[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-dtnwg-bp) 00 01 02 03 04 05 06

Delay-Tolerant Networking Working Group                     S. Burleigh
Internet Draft                          JPL, Calif. Inst. Of Technology
Intended status: Standards Track                                K. Fall
Expires: May 2017                      Carnegie Mellon University / SEI
                                                             E. Birrane
                                          APL, Johns Hopkins University
                                                       October 29, 2016

                              Bundle Protocol
                        draft-ietf-dtn-bpbis-06.txt


Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other documents
   at any time.  It is inappropriate to use Internet-Drafts as
   reference material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   This Internet-Draft will expire on May 2, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with
   respect to this document.  Code Components extracted from this
   document must include Simplified BSD License text as described in




Burleigh                   Expires May 2017                    [Page 1]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   Section 4.e of the Trust Legal Provisions and are provided without
   warranty as described in the Simplified BSD License.

Abstract

   This Internet Draft presents a specification for Bundle Protocol,
   adapted from the experimental Bundle Protocol specification
   developed by the Delay-Tolerant Networking Research group of the
   Internet Research Task Force and documented in RFC 5050.

Table of Contents


   1. Introduction...................................................3
   2. Conventions used in this document..............................5
   3. Service Description............................................5
      3.1. Definitions...............................................5
      3.2. Discussion of BP concepts.................................9
      3.3. Services Offered by Bundle Protocol Agents...............14
   4. Bundle Format.................................................14
      4.1. BP Fundamental Data Structures...........................15
         4.1.1. CRC Type............................................15
         4.1.2. CRC.................................................15
         4.1.3. Bundle Processing Control Flags.....................15
         4.1.4. Block Processing Control Flags......................17
         4.1.5. Identifiers.........................................18
            4.1.5.1. Endpoint ID....................................18
            4.1.5.2. Node ID........................................19
         4.1.6. DTN Time............................................19
         4.1.7. Creation Timestamp..................................19
         4.1.8. Block-type-specific Data............................19
      4.2. Bundle Representation....................................20
         4.2.1. Bundle..............................................20
         4.2.2. Primary Bundle Block................................20
         4.2.3. Canonical Bundle Block Format.......................22
      4.3. Extension Blocks.........................................23
         4.3.1. Current Custodian...................................24
         4.3.2. Previous Node.......................................24
         4.3.3. Bundle Age..........................................24
         4.3.4. Hop Count...........................................25
   5. Bundle Processing.............................................25
      5.1. Generation of Administrative Records.....................25
      5.2. Bundle Transmission......................................26
      5.3. Bundle Dispatching.......................................27
      5.4. Bundle Forwarding........................................27
         5.4.1. Forwarding Contraindicated..........................29
         5.4.2. Forwarding Failed...................................29


Burleigh                   Expires May 2017                    [Page 2]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


      5.5. Bundle Expiration........................................30
      5.6. Bundle Reception.........................................30
      5.7. Local Bundle Delivery....................................31
      5.8. Bundle Fragmentation.....................................32
      5.9. Application Data Unit Reassembly.........................33
      5.10. Custody Transfer........................................34
         5.10.1. Custody Acceptance.................................34
         5.10.2. Custody Release....................................35
      5.11. Custody Transfer Success................................35
      5.12. Custody Transfer Failure................................35
      5.13. Custody Transfer Deferral...............................36
      5.14. Bundle Deletion.........................................36
      5.15. Discarding a Bundle.....................................37
      5.16. Canceling a Transmission................................37
   6. Administrative Record Processing..............................37
      6.1. Administrative Records...................................37
         6.1.1. Bundle Status Reports...............................38
         6.1.2. Custody Signals.....................................40
      6.2. Generation of Administrative Records.....................43
      6.3. Reception of Custody Signals.............................44
   7. Services Required of the Convergence Layer....................44
      7.1. The Convergence Layer....................................44
      7.2. Summary of Convergence Layer Services....................44
   8. Security Considerations.......................................45
   9. IANA Considerations...........................................46
   10. References...................................................46
      10.1. Normative References....................................46
      10.2. Informative References..................................47
   11. Acknowledgments..............................................47
   12. Significant Changes from RFC 5050............................48
   Appendix A. For More Information.................................49
   Appendix B. CDDL expression......................................50

1. Introduction

   Since the publication of the Bundle Protocol Specification
   (Experimental RFC 5050[RFC5050]) in 2007, the Delay-Tolerant
   Networking Bundle Protocol has been implemented in multiple
   programming languages and deployed to a wide variety of computing
   platforms for a wide range of successful exercises.  This
   implementation and deployment experience has demonstrated the
   general utility of the protocol for challenged network operations.

   It has also, as expected, identified opportunities for making the
   protocol simpler, more capable, and easier to use.  The present
   document, standardizing the Bundle Protocol (BP), is adapted from
   RFC 5050 in that context.


Burleigh                   Expires May 2017                    [Page 3]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   This document describes version 7 of BP.

   Delay Tolerant Networking is a network architecture providing
   communications in and/or through highly stressed environments.
   Stressed networking environments include those with intermittent
   connectivity, large and/or variable delays, and high bit error
   rates.  To provide its services, BP may be viewed as sitting at the
   application layer of some number of constituent networks, forming a
   store-carry-forward overlay network.  Key capabilities of BP
   include:

     . Custodial forwarding
     . Ability to cope with intermittent connectivity, including cases
        where the sender and receiver are not concurrently present in
        the network
     . Ability to take advantage of scheduled, predicted, and
        opportunistic connectivity, whether bidirectional or
        unidirectional, in addition to continuous connectivity
     . Late binding of overlay network endpoint identifiers to
        underlying constituent network addresses

   For descriptions of these capabilities and the rationale for the DTN
   architecture, see [ARCH] and [SIGC].  [TUT] contains a tutorial-
   level overview of DTN concepts.

   BP's location within the standard protocol stack is as shown in
   Figure 1.  BP uses underlying "native" transport and/or network
   protocols for communications within a given constituent network.

   The interface between the bundle protocol and a specific underlying
   protocol is termed a "convergence layer adapter".

   Figure 1 shows three distinct transport and network protocols
   (denoted T1/N1, T2/N2, and T3/N3).

   +-----------+                                         +-----------+
   |   BP app  |                                         |   BP app  |
   +---------v-|   +->>>>>>>>>>v-+     +->>>>>>>>>>v-+   +-^---------+
   |   BP    v |   | ^    BP   v |     | ^   BP    v |   | ^   BP    |
   +---------v-+   +-^---------v-+     +-^---------v-+   +-^---------+
   | Trans1  v |   + ^  T1/T2  v |     + ^  T2/T3  v |   | ^ Trans3  |
   +---------v-+   +-^---------v-+     +-^---------v +   +-^---------+
   | Net1    v |   | ^  N1/N2  v |     | ^  N2/N3  v |   | ^ Net3    |
   +---------v-+   +-^---------v +     +-^---------v-+   +-^---------+
   |         >>>>>>>>^         >>>>>>>>>>^         >>>>>>>>^         |
   +-----------+   +-------------+     +-------------+   +-----------+
   |                     |                     |                     |


Burleigh                   Expires May 2017                    [Page 4]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   |<---- A network ---->|                     |<---- A network ---->|
   |                     |                     |                     |

         Figure 1: The Bundle Protocol in the Protocol Stack Model

   This document describes the format of the protocol data units
   (called "bundles") passed between entities participating in BP
   communications.

   The entities are referred to as "bundle nodes". This document does
   not address:

     . Operations in the convergence layer adapters that bundle nodes
        use to transport data through specific types of internets.
        (However, the document does discuss the services that must be
        provided by each adapter at the convergence layer.)
     . The bundle route computation algorithm.
     . Mechanisms for populating the routing or forwarding information
        bases of bundle nodes.
     . The mechanisms for securing bundles en route.
     . The mechanisms for managing bundle nodes.

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119 [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying RFC-2119 significance.

3. Service Description

3.1. Definitions

   Bundle - A bundle is a protocol data unit of BP, so named because
   negotiation of the parameters of a data exchange may be impractical
   in a delay-tolerant network: it is often better practice to "bundle"
   with a unit of data all metadata that might be needed in order to
   make the data immediately usable when delivered to applications.
   Each bundle comprises a sequence of two or more "blocks" of protocol
   data, which serve various purposes.

   Block - A bundle protocol block is one of the protocol data
   structures that together constitute a well-formed bundle.



Burleigh                   Expires May 2017                    [Page 5]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   Bundle payload - A bundle payload (or simply "payload") is the
   application data whose conveyance to the bundle's destination is the
   purpose for the transmission of a given bundle; it is the content of
   the bundle's payload block. The terms "bundle content", "bundle
   payload", and "payload" are used interchangeably in this document.

   Partial payload - A partial payload is a payload that comprises
   either the first N bytes or the last N bytes of some other payload
   of length M, such that 0 < N < M.

   Fragment - A fragment is a bundle whose payload block contains a
   partial payload.

   Bundle node - A bundle node (or, in the context of this document,
   simply a "node") is any entity that can send and/or receive bundles.
   Each bundle node has three conceptual components, defined below, as
   shown in Figure 2: a "bundle protocol agent", a set of zero or more
   "convergence layer adapters", and an "application agent".

   +-----------------------------------------------------------+
   |Node                                                       |
   |                                                           |
   | +-------------------------------------------------------+ |
   | |Application Agent                                      | |
   | |                                                       | |
   | | +--------------------------+ +----------------------+ | |
   | | |Administrative element    | |Application-specific  | | |
   | | |                          | |element               | | |
   | | |                          | |                      | | |
   | | +--------------------------+ +----------------------+ | |
   | |                ^                          ^           | |
   | |           Admin|records        Application|data       | |
   | |                |                          |           | |
   | +----------------v--------------------------v-----------+ |
   |                               ^                           |
   |                               | ADUs                      |
   |                               |                           |
   | +-----------------------------v-------------------------+ |
   | |Bundle Protocol Agent                                  | |
   | |                                                       | |
   | |                                                       | |
   | +-------------------------------------------------------+ |
   |        ^                 ^                        ^       |
   |        | Bundles         | Bundles        Bundles |       |
   |        |                 |                        |       |
   | +------v-----+     +-----v------+           +-----v-----+ |
   | |CLA 1       |     |CLA 2       |           |CLA n      | |


Burleigh                   Expires May 2017                    [Page 6]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   | |            |     |            |   . . .   |           | |
   | |            |     |            |           |           | |
   +-+------------+-----+------------+-----------+-----------+-+
            ^                 ^                        ^
         CL1|PDUs          CL2|PDUs                 CLn|PDUs
            |                 |                        |
     +------v-----+     +-----v------+           +-----v-----+
      Network 1          Network 2                Network n

                     Figure 2: Components of a BP Node

   Bundle protocol agent - The bundle protocol agent (BPA) of a node is
   the node component that offers the BP services and executes the
   procedures of the bundle protocol.

   Convergence layer adapter - A convergence layer adapter (CLA) is a
   node component that sends and receives bundles on behalf of the BPA,
   utilizing the services of some 'native' protocol stack that is
   supported in one of the networks within which the node is
   functionally located.

   Application agent - The application agent (AA) of a node is the node
   component that utilizes the BP services to effect communication for
   some user purpose. The application agent in turn has two elements,
   an administrative element and an application-specific element.

   Application-specific element - The application-specific element of
   an AA is the node component that constructs, requests transmission
   of, accepts delivery of, and processes units of user application
   data.

   Administrative element - The administrative element of an AA is the
   node component that constructs and requests transmission of
   administrative records (defined below), including status reports and
   custody signals, and accepts delivery of and processes any custody
   signals that the node receives.

   Administrative record - A BP administrative record is an application
   data unit that is exchanged between the administrative elements of
   nodes' application agents for some BP administrative purpose.  The
   formats of some fundamental administrative records (and of no other
   application data units) are defined in this specification.

   Bundle endpoint - A bundle endpoint (or simply "endpoint") is a set
   of zero or more bundle nodes that all identify themselves for BP
   purposes by some common identifier, called a "bundle endpoint ID"



Burleigh                   Expires May 2017                    [Page 7]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   (or, in this document, simply "endpoint ID"; endpoint IDs are
   described in detail in Section 4.4.1 below).

   Singleton endpoint - A singleton endpoint is an endpoint that always
   contains exactly one member.

   Registration - A registration is the state machine characterizing a
   given node's membership in a given endpoint.  Any single
   registration has an associated delivery failure action as defined
   below and must at any time be in one of two states: Active or
   Passive.

   Delivery - A bundle is considered to have been delivered at a node
   subject to a registration as soon as the application data unit that
   is the payload of the bundle, together with any relevant metadata
   (an implementation matter), has been presented to the node's
   application agent in a manner consistent with the state of that
   registration.

   Deliverability - A bundle is considered "deliverable" subject to a
   registration if and only if (a) the bundle's destination endpoint is
   the endpoint with which the registration is associated, (b) the
   bundle has not yet been delivered subject to this registration, and
   (c) the bundle has not yet been "abandoned" (as defined below)
   subject to this registration.

   Abandonment - To abandon a bundle subject to some registration is to
   assert that the bundle is not deliverable subject to that
   registration.

   Delivery failure action - The delivery failure action of a
   registration is the action that is to be taken when a bundle that is
   "deliverable" subject to that registration is received at a time
   when the registration is in the Passive state.

   Destination - The destination of a bundle is the endpoint comprising
   the node(s) at which the bundle is to be delivered (as defined
   below).

   Minimum reception group - The minimum reception group of an endpoint
   is the minimum number of members of the endpoint (nodes) at which
   the bundle must have been delivered in order for the bundle to be
   considered delivered to the endpoint.

   Transmission - A transmission is an attempt by a node's BPA to cause
   copies of a bundle to be delivered at all nodes in the minimum
   reception group of some endpoint (the bundle's destination) in


Burleigh                   Expires May 2017                    [Page 8]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   response to a transmission request issued by the node's application
   agent.

   Forwarding - To forward a bundle to a node is to invoke the services
   of a CLA in a sustained effort to cause a copy of the bundle to be
   received by that node.

   Discarding - To discard a bundle is to cease all operations on the
   bundle and functionally erase all references to it.  The specific
   procedures by which this is accomplished are an implementation
   matter.

   Retention constraint - A retention constraint is an element of the
   state of a bundle that prevents the bundle from being discarded.
   That is, a bundle cannot be discarded while it has any retention
   constraints.

   Deletion - To delete a bundle is to remove unconditionally all of
   the bundle's retention constraints, enabling the bundle to be
   discarded.

   Custodian - A custodian of a bundle is a node that has determined
   that it will retain a copy of that bundle for an indefinite period
   of time, forwarding and possibly re-forwarding the bundle as
   appropriate, until it detects one of the conditions under which it
   may cease being a custodian of that bundle (discussed later).

   Taking custody - To take custody of a bundle is to become a
   custodian of that bundle.

   Accepting custody - To accept custody of a bundle is to take custody
   of the bundle, mark the bundle in such a way as to indicate this
   custodianship to nodes that subsequently receive copies of the
   bundle, and announce this custodianship to all current custodians of
   the bundle.

   Refusing custody - To "refuse custody" of a bundle is to notify all
   current custodians of that bundle that an opportunity to take
   custody of the bundle has been declined.

   Releasing custody - To release custody of a bundle is to cease to be
   a custodian of the bundle.

3.2. Discussion of BP concepts

   Multiple instances of the same bundle (the same unit of DTN protocol
   data) might exist concurrently in different parts of a network --


Burleigh                   Expires May 2017                    [Page 9]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   possibly differing in some blocks -- in the memory local to one or
   more bundle nodes and/or in transit between nodes. In the context of
   the operation of a bundle node, a bundle is an instance (copy), in
   that node's local memory, of some bundle that is in the network.

   The payload for a bundle forwarded in response to a bundle
   transmission request is the application data unit whose location is
   provided as a parameter to that request. The payload for a bundle
   forwarded in response to reception of a bundle is the payload of the
   received bundle.

   In the most familiar case, a bundle node is instantiated as a single
   process running on a general-purpose computer, but in general the
   definition is meant to be broader: a bundle node might alternatively
   be a thread, an object in an object-oriented operating system, a
   special-purpose hardware device, etc.

   The manner in which the functions of the BPA are performed is wholly
   an implementation matter. For example, BPA functionality might be
   coded into each node individually; it might be implemented as a
   shared library that is used in common by any number of bundle nodes
   on a single computer; it might be implemented as a daemon whose
   services are invoked via inter-process or network communication by
   any number of bundle nodes on one or more computers; it might be
   implemented in hardware.

   Every CLA implements its own thin layer of protocol, interposed
   between BP and the (usually "top") protocol(s) of the underlying
   native protocol stack; this "CL protocol" may only serve to
   multiplex and de-multiplex bundles to and from the underlying native
   protocol, or it may offer additional CL-specific functionality. The
   manner in which a CLA sends and receives bundles is, again, wholly
   an implementation matter.  The definitions of CLAs and CL protocols
   are beyond the scope of this specification.

   Note that the administrative element of a node's application agent
   may itself, in some cases, function as a convergence-layer adapter.
   That is, outgoing bundles may be "tunneled" through encapsulating
   bundles:

     . An outgoing bundle constitutes a byte array. This byte array
        may, like any other, be presented to the bundle protocol agent
        as an application data unit that is to be transmitted to some
        endpoint.
     . The original bundle thus forms the payload of an encapsulating
        bundle that is forwarded using some other convergence-layer
        protocol(s).


Burleigh                   Expires May 2017                   [Page 10]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


     . When the encapsulating bundle is received, its payload is
        delivered to the peer application agent administrative element,
        which then instructs the bundle protocol agent to dispatch that
        original bundle in the usual way.

   The purposes for which this technique may be useful (such as cross-
   domain security) are beyond the scope of this specification.

   The only interface between the BPA and the application-specific
   element of the AA is the BP service interface. But between the BPA
   and the administrative element of the AA there is a (conceptual)
   private control interface in addition to the BP service interface.
   This private control interface enables the BPA and the
   administrative element of the AA to direct each other to take action
   under specific circumstances

   In the case of a node that serves simply as a BP "router", the AA
   may have no application-specific element at all. The application-
   specific elements of other nodes' AAs may perform arbitrarily
   complex application functions, perhaps even offering multiplexed DTN
   communication services to a number of other applications. As with
   the BPA, the manner in which the AA performs its functions is wholly
   an implementation matter.

   Singletons are the most familiar sort of endpoint, but in general
   the endpoint notion is meant to be broader. For example, the nodes
   in a sensor network might constitute a set of bundle nodes that
   identify themselves by a single common endpoint ID and thus form a
   single bundle endpoint. *Note* too that a given bundle node might
   identify itself by multiple endpoint IDs and thus be a member of
   multiple bundle endpoints.

   The destination of every bundle is an endpoint, which may or may not
   be singleton.  The source of every bundle is a node, identified by
   the endpoint ID for some singleton endpoint that contains that node.

   The minimum reception group of an endpoint may be any one of the
   following: (a) ALL of the nodes registered in an endpoint that is
   permitted to contain multiple nodes (in which case forwarding to the
   endpoint is functionally similar to "multicast" operations in the
   Internet, though possibly very different in implementation); (b) ANY
   N of the nodes registered in an endpoint that is permitted to
   contain multiple nodes, where N is in the range from zero to the
   cardinality of the endpoint; or (c) THE SOLE NODE registered in a
   singleton endpoint (in which case forwarding to the endpoint is
   functionally similar to "unicast" operations in the Internet).



Burleigh                   Expires May 2017                   [Page 11]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   The nature of the minimum reception group for a given endpoint can
   typically be determined from the endpoint's ID.  For some endpoint
   ID "schemes", the nature of the minimum reception group is fixed -
   in a manner that is defined by the scheme - for all endpoints
   identified under the scheme.  For other schemes, the nature of the
   minimum reception group is indicated by some lexical feature of the
   "scheme-specific part" of the endpoint ID, in a manner that is
   defined by the scheme.

   Any number of transmissions may be concurrently undertaken by the
   bundle protocol agent of a given node.

   When the bundle protocol agent of a node determines that a bundle
   must be forwarded to a node (either to a node that is a member of
   the bundle's destination endpoint or to some intermediate forwarding
   node) in the course of completing the successful transmission of
   that bundle, it invokes the services of a CLA in a sustained effort
   to cause a copy of the bundle to be received by that node.

   Upon reception, the processing of a bundle that has been received by
   a given node depends on whether or not the receiving node is
   registered in the bundle's destination endpoint. If it is, and if
   the payload of the bundle is non-fragmentary (possibly as a result
   of successful payload reassembly from fragmentary payloads,
   including the original payload of the newly received bundle), then
   the bundle is normally delivered to the node's application agent
   subject to the registration characterizing the node's membership in
   the destination endpoint.

   Whenever, for some implementation-specific reason, a node's BPA
   finds it impossible to immediately deliver a bundle that is
   deliverable, delivery of the bundle has failed.  In this event, the
   delivery failure action associated with the applicable registration
   must be taken. Delivery failure action MUST be one of the following:

     . defer delivery of the bundle subject to this registration until
        (a) this bundle is the least recently received of all bundles
        currently deliverable subject to this registration and (b)
        either the registration is polled or else the registration is
        in the Active state; or

     . abandon delivery of the bundle subject to this registration.

   An additional implementation-specific delivery deferral procedure
   MAY optionally be associated with the registration.




Burleigh                   Expires May 2017                   [Page 12]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   While the state of a registration is Passive, reception of a bundle
   that is deliverable subject to this registration MUST cause delivery
   of the bundle to be abandoned or deferred as mandated by the
   registration's current delivery failure action; in the latter case,
   any additional delivery deferral procedure associated with the
   registration MUST also be performed.

   While the state of a registration is Active, reception of a bundle
   that is deliverable subject to this registration MUST cause the
   bundle to be delivered automatically as soon as it is the next
   bundle that is due for delivery according to the BPA's bundle
   delivery scheduling policy, an implementation matter.

   Normally only registrations' registered delivery failure actions
   cause deliveries to be abandoned.

   Custody of a bundle MAY be taken only if the destination of the
   bundle is a singleton endpoint. Custody MAY be released only when
   either (a) notification is received that some other node has
   accepted custody of the same bundle; (b) notification is received
   that the bundle has been delivered at the (sole) node registered in
   the bundle's destination endpoint; (c) the current custodian chooses
   to fragment the bundle, releasing custody of the original bundle and
   taking custody of the fragments instead, or (d) the bundle is
   explicitly deleted for some reason, such as lifetime expiration.

   The custody transfer mechanism in BP provides a means of recovering
   from data loss along the path to the destination node.  When the
   custodian of a bundle forwards that bundle it SHOULD set a
   retransmission timer; reception of a responding custody signal of
   any kind prior to timer expiration MUST disable that timer. Upon
   expiration of that timer, the custodian MUST re-forward the bundle.
   When a bundle for which custody has been taken arrives at a node
   from which it must be forwarded, and that node determines that it
   will forward the bundle but will not take custody, the receiving
   node SHOULD send a "custody delegation" signal back to the custodian
   indicating the next node to which the bundle will be forwarded
   together with an estimate of the interval that will elapse between
   the time the bundle was received and the time at which it will be
   forwarded.  This mechanism is intended to facilitate accurate
   timeout interval calculation for this bundle.

   Computation of the timeout interval for a bundle's custody transfer
   timer (i.e., determination of the moment at which a responding
   custody signal is expected) is an implementation matter and may be
   dynamically responsive to changes in connectivity.  In some
   environments it may be impossible to compute this interval with


Burleigh                   Expires May 2017                   [Page 13]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   operationally satisfactory accuracy; in such environments the use of
   custody transfer services is contraindicated.

   Alternatively, when custody transfer for a given bundle is not
   requested, data loss along the path to the destination node can be
   minimized by utilizing reliable convergence-layer protocols between
   neighbors on all segments of the end-to-end path.  This approach may
   make more efficient use of links than custody transfer because a
   convergence-layer protocol may perform finer-grained retransmission
   than custody transfer does, retransmitting only the specific
   portions of a transmitted bundle that were not received, rather than
   the entire bundle.  However, in some environments there may be
   segments of the end-to-end path for which no reliable convergence-
   layer protocol is available; in such environments the use of
   reliable convergence-layer protocols wherever possible can reduce
   the incidence of data loss.

3.3. Services Offered by Bundle Protocol Agents

   The BPA of each node is expected to provide the following services
   to the node's application agent:

     . commencing a registration (registering the node in an
        endpoint);
     . terminating a registration;
     . switching a registration between Active and Passive states;
     . transmitting a bundle to an identified bundle endpoint;
     . canceling a transmission;
     . polling a registration that is in the Passive state;
     . delivering a received bundle.

4. Bundle Format

   The format of bundles SHALL conform to the Concise Binary Object
   Representation (CBOR [RFC7049]).

   Each bundle SHALL be a concatenated sequence of at least two blocks,
   represented as a CBOR indefinite-length array.  The first block in
   the sequence (the first item of the array) MUST be a primary bundle
   block in CBOR representation as described below; the bundle MUST
   have exactly one primary bundle block. The primary block MUST be
   followed by one or more canonical bundle blocks (additional array
   items) in CBOR representation as described below.  The last such
   block MUST be a payload block; the bundle MUST have exactly one
   payload block.  The last item of the array, immediately following
   the payload block, SHALL be a CBOR "break" stop code.



Burleigh                   Expires May 2017                   [Page 14]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


4.1. BP Fundamental Data Structures

4.1.1. CRC Type

   CRC type is an unsigned integer type code for which the following
   values (and no others) are valid:

     . 0 indicates "no CRC is present."
     . 1 indicates "a CRC-16 (a.k.a., CRC-16-ANSI) is present."
     . 2 indicates "a standard IEEE 802.3 CRC-32 is present."

   CRC type SHALL be represented as a CBOR unsigned integer.

4.1.2. CRC

   CRC SHALL be omitted from a block if and only if the block's CRC
   type code is zero.

   When not omitted, the CRC SHALL be represented as a CBOR unsigned
   integer.

4.1.3. Bundle Processing Control Flags

   Bundle processing control flags assert properties of the bundle as a
   whole rather than of any particular block of the bundle.  They are
   conveyed in the primary block of the bundle.

   The following properties are asserted by the bundle processing
   control flags:

     . The bundle is a fragment.  (Boolean)

     . The bundle's payload is an administrative record.  (Boolean)

     . The bundle must not be fragmented.  (Boolean)

     . Custody transfer requested for this bundle.  (Boolean)

     . The bundle's destination endpoint is a singleton.  (Boolean)

     . Acknowledgment by the user application is requested.  (Boolean)

     . Status time is requested in all status reports.  (Boolean)

     . The bundle contains a "manifest" extension block.  (Boolean)

     . Flags requesting types of status reports (all Boolean):


Burleigh                   Expires May 2017                   [Page 15]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


          o Request reporting of bundle reception.

          o Request reporting of custody transfer request processing.

          o Request reporting of bundle forwarding.

          o Request reporting of bundle delivery.

          o Request reporting of bundle deletion.

   If the bundle processing control flags indicate that the bundle's
   application data unit is an administrative record, then the custody
   transfer requested flag value must be zero and all status report
   request flag values must be zero.

   If the custody transfer requested flag value is 1, then the source
   node is requesting that every receiving node accept custody of the
   bundle.

   If the bundle's source node is omitted (i.e., the source node ID is
   the ID of the null endpoint, which has no members as discussed
   below; this option enables anonymous bundle transmission), then the
   bundle is not uniquely identifiable and all bundle protocol features
   that rely on bundle identity must therefore be disabled: the
   bundle's custody transfer requested flag value must be zero, the
   "Bundle must not be fragmented" flag value must be 1, and all status
   report request flag values must be zero.

   The bundle processing control flags SHALL be represented as a CBOR
   unsigned integer item containing a bit field of 16 bits indicating
   the control flag values as follows:

     . Bit 0 (the high-order bit, 0x8000): reserved.
     . Bit 1 (0x4000): reserved.
     . Bit 2 (0x2000): reserved.
     . Bit 3(0x1000): bundle deletion status reports are requested.
     . Bit 4(0x0800): bundle delivery status reports are requested.
     . Bit 5(0x0400): bundle forwarding status reports are requested.
     . Bit 6(0x0200): custody request processing status reports are
        requested.
     . Bit 7(0x0100): bundle reception status reports are requested.
     . Bit 8(0x0080): bundle contains a Manifest block.
     . Bit 9(0x0040): status time is requested in all status reports.
     . Bit 10(0x0020): user application acknowledgement is requested.
     . Bit 11(0x0010): destination is a singleton endpoint.
     . Bit 12(0x0008): custody transfer is requested.
     . Bit 13(0x0004): bundle must not be fragmented.


Burleigh                   Expires May 2017                   [Page 16]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


     . Bit 14(0x0002): payload is an administrative record.
     . Bit 15 (the low-order bit, 0x0001: bundle is a fragment.

4.1.4. Block Processing Control Flags

   The block processing control flags assert properties of canonical
   bundle blocks.  They are conveyed in the header of the block to
   which they pertain.

   The following properties are asserted by the block processing
   control flags:

     . This block must be replicated in every fragment.  (Boolean)

     . Status report must be transmitted if this block can't be
        processed.  (Boolean)

     . Block must be removed from the bundle if it can't be processed.
        (Boolean)

     . Bundle must be deleted if this block can't be processed.
        (Boolean)

   For each bundle whose bundle processing control flags indicate that
   the bundle's application data unit is an administrative record, or
   whose source node ID is the null endpoint ID as defined below, the
   value of the "Transmit status report if block can't be processed"
   flag in every canonical block of the bundle must be zero.

   The block processing control flags SHALL be represented as a CBOR
   unsigned integer item containing a bit field of 8 bits indicating
   the control flag values as follows:

     . Bit 0 (the high-order bit, 0x80): reserved.
     . Bit 1 (0x40): reserved.
     . Bit 2(0x20): reserved.
     . Bit 3(0x10): reserved.
     . Bit 4(0x08): bundle must be deleted if block can't be
        processed.
     . Bit 5(0x04): status report must be transmitted if block can't
        be processed.
     . Bit 6(0x02): block must be removed from bundle if it can't be
        processed.
     . Bit 7(the low-order bit, 0x01): block must be replicated in
        every fragment.




Burleigh                   Expires May 2017                   [Page 17]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


4.1.5. Identifiers

4.1.5.1. Endpoint ID

   The destinations of bundles are bundle endpoints, identified by text
   strings termed "endpoint IDs" (see Section 3.1). Each endpoint ID
   (EID) is a Uniform Resource Identifier (URI; [URI]). As such, each
   endpoint ID can be characterized as having this general structure:

   < scheme name > : < scheme-specific part, or "SSP" >

   The scheme identified by the < scheme name > in an endpoint ID is a
   set of syntactic and semantic rules that fully explain how to parse
   and interpret the SSP. The set of allowable schemes is effectively
   unlimited. Any scheme conforming to [URIREG] may be used in a bundle
   protocol endpoint ID.

   Note that, although endpoint IDs are URIs, implementations of the BP
   service interface may support expression of endpoint IDs in some
   internationalized manner (e.g., Internationalized Resource
   Identifiers (IRIs); see [RFC3987]).

   The endpoint ID "dtn:none" identifies the "null endpoint", the
   endpoint that by definition never has any members.

   Each BP endpoint ID (EID) SHALL be represented as a CBOR array
   comprising a 2-tuple.

   The first item of the array SHALL be the code number identifying the
   endpoint's URI scheme [URI], as defined in the registry of URI
   scheme code numbers for Bundle Protocol maintained by IANA as
   described in Section 9. [URIREG].  Each URI scheme code number SHALL
   be represented as a CBOR unsigned integer.

   The second item of the array SHALL be the applicable CBOR
   representation of the scheme-specific part (SSP) of the EID, defined
   as follows:

     . If the EID's URI scheme is "dtn" then the SSP SHALL be
        represented as a CBOR text string unless the EID's SSP is
        "none", in which case the SSP SHALL be represented as a CBOR
        unsigned integer with the value zero.
     . If the EID's URI scheme is "ipn" then the SSP SHALL be
        represented as a CBOR array comprising a 2-tuple.  The first
        item of this array SHALL be the EID's node number represented
        as a CBOR unsigned integer.  The second item of this array



Burleigh                   Expires May 2017                   [Page 18]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


        SHALL be the EID's service number represented as a CBOR
        unsigned integer.
     . Definitions of the CBOR representations of the SSPs of EIDs
        encoded in other URI schemes are included in the specifications
        defining those schemes.

4.1.5.2. Node ID

   For many purposes of the Bundle Protocol it is important to identify
   the node that is operative in some context.

   As discussed in 3.1 above, nodes are distinct from endpoints;
   specifically, an endpoint is a set of zero or more nodes.  But
   rather than define a separate namespace for node identifiers, we
   instead use endpoint identifiers to identify nodes, subject to the
   following restrictions:

      . Every node MUST be a member of at least one singleton endpoint.
      . The EID of any singleton endpoint of which a node is a member
        MAY be used to identify that node. A "node ID" is an EID that
        is used in this way.
      . A node's membership in a given singleton endpoint MUST be
        sustained at least until the nominal operation of the Bundle
        Protocol no longer depends on the identification of that node
        using that endpoint's ID.

4.1.6. DTN Time

   A DTN time is an unsigned integer indicating a count of seconds
   since the start of the year 2000 on the Coordinated Universal Time
   (UTC) scale [UTC].  Each DTN time SHALL be represented as a CBOR
   unsigned integer item.

4.1.7. Creation Timestamp

   Each creation timestamp SHALL be represented as a CBOR array item
   comprising a 2-tuple.

   The first item of the array SHALL be a DTN time.

   The second item of the array SHALL be the creation timestamp's
   sequence number, represented as a CBOR unsigned integer.

4.1.8. Block-type-specific Data

   Block-type-specific data in each block (other than the primary
   block) SHALL be the applicable CBOR representation of the content of


Burleigh                   Expires May 2017                   [Page 19]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   the block.  Details of this representation are included in the
   specification defining the block type.

4.2. Bundle Representation

   This section describes the primary block in detail and non-primary
   blocks in general. Rules for processing these blocks appear in
   Section 5 of this document.

   Note that supplementary DTN protocol specifications (including, but
   not restricted to, the Bundle Security Protocol [BPSEC]) may require
   that BP implementations conforming to those protocols construct and
   process additional blocks.

4.2.1. Bundle

   Each bundle SHALL be represented as a CBOR indefinite-length array.
   The first item of this array SHALL be the CBOR representation of a
   Primary Block.  Every other item of the array except the last SHALL
   be the CBOR representation of a Canonical Block.  The last item of
   the array SHALL be a CBOR "break" stop code.

4.2.2. Primary Bundle Block

   The primary bundle block contains the basic information needed to
   forward bundles to their destinations.

   Each primary block SHALL be represented as a CBOR array; the number
   of elements in the array SHALL be 8 (if the bundle is not a fragment
   and CRC type is zero) or 9 (if the bundle is not a fragment and CRC
   type is non-zero) or 10 (if the bundle is a fragment and CRC type is
   zero) or 11 (if the bundle is a fragment and CRC-type is non-zero).

   The fields of the primary bundle block SHALL be as follows, listed
   in the order in which they MUST appear:

   Version: An unsigned integer value indicating the version of the
   bundle protocol that constructed this block. The present document
   describes version 7 of the bundle protocol. Version number SHALL be
   represented as a CBOR unsigned integer item.

   Bundle Processing Control Flags: The Bundle Processing Control Flags
   are discussed in Section 4.1.3. above.

   CRC Type: CRC Type codes are discussed in Section 4.1.1. above.




Burleigh                   Expires May 2017                   [Page 20]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   Destination EID: The Destination EID field identifies the bundle
   endpoint that is the bundle's destination, i.e., the endpoint that
   contains the node(s) at which the bundle is to be delivered.

   Source node ID: The Source node ID field identifies the bundle node
   at which the bundle was initially transmitted, except that Source
   node ID may be the null endpoint ID in the event that the bundle's
   source chooses to remain anonymous.

   Report-to EID: The Report-to EID field identifies the bundle
   endpoint to which status reports pertaining to the forwarding and
   delivery of this bundle are to be transmitted.

   Creation Timestamp: The creation timestamp is a pair of unsigned
   integers that, together with the source node ID and (if the bundle
   is a fragment) the fragment offset, serve to identify the bundle.
   The first of these integers is the bundle's creation time, while the
   second is the bundle's creation timestamp sequence number. Bundle
   creation time shall be the time - expressed in seconds since the
   start of the year 2000, on the Coordinated Universal Time (UTC)
   scale [UTC] - at which the transmission request was received that
   resulted in the creation of the bundle. Sequence count shall be the
   latest value (as of the time at which that transmission request was
   received) of a monotonically increasing positive integer counter
   managed by the source node's bundle protocol agent that may be reset
   to zero whenever the current time advances by one second. For nodes
   that lack accurate clocks (that is, nodes that are not at all
   moments able to determine the current UTC time to within 30
   seconds), bundle creation time MUST be set to zero and the counter
   used as the source of the bundle sequence count MUST NEVER be reset
   to zero. In any case, a source Bundle Protocol Agent MUST NEVER
   create two distinct bundles with the same source node ID and bundle
   creation timestamp. The combination of source node ID and bundle
   creation timestamp serves to identify a single transmission request,
   enabling it to be acknowledged by the receiving application
   (provided the source node ID is not the null endpoint ID).

   Lifetime: The lifetime field is an unsigned integer that indicates
   the time at which the bundle's payload will no longer be useful,
   encoded as a number of seconds past the creation time. When a
   bundle's age exceeds its lifetime, bundle nodes need no longer
   retain or forward the bundle; the bundle SHOULD be deleted from the
   network. Bundle lifetime SHALL be represented as a CBOR unsigned
   integer item.

   Fragment offset: If and only if the Bundle Processing Control Flags
   of this Primary block indicate that the bundle is a fragment,


Burleigh                   Expires May 2017                   [Page 21]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   fragment offset SHALL be present in the primary block. Fragment
   offset SHALL be represented as a CBOR unsigned integer indicating
   the offset from the start of the original application data unit at
   which the bytes comprising the payload of this bundle were located.

   Total Application Data Unit Length: If and only if the Bundle
   Processing Control Flags of this Primary block indicate that the
   bundle is a fragment, total application data unit length SHALL be
   present in the primary block. Total application data unit length
   SHALL be represented as aCBOR unsigned integer indicating the total
   length of the original application data unit of which this bundle's
   payload is a part.

   CRC: If and only if the value of the CRC type field of this Primary
   block is non-zero, a CRC SHALL be present in the primary block.  The
   length and nature of the CRC SHALL be as indicated by the CRC type.
   The CRC SHALL be computed over the concatenation of all bytes of the
   primary block including the CRC field itself, which for this purpose
   SHALL be temporarily populated with the value zero.

4.2.3. Canonical Bundle Block Format

   Every block other than the primary block (which blocks are termed
   "canonical" blocks) SHALL be represented as a CBOR array; the number
   of elements in the array SHALL be 6 (if CRC type is zero) or 7
   (otherwise).

   The fields of every canonical block SHALL be as follows, listed in
   the order in which they MUST appear:

     . Block type code, an unsigned integer. Bundle block type code 1
        indicates that the block is a bundle payload block. Block type
        codes 2 through 9 are explicitly reserved as noted later in
        this specification.  Block type codes 192 through 255 are not
        reserved and are available for private and/or experimental use.
        All other block type code values are reserved for future use.
     . Block number, an unsigned integer. The block number uniquely
        identifies the block within the bundle, enabling blocks
        (notably bundle security protocol blocks) to explicitly
        reference other blocks in the same bundle. Block numbers need
        not be in continuous sequence, and blocks need not appear in
        block number sequence in the bundle. The block number of the
        payload block is always zero.
     . Block processing control flags as discussed in Section 4.1.4
        above.
     . CRC type as discussed in Section 4.1.1 above.



Burleigh                   Expires May 2017                   [Page 22]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


     . If and only if the value of the CRC type field of this block is
        non-zero, a CRC. If present, the length and nature of the CRC
        SHALL be as indicated by the CRC type and the CRC SHALL be
        computed over the concatenation of all bytes of the block
        including the CRC field itself, which for this purpose SHALL be
        temporarily populated with the value zero.
     . Block data length, an unsigned integer. The block data length
        field SHALL contain the aggregate length of all remaining
        fields of the block, i.e., the block-type-specific data fields.
        Block data length SHALL be represented as a CBOR unsigned
        integer item.
     . Block-type-specific data fields, whose nature and order are
        type-specific and whose aggregate length in octets is the value
        of the block data length field.  For the Payload Block in
        particular (block type 1), there SHALL be exactly one block-
        type-specific data field, termed the "payload", which SHALL be
        an application data unit, or some contiguous extent thereof,
        represented as a CBOR byte string.

4.3. Extension Blocks

   "Extension blocks" are all blocks other than the primary and payload
   blocks. Because not all extension blocks are defined in the Bundle
   Protocol specification (the present document), not all nodes
   conforming to this specification will necessarily instantiate Bundle
   Protocol implementations that include procedures for processing
   (that is, recognizing, parsing, acting on, and/or producing) all
   extension blocks. It is therefore possible for a node to receive a
   bundle that includes extension blocks that the node cannot process.
   The values of the block processing control flags indicate the action
   to be taken by the bundle protocol agent when this is the case.

   (Note that, while CBOR permits considerable flexibility in the
   encoding of bundles, this flexibility must not be interpreted as
   inviting increased complexity in protocol data unit structure.)

   The following extension blocks are defined in other DTN protocol
   specification documents as noted:

     . Block Integrity Block (block type 2) and Block Confidentiality
        Block (block type 3) are defined in the Bundle Security
        Protocol specification (work in progress).
     . Manifest Block (block type 4) is defined in the Manifest
        Extension Block specification (TBD). The manifest block
        identifies the blocks that were present in the bundle at the
        time it was created.  The bundle MUST contain one (1)
        occurrence of this type of block if the value of the "manifest"


Burleigh                   Expires May 2017                   [Page 23]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


        flag in the bundle processing control flags is 1; otherwise the
        bundle MUST NOT contain any Manifest block.
     . The Flow Label Block (block type 6) is defined in the Flow
        Label Extension Block specification (TBD).  The flow label
        block is intended to govern transmission of the bundle by
        convergence-layer adapters.

   The following extension blocks are defined in the current document.

4.3.1. Current Custodian

   The Current Custodian block, block type 5, identifies a node that is
   known to have accepted custody of the bundle.  The block-type-
   specific data of this block is the node ID of a custodian, which
   SHALL take the form of an endpoint ID represented as described in
   Section 4.1.5.2. above.  The bundle MAY contain one or more
   occurrences of this type of block.

4.3.2. Previous Node

   The Previous Node block, block type 7, identifies the node that
   forwarded this bundle to the local node (i.e., to the node at which
   the bundle currently resides); its block-type-specific data is the
   node ID of that forwarder node which SHALL take the form of a node
   ID represented as described in Section 4.1.5.2. above.  If the local
   node is the source of the bundle, then the bundle MUST NOT contain
   any previous node block.  Otherwise the bundle MUST contain one (1)
   occurrence of this type of block.  If present, the previous node
   block MUST be the FIRST block following the primary block, as the
   processing of other extension blocks may depend on its value.

4.3.3. Bundle Age

   The Bundle Age block, block type 8, contains the number of seconds
   that have elapsed between the time the bundle was created and time
   at which it was most recently forwarded.  It is intended for use by
   nodes lacking access to an accurate clock, to aid in determining the
   time at which a bundle's lifetime expires. The block-type-specific
   data of this block is an unsigned integer containing the age of the
   bundle in seconds, which SHALL be represented as a CBOR unsigned
   integer item. (The age of the bundle is the sum of all known
   intervals of the bundle's residence at forwarding nodes, up to the
   time at which the bundle was most recently forwarded, plus the
   summation of signal propagation time over all episodes of
   transmission between forwarding nodes.  Determination of these
   values is an implementation matter.) If the bundle's creation time
   is zero, then the bundle MUST contain exactly one (1) occurrence of


Burleigh                   Expires May 2017                   [Page 24]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   this type of block; otherwise, the bundle MAY contain at most one
   (1) occurrence of this type of block.

4.3.4. Hop Count

   The Hop Count block, block type 9, contains two unsigned integers,
   hop limit and hop count.  A "hop" is here defined as an occasion on
   which a bundle was forwarded from one node to another node.  The hop
   count block is mainly intended as a safety mechanism, a means of
   identifying bundles for removal from the network that can never be
   delivered due to a persistent forwarding error: a bundle SHOULD be
   deleted when its hop count exceeds its hop limit.  Procedures for
   determining the appropriate hop limit for a block are beyond the
   scope of this specification.  The block-type-specific data in a hop
   count block SHALL be represented as a CBOR array comprising a 2-
   tuple.  The first item of this array SHALL be the bundle's hop
   limit, represented as a CBOR unsigned integer.  The second item of
   this array SHALL be the bundle's hop count, represented as a CBOR
   unsigned integer. A bundle MAY contain at most one (1) occurrence of
   this type of block.

5. Bundle Processing

   The bundle processing procedures mandated in this section and in
   Section 6 govern the operation of the Bundle Protocol Agent and the
   Application Agent administrative element of each bundle node. They
   are neither exhaustive nor exclusive. Supplementary DTN protocol
   specifications (including, but not restricted to, the Bundle
   Security Protocol [BPSEC]) may augment, override, or supersede the
   mandates of this document.

5.1. Generation of Administrative Records

   All transmission of bundles is in response to bundle transmission
   requests presented by nodes' application agents. When required to
   "generate" an administrative record (such as a bundle status report
   or a custody signal), the bundle protocol agent itself is
   responsible for causing a new bundle to be transmitted, conveying
   that record. In concept, the bundle protocol agent discharges this
   responsibility by directing the administrative element of the node's
   application agent to construct the record and request its
   transmission as detailed in Section 6 below. In practice, the manner
   in which administrative record generation is accomplished is an
   implementation matter, provided the constraints noted in Section 6
   are observed.




Burleigh                   Expires May 2017                   [Page 25]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   Under some circumstances, the requesting of status reports could
   result in an unacceptable increase in the bundle traffic in the
   network. For this reason, the generation of status reports is
   mandatory only in two cases:

     . the reception of a bundle containing at least one block that
        cannot be processed, for which the value of the "transmit
        status report if block could not be processed" block processing
        flag is 1, and
     . the deletion of a bundle for which custody transfer is
        requested.

   In all other cases, the decision on whether or not to generate a
   requested status report is left to the discretion of the bundle
   protocol agent. Mechanisms that could assist in making such
   decisions, such as pre-placed agreements authorizing the generation
   of status reports under specified circumstances, are beyond the
   scope of this specification.

   Notes on administrative record terminology:

     . A "bundle reception status report" is a bundle status report
        with the "reporting node received bundle" flag set to 1.
     . A "custody transfer status report" is a bundle status report
        with the "reporting node attempted custody transfer" flag set
        to 1.
     . A "bundle forwarding status report" is a bundle status report
        with the "reporting node forwarded the bundle" flag set to 1.
     . A "bundle delivery status report" is a bundle status report
        with the "reporting node delivered the bundle" flag set to 1.
     . A "bundle deletion status report" is a bundle status report
        with the "reporting node deleted the bundle" flag set to 1.
     . A "current custodian" of a bundle is a node identified in a
        Current Custodian extension block of that bundle.

5.2. Bundle Transmission

   The steps in processing a bundle transmission request are:

   Step 1: If custody transfer is requested for this bundle
   transmission then the destination MUST be a singleton endpoint.  If,
   moreover, custody acceptance by the source node is required when
   custody is requested (an implementation matter) but the conditions
   under which custody of the bundle may be accepted are not satisfied,
   then the request cannot be honored and all remaining steps of this
   procedure MUST be skipped.



Burleigh                   Expires May 2017                   [Page 26]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   Step 2: Transmission of the bundle is initiated. An outbound bundle
   MUST be created per the parameters of the bundle transmission
   request, with the retention constraint "Dispatch pending". The
   source node ID of the bundle MUST be either the null endpoint ID,
   indicating that the source of the bundle is anonymous, or else the
   EID of a singleton endpoint whose only member is the node of which
   the BPA is a component.

   Step 3: Processing proceeds from Step 1 of Section 5.4.

5.3. Bundle Dispatching

   The steps in dispatching a bundle are:

   Step 1: If the bundle's destination endpoint is an endpoint of which
   the node is a member, the bundle delivery procedure defined in
   Section 5.7 MUST be followed.

   Step 2: Processing proceeds from Step 1 of Section 5.4.

5.4. Bundle Forwarding

   The steps in forwarding a bundle are:

   Step 1: The retention constraint "Forward pending" MUST be added to
   the bundle, and the bundle's "Dispatch pending" retention constraint
   MUST be removed.

   Step 2: The bundle protocol agent MUST determine whether or not
   forwarding is contraindicated for any of the reasons listed in
   Figure 4. In particular:

     . The bundle protocol agent MUST determine which node(s) to
        forward the bundle to.  The bundle protocol agent MAY choose
        either to forward the bundle directly to its destination
        node(s) (if possible) or to forward the bundle to some other
        node(s) for further forwarding. The manner in which this
        decision is made may depend on the scheme name in the
        destination endpoint ID and/or on other state but in any case
        is beyond the scope of this document. If the BPA elects to
        forward the bundle to some other node(s) for further forwarding
        but finds it impossible to select any node(s) to forward the
        bundle to, then forwarding is contraindicated.
     . Provided the bundle protocol agent succeeded in selecting the
        node(s) to forward the bundle to, the bundle protocol agent
        MUST select the convergence layer adapter(s) whose services
        will enable the node to send the bundle to those nodes.  The


Burleigh                   Expires May 2017                   [Page 27]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


        manner in which specific appropriate convergence layer adapters
        are selected is beyond the scope of this document. If the agent
        finds it impossible to select any appropriate convergence layer
        adapter(s) to use in forwarding this bundle, then forwarding is
        contraindicated.

   Step 3: If forwarding of the bundle is determined to be
   contraindicated for any of the reasons listed in Figure 4, then the
   Forwarding Contraindicated procedure defined in Section 5.4.1 MUST
   be followed; the remaining steps of Section 5 are skipped at this
   time.

   Step 4: If the bundle's custody transfer requested flag (in the
   bundle processing flags field) is set to 1, then the custody
   transfer procedure defined in Section 5.10 MUST be followed.

   Step 5: For each node selected for forwarding, the bundle protocol
   agent MUST invoke the services of the selected convergence layer
   adapter(s) in order to effect the sending of the bundle to that
   node. Determining the time at which the bundle protocol agent
   invokes convergence layer adapter services is a BPA implementation
   matter.  Determining the time at which each convergence layer
   adapter subsequently responds to this service invocation by sending
   the bundle is a convergence-layer adapter implementation matter.
   Note that:

     . If the bundle contains a flow label extension block then that
        flow label value MAY identify procedures for determining the
        order in which convergence layer adapters must send bundles,
        e.g., considering bundle source when determining the order in
        which bundles are sent.  The definition of such procedures is
        beyond the scope of this specification.
     . If the bundle has a bundle age block, then at the last possible
        moment before the CLA initiates conveyance of the bundle node
        via the CL protocol the bundle age value MUST be increased by
        the difference between the current time and the time at which
        the bundle was received (or, if the local node is the source of
        the bundle, created).

   Step 6: When all selected convergence layer adapters have informed
   the bundle protocol agent that they have concluded their data
   sending procedures with regard to this bundle:

     . If the "request reporting of bundle forwarding" flag in the
        bundle's status report request field is set to 1, then a bundle
        forwarding status report SHOULD be generated, destined for the
        bundle's report-to endpoint ID. If the bundle has the retention


Burleigh                   Expires May 2017                   [Page 28]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


        constraint "custody accepted" and all of the nodes to which the
        bundle was forwarded are known to be unable to send bundles
        back to this node, then the reason code on this bundle
        forwarding status report MUST be "forwarded over unidirectional
        link"; otherwise, the reason code MUST be "no additional
        information".
     . The bundle's "Forward pending" retention constraint MUST be
        removed.

5.4.1. Forwarding Contraindicated

   The steps in responding to contraindication of forwarding are:

   Step 1: The bundle protocol agent MUST determine whether or not to
   declare failure in forwarding the bundle. Note: this decision is
   likely to be influenced by the reason for which forwarding is
   contraindicated.

   Step 2: If forwarding failure is declared, then the Forwarding
   Failed procedure defined in Section 5.4.2 MUST be followed.

   Otherwise, (a) if the bundle's custody transfer requested flag (in
   the bundle processing flags field) is set to 1, then the custody
   transfer procedure defined in Section 5.10 MUST be followed; (b)
   when -- at some future time - the forwarding of this bundle ceases
   to be contraindicated, processing proceeds from Step 5 of Section
   5.4.

5.4.2. Forwarding Failed

   The steps in responding to a declaration of forwarding failure are:

   Step 1: If the bundle's custody transfer requested flag (in the
   bundle processing flags field) is set to 1, custody transfer failure
   must be handled. The bundle protocol agent MUST handle the custody
   transfer failure by generating a custody signal of type 1 (custody
   refusal) for the bundle, destined for the bundle's current
   custodian(s); the custody signal MUST contain a reason code
   corresponding to the reason for which forwarding was determined to
   be contraindicated. (Note that discarding the bundle will not delete
   it from the network, since each current custodian still has a copy.)
   In addition, if the "request reporting of custody transfer
   attempted" flag in the bundle's status report request field is set
   to 1, a custody transfer status report with the same reason code
   SHOULD be generated, destined for the report-to endpoint ID of the
   bundle.



Burleigh                   Expires May 2017                   [Page 29]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   If the bundle's custody transfer requested flag (in the bundle
   processing flags field) is set to 0, then the bundle protocol agent
   MAY forward the bundle back to the node that sent it, as identified
   by the Previous Node block.

   Step 2: If the bundle's destination endpoint is an endpoint of which
   the node is a member, then the bundle's "Forward pending" retention
   constraint MUST be removed. Otherwise, the bundle MUST be deleted:
   the bundle deletion procedure defined in Section 5.14 MUST be
   followed, citing the reason for which forwarding was determined to
   be contraindicated.

5.5. Bundle Expiration

   A bundle expires when the bundle's age exceeds its lifetime as
   specified in the primary bundle block. Bundle age MAY be determined
   by subtracting the bundle's creation timestamp time from the current
   time if (a) that timestamp time is not zero and (b) the local node's
   clock is known to be accurate (as discussed in section 4.5.1 above);
   otherwise bundle age MUST be obtained from the Bundle Age extension
   block.  Bundle expiration MAY occur at any point in the processing
   of a bundle. When a bundle expires, the bundle protocol agent MUST
   delete the bundle for the reason "lifetime expired": the bundle
   deletion procedure defined in Section 5.14 MUST be followed.

5.6. Bundle Reception

   The steps in processing a bundle that has been received from another
   node are:

   Step 1: The retention constraint "Dispatch pending" MUST be added to
   the bundle.

   Step 2: If the "request reporting of bundle reception" flag in the
   bundle's status report request field is set to 1, then a bundle
   reception status report with reason code "No additional information"
   SHOULD be generated, destined for the bundle's report-to endpoint
   ID.

   Step 3: For each block in the bundle that is an extension block that
   the bundle protocol agent cannot process:

     . If the block processing flags in that block indicate that a
        status report is requested in this event, then a bundle
        reception status report with reason code "Block unintelligible"
        SHOULD be generated, destined for the bundle's report-to
        endpoint ID.


Burleigh                   Expires May 2017                   [Page 30]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


     . If the block processing flags in that block indicate that the
        bundle must be deleted in this event, then the bundle protocol
        agent MUST delete the bundle for the reason "Block
        unintelligible"; the bundle deletion procedure defined in
        Section 5.14 MUST be followed and all remaining steps of the
        bundle reception procedure MUST be skipped.
     . If the block processing flags in that block do NOT indicate
        that the bundle must be deleted in this event but do indicate
        that the block must be discarded, then the bundle protocol
        agent MUST remove this block from the bundle.
     . If the block processing flags in that block indicate neither
        that the bundle must be deleted nor that that the block must be
        discarded, then processing continues with the next extension
        block that the bundle protocol agent cannot process, if any;
        otherwise, processing proceeds from step 4.

   Step 4: If the bundle's custody transfer requested flag (in the
   bundle processing flags field) is set to 1 and the bundle has the
   same source node ID, creation timestamp, and (if the bundle is a
   fragment) fragment offset as another bundle that (a) has not been
   discarded and (b) currently has the retention constraint "Custody
   accepted", then custody transfer redundancy MUST be handled;
   otherwise, processing proceeds from Step 5. The bundle protocol
   agent MUST handle custody transfer redundancy by generating a
   custody signal of type 1 (custody refusal) for this bundle with
   reason code "Redundant reception", destined for this bundle's
   current custodian, and removing this bundle's "Dispatch pending"
   retention constraint.

   Step 5: Processing proceeds from Step 1 of Section 5.3.

5.7. Local Bundle Delivery

   The steps in processing a bundle that is destined for an endpoint of
   which this node is a member are:

   Step 1: If the received bundle is a fragment, the application data
   unit reassembly procedure described in Section 5.9 MUST be followed.
   If this procedure results in reassembly of the entire original
   application data unit, processing of this bundle (whose fragmentary
   payload has been replaced by the reassembled application data unit)
   proceeds from Step 2; otherwise, the retention constraint
   "Reassembly pending" MUST be added to the bundle and all remaining
   steps of this procedure MUST be skipped.

   Step 2: Delivery depends on the state of the registration whose
   endpoint ID matches that of the destination of the bundle:


Burleigh                   Expires May 2017                   [Page 31]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


     . If the registration is in the Active state, then the bundle
        MUST be delivered subject to this registration (see Section 3.1
        above) as soon as all previously received bundles that are
        deliverable subject to this registration have been delivered.
     . If the registration is in the Passive state, then the
        registration's delivery failure action MUST be taken (see
        Section 3.1 above).

   Step 3: As soon as the bundle has been delivered:

     . If the "request reporting of bundle delivery" flag in the
        bundle's status report request field is set to 1, then a bundle
        delivery status report SHOULD be generated, destined for the
        bundle's report-to endpoint ID. Note that this status report
        only states that the payload has been delivered to the
        application agent, not that the application agent has processed
        that payload.
     . If the bundle's custody transfer requested flag (in the bundle
        processing flags field) is set to 1, custodial delivery MUST be
        reported. The bundle protocol agent MUST report custodial
        delivery by generating a custody signal of type 0 (custody
        acceptance) for the bundle, destined for the bundle's current
        custodian(s).

5.8. Bundle Fragmentation

   It may at times be advantageous for bundle protocol agents to reduce
   the sizes of bundles in order to forward them. This might be the
   case, for example, if a node to which a bundle is to be forwarded is
   accessible only via intermittent contacts and no upcoming contact is
   long enough to enable the forwarding of the entire bundle.

   The size of a bundle can be reduced by "fragmenting" the bundle. To
   fragment a bundle whose payload is of size M is to replace it with
   two "fragments" -- new bundles with the same source node ID and
   creation timestamp as the original bundle -- whose payloads are the
   first N and the last (M - N) bytes of the original bundle's payload,
   where 0 < N < M. Note that fragments may themselves be fragmented,
   so fragmentation may in effect replace the original bundle with more
   than two fragments. (However, there is only one 'level' of
   fragmentation, as in IP fragmentation.)

   Any bundle that has any Current Custodian extension block citing any
   node other than the local node MUST NOT be fragmented.  This
   restriction aside, any bundle whose primary block's bundle
   processing flags do NOT indicate that it must not be fragmented MAY



Burleigh                   Expires May 2017                   [Page 32]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   be fragmented at any time, for any purpose, at the discretion of the
   bundle protocol agent.

   Fragmentation SHALL be constrained as follows:

     . The concatenation of the payloads of all fragments produced by
        fragmentation MUST always be identical to the payload of the
        fragmented bundle (that is, the bundle that is being
        fragmented). Note that the payloads of fragments resulting from
        different fragmentation episodes, in different parts of the
        network, may be overlapping subsets of the fragmented bundle's
        payload.
     . The primary block of each fragment MUST differ from that of the
        fragmented bundle, in that the bundle processing flags of the
        fragment MUST indicate that the bundle is a fragment and both
        fragment offset and total application data unit length must be
        provided.  Additionally, the CRC of the fragmented bundle, if
        any, MUST be replaced in each fragment by a new CRC computed
        for the primary block of that fragment.
     . The payload blocks of fragments will differ from that of the
        fragmented bundle as noted above.
     . If the fragmented bundle is not a fragment or is the fragment
        with offset zero, then all extension blocks of the fragmented
        bundle MUST be replicated in the fragment whose offset is zero.
     . Each of the fragmented bundle's extension blocks whose "Block
        must be replicated in every fragment" flag is set to 1 MUST be
        replicated in every fragment.
     . Beyond these rules, replication of extension blocks in the
        fragments is an implementation matter.
     . If the local node is a custodian of the fragmented bundle, then
        the BPA MUST release custody of the fragmented bundle before
        fragmentation occurs and MUST take custody of every fragment.

5.9. Application Data Unit Reassembly

   If the concatenation -- as informed by fragment offsets and payload
   lengths -- of the payloads of all previously received fragments with
   the same source node ID and creation timestamp as this fragment,
   together with the payload of this fragment, forms a byte array whose
   length is equal to the total application data unit length in the
   fragment's primary block, then:

     . This byte array -- the reassembled application data unit --
        MUST replace the payload of this fragment.
     . The BPA MUST take custody of each fragmentary bundle whose
        payload is a subset of the reassembled application data unit,



Burleigh                   Expires May 2017                   [Page 33]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


        for which custody transfer is requested but the BPA has not yet
        taken custody.
     . The BPA MUST then release custody of every fragment whose
        payload is a subset of the reassembled application data unit,
        for which it has taken custody.
     . The "Reassembly pending" retention constraint MUST be removed
        from every other fragment whose payload is a subset of the
        reassembled application data unit.

   Note: reassembly of application data units from fragments occurs at
   the nodes that are members of destination endpoints as necessary; an
   application data unit MAY also be reassembled at some other node on
   the path to the destination.

5.10. Custody Transfer

   The decision as to whether or not to accept custody of a bundle is
   an implementation matter that may involve both resource and policy
   considerations.

   If the bundle protocol agent elects to accept custody of the bundle,
   then it must follow the custody acceptance procedure defined in
   Section 5.10.1.

5.10.1. Custody Acceptance

   Procedures for acceptance of custody of a bundle are defined as
   follows.

   The retention constraint "Custody accepted" MUST be added to the
   bundle.

   If the "request reporting of custody transfer attempted" flag in the
   bundle's status report request field is set to 1, a custody transfer
   status report with reason code 0 SHOULD be generated, destined for
   the report-to endpoint ID of the bundle. However, if a bundle
   reception status report was generated for this bundle (Step 2 of
   Section 5.6) but has not yet been transmitted, then this report
   SHOULD be generated by simply turning on the "Reporting node
   attempted custody transfer" flag in that earlier report.

   The bundle protocol agent MUST generate a custody signal of type 0
   (custody acceptance) for the bundle, destined for the bundle's
   current custodian(s).

   The bundle protocol agent MUST assert the new current custodian for
   the bundle. It does so by deleting all of the bundle's existing


Burleigh                   Expires May 2017                   [Page 34]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   Current Custodian extension blocks and inserting a new Current
   Custodian extension block whose value is the node ID of the local
   node.

   If the value of a custody transfer timer interval for this bundle
   can be calculated with operationally satisfactory accuracy, then the
   bundle protocol agent SHOULD set a custody transfer countdown timer
   for the bundle; upon expiration of this timer prior to expiration of
   the bundle itself and prior to custody transfer success for this
   bundle, the custody transfer failure procedure detailed in Section
   5.12 MUST be followed. The manner in which the countdown interval
   for such a timer is determined is an implementation matter.

   The bundle SHOULD be retained in persistent storage if possible.

5.10.2. Custody Release

   When custody of a bundle is released, the "Custody accepted"
   retention constraint MUST be removed from the bundle and any custody
   transfer timer that has been established for this bundle SHOULD be
   destroyed.

5.11. Custody Transfer Success

   Upon receipt of a custody signal of type 0 (custody acceptance) at a
   node that is a custodial node of the bundle identified in the
   custody signal, custody of the bundle MUST be released as described
   in Section 5.10.2.

5.12. Custody Transfer Failure

   Custody transfer is determined to have failed at a custodial node
   for a given bundle when either (a) that node's custody transfer
   timer for that bundle (if any) expires or (b) a custody signal of
   type 1 (custody refusal) for that bundle is received at that node.

   Upon determination of custody transfer failure due to expiration of
   a custody transfer countdown timer, the bundle protocol agent MUST
   re-forward the bundle, possibly on a different route (Section 5.4).

   Upon determination of custody transfer failure due to reception of a
   custody signal of type 1 (custody refusal), the action taken by the
   bundle protocol agent is implementation-specific and may depend on
   the reason code cited for the refusal. For example, if the custody
   signal's reason code was "Depleted storage", the bundle protocol
   agent might choose to re-forward the bundle, possibly on a different
   route (Section 5.4). If the reason code was "Redundant reception",


Burleigh                   Expires May 2017                   [Page 35]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   on the other hand, this might cause the bundle protocol agent to
   release custody of the bundle and to revise its algorithm for
   computing countdown intervals for custody transfer timers.

5.13. Custody Transfer Deferral

   Upon receipt of a bundle for which custody transfer retransmission
   service has been requested, which the bundle protocol agent plans to
   forward but for which it elects not to accept custody, the bundle
   protocol agent SHOULD generate a custody signal of type 2 (custody
   delegation) for the bundle, destined for the bundle's current
   custodian(s).

   Custody transfer is determined to have been deferred at a custodial
   node for given bundle when a custody signal of type 2 (custody
   delegation) for that bundle is received at that node.  The action
   taken by the bundle protocol agent in this event is implementation-
   specific.  Notionally, this is an opportunity for the bundle
   protocol agent to revise its retransmission timeout interval for
   this bundle, based on the information provided in the custody
   signal: the next candidate custodian for the bundle is now known,
   and the minimum length of time before a custody acceptance signal
   will arrive can now be adjusted accordingly.

5.14. Bundle Deletion

   The steps in deleting a bundle are:

   Step 1: If the retention constraint "Custody accepted" currently
   prevents this bundle from being discarded, then:

     . Custody of the bundle is released as described in Section
        5.10.2.
     . A bundle deletion status report citing the reason for deletion
        MUST be generated, destined for the bundle's report-to endpoint
        ID.

   Otherwise, if the "request reporting of bundle deletion" flag in the
   bundle's status report request field is set to 1, then a bundle
   deletion status report citing the reason for deletion SHOULD be
   generated, destined for the bundle's report-to endpoint ID.

   Step 2: All of the bundle's retention constraints MUST be removed.






Burleigh                   Expires May 2017                   [Page 36]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


5.15. Discarding a Bundle

   As soon as a bundle has no remaining retention constraints it MAY be
   discarded, thereby releasing any persistent storage that may have
   been allocated to it.

5.16. Canceling a Transmission

   When requested to cancel a specified transmission, where the bundle
   created upon initiation of the indicated transmission has not yet
   been discarded, the bundle protocol agent MUST delete that bundle
   for the reason "transmission cancelled". For this purpose, the
   procedure defined in Section 5.14 MUST be followed.

6. Administrative Record Processing

6.1. Administrative Records

   Administrative records are standard application data units that are
   used in providing some of the features of the Bundle Protocol. Two
   types of administrative records have been defined to date: bundle
   status reports and custody signals.  Note that additional types of
   administrative records may be defined by supplementary DTN protocol
   specification documents.

   Every administrative record consists of:

      . Record type code (an unsigned integer for which valid values
        are as defined below).
      . Record content in type-specific format.

   Valid administrative record type codes are defined as follows:

   +---------+--------------------------------------------+

   |  Value  |                   Meaning                  |

   +=========+============================================+

   |     1   | Bundle status report.                      |

   +---------+--------------------------------------------+

   |     2   | Custody signal.                            |

   +---------+--------------------------------------------+



Burleigh                   Expires May 2017                   [Page 37]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   | (other) | Reserved for future use.                   |

   +---------+--------------------------------------------+

                Figure 3: Administrative Record Type Codes

   Each BP administrative record SHALL be represented as a CBOR array
   comprising a 2-tuple.

   The first item of the array SHALL be a record type code, which SHALL
   be represented as a CBOR unsigned integer.

   The second element of this array SHALL be the applicable CBOR
   representation of the content of the record.  Details of the CBOR
   representation of administrative record types 1 and 2 are provided
   below.  Details of the CBOR representation of other types of
   administrative record type are included in the specifications
   defining those records.

6.1.1. Bundle Status Reports

   The transmission of "bundle status reports" under specified
   conditions is an option that can be invoked when transmission of a
   bundle is requested. These reports are intended to provide
   information about how bundles are progressing through the system,
   including notices of receipt, custody transfer, forwarding, final
   delivery, and deletion. They are transmitted to the Report-to
   endpoints of bundles.

   Each bundle status report SHALL be represented as a CBOR array.  The
   number of elements in the array SHALL be either 6 (if the subject
   bundle is a fragment) or 4 (otherwise).

   The first item of the bundle status report array SHALL be bundle
   status information represented as a CBOR array of 5 elements.  The
   five items of the bundle status information array shall provide
   information on the following five status assertions, in this order:

     . Reporting node received bundle.
     . Reporting node attempted custody transfer.  When this status is
        asserted, a reason code value of 0 ("No additional
        information") SHALL indicate that custody was accepted.
     . Reporting node forwarded the bundle.
     . Reporting node delivered the bundle.
     . Reporting node deleted the bundle.




Burleigh                   Expires May 2017                   [Page 38]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   Each item of the bundle status information array SHALL be a bundle
   status item represented as a CBOR array; the number of elements in
   each such array SHALL be either 2 (if the value of the first item of
   this bundle status item is 1 AND the "Report status time" flag was
   set to 1 in the bundle processing flags of the bundle whose status
   is being reported) or 1 (otherwise).  The first item of the bundle
   status item array SHALL be a status indicator, a Boolean value
   indicating whether or not the corresponding bundle status is
   asserted, represented as a CBOR Boolean value.  The second item of
   the bundle status item array, if present, SHALL indicate the time
   (as reported by the local system clock, an implementation matter) at
   which the indicated status was asserted for this bundle, represented
   as a DTN time as described in Section 4.1.6. above.

   The second item of the bundle status report array SHALL be the
   bundle status report reason code explaining the value of the status
   indicator, represented as a CBOR unsigned integer. Valid status
   report reason codes are defined in Figure 4 below but the list of
   status report reason codes provided here is neither exhaustive nor
   exclusive; supplementary DTN protocol specifications (including, but
   not restricted to, the Bundle Security Protocol [BPSEC]) may define
   additional reason codes.

   +---------+--------------------------------------------+

   | Value   |                  Meaning                   |

   +=========+============================================+

   |    0    | No additional information.                 |

   +---------+--------------------------------------------+

   |    1    | Lifetime expired.                          |

   +---------+--------------------------------------------+

   |    2    | Forwarded over unidirectional link.        |

   +---------+--------------------------------------------+

   |    3    | Transmission canceled.                     |

   +---------+--------------------------------------------+

   |    4    | Depleted storage.                          |



Burleigh                   Expires May 2017                   [Page 39]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   +---------+--------------------------------------------+

   |    5    | Destination endpoint ID unintelligible.    |

   +---------+--------------------------------------------+

   |    6    | No known route to destination from here.   |

   +---------+--------------------------------------------+

   |    7    | No timely contact with next node on route. |

   +---------+--------------------------------------------+

   |    8    | Block unintelligible.                      |

   +---------+--------------------------------------------+

   | (other) | Reserved for future use.                   |

   +---------+--------------------------------------------+

                   Figure 4: Status Report Reason Codes

   The third item of the bundle status report array SHALL be the source
   node ID identifying the source of the bundle whose status is being
   reported, represented as described in Section 4.1.5.2. above.

   The fourth item of the bundle status report array SHALL be the
   creation timestamp of the bundle whose status is being reported,
   represented as described in Section 4.1.7. above.

   The fifth item of the bundle status report array SHALL be present if
   and only if the bundle whose status is being reported contained a
   fragment offset.  If present, it SHALL be the subject bundle's
   fragment offset represented as a CBOR unsigned integer item.

   The sixth item of the bundle status report array SHALL be present if
   and only if the bundle whose status is being reported contained a
   fragment offset.  If present, it SHALL be the length of the subject
   bundle's payload represented as a CBOR unsigned integer item.

6.1.2. Custody Signals

   Custody signals are administrative records that effect custody
   transfer operations. They are transmitted to the nodes that are the
   current custodians of bundles.


Burleigh                   Expires May 2017                   [Page 40]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   Each custody signal SHALL be represented as a CBOR array. The number
   of elements in the array SHALL be 6 (if the subject bundle is a
   fragment) or 4 (otherwise).

   The first item of the custody signal array SHALL be a signal type
   code represented as a CBOR unsigned integer. Valid custody signal
   types are defined as follows:

   +---------+--------------------------------------------+

   | Value   |                  Meaning                   |

   +=========+============================================+

   |    0    | Custody acceptance.  The reporting node    |

   |         | accepted custody of the bundle.            |

   +---------+--------------------------------------------+

   |    1    | Custody refusal.  The reporting node       |

   |         | refused custody of the bundle.             |

   +---------+--------------------------------------------+

   |    2    | Custody delegation: the bundle will be     |

   |         | forwarded but custody was not taken.       |

   +---------+--------------------------------------------+

   | (other) | Reserved for future use.                   |

   +---------+--------------------------------------------+

                    Figure 5: Custody Signal Type Codes

   The second item of the custody signal array SHALL be additional
   information amplifying the signal type code, represented as a CBOR
   array.  The number of elements in the array SHALL be either 2 (if
   the signal type is 2) or 1 (otherwise).

   When signal type is 0 or 1, the sole item in the additional
   information array SHALL be a custody signal reason code, represented
   as a CBOR unsigned integer. Valid custody signal reason codes are
   defined as follows:


Burleigh                   Expires May 2017                   [Page 41]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   +---------+--------------------------------------------+

   | Value   |                  Meaning                   |

   +=========+============================================+

   |    0    | No additional information.                 |

   +---------+--------------------------------------------+

   |    1    | Reserved for future use.                   |

   +---------+--------------------------------------------+

   |    2    | Reserved for future use.                   |

   +---------+--------------------------------------------+

   |    3    | Redundant (reception by a node that is a   |

   |         | custodial node for this bundle).           |

   +---------+--------------------------------------------+

   |    4    | Depleted storage.                          |

   +---------+--------------------------------------------+

   |    5    | Destination endpoint ID unintelligible.    |

   +---------+--------------------------------------------+

   |    6    | No known route destination from here.      |

   +---------+--------------------------------------------+

   |    7    | No timely contact with next node on route. |

   +---------+--------------------------------------------+

   |    8    | Block unintelligible.                      |

   +---------+--------------------------------------------+

   | (other) | Reserved for future use.                   |

   +---------+--------------------------------------------+


Burleigh                   Expires May 2017                   [Page 42]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


                   Figure 6: Custody Signal Reason Codes

   When signal type is 2, the first item in the additional information
   array SHALL be the node ID of the node to which the reporting node
   anticipates forwarding the bundle, represented as described in
   Section 4.1.5.2. above, and the second item in this array SHALL be
   an estimate of the number of seconds that will have elapsed since
   reception of the bundle before the anticipated forwarding begins,
   represented as a CBOR unsigned integer.

   The third item of the custody signal array SHALL be the source node
   ID identifying the source of the bundle for which custodial activity
   is being reported, represented as described in Section 4.1.5.2.
   above.

   The fourth item of the custody signal array SHALL be the creation
   timestamp of the bundle for which custodial activity is being
   reported, represented as described in Section 4.1.7. above.

   The fifth item of the custody signal array SHALL be present if and
   only if the bundle for which custodial activity is being reported
   contained a fragment offset.  If present, it SHALL be the subject
   bundle's fragment offset represented as a CBOR unsigned integer
   item.

   The sixth item of the custody signal array SHALL be present if and
   only if the bundle for which custodial activity is being reported
   contained a fragment offset.  If present, it SHALL be the length of
   the subject bundle's payload represented as a CBOR unsigned integer
   item.

6.2. Generation of Administrative Records

   Whenever the application agent's administrative element is directed
   by the bundle protocol agent to generate an administrative record
   with reference to some bundle, the following procedure must be
   followed:

   Step 1: The administrative record must be constructed. If the
   referenced bundle is a fragment, the administrative record MUST
   contain the fragment offset and fragment length.

   Step 2: A request for transmission of a bundle whose payload is this
   administrative record MUST be presented to the bundle protocol
   agent.




Burleigh                   Expires May 2017                   [Page 43]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


6.3. Reception of Custody Signals

   For each received custody signal that has signal type zero (custody
   acceptance), the administrative element of the application agent
   MUST direct the bundle protocol agent to follow the custody transfer
   success procedure in Section 5.11.

   For each received custody signal that has signal type 1 (custody
   refusal), the administrative element of the application agent MUST
   direct the bundle protocol agent to follow the custody transfer
   failure procedure in Section 5.12.

   For each received custody signal that has signal type 2 (custody
   delegation), the administrative element of the application agent
   MUST direct the bundle protocol agent to follow the custody
   delegation procedure in Section 5.13.

7. Services Required of the Convergence Layer

7.1. The Convergence Layer

   The successful operation of the end-to-end bundle protocol depends
   on the operation of underlying protocols at what is termed the
   "convergence layer"; these protocols accomplish communication
   between nodes. A wide variety of protocols may serve this purpose,
   so long as each convergence layer protocol adapter provides a
   defined minimal set of services to the bundle protocol agent. This
   convergence layer service specification enumerates those services.

7.2. Summary of Convergence Layer Services

   Each convergence layer protocol adapter is expected to provide the
   following services to the bundle protocol agent:

     . sending a bundle to a bundle node that is reachable via the
        convergence layer protocol;
     . delivering to the bundle protocol agent a bundle that was sent
        by a bundle node via the convergence layer protocol.

   The convergence layer service interface specified here is neither
   exhaustive nor exclusive. That is, supplementary DTN protocol
   specifications (including, but not restricted to, the Bundle
   Security Protocol [BPSEC]) may expect convergence layer adapters
   that serve BP implementations conforming to those protocols to
   provide additional services such as reporting on the transmission
   and/or reception progress of individual bundles (at completion
   and/or incrementally), retransmitting data that were lost in


Burleigh                   Expires May 2017                   [Page 44]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   transit, discarding bundle-conveying data units that the convergence
   layer protocol determines are corrupt or inauthentic, or reporting
   on the integrity and/or authenticity of delivered bundles.

8. Security Considerations

   The bundle protocol has taken security into concern from the outset
   of its design. It was always assumed that security services would be
   needed in the use of the bundle protocol. As a result, the bundle
   protocol security architecture and the available security services
   are specified in an accompanying document, the Bundle Security
   Protocol specification [BPSEC]; an informative overview of this
   architecture is provided in [SECO].

   The bundle protocol has been designed with the notion that it may be
   run over networks with scarce resources. For example, the networks
   might have limited bandwidth, limited connectivity, constrained
   storage in relay nodes, etc. Therefore, the bundle protocol must
   ensure that only those entities authorized to send bundles over such
   constrained environments are actually allowed to do so. All
   unauthorized entities should be prevented from consuming valuable
   resources as soon as practicable.

   Likewise, because of the potentially high latencies and delays
   involved in the networks that make use of the bundle protocol, data
   sources should be concerned with the integrity of the data received
   at the intended destination(s) and may also be concerned with
   ensuring confidentiality of the data as it traverses the network.
   Without integrity, the bundle payload data might be corrupted while
   in transit without the destination able to detect it. Similarly, the
   data source can be concerned with ensuring that the data can only be
   used by those authorized, hence the need for confidentiality.

   Internal to the bundle-aware overlay network, the bundle nodes
   should be concerned with the authenticity of other bundle nodes as
   well as the preservation of bundle payload data integrity as it is
   forwarded between bundle nodes.

   As a result, bundle security is concerned with the authenticity,
   integrity, and confidentiality of bundles conveyed among bundle
   nodes. This is accomplished via the use of two independent security-
   specific bundle blocks, which may be used together to provide
   multiple bundle security services or independently of one another,
   depending on perceived security threats, mandated security
   requirements, and security policies that must be enforced.




Burleigh                   Expires May 2017                   [Page 45]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   To provide end-to-end bundle authenticity and integrity, the Block
   Integrity Block (BIB) is used. The BIB allows any security-enabled
   entity along the delivery path to ensure the integrity of the
   bundle's payload or any other block other than a Block
   Confidentiality Block.

   To provide payload confidentiality, the use of the Block
   Confidentiality Block (BCB) is available. The bundle payload, or any
   other block aside from the primary block and the Bundle Security
   Protocol blocks, may be encrypted to provide end-to-end payload
   confidentiality/privacy.

   Additionally, convergence-layer protocols that ensure authenticity
   of communication between adjacent nodes in BP network topology
   SHOULD be used where available, to minimize the ability of
   unauthenticated nodes to introduce inauthentic traffic into the
   network.

   Bundle security MUST NOT be invalidated by forwarding nodes even
   though they themselves might not use the Bundle Security Protocol.

   In particular, while blocks MAY be added to bundles transiting
   intermediate nodes, removal of blocks with the 'Discard block if it
   can't be processed' flag set in the block processing control flags
   may cause security to fail.

   Inclusion of the Bundle Security Protocol in any Bundle Protocol
   implementation is RECOMMENDED. Use of the Bundle Security Protocol
   in Bundle Protocol operations is OPTIONAL.

9. IANA Considerations

   The "dtn" and "ipn" URI schemes have been provisionally registered
   by IANA. See http://www.iana.org/assignments/uri-schemes.html for
   the latest details.

   Registries of URI scheme type numbers, extension block type numbers,
   and administrative record type numbers will be required.

10. References

10.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels", BCP 14, RFC 2119, March 1997.




Burleigh                   Expires May 2017                   [Page 46]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   [RFC7049] Borman, C. and P. Hoffman, "Concise Binary Object
   Representation (CBOR)", RFC 7049, October 2013.

   [URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
   Resource Identifier (URI): Generic Syntax", RFC 3986, STD 66,
   January 2005.

   [URIREG] Thaler, D., Hansen, T., and T. Hardie, "Guidelines and
   Registration Procedures for URI Schemes", RFC 7595, BCP 35, June
   2015.

10.2. Informative References

   [ARCH] V. Cerf et al., "Delay-Tolerant Network Architecture", RFC
   4838, April 2007.

   [BPSEC] Birrane, E., "Bundle Security Protocol Specification", Work
   In Progress, October 2015.

   [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
   Identifiers (IRIs)", RFC 3987, January 2005.

   [RFC5050] Scott, M. and S. Burleigh, "Bundle Protocol
   Specification", RFC 5050, November 2007.

   [SECO] Farrell, S., Symington, S., Weiss, H., and P. Lovell, "Delay-
   Tolerant Networking Security Overview", Work Progress, July 2007.

   [SIGC] Fall, K., "A Delay-Tolerant Network Architecture for
   Challenged Internets", SIGCOMM 2003.

   [TUT] Warthman, F., "Delay-Tolerant Networks (DTNs): A Tutorial",
   <http://www.dtnrg.org>.

   [UTC] Arias, E. and B. Guinot, "Coordinated universal time UTC:
   historical background and perspectives" in "Journees systemes de
   reference spatio-temporels", 2004.

11. Acknowledgments

   This work is freely adapted from [RFC5050], which was an effort of
   the Delay Tolerant Networking Research Group. The following DTNRG
   participants contributed significant technical material and/or
   inputs to that document: Dr. Vinton Cerf of Google, Scott Burleigh,
   Adrian Hooke, and Leigh Torgerson of the Jet Propulsion Laboratory,
   Michael Demmer of the University of California at Berkeley, Robert
   Durst, Keith Scott, and Susan Symington of The MITRE Corporation,


Burleigh                   Expires May 2017                   [Page 47]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   Kevin Fall of Carnegie Mellon University, Stephen Farrell of Trinity
   College Dublin, Peter Lovell of SPARTA, Inc., Manikantan Ramadas of
   Ohio University, and Howard Weiss of SPARTA, Inc.

   This document was prepared using 2-Word-v2.0.template.dot.

12. Significant Changes from RFC 5050

   Points on which this draft significantly differs from RFC 5050
   include the following:

     . Clarify the difference between transmission and forwarding.
     . Amplify discussion of custody transfer.  Move current custodian
        to an extension block, of which there can be multiple
        occurrences (possible support for the MITRE idea of multiple
        concurrent custodians, from several years ago); define that
        block in this specification.
     . Introduce the concept of "node ID" as functionally distinct
        from endpoint ID, while having the same syntax.
     . Restructure primary block, making it immutable.  Add optional
        CRC.
     . Add optional CRCs to non-primary blocks.
     . Add block ID number to canonical block format (to support
        streamlined BSP).
     . Add bundle age extension block, defined in this specification.
     . Add previous node extension block, defined in this
        specification.
     . Add flow label extension block, *not* defined in this
        specification.
     . Add manifest extension block, *not* defined in this
        specification.
     . Add hop count extension block, defined in this specification.
     . Clean up a conflict between fragmentation and custody transfer
        that Ed Birrane pointed out.















Burleigh                   Expires May 2017                   [Page 48]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


Appendix A.                 For More Information

   Please refer comments to dtn@ietf.org. The Delay Tolerant Networking
   Research Group (DTNRG) Web site is located at http://www.dtnrg.org.

   Copyright (c) 2016 IETF Trust and the persons identified as authors
   of the code. All rights reserved.

   Redistribution and use in source and binary forms, with or without
   modification, is permitted pursuant to, and subject to the license
   terms contained in, the Simplified BSD License set forth in Section
   4.c of the IETF Trust's Legal Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info).




































Burleigh                   Expires May 2017                   [Page 49]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


Appendix B.                  CDDL expression

   For informational purposes, Carsten Bormann has kindly provided an
   expression of the Bundle Protocol specification in the CBOR Data
   Definition Language (CDDL).  That CDDL expression is presented
   below, somewhat edited by the authors.  Note that wherever the CDDL
   expression is in disagreement with the textual representation of the
   BP specification presented in the earlier sections of this document,
   the textual representation rules.

   start = bundle

   dtn-time = uint

   creation-timestamp = [dtn-time, sequence: uint]

   eid-generic = [uri-code, SSP: any]

   uri-code = uint

   eid = eid-choice .within eid-generic

   eid-choice /= [dtn-code, SSP: bytes]

   dtn-code = 1 ; TBD

   eid-choice /= [ipn-code, SSP: [nodenum: uint, servicenum: uint]]

   ipn-code = 2 ; TBD

   bundle-control-flags = uint .bits bundleflagbits

   bundleflagbits = &(

     reserved: 15

     reserved: 14

     reserved: 13

     bundle-deletion-status-reports-are-requested: 12

     bundle-delivery-status-reports-are-requested: 11

     bundle-forwarding-status-reports-are-requested: 10

     custody-transfer-status-reports-are-requested: 9


Burleigh                   Expires May 2017                   [Page 50]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


     bundle-reception-status-reports-are-requested: 8

     bundle-contains-a-Manifest-block: 7

     status-time-is-requested-in-all-status-reports: 6

     user-application-acknowledgement-is-requested: 5

     destination-is-a-singleton-endpoint: 4

     custody-transfer-is-requested: 3

     bundle-must-not-be-fragmented: 2

     payload-is-an-administrative-record: 1

     bundle-is-a-fragment: 0

   )

   crc = uint

   block-control-flags = uint .bits blockflagbits

   blockflagbits = &(

     reserved: 7

     reserved: 6

     reserved: 5

     reserved: 4

     bundle-must-be-deleted-if-block-cannot-be-processed: 3

     status-report-must-be-transmitted-if-block-cannot-be-processed: 2

     block-must-be-removed-from-bundle-if-it-cannot-be-processed: 1

     block-must-be-replicated-in-every-fragment: 0

   )

   bundle = [primary-block, *extension-block, payload-block]

   primary-block = [


Burleigh                   Expires May 2017                   [Page 51]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


                 version: 7,

                 bundle-control-flags,

                 crc-type: uint,

                 destination: eid,

                 source-node: eid,

                 report-to: eid,

                 creation-timestamp,

                 lifetime: uint,

                 ? fragment-offset: uint,

                 ? total-application-data-length: uint,

                 ? crc,

   ]

   canonical-block-generic = [

                           block-type-code: uint,

                           canonical-block-common,

                           content: any

                           ]

   canonical-block-common = (

                          block-number: uint,

                          block-control-flags,

                          crc-type: uint,

                          ? crc,

                          )




Burleigh                   Expires May 2017                   [Page 52]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


   canonical-block = canonical-block-choice .within canonical-block-
   generic

   canonical-block-choice /= payload-block

   payload-block = [1, canonical-block-common, adu-extent: payload]

   payload = bytes / bytes .cbor admin-record

   canonical-block-choice /= extension-block

   extension-block = extension-block-choice .within canonical-block

   extension-block-choice /= current-custodian-block

   current-custodian-block = [5, canonical-block-common, eid]

   extension-block-choice /= previous-node-block

   previous-node-block = [7, canonical-block-common, eid]

   extension-block-choice /= bundle-age-block

   bundle-age-block = [8, canonical-block-common, bundle-age: uint]

   extension-block-choice /= hop-count-block

   hop-count-block = [9, canonical-block-common,

                   [hop-limit: uint,

                    hop-count: uint]]

   admin-record-generic = [record-type: uint, any]

   admin-record = admin-record-choice .within admin-record-generic

   admin-record-choice /= bundle-status-report

   bundle-status-report = [1, [bundle-status-information,

                               bundle-status-reason: uint,

                               admin-common]]

   admin-common = (



Burleigh                   Expires May 2017                   [Page 53]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


                 source-node: eid,

                 creation-timestamp,

                 ? fragment-offset: uint,

                 ? payload-length: uint)

   bundle-status-information = [

     reporting-node-received-bundle: bundle-status-item,

     reporting-node-attempted-custody-transfer: bundle-status-item,

     reporting-node-forwarded-the-bundle: bundle-status-item,

     reporting-node-delivered-the-bundle: bundle-status-item,

     reporting-node-deleted-the-bundle: bundle-status-item,

   ]

   bundle-status-item = (

                  asserted: Boolean,

                  ? time-of-assertion: dtn-time)

   admin-record-choice /= custody-signal

   custody-signal = [2, [custody-signal-type-code: uint,

                         custody-signal-information,

                         admin-common]]

   custody-signal-information = custody-reason-code: uint / delegation-
   information

   delegation-information = (

                   next-hop-node: eid,

                   seconds-until-forwarding: uint)





Burleigh                   Expires May 2017                   [Page 54]


Internet-Draft     Proposed Revised Bundle Protocol        October 2016


Authors' Addresses

   Scott Burleigh
   Jet Propulsion Laboratory, California Institute of Technology
   4800 Oak Grove Dr.
   Pasadena, CA 91109-8099
   US
   Phone: +1 818 393 3353
   Email: Scott.Burleigh@jpl.nasa.gov

   Kevin Fall
   Carnegie Mellon University / Software Engineering Institute
   4500 Fifth Avenue
   Pittsburgh, PA 15213
   US
   Phone: +1 412 268 3304
   Email: kfall@cmu.edu

   Edward J. Birrane
   Johns Hopkins University Applied Physics Laboratory
   11100 Johns Hopkins Rd
   Laurel, MD 20723
   US
   Phone: +1 443 778 7423
   Email: Edward.Birrane@jhuapl.edu
























Burleigh                   Expires May 2017                   [Page 55]


Html markup produced by rfcmarkup 1.121, available from https://tools.ietf.org/tools/rfcmarkup/