 2983 reporting-node-deleted-bundle: status-info-content 2985 ] 2987 status-info-content = [ 2989 status-indicator: bool, 2991 ? timestamp: dtn-time 2993 ] 2995 ; Previous Node extension block 2997 $extension-block-structure /= 2999 extension-block-use<6, embedded-cbor> 3001 ext-data-previous-node = eid 3003 ; Bundle Age extension block 3005 $extension-block-structure /= 3007 extension-block-use<7, embedded-cbor> 3009 ext-data-bundle-age = uint 3011 ; Hop Count extension block 3012 $extension-block-structure /= 3014 extension-block-use<10, embedded-cbor> 3016 ext-data-hop-count = [ 3018 hop-limit: uint, 3020 hop-count: uint 3022 ] 3024 Authors' Addresses 3026 Scott Burleigh 3027 Jet Propulsion Laboratory, California Institute of Technology 3028 4800 Oak Grove Dr. 3029 Pasadena, CA 91109-8099 3030 US 3031 Phone: +1 818 393 3353 3032 Email: Scott.C.Burleigh@jpl.nasa.gov 3034 Kevin Fall 3035 Roland Computing Services 3036 3871 Piedmont Ave. Suite 8 3037 Oakland, CA 94611 3038 US 3039 Email: kfall+rcs@kfall.com 3041 Edward J. Birrane 3042 Johns Hopkins University Applied Physics Laboratory 3043 11100 Johns Hopkins Rd 3044 Laurel, MD 20723 3045 US 3046 Phone: +1 443 778 7423 3047 Email: Edward.Birrane@jhuapl.edu