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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: December 2015 Carnegie Mellon University / SEI 5 E. Birrane 6 APL, Johns Hopkins University 7 June 21, 2015 9 Bundle Protocol 10 draft-dtnwg-bp-00.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 This document may contain material from IETF Documents or IETF 18 Contributions published or made publicly available before November 19 10, 2008. The person(s) controlling the copyright in some of this 20 material may not have granted the IETF Trust the right to allow 21 modifications of such material outside the IETF Standards Process. 22 Without obtaining an adequate license from the person(s) controlling 23 the copyright in such materials, this document may not be modified 24 outside the IETF Standards Process, and derivative works of it may 25 not be created outside the IETF Standards Process, except to format 26 it for publication as an RFC or to translate it into languages other 27 than English. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF), its areas, and its working groups. Note that 31 other groups may also distribute working documents as Internet- 32 Drafts. 34 Internet-Drafts are draft documents valid for a maximum of six 35 months and may be updated, replaced, or obsoleted by other documents 36 at any time. It is inappropriate to use Internet-Drafts as 37 reference material or to cite them other than as "work in progress." 39 The list of current Internet-Drafts can be accessed at 40 http://www.ietf.org/ietf/1id-abstracts.txt 42 The list of Internet-Draft Shadow Directories can be accessed at 43 http://www.ietf.org/shadow.html 45 This Internet-Draft will expire on July 21, 2015. 47 Copyright Notice 49 Copyright (c) 2015 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (http://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with 57 respect to this document. 59 Abstract 61 This Internet Draft presents a specification for Bundle Protocol, 62 adapted from the experimental Bundle Protocol specification 63 developed by the Delay-Tolerant Networking Research group of the 64 Internet Research Task Force and documented in RFC 5050. 66 Table of Contents 68 1. Introduction...................................................4 69 2. Conventions used in this document..............................6 70 3. Service Description............................................6 71 3.1. Definitions...............................................6 72 3.2. Implementation Architectures.............................12 73 3.2.1. Bundle protocol application server..................12 74 3.2.2. Peer application nodes..............................13 75 3.2.3. Sensor network nodes................................13 76 3.2.4. Dedicated bundle router.............................13 77 3.3. Services Offered by Bundle Protocol Agents...............13 78 4. Bundle Format.................................................14 79 4.1. Self-Delimiting Numeric Values (SDNVs)...................14 80 4.2. Bundle Processing Control Flags..........................16 81 4.3. Block Processing Control Flags...........................18 82 4.4. Identifiers..............................................19 83 4.4.1. Endpoint ID.........................................19 84 4.4.2. Node ID.............................................20 85 4.5. Formats of Bundle Blocks.................................21 86 4.5.1. Primary Bundle Block................................23 87 4.5.2. Canonical Bundle Block Format.......................25 88 4.5.3. Bundle Payload Block................................26 89 4.6. Extension Blocks.........................................27 90 4.6.1. Current Custodian...................................27 91 4.6.2. Flow Label..........................................28 92 4.6.3. Previous Node ID....................................28 93 4.6.4. Bundle Age..........................................28 94 4.6.5. Hop Count...........................................28 95 5. Bundle Processing.............................................29 96 5.1. Generation of Administrative Records.....................29 97 5.2. Bundle Transmission......................................30 98 5.3. Bundle Dispatching.......................................30 99 5.4. Bundle Forwarding........................................31 100 5.4.1. Forwarding Contraindicated..........................33 101 5.4.2. Forwarding Failed...................................33 102 5.5. Bundle Expiration........................................34 103 5.6. Bundle Reception.........................................34 104 5.7. Local Bundle Delivery....................................35 105 5.8. Bundle Fragmentation.....................................36 106 5.9. Application Data Unit Reassembly.........................37 107 5.10. Custody Transfer........................................38 108 5.10.1. Custody Acceptance.................................38 109 5.10.2. Custody Release....................................39 110 5.11. Custody Transfer Success................................39 111 5.12. Custody Transfer Failure................................39 112 5.13. Bundle Deletion.........................................39 113 5.14. Discarding a Bundle.....................................40 114 5.15. Canceling a Transmission................................40 115 6. Administrative Record Processing..............................40 116 6.1. Administrative Records...................................40 117 6.1.1. Bundle Status Reports...............................41 118 6.1.2. Custody Signals.....................................45 119 6.2. Generation of Administrative Records.....................47 120 6.3. Reception of Custody Signals.............................48 121 7. Services Required of the Convergence Layer....................48 122 7.1. The Convergence Layer....................................48 123 7.2. Summary of Convergence Layer Services....................48 124 8. Security Considerations.......................................49 125 9. IANA Considerations...........................................50 126 10. References...................................................50 127 10.1. Normative References....................................50 128 10.2. Informative References..................................51 129 11. Acknowledgments..............................................51 130 12. Significant Changes From RFC 5050............................52 131 13. Open Issues..................................................52 132 13.1. Definitions section structure...........................52 133 13.2. Payload nomenclature....................................53 134 13.3. Application Agent.......................................53 135 13.4. Bundle Endpoint definition..............................53 136 13.5. Alignment with ICN......................................53 137 13.6. Implementation Architectures............................53 138 13.7. Security protocol name..................................54 139 13.8. Bundle format...........................................54 140 13.9. SDNVs...................................................54 141 13.10. Bundle Processing Control Flags........................54 142 13.11. Extended class of service features.....................54 143 13.12. Primary block CRC type.................................54 144 13.13. Inventory..............................................54 145 13.14. Block numbers..........................................55 146 13.15. Clearing flag..........................................55 147 13.16. Overriding BP spec.....................................55 148 13.17. Time of forwarding.....................................55 149 13.18. Block multiplicity.....................................55 150 Appendix A. For More Information.................................56 152 1. Introduction 154 Since the publication of the Bundle Protocol Specification 155 (Experimental RFC 5050[RFC5050]) in 2007, the Delay-Tolerant 156 Networking Bundle Protocol has been implemented in multiple 157 programming languages and deployed to a wide variety of computing 158 platforms for a wide range of successful exercises. This 159 implementation and deployment experience has demonstrated the 160 general utility of the protocol for challenged network operations. 162 It has also, as expected, identified opportunities for making the 163 protocol simpler, more capable, and easier to use. The present 164 document, standardizing the Bundle Protocol (BP), is adapted from 165 RFC 5050 in that context. 167 This document describes version 7 of BP. 169 Delay Tolerant Networking is a network architecture providing 170 communications in and/or through highly stressed environments. 171 Stressed networking environments include those with intermittent 172 connectivity, large and/or variable delays, and high bit error 173 rates. To provide its services, BP sits at the application layer of 174 some number of constituent networks, forming a store-carry-forward 175 overlay network. Key capabilities of BP include: 177 . Custodial forwarding 178 . Ability to cope with intermittent connectivity 179 . Ability to take advantage of scheduled, predicted, and 180 opportunistic connectivity (in addition to continuous 181 connectivity) 182 . Late binding of overlay network endpoint identifiers to 183 underlying constituent network addresses 185 For descriptions of these capabilities and the rationale for the DTN 186 architecture, see [ARCH] and [SIGC]. [TUT] contains a tutorial- 187 level overview of DTN concepts. 189 BP's location within the standard protocol stack is as shown in 190 Figure 1. BP uses underlying "native" network protocols for 191 communications within a given constituent network. 193 The interface between the bundle protocol and a specific underlying 194 protocol is termed a "convergence layer adapter". 196 Figure 1 shows three distinct transport and network protocols 197 (denoted T1/N1, T2/N2, and T3/N3). 199 +-----------+ +-----------+ 200 | BP app | | BP app | 201 +---------v-| +->>>>>>>>>>v-+ +->>>>>>>>>>v-+ +-^---------+ 202 | BP v | | ^ BP v | | ^ BP v | | ^ BP | 203 +---------v-+ +-^---------v-+ +-^---------v-+ +-^---------+ 204 | Trans1 v | + ^ T1/T2 v | + ^ T2/T3 v | | ^ Trans3 | 205 +---------v-+ +-^---------v-+ +-^---------v + +-^---------+ 206 | Net1 v | | ^ N1/N2 v | | ^ N2/N3 v | | ^ Net3 | 207 +---------v-+ +-^---------v + +-^---------v-+ +-^---------+ 208 | >>>>>>>>^ >>>>>>>>>>^ >>>>>>>>^ | 209 +-----------+ +-------------+ +-------------+ +-----------+ 210 | | | | 211 |<---- A network ---->| |<---- A network ---->| 212 | | | | 214 Figure 1: The Bundle Protocol Sits at the Application Layer of the 215 Protocol Stack Model 217 This document describes the format of the protocol data units 218 (called bundles) passed between entities participating in BP 219 communications. 221 The entities are referred to as "bundle nodes". This document does 222 not address: 224 . Operations in the convergence layer adapters that bundle nodes 225 use to transport data through specific types of internets. 226 (However, the document does discuss the services that must be 227 provided by each adapter at the convergence layer.) 228 . The bundle route computation algorithm. 229 . Mechanisms for populating the routing or forwarding information 230 bases of bundle nodes. 231 . The mechanisms for securing bundles en-route. 233 . The mechanisms for managing bundle nodes. 235 2. Conventions used in this document 237 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 238 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 239 document are to be interpreted as described in RFC-2119 [RFC2119]. 241 In this document, these words will appear with that interpretation 242 only when in ALL CAPS. Lower case uses of these words are not to be 243 interpreted as carrying RFC-2119 significance. 245 3. Service Description 247 3.1. Definitions 249 Bundle - A bundle is a protocol data unit of BP, so named because 250 negotiation of the parameters of a data exchange may be impractical 251 in a delay-tolerant network: it is often better practice to "bundle" 252 with a unit of data all metadata that might be needed in order to 253 make the data immediately usable when delivered to applications. 254 Each bundle comprises a sequence of two or more "blocks" of protocol 255 data, which serve various purposes. Multiple instances of the same 256 bundle (the same unit of DTN protocol data) might exist concurrently 257 in different parts of a network -- possibly in different 258 representations and/or differing in some blocks -- in the memory 259 local to one or more bundle nodes and/or in transit between nodes. 260 In the context of the operation of a bundle node, a bundle is an 261 instance of some bundle in the network that is in that node's local 262 memory. 264 Bundle payload - A bundle payload (or simply "payload") is the 265 application data whose conveyance to the bundle's destination is the 266 purpose for the transmission of a given bundle. The terms "bundle 267 content", "bundle payload", and "payload" are used interchangeably 268 in this document. The "nominal" payload for a bundle forwarded in 269 response to a bundle transmission request is the application data 270 unit whose location is provided as a parameter to that request. The 271 nominal payload for a bundle forwarded in response to reception of 272 that bundle is the payload of the received bundle. 274 Fragment - A fragment is a bundle whose payload block contains a 275 fragmentary payload. A fragmentary payload is either the first N 276 bytes or the last N bytes of some other payload -- either a nominal 277 payload or a fragmentary payload -- of length M, such that 0 < N < 278 M. 280 Bundle node - A bundle node (or, in the context of this document, 281 simply a "node") is any entity that can send and/or receive bundles. 282 In the most familiar case, a bundle node is instantiated as a single 283 process running on a general-purpose computer, but in general the 284 definition is meant to be broader: a bundle node might alternatively 285 be a thread, an object in an object-oriented operating system, a 286 special-purpose hardware device, etc. Each bundle node has three 287 conceptual components, defined below: a "bundle protocol agent", a 288 set of zero or more "convergence layer adapters", and an 289 "application agent". 291 Bundle protocol agent - The bundle protocol agent (BPA) of a node is 292 the node component that offers the BP services and executes the 293 procedures of the bundle protocol. The manner in which it does so is 294 wholly an implementation matter. For example, BPA functionality 295 might be coded into each node individually; it might be implemented 296 as a shared library that is used in common by any number of bundle 297 nodes on a single computer; it might be implemented as a daemon 298 whose services are invoked via inter-process or network 299 communication by any number of bundle nodes on one or more 300 computers; it might be implemented in hardware. 302 Convergence layer adapters - A convergence layer adapter (CLA) sends 303 and receives bundles on behalf of the BPA, utilizing the services 304 of some 'native' protocol stack that is supported in one of the 305 networks within which the node is functionally located. As such, 306 every CLA implements its own thin layer of protocol, interposed 307 between BP and the (usually "top") protocol(s) of the underlying 308 native protocol stack; this "CL protocol" may only serve to 309 multiplex and de-multiplex bundles to and from the underlying native 310 protocol, or it may offer additional CL-specific functionality. The 311 manner in which a CLA sends and receives bundles is wholly an 312 implementation matter, exactly as described for the BPA. The 313 definitions of CLAs and CL protocols are beyond the scope of this 314 specification. 316 Application agent - The application agent (AA) of a node is the node 317 component that utilizes the BP services to effect communication for 318 some purpose. The application agent in turn has two elements, an 319 administrative element and an application-specific element. The 320 application-specific element of an AA constructs, requests 321 transmission of, accepts delivery of, and processes application- 322 specific application data units; the only interface between the BPA 323 and the application-specific element of the AA is the BP service 324 interface. The administrative element of an AA constructs and 325 requests transmission of administrative records (including status 326 reports and custody signals), and it accepts delivery of and 327 processes any custody signals that the node receives. In addition to 328 the BP service interface, there is a (conceptual) private control 329 interface between the BPA and the administrative element of the AA 330 that enables each to direct the other to take action under specific 331 circumstances. In the case of a node that serves simply as a BP 332 "router", the AA may have no application-specific element at all. 333 The application-specific elements of other nodes' AAs may perform 334 arbitrarily complex application functions, perhaps even offering 335 multiplexed DTN communication services to a number of other 336 applications. As with the BPA, the manner in which the AA performs 337 its functions is wholly an implementation matter. 339 Administrative record - A BP administrative record is an application 340 data unit that is exchanged between the administrative elements of 341 nodes' application agents for some BP administrative purpose. The 342 formats of some fundamental administrative records (and of no other 343 application data units) are defined in this specification. 345 Bundle endpoint - A bundle endpoint (or simply "endpoint") is a set 346 of zero or more bundle nodes that all identify themselves for BP 347 purposes by some common identifier, called a "bundle endpoint ID" 348 (or, in this document, simply "endpoint ID"; endpoint IDs are 349 described in detail in Section 4.4.4 below). The special case of an 350 endpoint that contains exactly one node is termed a "singleton" 351 endpoint. Singletons are the most familiar sort of endpoint, but in 352 general the endpoint notion is meant to be broader. For example, the 353 nodes in a sensor network might constitute a set of bundle nodes 354 that identify themselves by a single common endpoint ID and thus 355 form a single bundle endpoint. For a bundle to be considered 356 "delivered" to an endpoint, a minimum number of receiving nodes may 357 be required to receive it successfully. This lower limit is called 358 the minimum reception group, and is defined in the Transmission 359 discussion below. *Note* too that a given bundle node might 360 identify itself by multiple endpoint IDs and thus be a member of 361 multiple bundle endpoints. The destination of every bundle is an 362 endpoint, which may or may not be singleton. The source of every 363 bundle is a singleton endpoint. 365 Transmission - A transmission is an attempt by a node's BPA to cause 366 copies of a bundle to be delivered at all nodes in the minimum 367 reception group of some endpoint (the bundle's destination) in 368 response to a transmission request issued by the node's application 369 agent. The minimum reception group of an endpoint may be any one of 370 the following: (a) ALL of the nodes registered (see definition 371 below) in an endpoint that is permitted to contain multiple nodes 372 (in which case forwarding to the endpoint is functionally similar to 373 "multicast" operations in the Internet, though possibly very 374 different in implementation); (b) ANY N of the nodes registered in 375 an endpoint that is permitted to contain multiple nodes, where N is 376 in the range from zero to the cardinality of the endpoint; or (c) 377 THE SOLE NODE registered in a singleton endpoint (in which case 378 forwarding to the endpoint is functionally similar to "unicast" 379 operations in the Internet). The nature of the minimum reception 380 group for a given endpoint can be determined from the endpoint's ID 381 (again, see Section 4.4 below): for some endpoint ID "schemes", the 382 nature of the minimum reception group is fixed - in a manner that is 383 defined by the scheme - for all endpoints identified under the 384 scheme; for other schemes, the nature of the minimum reception group 385 is indicated by some lexical feature of the "scheme-specific part" 386 of the endpoint ID, in a manner that is defined by the scheme. Any 387 number of transmissions may be concurrently undertaken by the bundle 388 protocol agent of a given node. 390 Forwarding - When the bundle protocol agent of a node determines 391 that a bundle must be "forwarded" to a node (either a node that is a 392 member of the bundle's destination endpoint or some intermediate 393 forwarding node) in the course of completing the successful 394 transmission of that bundle, it invokes the services of a CLA in a 395 sustained effort to cause a copy of the bundle to be received by 396 that node. 398 Registration - A registration is the state machine characterizing a 399 given node's membership in a given endpoint. Any number of 400 registrations may be concurrently associated with a given endpoint, 401 and any number of registrations may be concurrently associated with 402 a given node. Any single registration must at any time be in one of 403 two states: Active or Passive. A registration always has an 404 associated "delivery failure action", the action that is to be taken 405 when a bundle that is "deliverable" (see below) subject to that 406 registration is received at a time when the registration is in the 407 Passive state. Delivery failure action must be one of the following: 409 . defer "delivery" (see below) of the bundle subject to this 410 registration until (a) this bundle is the least recently 411 received of all bundles currently deliverable subject to this 412 registration and (b) either the registration is polled or else 413 the registration is in the Active state; or 414 . "abandon" (see below) delivery of the bundle subject to this 415 registration. 417 An additional implementation-specific delivery deferral procedure 418 may optionally be associated with the registration. While the state 419 of a registration is Active, reception of a bundle that is 420 deliverable subject to this registration must cause the bundle to be 421 delivered automatically as soon as it is the next bundle that is due 422 for delivery according to the BPA's bundle delivery scheduling 423 policy, an implementation matter. While the state of a registration 424 is Passive, reception of a bundle that is deliverable subject to 425 this registration must cause delivery of the bundle to be abandoned 426 or deferred as mandated by the registration's current delivery 427 failure action; in the latter case, any additional delivery deferral 428 procedure associated with the registration must also be performed. 430 Delivery - Upon reception, the processing of a bundle that has been 431 received by a given node depends on whether or not the receiving 432 node is registered in the bundle's destination endpoint. If it is, 433 and if the payload of the bundle is non-fragmentary (possibly as a 434 result of successful payload reassembly from fragmentary payloads, 435 including the original payload of the received bundle), then the 436 bundle is normally "delivered" to the node's application agent 437 subject to the registration characterizing the node's membership in 438 the destination endpoint. A bundle is considered to have been 439 delivered at a node subject to a registration as soon as the 440 application data unit that is the payload of the bundle, together 441 with the value of the bundle's "Acknowledgement by application is 442 requested" flag and any other relevant metadata (an implementation 443 matter), has been presented to the node's application agent in a 444 manner consistent with the state of that registration and, as 445 applicable, the registration's delivery failure action. 447 Deliverability, Abandonment - A bundle is considered "deliverable" 448 subject to a registration if and only if (a) the bundle's 449 destination endpoint is the endpoint with which the registration is 450 associated, (b) the bundle has not yet been delivered subject to 451 this registration, and (c) delivery of the bundle subject to this 452 registration has not been abandoned. To "abandon" delivery of a 453 bundle subject to a registration is simply to declare it no longer 454 deliverable subject to that registration; normally only 455 registrations' registered delivery failure actions cause deliveries 456 to be abandoned. 458 Deletion, Discarding - A bundle protocol agent "discards" a bundle 459 by simply ceasing all operations on the bundle and functionally 460 erasing all references to it; the specific procedures by which this 461 is accomplished are an implementation matter. Bundles are discarded 462 silently; i.e., the discarding of a bundle does not result in 463 generation of an administrative record. "Retention constraints" are 464 elements of the bundle state that prevent a bundle from being 465 discarded; a bundle cannot be discarded while it has any retention 466 constraints. A bundle protocol agent "deletes" a bundle in response 467 to some anomalous condition by notifying the bundle's report-to node 468 of the deletion (provided such notification is warranted; see 469 Section 5.13 for details) and then arbitrarily removing all of the 470 bundle's retention constraints, enabling the bundle to be discarded. 472 Custody - A node "takes custody" of a bundle when it determines that 473 it will retain a copy of the bundle for some period, forwarding and 474 possibly re-forwarding the bundle as appropriate and destroying that 475 retained copy only when custody of that bundle is formally 476 "released". Custody of a bundle may only be taken if the destination 477 of the bundle is a singleton endpoint. A "custodial node" (or 478 "custodian") of a bundle is a node that has taken custody of the 479 bundle and has not yet released that custody. To "accept custody" 480 upon receiving a bundle is to take custody of the bundle, mark the 481 bundle in such a way as to indicate to nodes that subsequently 482 receive the bundle that it has taken custody, and notify all current 483 custodians of the bundle that it has taken custody. Custody may only 484 be released when either (a) notification is received that some other 485 node has accepted custody of the same bundle; (b) notification is 486 received that the bundle has been delivered at the (sole) node 487 registered in the bundle's destination endpoint; (c) the current 488 custodian chooses to fragment the bundle, releasing custody of the 489 original bundle and taking custody of the fragments instead, or (d) 490 the bundle is explicitly deleted for some reason, such as lifetime 491 expiration. To "refuse custody" of a bundle is to notify all current 492 custodians of that bundle that an opportunity to take custody of the 493 bundle has been declined. 495 The custody transfer mechanism in BP is primarily intended as a 496 means of recovering from forwarding failures. When a bundle arrives 497 at a node from which it cannot be forwarded, BP must recover from 498 this error. BP can "return" the bundle back toward some node for 499 forwarding along some different path in the network, or else it can 500 instead send a small "signal" bundle back to such a node, in the 501 event that this node has retained a copy of the bundle ("taken 502 custody") and is therefore able to re-forward the bundle without 503 receiving a copy. Custody transfer sharply reduces the network 504 traffic required for recovery from forwarding failures, at the cost 505 of increased buffer occupancy and state management at the custodial 506 nodes. 508 Note that custodial re-forwarding can also be initiated by 509 expiration of a timer prior to reception of a custody acceptance 510 signal. Since the absence of a custody acceptance signal might be 511 caused by failure to receive the bundle, rather than only a 512 disinclination to take custody, custody transfer can additionally 513 serve as an automated retransmission mechanism. Because custody 514 transfer's only remedy for loss of any part of a bundle is 515 retransmission of the entire bundle (not just the lost portion), 516 custody transfer is a less efficient automated retransmission 517 mechanism than the reliable transport protocols that are typically 518 available at the convergence layer; configuring BPAs to use reliable 519 convergence-layer protocols between nodes is generally the best 520 means of ensuring bundle delivery at the destination node(s). But 521 there are some use cases (typically involving unidirectional links) 522 in which custody transfer in BP may be a more cost-effective 523 solution for reliable transmission between two BP agents than 524 operating retransmission protocols at the convergence layer. 526 Embargo - Forwarding failures are not just operational anomalies; 527 they may also convey information about the network, i.e., a 528 forwarding failure may indicate a sustained lapse in forwarding 529 capability. Since forwarding a bundle to a dead end wastes time and 530 bandwidth, the bundle protocol agent may choose to manage such a 531 lapse by imposing a temporary "embargo" on subsequent forwarding 532 activity that is similar to the forwarding attempt that has been 533 seen to fail. Mechanisms for motivating, imposing, enforcing, and 534 lifting embargoes are beyond the scope of this document. 536 3.2. Implementation Architectures 538 The above definitions are intended to enable the bundle protocol's 539 operations to be specified in a manner that minimizes bias toward 540 any particular implementation architecture. To illustrate the range 541 of interoperable implementation models that might conform to this 542 specification, four example architectures are briefly described 543 below. 545 3.2.1. Bundle protocol application server 547 A single bundle protocol application server, constituting a single 548 bundle node, runs as a daemon process on each computer. The daemon's 549 functionality includes all functions of the bundle protocol agent, 550 all convergence layer adapters, and both the administrative and 551 application-specific elements of the application agent. The 552 application-specific element of the application agent functions as a 553 server, offering bundle protocol service over a local area network: 554 it responds to remote procedure calls from application processes (on 555 the same computer and/or remote computers) that need to communicate 556 via the bundle protocol. The server supports its clients by creating 557 a new (conceptual) node for each one and registering each such node 558 in a client-specified endpoint. The conceptual nodes managed by the 559 server function as clients' bundle protocol service access points. 561 3.2.2. Peer application nodes 563 Any number of bundle protocol application processes, each one 564 constituting a single bundle node, run on each computer. The 565 functionality of the bundle protocol agent, all convergence layer 566 adapters, and the administrative element of the application agent is 567 provided by a library to which each node process is dynamically 568 linked at run time. The application-specific element of each node's 569 application agent is node-specific application code. 571 3.2.3. Sensor network nodes 573 Each node of the sensor network is the self-contained implementation 574 of a single bundle node. All functions of the bundle protocol agent, 575 all convergence layer adapters, and the administrative element of 576 the application agent are implemented in simplified form in 577 hardware, while the application-specific element of each node's 578 application agent is implemented in a programmable microcontroller. 579 Forwarding is rudimentary: all bundles are forwarded on a hard-coded 580 default route. 582 3.2.4. Dedicated bundle router 584 Each computer constitutes a single bundle node that functions solely 585 as a high-performance bundle forwarder. Many standard functions of 586 the bundle protocol agent, the convergence layer adapters, and the 587 administrative element of the application agent are implemented in 588 specialized hardware, but some functions are implemented in a high- 589 speed processor to enable reprogramming as necessary. The node's 590 application agent has no application-specific element. Substantial 591 non-volatile storage resources are provided, and arbitrarily complex 592 forwarding algorithms are supported. 594 3.3. Services Offered by Bundle Protocol Agents 596 The BPA of each node is expected to provide the following services 597 to the node's application agent: 599 . commencing a registration (registering the node in an 600 endpoint); 601 . terminating a registration; 602 . switching a registration between Active and Passive states; 603 . transmitting a bundle to an identified bundle endpoint; 604 . canceling a transmission; 605 . polling a registration that is in the passive state; 606 . delivering a received bundle. 608 4. Bundle Format 610 Each bundle shall be a concatenated sequence of at least two block 611 structures. The first block in the sequence must be a primary bundle 612 block, and no bundle may have more than one primary bundle block. 613 Additional bundle protocol blocks of other types may follow the 614 primary block to support extensions to the bundle protocol, such as 615 the Bundle Security Protocol [BSP]. Exactly one of the blocks in the 616 sequence must be a payload block. The last block in the sequence 617 must have the "last block" flag (in its block processing control 618 flags) set to 1; for every other block in the bundle after the 619 primary block, this flag must be set to zero. 621 4.1. Self-Delimiting Numeric Values (SDNVs) 623 The design of the bundle protocol attempts to reconcile minimal 624 consumption of transmission bandwidth with: 626 . extensibility to address requirements not yet identified, and 627 . scalability across a wide range of network scales and payload 628 sizes. 630 A key strategic element in the design is the use of self-delimiting 631 numeric values (SDNVs). The SDNV encoding scheme is closely adapted 632 from the Abstract Syntax Notation One Basic Encoding Rules for sub- 633 identifiers within an object identifier value [ASN1]. An SDNV is a 634 numeric value encoded in N octets, the last of which has its most 635 significant bit (MSB) set to zero; the MSB of every other octet in 636 the SDNV must be set to 1. The value encoded in an SDNV is the 637 unsigned binary number obtained by concatenating into a single bit 638 string the 7 least significant bits of each octet of the SDNV. The 639 following examples illustrate the encoding scheme for various 640 hexadecimal values. 642 0xABC : 1010 1011 1100 644 is encoded as 646 {1 00 10101} {0 0111100} 648 = 10010101 00111100 650 0x1234 : 0001 0010 0011 0100 652 = 1 0010 0011 0100 654 is encoded as 655 {1 0 100100} {0 0110100} 657 = 10100100 00110100 659 0x4234 : 0100 0010 0011 0100 661 = 100 0010 0011 0100 663 is encoded as 665 {1 000000 1} {1 0000100} {0 0110100} 667 = 10000001 10000100 00110100 669 0x7F : 0111 1111 671 = 111 1111 673 is encoded as 675 {0 1111111} 677 = 01111111 679 Figure 2: SDNV Example 681 Note: Care must be taken to make sure that the value to be encoded 682 is (in concept) padded with high-order zero bits to make its bitwise 683 length a multiple of 7 before encoding. Also note that, while there 684 is no theoretical limit on the size of an SDNV field, the overhead 685 of the SDNV scheme is 1:7, i.e., one bit of overhead for every 7 686 bits of actual data to be encoded. Thus, a 7-octet value (a 56-bit 687 quantity with no leading zeroes) would be encoded in an 8-octet 688 SDNV; an 8-octet value (a 64-bit quantity with no leading zeroes) 689 would be encoded in a 10-octet SDNV (one octet containing the high- 690 order bit of the value padded with six leading zero bits, followed 691 by nine octets containing the remaining 63 bits of the value). 148 692 bits of overhead would be consumed in encoding a 1024-bit RSA 693 encryption key directly in an SDNV. In general, an N-bit quantity 694 with no leading zeroes is encoded in an SDNV occupying ceil(N/7) 695 octets, where ceil is the integer ceiling function. 697 Implementations of the bundle protocol may handle as an invalid 698 numeric value any SDNV that encodes an integer larger than (2^64 - 699 1). 701 An SDNV can be used to represent both very large and very small 702 integer values. However, SDNV is clearly not the best way to 703 represent every numeric value. For example, an SDNV is a poor way to 704 represent an integer whose value typically falls in the range 128 to 705 255. In general, though, we believe that SDNV representation of 706 numeric values in bundle blocks yields the smallest block sizes 707 without sacrificing scalability. 709 4.2. Bundle Processing Control Flags 711 The bundle processing control flags field in the primary bundle 712 block of each bundle is an SDNV; the value encoded in this SDNV is a 713 string of bits used to invoke selected bundle processing control 714 features. The significance of the value in each currently defined 715 position of this bit string is described here. Note that in the 716 figure and descriptions, the bit label numbers denote position (from 717 least significant ('0') to most significant) within the decoded bit 718 string, and not within the representation of the bits on the wire. 719 This is why the descriptions in this section and the next do not 720 follow standard RFC conventions with bit 0 on the left; if fields 721 are added in the future, the SDNV will grow to the left, and using 722 this representation allows the references here to remain valid. 724 2 1 0 726 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 728 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 730 |Status Report|Class of Svc.|CRC| General | 732 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 734 Figure 3: Bundle Processing Control Flags Bit Layout 736 The bits in positions 0 through 13 of the value of the bundle 737 processing control flags SDNV are flags that characterize the bundle 738 as follows: 740 0 -- Bundle is a fragment. 742 1 -- Payload is an administrative record. 744 2 -- Bundle must not be fragmented. 746 3 -- Custody transfer is requested. 748 4 -- Destination endpoint is a singleton. 750 5 -- Acknowledgement by application is requested. 752 6 -- Bundle is critical. 754 7 -- Best-efforts forwarding is requested. 756 8 -- Reliable forwarding is requested. 758 9-11 -- Reserved for future use. 760 The bits in positions 12 through 13 are used to indicate the type of 761 CRC that is present at the end of the primary block. The options 762 are: 764 0 -- No CRC. 766 1 -- CRC-8. 768 2 -- CRC-16. 770 3 -- CRC-32. 772 The bits in positions 14 through 20 are used to indicate the 773 bundle's class of service. They constitute a seven-bit priority 774 field indicating the bundle's priority, a value from 0 to 127, with 775 higher values being of higher priority (greater urgency). Within 776 this field, bit 20 is the most significant bit. 778 The bits in positions 21 through 27 are status report request flags. 779 These flags are used to request status reports as follows: 781 21 -- Request reporting of bundle reception. 783 22 -- Request reporting of custody acceptance. 785 23 -- Request reporting of bundle forwarding. 787 24 -- Request reporting of bundle delivery. 789 25 -- Request reporting of bundle deletion. 791 26 -- Reserved for future use. 793 27 -- Reserved for future use. 795 If the bundle processing control flags indicate that the bundle's 796 application data unit is an administrative record, then the custody 797 transfer requested flag must be zero and all status report request 798 flags must be zero. If the custody transfer requested flag is 1, 799 then the source node requests that every receiving node accept 800 custody of the bundle. If the bundle's source endpoint is the null 801 endpoint (see below), then the bundle is not uniquely identifiable 802 and all bundle protocol features that rely on bundle identity must 803 therefore be disabled: the bundle's custody transfer requested flag 804 must be zero, the "Bundle must not be fragmented" flag must be 1, 805 and all status report request flags must be zero. 807 4.3. Block Processing Control Flags 809 The block processing control flags field in every block other than 810 the primary bundle block is an SDNV; the value encoded in this SDNV 811 is a string of bits used to invoke selected block processing control 812 features. The significance of the values in all currently defined 813 positions of this bit string, in order from least significant 814 position in the decoded bit string (labeled '0') to most significant 815 (labeled '6'), is described here. 817 0 819 6 5 4 3 2 1 0 821 +-+-+-+-+-+-+-+ 823 | Flags | 825 +-+-+-+-+-+-+-+ 827 Figure 4: Block Processing Control Flags Bit Layout 829 0 - Block must be replicated in every fragment. 831 1 - Transmit status report if block can't be processed. 833 2 - Delete bundle if block can't be processed. 835 3 - Last block. 837 4 - Discard block if it can't be processed. 839 5 - Block was forwarded without being processed. 841 6 - Reserved for future use. 843 For each bundle whose primary block's bundle processing control 844 flags (see above) indicate that the bundle's application data unit 845 is an administrative record, the "Transmit status report if block 846 can't be processed" flag in the block processing flags field of 847 every other block in the bundle must be zero. 849 The 'Block must be replicated in every fragment' bit in the block 850 processing flags must be set to zero on all blocks that follow the 851 payload block. 853 4.4. Identifiers 855 4.4.1. Endpoint ID 857 The destinations of bundles are bundle endpoints, identified by text 858 strings termed "endpoint IDs" (see Section 3.1). Each endpoint ID 859 (EID) conveyed in any bundle block takes the form of a Uniform 860 Resource Identifier (URI; [URI]). As such, each endpoint ID can be 861 characterized as having this general structure: 863 < scheme name > : < scheme-specific part, or "SSP" > 865 The scheme identified by the < scheme name > in an endpoint ID is a 866 set of syntactic and semantic rules that fully explain how to parse 867 and interpret the SSP. The set of allowable schemes is effectively 868 unlimited. Any scheme conforming to [URIREG] may be used in a bundle 869 protocol endpoint ID. 871 As used for the purposes of the bundle protocol, the length of an 872 SSP must not exceed 1023 bytes. 874 Note that, although endpoint IDs are URIs, implementations of the BP 875 service interface may support expression of endpoint IDs in some 876 internationalized manner (e.g., Internationalized Resource 877 Identifiers (IRIs); see [RFC3987]). 879 The endpoint ID "dtn:none" identifies the "null endpoint", the 880 endpoint that by definition never has any members. 882 Whenever an endpoint ID appears in a bundle block, it is encoded not 883 in its native URI representation but rather in an encoded 884 representation that reduces consumption of transmission bandwidth. 885 The encoded representation of an endpoint ID is as follows: 887 . An SDNV identifying the scheme of the EID (as discussed below), 888 followed by 889 . the encoded representation of the EID's scheme-specific part. 891 The encoded representation of the null endpoint ID is scheme 892 identifier zero, followed by zero octets of scheme-specific part. 894 Every URI scheme used for forming any other EID is classified as 895 either "numeric", meaning that all information conveyed in the 896 scheme-specific part is to be encoded as a sequence of one or more 897 unsigned integers in SDNV representation, or else "non-numeric" 898 (otherwise). The scheme identifier numbers used in the encoded 899 representations of EIDs are assigned as follows: 901 . Scheme identifier zero is reserved for the null endpoint ID. 902 . Scheme identifier numbers in the range 1-63 are used 903 exclusively for numeric EID schemes. 904 . All other scheme identifier numbers are used exclusively for 905 non-numeric EID schemes. 907 Note that scheme of the EID is numeric if and only if the scheme 908 identifier is non-zero and the two high-order bits of the first 909 octet of the scheme identifier are both zero. 911 For each numeric EID scheme, the encoded representation of the EID's 912 scheme-specific part shall be a sequence of from 1 to 100 SDNVs as 913 mandated by the definition of the scheme. 915 For each non-numeric EID scheme, the encoded representation of the 916 EID's scheme-specific part shall comprise: 918 . a single SDNV indicating the length of the remainder of the 919 encoded representation of the scheme-specific part of the EID, 920 followed by 921 . the remainder of the encoded representation of the scheme- 922 specific part of the EID, formed according to the definition of 923 the scheme. If the scheme's definition does not include a 924 specification for encoded representation, then the EID's native 925 scheme-specific part appears here without alteration. 927 It is important to note that not all BP implementations are required 928 to implement the definitions of all EID schemes. The BP 929 implementations used to instantiate nodes in a given network must be 930 chosen with care in order for every node to be able to exchange 931 bundles with every other node. 933 4.4.2. Node ID 935 For many purposes of the Bundle Protocol it is important to identify 936 the node that is operative in some context. 938 As discussed in 3.1 above, nodes are distinct from endpoints; 939 specifically, an endpoint is a set of zero or more nodes. But 940 rather than define a separate namespace for node identifiers, we 941 instead use endpoint identifiers to identify nodes, subject to the 942 following restrictions: 944 . Every node must be a member of at least one singleton endpoint. 945 . The EID of any singleton endpoint of which a node is a member 946 may be used to identify that node. A "node ID" is an EID that 947 is used in this way. 948 . A node's membership in a given singleton endpoint must be 949 sustained at least until the nominal operation of the Bundle 950 Protocol no longer depends on the identification of that node 951 by that endpoint's ID. 953 4.5. Formats of Bundle Blocks 955 This section describes the formats of the primary block and payload 956 block. Rules for processing these blocks appear in Section 5 of this 957 document. 959 Note that supplementary DTN protocol specifications (including, but 960 not restricted to, the Bundle Security Protocol [BSP]) may require 961 that BP implementations conforming to those protocols construct and 962 process additional blocks. 964 The format of these two basic BP blocks is shown in Figure 5 below. 966 Primary Bundle Block 968 +---------+-----------------------+----------------+---------------+ 970 | Version | Block length | Bundle Processing flags (*) | 972 +---------+-----------------------+----------------+---------------+ 974 | Destination EID (*) | Source Node ID (*) | 976 +----------------+----------------+----------------+---------------+ 978 | Report-to EID (*) | Creation timestamp time (*) | 980 +----------------+----------------+----------------+---------------+ 982 | Creation Timestamp sequence number (*) | Lifetime (*) | 984 +----------------+----------------+----------------+---------------+ 985 | Inventory len. | Inventory (*) | [Fragment offset (*)] | 987 +----------------+----------------+----------------+---------------+ 989 | [Total application data unit length (*)] | [CRC (*)] | 991 +----------------+----------------+----------------+---------------+ 993 Bundle Payload Block 995 +----------------+----------------+----------------+---------------+ 997 | Block type |Block number (*)| Proc. flags (*)| Blk length(*) | 999 +----------------+----------------+----------------+---------------+ 1001 / Bundle payload (variable) / 1003 +------------------------------------------------------------------+ 1005 Figure 5: Basic Bundle Block Formats 1007 (*) Notes: 1009 The bundle processing control flags field in the Primary Bundle 1010 Block is an SDNV and is therefore of variable length. A two-octet 1011 SDNV is shown here for convenience in representation. 1013 The destination EID, source node ID, and report-to EID in the 1014 Primary Bundle Block are EIDs in encoded representation and are 1015 therefore of variable length. Two-octet fields are shown here for 1016 convenience in representation. 1018 The creation timestamp time in the Primary Bundle Block is an SDNV 1019 and is therefore of variable length. A two-octet SDNV is shown here 1020 for convenience in representation. 1022 The creation timestamp sequence number field in the Primary Bundle 1023 Block is an SDNV and is therefore of variable length. A three-octet 1024 SDNV is shown here for convenience in representation. 1026 The lifetime field in the Primary Bundle Block is an SDNV and is 1027 therefore of variable length. A one-octet SDNV is shown here for 1028 convenience in representation. 1030 The inventory field in the Primary Bundle Block is an array of block 1031 types (one octet each) whose length is given by the value of the 1032 Inventory Length field and is therefore variable. A one-octet 1033 inventory array is shown here for convenience in representation. 1035 The fragment offset field of the Primary Bundle Block is present 1036 only if the Fragment flag in the block's processing flags field is 1037 set to 1. It is an SDNV and is therefore of variable length; a two- 1038 octet SDNV is shown here for convenience in representation. 1040 The total application data unit length field of the Primary Bundle 1041 Block is present only if the Fragment flag in the block's processing 1042 flags field is set to 1. It is an SDNV and is therefore of variable 1043 length; a three-octet SDNV is shown here for convenience in 1044 representation. 1046 The CRC field of the Primary Bundle Block is present only if the CRC 1047 type field in the block's processing flags field is non-zero. Its 1048 actual length depends on the CRC type; a one-octet CRC is shown here 1049 for convenience in representation. 1051 The block processing control flags ("Proc. flags") field of the 1052 Payload Block is an SDNV and is therefore of variable length. A one- 1053 octet SDNV is shown here for convenience in representation. 1055 The block length ("Blk length") field of the Payload Block is an 1056 SDNV and is therefore of variable length. A one-octet SDNV is shown 1057 here for convenience in representation. 1059 4.5.1. Primary Bundle Block 1061 The primary bundle block contains the basic information needed to 1062 forward bundles to their destinations. The fields of the primary 1063 bundle block are: 1065 Version: A 4-bit field indicating the version of the bundle protocol 1066 that constructed this block. The present document describes version 1067 0x07 of the bundle protocol. 1069 Block Length: a 12-bit field that contains the aggregate length (in 1070 bytes) of all remaining fields of the primary block. Note that, 1071 although many fields of the primary bundle block are variable-length 1072 SDNVs, the lengths of all of these SDNVs are in practice limited; 1073 the lengths of the scheme-specific parts of non-numeric EIDs are 1074 likewise limited. These limitations make it reasonable to limit the 1075 total length of the primary block to 4095 octets. 1077 Bundle Processing Control Flags: The Bundle Processing Control Flags 1078 field is an SDNV that contains the bundle processing control flags 1079 discussed in Section 4.2 above. 1081 Destination EID: The Destination EID field contains the encoded 1082 representation of the endpoint ID of the bundle's destination, i.e., 1083 the endpoint containing the node(s) at which the bundle is to be 1084 delivered. 1086 Source node ID: The Source node ID field contains the encoded 1087 representation of an endpoint ID that identifies the node from which 1088 the bundle was initially transmitted, except that it may contain the 1089 null endpoint ID in the event that the bundle's source chooses to 1090 remain anonymous. 1092 Report-to EID: The Report-to EID field contains the encoded 1093 representation of the ID of the endpoint to which status reports 1094 pertaining to the forwarding and delivery of this bundle are to be 1095 transmitted. 1097 Creation Timestamp: The creation timestamp is a pair of SDNVs that, 1098 together with the source node ID and (if the bundle is a fragment) 1099 the fragment offset and payload length, serve to identify the 1100 bundle. The first SDNV of the timestamp is the bundle's creation 1101 time, while the second is the bundle's creation timestamp sequence 1102 number. Bundle creation time is the time -- expressed in seconds 1103 since the start of the year 2000, on the Coordinated Universal Time 1104 (UTC) scale [UTC] -- at which the transmission request was received 1105 that resulted in the creation of the bundle. Sequence count is the 1106 latest value (as of the time at which that transmission request was 1107 received) of a monotonically increasing positive integer counter 1108 managed by the source node's bundle protocol agent that may be reset 1109 to zero whenever the current time advances by one second. For nodes 1110 that lack accurate clocks (that is, nodes that are not at all 1111 moments able to determine the current UTC time to within 30 1112 seconds), bundle creation time MUST be set to zero and the counter 1113 used as the source of the bundle sequence count MUST NEVER be reset 1114 to zero. In either case, a source Bundle Protocol Agent must never 1115 create two distinct bundles with the same source node ID and bundle 1116 creation timestamp. The combination of source node ID and bundle 1117 creation timestamp serves to identify a single transmission request, 1118 enabling it to be acknowledged by the receiving application 1119 (provided the source node ID is not the null endpoint ID). 1121 Lifetime: The lifetime field is an SDNV that indicates the time at 1122 which the bundle's payload will no longer be useful, encoded as a 1123 number of seconds past the creation time. When bundle's age exceeds 1124 its lifetime, bundle nodes need no longer retain or forward the 1125 bundle; the bundle SHOULD be deleted from the network. 1127 Inventory: The Primary block may contain an accounting of all blocks 1128 that were in the bundle at the time it was transmitted from the 1129 source node. This accounting comprises an inventory list length (an 1130 SDNV) followed by an inventory list (an array of N octets, where N 1131 is the value of the inventory list length). This feature is 1132 optional: if the inventory is to be omitted, the inventory length 1133 must be set to zero. Otherwise the values of the octets in the 1134 inventory list must be the block types of all of the non-primary 1135 blocks in the bundle as originally transmitted, exactly one list 1136 element per block. Since a bundle may contain multiple instances of 1137 a given block type, multiple elements of the inventory list may have 1138 the same value. The order of block types appearing in the inventory 1139 list is undefined. 1141 Fragment Offset: If the Bundle Processing Control Flags of this 1142 Primary block indicate that the bundle is a fragment, then the 1143 Fragment Offset field is an SDNV indicating the offset from the 1144 start of the original application data unit at which the bytes 1145 comprising the payload of this bundle were located. If not, then the 1146 Fragment Offset field is omitted from the block. 1148 Total Application Data Unit Length: If the Bundle Processing Control 1149 Flags of this Primary block indicate that the bundle is a fragment, 1150 then the Total Application Data Unit Length field is an SDNV 1151 indicating the total length of the original application data unit of 1152 which this bundle's payload is a part. If not, then the Total 1153 Application Data Unit Length field is omitted from the block. 1155 CRC: If and only if the CRC type in the Bundle Processing Control 1156 Flags of this Primary block is non-zero, a CRC is appended to the 1157 primary block. The length of the CRC is 8 bits, 16 bits, or 32 bits 1158 as indicated by the CRC type. The CRC is computed over the 1159 concatenation of all bytes of the primary block including the CRC 1160 field itself, which for this purpose is temporarily populated with 1161 the value zero. 1163 4.5.2. Canonical Bundle Block Format 1165 Every bundle block of every type other than the primary bundle block 1166 comprises the following fields, in this order: 1168 . Block type code, expressed as an 8-bit unsigned binary integer. 1169 Bundle block type code 1 indicates that the block is a bundle 1170 payload block. Block type codes 2 through 10 are defined as 1171 noted later in this specification. Block type codes 192 1172 through 255 are not defined in this specification and are 1173 available for private and/or experimental use. All other values 1174 of the block type code are reserved for future use. 1175 . Block number, an unsigned integer expressed as an SDNV. The 1176 block number uniquely identifies the block within the bundle, 1177 enabling blocks (notably bundle security protocol blocks) to 1178 explicitly reference other blocks in the same bundle. Block 1179 numbers need not be in continuous sequence, and blocks need not 1180 appear in block number sequence in the bundle. The block number 1181 of the payload block is always zero. 1182 . Block processing control flags, an unsigned integer expressed 1183 as an SDNV. The individual bits of this integer are used to 1184 invoke selected block processing control features. 1185 . Block data length, an unsigned integer expressed as an SDNV. 1186 The Block data length field contains the aggregate length of 1187 all remaining fields of the block, i.e., the block-type- 1188 specific data fields. 1189 . Block-type-specific data fields, whose format and order are 1190 type-specific and whose aggregate length in octets is the value 1191 of the block data length field. All multi-byte block-type- 1192 specific data fields are represented in network byte order. 1194 +----------------+----------------+----------------+---------------+ 1196 | Block type |Block number (*)| Proc. Flags (*)| Blk length(*) | 1198 +----------------+----------------+----------------+---------------+ 1200 / Block body data (variable) / 1202 +------------------------------------------------------------------+ 1204 Figure 6: Block Layout 1206 4.5.3. Bundle Payload Block 1208 The fields of the bundle payload block are: 1210 Block Type: The Block Type field is a 1-byte field that indicates 1211 the type of the block. For the bundle payload block, this field 1212 contains the value 1. 1214 Block Number: The Block Number field is an SDNV that contains the 1215 unique identifying number of the block. The block number of the 1216 bundle payload block is always zero. 1218 Block Processing Control Flags: The Block Processing Control Flags 1219 field is an SDNV that contains the block processing control flags 1220 discussed in Section 4.3 above. 1222 Block Data Length: The Block Data Length field is an SDNV that 1223 contains the aggregate length of all remaining fields of the Payload 1224 block - which is to say, the length of the bundle's payload. 1226 Block-type-specific Data: The Block-type-specific Data field of the 1227 Payload Block contains the "payload", i.e., the application data 1228 carried by this bundle. 1230 That is, bundle payload blocks conform to the canonical format 1231 described in the previous section. 1233 4.6. Extension Blocks 1235 "Extension blocks" are all blocks other than the primary and payload 1236 blocks. Because not all extension blocks are defined in the Bundle 1237 Protocol specification (the present document), not all nodes 1238 conforming to this specification will necessarily instantiate Bundle 1239 Protocol implementations that include procedures for processing 1240 (that is, recognizing, parsing, acting on, and/or producing) all 1241 extension blocks. It is therefore possible for a node to receive a 1242 bundle that includes extension blocks that the node cannot process. 1244 Whenever a bundle is forwarded that contains one or more extension 1245 blocks that could not be processed, the "Block was forwarded without 1246 being processed" flag must be set to 1 within the block processing 1247 flags of each such block. For each block flagged in this way, the 1248 flag may optionally be cleared (i.e., set to zero) by another node 1249 that subsequently receives the bundle and is able to process that 1250 block; the specifications defining the various extension blocks are 1251 expected to define the circumstances under which this flag may be 1252 cleared, if any. 1254 The extension blocks of the Bundle Security Protocol (block types 2, 1255 3, and 4) are defined separately in the Bundle Security Protocol 1256 specification (work in progress). 1258 The following extension blocks are defined in the current document. 1260 4.6.1. Current Custodian 1262 The Current Custodian block, block type 5, identifies a node that is 1263 known to have accepted custody of the bundle. The block-type- 1264 specific data of this block is the encoded representation of the 1265 node ID of a custodian. The bundle MAY contain one or more 1266 occurrences of this type of block. 1268 4.6.2. Flow Label 1270 The Flow Label block, block type 6, indicates the flow label that is 1271 intended to govern transmission of the bundle by convergence-layer 1272 adapters. The syntax and semantics of BP flow labels are beyond the 1273 scope of this document. 1275 4.6.3. Previous Node ID 1277 The Previous Node ID block, block type 7, identifies the node that 1278 forwarded this bundle to the local node; its block-type-specific 1279 data is the encoded representation of the node ID of that node. If 1280 the local node is the source of the bundle, then the bundle MUST NOT 1281 contain any Previous Node ID block. Otherwise the bundle MUST 1282 contain one (1) occurrence of this type of block. If present, the 1283 Previous Node ID block MUST be the FIRST block following the primary 1284 block, as the processing of other extension blocks may depend on its 1285 value. 1287 4.6.4. Bundle Age 1289 The Bundle Age block, block type 9, contains the number of seconds 1290 that have elapsed between the time the bundle was created and time 1291 at which it was most recently forwarded. It is intended for use by 1292 nodes lacking access to an accurate clock, to aid in determining the 1293 time at which a bundle's lifetime expires. The block-type-specific 1294 data of this block is an SDNV containing the age of the bundle (the 1295 sum of all known intervals of the bundle's residence at forwarding 1296 nodes, up to the time at which the bundle was most recently 1297 forwarded) in seconds. If the bundle's creation time is zero, then 1298 the bundle MUST contain exactly one (1) occurrence of this type of 1299 block; otherwise, the bundle MAY contain at most one (1) occurrence 1300 of this type of block. 1302 4.6.5. Hop Count 1304 The Hop Count block, block type 10, contains two SDNVs, hop limit 1305 and hop count, in that order. It is mainly intended as a safety 1306 mechanism, a means of identifying bundles for removal from the 1307 network that can never be delivered due to a persistent forwarding 1308 error: a bundle may be deleted when its hop count exceeds its hop 1309 limit. Procedures for determining the appropriate hop limit for a 1310 block are beyond the scope of this specification. A bundle MAY 1311 contain at most one (1) occurrence of this type of block. 1313 5. Bundle Processing 1315 The bundle processing procedures mandated in this section and in 1316 Section 6 govern the operation of the Bundle Protocol Agent and the 1317 Application Agent administrative element of each bundle node. They 1318 are neither exhaustive nor exclusive. That is, supplementary DTN 1319 protocol specifications (including, but not restricted to, the 1320 Bundle Security Protocol [BSP]) may require that additional measures 1321 be taken at specified junctures in these procedures. Such additional 1322 measures shall not override or supersede the mandated bundle 1323 protocol procedures, except that they may in some cases make these 1324 procedures moot by requiring, for example, that implementations 1325 conforming to the supplementary protocol terminate the processing of 1326 a given incoming or outgoing bundle due to a fault condition 1327 recognized by that protocol. 1329 5.1. Generation of Administrative Records 1331 All transmission of bundles is in response to bundle transmission 1332 requests presented by nodes' application agents. When required to 1333 "generate" an administrative record (such as a bundle status report 1334 or a custody signal), the bundle protocol agent itself is 1335 responsible for causing a new bundle to be transmitted, conveying 1336 that record. In concept, the bundle protocol agent discharges this 1337 responsibility by directing the administrative element of the node's 1338 application agent to construct the record and request its 1339 transmission as detailed in Section 6 below. In practice, the manner 1340 in which administrative record generation is accomplished is an 1341 implementation matter, provided the constraints noted in Section 6 1342 are observed. 1344 Under some circumstances, the requesting of status reports could 1345 result in an unacceptable increase in the bundle traffic in the 1346 network. For this reason, the generation of status reports is 1347 mandatory only in one case, the deletion of a bundle for which 1348 custody transfer is requested. In all other cases, the decision on 1349 whether or not to generate a requested status report is left to the 1350 discretion of the bundle protocol agent. Mechanisms that could 1351 assist in making such decisions, such as pre-placed agreements 1352 authorizing the generation of status reports under specified 1353 circumstances, are beyond the scope of this specification. 1355 Notes on administrative record terminology: 1357 . A "bundle reception status report" is a bundle status report 1358 with the "reporting node received bundle" flag set to 1. 1360 . A "custody acceptance status report" is a bundle status report 1361 with the "reporting node accepted custody of bundle" flag set 1362 to 1. 1363 . A "bundle forwarding status report" is a bundle status report 1364 with the "reporting node forwarded the bundle" flag set to 1. 1365 . A "bundle delivery status report" is a bundle status report 1366 with the "reporting node delivered the bundle" flag set to 1. 1367 . A "bundle deletion status report" is a bundle status report 1368 with the "reporting node deleted the bundle" flag set to 1. 1369 . A "Succeeded" custody signal is a custody signal with the 1370 "custody transfer succeeded" flag set to 1. 1371 . A "Failed" custody signal is a custody signal with the "custody 1372 transfer succeeded" flag set to zero. 1373 . A "current custodian" of a bundle is a node identified in a 1374 Current Custodian extension block of that bundle. 1376 5.2. Bundle Transmission 1378 The steps in processing a bundle transmission request are: 1380 Step 1: If custody transfer is requested for this bundle 1381 transmission then the destination must be a singleton endpoint. If, 1382 moreover, custody acceptance by the source node is required but the 1383 conditions under which custody of the bundle may be accepted are not 1384 satisfied, then the request cannot be honored and all remaining 1385 steps of this procedure must be skipped. 1387 Step 2: Transmission of the bundle is initiated. An outbound bundle 1388 must be created per the parameters of the bundle transmission 1389 request, with the retention constraint "Dispatch pending". The 1390 source node ID of the bundle must be either the EID of a singleton 1391 endpoint whose only member is the node of which the BPA is a 1392 component or else the null endpoint ID, indicating that the source 1393 of the bundle is anonymous. 1395 Step 3: Processing proceeds from Step 1 of Section 5.4. 1397 5.3. Bundle Dispatching 1399 The steps in dispatching a bundle are: 1401 Step 1: If the bundle's destination endpoint is an endpoint of which 1402 the node is a member, the bundle delivery procedure defined in 1403 Section 5.7 must be followed. 1405 Step 2: Processing proceeds from Step 1 of Section 5.4. 1407 5.4. Bundle Forwarding 1409 The steps in forwarding a bundle are: 1411 Step 1: The retention constraint "Forward pending" must be added to 1412 the bundle, and the bundle's "Dispatch pending" retention constraint 1413 must be removed. 1415 Step 2: The bundle protocol agent must determine whether or not 1416 forwarding is contraindicated for any of the reasons listed in 1417 Figure 12. In particular: 1419 . The bundle protocol agent must determine which node(s) to 1420 forward the bundle to. The bundle protocol agent may choose 1421 either to forward the bundle directly to its destination 1422 node(s) (if possible) or to forward the bundle to some other 1423 node(s) for further forwarding. The manner in which this 1424 decision is made may depend on the scheme name in the 1425 destination endpoint ID and/or other state but in any case is 1426 beyond the scope of this document. If the BPA elects to forward 1427 the bundle to some other node(s) for further forwarding: 1428 o If the "Bundle is critical" flag (in the bundle processing 1429 flags) is set to 1, then ALL nodes that have some 1430 plausible prospect of forwarding the bundle to its 1431 destination node(s) SHOULD be selected for this purpose. 1432 o If the agent finds it impossible to select any node(s) to 1433 forward the bundle to, then forwarding is contraindicated. 1434 . Provided the bundle protocol agent succeeded in selecting the 1435 node(s) to forward the bundle to, the bundle protocol agent 1436 must select the convergence layer adapter(s) whose services 1437 will enable the node to send the bundle to those nodes. If 1438 both the "Best-efforts forwarding requested" and the "Reliable 1439 forwarding is requested" bundle processing flags are set to 1, 1440 then all selected CLAs MUST be for bundle streaming CL 1441 protocols such as the proposed Bundle Streaming Service 1442 Protocol. Otherwise, if only the "Reliable forwarding is 1443 requested" bundle processing flag is set to 1, then all 1444 selected CLAs MUST be for reliable protocols such as TCP/IP. 1445 Otherwise, if only the "Best-efforts forwarding requested" 1446 bundle processing flag is set to 1, then all selected CLAs MUST 1447 be for best-efforts protocols such as UDP/IP. Otherwise, any 1448 available CLAs may be selected. The manner in which specific 1449 appropriate convergence layer adapters are selected is beyond 1450 the scope of this document. If the agent finds it impossible to 1451 select appropriate convergence layer adapters to use in 1452 forwarding this bundle, then forwarding is contraindicated. 1454 Step 3: If forwarding of the bundle is determined to be 1455 contraindicated for any of the reasons listed in Figure 12, then the 1456 Forwarding Contraindicated procedure defined in Section 5.4.1 must 1457 be followed; the remaining steps of Section 5 are skipped at this 1458 time. 1460 Step 4: If the bundle's custody transfer requested flag (in the 1461 bundle processing flags field) is set to 1, then the custody 1462 transfer procedure defined in Section 5.10.2 must be followed. 1464 Step 5: For each node selected for forwarding, the bundle protocol 1465 agent must invoke the services of the selected convergence layer 1466 adapter(s) in order to effect the sending of the bundle to that 1467 node. Determining the time at which the bundle is to be sent by each 1468 convergence layer adapter is an implementation matter. Note that: 1470 . The order in which convergence layer adapters send bundles 1471 SHOULD normally conform to the priority indicated in each 1472 bundle's bundle processing control flags field: all bundles of 1473 priority 255 sent from any single source should be sent before 1474 all bundles of priority 254 sent from the same source and so 1475 on. 1476 . But if the bundle contains a flow label extension block then 1477 that flow label value may identify overriding procedures for 1478 determining the order in which convergence layer adapters must 1479 send bundles, e.g., considering bundle source when determining 1480 the order in which bundles are sent. The definition of such 1481 procedures is beyond the scope of this specification. 1482 . If the bundle has a bundle age block, then at the last possible 1483 moment before the CLA initiates conveyance of the bundle node 1484 via the CL protocol the bundle age value MUST be increased by 1485 the difference between the current time and the time at which 1486 the bundle was received (or, if the local node is the source of 1487 the bundle, created). 1489 Step 6: When all selected convergence layer adapters have informed 1490 the bundle protocol agent that they have concluded their data 1491 sending procedures with regard to this bundle: 1493 . If the "request reporting of bundle forwarding" flag in the 1494 bundle's status report request field is set to 1, then a bundle 1495 forwarding status report should be generated, destined for the 1496 bundle's report-to endpoint ID. If the bundle has the retention 1497 constraint "custody accepted" and all of the nodes to which the 1498 bundle was forwarded are known to be unable to send bundles 1499 back to this node, then the reason code on this bundle 1500 forwarding status report must be "forwarded over unidirectional 1501 link"; otherwise, the reason code must be "no additional 1502 information". 1503 . The bundle's "Forward pending" retention constraint must be 1504 removed. 1506 5.4.1. Forwarding Contraindicated 1508 The steps in responding to contraindication of forwarding for some 1509 reason are: 1511 Step 1: The bundle protocol agent must determine whether or not to 1512 declare failure in forwarding the bundle for this reason. Note: this 1513 decision is likely to be influenced by the reason for which 1514 forwarding is contraindicated. 1516 Step 2: If forwarding failure is declared, then the Forwarding 1517 Failed procedure defined in Section 5.4.2 MUST be followed. 1519 Otherwise, (a) if the bundle's custody transfer requested flag (in 1520 the bundle processing flags field) is set to 1, then the custody 1521 transfer procedure defined in Section 5.10 MUST be followed; (b) 1522 when -- at some future time - the forwarding of this bundle ceases 1523 to be contraindicated, processing proceeds from Step 5 of Section 1524 5.4. 1526 5.4.2. Forwarding Failed 1528 The steps in responding to a declaration of forwarding failure for 1529 some reason are: 1531 Step 1: If the bundle's custody transfer requested flag (in the 1532 bundle processing flags field) is set to 1, custody transfer failure 1533 must be handled. The bundle protocol agent MUST handle the custody 1534 transfer failure by generating a "Failed" custody signal for the 1535 bundle, destined for the bundle's current custodian(s); the custody 1536 signal must contain a reason code corresponding to the reason for 1537 which forwarding was determined to be contraindicated. (Note that 1538 discarding the bundle will not delete it from the network, since 1539 each current custodian still has a copy.) 1541 If the bundle's custody transfer requested flag (in the bundle 1542 processing flags field) is set to 0, then the bundle protocol agent 1543 MAY forward the bundle back to the node that sent it, as identified 1544 by the Previous Node ID block. 1546 Step 2: If the bundle's destination endpoint is an endpoint of which 1547 the node is a member, then the bundle's "Forward pending" retention 1548 constraint must be removed. Otherwise, the bundle must be deleted: 1549 the bundle deletion procedure defined in Section 5.13 must be 1550 followed, citing the reason for which forwarding was determined to 1551 be contraindicated. 1553 5.5. Bundle Expiration 1555 A bundle expires when the bundle's age exceeds its lifetime as 1556 specified in the primary bundle block. Bundle age MAY be determined 1557 by subtracting the bundle's creation timestamp time from the current 1558 time if (a) that timestamp time is not zero and (b) the local node's 1559 clock is known to be accurate (as discussed in section 4.5.1 above); 1560 otherwise bundle age MUST be obtained from the Bundle Age extension 1561 block. Bundle expiration MAY occur at any point in the processing 1562 of a bundle. When a bundle expires, the bundle protocol agent MUST 1563 delete the bundle for the reason "lifetime expired": the bundle 1564 deletion procedure defined in Section 5.13 MUST be followed. 1566 5.6. Bundle Reception 1568 The steps in processing a bundle received from another node are: 1570 Step 1: The retention constraint "Dispatch pending" must be added to 1571 the bundle. 1573 Step 2: If the "request reporting of bundle reception" flag in the 1574 bundle's status report request field is set to 1, then a bundle 1575 reception status report with reason code "No additional information" 1576 should be generated, destined for the bundle's report-to endpoint 1577 ID. 1579 Step 3: For each block in the bundle that is an extension block that 1580 the bundle protocol agent cannot process: 1582 . If the block processing flags in that block indicate that a 1583 status report is requested in this event, then a bundle 1584 reception status report with reason code "Block unintelligible" 1585 should be generated, destined for the bundle's report-to 1586 endpoint ID. 1587 . If the block processing flags in that block indicate that the 1588 bundle must be deleted in this event, then the bundle protocol 1589 agent must delete the bundle for the reason "Block 1590 unintelligible"; the bundle deletion procedure defined in 1591 Section 5.13 must be followed and all remaining steps of the 1592 bundle reception procedure must be skipped. 1593 . If the block processing flags in that block do NOT indicate 1594 that the bundle must be deleted in this event but do indicate 1595 that the block must be discarded, then the bundle protocol 1596 agent must remove this block from the bundle. 1597 . If the block processing flags in that block indicate NEITHER 1598 that the bundle must be deleted NOR that the block must be 1599 discarded, then the bundle protocol agent must set to 1 the 1600 "Block was forwarded without being processed" flag in the block 1601 processing flags of the block. 1603 Step 4: If the bundle's custody transfer requested flag (in the 1604 bundle processing flags field) is set to 1 and the bundle has the 1605 same source node ID, creation timestamp, and (if the bundle is a 1606 fragment) fragment offset and payload length as another bundle that 1607 (a) has not been discarded and (b) currently has the retention 1608 constraint "Custody accepted", custody transfer redundancy must be 1609 handled. Otherwise, processing proceeds from Step 5. The bundle 1610 protocol agent must handle custody transfer redundancy by generating 1611 a "Failed" custody signal for this bundle with reason code 1612 "Redundant reception", destined for this bundle's current custodian, 1613 and removing this bundle's "Dispatch pending" retention constraint. 1615 Step 5: Processing proceeds from Step 1 of Section 5.3. 1617 5.7. Local Bundle Delivery 1619 The steps in processing a bundle that is destined for an endpoint of 1620 which this node is a member are: 1622 Step 1: If the received bundle is a fragment, the application data 1623 unit reassembly procedure described in Section 5.9 must be followed. 1624 If this procedure results in reassembly of the entire original 1625 application data unit, processing of this bundle (whose fragmentary 1626 payload has been replaced by the reassembled application data unit) 1627 proceeds from Step 2; otherwise, the retention constraint 1628 "Reassembly pending" must be added to the bundle and all remaining 1629 steps of this procedure must be skipped. 1631 Step 2: Delivery depends on the state of the registration whose 1632 endpoint ID matches that of the destination of the bundle: 1634 . If the registration is in the Active state, then the bundle 1635 must be delivered subject to this registration (see Section 3.1 1636 above) as soon as all previously received bundles that are 1637 deliverable subject to this registration have been delivered. 1638 . If the registration is in the Passive state, then the 1639 registration's delivery failure action must be taken (see 1640 Section 3.1 above). 1642 Step 3: As soon as the bundle has been delivered: 1644 . If the "request reporting of bundle delivery" flag in the 1645 bundle's status report request field is set to 1, then a bundle 1646 delivery status report should be generated, destined for the 1647 bundle's report-to endpoint ID. Note that this status report 1648 only states that the payload has been delivered to the 1649 application agent, not that the application agent has processed 1650 that payload. 1651 . If the bundle's custody transfer requested flag (in the bundle 1652 processing flags field) is set to 1, custodial delivery must be 1653 reported. The bundle protocol agent must report custodial 1654 delivery by generating a "Succeeded" custody signal for the 1655 bundle, destined for the bundle's current custodian(s). 1657 5.8. Bundle Fragmentation 1659 It may at times be advantageous for bundle protocol agents to reduce 1660 the sizes of bundles in order to forward them. This might be the 1661 case, for example, if a node to which a bundle is to be forwarded is 1662 accessible only via intermittent contacts and no upcoming contact is 1663 long enough to enable the forwarding of the entire bundle. 1665 The size of a bundle can be reduced by "fragmenting" the bundle. To 1666 fragment a bundle whose payload is of size M is to replace it with 1667 two "fragments" -- new bundles with the same source node ID and 1668 creation timestamp as the original bundle -- whose payloads are the 1669 first N and the last (M - N) bytes of the original bundle's payload, 1670 where 0 < N < M. Note that fragments may themselves be fragmented, 1671 so fragmentation may in effect replace the original bundle with more 1672 than two fragments. (However, there is only one 'level' of 1673 fragmentation, as in IP fragmentation.) 1675 Any bundle that has any Current Custodian extension block citing any 1676 node other than the local node MUST NOT be fragmented. This 1677 restriction aside, any bundle whose primary block's bundle 1678 processing flags do NOT indicate that it must not be fragmented may 1679 be fragmented at any time, for any purpose, at the discretion of the 1680 bundle protocol agent. 1682 Fragmentation shall be constrained as follows: 1684 . The concatenation of the payloads of all fragments produced by 1685 fragmentation must always be identical to the payload of the 1686 bundle that was fragmented. Note that the payloads of fragments 1687 resulting from different fragmentation episodes, in different 1688 parts of the network, may be overlapping subsets of the 1689 original bundle's payload. 1690 . The bundle processing flags in the primary block of each 1691 fragment must differ from those of the bundle that is being 1692 fragmented, in that they must indicate that the bundle is a 1693 fragment, and both fragment offset and total application data 1694 unit length must be provided at the end of each fragment's 1695 primary bundle block. Additionally, the CRC of the bundle that 1696 is being fragmented, if any, must be replaced in each fragment 1697 by a new CRC computed for the primary block of that fragment. 1698 . The primary blocks of the fragments will differ from that of 1699 the fragmented bundle as noted above. 1700 . The payload blocks of fragments will differ from that of the 1701 fragmented bundle as noted above. 1702 . If the bundle being fragmented is not a fragment or is the 1703 fragment with offset zero, then all extension blocks of the 1704 bundle being fragmented MUST be replicated in the fragment 1705 whose offset is zero. 1706 . Each extension block whose "Block must be replicated in every 1707 fragment" flag, in the block processing flags, is set to 1 MUST 1708 be replicated in every fragment. 1709 . Beyond these rules, replication of extension blocks in the 1710 fragments is an implementation matter. 1711 . If the local node had taken custody of the fragmented bundle, 1712 then the BPA MUST release custody of the fragmented bundle 1713 before fragmentation occurs and MUST take custody of every 1714 fragment. 1716 5.9. Application Data Unit Reassembly 1718 If the concatenation -- as informed by fragment offsets and payload 1719 lengths -- of the payloads of all previously received fragments with 1720 the same source node ID and creation timestamp as this fragment, 1721 together with the payload of this fragment, forms a byte array whose 1722 length is equal to the total application data unit length in the 1723 fragment's primary block, then: 1725 . This byte array -- the reassembled application data unit -- 1726 must replace the payload of this fragment. 1727 . For each fragmentary bundle whose payload is a subset of the 1728 reassembled application data unit, for which custody transfer 1729 is requested but the BPA has not yet taken custody, the BPA 1730 must take custody of that bundle. 1731 . The BPA must then release custody of all fragments whose 1732 payload is a subset of the reassembled application data unit, 1733 for which it has taken custody. 1735 . The "Reassembly pending" retention constraint must be removed 1736 from every other fragment whose payload is a subset of the 1737 reassembled application data unit. 1739 Note: reassembly of application data units from fragments occurs at 1740 the nodes that are members of destination endpoints as necessary; an 1741 application data unit may also be reassembled at some other node on 1742 the path to the destination. 1744 5.10. Custody Transfer 1746 The decision as to whether or not to accept custody of a bundle is 1747 an implementation matter that may involve both resource and policy 1748 considerations. 1750 If the bundle protocol agent elects to accept custody of the bundle, 1751 then it must follow the custody acceptance procedure defined in 1752 Section 5.10.1. 1754 5.10.1. Custody Acceptance 1756 Procedures for acceptance of custody of a bundle are defined as 1757 follows. 1759 The retention constraint "Custody accepted" must be added to the 1760 bundle. 1762 If the "request reporting of custody acceptance" flag in the 1763 bundle's status report request field is set to 1, a custody 1764 acceptance status report should be generated, destined for the 1765 report-to endpoint ID of the bundle. However, if a bundle reception 1766 status report was generated for this bundle (Step 1 of Section 5.6), 1767 then this report SHOULD be generated by simply turning on the 1768 "Reporting node accepted custody of bundle" flag in that earlier 1769 report's status flags byte. 1771 The bundle protocol agent must generate a "Succeeded" custody signal 1772 for the bundle, destined for the bundle's current custodian(s). 1774 The bundle protocol agent must assert the new current custodian for 1775 the bundle. It does so by inserting a new Current Custodian 1776 extension block whose value is the node ID of the local node or by 1777 changing the value of an existing Current Custodian extension block 1778 to the local node ID. 1780 The bundle protocol agent may set a custody transfer countdown timer 1781 for this bundle; upon expiration of this timer prior to expiration 1782 of the bundle itself and prior to custody transfer success for this 1783 bundle, the custody transfer failure procedure detailed in Section 1784 5.12 may be followed. The manner in which the countdown interval for 1785 such a timer is determined is an implementation matter. 1787 The bundle should be retained in persistent storage if possible. 1789 5.10.2. Custody Release 1791 When custody of a bundle is released, the "Custody accepted" 1792 retention constraint must be removed from the bundle and any custody 1793 transfer timer that has been established for this bundle should be 1794 destroyed. 1796 5.11. Custody Transfer Success 1798 Upon receipt of a "Succeeded" custody signal at a node that is a 1799 custodial node of the bundle identified in the custody signal, 1800 custody of the bundle must be released as described in Section 1801 5.10.2. 1803 5.12. Custody Transfer Failure 1805 Custody transfer is determined to have failed at a custodial node 1806 for that bundle when either (a) that node's custody transfer timer 1807 for that bundle (if any) expires or (b) a "Failed" custody signal 1808 for that bundle is received at that node. 1810 Upon determination of custody transfer failure, the action taken by 1811 the bundle protocol agent is implementation-specific and may depend 1812 on the nature of the failure. For example, if custody transfer 1813 failure was inferred from expiration of a custody transfer timer or 1814 was asserted by a "Failed" custody signal with the "Depleted 1815 storage" reason code, the bundle protocol agent might choose to re- 1816 forward the bundle, possibly on a different route (Section 5.4). 1817 Receipt of a "Failed" custody signal with the "Redundant reception" 1818 reason code, on the other hand, might cause the bundle protocol 1819 agent to release custody of the bundle and to revise its algorithm 1820 for computing countdown intervals for custody transfer timers. 1822 5.13. Bundle Deletion 1824 The steps in deleting a bundle are: 1826 Step 1: If the retention constraint "Custody accepted" currently 1827 prevents this bundle from being discarded, then: 1829 . Custody of the node is released as described in Section 5.10.2. 1830 . A bundle deletion status report citing the reason for deletion 1831 must be generated, destined for the bundle's report-to endpoint 1832 ID. 1834 Otherwise, if the "request reporting of bundle deletion" flag in the 1835 bundle's status report request field is set to 1, then a bundle 1836 deletion status report citing the reason for deletion should be 1837 generated, destined for the bundle's report-to endpoint ID. 1839 Step 2: All of the bundle's retention constraints must be removed. 1841 5.14. Discarding a Bundle 1843 As soon as a bundle has no remaining retention constraints it may be 1844 discarded. 1846 5.15. Canceling a Transmission 1848 When requested to cancel a specified transmission, where the bundle 1849 created upon initiation of the indicated transmission has not yet 1850 been discarded, the bundle protocol agent must delete that bundle 1851 for the reason "transmission cancelled". For this purpose, the 1852 procedure defined in Section 5.13 must be followed. 1854 6. Administrative Record Processing 1856 6.1. Administrative Records 1858 Administrative records are standard application data units that are 1859 used in providing some of the features of the Bundle Protocol. Two 1860 types of administrative records have been defined to date: bundle 1861 status reports and custody signals. Note that additional types of 1862 administrative records may be defined by supplementary DTN protocol 1863 specification documents. 1865 Every administrative record consists of a five-bit record type code 1866 followed by three bits of administrative record flags, followed by 1867 record content in type-specific format. Record type codes are 1868 defined as follows: 1870 +---------+--------------------------------------------+ 1872 | Value | Meaning | 1874 +=========+============================================+ 1875 | 00001 | Bundle status report. | 1877 +---------+--------------------------------------------+ 1879 | 00010 | Custody signal. | 1881 +---------+--------------------------------------------+ 1883 | (other) | Reserved for future use. | 1885 +---------+--------------------------------------------+ 1887 Figure 8: Administrative Record Type Codes 1889 +---------+--------------------------------------------+ 1891 | Value | Meaning | 1893 +=========+============================================+ 1895 | 0001 | Record is for a fragment; fragment | 1897 | | offset and length fields are present. | 1899 +---------+--------------------------------------------+ 1901 | (other) | Reserved for future use. | 1903 +---------+--------------------------------------------+ 1905 Figure 9: Administrative Record Flags 1907 The contents of the two types of administrative records defined in 1908 the present document are described below. 1910 6.1.1. Bundle Status Reports 1912 The transmission of 'bundle status reports' under specified 1913 conditions is an option that can be invoked when transmission of a 1914 bundle is requested. These reports are intended to provide 1915 information about how bundles are progressing through the system, 1916 including notices of receipt, custody transfer, forwarding, final 1917 delivery, and deletion. They are transmitted to the Report-to 1918 endpoints of bundles. 1920 +----------------+----------------+----------------+---------------+ 1921 | Status Flags | Reason code | Fragment offset (*) (if 1923 +----------------+----------------+----------------+---------------+ 1925 present) | Fragment length (*) (if present) | 1927 +----------------+----------------+----------------+---------------+ 1929 | Source node ID of bundle X (*) | 1931 +----------------+----------------+----------------+---------------+ 1933 | Copy of bundle X's Creation Timestamp time (*) | 1935 +----------------+----------------+----------------+---------------+ 1937 | Copy of bundle X's Creation Timestamp sequence number (*) | 1939 +----------------+----------------+----------------+---------------+ 1941 Figure 10: Bundle Status Report Format 1943 (*) Notes: 1945 The Fragment Offset field, if present, is an SDNV and is therefore 1946 variable length. A three-octet SDNV is shown here for convenience in 1947 representation. 1949 The Fragment Length field, if present, is an SDNV and is therefore 1950 variable length. A three-octet SDNV is shown here for convenience in 1951 representation. 1953 The Source Node ID and Creation Timestamp fields replicate the 1954 Source Node ID and Creation Timestamp fields in the primary block of 1955 the subject bundle. As such they are of variable length. Four-octet 1956 values are shown here for convenience in representation. 1958 The fields in a bundle status report are: 1960 Status Flags: A 1-byte field containing the following flags: 1962 +----------+--------------------------------------------+ 1964 | Value | Meaning | 1966 +==========+============================================+ 1967 | 00000001 | Reporting node received bundle. | 1969 +----------+--------------------------------------------+ 1971 | 00000010 | Reporting node accepted custody of bundle. | 1973 +----------+--------------------------------------------+ 1975 | 00000100 | Reporting node forwarded the bundle. | 1977 +----------+--------------------------------------------+ 1979 | 00001000 | Reporting node delivered the bundle. | 1981 +----------+--------------------------------------------+ 1983 | 00010000 | Reporting node deleted the bundle. | 1985 +----------+--------------------------------------------+ 1987 | 00100000 | Unused. | 1989 +----------+--------------------------------------------+ 1991 | 01000000 | Unused. | 1993 +----------+--------------------------------------------+ 1995 | 10000000 | Unused. | 1997 +----------+--------------------------------------------+ 1999 Figure 11: Status Flags for Bundle Status Reports 2001 Reason Code: A 1-byte field explaining the value of the flags in the 2002 status flags byte. The list of status report reason codes provided 2003 here is neither exhaustive nor exclusive; supplementary DTN protocol 2004 specifications (including, but not restricted to, the Bundle 2005 Security Protocol [BSP]) may define additional reason codes. Status 2006 report reason codes are defined as follows: 2008 +---------+--------------------------------------------+ 2010 | Value | Meaning | 2012 +=========+============================================+ 2013 | 0x00 | No additional information. | 2015 +---------+--------------------------------------------+ 2017 | 0x01 | Lifetime expired. | 2019 +---------+--------------------------------------------+ 2021 | 0x02 | Forwarded over unidirectional link. | 2023 +---------+--------------------------------------------+ 2025 | 0x03 | Transmission canceled. | 2027 +---------+--------------------------------------------+ 2029 | 0x04 | Depleted storage. | 2031 +---------+--------------------------------------------+ 2033 | 0x05 | Destination endpoint ID unintelligible. | 2035 +---------+--------------------------------------------+ 2037 | 0x06 | No known route to destination from here. | 2039 +---------+--------------------------------------------+ 2041 | 0x07 | No timely contact with next node on route. | 2043 +---------+--------------------------------------------+ 2045 | 0x08 | Block unintelligible. | 2047 +---------+--------------------------------------------+ 2049 | (other) | Reserved for future use. | 2051 +---------+--------------------------------------------+ 2053 Figure 12: Status Report Reason Codes 2055 Fragment Offset: If the bundle fragment bit is set in the status 2056 flags, then the offset (within the original application data unit) 2057 of the payload of the bundle that caused the status report to be 2058 generated is included here. 2060 Fragment length: If the bundle fragment bit is set in the status 2061 flags, then the length of the payload of the subject bundle is 2062 included here. 2064 Source Node ID of Subject Bundle: The source node ID of the bundle 2065 that caused the status report to be generated. 2067 Creation Timestamp of Subject Bundle: A copy of the creation 2068 timestamp of the bundle that caused the status report to be 2069 generated. 2071 6.1.2. Custody Signals 2073 Custody signals are administrative records that effect custody 2074 transfer operations. They are transmitted to the nodes that are the 2075 current custodians of bundles. 2077 Custody signals have the following format. 2079 Custody signal regarding bundle 'X': 2081 +----------------+----------------+----------------+---------------+ 2083 | Status | Fragment offset (*) (if present) | 2085 +----------------+----------------+----------------+---------------+ 2087 | Fragment length (*) (if present) | 2089 +----------------+----------------+----------------+---------------+ 2091 | Source node ID of bundle X (*) | 2093 +----------------+----------------+----------------+---------------+ 2095 | Copy of bundle X's Creation Timestamp time (*) | 2097 +----------------+----------------+----------------+---------------+ 2099 | Copy of bundle X's Creation Timestamp sequence number (*) | 2101 +----------------+----------------+----------------+---------------+ 2103 Figure 13: Custody Signal Format 2105 (*) Notes: 2107 The Fragment Offset field, if present, is an SDNV and is therefore 2108 variable length. A three-octet SDNV is shown here for convenience in 2109 representation. 2111 The Fragment Length field, if present, is an SDNV and is therefore 2112 variable length. A four-octet SDNV is shown here for convenience in 2113 representation. 2115 The Source Node ID and Creation Timestamp fields replicate the 2116 Source Node ID and Creation Timestamp fields in the primary block of 2117 the subject bundle. As such they are of variable length. Four-octet 2118 values are shown here for convenience in representation. 2120 The fields in a custody signal are: 2122 Status: A 1-byte field containing a 1-bit "custody transfer 2123 succeeded" flag followed by a 7-bit reason code explaining the value 2124 of that flag. Custody signal reason codes are defined as follows: 2126 +---------+--------------------------------------------+ 2128 | Value | Meaning | 2130 +=========+============================================+ 2132 | 0x00 | No additional information. | 2134 +---------+--------------------------------------------+ 2136 | 0x01 | Reserved for future use. | 2138 +---------+--------------------------------------------+ 2140 | 0x02 | Reserved for future use. | 2142 +---------+--------------------------------------------+ 2144 | 0x03 | Redundant (reception by a node that is a | 2146 | | custodial node for this bundle). | 2148 +---------+--------------------------------------------+ 2150 | 0x04 | Depleted storage. | 2152 +---------+--------------------------------------------+ 2153 | 0x05 | Destination endpoint ID unintelligible. | 2155 +---------+--------------------------------------------+ 2157 | 0x06 | No known route destination from here. | 2159 +---------+--------------------------------------------+ 2161 | 0x07 | No timely contact with next node on route. | 2163 +---------+--------------------------------------------+ 2165 | 0x08 | Block unintelligible. | 2167 +---------+--------------------------------------------+ 2169 | (other) | Reserved for future use. | 2171 +---------+--------------------------------------------+ 2173 Figure 14: Custody Signal Reason Codes 2175 Fragment offset: If the bundle fragment bit is set in the status 2176 flags, then the offset (within the original application data unit) 2177 of the payload of the bundle that caused the custody signal to be 2178 generated is included here. 2180 Fragment length: If the bundle fragment bit is set in the status 2181 flags, then the length of the payload of the subject bundle is 2182 included here. 2184 Source Node ID of Subject Bundle: The source node ID of the bundle 2185 that caused the custody signal to be generated. 2187 Creation Timestamp of Subject Bundle: A copy of the creation 2188 timestamp of the bundle to which the signal applies. 2190 6.2. Generation of Administrative Records 2192 Whenever the application agent's administrative element is directed 2193 by the bundle protocol agent to generate an administrative record 2194 with reference to some bundle, the following procedure must be 2195 followed: 2197 Step 1: The administrative record must be constructed. If the 2198 referenced bundle is a fragment, the administrative record must have 2199 the Fragment flag set and must contain the fragment offset and 2200 fragment length fields. The value of the fragment offset field must 2201 be the value of the referenced bundle's fragment offset, and the 2202 value of the fragment length field must be the length of the 2203 referenced bundle's payload. 2205 Step 2: A request for transmission of a bundle whose payload is this 2206 administrative record must be presented to the bundle protocol 2207 agent. 2209 6.3. Reception of Custody Signals 2211 For each received custody signal that has the "custody transfer 2212 succeeded" flag set to 1, the administrative element of the 2213 application agent must direct the bundle protocol agent to follow 2214 the custody transfer success procedure in Section 5.11. 2216 For each received custody signal that has the "custody transfer 2217 succeeded" flag set to 0, the administrative element of the 2218 application agent must direct the bundle protocol agent to follow 2219 the custody transfer failure procedure in Section 5.12. 2221 7. Services Required of the Convergence Layer 2223 7.1. The Convergence Layer 2225 The successful operation of the end-to-end bundle protocol depends 2226 on the operation of underlying protocols at what is termed the 2227 "convergence layer"; these protocols accomplish communication 2228 between nodes. A wide variety of protocols may serve this purpose, 2229 so long as each convergence layer protocol adapter provides a 2230 defined minimal set of services to the bundle protocol agent. This 2231 convergence layer service specification enumerates those services. 2233 7.2. Summary of Convergence Layer Services 2235 Each convergence layer protocol adapter is expected to provide the 2236 following services to the bundle protocol agent: 2238 . sending a bundle to a bundle node that is reachable via the 2239 convergence layer protocol; 2240 . delivering to the bundle protocol agent a bundle that was sent 2241 by a bundle node via the convergence layer protocol. 2243 The convergence layer service interface specified here is neither 2244 exhaustive nor exclusive. That is, supplementary DTN protocol 2245 specifications (including, but not restricted to, the Bundle 2246 Security Protocol [BSP]) may expect convergence layer adapters that 2247 serve BP implementations conforming to those protocols to provide 2248 additional services such as retransmitting data that were lost in 2249 transit, discarding bundle-conveying data units that the convergence 2250 layer protocol determines are corrupt or inauthentic, or reporting 2251 on the integrity and/or authenticity of delivered bundles. 2253 8. Security Considerations 2255 The bundle protocol has taken security into concern from the outset 2256 of its design. It was always assumed that security services would be 2257 needed in the use of the bundle protocol. As a result, the bundle 2258 protocol security architecture and the available security services 2259 are specified in an accompanying document, the Bundle Security 2260 Protocol specification [BSP]; an informative overview of this 2261 architecture is provided in [SECO]. 2263 The bundle protocol has been designed with the notion that it will 2264 be run over networks with scarce resources. For example, the 2265 networks might have limited bandwidth, limited connectivity, 2266 constrained storage in relay nodes, etc. Therefore, the bundle 2267 protocol must ensure that only those entities authorized to send 2268 bundles over such constrained environments are actually allowed to 2269 do so. All unauthorized entities should be prevented from consuming 2270 valuable resources as soon as practicable. 2272 Likewise, because of the potentially high latencies and delays 2273 involved in the networks that make use of the bundle protocol, data 2274 sources should be concerned with the integrity of the data received 2275 at the intended destination(s) and may also be concerned with 2276 ensuring confidentiality of the data as it traverses the network. 2277 Without integrity, the bundle payload data might be corrupted while 2278 in transit without the destination able to detect it. Similarly, the 2279 data source can be concerned with ensuring that the data can only be 2280 used by those authorized, hence the need for confidentiality. 2282 Internal to the bundle-aware overlay network, the bundle nodes 2283 should be concerned with the authenticity of other bundle nodes as 2284 well as the preservation of bundle payload data integrity as it is 2285 forwarded between bundle nodes. 2287 As a result, bundle security is concerned with the authenticity, 2288 integrity, and confidentiality of bundles conveyed among bundle 2289 nodes. This is accomplished via the use of two independent security- 2290 specific bundle blocks, which may be used together to provide 2291 multiple bundle security services or independently of one another, 2292 depending on perceived security threats, mandated security 2293 requirements, and security policies that must be enforced. 2295 To provide end-to-end bundle authenticity and integrity, the Block 2296 Integrity Block (BIB) is used. The BIB allows any security-enabled 2297 entity along the delivery path to ensure the integrity of the 2298 bundle's payload or any other block other than a Block 2299 Confidentiality Block. 2301 To provide payload confidentiality, the use of the Block 2302 Confidentiality Block (BCB) is available. The bundle payload, or any 2303 other block aside from the primary block and the Bundle Security 2304 Protocol blocks, may be encrypted to provide end-to-end payload 2305 confidentiality/privacy. 2307 Additionally, convergence-layer protocols that ensure authenticity 2308 of communication between adjacent nodes in BP network topology 2309 SHOULD be used where available, to minimize the ability of 2310 unauthenticated nodes to introduce inauthentic traffic into the 2311 network. 2313 Bundle security must not be invalidated by forwarding nodes even 2314 though they themselves might not use the Bundle Security Protocol. 2316 In particular, while blocks may be added to bundles transiting 2317 intermediate nodes, removal of blocks with the 'Discard block if it 2318 can't be processed' flag unset in the block processing control flags 2319 may cause security to fail. 2321 Inclusion of the Bundle Security Protocol in any Bundle Protocol 2322 implementation is RECOMMENDED. Use of the Bundle Security Protocol 2323 in Bundle Protocol operations is OPTIONAL. 2325 9. IANA Considerations 2327 The "dtn" and "ipn" URI schemes have been provisionally registered 2328 by IANA. See http://www.iana.org/assignments/uri-schemes.html for 2329 the latest details. 2331 Registries of scheme type numbers, extension block type numbers, and 2332 administrative record type numbers will be required. 2334 10. References 2336 10.1. Normative References 2338 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2339 Requirement Levels", BCP 14, RFC 2119, March 1997. 2341 [URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 2342 Resource Identifier (URI): Generic Syntax", RFC 3986, STD 66, 2343 January 2005. 2345 [URIREG] Thaler, D., Hansen, T., and T. Hardie, "Guidelines and 2346 Registration Procedures for URI Schemes", RFC 7595, BCP 35, June 2347 2015. 2349 10.2. Informative References 2351 [ARCH] V. Cerf et. al., "Delay-Tolerant Network Architecture", RFC 2352 4838, April 2007. 2354 [ASN1] "Abstract Syntax Notation One (ASN.1), "ASN.1 Encoding Rules: 2355 Specification of Basic Encoding Rules (BER), Canonical Encoding 2356 Rules (CER) and Distinguished Encoding Rules (DER)," ITU-T Rec. 2357 X.690 (2002) | ISO/IEC 8825- 1:2002", 2003. 2359 [BSP] Symington, S., "Bundle Security Protocol Specification", Work 2360 Progress, October 2007. 2362 [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource 2363 Identifiers (IRIs)", RFC 3987, January 2005. 2365 [RFC5050] Scott, M. and S. Burleigh, "Bundle Protocol 2366 Specification", RFC 5050, November 2007. 2368 [SECO] Farrell, S., Symington, S., Weiss, H., and P. Lovell, "Delay- 2369 Tolerant Networking Security Overview", Work Progress, July 2007. 2371 [SIGC] Fall, K., "A Delay-Tolerant Network Architecture for 2372 Challenged Internets", SIGCOMM 2003. 2374 [TUT] Warthman, F., "Delay-Tolerant Networks (DTNs): A Tutorial", 2375 . 2377 [UTC] Arias, E. and B. Guinot, "Coordinated universal time UTC: 2378 historical background and perspectives" in "Journees systemes de 2379 reference spatio-temporels", 2004. 2381 11. Acknowledgments 2383 This work is freely adapted from [RFC5050], which was an effort of 2384 the Delay Tolerant Networking Research Group. The following DTNRG 2385 participants contributed significant technical material and/or 2386 inputs to that document: Dr. Vinton Cerf of Google, Scott Burleigh, 2387 Adrian Hooke, and Leigh Torgerson of the Jet Propulsion Laboratory, 2388 Michael Demmer of the University of California at Berkeley, Robert 2389 Durst, Keith Scott, and Susan Symington of The MITRE Corporation, 2390 Kevin Fall of Intel Research, Stephen Farrell of Trinity College 2391 Dublin, Peter Lovell of SPARTA, Inc., Manikantan Ramadas of Ohio 2392 University, and Howard Weiss of SPARTA, Inc. 2394 This document was prepared using 2-Word-v2.0.template.dot. 2396 12. Significant Changes From RFC 5050 2398 Points on which this draft significantly differs from RFC 5050 2399 include the following: 2401 . Clarify the difference between transmission and forwarding. 2402 . Amplify discussion of custody transfer. Move current custodian 2403 to an extension block, of which there can be multiple 2404 occurrences (possible support for the MITRE idea of multiple 2405 concurrent custodians, from several years ago); define that 2406 block in this specification. 2407 . Introduce the concept of "node ID" as functionally distinct 2408 from endpoint ID, while having the same syntax. 2409 . Introduce a new method of encoding endpoint IDs (including node 2410 IDs) in a transmitted bundle, replacing both the "dictionary" 2411 and the CBHE compression mechanism. 2412 . Add ECOS features to primary block. 2413 . Restrict the scope of bundle prioritization to all bundles from 2414 the same source. 2415 . Restructure primary block, making it immutable. Add optional 2416 CRC and inventory. 2417 . Add optional CRCs to non-primary blocks. 2418 . Add block ID number to canonical block format (to support 2419 streamlined BSP). 2420 . Add bundle age extension block, defined in this specification. 2421 . Add previous node ID extension block, defined in this 2422 specification. 2423 . Add flow label block, *not* defined in this specification. 2424 . Add hop count extension block, defined in this specification. 2425 . Clean up a disconnect between fragmentation and custody 2426 transfer that Ed pointed out. 2427 . Remove "DTN time" values from admin records. 2429 13. Open Issues 2431 13.1. Definitions section structure 2433 Would it be better to restrict the Definitions section to 2434 definitions only, and move description, conceptual operation, 2435 potential implementation, justification, and commentary to one or 2436 more additional sections? Or would fractionating this information 2437 across multiple sections would make it harder to grasp? 2439 13.2. Payload nomenclature 2441 It has been proposed that (a) there is no need to define "nominal 2442 payload" and (b) "partial" payload would be better than 2443 "fragmentary" payload. (The term "nominal payload" is used in the 2444 definition of fragmentation.) 2446 13.3. Application Agent 2448 Does the discussion of Application Agent functionality need to be in 2449 the BP spec? If so, should there be a diagram explaining how the 2450 various components of the BPA interact? 2452 13.4. Bundle Endpoint definition 2454 Is the source of a bundle always a node, or do we want to define a 2455 way in which a set of nodes (an endpoint) can collectively transmit 2456 a bundle? Does the latter trace back to a use case we need to 2457 support? 2459 Is a bundle custodian always a node, or do we want to define a way 2460 in which a set of nodes (an endpoint) can collectively take custody 2461 of a bundle? Does the latter trace back to a use case we need to 2462 support?. 2464 13.5. Alignment with ICN 2466 Is it necessary to modify the bundle transmission procedure to 2467 enable BP to be used for information-centric networking, i.e., 2468 delivering data to a node who requests that data after it has 2469 already been transmitted? Specifically, would a DTN ICN cache point 2470 "transmit" data to a client (i.e., source a new bundle) or would it 2471 merely "forward" a previously transmitted bundle of which it has 2472 retained a copy? 2474 13.6. Implementation Architectures 2476 Should the BP spec be divided into two documents? One to talk about 2477 conops and context and one that focuses specifically on the 2478 protocol? 2480 13.7. Security protocol name 2482 Will the name of the DTN security protocol be Bundle Security 2483 Protocol or Streamlined Bundle Security Protocol? 2485 13.8. Bundle format 2487 Should the rules for defining block structure be presented at the 2488 start of section 4 or in the discussion of the payload block and the 2489 "last block" flag? Should we require that the payload block always 2490 be the last block of the bundle, so that the "last block" flag is no 2491 longer needed? (This would make reactive fragmentation easier.) 2493 13.9. SDNVs 2495 Should the SDNV discussion in 4.1 be deleted? 2497 13.10. Bundle Processing Control Flags 2499 Should the bit numbering convention described in section 4.2 be 2500 moved to another location in the document? 2502 13.11. Extended class of service features 2504 Should these features (critical bundle, best-efforts forwarding 2505 requested, reliable forwarding requested) be omitted from the 2506 primary block? If they are omitted, should these application- 2507 selected CoS markings be supported in some other way? If the 2508 "critical" CoS feature is retained, should it have a different 2509 name? 2511 Note: a node selection (route computation) procedure might consider 2512 the availability of CLAs that match the bundle's CoS when selecting 2513 a node to forward to, and that is entirely the business of the route 2514 computation procedure. (Not all route computation procedures will 2515 do so.) 2517 13.12. Primary block CRC type 2519 What are the best CRC options to support here? CRC-16-ARINC, CRC- 2520 16-CCITT, CRC-16-CDMA2000, CRC-16-DECT, etc.? Are there more than 4? 2522 13.13. Inventory 2524 Is a list of the block types of all blocks in the bundle as 2525 forwarded by the source node a good implementation of the requested 2526 "inventory" feature? If not, what would be better? 2528 13.14. Block numbers 2530 Should the payload always have block number zero? 2532 13.15. Clearing flag 2534 Should an node that is able to process a given extension block be 2535 permitted to clear block's "Block was forwarded without being 2536 processed" flag? 2538 13.16. Overriding BP spec 2540 Is a supplementary DTN protocol specification allowed to override or 2541 supersede the BP specification (other than making some BP procedures 2542 moot by requiring that the processing of a bundle be terminated 2543 under fault conditions recognized by that protocol)? 2545 13.17. Time of forwarding 2547 Should the BPA control the time at which a bundle is to be forwarded 2548 to another node, or should that determination be left to the 2549 selected convergence-layer protocol adapter(s)? 2551 13.18. Block multiplicity 2553 Would it be good to restrict BP extensions to one extension block 2554 per extension per bundle? That is, should we require that all 2555 information needed to implement a given BP extension for a given 2556 bundle be contained in a single extension block? 2558 This would entail encapsulating any necessary multiplicity for a 2559 given extension (for example, multiple Metadata records) within a 2560 single block. 2562 Among the advantages: no need for block numbers (block type would 2563 always be sufficient to identify the block), therefore no need for a 2564 block number generation mechanism; shorter and simpler inventory; 2565 simpler extension implementation (all information is in one block, 2566 no need to search through extension blocks for additional relevant 2567 information). 2569 Among the disadvantages: very different from RFC 5050; would in some 2570 cases require that security blocks operate on data structures that 2571 are internal to extension blocks rather than always operate on 2572 entire extension blocks. 2574 Appendix A. For More Information 2576 Please refer comments to dtn@ietf.org. The Delay Tolerant Networking 2577 Research Group (DTNRG) Web site is located at http://www.dtnrg.org. 2579 Copyright (c) 2015 IETF Trust and the persons identified as authors 2580 of the code. All rights reserved. 2582 Redistribution and use in source and binary forms, with or without 2583 modification, is permitted pursuant to, and subject to the license 2584 terms contained in, the Simplified BSD License set forth in Section 2585 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents 2586 (http://trustee.ietf.org/license-info). 2588 Authors' Addresses 2590 Scott Burleigh 2591 Jet Propulsion Laboratory, California Institute of Technology 2592 4800 Oak Grove Dr. 2593 Pasadena, CA 91109-8099 2594 US 2595 Phone: +1 818 393 3353 2596 EMail: Scott.Burleigh@jpl.nasa.gov 2598 Kevin Fall 2599 Carnegie Mellon University / Software Engineering Institute 2600 4500 Fifth Avenue 2601 Pittsburgh, PA 15213 2602 US 2603 Phone: +1 412 268 3304 2604 Email: kfall@cmu.edu 2606 Edward J. Birrane 2607 Johns Hopkins University Applied Physics Laboratory 2608 11100 Johns Hopkins Rd 2609 Laurel, MD 20723 2610 US 2611 Phone: +1 443 778 7423 2612 Email: Edward.Birrane@jhuapl.edu