Bundle Protocol Specification
draft-irtf-dtnrg-bundle-spec-10

Versions: 00 01 02 03 04 05 06 07 08 09 10 rfc5050                      
   Delay Tolerant Networking Research Group                    K. Scott
   Internet Draft                                 The MITRE Corporation
   <draft-irtf-dtnrg-bundle-spec-04.txt>
   November 2005                                            S. Burleigh
   Expires: May 2006                          Jet Propulsion Laboratory



                       Bundle Protocol Specification


Status of this Memo

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   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she
   becomes aware will be disclosed, in accordance with Section 6 of BCP
   79.

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   This document was produced within the IRTF's Delay Tolerant
   Networking Research Group (DTNRG).  See http://www.dtnrg.org for more
   information.

Abstract

   This document describes the end-to-end protocol, header formats, and
   abstract service description for the exchange of messages (bundles)
   in Delay Tolerant Networking (DTN).

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 [1].



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Table of Contents

   1.          Introduction..........................................3
   2.          Service Description...................................4
      2.1      Definitions...........................................4
      2.2      Implementation architectures..........................8
      2.3      Services offered by bundle protocol agents............9
   3.          Bundle Format........................................10
      3.1      Canonical Bundle Header Format.......................10
      3.2      Bundle Processing Flags..............................10
      3.3      Header Processing Flags..............................11
      3.4      Self-Delimiting Numeric Values (SDNV)................11
      3.5      Endpoint IDs.........................................12
      3.6      Formats of Bundle Headers............................13
        3.6.1  Primary Bundle Header................................15
        3.6.2  Bundle Payload Header................................18
   4.          Bundle Processing....................................18
      4.1      Generation of administrative records.................19
      4.2      Bundle transmission..................................19
      4.3      Bundle dispatching...................................20
      4.4      Bundle forwarding....................................20
        4.4.1  Forwarding Contraindicated...........................21
        4.4.2  Forwarding Failed....................................22
      4.5      Bundle expiration....................................22
      4.6      Bundle reception.....................................23
      4.7      Local bundle delivery................................23
      4.8      Bundle Fragmentation.................................24
      4.9      Application Data Unit Reassembly.....................25
      4.10     Custody transfer.....................................26
        4.10.1 Custody acceptance...................................26
        4.10.2 Custody release......................................27
      4.11     Custody transfer success.............................27
      4.12     Custody transfer failure.............................27
      4.13     Bundle deletion......................................28
      4.14     Discarding a bundle..................................28
      4.15     Canceling a transmission.............................28
      4.16     Polling..............................................28
      4.17     Acknowledging an application data unit...............28
   5.          Administrative record processing.....................29
      5.1      Administrative records...............................29
        5.1.1  Bundle Status Reports................................29
        5.1.2  Custody Signals......................................33
      5.2      Generation of administrative records.................35
      5.3      Reception of custody signals.........................36
   6.          Services Required of the Convergence Layer...........36
      6.1      The Convergence Layer................................36
      6.2      Summary of Convergence Layer Services................36
   7.          Security Considerations..............................37
   8.          IANA Considerations..................................38
   9.          Normative References.................................38
   10.         Informative References...............................38


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1.   Introduction

   This document describes version 4 of the Delay Tolerant
   Networking (DTN) "bundle" protocol (BP).  Delay Tolerant Networking
   is an end-to-end 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 sits at the application layer of some number of
   constituent internets, forming a store-and-forward overlay network.
   Key capabilities of BP include:

     o  Custody-based retransmission
     o  Ability to cope with intermittent connectivity
     o  Ability to take advantage of scheduled, predicted, and
        opportunistic connectivity (in addition to continuous
        connectivity)
     o  Late binding of overlay network endpoint identifiers to
        constituent internet addresses

   For descriptions of these capabilities and the rationale for the DTN
   architecture, see [2] and [8].  [3] contains a tutorial-level
   overview of DTN concepts.

   BP's location within the standard protocol stack is as shown in
   Figure 1.  BP uses the 'native' internet protocols for communications
   within a given internet.  Note that 'internet' in the preceding is
   used in a general sense and does not necessarily refer to TCP/IP.
   The interface between the common bundle protocol and a specific
   internetwork protocol suite 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-+   +-^---------+
   |         >>>>>>>>^         >>>>>>>>>>^         >>>>>>>>^         |
   +-----------+   +------------+      +-------------+   +-----------+

   |                     |                    |                      |
   |<--  An internet --->|                    |<--- An internet  --->|
   |                     |                    |                      |

   Figure 1: The bundle protocol sits at the application layer of the
             Internet model.


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   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:

     o  Operations in the convergence layer adapters that bundle nodes
        use to transport data through specific types of internet.
        (However, the document does discuss the services that must be
        provided by each adapter at the convergence layer.)

     o  The bundle routing algorithm.

     o  Mechanisms for populating the routing or forwarding information
        bases of bundle nodes.

2.   Service Description

2.1 Definitions

   Bundle – A bundle is a protocol data unit of the DTN bundle protocol.
   Multiple instances of the same bundle (the same unit of DTN protocol
   data) might exist concurrently in different parts of a network -
   possibly in different representations - 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 of some
   bundle in the network that is in that node's local memory.

   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.  The terms "bundle
   content", "bundle payload", and "payload" are used interchangeably in
   this document.  The "nominal" 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
   nominal payload for a bundle forwarded in response to reception of
   that bundle is the payload of the received bundle.

   Fragment – A fragment is a bundle whose payload header contains a
   fragmentary payload.  A fragmentary payload is either the first N
   bytes or the last N bytes of some other payload – either a nominal
   payload or a fragmentary payload – of length M, such that 0 < N < M.

   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.
   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.  Each bundle node has three
   conceptual components, defined below: a "bundle protocol agent", a


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   set of zero or more "convergence layer adapters", and an "application
   agent".

   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.  The manner in which it does so 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.

   Convergence layer adapters – A convergence layer adapter (CLA) sends
   and receives bundles on behalf of the BPA, utilizing the services of
   some 'native' internet protocol that is supported in one of the
   internets within which the node is functionally located.  The manner
   in which a CLA sends and receives bundles is wholly an implementation
   matter, exactly as described for the BPA.

   Application agent – The application agent (AA) of a node is the node
   component that utilizes the BP services to effect communication for
   some purpose.  The application agent in turn has two elements, an
   administrative element and an application-specific element.  The
   application-specific element of an AA constructs, requests
   transmission of, accepts delivery of, and processes application-
   specific application data units; the only interface between the BPA
   and the application-specific element of the AA is the BP service
   interface.  The administrative element of an AA constructs and
   requests transmission of administrative records (status reports and
   custody signals), and it accepts delivery of and processes any
   custody signals that the node receives; in addition to the BP service
   interface, there is a (conceptual) private control interface between
   the BPA and the administrative element of the AA that enables each to
   direct the other to take action under specific circumstances.  In the
   case of a node that serves simply as a "router" in the overlay
   network, 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; in particular, the
   administrative element of an AA might be built into the library or
   daemon or hardware that implements the BPA, and the application-
   specific element of an AA might be implemented either in software or
   in hardware.

   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 single text string, called a "bundle endpoint ID"


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   (or, in this document, simply "endpoint ID"; endpoint IDs are
   described in detail in 3.5 below).   The special case of an endpoint
   that never contains more than one node is termed a "singleton"
   endpoint; every bundle node must be a member of at least one
   singleton endpoint.  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.

   Forwarding - When the bundle protocol agent of a node determines that
   a bundle must be "forwarded" to an endpoint, it causes the bundle to
   be sent to all of the nodes that the bundle protocol agent currently
   believes are in the "minimum reception group" of that endpoint.  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 (in which case forwarding to the endpoint is
   functionally similar to "anycast" operations in the Internet); (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).  The nature of the minimum reception
   group for a given endpoint can be determined from the endpoint's ID
   (again, see 3.5 below): 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.

   Registration – A registration is the state machine characterizing a
   given node's membership in a given endpoint.  Any number of
   registrations may be concurrently associated with a given endpoint,
   and any number of registrations may be concurrently associated with a
   given node.  Any single registration must at any time be in one of
   two states: Active, Passive.  A registration always has an associated
   "delivery failure action", the action that is to be taken when a
   bundle that is "deliverable" (see below) subject to that registration
   is received at a time when the registration is in the Passive state.
   Delivery failure action must be one of the following:

      o defer "delivery" (see below) 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


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        the registration is in Active state;

      o "abandon" (see below) delivery of the bundle subject to this
        registration.

   An additional implementation-specific delivery deferral procedure may
   optionally be associated with the registration.  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 least recently received bundle
   that is currently deliverable subject to the registration.  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.

   Delivery – Upon reception, the processing of a bundle that has been
   sent to 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 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.  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 relevant metadata (an
   implementation matter), has been presented to the node's application
   agent in a manner consistent with the state of that registration and,
   as applicable, the registration's delivery failure action.

   Deliverability, Abandonment – 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) delivery of the bundle subject to this
   registration has not been abandoned.  To "abandon" delivery of a
   bundle subject to a registration is simply to declare it no longer
   deliverable subject to that registration; normally only
   registrations' registered delivery failure actions cause deliveries
   to be abandoned.

   Deletion, Discarding – A bundle protocol agent "discards" a bundle by
   simply ceasing all operations on the bundle and functionally erasing
   all references to it; the specific procedures by which this is
   accomplished are an implementation matter.  Bundles are discarded
   silently, i.e., the discarding of a bundle does not result in
   generation of an administrative record.  "Retention constraints" are
   elements of bundle state that prevent a bundle from being discarded;


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   a bundle cannot be discarded while it has any retention constraints.
   A bundle protocol agent "deletes" a bundle in response to some
   anomalous condition by notifying the bundle's report-to endpoint of
   the deletion (provided such notification is warranted; see 4.13 for
   details) and then arbitrarily removing all of the bundle's retention
   constraints, enabling the bundle to be discarded.

   Transmission – A transmission is a sustained effort by a node's
   bundle protocol agent to cause a bundle to be sent to all nodes in
   the minimum reception group of some endpoint (which may be the
   bundle's destination or may be some intermediate forwarding endpoint)
   in response to a transmission request issued by the node's
   application agent.  Any number of transmissions may be concurrently
   undertaken by the bundle protocol agent of a given node.

   Custody – To "accept custody" upon forwarding a bundle is to commit
   to retaining a copy of the bundle - possibly re-forwarding the bundle
   when the necessity to do so is determined - until custody of that
   bundle is "released".  Custody of a bundle whose destination is a
   singleton endpoint is released 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, or (c) the bundle is explicitly deleted for some reason,
   such as lifetime expiration; the condition(s) under which custody of
   a bundle whose destination is not a singleton endpoint may be
   released are not defined in this specification.  To "refuse custody"
   of a bundle is to decide not to accept custody of the bundle.  A
   "custodial node" of a bundle is a node that has accepted custody of
   the bundle and has not yet released that custody.  A "custodian" of a
   bundle is a singleton endpoint whose sole member is one of the
   bundle's custodial nodes.

2.2 Implementation architectures

   The above definitions are intended to enable the bundle protocol's
   operations to be specified in a manner that minimizes bias toward any
   particular implementation architecture.  To illustrate the range of
   interoperable implementation models that might conform to this
   specification, four example architectures are briefly described
   below.

   a) Bundle protocol application server

   A single bundle protocol application server, constituting a single
   bundle node, runs as a daemon process on each computer.  The daemon's
   functionality includes all functions of the bundle protocol agent,
   all convergence layer adapters, and both the administrative and
   application-specific elements of the application agent.  The
   application-specific element of the application agent functions as a
   server, offering bundle protocol service over a local area network:


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   it responds to remote procedure calls from application processes (on
   the same computer and/or remote computers) that need to communicate
   via the bundle protocol.  The server supports its clients by creating
   a new (conceptual) node for each one and registering each such node
   in a client-specified endpoint; the conceptual nodes managed by the
   server function as clients' Bundle Protocol service access points.

   b) Peer application nodes

   Any number of bundle protocol application processes, each one
   constituting a single bundle node, run in ad-hoc fashion on each
   computer.  The functionality of the bundle protocol agent, all
   convergence layer adapters, and the administrative element of the
   application agent is provided by a library to which each node process
   is dynamically linked at run time; the application-specific element
   of each node's application agent is node-specific application code.

   c) Sensor network nodes

   Each node of the sensor network is the self-contained implementation
   of a single bundle node.  All functions of the bundle protocol agent,
   all convergence layer adapters, and the administrative element of the
   application agent are implemented in simplified form in ASICs, while
   the application-specific element of each node's application agent is
   implemented in a programmable microcontroller.  Forwarding is
   rudimentary: all bundles are forwarded on a hard-coded default route.

   d) Dedicated bundle router

   Each computer constitutes a single bundle node that functions solely
   as a high-performance bundle forwarder.  Many standard functions of
   the bundle protocol agent, the convergence layer adapters, and the
   administrative element of the application agent are implemented in
   ASICs, but some functions are implemented in a high-speed processor
   to enable reprogramming as necessary.  The node's application agent
   has no application-specific element.  Substantial non-volatile
   storage resources are provided, and arbitrarily complex forwarding
   algorithms are supported.

2.3 Services offered by bundle protocol agents

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

      a) commencing a registration (registering a node in an endpoint);
      b) terminating a registration;
      c) switching a registration between Active and Passive state;
      d) transmitting a bundle to an identified bundle endpoint;
      e) canceling a transmission;
      f) polling a registration that is in passive state;
      g) delivering a received bundle;


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      h) acknowledging receipt of a bundle's contents.

3.   Bundle Format

   Each bundle shall be a concatenated sequence of at least two bundle
   header structures.  The first header in the sequence must be a
   primary bundle header, and no bundle may have more than one primary
   bundle header.  Additional bundle protocol headers of other types may
   follow the primary header to support extensions to the Bundle
   Protocol, such as the Bundle Security Protocol.  At most one of the
   headers in the sequence may be a payload header.  The last header in
   the sequence must have the "last header" flag (in its header
   processing control flags) set to 1; for every other header in the
   bundle after the primary header, this flag must be set to zero.

3.1 Canonical Bundle Header Format

   Every bundle header of every type other than the primary bundle
   header comprises the following elements, in this order:
      o Header type code, expressed as an 8-bit unsigned binary
        integer.  Bundle header type code 1 indicates that the header
        is a bundle payload header.  All other values of the header
        type code are reserved for future use.
      o Header processing control flags, a set of eight 1-bit flag
        values.
      o Header data length, an unsigned integer expressed as an SDNV
        (explained below).  The Header data length field contains the
        aggregate length of all remaining fields of the header, i.e.,
        the header-type-specific data fields.
      o Header-type-specific data fields, whose format and order are
        type-specific and whose aggregate length in octets is the value
        of the header data length field.  All multi-byte header-type-
        specific data fields are represented in network byte order.

3.2 Bundle Processing Flags

   The following Boolean processing control flags are present only in
   the bundle processing control flags byte of the primary bundle header
   of each bundle:

   00000001 -  Bundle is a fragment.
   00000010 -  Application data unit is an administrative record.
   00000100 -  Bundle must not be fragmented.
   00001000 -  Custody transfer is requested.
   00010000 -  Destination endpoint is a singleton.
   00100000 -  Reserved for future use.
   01000000 -  Reserved for future use.
   10000000 -  Reserved for future use.

   If the bundle processing control flags indicate that the bundle's
   application data unit is an administrative record, then the custody


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   transfer requested flag must be zero.  If the custody transfer
   requested flag is 1 then the sending node requests that the receiving
   node accept custody of the bundle.

3.3 Header Processing Flags

   The following Boolean processing control flags are present in the
   header processing control flags byte of every bundle header other
   than the primary bundle header of each bundle:

   00000001 -  Header must be replicated in every fragment.
   00000010 -  Transmit status report if header can't be processed.
   00000100 -  Discard bundle if header can't be processed.
   00001000 -  Last header.
   00010000 -  Reserved for future use.
   00100000 -  Reserved for future use.
   01000000 -  Reserved for future use.
   10000000 -  Reserved for future use.

   For each bundle whose primary header's bundle processing control
   flags (see above) indicate that the bundle's application data unit is
   an administrative record, the "Transmit status report if header can't
   be processed" flag in the header processing flags element of every
   other header in the bundle must be zero.

3.4 Self-Delimiting Numeric Values (SDNV)

   The design of the bundle protocol attempts to reconcile minimal
   consumption of transmission bandwidth with:
      o extensibility to address requirements not yet identified, and
      o scalability across a wide range of network scales and payload
        sizes.

   A key strategic element in the design is the use of self-delimiting
   numeric values (SDNVs).  The SDNV encoding scheme is closely adapted
   from the Abstract Syntax Notation One [ASN1] scheme for encoding
   Object Identifier Arcs.  An SDNV is a numeric value encoded in N
   octets, the last of which has its most significant bit (MSB) set to
   zero; the MSB of every other octet in the SDNV must be set to 1.  The
   value encoded in an SDNV is the unsigned binary number obtained by
   concatenating into a single bit string the 7 least significant bits
   of each octet of the SDNV.

   The following examples illustrate the encoding scheme for various
   hexadecimal values.

   0xABC  : 1010 1011 1100
            is encoded as
            {100 1010 1} {0 011 1100}
            = 10010101 00111100



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   0x1234 : 0001 0010 0011 0100
          =    1 0010 0011 0100
            is encoded as
            {10 1 0010 0} {0 011 0100}
            = 10100100 00110100

   0x4234 : 0100 0010 0011 0100
          =  100 0010 0011 0100
            is encoded as
            {1000000 1} {1 00 0010 0} {0 011 0100}
            = 10000001 10000100 00110100

   0x7F   : 0111 1111
          =  111 1111
            is encoded as
            {0 111 1111}
            = 01111111

   Note: Care must be taken to make sure that the value to be encoded is
   (in concept) padded with high-order zero bits to make its bitwise
   length a multiple of 7 before encoding.  Also note that, while there
   is no theoretical limit on the size of an SDNV field, the overhead of
   the SDNV scheme is 1/8-th of the bitwise length of the value to be
   encoded.  In order to encode an 64-bit numeric value, an SDNV field
   of 9 octets is required.  128 bits of overhead would be consumed in
   encoding a 1024-bit RSA encryption key directly in an SDNV.

   An SDNV can be used to represent both very large and very small
   integer values.  However, SDNV is clearly not the best way to
   represent every numeric value.  For example, an SDNV is a poor way to
   represent an integer whose value typically falls in the range 128 to
   255.  In general, though, we believe that SDNV representation of
   numeric values in bundle headers yields the smallest bundle header
   sizes without sacrificing scalability.

3.5 Endpoint IDs

   The destinations of bundles are bundle endpoints, identified by text
   strings termed "endpoint IDs" (see section 2.1).  Each endpoint ID
   conveyed in any bundle header takes the form of a Uniform Resource
   Identifier (URI; [RFC3986]).  As such, each endpoint ID can be
   characterized as having this general structure:

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

   As used for the purposes of the bundle protocol, neither the length
   of a scheme name nor the length of an SSP may exceed 1023 bytes.

   Bundle headers cite a number of endpoint IDs for various purposes of
   the bundle protocol.  Many, though not necessarily all, of the
   endpoint IDs referred to in the headers of a given bundle are


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   conveyed in the "dictionary" byte array in the bundle's primary
   header.  This array is simply the concatenation of any number of
   null-terminated scheme names and SSPs.

   "Endpoint ID references" are used to cite endpoint IDs that are
   contained in the dictionary; all endpoint ID citations in the primary
   bundle header are endpoint ID references, and other bundle headers
   may contain endpoint ID references as well.  Each endpoint ID
   reference is an ordered pair of 16-bit unsigned integers:

      o The offset, within the dictionary, of the first character of
        the referenced endpoint ID's scheme name.

      o The offset, within the dictionary, of the first character of
        the referenced endpoint ID's SSP.

   This encoding enables a degree of header compression: when the source
   and report-to of a bundle are the same endpoint, for example, the
   text of that endpoint's ID may be cited twice yet appear only once in
   the dictionary.

   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 [RFC2717] may be used in a
   bundle protocol endpoint ID.  In addition, a single additional scheme
   is defined by the present document:

     o The "dtn" scheme, which is used at minimum in the
        representation of the null endpoint ID "dtn:none".  The
        forwarding of a bundle to the null endpoint is never
        contraindicated, and the minimum reception group for the null
        endpoint is the empty set.

   Note that, although the endpoint IDs conveyed in bundle headers are
   expressed as URIs, implementations of the BP service interface may
   support expression of endpoint IDs in some internationalized manner
   (e.g., IRIs; see RFC 3987).

3.6 Formats of Bundle Headers

   This section describes the formats of the primary header and payload
   header.  Rules for processing these headers appear in section 4 of
   this document.

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

   The format of the two basic BP headers is shown in Figure 2 below.


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Primary Bundle Header
+----------------+----------------+----------------+----------------+
|    Version     |  Proc. Flags   |   COS Flags    |   SRR Flags    |
+----------------+----------------+----------------+----------------+
|                          [Header length (*)]                      |
+----------------+----------------+---------------------------------+
|   Destination scheme offset     |     Destination SSP offset      |
+----------------+----------------+----------------+----------------+
|      Source scheme offset       |        Source SSP offset        |
+----------------+----------------+----------------+----------------+
|    Report-to scheme offset      |      Report-to SSP offset       |
+----------------+----------------+----------------+----------------+
|    Custodian scheme offset      |      Custodian SSP offset       |
+----------------+----------------+----------------+----------------+
|                                                                   |
+                    Creation Timestamp (8 bytes)                   +
|                                                                   |
+---------------------------------+---------------------------------+
|                             Lifetime                              |
+----------------+----------------+----------------+----------------+
|                        Dictionary length (**)                     |
+----------------+----------------+----------------+----------------+
|                  Dictionary byte array (variable)                 |
+----------------+----------------+---------------------------------+
|                      [Fragment offset (***)]                      |
+----------------+----------------+---------------------------------+
|              [Total application data unit length (****)]          |
+----------------+----------------+---------------------------------+



Bundle Payload Header
+----------------+----------------+----------------+----------------+
|  Header type   |  Proc. Flags   |        Header length(*****)     |
+----------------+----------------+----------------+----------------+
|                                                                   |
|                     Bundle Payload (variable)                     |
|                                                                   |
/                                                                   /
/                                                                   /
|                                                                   |
+-------------------------------------------------------------------+

                 Figure 2:   Bundle header formats.
   Notes:

   (*)  The header length field of the Primary Bundle Header is an SDNV
   and is therefore variable-length.  A four-octet SDNV is shown here
   for convenience in representation.

   (**)  The dictionary length field of the Primary Bundle Header is an


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   SDNV and is therefore variable-length.  A four-octet SDNV is shown
   here for convenience in representation.

   (***)  The fragment offset field of the Primary Bundle Header is
   present only if the Fragment flag in the header's processing flags
   byte is set to 1.  It is an SDNV and is therefore variable-length; a
   four-octet SDNV is shown here for convenience in representation.

   (****)  The total application data unit length field of the Primary
   Bundle Header is present only if the Fragment flag in the header's
   processing flags byte is set to 1.  It is an SDNV and is therefore
   variable-length; a four-octet SDNV is shown here for convenience in
   representation.

   (*****)  The header length field of the Payload Header is an SDNV and
   is therefore variable-length.  A two-octet SDNV is shown here for
   convenience in representation.

3.6.1 Primary Bundle Header

   The primary bundle header contains the basic information needed to
   route bundles to their destinations.  The fields of the primary
   bundle header are:

   Version.  A 1-byte field indicating the version of the bundle
          protocol that constructed this header.  The present document
          describes version 0x04 of the bundle protocol.

   Bundle Processing Control Flags.  The Bundle Processing Control Flags
          field is a 1-byte field that contains the bundle processing
          control flags discussed in section 3.2 above.

   Class of Service Flags.  The COS Flags byte consists of two (2) bits
          of priority followed by six (6) bits that are reserved for
          future use.  The two-bit priority field indicates the bundle's
          priority, with higher values being of higher priority: 00 =
          bulk, 01 = normal, 10 = expedited, 11 is reserved for future
          use.

   Status Report Request Flags.  The status report request flags
          indicate the source node's requests for bundle status report
          generation.  If the bundle processing control flags indicate
          that the bundle's application data unit is an administrative
          record, then all status report request flags must be zero.
          The interpretation of the status report request flags is as
          follows.







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         Table 1: Status Report Request Flag Meanings

         +---------+--------------------------------------------+
         |  Value  |                  Meaning                   |
         +=========+============================================+
         |   0x00  |  No status reports requested.              |
         +---------+--------------------------------------------+
         |   0x01  |  Request reporting of bundle reception.    |
         +---------+--------------------------------------------+
         |   0x02  |  Request reporting of custody acceptance.  |
         +---------+--------------------------------------------+
         |   0x04  |  Request reporting of bundle forwarding.   |
         +---------+--------------------------------------------+
         |   0x08  |  Request reporting of bundle delivery.     |
         +---------+--------------------------------------------+
         |   0x10  |  Request reporting of bundle deletion.     |
         +---------+--------------------------------------------+
         |   0x20  |  Request acknowledgement by application.   |
         +---------+--------------------------------------------+
         |   0x40  |  Unused.                                   |
         +---------+--------------------------------------------+
         |   0x80  |  Unused.                                   |
         +---------+--------------------------------------------+

   Header Length.  The Header Length field is an SDNV that contains the
          aggregate length of all remaining fields of the header.

   Destination Scheme Offset.  The Destination Scheme Offset field
          contains the offset within the dictionary byte array of the
          scheme name of the endpoint ID of the bundle's destination,
          i.e., the endpoint containing the node(s) at which the bundle
          is to be delivered.

   Destination SSP Offset.  The Destination SSP Offset field contains
          the offset within the dictionary byte array of the scheme-
          specific part of the endpoint ID of the bundle's destination.

   Source Scheme Offset.  The Source Scheme Offset field contains the
          offset within the dictionary byte array of the scheme name of
          the endpoint ID of the bundle's nominal source, i.e., the
          endpoint nominally containing the node from which the bundle
          was initially transmitted.

   Source SSP Offset.  The Source SSP Offset field contains the offset
          within the dictionary byte array of the scheme-specific part
          of the endpoint ID of the bundle's nominal source.

   Report-to Scheme Offset.  The Report-to Scheme Offset field contains
          the offset within the dictionary byte array of the scheme name
          of the ID of the endpoint to which status reports pertaining
          to the forwarding and delivery of this bundle are to be


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          transmitted.

   Report-to SSP Offset.  The Report-to SSP Offset field contains the
          offset within the dictionary byte array of the scheme-specific
          part of the ID of the endpoint to which status reports
          pertaining to the forwarding and delivery of this bundle are
          to be transmitted.

   Custodian Scheme Offset.  The "current custodian endpoint ID" of a
          primary bundle header identifies an endpoint whose membership
          includes the node that most recently accepted custody of the
          bundle upon forwarding this bundle.  The Custodian Scheme
          Offset field contains the offset within the dictionary byte
          array of the scheme name of the current custodian endpoint ID.

   Custodian SSP Offset.  The Destination SSP Offset field contains the
          offset within the dictionary byte array of the scheme-specific
          part of the current custodian endpoint ID.

   Creation Timestamp.  The creation timestamp is an 8-byte field that,
          together with the source endpoint ID and (if applicable) the
          fragment offset, serves to identify the bundle.  The high-
          order four bytes of the timestamp are the bundle's creation
          time while its low-order four bytes are the bundle's creation
          timestamp sequence number.  Bundle creation time is the time -
          expressed in seconds since the start of the year 2000, on the
          Coordinated Universal Time (UTC) scale [7] - at which the
          transmission request was received that resulted in the
          creation of the bundle.  Sequence count is 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.  A source Bundle Protocol Agent must never
          create two distinct bundles with the same source endpoint ID
          and bundle creation timestamp.  The combination of source
          endpoint ID and bundle creation timestamp therefore serves to
          identify a single transmission request, enabling it to be
          acknowledged by the receiving application.

   Lifetime.   The four-byte lifetime field 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 the current
          time is greater than the creation time plus the lifetime,
          bundle nodes need no longer retain or forward the bundle; the
          bundle may be deleted from the network.

   Dictionary Length.  The Dictionary Length field is an SDNV that
          contains the length of the dictionary byte array.

   Dictionary.  The Dictionary field is an array of bytes formed by


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          concatenating the null-terminated scheme names and SSPs of all
          endpoint IDs referenced by any fields in this Primary Header
          together with, potentially, other endpoint IDs referenced by
          fields in other TBD DTN protocol headers.  Its length is given
          by the value of the Dictionary Length field.

   Fragment Offset.  If the Bundle Processing Control Flags of this
          Primary header indicate that the bundle is a fragment, then
          the Fragment Offset field is an SDNV indicating the offset
          from the start of the original application data unit at which
          the bytes comprising the payload of this bundle were located.
          If not, then the Fragment Offset field is omitted from the
          header.

   Total Application Data Unit Length.  If the Bundle Processing Control
          Flags of this Primary header indicate that the bundle is a
          fragment, then the Total Application Data Unit Length field is
          an SDNV indicating the total length of the original
          application data unit of which this bundle's payload is a
          part.  If not, then the Total Application Data Unit Length
          field is omitted from the header.

3.6.2 Bundle Payload Header

   The fields of the bundle payload header are:

   Header Type.  The Header Type field is a 1-byte field that indicates
          the type of the header.  For the bundle payload header this
          field contains the value 1.

   Header Processing Control Flags.  The Header Processing Control Flags
          field is a 1-byte field that contains the header processing
          control flags discussed in section 3.3 above.

   Header Length.  The Header Length field is an SDNV that contains the
          aggregate length of all remaining fields of the header – which
          is to say, the length of the bundle's payload.

   Payload.  The application data carried by this bundle.

4.   Bundle Processing

   The bundle processing procedures mandated in this section and in
   section 5 govern the operation of the Bundle Protocol Agent and the
   Application Agent administrative element of each bundle node.  They
   are neither exhaustive nor exclusive.  That is, supplementary DTN
   protocol specifications (including, but not restricted to, the Bundle
   Security Protocol) may require that additional measures be taken at
   specified junctures in these procedures.  Such additional measures
   shall not override or supersede the mandated bundle protocol
   procedures, except that they may in some cases make these procedures


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   moot by requiring, for example, that implementations conforming to
   the supplementary protocol terminate the processing of a given
   incoming or outgoing bundle due to a fault condition recognized by
   that protocol.

4.1 Generation of administrative records

   All initial transmission of bundles is in response to bundle
   transmission requests presented by nodes' application agents.  When
   required to "generate" an administrative record (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 5 below; in practice, the manner
   in which administrative record generation is accomplished is an
   implementation matter, provided the constraints noted in section 5
   are observed.

   Notes on administrative record terminology:

   a. A "bundle reception status report" is a bundle status report with
   the "reporting node received bundle" flag set to 1.

   b. A "custody acceptance status report" is a bundle status report
   with the "reporting node accepted custody of bundle" flag set to 1.

   c. A "bundle forwarding status report" is a bundle status report with
   the "reporting node forwarded the bundle" flag set to 1.

   d. A "bundle delivery status report" is a bundle status report with
   the "reporting node delivered the bundle" flag set to 1.

   e. A "bundle deletion status report" is a bundle status report with
   the "reporting node deleted the bundle" flag set to 1.

   f. An "acknowledgement status report" is a bundle status report with
   the "acknowledged by application" flag set to 1.

   g. A "Succeeded" custody signal is a custody signal with the "custody
   transfer succeeded" flag set to 1.

   h. A "Failed" custody signal is a custody signal with the "custody
   transfer succeeded" flag set to zero.

   i. The "current custodian" of a bundle is the endpoint identified by
   the current custodian endpoint ID in the bundle's primary header.

4.2 Bundle transmission



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   The steps in processing a bundle transmission request are:

   Step 1: If custody transfer is requested for this bundle transmission
      and, moreover, custody acceptance by the source node is required,
      then either the bundle protocol agent must commit to accepting
      custody of the bundle – in which case processing proceeds from
      Step 2 - or else the request cannot be honored and all remaining
      steps of this procedure must be skipped.

   Step 2: Transmission of the bundle is initiated.  An outbound bundle
      must be created per the parameters of the bundle transmission
      request, with current custodian endpoint ID set to the null
      endpoint ID "dtn:none" and with the retention constraint "Dispatch
      pending".  The source endpoint ID of the bundle must be either the
      ID of an endpoint of which the node is a member or else the null
      endpoint ID "dtn:none".

   Step 3: Processing proceeds from Step 1 of section 4.3.

4.3 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 4.7
      must be followed.

   Step 2: Processing proceeds from Step 1 of section 4.4.

4.4 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
      Table 5.  In particular:

     o The bundle protocol agent must determine which endpoint(s) to
        forward the bundle to.  The bundle protocol agent may choose
        either to forward the bundle directly to its destination
        endpoint (if possible) or else to forward the bundle to some
        other endpoint(s) for further forwarding.  The manner in which
        this decision is made may depend on the scheme name in the
        destination endpoint ID but in any case is beyond the scope of
        this document.  If the agent finds it impossible to select any
        endpoint(s) to forward the bundle to, then forwarding is
        contraindicated.


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     o Provided the bundle protocol agent succeeded in selecting the
        endpoint(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 the nodes of the
        minimum reception group of each selected endpoint.  The manner
        in which the appropriate convergence layer adapters are
        selected may depend on the scheme name in the destination
        endpoint ID but in any case is beyond the scope of this
        document.  If the agent finds it impossible to select
        convergence layer adapters 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 Table 5, then the
      Forwarding Contraindicated procedure defined in 4.4.1 must be
      followed; the remaining steps of section 4 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 4.10 must be followed.

   Step 5: For each endpoint 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 the nodes constituting the minimum reception group of
      that endpoint.  Determining the time at which the bundle is to be
      sent by each convergence layer adapter is an implementation
      matter.

   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:

      o  If the "request reporting of bundle forwarding" flag in the
          bundle's class of service field is set to 1, then a bundle
          forwarding status report must be generated, destined for the
          bundle's report-to endpoint ID.  If the bundle has the
          retention constraint "custody accepted" and all of the nodes
          in the minimum reception group of the endpoint selected for
          forwarding 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".

      o  The bundle's "Forward pending" retention constraint must be
          removed.

4.4.1 Forwarding Contraindicated



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   The steps in responding to contraindication of forwarding for some
   reason are:

   Step 1: The bundle protocol agent must determine whether or not to
      declare failure in forwarding the bundle for this reason.  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 4.4.2 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 4.10 must be followed; (b) when - at
      some future time - the forwarding of this bundle ceases to be
      contraindicated, processing proceeds from Step 5 of 4.4.

4.4.2 Forwarding Failed

   The steps in responding to a declaration of forwarding failure for
   some reason 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.  Procedures for handling failure of
      custody transfer for a bundle whose destination is not a singleton
      endpoint are not defined in this specification.  For a bundle
      whose destination is a singleton endpoint, the bundle protocol
      agent must handle the custody transfer failure by generating a
      "Failed" custody signal for the bundle, destined for the bundle's
      current custodian; 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 the current custodian still has
      a copy.)

   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 4.13 must be
      followed, citing the reason for which forwarding was determined to
      be contraindicated.

4.5 Bundle expiration

   A bundle expires when the current time is greater than the bundle's
   creation time plus its lifetime as specified in the primary bundle
   header.  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 4.13 must be followed.



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4.6 Bundle reception

   The steps in processing a bundle 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 class of service field is set to 1, then a bundle
      reception status report with reason code "No additional
      information" must be generated, destined for the bundle's report-
      to endpoint ID.

   Step 3: If any header in the bundle cannot be processed:

      o  If the header processing flags in the header indicate that a
          status report must be generated in this event, then a bundle
          reception status report with reason code "Header
          unintelligible" must be generated, destined for the bundle's
          report-to endpoint ID.

     o  If the header processing flags in that header indicate that
          the bundle must be discarded in this event, then the bundle
          protocol agent must delete the bundle for the reason "Header
          unintelligible": the bundle deletion procedure defined in 4.13
          must be followed.  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 endpoint ID, creation timestamp, and fragment offset
      as another bundle that (a) has not been discarded and (b)
      currently has the retention constraint "Custody accepted", custody
      transfer redundancy must be handled; otherwise, processing
      proceeds from Step 5.  Procedures for handling redundancy in
      custody transfer for a bundle whose destination is not a singleton
      endpoint are not defined in this specification.  For a bundle
      whose destination is a singleton endpoint, the bundle protocol
      agent must handle custody transfer redundancy by generating a
      "Failed" custody signal 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 4.3.

4.7 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


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      unit reassembly procedure described in 4.9 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 are skipped.

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

      o  If the registration is in the Active state, then the bundle
          must be delivered subject to this registration (see 2.1 above)
          as soon as all previously received bundles that are
          deliverable subject to this registration have been delivered.

     o  If the registration is in the Passive state, then the
          registration's delivery failure action must be taken (see 2.1
          above).

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

      o  If the "request reporting of bundle delivery" flag in the
          bundle's class of service field is set to 1, then a bundle
          delivery status report must 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.

      o  If the bundle's custody transfer requested flag (in the bundle
          processing flags field) is set to 1, custodial delivery must
          be reported.  Procedures for reporting custodial delivery for
          a bundle whose destination is not a singleton endpoint are not
          defined in this specification.  For a bundle whose destination
          is a singleton endpoint, the bundle protocol agent must report
          custodial delivery by generating a "Succeeded" custody signal
          for the bundle, destined for the bundle's current custodian.

4.8
    Bundle Fragmentation

   It may at times be necessary for bundle protocol agents to reduce the
   sizes of bundles in order to forward them.  This might be the case,
   for example, if the endpoint 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 endpoint ID and
   creation timestamp as the original bundle – whose payloads are the


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   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 whose primary header's bundle processing flags do NOT
   indicate that it must not be fragmented may be fragmented at any
   time, for any purpose, at the discretion of the bundle protocol
   agent.

   Fragmentation shall be constrained as follows:

     o  The concatenation of the payloads of all fragments produced by
        a fragmentation must always be identical to the payload of the
        bundle that was fragmented.  Note that the payloads of
        fragments resulting from different fragmentation episodes, in
        different parts of the network, may be overlapping subsets of
        the original bundle's payload.

     o  The bundle processing flags in the primary header of each
        fragment must be modified to indicate that the bundle is a
        fragment, and both fragment offset and total application data
        unit length must be provided at the end of each fragment's
        primary bundle header.

      o All fragments must contain the same headers as the original
        bundle, except that (a) the primary headers of the fragments
        will differ from that of the fragmented bundle as noted above,
        (b) the payload headers of fragments will differ from that of
        the fragmented bundle, and (c) any header whose header
        processing flags do NOT indicate that the header must be
        replicated in every fragment should be replicated only in the
        fragment whose fragment offset is zero.

4.9 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 endpoint 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 header, then:

     o  This byte array – the reassembled application data unit – must
        replace the payload of this fragment.

     o  The "Reassembly pending" retention constraint must be removed
        from every other fragment whose payload is a subset of the
        reassembled application data unit.



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  Note: reassembly of application data units from fragments occurs at
  destination endpoints as necessary; an application data unit may also
  be reassembled at some other endpoint on the route to the
  destination.

4.10 Custody transfer

  The conditions under which a node may accept custody of a bundle
  whose destination is not a singleton endpoint are not defined in this
  specification.

  The decision as to whether or not to accept custody of a bundle whose
  destination is a singleton endpoint is an implementation matter which
  may involve both resource and policy considerations; however, if the
  bundle protocol agent has committed to accepting custody of the
  bundle (as described in Step 1 of 4.2) then custody must be accepted.

  If the bundle protocol agent elects to accept custody of the bundle,
  then it must follow the custody acceptance procedure defined in
  4.10.1.

4.10.1
       Custody acceptance

  Procedures for acceptance of custody of a bundle whose destination is
  not a singleton endpoint are not defined in this specification.

  Procedures for acceptance of custody of a bundle whose destination is
  a singleton endpoint are defined as follows.

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

  If the "request custody acceptance reporting" flag in the bundle's
  class of service field is set to 1, a custody acceptance status
  report must 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 1 of 4.6) then this report should be
  generated by simply turning on the "Reporting node accepted custody
  of bundle" flag in that earlier report's status flags byte.

  The bundle protocol agent must generate a "Succeeded" custody signal
  for the bundle, destined for the bundle's current custodian.

  The bundle protocol agent must assert the new current custodian for
  the bundle.  It does so by changing the current custodian endpoint ID
  in the bundle's primary header to the endpoint ID of one of the
  singleton endpoints in which the node is registered.  This may entail
  appending that endpoint ID's null-terminated scheme name and SSP to
  the dictionary byte array in the bundle's primary header, and in some
  case it may also enable the (optional) removal of the current
  custodian endpoint ID's scheme name and/or SSP from the dictionary.


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  The bundle protocol agent may set a custody transfer countdown timer
  for this 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
  4.12 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.

4.10.2
       Custody release

  Procedures for release of custody of a bundle whose destination is
  not a singleton endpoint are not defined in this specification.

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

4.11 Custody transfer success

   Procedures for determining custody transfer success for a bundle
   whose destination is not a singleton endpoint are not defined in this
   specification.

   Upon receipt of a "Succeeded" custody signal at a node that is a
   custodial node of the bundle identified in the custody signal, where
   the destination of the bundle is a singleton endpoint, custody of the
   bundle must be released as described in 4.10.2.

4.12 Custody transfer failure

   Procedures for determining custody transfer failure for a bundle
   whose destination is not a singleton endpoint are not defined in this
   specification.  Custody transfer for a bundle whose destination is a
   singleton endpoint is determined to have failed at a custodial node
   for that bundle when either (a) that node's custody transfer timer
   for that bundle (if any) expires or (b) a "Failed" custody signal for
   that bundle is received at that node.

   Upon determination of custody transfer failure, the action taken by
   the bundle protocol agent is implementation-specific and may depend
   on the nature of the failure.  For example, if custody transfer
   failure was inferred from expiration of a custody transfer timer or
   was asserted by a "Failed" custody signal with the "Depleted storage"
   reason code, the bundle protocol agent might choose to re-forward the
   bundle, possibly on a different route (section 4.4).  Receipt of a
   "Failed" custody signal with the "Redundant reception" reason code,
   on the other hand, might cause the bundle protocol agent to release
   custody of the bundle and to revise its algorithm for computing


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   countdown intervals for custody transfer timers.

4.13 Bundle deletion

   The steps in deleting a bundle are:

   Step 1: If the retention constraint "Custody accepted" currently
      prevents this bundle from being discarded, and the destination of
      the bundle is a singleton endpoint, then:

      o  Custody of the node is released as described in 4.10.2.

      o  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 class of service field is set to 1, then a bundle
      deletion status report citing the reason for deletion must be
      generated, destined for the bundle's report-to endpoint ID.

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

4.14 Discarding a bundle

   As soon as a bundle has no remaining retention constraints it may be
   discarded.

4.15 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 canceled".  For this purpose, the procedure
   defined in 4.13 must be followed.

4.16 Polling

   When requested to poll a specified registration that is in Passive
   state, the bundle protocol agent must immediately deliver the least
   recently received bundle that is deliverable subject to the indicated
   registration, if any.

4.17 Acknowledging an application data unit

   When requested to acknowledge to an indicated report-to endpoint the
   bundle transmission request identified by an indicated source
   endpoint ID and bundle creation timestamp, the bundle protocol agent
   must generate an acknowledgement status report for that transmission
   request, destined for that report-to-endpoint.



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5.   Administrative record processing

5.1 Administrative records

   Two types of administrative records have been defined to date: bundle
   status reports and custody signals.

   Every administrative record consists of a four-bit record type code
   followed by four bits of administrative record flags, followed by
   record content in type-specific format.  Record type codes are
   defined as follows:

         Table 2: Administrative Record Type Codes

         +---------+--------------------------------------------+
         |  Value  |                  Meaning                   |
         +=========+============================================+
         |  0x01   |  Bundle status report.                     |
         +---------+--------------------------------------------+
         |  0x02   |  Custody signal.                           |
         +---------+--------------------------------------------+
         | (other) |  Reserved for future use.                  |
         +---------+--------------------------------------------+

   Administrative record flags are defined as follows:

         Table 3: Administrative Record Flags

         +---------+--------------------------------------------+
         |  Value  |                  Meaning                   |
         +=========+============================================+
         |  0x01   |  Record is for a fragment; fragment        |
         |         |  offset and length fields are present.     |
         +---------+--------------------------------------------+
         | (other) |  Reserved for future use.                  |
         +---------+--------------------------------------------+

   All time values in administrative records are UTC times expressed in
   "DTN time" representation.  A DTN time consists of a 32-bit number in
   network byte order indicating the number of seconds since the start
   of the year 2000, followed by a 32-bit number in network byte order
   indicating the number of nanoseconds since the start of the indicated
   second.

   The contents of the various types of administrative records are
   described below.

5.1.1 Bundle Status Reports

   The transmission of 'bundle status reports' under specified
   conditions is an option that can be invoked when transmission of a


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   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.

   Format of Bundle Status Report for bundle 'X':

+----------------+----------------+----------------+----------------+
|  Status Flags  |  Reason code   |       Fragment offset (*) (if
+----------------+----------------+----------------+----------------+
    present)     |      Fragment length (**) (if present)           |
+----------------+----------------+----------------+----------------+
|
+        Time of receipt of bundle X (8 bytes, if present)          +
                                                                    |
+----------------+----------------+----------------+----------------+
|
+   Time of custody acceptance of bundle X (8 bytes, if present)    +
                                                                    |
+----------------+----------------+----------------+----------------+
|
+       Time of forwarding of bundle X (8 bytes, if present)        +
                                                                    |
+----------------+----------------+----------------+----------------+
|
+        Time of delivery of bundle X (8 bytes, if present)         +
                                                                    |
+----------------+----------------+----------------+----------------+
|
+        Time of deletion of bundle X (8 bytes, if present)         +
                                                                    |
+----------------+----------------+----------------+----------------+
|
+     Time of acknowledgement of bundle X (8 bytes, if present)     +
                                                                    |
+----------------+----------------+----------------+----------------+
|
+           Copy of bundle X's Creation Timestamp (8 bytes)         +
                                                                    |
+----------------+----------------+----------------+----------------+
|      Length of X's source endpoint ID (***)      |   Source
+----------------+---------------------------------+                +
                     endpoint ID of bundle X (variable)             |
+----------------+----------------+----------------+----------------+


   Notes:

   (*)  The Fragment Offset field, if present, is an SDNV and is
   therefore variable-length.  A three-octet SDNV is shown here for


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   convenience in representation.

   (**)  The Fragment Length field, if present, is an SDNV and is
   therefore variable-length.  A three-octet SDNV is shown here for
   convenience in representation.

   (***)  The source endpoint ID length field is an SDNV and is
   therefore variable-length.  A three-octet SDNV is shown here for
   convenience in representation.

   The fields in a bundle status report are:

   Status Flags.  A 1-byte field containing the following flags:

         Table 4: Status Flags for Bundle Status Reports

         +---------+--------------------------------------------+
         |  Value  |                  Meaning                   |
         +=========+============================================+
         |  0x01   |  Reporting node received bundle.           |
         +---------+--------------------------------------------+
         |  0x02   |  Reporting node accepted custody of bundle.|
         +---------+--------------------------------------------+
         |  0x04   |  Reporting node forwarded the bundle.      |
         +---------+--------------------------------------------+
         |  0x08   |  Reporting node delivered the bundle.      |
         +---------+--------------------------------------------+
         |  0x10   |  Reporting node deleted the bundle.        |
         +---------+--------------------------------------------+
         |  0x20   |  Acknowledged by application.              |
         +---------+--------------------------------------------+
         |  0x40   |  Unused.                                   |
         +---------+--------------------------------------------+
         |  0x80   |  Unused.                                   |
         +---------+--------------------------------------------+

   Reason code.  A 1-byte field explaining the value of the flags in the
          status flags byte.  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) may define
          additional reason codes.  Status report reason codes are
          defined as follows:










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         Table 5: Status Report Reason Codes

         +---------+--------------------------------------------+
         |  Value  |                  Meaning                   |
         +=========+============================================+
         |  0x00   |  No additional information.                |
         +---------+--------------------------------------------+
         |  0x01   |  Lifetime expired.                         |
         +---------+--------------------------------------------+
         |  0x02   |  Forwarded over unidirectional link.       |
         +---------+--------------------------------------------+
         |  0x03   |  Transmission canceled.                    |
         +---------+--------------------------------------------+
         |  0x04   |  Depleted storage.                         |
         +---------+--------------------------------------------+
         |  0x05   |  Destination endpoint ID unintelligible.   |
         +---------+--------------------------------------------+
         |  0x06   |  No known route to destination from here.  |
         +---------+--------------------------------------------+
         |  0x07   |  No timely contact with next node on route.|
         +---------+--------------------------------------------+
         |  0x08   |  Header unintelligible.                    |
         +---------+--------------------------------------------+
         | (other) |  Reserved for future use.                  |
         +---------+--------------------------------------------+

   Fragment offset.  If the bundle fragment bit is set in the status
          flags, then the offset (within the original application data
          unit) of the payload of the bundle that caused the status
          report to be generated is included here.

   Fragment length.  If the bundle fragment bit is set in the status
          flags, then the length of the payload of the subject bundle is
          included here.

   Time of Receipt (if present).  If the bundle-received bit is set in
          the status flags, then a DTN time indicating the time at which
          the bundle was received at the reporting node is included
          here.

   Time of Custody Acceptance (if present).  If the custody-accepted bit
          is set in the status flags, then a DTN time indicating the
          time at which custody was accepted at the reporting node is
          included here.

   Time of Forward (if present).  If the bundle-forwarded bit is set in
          the status flags, then a DTN time indicating the time at which
          the bundle was first forwarded at the reporting node is
          included here.



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   Time of Delivery (if present).  If the bundle-delivered bit is set in
          the status flags, then a DTN time indicating the time at which
          the bundle was delivered at the reporting node is included
          here.

   Time of Deletion (if present).  If the bundle-deleted bit is set in
          the status flags, then a DTN time indicating the time at which
          the bundle was deleted at the reporting node is included here.

   Time of Acknowledgement (if present).  If the bundle-acknowledged-by-
          application bit is set in the status flags, then a DTN time
          indicating the time at which the bundle was acknowledged by
          the application at the reporting node is included here.

   Creation Timestamp of Subject Bundle.  A copy of the creation
          timestamp of the bundle that caused the status report to be
          generated.

   Length of Source Endpoint ID.  The length in bytes of the source
          endpoint ID of the bundle that caused the status report to be
          generated.

  Source Endpoint ID text.  The text of the source endpoint ID of the
          bundle that caused the status report to be generated.

5.1.2 Custody Signals

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

   Custody signals have the following format.





















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   Custody Signal regarding bundle 'X':

+----------------+----------------+----------------+----------------+
|     Status     |      Fragment offset (*) (if present)            |
+----------------+----------------+----------------+----------------+
|                   Fragment length (**) (if present)               |
+----------------+----------------+----------------+----------------+
|
+                      Time of signal (8 bytes)                     +
                                                                    |
+----------------+----------------+----------------+----------------+
|
+           Copy of bundle X's Creation Timestamp (8 bytes)         +
                                                                    |
+----------------+----------------+----------------+----------------+
|      Length of X's source endpoint ID (***)      |   Source
+----------------+---------------------------------+                +
                     endpoint ID of bundle X (variable)             |
+----------------+----------------+----------------+----------------+

   Notes:

   (*)  The Fragment Offset field, if present, is an SDNV and is
   therefore variable-length.  A three-octet SDNV is shown here for
   convenience in representation.

   (**)  The Fragment Length field, if present, is an SDNV and is
   therefore variable-length.  A four-octet SDNV is shown here for
   convenience in representation.

   (***)  The source endpoint ID length field is an SDNV and is
   therefore variable-length.  A three-octet SDNV is shown here for
   convenience in representation.

   The fields in a custody signal are:

   Status.  A 1-byte field containing a 1-bit "custody transfer
   succeeded" flag followed by a 7-bit reason code explaining the value
   of that flag.  Custody signal reason codes are defined as follows:














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         Table 6: Custody Signal Reason Codes

         +---------+--------------------------------------------+
         |  Value  |                  Meaning                   |
         +=========+============================================+
         |  0x00   |  No additional information.                |
         +---------+--------------------------------------------+
         |  0x01   |  Reserved for future use.                  |
         +---------+--------------------------------------------+
         |  0x02   |  Reserved for future use.                  |
         +---------+--------------------------------------------+
         |  0x03   |  Redundant reception (reception by a node  |
         |         |  that is a custodial node for this bundle).|
         +---------+--------------------------------------------+
         |  0x04   |  Depleted storage.                         |
         +---------+--------------------------------------------+
         |  0x05   |  Destination endpoint ID unintelligible.   |
         +---------+--------------------------------------------+
         |  0x06   |  No known route to destination from here.  |
         +---------+--------------------------------------------+
         |  0x07   |  No timely contact with next node on route.|
         +---------+--------------------------------------------+
         |  0x08   |  Header unintelligible.                    |
         +---------+--------------------------------------------+
         | (other) |  Reserved for future use.                  |
         +---------+--------------------------------------------+

   Fragment offset.  If the bundle fragment bit is set in the status
          flags, then the offset (within the original application data
          unit) of the payload of the bundle that caused the status
          report to be generated is included here.

   Fragment length.  If the bundle fragment bit is set in the status
          flags, then the length of the payload of the subject bundle is
          included here.

   Time of Signal.  A DTN time indicating the time at which the signal
          was generated.

   Creation Timestamp of Subject Bundle.  A copy of the creation
          timestamp of the bundle to which the signal applies.

   Length of Source Endpoint ID.  The length in bytes of the source
          endpoint ID of the bundle to which the signal applied.

  Source Endpoint ID text.  The text of the source endpoint ID of the
          bundle to which the signal applies.

5.2 Generation of administrative records



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   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
      have the Fragment flag set and must contain the fragment offset
      and fragment length fields; the value of the fragment offset field
      must be the value of the referenced bundle's fragment offset, and
      the value of the fragment length field must be the length of the
      referenced bundle's payload.

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

5.3 Reception of custody signals

   For each received custody signal that has the Custody Transfer
   Succeeded  flag  set  to  1,  the  administrative  element  of  the
   application agent must direct the bundle protocol agent to follow the
   custody transfer success procedure in 4.11.

   For each received custody signal that has the Custody Transfer
   Succeeded  flag  set  to  0,  the  administrative  element  of  the
   application agent must direct the bundle protocol agent to follow the
   custody transfer failure procedure in 4.12.

6.   Services Required of the Convergence Layer

6.1 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.

6.2 Summary of Convergence Layer Services

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

      a) sending a bundle to all bundle nodes in the minimum reception
        group of the endpoint identified by a specified endpoint ID
        that are reachable via the convergence layer protocol;

      b) delivering to the bundle protocol agent a bundle that was sent


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        by a remote 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) may expect convergence layer adapters which serve BP
   implementations conforming to those protocols to provide additional
   services.

7. 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 [5]; an informative overview of this
   architecture is provided in [6].

   The bundle protocol has been designed with the notion that it will 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.

   Likewise, because of the potentially long 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 three, independent
   security specific bundle headers 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.



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   The Bundle Authentication Header (BAH) ensures the authenticity and
   integrity of bundles on a hop-by-hop basis between bundle nodes.  The
   BAH allows each bundle node to verify a bundle’s authenticity before
   processing or forwarding the bundle.  In this way, entities that are
   not authorized to send bundles will have unauthorized transmissions
   blocked by security-aware bundle nodes.

   Additionally, to provide "security-source" to "security-destination"
   bundle authenticity and integrity, the Payload Security Header (PSH)
   is used.  A "security-source" may not actually be the origination
   point of the bundle but instead may be the first point along the path
   that is security-aware and is able to apply security services.  For
   example, an enclave of networked systems may generate bundles but
   only their gateway may be required and/or able to apply security
   services.  The PSH allows any security-enabled entity along the
   delivery path, in addition to the "security-destination" (the
   recipient counterpart to the "security-source"), to ensure the
   bundle’s authenticity.

   Finally, to provide payload confidentiality, the use of the
   Confidentiality Header (CH) is available.  The bundle payload may be
   encrypted to provide "security-source" to "security-destination"
   payload confidentiality/privacy.  The CH indicates the cryptographic
   algorithm and key IDs that were used to encrypt the payload.

   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.

8. IANA Considerations

   The new Uniform Resource Identifier scheme "dtn", defined by the
   Bundle Protocol, will need to be documented.

9.   Normative References

   [RFC3978]   Bradner, S., "IETF Rights in Contributions", BCP 78, RFC
   3978, March 2005.

   [RFC3979]   Bradner, S., "Intellectual Property Rights in IETF
   Technology", BCP 79, RFC 3979, March 2005.

   [RFC3986]   T. Berners-Lee, R. Fielding, L. Masinter, "Uniform
   Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, Jan
   2005.

   [RFC2717]   Petke, R. and I. King, "Registration Procedures for URL
   Scheme Names", BCP 35, RFC 2717, November 1999.

10.  Informative References



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

   [2] V. Cerf, et. al., "Delay-Tolerant Network Architecture," work in
       progress, draft-irtf-dtnrg-arch-03.txt, July 2005

   [3] F. Warthman, "Delay-Tolerant Networks (DTNs): A Tutorial",
       Warthman Associates, available from http://www.dtnrg.org

   [4] Mills, D., "Network Time Protocol (Version 3) Specification,
       Implementation and Analysis", RFC 1305, March 1992

   [5] S. Symington, et. al., "Bundle Security Protocol Specification,"
       draft-irtf-dtnrg-bundle-security-00.txt, June 2005

   [6] S. Farrell, S. Symington, and H. Weiss, "Delay-Tolerant
       Networking Security Overview," draft-irtf-dtnrg-sec-overview-
       00.txt, September 2005

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

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

Author's Addresses

   Dr. Keith L. Scott              Scott C. Burleigh
   The MITRE Corporation           Jet Propulsion Laboratory
   7515 Colshire Drive             4800 Oak Grove Drive
   McLean, VA 22102                M/S: 179-206
   Telephone  +1 (703) 883-6547    Pasadena, CA 91109-8099
   FAX +1 (703) 883-7142           Telephone +1 (818) 393-3353
   Email kscott@mitre.org          FAX +1 (818) 354-1075
                                   Email Scott.Burleigh@jpl.nasa.gov

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

Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights


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   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at ietf-
   ipr@ietf.org.

Disclaimer

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Copyright Notice

   Copyright (C) The Internet Society (2005).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.

Acknowledgements

   The authors gratefully acknowledge the contributions of Dr. Vint Cerf
   of MCI, Dr. Kevin Fall and Michael Demmer of Intel Corporation,
   Adrian Hooke and Leigh Torgerson of the Jet Propulsion Laboratory,
   Stephen Farrell of Trinity College Dublin, and Robert Durst and Susan
   Symington of The MITRE Corporation.  Thanks to Howard Weiss of
   SPARTA, Inc., for the text of section 7 and to Manikantan Ramadas of
   Ohio University for most of the text of section 3.4, which is adapted
   from the specification for the Licklider Transmission Protocol.









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