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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Possible downref: Non-RFC (?) normative reference: ref. 'BPSEC' -- Possible downref: Non-RFC (?) normative reference: ref. 'CRC16' -- Possible downref: Non-RFC (?) normative reference: ref. 'CRC32C' -- Possible downref: Non-RFC (?) normative reference: ref. 'EPOCH' ** Obsolete normative reference: RFC 7049 (Obsoleted by RFC 8949) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 5 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 28, 2020 Roland Computing Services 5 E. Birrane 6 APL, Johns Hopkins University 7 October 26, 2019 9 Bundle Protocol Version 7 10 draft-ietf-dtn-bpbis-17.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 28, 2020. 35 Copyright Notice 37 Copyright (c) 2019 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 Bundle Protocol, 53 adapted from the experimental Bundle Protocol specification 54 developed by the Delay-Tolerant Networking Research group of the 55 Internet Research Task Force and documented in RFC 5050. 57 Table of Contents 59 1. Introduction...................................................3 60 2. Conventions used in this document..............................5 61 3. Service Description............................................6 62 3.1. Definitions...............................................6 63 3.2. Discussion of BP concepts.................................9 64 3.3. Services Offered by Bundle Protocol Agents...............12 65 4. Bundle Format.................................................13 66 4.1. BP Fundamental Data Structures...........................13 67 4.1.1. CRC Type............................................13 68 4.1.2. CRC.................................................14 69 4.1.3. Bundle Processing Control Flags.....................14 70 4.1.4. Block Processing Control Flags......................16 71 4.1.5. Identifiers.........................................17 72 4.1.5.1. Endpoint ID....................................17 73 4.1.5.2. Node ID........................................18 74 4.1.6. DTN Time............................................18 75 4.1.7. Creation Timestamp..................................20 76 4.1.8. Block-type-specific Data............................20 77 4.2. Bundle Representation....................................20 78 4.2.1. Bundle..............................................21 79 4.2.2. Primary Bundle Block................................21 80 4.2.3. Canonical Bundle Block Format.......................23 81 4.3. Extension Blocks.........................................24 82 4.3.1. Previous Node.......................................25 83 4.3.2. Bundle Age..........................................25 84 4.3.3. Hop Count...........................................26 85 5. Bundle Processing.............................................26 86 5.1. Generation of Administrative Records.....................26 87 5.2. Bundle Transmission......................................27 88 5.3. Bundle Dispatching.......................................28 89 5.4. Bundle Forwarding........................................28 90 5.4.1. Forwarding Contraindicated..........................30 91 5.4.2. Forwarding Failed...................................30 92 5.5. Bundle Expiration........................................31 93 5.6. Bundle Reception.........................................31 94 5.7. Local Bundle Delivery....................................32 95 5.8. Bundle Fragmentation.....................................33 96 5.9. Application Data Unit Reassembly.........................34 97 5.10. Bundle Deletion.........................................34 98 5.11. Discarding a Bundle.....................................35 99 5.12. Canceling a Transmission................................35 100 6. Administrative Record Processing..............................35 101 6.1. Administrative Records...................................35 102 6.1.1. Bundle Status Reports...............................36 103 6.2. Generation of Administrative Records.....................39 104 7. Services Required of the Convergence Layer....................39 105 7.1. The Convergence Layer....................................39 106 7.2. Summary of Convergence Layer Services....................39 107 8. Implementation Status.........................................40 108 9. Security Considerations.......................................41 109 10. IANA Considerations..........................................43 110 10.1. Bundle Block Types......................................43 111 10.2. Primary Bundle Protocol Version.........................44 112 10.3. Bundle Processing Control Flags.........................44 113 10.4. Block Processing Control Flags..........................46 114 10.5. Bundle Status Report Reason Codes.......................47 115 10.6. Bundle Protocol URI scheme types........................49 116 10.7. URI scheme "dtn"........................................50 117 10.8. Change status of URI scheme "ipn".......................52 118 11. References...................................................52 119 11.1. Normative References....................................52 120 11.2. Informative References..................................53 121 12. Acknowledgments..............................................53 122 13. Significant Changes from RFC 5050............................54 123 Appendix A. For More Information.................................55 124 Appendix B. CDDL expression......................................56 126 1. Introduction 128 Since the publication of the Bundle Protocol Specification 129 (Experimental RFC 5050) in 2007, the Delay-Tolerant Networking (DTN) 130 Bundle Protocol has been implemented in multiple programming 131 languages and deployed to a wide variety of computing platforms. 132 This implementation and deployment experience has identified 133 opportunities for making the protocol simpler, more capable, and 134 easier to use. The present document, standardizing the Bundle 135 Protocol (BP), is adapted from RFC 5050 in that context. 136 Significant changes from the Bundle Protocol specification defined 137 in RFC 5050 are listed in section 13. 139 This document describes version 7 of BP. 141 Delay Tolerant Networking is a network architecture providing 142 communications in and/or through highly stressed environments. 143 Stressed networking environments include those with intermittent 144 connectivity, large and/or variable delays, and high bit error 145 rates. To provide its services, BP may be viewed as sitting at the 146 application layer of some number of constituent networks, forming a 147 store-carry-forward overlay network. Key capabilities of BP 148 include: 150 . Ability to use physical motility for the movement of data 151 . Ability to move the responsibility for error control from one 152 node to another 153 . Ability to cope with intermittent connectivity, including cases 154 where the sender and receiver are not concurrently present in 155 the network 156 . Ability to take advantage of scheduled, predicted, and 157 opportunistic connectivity, whether bidirectional or 158 unidirectional, in addition to continuous connectivity 159 . Late binding of overlay network endpoint identifiers to 160 underlying constituent network addresses 162 For descriptions of these capabilities and the rationale for the DTN 163 architecture, see [ARCH] and [SIGC]. 165 BP's location within the standard protocol stack is as shown in 166 Figure 1. BP uses underlying "native" transport and/or network 167 protocols for communications within a given constituent network. 169 The interface between the bundle protocol and a specific underlying 170 protocol is termed a "convergence layer adapter". 172 Figure 1 shows three distinct transport and network protocols 173 (denoted T1/N1, T2/N2, and T3/N3). 175 +-----------+ +-----------+ 176 | BP app | | BP app | 177 +---------v-| +->>>>>>>>>>v-+ +->>>>>>>>>>v-+ +-^---------+ 178 | BP v | | ^ BP v | | ^ BP v | | ^ BP | 179 +---------v-+ +-^---------v-+ +-^---------v-+ +-^---------+ 180 | T1 v | + ^ T1/T2 v | + ^ T2/T3 v | | ^ T3 | 181 +---------v-+ +-^---------v-+ +-^---------v + +-^---------+ 182 | N1 v | | ^ N1/N2 v | | ^ N2/N3 v | | ^ N3 | 183 +---------v-+ +-^---------v + +-^---------v-+ +-^---------+ 184 | >>>>>>>>^ >>>>>>>>>>^ >>>>>>>>^ | 185 +-----------+ +-------------+ +-------------+ +-----------+ 186 | | | | 187 |<---- A network ---->| |<---- A network ---->| 188 | | | | 190 Figure 1: The Bundle Protocol in the Protocol Stack Model 192 This document describes the format of the protocol data units 193 (called "bundles") passed between entities participating in BP 194 communications. 196 The entities are referred to as "bundle nodes". This document does 197 not address: 199 . Operations in the convergence layer adapters that bundle nodes 200 use to transport data through specific types of internets. 201 (However, the document does discuss the services that must be 202 provided by each adapter at the convergence layer.) 203 . The bundle route computation algorithm. 204 . Mechanisms for populating the routing or forwarding information 205 bases of bundle nodes. 206 . The mechanisms for securing bundles en route. 207 . The mechanisms for managing bundle nodes. 209 Note that implementations of the specification presented in this 210 document will not be interoperable with implementations of RFC 5050. 212 2. Conventions used in this document 214 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 215 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 216 "OPTIONAL" in this document are to be interpreted as described in 217 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 218 capitals, as shown here. 220 3. Service Description 222 3.1. Definitions 224 Bundle - A bundle is a protocol data unit of BP, so named because 225 negotiation of the parameters of a data exchange may be impractical 226 in a delay-tolerant network: it is often better practice to "bundle" 227 with a unit of application data all metadata that might be needed in 228 order to make the data immediately usable when delivered to the 229 application. Each bundle comprises a sequence of two or more 230 "blocks" of protocol data, which serve various purposes. 232 Block - A bundle protocol block is one of the protocol data 233 structures that together constitute a well-formed bundle. 235 Application Data Unit (ADU) - An application data unit is the unit 236 of data whose conveyance to the bundle's destination is the purpose 237 for the transmission of some bundle that is not a fragment (as 238 defined below). 240 Bundle payload - A bundle payload (or simply "payload") is the 241 content of the bundle's payload block. The terms "bundle content", 242 "bundle payload", and "payload" are used interchangeably in this 243 document. For a bundle that is not a fragment (as defined below), 244 the payload is an application data unit. 246 Partial payload - A partial payload is a payload that comprises 247 either the first N bytes or the last N bytes of some other payload 248 of length M, such that 0 < N < M. Note that every partial payload 249 is a payload and therefore can be further subdivided into partial 250 payloads. 252 Fragment - A fragment is a bundle whose payload block contains a 253 partial payload. 255 Bundle node - A bundle node (or, in the context of this document, 256 simply a "node") is any entity that can send and/or receive bundles. 257 Each bundle node has three conceptual components, defined below, as 258 shown in Figure 2: a "bundle protocol agent", a set of zero or more 259 "convergence layer adapters", and an "application agent". 261 +-----------------------------------------------------------+ 262 |Node | 263 | | 264 | +-------------------------------------------------------+ | 265 | |Application Agent | | 266 | | | | 267 | | +--------------------------+ +----------------------+ | | 268 | | |Administrative element | |Application-specific | | | 269 | | | | |element | | | 270 | | | | | | | | 271 | | +--------------------------+ +----------------------+ | | 272 | | ^ ^ | | 273 | | Admin|records Application|data | | 274 | | | | | | 275 | +----------------v--------------------------v-----------+ | 276 | ^ | 277 | | ADUs | 278 | | | 279 | +-----------------------------v-------------------------+ | 280 | |Bundle Protocol Agent | | 281 | | | | 282 | | | | 283 | +-------------------------------------------------------+ | 284 | ^ ^ ^ | 285 | | Bundles | Bundles Bundles | | 286 | | | | | 287 | +------v-----+ +-----v------+ +-----v-----+ | 288 | |CLA 1 | |CLA 2 | |CLA n | | 289 | | | | | . . . | | | 290 | | | | | | | | 291 +-+------------+-----+------------+-----------+-----------+-+ 292 ^ ^ ^ 293 CL1|PDUs CL2|PDUs CLn|PDUs 294 | | | 295 +------v-----+ +-----v------+ +-----v-----+ 296 Network 1 Network 2 Network n 298 Figure 2: Components of a Bundle Node 300 Bundle protocol agent - The bundle protocol agent (BPA) of a node is 301 the node component that offers the BP services and executes the 302 procedures of the bundle protocol. 304 Convergence layer adapter - A convergence layer adapter (CLA) is a 305 node component that sends and receives bundles on behalf of the BPA, 306 utilizing the services of some 'native' protocol stack that is 307 supported in one of the networks within which the node is 308 functionally located. 310 Application agent - The application agent (AA) of a node is the node 311 component that utilizes the BP services to effect communication for 312 some user purpose. The application agent in turn has two elements, 313 an administrative element and an application-specific element. 315 Application-specific element - The application-specific element of 316 an AA is the node component that constructs, requests transmission 317 of, accepts delivery of, and processes units of user application 318 data. 320 Administrative element - The administrative element of an AA is the 321 node component that constructs and requests transmission of 322 administrative records (defined below), including status reports, 323 and accepts delivery of and processes any administrative records 324 that the node receives. 326 Administrative record - A BP administrative record is an application 327 data unit that is exchanged between the administrative elements of 328 nodes' application agents for some BP administrative purpose. The 329 only administrative record defined in this specification is the 330 status report, discussed later. 332 Bundle endpoint - A bundle endpoint (or simply "endpoint") is a set 333 of zero or more bundle nodes that all identify themselves for BP 334 purposes by some common identifier, called a "bundle endpoint ID" 335 (or, in this document, simply "endpoint ID"; endpoint IDs are 336 described in detail in Section 4.4.1 below). 338 Singleton endpoint - A singleton endpoint is an endpoint that always 339 contains exactly one member. 341 Registration - A registration is the state machine characterizing a 342 given node's membership in a given endpoint. Any single 343 registration has an associated delivery failure action as defined 344 below and must at any time be in one of two states: Active or 345 Passive. 347 Delivery - A bundle is considered to have been delivered at a node 348 subject to a registration as soon as the application data unit that 349 is the payload of the bundle, together with any relevant metadata 350 (an implementation matter), has been presented to the node's 351 application agent in a manner consistent with the state of that 352 registration. 354 Deliverability - A bundle is considered "deliverable" subject to a 355 registration if and only if (a) the bundle's destination endpoint is 356 the endpoint with which the registration is associated, (b) the 357 bundle has not yet been delivered subject to this registration, and 358 (c) the bundle has not yet been "abandoned" (as defined below) 359 subject to this registration. 361 Abandonment - To abandon a bundle subject to some registration is to 362 assert that the bundle is not deliverable subject to that 363 registration. 365 Delivery failure action - The delivery failure action of a 366 registration is the action that is to be taken when a bundle that is 367 "deliverable" subject to that registration is received at a time 368 when the registration is in the Passive state. 370 Destination - The destination of a bundle is the endpoint comprising 371 the node(s) at which the bundle is to be delivered (as defined 372 above). 374 Transmission - A transmission is an attempt by a node's BPA to cause 375 copies of a bundle to be delivered to one or more of the nodes that 376 are members of some endpoint (the bundle's destination) in response 377 to a transmission request issued by the node's application agent. 379 Forwarding - To forward a bundle to a node is to invoke the services 380 of one or more CLAs in a sustained effort to cause a copy of the 381 bundle to be received by that node. 383 Discarding - To discard a bundle is to cease all operations on the 384 bundle and functionally erase all references to it. The specific 385 procedures by which this is accomplished are an implementation 386 matter. 388 Retention constraint - A retention constraint is an element of the 389 state of a bundle that prevents the bundle from being discarded. 390 That is, a bundle cannot be discarded while it has any retention 391 constraints. 393 Deletion - To delete a bundle is to remove unconditionally all of 394 the bundle's retention constraints, enabling the bundle to be 395 discarded. 397 3.2. Discussion of BP concepts 399 Multiple instances of the same bundle (the same unit of DTN protocol 400 data) might exist concurrently in different parts of a network -- 401 possibly differing in some blocks -- in the memory local to one or 402 more bundle nodes and/or in transit between nodes. In the context of 403 the operation of a bundle node, a bundle is an instance (copy), in 404 that node's local memory, of some bundle that is in the network. 406 The payload for a bundle forwarded in response to a bundle 407 transmission request is the application data unit whose location is 408 provided as a parameter to that request. The payload for a bundle 409 forwarded in response to reception of a bundle is the payload of the 410 received bundle. 412 In the most familiar case, a bundle node is instantiated as a single 413 process running on a general-purpose computer, but in general the 414 definition is meant to be broader: a bundle node might alternatively 415 be a thread, an object in an object-oriented operating system, a 416 special-purpose hardware device, etc. 418 The manner in which the functions of the BPA are performed is wholly 419 an implementation matter. For example, BPA functionality might be 420 coded into each node individually; it might be implemented as a 421 shared library that is used in common by any number of bundle nodes 422 on a single computer; it might be implemented as a daemon whose 423 services are invoked via inter-process or network communication by 424 any number of bundle nodes on one or more computers; it might be 425 implemented in hardware. 427 Every CLA implements its own thin layer of protocol, interposed 428 between BP and the (usually "top") protocol(s) of the underlying 429 native protocol stack; this "CL protocol" may only serve to 430 multiplex and de-multiplex bundles to and from the underlying native 431 protocol, or it may offer additional CL-specific functionality. The 432 manner in which a CLA sends and receives bundles, as well as the 433 definitions of CLAs and CL protocols, are beyond the scope of this 434 specification. 436 Note that the administrative element of a node's application agent 437 may itself, in some cases, function as a convergence-layer adapter. 438 That is, outgoing bundles may be "tunneled" through encapsulating 439 bundles: 441 . An outgoing bundle constitutes a byte array. This byte array 442 may, like any other, be presented to the bundle protocol agent 443 as an application data unit that is to be transmitted to some 444 endpoint. 445 . The original bundle thus forms the payload of an encapsulating 446 bundle that is forwarded using some other convergence-layer 447 protocol(s). 449 . When the encapsulating bundle is received, its payload is 450 delivered to the peer application agent administrative element, 451 which then instructs the bundle protocol agent to dispatch that 452 original bundle in the usual way. 454 The purposes for which this technique may be useful (such as cross- 455 domain security) are beyond the scope of this specification. 457 The only interface between the BPA and the application-specific 458 element of the AA is the BP service interface. But between the BPA 459 and the administrative element of the AA there is a (conceptual) 460 private control interface in addition to the BP service interface. 461 This private control interface enables the BPA and the 462 administrative element of the AA to direct each other to take action 463 under specific circumstances. 465 In the case of a node that serves simply as a BP "router", the AA 466 may have no application-specific element at all. The application- 467 specific elements of other nodes' AAs may perform arbitrarily 468 complex application functions, perhaps even offering multiplexed DTN 469 communication services to a number of other applications. As with 470 the BPA, the manner in which the AA performs its functions is wholly 471 an implementation matter. 473 Singletons are the most familiar sort of endpoint, but in general 474 the endpoint notion is meant to be broader. For example, the nodes 475 in a sensor network might constitute a set of bundle nodes that 476 identify themselves by a single common endpoint ID and thus form a 477 single bundle endpoint. *Note* too that a given bundle node might 478 identify itself by multiple endpoint IDs and thus be a member of 479 multiple bundle endpoints. 481 The destination of every bundle is an endpoint, which may or may not 482 be singleton. The source of every bundle is a node, identified by 483 the endpoint ID for some singleton endpoint that contains that node. 484 Note, though, that the source node ID asserted in a given bundle may 485 be the null endpoint ID (as described later) rather than the 486 endpoint ID of the actual source node; bundles for which the 487 asserted source node ID is the null endpoint ID are termed 488 "anonymous" bundles. 490 Any number of transmissions may be concurrently undertaken by the 491 bundle protocol agent of a given node. 493 When the bundle protocol agent of a node determines that a bundle 494 must be forwarded to a node (either to a node that is a member of 495 the bundle's destination endpoint or to some intermediate forwarding 496 node) in the course of completing the successful transmission of 497 that bundle, the bundle protocol agent invokes the services of one 498 or more CLAs in a sustained effort to cause a copy of the bundle to 499 be received by that node. 501 Upon reception, the processing of a bundle that has been received by 502 a given node depends on whether or not the receiving node is 503 registered in the bundle's destination endpoint. If it is, and if 504 the payload of the bundle is non-fragmentary (possibly as a result 505 of successful payload reassembly from fragmentary payloads, 506 including the original payload of the newly received bundle), then 507 the bundle is normally delivered to the node's application agent 508 subject to the registration characterizing the node's membership in 509 the destination endpoint. 511 The bundle protocol does not natively ensure delivery of a bundle to 512 its destination. Data loss along the path to the destination node 513 can be minimized by utilizing reliable convergence-layer protocols 514 between neighbors on all segments of the end-to-end path, but for 515 end-to-end bundle delivery assurance it will be necessary to develop 516 extensions to the bundle protocol and/or application-layer 517 mechanisms. 519 The bundle protocol is designed for extensibility. Bundle protocol 520 extensions, documented elsewhere, may extend this specification by: 522 . defining additional blocks; 523 . defining additional administrative records; 524 . defining additional bundle processing flags; 525 . defining additional block processing flags; 526 . defining additional types of bundle status reports; 527 . defining additional bundle status report reason codes; 528 . defining additional mandates and constraints on processing 529 that conformant bundle protocol agents must perform at 530 specified points in the inbound and outbound bundle processing 531 cycles. 533 3.3. Services Offered by Bundle Protocol Agents 535 The BPA of each node is expected to provide the following services 536 to the node's application agent: 538 . commencing a registration (registering the node in an 539 endpoint); 540 . terminating a registration; 541 . switching a registration between Active and Passive states; 542 . transmitting a bundle to an identified bundle endpoint; 543 . canceling a transmission; 544 . polling a registration that is in the Passive state; 545 . delivering a received bundle. 547 4. Bundle Format 549 The format of bundles SHALL conform to the Concise Binary Object 550 Representation (CBOR [RFC7049]). 552 Each bundle SHALL be a concatenated sequence of at least two blocks, 553 represented as a CBOR indefinite-length array. The first block in 554 the sequence (the first item of the array) MUST be a primary bundle 555 block in CBOR representation as described below; the bundle MUST 556 have exactly one primary bundle block. The primary block MUST be 557 followed by one or more canonical bundle blocks (additional array 558 items) in CBOR representation as described in 4.2.3 below. The last 559 such block MUST be a payload block; the bundle MUST have exactly one 560 payload block. The last item of the array, immediately following 561 the payload block, SHALL be a CBOR "break" stop code. 563 (Note that, while CBOR permits considerable flexibility in the 564 encoding of bundles, this flexibility must not be interpreted as 565 inviting increased complexity in protocol data unit structure.) 567 An implementation of the Bundle Protocol MAY discard any sequence of 568 bytes that does not conform to the Bundle Protocol specification. 570 An implementation of the Bundle Protocol MAY accept a sequence of 571 bytes that does not conform to the Bundle Protocol specification 572 (e.g., one that represents data elements in fixed-length arrays 573 rather than indefinite-length arrays) and transform it into 574 conformant BP structure before processing it. Procedures for 575 accomplishing such a transformation are beyond the scope of this 576 specification. 578 4.1. BP Fundamental Data Structures 580 4.1.1. CRC Type 582 CRC type is an unsigned integer type code for which the following 583 values (and no others) are valid: 585 . 0 indicates "no CRC is present." 586 . 1 indicates "a standard X-25 CRC-16 is present." [CRC16] 587 . 2 indicates "a standard CRC32C (Castagnoli) CRC-32 is present." 588 [CRC32C] 590 CRC type SHALL be represented as a CBOR unsigned integer. 592 For examples of CRC32C CRCs, see Appendix A.4 of [RFC7143]. 594 4.1.2. CRC 596 CRC SHALL be omitted from a block if and only if the block's CRC 597 type code is zero. 599 When not omitted, the CRC SHALL be represented as a CBOR byte string 600 of two bytes (that is, CBOR additional information 2, if CRC type is 601 1) or of four bytes (that is, CBOR additional information 4, if CRC 602 type is 2); in each case the sequence of bytes SHALL constitute an 603 unsigned integer value (of 16 or 32 bits, respectively) in network 604 byte order. 606 4.1.3. Bundle Processing Control Flags 608 Bundle processing control flags assert properties of the bundle as a 609 whole rather than of any particular block of the bundle. They are 610 conveyed in the primary block of the bundle. 612 The following properties are asserted by the bundle processing 613 control flags: 615 . The bundle is a fragment. (Boolean) 617 . The bundle's payload is an administrative record. (Boolean) 619 . The bundle must not be fragmented. (Boolean) 621 . Acknowledgment by the user application is requested. (Boolean) 623 . Status time is requested in all status reports. (Boolean) 625 . The bundle contains a "manifest" extension block. (Boolean) 627 . Flags requesting types of status reports (all Boolean): 629 o Request reporting of bundle reception. 631 o Request reporting of bundle forwarding. 633 o Request reporting of bundle delivery. 635 o Request reporting of bundle deletion. 637 If the bundle processing control flags indicate that the bundle's 638 application data unit is an administrative record, then all status 639 report request flag values must be zero. 641 If the bundle's source node is omitted (i.e., the source node ID is 642 the ID of the null endpoint, which has no members as discussed 643 below; this option enables anonymous bundle transmission), then the 644 bundle is not uniquely identifiable and all bundle protocol features 645 that rely on bundle identity must therefore be disabled: the "Bundle 646 must not be fragmented" flag value must be 1 and all status report 647 request flag values must be zero. 649 The bundle processing control flags SHALL be represented as a CBOR 650 unsigned integer item, the value of which SHALL be processed as a 651 bit field indicating the control flag values as follows (note that 652 bit numbering in this instance is reversed from the usual practice, 653 beginning with the low-order bit instead of the high-order bit, in 654 recognition of the potential definition of additional control flag 655 values in the future): 657 . Bit 0 (the low-order bit, 0x000001: bundle is a fragment. 658 . Bit 1 (0x000002): payload is an administrative record. 659 . Bit 2 (0x000004): bundle must not be fragmented. 660 . Bit 3 (0x000008): reserved. 661 . Bit 4 (0x000010): reserved. 662 . Bit 5 (0x000020): user application acknowledgement is 663 requested. 664 . Bit 6 (0x000040): status time is requested in all status 665 reports. 666 . Bit 7 (0x000080): reserved. 667 . Bit 8 (0x000100): reserved. 668 . Bit 9 (0x000200): reserved. 669 . Bit 10(0x000400): reserved. 670 . Bit 11(0x000800): reserved. 671 . Bit 12(0x001000): reserved. 672 . Bit 13(0x002000): reserved. 673 . Bit 14(0x004000): bundle reception status reports are 674 requested. 675 . Bit 15(0x008000): reserved. 676 . Bit 16(0x010000): bundle forwarding status reports are 677 requested. 678 . Bit 17(0x020000): bundle delivery status reports are requested. 679 . Bit 18(0x040000): bundle deletion status reports are requested. 680 . Bits 19-20 are reserved. 681 . Bits 21-63 are unassigned. 683 4.1.4. Block Processing Control Flags 685 The block processing control flags assert properties of canonical 686 bundle blocks. They are conveyed in the header of the block to 687 which they pertain. 689 The following properties are asserted by the block processing 690 control flags: 692 . This block must be replicated in every fragment. (Boolean) 694 . Transmission of a status report is requested if this block 695 can't be processed. (Boolean) 697 . Block must be removed from the bundle if it can't be processed. 698 (Boolean) 700 . Bundle must be deleted if this block can't be processed. 701 (Boolean) 703 For each bundle whose bundle processing control flags indicate that 704 the bundle's application data unit is an administrative record, or 705 whose source node ID is the null endpoint ID as defined below, the 706 value of the "Transmit status report if block can't be processed" 707 flag in every canonical block of the bundle must be zero. 709 The block processing control flags SHALL be represented as a CBOR 710 unsigned integer item, the value of which SHALL be processed as a 711 bit field indicating the control flag values as follows (note that 712 bit numbering in this instance is reversed from the usual practice, 713 beginning with the low-order bit instead of the high-order bit, for 714 agreement with the bit numbering of the bundle processing control 715 flags): 717 . Bit 0(the low-order bit, 0x01): block must be replicated in 718 every fragment. 719 . Bit 1(0x02): transmission of a status report is requested if 720 block can't be processed. 721 . Bit 2(0x04): bundle must be deleted if block can't be 722 processed. 723 . Bit 3(0x08): reserved. 724 . Bit 4(0x10): block must be removed from bundle if it can't be 725 processed. 726 . Bit 5(0x20): reserved. 727 . Bit 6 (0x40): reserved. 728 . Bits 7-63 are unassigned. 730 4.1.5. Identifiers 732 4.1.5.1. Endpoint ID 734 The destinations of bundles are bundle endpoints, identified by text 735 strings termed "endpoint IDs" (see Section 3.1). Each endpoint ID 736 (EID) is a Uniform Resource Identifier (URI; [URI]). As such, each 737 endpoint ID can be characterized as having this general structure: 739 < scheme name > : < scheme-specific part, or "SSP" > 741 The scheme identified by the < scheme name > in an endpoint ID is a 742 set of syntactic and semantic rules that fully explain how to parse 743 and interpret the SSP. The set of allowable schemes is effectively 744 unlimited. Any scheme conforming to [URIREG] may be used in a bundle 745 protocol endpoint ID. 747 Note that, although endpoint IDs are URIs, implementations of the BP 748 service interface may support expression of endpoint IDs in some 749 internationalized manner (e.g., Internationalized Resource 750 Identifiers (IRIs); see [RFC3987]). 752 The endpoint ID "dtn:none" identifies the "null endpoint", the 753 endpoint that by definition never has any members. 755 Each BP endpoint ID (EID) SHALL be represented as a CBOR array 756 comprising a 2-tuple. 758 The first item of the array SHALL be the code number identifying the 759 endpoint's URI scheme [URI], as defined in the registry of URI 760 scheme code numbers for Bundle Protocol maintained by IANA as 761 described in Section 10. [URIREG]. Each URI scheme code number 762 SHALL be represented as a CBOR unsigned integer. 764 The second item of the array SHALL be the applicable CBOR 765 representation of the scheme-specific part (SSP) of the EID, defined 766 as follows: 768 . If the EID's URI scheme is "dtn" then the SSP SHALL be 769 represented as a CBOR text string unless the EID's SSP is 770 "none", in which case the SSP SHALL be represented as a CBOR 771 unsigned integer with the value zero. 772 . If the EID's URI scheme is "ipn" then the SSP SHALL be 773 represented as a CBOR array comprising a 2-tuple. The first 774 item of this array SHALL be the EID's node number represented 775 as a CBOR unsigned integer. The second item of this array 776 SHALL be the EID's service number represented as a CBOR 777 unsigned integer. 778 . Definitions of the CBOR representations of the SSPs of EIDs 779 encoded in other URI schemes are included in the specifications 780 defining those schemes. 782 4.1.5.2. Node ID 784 For many purposes of the Bundle Protocol it is important to identify 785 the node that is operative in some context. 787 As discussed in 3.1 above, nodes are distinct from endpoints; 788 specifically, an endpoint is a set of zero or more nodes. But 789 rather than define a separate namespace for node identifiers, we 790 instead use endpoint identifiers to identify nodes, subject to the 791 following restrictions: 793 . Every node MUST be a member of at least one singleton endpoint. 794 . The EID of any singleton endpoint of which a node is a member 795 MAY be used to identify that node. A "node ID" is an EID that 796 is used in this way. 797 . A node's membership in a given singleton endpoint MUST be 798 sustained at least until the nominal operation of the Bundle 799 Protocol no longer depends on the identification of that node 800 using that endpoint's ID. 802 4.1.6. DTN Time 804 A DTN time is an unsigned integer indicating an interval of Unix 805 epoch time [EPOCH] that has elapsed since the start of the year 2000 806 on the Coordinated Universal Time (UTC) scale [UTC], which is Unix 807 epoch timestamp 946684800. (Note that the DTN time that equates to 808 the current time as reported by the UNIX time() function can be 809 derived by subtracting 946684800 from that reported time value.) 810 Each DTN time SHALL be represented as a CBOR unsigned integer item. 812 Note: The choice of Unix epoch time as the scale on which time 813 values in DTN are expressed may need some explanation. 815 The computation of time intervals is integral to several DTN 816 protocol procedures. Inconsistency in the results of these 817 computations would result in inconsistent performance of those 818 procedures and would compromise the operation of the protocol. 820 So the key qualities sought in selecting the time scale to be used 821 for expressing DTN times were these: (a) the broadest possible 822 access to the value of the current time on the selected time scale, 823 enabling all nodes of the network to perform protocol procedures in 824 the same way using the same information, and (b) ease of time 825 interval computation. 827 UTC was an obvious candidate but fell short on both counts. First, 828 millions of devices can readily query the current UTC time, thanks 829 to NTP, but spacecraft operating beyond Earth orbit cannot. There 830 is currently no adaptation of NTP that operates over the long and 831 variable signal propagation delays between vehicles in deep space. 833 Moreover, computing the number of actual elapsed seconds between two 834 UTC times is non-trivial because UTC times include leap seconds. As 835 an illustration of the issue, consider the passage of UTC and TAI 836 time at a ground station antenna that began transmitting data at 837 8Kbps around midnight December 31, 2016 (UTC), when a leap second 838 was added (*): 840 UTC TAI Total bytes sent 842 t1 2016-12-31 23:59:58 2017-01-01 00:00:34 0 844 t2 2016-12-31 23:59:59 2017-01-01 00:00:35 1000 846 t3 2016-12-31 23:59:60* 2017-01-01 00:00:36 2000 848 t4 2017-01-01 00:00:00 2017-01-01 00:00:37 3000 850 t5 2017-01-01 00:00:01 2017-01-01 00:00:38 4000 852 Suppose we must compute the volume of data transmitted in the 853 interval between t1 and t5. If we use TAI time values, the elapsed 854 time interval is 4 seconds (00:00:38 minus 00:00:34); at 8Kbps, the 855 computed transmission volume is 4000 bytes, which is correct. If we 856 instead use UTC time values as stated, without special compensation 857 for the insertion of the leap second, the elapsed time interval is 3 858 seconds (00:00:01 minus 23:59:58); the computed transmission volume 859 is then 3000 bytes, which is incorrect. 861 TAI, then, would be an ideal time scale for DTN, as the interval in 862 seconds between two TAI times can be computed by simply subtracting 863 one from the other; there is no need to consult a table of leap 864 seconds each time a time interval is computed. Unfortunately the 865 current value of TAI, as tracked by atomic clocks on Earth and 866 carefully managed by the International Bureau of Weights and 867 Measures, is likewise not directly accessible to spacecraft. 869 Unix epoch time is the next best option. Like TAI, Unix epoch time 870 is simply a count of seconds elapsed since a standard epoch. Unlike 871 TAI, the current value of Unix epoch time is provided by virtually 872 all operating systems on which BP is likely to run. 874 Implementers of Bundle Protocol need to be aware that the difference 875 between DTN time and UTC time will increase with the passing years 876 as additional leap seconds are inserted into UTC. Converting DTN 877 time to the correct corresponding UTC time, in the event that such 878 conversion is needed, will require an understanding of the leap 879 second adjustments made to UTC over time; for software written in C, 880 the widely supported gmtime() function provides this service. 882 Implementers also need to be aware that DTN time values conveyed in 883 CBOR representation in bundles can conceivably exceed (2**32 - 1). 885 4.1.7. Creation Timestamp 887 Each creation timestamp SHALL be represented as a CBOR array item 888 comprising a 2-tuple. 890 The first item of the array SHALL be a DTN time. 892 The second item of the array SHALL be the creation timestamp's 893 sequence number, represented as a CBOR unsigned integer. 895 4.1.8. Block-type-specific Data 897 Block-type-specific data in each block (other than the primary 898 block) SHALL be the applicable CBOR representation of the content of 899 the block. Details of this representation are included in the 900 specification defining the block type. 902 4.2. Bundle Representation 904 This section describes the primary block in detail and non-primary 905 blocks in general. Rules for processing these blocks appear in 906 Section 5 of this document. 908 Note that supplementary DTN protocol specifications (including, but 909 not restricted to, the Bundle Security Protocol [BPSEC]) may require 910 that BP implementations conforming to those protocols construct and 911 process additional blocks. 913 4.2.1. Bundle 915 Each bundle SHALL be represented as a CBOR indefinite-length array. 916 The first item of this array SHALL be the CBOR representation of a 917 Primary Block. Every other item of the array except the last SHALL 918 be the CBOR representation of a Canonical Block. The last item of 919 the array SHALL be a CBOR "break" stop code. 921 Associated with each block of a bundle is a block number. The block 922 number uniquely identifies the block within the bundle, enabling 923 blocks (notably bundle security protocol blocks) to reference other 924 blocks in the same bundle without ambiguity. The block number of 925 the primary block is implicitly zero; the block numbers of all other 926 blocks are explicitly stated in block headers as noted below. Block 927 numbering is unrelated to the order in which blocks are sequenced in 928 the bundle. The block number of the payload block is always 1. 930 4.2.2. Primary Bundle Block 932 The primary bundle block contains the basic information needed to 933 forward bundles to their destinations. 935 Each primary block SHALL be represented as a CBOR array; the number 936 of elements in the array SHALL be 8 (if the bundle is not a fragment 937 and the block has no CRC), 9 (if the block has a CRC and the bundle 938 is not a fragment), 10 (if the bundle is a fragment and the block 939 has no CRC), or 11 (if the bundle is a fragment and the block has a 940 CRC). 942 The primary block of each bundle SHALL be immutable. The values of 943 all fields in the primary block must remain unchanged from the time 944 the block is created to the time it is delivered. 946 The fields of the primary bundle block SHALL be as follows, listed 947 in the order in which they MUST appear: 949 Version: An unsigned integer value indicating the version of the 950 bundle protocol that constructed this block. The present document 951 describes version 7 of the bundle protocol. Version number SHALL be 952 represented as a CBOR unsigned integer item. 954 Bundle Processing Control Flags: The Bundle Processing Control Flags 955 are discussed in Section 4.1.3. above. 957 CRC Type: CRC Type codes are discussed in Section 4.1.1. above. The 958 CRC Type code for the primary block MAY be zero if the bundle 959 contains a BPsec [BPSEC] Block Integrity Block whose target is the 960 primary block; otherwise the CRC Type code for the primary block 961 MUST be non-zero. 963 Destination EID: The Destination EID field identifies the bundle 964 endpoint that is the bundle's destination, i.e., the endpoint that 965 contains the node(s) at which the bundle is to be delivered. 967 Source node ID: The Source node ID field identifies the bundle node 968 at which the bundle was initially transmitted, except that Source 969 node ID may be the null endpoint ID in the event that the bundle's 970 source chooses to remain anonymous. 972 Report-to EID: The Report-to EID field identifies the bundle 973 endpoint to which status reports pertaining to the forwarding and 974 delivery of this bundle are to be transmitted. 976 Creation Timestamp: The creation timestamp (discussed in 4.1.7 977 above) comprises two unsigned integers that, together with the 978 source node ID and (if the bundle is a fragment) the fragment offset 979 and payload length, serve to identify the bundle. The first of these 980 integers is the bundle's creation time, while the second is the 981 bundle's creation timestamp sequence number. Bundle creation time 982 SHALL be the DTN time at which the transmission request was received 983 that resulted in the creation of the bundle. Sequence count SHALL be 984 the latest value (as of the time at which that transmission request 985 was received) of a monotonically increasing positive integer counter 986 managed by the source node's bundle protocol agent that MAY be reset 987 to zero whenever the current time advances by one second. For nodes 988 that lack accurate clocks, it is recommended that bundle creation 989 time be set to zero and that the counter used as the source of the 990 bundle sequence count never be reset to zero. Note that, in general, 991 the creation of two distinct bundles with the same source node ID 992 and bundle creation timestamp may result in unexpected network 993 behavior and/or suboptimal performance. The combination of source 994 node ID and bundle creation timestamp serves to identify a single 995 transmission request, enabling it to be acknowledged by the 996 receiving application (provided the source node ID is not the null 997 endpoint ID). 999 Lifetime: The lifetime field is an unsigned integer that indicates 1000 the time at which the bundle's payload will no longer be useful, 1001 encoded as a number of microseconds past the creation time. (For 1002 high-rate deployments with very brief disruptions, fine-grained 1003 expression of bundle lifetime may be useful.) When a bundle's age 1004 exceeds its lifetime, bundle nodes need no longer retain or forward 1005 the bundle; the bundle SHOULD be deleted from the network. For 1006 bundles originating at nodes that lack accurate clocks, it is 1007 recommended that bundle age be obtained from the Bundle Age 1008 extension block (see 4.3.2 below) rather than from the difference 1009 between current time and bundle creation time. Bundle lifetime 1010 SHALL be represented as a CBOR unsigned integer item. 1012 Fragment offset: If and only if the Bundle Processing Control Flags 1013 of this Primary block indicate that the bundle is a fragment, 1014 fragment offset SHALL be present in the primary block. Fragment 1015 offset SHALL be represented as a CBOR unsigned integer indicating 1016 the offset from the start of the original application data unit at 1017 which the bytes comprising the payload of this bundle were located. 1019 Total Application Data Unit Length: If and only if the Bundle 1020 Processing Control Flags of this Primary block indicate that the 1021 bundle is a fragment, total application data unit length SHALL be 1022 present in the primary block. Total application data unit length 1023 SHALL be represented as a CBOR unsigned integer indicating the total 1024 length of the original application data unit of which this bundle's 1025 payload is a part. 1027 CRC: A CRC SHALL be present in the primary block unless the bundle 1028 includes a BPsec [BPSEC] Block Integrity Block whose target is the 1029 primary block, in which case a CRC MAY be present in the primary 1030 block. The length and nature of the CRC SHALL be as indicated by 1031 the CRC type. The CRC SHALL be computed over the concatenation of 1032 all bytes (including CBOR "break" characters) of the primary block 1033 including the CRC field itself, which for this purpose SHALL be 1034 temporarily populated with the value zero. 1036 4.2.3. Canonical Bundle Block Format 1038 Every block other than the primary block (all such blocks are termed 1039 "canonical" blocks) SHALL be represented as a CBOR array; the number 1040 of elements in the array SHALL be 5 (if CRC type is zero) or 6 1041 (otherwise). 1043 The fields of every canonical block SHALL be as follows, listed in 1044 the order in which they MUST appear: 1046 . Block type code, an unsigned integer. Bundle block type code 1 1047 indicates that the block is a bundle payload block. Block type 1048 codes 2 through 9 are explicitly reserved as noted later in 1049 this specification. Block type codes 192 through 255 are not 1050 reserved and are available for private and/or experimental use. 1051 All other block type code values are reserved for future use. 1052 . Block number, an unsigned integer as discussed in 4.2.1 above. 1053 Block number SHALL be represented as a CBOR unsigned integer. 1055 . Block processing control flags as discussed in Section 4.1.4 1056 above. 1057 . CRC type as discussed in Section 4.1.1 above. 1058 . Block-type-specific data represented as a single definite- 1059 length CBOR byte string, i.e., a CBOR byte string that is not 1060 of indefinite length. For each type of block, the block-type- 1061 specific data byte string is the serialization, in a block- 1062 type-specific manner, of the data conveyed by that type of 1063 block; definitions of blocks are required to define the manner 1064 in which block-type-specific data are serialized within the 1065 block-type-specific data field. For the Payload Block in 1066 particular (block type 1), the block-type-specific data field, 1067 termed the "payload", SHALL be an application data unit, or 1068 some contiguous extent thereof, represented as a definite- 1069 length CBOR byte string. 1070 . If and only if the value of the CRC type field of this block is 1071 non-zero, a CRC. If present, the length and nature of the CRC 1072 SHALL be as indicated by the CRC type and the CRC SHALL be 1073 computed over the concatenation of all bytes of the block 1074 (including CBOR "break" characters) including the CRC field 1075 itself, which for this purpose SHALL be temporarily populated 1076 with the value zero. 1078 4.3. Extension Blocks 1080 "Extension blocks" are all blocks other than the primary and payload 1081 blocks. Because not all extension blocks are defined in the Bundle 1082 Protocol specification (the present document), not all nodes 1083 conforming to this specification will necessarily instantiate Bundle 1084 Protocol implementations that include procedures for processing 1085 (that is, recognizing, parsing, acting on, and/or producing) all 1086 extension blocks. It is therefore possible for a node to receive a 1087 bundle that includes extension blocks that the node cannot process. 1088 The values of the block processing control flags indicate the action 1089 to be taken by the bundle protocol agent when this is the case. 1091 Extension block types 11 and 12 are reserved for the Block Integrity 1092 Block and Block Confidentiality Block as defined in the Bundle 1093 Security Protocol specification [BPSEC]. 1095 The following extension block types are reserved for extension 1096 blocks for which a need is anticipated but for which no definitions 1097 yet exist: 1099 . Block type 13 is reserved for the anticipated Manifest Block. 1100 Note: it is anticipated that the manifest block will identify 1101 the blocks that were present in the bundle at the time it was 1102 created, implying that the bundle MUST contain one (1) 1103 occurrence of this type of block if the value of the "manifest" 1104 flag in the bundle processing control flags (anticipated but 1105 not yet defined) is 1, but otherwise the bundle MUST NOT 1106 contain any Manifest block. 1107 . Block type 14 is reserved for the anticipated Metadata Block. 1108 Note: the structure and function of the anticipated Metadata 1109 Block are currently undefined. 1110 . Block type 15 is reserved for the anticipated Data Label Block. 1111 Note: it is anticipated that the data label block will provide 1112 additional information that can assist nodes in making 1113 forwarding decisions. 1115 The following extension blocks are defined in the current document. 1117 4.3.1. Previous Node 1119 The Previous Node block, block type 6, identifies the node that 1120 forwarded this bundle to the local node (i.e., to the node at which 1121 the bundle currently resides); its block-type-specific data is the 1122 node ID of that forwarder node which SHALL take the form of a node 1123 ID represented as described in Section 4.1.5.2. above. If the local 1124 node is the source of the bundle, then the bundle MUST NOT contain 1125 any previous node block. Otherwise the bundle SHOULD contain one 1126 (1) occurrence of this type of block. 1128 4.3.2. Bundle Age 1130 The Bundle Age block, block type 7, contains the number of 1131 microseconds that have elapsed between the time the bundle was 1132 created and time at which it was most recently forwarded. It is 1133 intended for use by nodes lacking access to an accurate clock, to 1134 aid in determining the time at which a bundle's lifetime expires. 1135 The block-type-specific data of this block is an unsigned integer 1136 containing the age of the bundle in microseconds, which SHALL be 1137 represented as a CBOR unsigned integer item. (The age of the bundle 1138 is the sum of all known intervals of the bundle's residence at 1139 forwarding nodes, up to the time at which the bundle was most 1140 recently forwarded, plus the summation of signal propagation time 1141 over all episodes of transmission between forwarding nodes. 1142 Determination of these values is an implementation matter.) If the 1143 bundle's creation time is zero, then the bundle MUST contain exactly 1144 one (1) occurrence of this type of block; otherwise, the bundle MAY 1145 contain at most one (1) occurrence of this type of block. A bundle 1146 MUST NOT contain multiple occurrences of the bundle age block, as 1147 this could result in processing anomalies. 1149 4.3.3. Hop Count 1151 The Hop Count block, block type 10, contains two unsigned integers, 1152 hop limit and hop count. A "hop" is here defined as an occasion on 1153 which a bundle was forwarded from one node to another node. Hop 1154 limit MUST be in the range 1 through 255. The hop limit value SHOULD 1155 NOT be changed at any time after creation of the Hop Count block; 1156 the hop count value SHOULD initially be zero and SHOULD be increased 1157 by 1 on each hop. 1159 The hop count block is mainly intended as a safety mechanism, a 1160 means of identifying bundles for removal from the network that can 1161 never be delivered due to a persistent forwarding error. When a 1162 bundle's hop count exceeds its hop limit, the bundle SHOULD be 1163 deleted for the reason "hop limit exceeded", following the bundle 1164 deletion procedure defined in Section 5.10. . Procedures for 1165 determining the appropriate hop limit for a block are beyond the 1166 scope of this specification. The block-type-specific data in a hop 1167 count block SHALL be represented as a CBOR array comprising a 2- 1168 tuple. The first item of this array SHALL be the bundle's hop 1169 limit, represented as a CBOR unsigned integer. The second item of 1170 this array SHALL be the bundle's hop count, represented as a CBOR 1171 unsigned integer. A bundle MAY contain at most one (1) occurrence of 1172 this type of block. 1174 5. Bundle Processing 1176 The bundle processing procedures mandated in this section and in 1177 Section 6 govern the operation of the Bundle Protocol Agent and the 1178 Application Agent administrative element of each bundle node. They 1179 are neither exhaustive nor exclusive. Supplementary DTN protocol 1180 specifications (including, but not restricted to, the Bundle 1181 Security Protocol [BPSEC]) may augment, override, or supersede the 1182 mandates of this document. 1184 5.1. Generation of Administrative Records 1186 All transmission of bundles is in response to bundle transmission 1187 requests presented by nodes' application agents. When required to 1188 "generate" an administrative record (such as a bundle status 1189 report), the bundle protocol agent itself is responsible for causing 1190 a new bundle to be transmitted, conveying that record. In concept, 1191 the bundle protocol agent discharges this responsibility by 1192 directing the administrative element of the node's application agent 1193 to construct the record and request its transmission as detailed in 1194 Section 6 below. In practice, the manner in which administrative 1195 record generation is accomplished is an implementation matter, 1196 provided the constraints noted in Section 6 are observed. 1198 Note that requesting status reports for any single bundle might 1199 easily result in the generation of (1 + (2 *(N-1))) status report 1200 bundles, where N is the number of nodes on the path from the 1201 bundle's source to its destination, inclusive. That is, the 1202 requesting of status reports for large numbers of bundles could 1203 result in an unacceptable increase in the bundle traffic in the 1204 network. For this reason, the generation of status reports MUST be 1205 disabled by default and enabled only when the risk of excessive 1206 network traffic is deemed acceptable. 1208 When the generation of status reports is enabled, the decision on 1209 whether or not to generate a requested status report is left to the 1210 discretion of the bundle protocol agent. Mechanisms that could 1211 assist in making such decisions, such as pre-placed agreements 1212 authorizing the generation of status reports under specified 1213 circumstances, are beyond the scope of this specification. 1215 Notes on administrative record terminology: 1217 . A "bundle reception status report" is a bundle status report 1218 with the "reporting node received bundle" flag set to 1. 1219 . A "bundle forwarding status report" is a bundle status report 1220 with the "reporting node forwarded the bundle" flag set to 1. 1221 . A "bundle delivery status report" is a bundle status report 1222 with the "reporting node delivered the bundle" flag set to 1. 1223 . A "bundle deletion status report" is a bundle status report 1224 with the "reporting node deleted the bundle" flag set to 1. 1226 5.2. Bundle Transmission 1228 The steps in processing a bundle transmission request are: 1230 Step 1: Transmission of the bundle is initiated. An outbound bundle 1231 MUST be created per the parameters of the bundle transmission 1232 request, with the retention constraint "Dispatch pending". The 1233 source node ID of the bundle MUST be either the null endpoint ID, 1234 indicating that the source of the bundle is anonymous, or else the 1235 EID of a singleton endpoint whose only member is the node of which 1236 the BPA is a component. 1238 Step 2: Processing proceeds from Step 1 of Section 5.4. 1240 5.3. Bundle Dispatching 1242 The steps in dispatching a bundle are: 1244 Step 1: If the bundle's destination endpoint is an endpoint of which 1245 the node is a member, the bundle delivery procedure defined in 1246 Section 5.7 MUST be followed and for the purposes of all subsequent 1247 processing of this bundle at this node the node's membership in the 1248 bundle's destination endpoint SHALL be disavowed; specifically, even 1249 though the node is a member of the bundle's destination endpoint, 1250 the node SHALL NOT undertake to forward the bundle to itself in the 1251 course of performing the procedure described in Section 5.4. 1253 Step 2: Processing proceeds from Step 1 of Section 5.4. 1255 5.4. Bundle Forwarding 1257 The steps in forwarding a bundle are: 1259 Step 1: The retention constraint "Forward pending" MUST be added to 1260 the bundle, and the bundle's "Dispatch pending" retention constraint 1261 MUST be removed. 1263 Step 2: The bundle protocol agent MUST determine whether or not 1264 forwarding is contraindicated for any of the reasons listed in 1265 Figure 4. In particular: 1267 . The bundle protocol agent MAY choose either to forward the 1268 bundle directly to its destination node(s) (if possible) or to 1269 forward the bundle to some other node(s) for further 1270 forwarding. The manner in which this decision is made may 1271 depend on the scheme name in the destination endpoint ID and/or 1272 on other state but in any case is beyond the scope of this 1273 document. If the BPA elects to forward the bundle to some other 1274 node(s) for further forwarding but finds it impossible to 1275 select any node(s) to forward the bundle to, then forwarding is 1276 contraindicated. 1277 . Provided the bundle protocol agent succeeded in selecting the 1278 node(s) to forward the bundle to, the bundle protocol agent 1279 MUST subsequently select the convergence layer adapter(s) whose 1280 services will enable the node to send the bundle to those 1281 nodes. The manner in which specific appropriate convergence 1282 layer adapters are selected is beyond the scope of this 1283 document. If the agent finds it impossible to select any 1284 appropriate convergence layer adapter(s) to use in forwarding 1285 this bundle, then forwarding is contraindicated. 1287 Step 3: If forwarding of the bundle is determined to be 1288 contraindicated for any of the reasons listed in Figure 4, then the 1289 Forwarding Contraindicated procedure defined in Section 5.4.1 MUST 1290 be followed; the remaining steps of Section 5.4 are skipped at this 1291 time. 1293 Step 4: For each node selected for forwarding, the bundle protocol 1294 agent MUST invoke the services of the selected convergence layer 1295 adapter(s) in order to effect the sending of the bundle to that 1296 node. Determining the time at which the bundle protocol agent 1297 invokes convergence layer adapter services is a BPA implementation 1298 matter. Determining the time at which each convergence layer 1299 adapter subsequently responds to this service invocation by sending 1300 the bundle is a convergence-layer adapter implementation matter. 1301 Note that: 1303 . If the bundle contains a data label extension block (to be 1304 defined in a future document) then that data label value MAY 1305 identify procedures for determining the order in which 1306 convergence layer adapters must send bundles, e.g., considering 1307 bundle source when determining the order in which bundles are 1308 sent. The definition of such procedures is beyond the scope of 1309 this specification. 1310 . If the bundle has a bundle age block, as defined in 4.3.2. 1311 above, then at the last possible moment before the CLA 1312 initiates conveyance of the bundle via the CL protocol the 1313 bundle age value MUST be increased by the difference between 1314 the current time and the time at which the bundle was received 1315 (or, if the local node is the source of the bundle, created). 1317 Step 5: When all selected convergence layer adapters have informed 1318 the bundle protocol agent that they have concluded their data 1319 sending procedures with regard to this bundle, processing may depend 1320 on the results of those procedures. If completion of the data 1321 sending procedures by all selected convergence layer adapters has 1322 not resulted in successful forwarding of the bundle (an 1323 implementation-specific determination that is beyond the scope of 1324 this specification), then the bundle protocol agent MAY choose (in 1325 an implementation-specific manner, again beyond the scope of this 1326 specification) to initiate another attempt to forward the bundle. 1327 In that event, processing proceeds from Step 4 of Section 5.4. 1329 If completion of the data sending procedures by all selected 1330 convergence layer adapters HAS resulted in successful forwarding of 1331 the bundle, or if it has not but the bundle protocol agent does not 1332 choose to initiate another attempt to forward the bundle, then: 1334 . If the "request reporting of bundle forwarding" flag in the 1335 bundle's status report request field is set to 1, and status 1336 reporting is enabled, then a bundle forwarding status report 1337 SHOULD be generated, destined for the bundle's report-to 1338 endpoint ID. The reason code on this bundle forwarding status 1339 report MUST be "no additional information". 1340 . If any applicable bundle protocol extensions mandate generation 1341 of status reports upon conclusion of convergence-layer data 1342 sending procedures, all such status reports SHOULD be generated 1343 with extension-mandated reason codes. 1344 . The bundle's "Forward pending" retention constraint MUST be 1345 removed. 1347 5.4.1. Forwarding Contraindicated 1349 The steps in responding to contraindication of forwarding are: 1351 Step 1: The bundle protocol agent MUST determine whether or not to 1352 declare failure in forwarding the bundle. Note: this decision is 1353 likely to be influenced by the reason for which forwarding is 1354 contraindicated. 1356 Step 2: If forwarding failure is declared, then the Forwarding 1357 Failed procedure defined in Section 5.4.2 MUST be followed. 1359 Otherwise, when -- at some future time - the forwarding of this 1360 bundle ceases to be contraindicated, processing proceeds from Step 4 1361 of Section 5.4. 1363 5.4.2. Forwarding Failed 1365 The steps in responding to a declaration of forwarding failure are: 1367 Step 1: The bundle protocol agent MAY forward the bundle back to the 1368 node that sent it, as identified by the Previous Node block, if 1369 present. This forwarding, if performed, SHALL be accomplished by 1370 performing Step 4 and Step 5 of section 5.4 where the sole node 1371 selected for forwarding SHALL be the node that sent the bundle. 1373 Step 2: If the bundle's destination endpoint is an endpoint of which 1374 the node is a member, then the bundle's "Forward pending" retention 1375 constraint MUST be removed. Otherwise, the bundle MUST be deleted: 1376 the bundle deletion procedure defined in Section 5.10 MUST be 1377 followed, citing the reason for which forwarding was determined to 1378 be contraindicated. 1380 5.5. Bundle Expiration 1382 A bundle expires when the bundle's age exceeds its lifetime as 1383 specified in the primary bundle block. Bundle age MAY be determined 1384 by subtracting the bundle's creation timestamp time from the current 1385 time if (a) that timestamp time is not zero and (b) the local node's 1386 clock is known to be accurate; otherwise bundle age MUST be obtained 1387 from the Bundle Age extension block. Bundle expiration MAY occur at 1388 any point in the processing of a bundle. When a bundle expires, the 1389 bundle protocol agent MUST delete the bundle for the reason 1390 "lifetime expired": the bundle deletion procedure defined in Section 1391 5.10 MUST be followed. 1393 5.6. Bundle Reception 1395 The steps in processing a bundle that has been received from another 1396 node are: 1398 Step 1: The retention constraint "Dispatch pending" MUST be added to 1399 the bundle. 1401 Step 2: If the "request reporting of bundle reception" flag in the 1402 bundle's status report request field is set to 1, and status 1403 reporting is enabled, then a bundle reception status report with 1404 reason code "No additional information" SHOULD be generated, 1405 destined for the bundle's report-to endpoint ID. 1407 Step 3: CRCs SHOULD be computed for every block of the bundle that 1408 has an attached CRC. If any block of the bundle is malformed 1409 according to this specification, or if any block has an attached CRC 1410 and the CRC computed for this block upon reception differs from that 1411 attached CRC, then the bundle protocol agent MUST delete the bundle 1412 for the reason "Block unintelligible". The bundle deletion 1413 procedure defined in Section 5.10 MUST be followed and all remaining 1414 steps of the bundle reception procedure MUST be skipped. 1416 Step 4: For each block in the bundle that is an extension block that 1417 the bundle protocol agent cannot process: 1419 . If the block processing flags in that block indicate that a 1420 status report is requested in this event, and status reporting 1421 is enabled, then a bundle reception status report with reason 1422 code "Block unintelligible" SHOULD be generated, destined for 1423 the bundle's report-to endpoint ID. 1424 . If the block processing flags in that block indicate that the 1425 bundle must be deleted in this event, then the bundle protocol 1426 agent MUST delete the bundle for the reason "Block 1427 unintelligible"; the bundle deletion procedure defined in 1428 Section 5.10 MUST be followed and all remaining steps of the 1429 bundle reception procedure MUST be skipped. 1430 . If the block processing flags in that block do NOT indicate 1431 that the bundle must be deleted in this event but do indicate 1432 that the block must be discarded, then the bundle protocol 1433 agent MUST remove this block from the bundle. 1434 . If the block processing flags in that block indicate neither 1435 that the bundle must be deleted nor that that the block must be 1436 discarded, then processing continues with the next extension 1437 block that the bundle protocol agent cannot process, if any; 1438 otherwise, processing proceeds from step 5. 1440 Step 5: Processing proceeds from Step 1 of Section 5.3. 1442 5.7. Local Bundle Delivery 1444 The steps in processing a bundle that is destined for an endpoint of 1445 which this node is a member are: 1447 Step 1: If the received bundle is a fragment, the application data 1448 unit reassembly procedure described in Section 5.9 MUST be followed. 1449 If this procedure results in reassembly of the entire original 1450 application data unit, processing of this bundle (whose fragmentary 1451 payload has been replaced by the reassembled application data unit) 1452 proceeds from Step 2; otherwise, the retention constraint 1453 "Reassembly pending" MUST be added to the bundle and all remaining 1454 steps of this procedure MUST be skipped. 1456 Step 2: Delivery depends on the state of the registration whose 1457 endpoint ID matches that of the destination of the bundle: 1459 . An additional implementation-specific delivery deferral 1460 procedure MAY optionally be associated with the registration. 1461 . If the registration is in the Active state, then the bundle 1462 MUST be delivered automatically as soon as it is the next 1463 bundle that is due for delivery according to the BPA's bundle 1464 delivery scheduling policy, an implementation matter. 1465 . If the registration is in the Passive state, or if delivery of 1466 the bundle fails for some implementation-specific reason, then 1467 the registration's delivery failure action MUST be taken. 1468 Delivery failure action MUST be one of the following: 1470 o defer delivery of the bundle subject to this registration 1471 until (a) this bundle is the least recently received of 1472 all bundles currently deliverable subject to this 1473 registration and (b) either the registration is polled or 1474 else the registration is in the Active state, and also 1475 perform any additional delivery deferral procedure 1476 associated with the registration; or 1478 o abandon delivery of the bundle subject to this registration 1479 (as defined in 3.1. ). 1481 Step 3: As soon as the bundle has been delivered, if the "request 1482 reporting of bundle delivery" flag in the bundle's status report 1483 request field is set to 1 and bundle status reporting is enabled, 1484 then a bundle delivery status report SHOULD be generated, destined 1485 for the bundle's report-to endpoint ID. Note that this status report 1486 only states that the payload has been delivered to the application 1487 agent, not that the application agent has processed that payload. 1489 5.8. Bundle Fragmentation 1491 It may at times be advantageous for bundle protocol agents to reduce 1492 the sizes of bundles in order to forward them. This might be the 1493 case, for example, if a node to which a bundle is to be forwarded is 1494 accessible only via intermittent contacts and no upcoming contact is 1495 long enough to enable the forwarding of the entire bundle. 1497 The size of a bundle can be reduced by "fragmenting" the bundle. To 1498 fragment a bundle whose payload is of size M is to replace it with 1499 two "fragments" -- new bundles with the same source node ID and 1500 creation timestamp as the original bundle -- whose payloads are the 1501 first N and the last (M - N) bytes of the original bundle's payload, 1502 where 0 < N < M. Note that fragments may themselves be fragmented, 1503 so fragmentation may in effect replace the original bundle with more 1504 than two fragments. (However, there is only one 'level' of 1505 fragmentation, as in IP fragmentation.) 1507 Any bundle whose primary block's bundle processing flags do NOT 1508 indicate that it must not be fragmented MAY be fragmented at any 1509 time, for any purpose, at the discretion of the bundle protocol 1510 agent. NOTE, however, that some combinations of bundle 1511 fragmentation, replication, and routing might result in unexpected 1512 traffic patterns. 1514 Fragmentation SHALL be constrained as follows: 1516 . The concatenation of the payloads of all fragments produced by 1517 fragmentation MUST always be identical to the payload of the 1518 fragmented bundle (that is, the bundle that is being 1519 fragmented). Note that the payloads of fragments resulting from 1520 different fragmentation episodes, in different parts of the 1521 network, may be overlapping subsets of the fragmented bundle's 1522 payload. 1523 . The primary block of each fragment MUST differ from that of the 1524 fragmented bundle, in that the bundle processing flags of the 1525 fragment MUST indicate that the bundle is a fragment and both 1526 fragment offset and total application data unit length must be 1527 provided. Additionally, the CRC of the primary block of the 1528 fragmented bundle, if any, MUST be replaced in each fragment by 1529 a new CRC computed for the primary block of that fragment. 1530 . The payload blocks of fragments will differ from that of the 1531 fragmented bundle as noted above. 1532 . If the fragmented bundle is not a fragment or is the fragment 1533 with offset zero, then all extension blocks of the fragmented 1534 bundle MUST be replicated in the fragment whose offset is zero. 1535 . Each of the fragmented bundle's extension blocks whose "Block 1536 must be replicated in every fragment" flag is set to 1 MUST be 1537 replicated in every fragment. 1538 . Beyond these rules, replication of extension blocks in the 1539 fragments is an implementation matter. 1541 5.9. Application Data Unit Reassembly 1543 If the concatenation -- as informed by fragment offsets and payload 1544 lengths -- of the payloads of all previously received fragments with 1545 the same source node ID and creation timestamp as this fragment, 1546 together with the payload of this fragment, forms a byte array whose 1547 length is equal to the total application data unit length in the 1548 fragment's primary block, then: 1550 . This byte array -- the reassembled application data unit -- 1551 MUST replace the payload of this fragment. 1552 . The "Reassembly pending" retention constraint MUST be removed 1553 from every other fragment whose payload is a subset of the 1554 reassembled application data unit. 1556 Note: reassembly of application data units from fragments occurs at 1557 the nodes that are members of destination endpoints as necessary; an 1558 application data unit MAY also be reassembled at some other node on 1559 the path to the destination. 1561 5.10. Bundle Deletion 1563 The steps in deleting a bundle are: 1565 Step 1: If the "request reporting of bundle deletion" flag in the 1566 bundle's status report request field is set to 1, and if status 1567 reporting is enabled, then a bundle deletion status report citing 1568 the reason for deletion SHOULD be generated, destined for the 1569 bundle's report-to endpoint ID. 1571 Step 2: All of the bundle's retention constraints MUST be removed. 1573 5.11. Discarding a Bundle 1575 As soon as a bundle has no remaining retention constraints it MAY be 1576 discarded, thereby releasing any persistent storage that may have 1577 been allocated to it. 1579 5.12. Canceling a Transmission 1581 When requested to cancel a specified transmission, where the bundle 1582 created upon initiation of the indicated transmission has not yet 1583 been discarded, the bundle protocol agent MUST delete that bundle 1584 for the reason "transmission cancelled". For this purpose, the 1585 procedure defined in Section 5.10 MUST be followed. 1587 6. Administrative Record Processing 1589 6.1. Administrative Records 1591 Administrative records are standard application data units that are 1592 used in providing some of the features of the Bundle Protocol. One 1593 type of administrative record has been defined to date: bundle 1594 status reports. Note that additional types of administrative 1595 records may be defined by supplementary DTN protocol specification 1596 documents. 1598 Every administrative record consists of: 1600 . Record type code (an unsigned integer for which valid values 1601 are as defined below). 1602 . Record content in type-specific format. 1604 Valid administrative record type codes are defined as follows: 1606 +---------+--------------------------------------------+ 1608 | Value | Meaning | 1610 +=========+============================================+ 1612 | 1 | Bundle status report. | 1614 +---------+--------------------------------------------+ 1615 | (other) | Reserved for future use. | 1617 +---------+--------------------------------------------+ 1619 Figure 3: Administrative Record Type Codes 1621 Each BP administrative record SHALL be represented as a CBOR array 1622 comprising a 2-tuple. 1624 The first item of the array SHALL be a record type code, which SHALL 1625 be represented as a CBOR unsigned integer. 1627 The second element of this array SHALL be the applicable CBOR 1628 representation of the content of the record. Details of the CBOR 1629 representation of administrative record type 1 are provided below. 1630 Details of the CBOR representation of other types of administrative 1631 record type are included in the specifications defining those 1632 records. 1634 6.1.1. Bundle Status Reports 1636 The transmission of "bundle status reports" under specified 1637 conditions is an option that can be invoked when transmission of a 1638 bundle is requested. These reports are intended to provide 1639 information about how bundles are progressing through the system, 1640 including notices of receipt, forwarding, final delivery, and 1641 deletion. They are transmitted to the Report-to endpoints of 1642 bundles. 1644 Each bundle status report SHALL be represented as a CBOR array. The 1645 number of elements in the array SHALL be either 6 (if the subject 1646 bundle is a fragment) or 4 (otherwise). 1648 The first item of the bundle status report array SHALL be bundle 1649 status information represented as a CBOR array of at least 4 1650 elements. The first four items of the bundle status information 1651 array shall provide information on the following four status 1652 assertions, in this order: 1654 . Reporting node received bundle. 1655 . Reporting node forwarded the bundle. 1656 . Reporting node delivered the bundle. 1657 . Reporting node deleted the bundle. 1659 Each item of the bundle status information array SHALL be a bundle 1660 status item represented as a CBOR array; the number of elements in 1661 each such array SHALL be either 2 (if the value of the first item of 1662 this bundle status item is 1 AND the "Report status time" flag was 1663 set to 1 in the bundle processing flags of the bundle whose status 1664 is being reported) or 1 (otherwise). The first item of the bundle 1665 status item array SHALL be a status indicator, a Boolean value 1666 indicating whether or not the corresponding bundle status is 1667 asserted, represented as a CBOR Boolean value. The second item of 1668 the bundle status item array, if present, SHALL indicate the time 1669 (as reported by the local system clock, an implementation matter) at 1670 which the indicated status was asserted for this bundle, represented 1671 as a DTN time as described in Section 4.1.6. above. 1673 The second item of the bundle status report array SHALL be the 1674 bundle status report reason code explaining the value of the status 1675 indicator, represented as a CBOR unsigned integer. Valid status 1676 report reason codes are defined in Figure 4 below but the list of 1677 status report reason codes provided here is neither exhaustive nor 1678 exclusive; supplementary DTN protocol specifications (including, but 1679 not restricted to, the Bundle Security Protocol [BPSEC]) may define 1680 additional reason codes. 1682 +---------+--------------------------------------------+ 1684 | Value | Meaning | 1686 +=========+============================================+ 1688 | 0 | No additional information. | 1690 +---------+--------------------------------------------+ 1692 | 1 | Lifetime expired. | 1694 +---------+--------------------------------------------+ 1696 | 2 | Forwarded over unidirectional link. | 1698 +---------+--------------------------------------------+ 1700 | 3 | Transmission canceled. | 1702 +---------+--------------------------------------------+ 1704 | 4 | Depleted storage. | 1706 +---------+--------------------------------------------+ 1708 | 5 | Destination endpoint ID unintelligible. | 1709 +---------+--------------------------------------------+ 1711 | 6 | No known route to destination from here. | 1713 +---------+--------------------------------------------+ 1715 | 7 | No timely contact with next node on route. | 1717 +---------+--------------------------------------------+ 1719 | 8 | Block unintelligible. | 1721 +---------+--------------------------------------------+ 1723 | 9 | Hop limit exceeded. | 1725 +---------+--------------------------------------------+ 1727 | 10 | Traffic pared (e.g., status reports). | 1729 +---------+--------------------------------------------+ 1731 | (other) | Reserved for future use. | 1733 +---------+--------------------------------------------+ 1735 Figure 4: Status Report Reason Codes 1737 The third item of the bundle status report array SHALL be the source 1738 node ID identifying the source of the bundle whose status is being 1739 reported, represented as described in Section 4.1.5.2. above. 1741 The fourth item of the bundle status report array SHALL be the 1742 creation timestamp of the bundle whose status is being reported, 1743 represented as described in Section 4.1.7. above. 1745 The fifth item of the bundle status report array SHALL be present if 1746 and only if the bundle whose status is being reported contained a 1747 fragment offset. If present, it SHALL be the subject bundle's 1748 fragment offset represented as a CBOR unsigned integer item. 1750 The sixth item of the bundle status report array SHALL be present if 1751 and only if the bundle whose status is being reported contained a 1752 fragment offset. If present, it SHALL be the length of the subject 1753 bundle's payload represented as a CBOR unsigned integer item. 1755 Note that the forwarding parameters (such as lifetime, applicable 1756 security measures, etc.) of the bundle whose status is being 1757 reported MAY be reflected in the parameters governing the forwarding 1758 of the bundle that conveys a status report, but this is an 1759 implementation matter. Bundle protocol deployment experience to 1760 date has not been sufficient to suggest any clear guidance on this 1761 topic. 1763 6.2. Generation of Administrative Records 1765 Whenever the application agent's administrative element is directed 1766 by the bundle protocol agent to generate an administrative record 1767 with reference to some bundle, the following procedure must be 1768 followed: 1770 Step 1: The administrative record must be constructed. If the 1771 administrative record references a bundle and the referenced bundle 1772 is a fragment, the administrative record MUST contain the fragment 1773 offset and fragment length. 1775 Step 2: A request for transmission of a bundle whose payload is this 1776 administrative record MUST be presented to the bundle protocol 1777 agent. 1779 7. Services Required of the Convergence Layer 1781 7.1. The Convergence Layer 1783 The successful operation of the end-to-end bundle protocol depends 1784 on the operation of underlying protocols at what is termed the 1785 "convergence layer"; these protocols accomplish communication 1786 between nodes. A wide variety of protocols may serve this purpose, 1787 so long as each convergence layer protocol adapter provides a 1788 defined minimal set of services to the bundle protocol agent. This 1789 convergence layer service specification enumerates those services. 1791 7.2. Summary of Convergence Layer Services 1793 Each convergence layer protocol adapter is expected to provide the 1794 following services to the bundle protocol agent: 1796 . sending a bundle to a bundle node that is reachable via the 1797 convergence layer protocol; 1798 . notifying the bundle protocol agent when it has concluded its 1799 data sending procedures with regard to a bundle; 1800 . delivering to the bundle protocol agent a bundle that was sent 1801 by a bundle node via the convergence layer protocol. 1803 The convergence layer service interface specified here is neither 1804 exhaustive nor exclusive. That is, supplementary DTN protocol 1805 specifications (including, but not restricted to, the Bundle 1806 Security Protocol [BPSEC]) may expect convergence layer adapters 1807 that serve BP implementations conforming to those protocols to 1808 provide additional services such as reporting on the transmission 1809 and/or reception progress of individual bundles (at completion 1810 and/or incrementally), retransmitting data that were lost in 1811 transit, discarding bundle-conveying data units that the convergence 1812 layer protocol determines are corrupt or inauthentic, or reporting 1813 on the integrity and/or authenticity of delivered bundles. 1815 8. Implementation Status 1817 [NOTE to the RFC Editor: please remove this section before 1818 publication, as well as the reference to RFC 7942.] 1820 This section records the status of known implementations of the 1821 protocol defined by this specification at the time of posting of 1822 this Internet-Draft, and is based on a proposal described in RFC 1823 7942. The description of implementations in this section is 1824 intended to assist the IETF in its decision processes in progressing 1825 drafts to RFCs. Please note that the listing of any individual 1826 implementation here does not imply endorsement by the IETF. 1827 Furthermore, no effort has been spent to verify the information 1828 presented here that was supplied by IETF contributors. This is not 1829 intended as, and must not be construed to be, a catalog of available 1830 implementations or their features. Readers are advised to note that 1831 other implementations may exist. 1833 According to RFC 7942, "this will allow reviewers and working groups 1834 to assign due consideration to documents that have the benefit of 1835 running code, which may serve as evidence of valuable 1836 experimentation and feedback that have made the implemented 1837 protocols more mature. It is up to the individual working groups to 1838 use this information as they see fit". 1840 At the time of this writing, there are three known implementations 1841 of the current document. 1843 The first known implementation is microPCN (https://upcn.eu/). 1844 According to the developers: 1846 The Micro Planetary Communication Network (uPCN) is a free 1847 software project intended to offer an implementation of Delay- 1848 tolerant Networking protocols for POSIX operating systems (well, 1849 and for Linux) plus for the ARM Cortex STM32F4 microcontroller 1850 series. More precisely it currently provides an implementation of 1852 . the Bundle Protocol (BP, RFC 5050), 1853 . the Bundle Protocol version 7 specification draft (version 6), 1854 . the DTN IP Neighbor Discovery (IPND) protocol, and 1855 . a routing approach optimized for message-ferry micro LEO 1856 satellites. 1858 uPCN is written in C and is built upon the real-time operating 1859 system FreeRTOS. The source code of uPCN is released under the 1860 "BSD 3-Clause License". 1862 The project depends on an execution environment offering link 1863 layer protocols such as AX.25. The source code uses the USB 1864 subsystem to interact with the environment. 1866 The second known implementation is PyDTN, developed by X-works, 1867 s.r.o (https://x-works.sk/). The final third of the implementation 1868 was developed during the IETF 101 Hackathon. According to the 1869 developers, PyDTN implements bundle coding/decoding and neighbor 1870 discovery. PyDTN is written in Python and has been shown to be 1871 interoperable with uPCN. 1873 The third known implementation is "Terra" 1874 (https://github.com/RightMesh/Terra/), a Java implementation 1875 developed in the context of terrestrial DTN. It includes an 1876 implementation of a "minimal TCP" convergence layer adapter. 1878 9. Security Considerations 1880 The bundle protocol security architecture and the available security 1881 services are specified in an accompanying document, the Bundle 1882 Security Protocol specification [BPSEC]. 1884 The bpsec extensions to Bundle Protocol enable each block of a 1885 bundle (other than a bpsec extension block) to be individually 1886 authenticated by a signature block (Block Integrity Block, or BIB) 1887 and also enable each block of a bundle other than the primary block 1888 (and the bpsec extension blocks themselves) to be individually 1889 encrypted by a BCB. 1891 Because the security mechanisms are extension blocks that are 1892 themselves inserted into the bundle, the integrity and 1893 confidentiality of bundle blocks are protected while the bundle is 1894 at rest, awaiting transmission at the next forwarding opportunity, 1895 as well as in transit. 1897 Additionally, convergence-layer protocols that ensure authenticity 1898 of communication between adjacent nodes in BP network topology 1899 SHOULD be used where available, to minimize the ability of 1900 unauthenticated nodes to introduce inauthentic traffic into the 1901 network. Convergence-layer protocols that ensure confidentiality of 1902 communication between adjacent nodes in BP network topology SHOULD 1903 also be used where available, to minimize exposure of the bundle's 1904 primary block and other clear-text blocks, thereby offering some 1905 defense against traffic analysis. 1907 Note that, while the primary block must remain in the clear for 1908 routing purposes, the Bundle Protocol can be protected against 1909 traffic analysis to some extent by using bundle-in-bundle 1910 encapsulation to tunnel bundles to a safe forward distribution 1911 point: the encapsulated bundle forms the payload of an encapsulating 1912 bundle, and that payload block may be encrypted by a BCB. 1914 Note that the generation of bundle status reports is disabled by 1915 default because malicious initiation of bundle status reporting 1916 could result in the transmission of extremely large numbers of 1917 bundles, effecting a denial of service attack. 1919 The bpsec extensions accommodate an open-ended range of 1920 ciphersuites; different ciphersuites may be utilized to protect 1921 different blocks. One possible variation is to sign and/or encrypt 1922 blocks using symmetric keys securely formed by Diffie-Hellman 1923 procedures (such as EKDH) using the public and private keys of the 1924 sending and receiving nodes. For this purpose, the key distribution 1925 problem reduces to the problem of trustworthy delay-tolerant 1926 distribution of public keys, a current research topic. 1928 Bundle security MUST NOT be invalidated by forwarding nodes even 1929 though they themselves might not use the Bundle Security Protocol. 1931 In particular, while blocks MAY be added to bundles transiting 1932 intermediate nodes, removal of blocks with the "Discard block if it 1933 can't be processed" flag set in the block processing control flags 1934 may cause security to fail. 1936 Inclusion of the Bundle Security Protocol in any Bundle Protocol 1937 implementation is RECOMMENDED. Use of the Bundle Security Protocol 1938 in Bundle Protocol operations is OPTIONAL, subject to the following 1939 guidelines: 1941 . Every block (that is not a bpsec extension block) of every 1942 bundle SHOULD be authenticated by a BIB citing the ID of the 1943 node that inserted that block. (Note that a single BIB may 1944 authenticate multiple "target" blocks.) BIB authentication MAY 1945 be omitted on (and only on) any initial end-to-end path 1946 segments on which it would impose unacceptable overhead, 1947 provided that satisfactory authentication is ensured at the 1948 convergence layer and that BIB authentication is asserted on 1949 the first path segment on which the resulting overhead is 1950 acceptable and on all subsequent path segments. 1951 . If any segment of the end-to-end path of a bundle will traverse 1952 the Internet or any other potentially insecure communication 1953 environment, then the payload block SHOULD be encrypted by a 1954 BCB on this path segment and all subsequent segments of the 1955 end-to-end path. 1957 10. IANA Considerations 1959 The Bundle Protocol includes fields requiring registries managed by 1960 IANA. 1962 10.1. Bundle Block Types 1964 The current Bundle Block Types Registry is augmented by adding a 1965 column identifying the version of the Bundle protocol (Bundle 1966 Protocol Version) that applies to the new values, and by adding the 1967 following values, as described in section 4.3.1. The current values 1968 in the registry should have the Bundle Protocol Version set to the 1969 value "6", as shown below.. 1971 +----------+-------+-----------------------------+---------------+ 1973 | Bundle | Value | Description | Reference | 1975 | Protocol | | | | 1977 | Version | | | | 1979 +----------+-------+-----------------------------+---------------+ 1981 | none | 0 | Reserved | [RFC6255] | 1983 | 6,7 | 1 | Bundle Payload Block | [RFC5050] | 1985 | 6 | 2 | Bundle Authentication Block | [RFC6257] | 1987 | 6 | 3 | Payload Integrity Block | [RFC6257] | 1989 | 6 | 4 | Payload Confidentiality Blk | [RFC6257] | 1990 | 6 | 5 | Previous-Hop Insertion Block| [RFC6259] | 1992 | 7 | 6 | Previous node (proximate | 4.3.1 | 1994 | | | sender) | | 1996 | 7 | 7 | Bundle age (in seconds) | 4.3.2 | 1998 | 6 | 8 | Metadata Extension Block | [RFC6258] | 2000 | 6 | 9 | Extension Security Block | [RFC6257] | 2002 | 7 | 10 | Hop count (#prior xmit | 4.3.3 | 2004 | | | attempts) | | 2006 | 7 | 11-15 | Reserved as noted earlier | 4.3 | 2008 | | 16-191| Unassigned | | 2010 | 6 |192-255| Reserved for Private and/or | [RFC5050] | 2012 | | | Experimental Use | | 2014 +----------+-------+-----------------------------+---------------+ 2016 10.2. Primary Bundle Protocol Version 2018 The current Primary Bundle Protocol Version Registry is augmented by 2019 adding the following value. 2021 the following values:. 2023 +-------+-------------+---------------+ 2025 | Value | Description | Reference | 2027 +-------+-------------+---------------+ 2029 | 7 | Assigned | 4.2.2 | 2031 +-------+-------------+---------------+ 2033 10.3. Bundle Processing Control Flags 2035 The current Bundle Processing Control Flags Registry is augmented by 2036 adding a column identifying the version of the Bundle protocol 2037 (Bundle Protocol Version) that applies to the new values, and by 2038 adding the following values, as described in section 4.1.3. The 2039 current values in the registry should have the Bundle Protocol 2040 Version set to the value 6 or "6, 7", as shown below. 2041 Bundle Processing Control Flags Registry 2043 +--------------------+----------------------------------+----------+ 2045 | Bundle | Bit | Description | Reference| 2047 | Protocol| Position | | | 2049 | Version | (right | | | 2051 | | to left) | | | 2053 +--------------------+----------------------------------+----------+ 2055 | 6,7 | 0 | Bundle is a fragment | [RFC5050]| 2057 | 6,7 | 1 | Application data unit is an | [RFC5050]| 2059 | | | administrative record | | 2061 | 6,7 | 2 | Bundle must not be fragmented | [RFC5050]| 2063 | 6 | 3 | Custody transfer is requested | [RFC5050]| 2065 | 6 | 4 | Destination endpoint is singleton| [RFC5050]| 2067 | 6,7 | 5 | Acknowledgement by application | [RFC5050]| 2069 | | | is requested | | 2071 | 7 | 6 | Status time requested in reports | 4.1.3 | 2073 | 6 | 7 | Class of service, priority | [RFC5050]| 2075 | 6 | 8 | Class of service, priority | [RFC5050]| 2077 | 6 | 9 | Class of service, reserved | [RFC5050]| 2079 | 6 | 10 | Class of service, reserved | [RFC5050]| 2081 | 6 | 11 | Class of service, reserved | [RFC5050]| 2083 | 6 | 12 | Class of service, reserved | [RFC5050]| 2084 | 6 | 13 | Class of service, reserved | [RFC5050]| 2086 | 6,7 | 14 | Request reporting of bundle | [RFC5050]| 2088 | | | reception | | 2090 | 6 | 15 | Request reporting of custody | [RFC5050]| 2092 | | | acceptance | | 2094 | 6,7 | 16 | Request reporting of bundle | [RFC5050]| 2096 | | | forwarding | | 2098 | 6,7 | 17 | Request reporting of bundle | [RFC5050]| 2100 | | | delivery | | 2102 | 6,7 | 18 | Request reporting of bundle | [RFC5050]| 2104 | | | deletion | | 2106 | 6 | 19 | Reserved | [RFC5050]| 2108 | 6 | 20 | Reserved | [RFC5050]| 2110 | | 21-63 | Unassigned | | 2112 +--------------------+----------------------------------+----------+ 2114 The registration policy is changed to "Expert Review". Given the 2115 maximum number of bits available, the allocation should only be 2116 approved with a well-defined specification and proof of real usage. 2118 10.4. Block Processing Control Flags 2120 The current Block Processing Control Flags Registry is augmented by 2121 adding a column identifying the version of the Bundle protocol 2122 (Bundle Protocol Version) that applies to the related BP version. 2123 The current values in the registry should have the Bundle Protocol 2124 Version set to the value 6 or "6, 7", as shown below. 2126 Block Processing Control Flags Registry 2128 +--------------------+----------------------------------+----------+ 2130 | Bundle | Bit | Description | Reference| 2131 | Protocol| Position | | | 2133 | Version | (right | | | 2135 | | to left) | | | 2137 +--------------------+----------------------------------+----------+ 2139 | 6,7 | 0 | Block must be replicated in | [RFC5050]| 2141 | | | every fragment | | 2143 | 6,7 | 1 | Transmit status report if block | [RFC5050]| 2145 | | | can't be processed | | 2147 | 6,7 | 2 | Delete bundle if block can't be | [RFC5050]| 2149 | | | processed | | 2151 | 6 | 3 | Last block | [RFC5050]| 2153 | 6,7 | 4 | Discard block if it can't be | [RFC5050]| 2155 | | | processed | | 2157 | 6 | 5 | Block was forwarded without | [RFC5050]| 2159 | | | being processed | | 2161 | 6 | 6 | Block contains an EID reference | [RFC5050]| 2163 | | | field | | 2165 | | 7-63 | Unassigned | | 2167 +--------------------+----------------------------------+----------+ 2169 10.5. Bundle Status Report Reason Codes 2171 The current Bundle Status Report Reason Codes Registry is augmented 2172 by adding a column identifying the version of the Bundle protocol 2173 (Bundle Protocol Version) that applies to the new values, and by 2174 adding the following values, as described in section 6.1.1. The 2175 current values in the registry should have the Bundle Protocol 2176 Version set to the value 6 or 7 or "6, 7", as shown below. 2178 Bundle Status Report Reason Codes Registry 2180 +--------------------+----------------------------------+----------+ 2182 | Bundle | Value | Description | Reference| 2184 | Protocol| | | | 2186 | Version | | | | 2188 | | | | | 2190 +--------------------+----------------------------------+----------+ 2192 | 6,7 | 0 | No additional information | [RFC5050]| 2194 | 6,7 | 1 | Lifetime expired | [RFC5050]| 2196 | 6,7 | 2 | Forwarded over unidirectional | [RFC5050]| 2198 | | | link | | 2200 | 6,7 | 3 | Transmission canceled | [RFC5050]| 2202 | 6,7 | 4 | Depleted storage | [RFC5050]| 2204 | 6,7 | 5 | Destination endpoint ID | [RFC5050]| 2206 | | | unintelligible | | 2208 | 6,7 | 6 | No known route to destination | [RFC5050]| 2210 | | | from here | | 2212 | 6,7 | 7 | No timely contact with next node | [RFC5050]| 2214 | | | on route | | 2216 | 6,7 | 8 | Block unintelligible | [RFC6255]| 2218 | 7 | 9 | Hop limit exceeded | 6.1.1 | 2220 | 7 | 10 | Traffic pared | 6.1.1 | 2222 | | 11-254 | Unassigned | | 2224 | 6 | 255 | Reserved | [RFC6255]| 2225 +-------+-----------------------------------------------+----------+ 2227 10.6. Bundle Protocol URI scheme types 2229 The Bundle Protocol has a URI scheme type field - an unsigned 2230 integer of undefined length - for which IANA is requested to create 2231 and maintain a new registry named "Bundle Protocol URI Scheme Type 2232 Registry". Initial values for the Bundle Protocol URI scheme type 2233 registry are given below. 2235 The registration policy for this registry is: Specification 2236 Required. The nominated expert(s) verify that a specification exists 2237 and is readily accessible. Specifications for new registrations need 2238 to reference the documents defining the URIs for which new scheme 2239 types are being registered. Expert(s) are encouraged to be biased 2240 towards approving registrations unless they are abusive, frivolous, 2241 or actively harmful (not merely aesthetically displeasing, or 2242 architecturally dubious). 2244 The value range is: unsigned 8-bit integer. 2246 Each assignment consists of a URI scheme type name and its 2247 associated description and reference. 2249 Bundle Protocol URI Scheme Type Registry 2251 +--------------+-----------------------------+-------------------+ 2253 | Value | Description | Reference | 2255 +--------------+-----------------------------+-------------------+ 2257 | 0 | Reserved | | 2259 | 1 | dtn | 10.7 | 2261 | 2 | ipn | RFC6260, Section 4| 2263 | 3-254 | Unassigned | | 2265 | 255 | reserved | | 2267 +--------------+-----------------------------+-------------------+ 2269 10.7. URI scheme "dtn" 2271 IANA is requested to update the registration of the URI scheme with 2272 the string "dtn" as the scheme name, as follows: 2274 URI scheme name: "dtn" 2276 Status: permanent 2278 URI scheme syntax: 2280 This specification uses the Augmented Backus-Naur Form (ABNF) 2281 notation of [RFC5234]. 2283 dtn-uri = "dtn:" dtn-hier-part 2285 dtn-hier-part = "//" node-name name-delim demux ; a path-rootless 2287 node-name = 1*VCHAR 2289 name-delim = "/" 2291 demux = *VCHAR 2293 None of the reserved characters defined in the generic URI syntax 2294 are used as delimiters within URIs of the DTN scheme. 2296 URI scheme semantics: URIs of the DTN scheme are used as endpoint 2297 identifiers in the Delay-Tolerant Networking (DTN) Bundle Protocol 2298 (BP) as described in Section 4.1.5.1. 2300 Encoding considerations: URIs of the DTN scheme are encoded 2301 exclusively in US-ASCII characters. 2303 Applications and/or protocols that use this URI scheme name: the 2304 Delay-Tolerant Networking (DTN) Bundle Protocol (BP). 2306 Interoperability considerations: as noted above, URIs of the DTN 2307 scheme are encoded exclusively in US-ASCII characters. 2309 Security considerations: 2311 . Reliability and consistency: none of the BP endpoints 2312 identified by the URIs of the DTN scheme are guaranteed to be 2313 reachable at any time, and the identity of the processing 2314 entities operating on those endpoints is never guaranteed by 2315 the Bundle Protocol itself. Bundle authentication as defined by 2316 the Bundle Security Protocol is required for this purpose. 2317 . Malicious construction: malicious construction of a conformant 2318 DTN-scheme URI is limited to the malicious selection of node 2319 names and the malicious selection of demux strings. That is, a 2320 maliciously constructed DTN-scheme URI could be used to direct 2321 a bundle to an endpoint that might be damaged by the arrival of 2322 that bundle or, alternatively, to declare a false source for a 2323 bundle and thereby cause incorrect processing at a node that 2324 receives the bundle. In both cases (and indeed in all bundle 2325 processing), the node that receives a bundle should verify its 2326 authenticity and validity before operating on it in any way. 2327 . Back-end transcoding: the limited expressiveness of URIs of the 2328 DTN scheme effectively eliminates the possibility of threat due 2329 to errors in back-end transcoding. 2330 . Rare IP address formats: not relevant, as IP addresses do not 2331 appear anywhere in conformant DTN-scheme URIs. 2332 . Sensitive information: because DTN-scheme URIs are used only to 2333 represent the identities of Bundle Protocol endpoints, the risk 2334 of disclosure of sensitive information due to interception of 2335 these URIs is minimal. Examination of DTN-scheme URIs could be 2336 used to support traffic analysis; where traffic analysis is a 2337 plausible danger, bundles should be conveyed by secure 2338 convergence-layer protocols that do not expose endpoint IDs. 2339 . Semantic attacks: the simplicity of DTN-scheme URI syntax 2340 minimizes the possibility of misinterpretation of a URI by a 2341 human user. 2343 Contact: 2345 Scott Burleigh 2347 Jet Propulsion Laboratory, 2349 California Institute of Technology 2351 scott.c.burleigh@jpl.nasa.gov 2353 +1 (800) 393-3353 2355 Author/Change controller: 2357 Scott Burleigh 2359 Jet Propulsion Laboratory, 2361 California Institute of Technology 2362 scott.c.burleigh@jpl.nasa.gov 2364 10.8. Change status of URI scheme "ipn" 2366 IANA is requested to change to "permanent" the status of the URI 2367 scheme named "ipn". 2369 11. References 2371 11.1. Normative References 2373 [BPSEC] Birrane, E., "Bundle Security Protocol Specification", Work 2374 In Progress, October 2015. 2376 [CRC16] ITU-T Recommendation X.25, p. 9, section 2.2.7.4, 2377 International Telecommunications Union, October 1996. 2379 [CRC32C] Castagnoli, G., Brauer, S., and M. Herrmann, "Optimization 2380 of Cyclic Redundancy-Check Codes with 24 and 32 Parity Bits", IEEE 2381 Transact. on Communications, Vol. 41, No. 6, June 1993. 2383 [EPOCH] Thompson, K. and D. M. Ritchie, "UNIX Programmer's Manual, 2384 Fifth Edition", Bell Telephone Laboratories Inc., June 1974. See 2385 https://www.tuhs.org/Archive/Distributions/Research/Dennis_v5/v5man. 2386 pdf. 2388 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2389 Requirement Levels", BCP 14, RFC 2119, March 1997. 2391 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 2392 Specifications: ABNF", STD 68, RFC 5234, January 2008. 2394 [RFC7049] Borman, C. and P. Hoffman, "Concise Binary Object 2395 Representation (CBOR)", RFC 7049, October 2013. 2397 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2398 2119 Key Words", BCP 14, RFC 8174, May 2017. 2400 [URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 2401 Resource Identifier (URI): Generic Syntax", RFC 3986, STD 66, 2402 January 2005. 2404 [URIREG] Thaler, D., Hansen, T., and T. Hardie, "Guidelines and 2405 Registration Procedures for URI Schemes", RFC 7595, BCP 35, June 2406 2015. 2408 11.2. Informative References 2410 [ARCH] V. Cerf et al., "Delay-Tolerant Network Architecture", RFC 2411 4838, April 2007. 2413 [BIBE] Burleigh, S., "Bundle-in-Bundle Encapsulation", Work In 2414 Progress, June 2017. 2416 [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource 2417 Identifiers (IRIs)", RFC 3987, January 2005. 2419 [RFC5050] Scott, K. and S. Burleigh, "Bundle Protocol 2420 Specification", RFC 5050, November 2007. 2422 [RFC6255] Blanchet, M., "Delay-Tolerant Networking Bundle Protocol 2423 IANA Registries", RFC 6255, May 2011. 2425 [RFC6257] Symington, S., Farrell, S., Weiss, H., and P. Lovell, 2426 "Bundle Security Protocol Specification", RFC 6257, May 2011. 2428 [RFC6258] Symington, S., " Delay-Tolerant Networking Metadata 2429 Extension Block", RFC 6258, May 2011. 2431 [RFC6259] Symington, S., " Delay-Tolerant Networking Previous-Hop 2432 Insertion Block", RFC 6259, May 2011. 2434 [RFC7143] Chadalapaka, M., Satran, J., Meth, K., and D. Black, 2435 "Internet Small Computer System Interface (iSCSI) Protocol 2436 (Consolidated)", RFC 7143, April 2014. 2438 [SIGC] Fall, K., "A Delay-Tolerant Network Architecture for 2439 Challenged Internets", SIGCOMM 2003. 2441 [UTC] Arias, E. and B. Guinot, "Coordinated universal time UTC: 2442 historical background and perspectives" in "Journees systemes de 2443 reference spatio-temporels", 2004. 2445 12. Acknowledgments 2447 This work is freely adapted from RFC 5050, which was an effort of 2448 the Delay Tolerant Networking Research Group. The following DTNRG 2449 participants contributed significant technical material and/or 2450 inputs to that document: Dr. Vinton Cerf of Google, Scott Burleigh, 2451 Adrian Hooke, and Leigh Torgerson of the Jet Propulsion Laboratory, 2452 Michael Demmer of the University of California at Berkeley, Robert 2453 Durst, Keith Scott, and Susan Symington of The MITRE Corporation, 2454 Kevin Fall of Carnegie Mellon University, Stephen Farrell of Trinity 2455 College Dublin, Howard Weiss and Peter Lovell of SPARTA, Inc., and 2456 Manikantan Ramadas of Ohio University. 2458 This document was prepared using 2-Word-v2.0.template.dot. 2460 13. Significant Changes from RFC 5050 2462 Points on which this draft significantly differs from RFC 5050 2463 include the following: 2465 . Clarify the difference between transmission and forwarding. 2466 . Migrate custody transfer to the bundle-in-bundle encapsulation 2467 specification [BIBE]. 2468 . Introduce the concept of "node ID" as functionally distinct 2469 from endpoint ID, while having the same syntax. 2470 . Restructure primary block, making it immutable. Add optional 2471 CRC. 2472 . Add optional CRCs to non-primary blocks. 2473 . Add block ID number to canonical block format (to support 2474 BPSEC). 2475 . Add definition of bundle age extension block. 2476 . Add definition of previous node extension block. 2477 . Add definition of hop count extension block. 2478 . Remove Quality of Service markings. 2479 . Change from SDNVs to CBOR representation. 2481 Appendix A. For More Information 2483 Please refer comments to dtn@ietf.org. DTN Working Group documents 2484 are located at https://datatracker.ietf.org/wg/dtn/documents. The 2485 original Delay Tolerant Networking Research Group (DTNRG) Web site 2486 is located at https://irtf.org/concluded/dtnrg. 2488 Copyright (c) 2019 IETF Trust and the persons identified as authors 2489 of the code. All rights reserved. 2491 Redistribution and use in source and binary forms, with or without 2492 modification, is permitted pursuant to, and subject to the license 2493 terms contained in, the Simplified BSD License set forth in Section 2494 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents 2495 (http://trustee.ietf.org/license-info). 2497 Appendix B. CDDL expression 2499 For informational purposes, Carsten Bormann and Brian Sipos have 2500 kindly provided an expression of the Bundle Protocol specification 2501 in the Concise Data Definition Language (CDDL). That CDDL 2502 expression is presented below. Note that wherever the CDDL 2503 expression is in disagreement with the textual representation of the 2504 BP specification presented in the earlier sections of this document, 2505 the textual representation rules. 2507 start = bundle / #6.55799(bundle) 2509 ; Times before 2000 are invalid 2511 dtn-time = uint 2513 ; CRC enumerated type 2515 crc-type = &( 2517 crc-none: 0, 2519 crc-16bit: 1, 2521 crc-32bit: 2 2523 ) 2525 ; Either 16-bit or 32-bit 2527 crc-value = (bstr .size 2) / (bstr .size 4) 2529 creation-timestamp = [ 2531 dtn-time, ; absolute time of creation 2533 sequence: uint ; sequence within the time 2535 ] 2537 eid = $eid .within eid-structure 2539 eid-structure = [ 2541 uri-code: uint, 2542 SSP: any 2544 ] 2546 $eid /= [ 2548 uri-code: 1, 2550 SSP: (tstr / 0) 2552 ] 2554 $eid /= [ 2556 uri-code: 2, 2558 SSP: [ 2560 nodenum: uint, 2562 servicenum: uint 2564 ] 2566 ] 2568 ; The root bundle array 2570 bundle = [primary-block, *extension-block, payload-block] 2572 primary-block = [ 2574 version: 7, 2576 bundle-control-flags, 2578 crc-type, 2580 destination: eid, 2582 source-node: eid, 2584 report-to: eid, 2586 creation-timestamp, 2588 lifetime: uint, 2589 ? ( 2591 fragment-offset: uint, 2593 total-application-data-length: uint 2595 ), 2597 ? crc-value, 2599 ] 2601 bundle-control-flags = uint .bits bundleflagbits 2603 bundleflagbits = &( 2605 reserved: 21, 2607 reserved: 20, 2609 reserved: 19, 2611 bundle-deletion-status-reports-are-requested: 18, 2613 bundle-delivery-status-reports-are-requested: 17, 2615 bundle-forwarding-status-reports-are-requested: 16, 2617 reserved: 15, 2619 bundle-reception-status-reports-are-requested: 14, 2621 reserved: 13, 2623 reserved: 12, 2625 reserved: 11, 2627 reserved: 10, 2629 reserved: 9, 2631 reserved: 8, 2633 reserved: 7, 2634 status-time-is-requested-in-all-status-reports: 6, 2636 user-application-acknowledgement-is-requested: 5, 2638 reserved: 4, 2640 reserved: 3, 2642 bundle-must-not-be-fragmented: 2, 2644 payload-is-an-administrative-record: 1, 2646 bundle-is-a-fragment: 0 2648 ) 2650 ; Abstract shared structure of all non-primary blocks 2652 canonical-block-structure = [ 2654 block-type-code: uint, 2656 block-number: uint, 2658 block-control-flags, 2660 crc-type, 2662 ; Each block type defines the content within the bytestring 2664 block-type-specific-data, 2666 ? crc-value 2668 ] 2670 block-control-flags = uint .bits blockflagbits 2672 blockflagbits = &( 2674 reserved: 7, 2676 reserved: 6, 2678 reserved: 5, 2680 block-must-be-removed-from-bundle-if-it-cannot-be-processed: 4, 2681 reserved: 3, 2683 bundle-must-be-deleted-if-block-cannot-be-processed: 2, 2685 status-report-must-be-transmitted-if-block-cannot-be-processed: 1, 2687 block-must-be-replicated-in-every-fragment: 0 2689 ) 2691 block-type-specific-data = bstr / #6.24(bstr) 2693 ; Actual CBOR data embedded in a bytestring, with optional tag to 2694 indicate so 2696 embedded-cbor = (bstr .cbor Item) / #6.24(bstr .cbor Item) 2698 ; Extension block type, which does not specialize other than the 2699 code/number 2701 extension-block = $extension-block-structure .within canonical- 2702 block-structure 2704 ; Generic shared structure of all non-primary blocks 2706 extension-block-use = [ 2708 block-type-code: CodeValue, 2710 block-number: (uint .gt 1), 2712 block-control-flags, 2714 crc-type, 2716 BlockData, 2718 ? crc-value 2720 ] 2722 ; Payload block type 2724 payload-block = payload-block-structure .within canonical-block- 2725 structure 2726 payload-block-structure = [ 2728 block-type-code: 1, 2730 block-number: 1, 2732 block-control-flags, 2734 crc-type, 2736 $payload-block-data, 2738 ? crc-value 2740 ] 2742 ; Arbitrary payload data, including non-CBOR bytestring 2744 $payload-block-data /= block-type-specific-data 2746 ; Administrative record as a payload data specialization 2748 $payload-block-data /= embedded-cbor 2750 admin-record = $admin-record .within admin-record-structure 2752 admin-record-structure = [ 2754 record-type-code: uint, 2756 record-content: any 2758 ] 2760 ; Only one defined record type 2762 $admin-record /= [1, status-record-content] 2764 status-record-content = [ 2766 bundle-status-information, 2768 status-report-reason-code: uint, 2770 source-node-eid: eid, 2772 subject-creation-timestamp: creation-timestamp, 2773 ? ( 2775 subject-payload-offset: uint, 2777 subject-payload-length: uint 2779 ) 2781 ] 2783 bundle-status-information = [ 2785 reporting-node-received-bundle: status-info-content, 2787 reporting-node-forwarded-bundle: status-info-content, 2789 reporting-node-delivered-bundle: status-info-content, 2791 reporting-node-deleted-bundle: status-info-content 2793 ] 2795 status-info-content = [ 2797 status-indicator: bool, 2799 ? timestamp: dtn-time 2801 ] 2803 ; Previous Node extension block 2805 $extension-block-structure /= 2807 extension-block-use<7, embedded-cbor> 2809 ext-data-previous-node = eid 2811 ; Bundle Age extension block 2813 $extension-block-structure /= 2815 extension-block-use<8, embedded-cbor> 2817 ext-data-bundle-age = uint 2819 ; Hop Count extension block 2820 $extension-block-structure /= 2822 extension-block-use<9, embedded-cbor> 2824 ext-data-hop-count = [ 2826 hop-limit: uint, 2828 hop-count: uint 2830 ] 2832 Authors' Addresses 2834 Scott Burleigh 2835 Jet Propulsion Laboratory, California Institute of Technology 2836 4800 Oak Grove Dr. 2837 Pasadena, CA 91109-8099 2838 US 2839 Phone: +1 818 393 3353 2840 Email: Scott.C.Burleigh@jpl.nasa.gov 2842 Kevin Fall 2843 Roland Computing Services 2844 3871 Piedmont Ave. Suite 8 2845 Oakland, CA 94611 2846 US 2847 Email: kfall+rcs@kfall.com 2849 Edward J. Birrane 2850 Johns Hopkins University Applied Physics Laboratory 2851 11100 Johns Hopkins Rd 2852 Laurel, MD 20723 2853 US 2854 Phone: +1 443 778 7423 2855 Email: Edward.Birrane@jhuapl.edu