Bundle Protocol
draft-ietf-dtn-bpbis-05
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9171.
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|---|---|---|---|
| Authors | Scott C. Burleigh , Kevin Fall , Edward J. Birrane | ||
| Last updated | 2016-09-07 | ||
| Replaces | draft-dtnwg-bp | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-dtn-bpbis-05
Delay-Tolerant Networking Working Group S. Burleigh
Internet Draft JPL, Calif. Inst. Of Technology
Intended status: Standards Track K. Fall
Expires: March 2017 Carnegie Mellon University / SEI
E. Birrane
APL, Johns Hopkins University
September 7, 2016
Bundle Protocol
draft-ietf-dtn-bpbis-05.txt
Status of this Memo
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This Internet-Draft will expire on March 11, 2017.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
document must include Simplified BSD License text as described in
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Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Simplified BSD License.
Abstract
This Internet Draft presents a specification for Bundle Protocol,
adapted from the experimental Bundle Protocol specification
developed by the Delay-Tolerant Networking Research group of the
Internet Research Task Force and documented in RFC 5050.
Table of Contents
1. Introduction...................................................3
2. Conventions used in this document..............................5
3. Service Description............................................5
3.1. Definitions...............................................5
3.2. Discussion of BP concepts.................................9
3.3. Services Offered by Bundle Protocol Agents...............15
4. Bundle Format.................................................15
4.1. BP Fundamental Data Structures...........................15
4.1.1. CRC Type............................................15
4.1.2. CRC.................................................16
4.1.3. Bundle Processing Control Flags.....................16
4.1.4. Block Processing Control Flags......................17
4.1.5. Identifiers.........................................18
4.1.5.1. Endpoint ID....................................18
4.1.5.2. Node ID........................................20
4.1.6. DTN Time............................................20
4.1.7. Creation Timestamp..................................20
4.1.8. Fragment ID.........................................20
4.1.9. Block-type-specific Data............................21
4.2. Bundle Representation....................................21
4.2.1. Bundle..............................................21
4.2.2. Primary Bundle Block................................21
4.2.3. Canonical Bundle Block Format.......................24
4.3. Extension Blocks.........................................26
4.3.1. Current Custodian...................................26
4.3.2. Previous Node.......................................27
4.3.3. Bundle Age..........................................27
4.3.4. Hop Count...........................................27
5. Bundle Processing.............................................28
5.1. Generation of Administrative Records.....................28
5.2. Bundle Transmission......................................29
5.3. Bundle Dispatching.......................................29
5.4. Bundle Forwarding........................................30
5.4.1. Forwarding Contraindicated..........................31
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5.4.2. Forwarding Failed...................................32
5.5. Bundle Expiration........................................32
5.6. Bundle Reception.........................................33
5.7. Local Bundle Delivery....................................34
5.8. Bundle Fragmentation.....................................35
5.9. Application Data Unit Reassembly.........................36
5.10. Custody Transfer........................................37
5.10.1. Custody Acceptance.................................37
5.10.2. Custody Release....................................38
5.11. Custody Transfer Success................................38
5.12. Custody Transfer Failure................................38
5.13. Custody Transfer Deferral...............................38
5.14. Bundle Deletion.........................................39
5.15. Discarding a Bundle.....................................39
5.16. Canceling a Transmission................................39
6. Administrative Record Processing..............................40
6.1. Administrative Records...................................40
6.1.1. Bundle Status Reports...............................41
6.1.2. Custody Signals.....................................43
6.2. Generation of Administrative Records.....................46
6.3. Reception of Custody Signals.............................46
7. Services Required of the Convergence Layer....................47
7.1. The Convergence Layer....................................47
7.2. Summary of Convergence Layer Services....................47
8. Security Considerations.......................................48
9. IANA Considerations...........................................49
10. References...................................................49
10.1. Normative References....................................49
10.2. Informative References..................................50
11. Acknowledgments..............................................50
12. Significant Changes from RFC 5050............................51
Appendix A. For More Information.................................52
1. Introduction
Since the publication of the Bundle Protocol Specification
(Experimental RFC 5050[RFC5050]) in 2007, the Delay-Tolerant
Networking Bundle Protocol has been implemented in multiple
programming languages and deployed to a wide variety of computing
platforms for a wide range of successful exercises. This
implementation and deployment experience has demonstrated the
general utility of the protocol for challenged network operations.
It has also, as expected, identified opportunities for making the
protocol simpler, more capable, and easier to use. The present
document, standardizing the Bundle Protocol (BP), is adapted from
RFC 5050 in that context.
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This document describes version 7 of BP.
Delay Tolerant Networking is a network architecture providing
communications in and/or through highly stressed environments.
Stressed networking environments include those with intermittent
connectivity, large and/or variable delays, and high bit error
rates. To provide its services, BP may be viewed as sitting at the
application layer of some number of constituent networks, forming a
store-carry-forward overlay network. Key capabilities of BP
include:
. Custodial forwarding
. Ability to cope with intermittent connectivity, including cases
where the sender and receiver are not concurrently present in
the network
. Ability to take advantage of scheduled, predicted, and
opportunistic connectivity, whether bidirectional or
unidirectional, in addition to continuous connectivity
. Late binding of overlay network endpoint identifiers to
underlying constituent network addresses
For descriptions of these capabilities and the rationale for the DTN
architecture, see [ARCH] and [SIGC]. [TUT] contains a tutorial-
level overview of DTN concepts.
BP's location within the standard protocol stack is as shown in
Figure 1. BP uses underlying "native" transport and/or network
protocols for communications within a given constituent network.
The interface between the bundle protocol and a specific underlying
protocol is termed a "convergence layer adapter".
Figure 1 shows three distinct transport and network protocols
(denoted T1/N1, T2/N2, and T3/N3).
+-----------+ +-----------+
| BP app | | BP app |
+---------v-| +->>>>>>>>>>v-+ +->>>>>>>>>>v-+ +-^---------+
| BP v | | ^ BP v | | ^ BP v | | ^ BP |
+---------v-+ +-^---------v-+ +-^---------v-+ +-^---------+
| Trans1 v | + ^ T1/T2 v | + ^ T2/T3 v | | ^ Trans3 |
+---------v-+ +-^---------v-+ +-^---------v + +-^---------+
| Net1 v | | ^ N1/N2 v | | ^ N2/N3 v | | ^ Net3 |
+---------v-+ +-^---------v + +-^---------v-+ +-^---------+
| >>>>>>>>^ >>>>>>>>>>^ >>>>>>>>^ |
+-----------+ +-------------+ +-------------+ +-----------+
| | | |
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|<---- A network ---->| |<---- A network ---->|
| | | |
Figure 1: The Bundle Protocol in the Protocol Stack Model
This document describes the format of the protocol data units
(called "bundles") passed between entities participating in BP
communications.
The entities are referred to as "bundle nodes". This document does
not address:
. Operations in the convergence layer adapters that bundle nodes
use to transport data through specific types of internets.
(However, the document does discuss the services that must be
provided by each adapter at the convergence layer.)
. The bundle route computation algorithm.
. Mechanisms for populating the routing or forwarding information
bases of bundle nodes.
. The mechanisms for securing bundles en route.
. The mechanisms for managing bundle nodes.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
3. Service Description
3.1. Definitions
Bundle - A bundle is a protocol data unit of BP, so named because
negotiation of the parameters of a data exchange may be impractical
in a delay-tolerant network: it is often better practice to "bundle"
with a unit of data all metadata that might be needed in order to
make the data immediately usable when delivered to applications.
Each bundle comprises a sequence of two or more "blocks" of protocol
data, which serve various purposes.
Block - A bundle protocol block is one of the protocol data
structures that together constitute a well-formed bundle.
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Bundle payload - A bundle payload (or simply "payload") is the
application data whose conveyance to the bundle's destination is the
purpose for the transmission of a given bundle; it is the content of
the bundle's payload block. The terms "bundle content", "bundle
payload", and "payload" are used interchangeably in this document.
Partial payload - A partial payload is a payload that comprises
either the first N bytes or the last N bytes of some other payload
of length M, such that 0 < N < M.
Fragment - A fragment is a bundle whose payload block contains a
partial payload.
Bundle node - A bundle node (or, in the context of this document,
simply a "node") is any entity that can send and/or receive bundles.
Each bundle node has three conceptual components, defined below, as
shown in Figure 2: a "bundle protocol agent", a set of zero or more
"convergence layer adapters", and an "application agent".
+-----------------------------------------------------------+
|Node |
| |
| +-------------------------------------------------------+ |
| |Application Agent | |
| | | |
| | +--------------------------+ +----------------------+ | |
| | |Administrative element | |Application-specific | | |
| | | | |element | | |
| | | | | | | |
| | +--------------------------+ +----------------------+ | |
| | ^ ^ | |
| | Admin|records Application|data | |
| | | | | |
| +----------------v--------------------------v-----------+ |
| ^ |
| | ADUs |
| | |
| +-----------------------------v-------------------------+ |
| |Bundle Protocol Agent | |
| | | |
| | | |
| +-------------------------------------------------------+ |
| ^ ^ ^ |
| | Bundles | Bundles Bundles | |
| | | | |
| +------v-----+ +-----v------+ +-----v-----+ |
| |CLA 1 | |CLA 2 | |CLA n | |
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| | | | | . . . | | |
| | | | | | | |
+-+------------+-----+------------+-----------+-----------+-+
^ ^ ^
CL1|PDUs CL2|PDUs CLn|PDUs
| | |
+------v-----+ +-----v------+ +-----v-----+
Network 1 Network 2 Network n
Figure 2: Components of a BP Node
Bundle protocol agent - The bundle protocol agent (BPA) of a node is
the node component that offers the BP services and executes the
procedures of the bundle protocol.
Convergence layer adapter - A convergence layer adapter (CLA) is a
node component that sends and receives bundles on behalf of the BPA,
utilizing the services of some 'native' protocol stack that is
supported in one of the networks within which the node is
functionally located.
Application agent - The application agent (AA) of a node is the node
component that utilizes the BP services to effect communication for
some user purpose. The application agent in turn has two elements,
an administrative element and an application-specific element.
Application-specific element - The application-specific element of
an AA is the node component that constructs, requests transmission
of, accepts delivery of, and processes units of user application
data.
Administrative element - The administrative element of an AA is the
node component that constructs and requests transmission of
administrative records (defined below), including status reports and
custody signals, and accepts delivery of and processes any custody
signals that the node receives.
Administrative record - A BP administrative record is an application
data unit that is exchanged between the administrative elements of
nodes' application agents for some BP administrative purpose. The
formats of some fundamental administrative records (and of no other
application data units) are defined in this specification.
Bundle endpoint - A bundle endpoint (or simply "endpoint") is a set
of zero or more bundle nodes that all identify themselves for BP
purposes by some common identifier, called a "bundle endpoint ID"
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(or, in this document, simply "endpoint ID"; endpoint IDs are
described in detail in Section 4.4.1 below).
Singleton endpoint - A singleton endpoint is an endpoint that always
contains exactly one member.
Registration - A registration is the state machine characterizing a
given node's membership in a given endpoint. Any single
registration has an associated delivery failure action as defined
below and must at any time be in one of two states: Active or
Passive.
Delivery - A bundle is considered to have been delivered at a node
subject to a registration as soon as the application data unit that
is the payload of the bundle, together with any relevant metadata
(an implementation matter), has been presented to the node's
application agent in a manner consistent with the state of that
registration.
Deliverability - A bundle is considered "deliverable" subject to a
registration if and only if (a) the bundle's destination endpoint is
the endpoint with which the registration is associated, (b) the
bundle has not yet been delivered subject to this registration, and
(c) the bundle has not yet been "abandoned" (as defined below)
subject to this registration.
Abandonment - To abandon a bundle subject to some registration is to
assert that the bundle is not deliverable subject to that
registration.
Delivery failure action - The delivery failure action of a
registration is the action that is to be taken when a bundle that is
"deliverable" subject to that registration is received at a time
when the registration is in the Passive state.
Destination - The destination of a bundle is the endpoint comprising
the node(s) at which the bundle is to be delivered (as defined
below).
Minimum reception group - The minimum reception group of an endpoint
is the minimum number of members of the endpoint (nodes) at which
the bundle must have been delivered in order for the bundle to be
considered delivered to the endpoint.
Transmission - A transmission is an attempt by a node's BPA to cause
copies of a bundle to be delivered at all nodes in the minimum
reception group of some endpoint (the bundle's destination) in
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response to a transmission request issued by the node's application
agent.
Forwarding - To forward a bundle to a node is to invoke the services
of a CLA in a sustained effort to cause a copy of the bundle to be
received by that node.
Discarding - To discard a bundle is to cease all operations on the
bundle and functionally erase all references to it. The specific
procedures by which this is accomplished are an implementation
matter.
Retention constraint - A retention constraint is an element of the
state of a bundle that prevents the bundle from being discarded.
That is, a bundle cannot be discarded while it has any retention
constraints.
Deletion - To delete a bundle is to remove unconditionally all of
the bundle's retention constraints, enabling the bundle to be
discarded.
Custodian - A custodian of a bundle is a node that has determined
that it will retain a copy of that bundle for an indefinite period
of time, forwarding and possibly re-forwarding the bundle as
appropriate, until it detects one of the conditions under which it
may cease being a custodian of that bundle (discussed later).
Taking custody - To take custody of a bundle is to become a
custodian of that bundle.
Accepting custody - To accept custody of a bundle is to take custody
of the bundle, mark the bundle in such a way as to indicate this
custodianship to nodes that subsequently receive copies of the
bundle, and announce this custodianship to all current custodians of
the bundle.
Refusing custody - To "refuse custody" of a bundle is to notify all
current custodians of that bundle that an opportunity to take
custody of the bundle has been declined.
Releasing custody - To release custody of a bundle is to cease to be
a custodian of the bundle.
3.2. Discussion of BP concepts
Multiple instances of the same bundle (the same unit of DTN protocol
data) might exist concurrently in different parts of a network --
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possibly differing in some blocks -- in the memory local to one or
more bundle nodes and/or in transit between nodes. In the context of
the operation of a bundle node, a bundle is an instance (copy), in
that node's local memory, of some bundle that is in the network.
The payload for a bundle forwarded in response to a bundle
transmission request is the application data unit whose location is
provided as a parameter to that request. The payload for a bundle
forwarded in response to reception of a bundle is the payload of the
received bundle.
In the most familiar case, a bundle node is instantiated as a single
process running on a general-purpose computer, but in general the
definition is meant to be broader: a bundle node might alternatively
be a thread, an object in an object-oriented operating system, a
special-purpose hardware device, etc.
The manner in which the functions of the BPA are performed is wholly
an implementation matter. For example, BPA functionality might be
coded into each node individually; it might be implemented as a
shared library that is used in common by any number of bundle nodes
on a single computer; it might be implemented as a daemon whose
services are invoked via inter-process or network communication by
any number of bundle nodes on one or more computers; it might be
implemented in hardware.
Every CLA implements its own thin layer of protocol, interposed
between BP and the (usually "top") protocol(s) of the underlying
native protocol stack; this "CL protocol" may only serve to
multiplex and de-multiplex bundles to and from the underlying native
protocol, or it may offer additional CL-specific functionality. The
manner in which a CLA sends and receives bundles is, again, wholly
an implementation matter. The definitions of CLAs and CL protocols
are beyond the scope of this specification.
Note that the administrative element of a node's application agent
may itself, in some cases, function as a convergence-layer adapter.
That is, outgoing bundles may be "tunneled" through encapsulating
bundles:
. An outgoing bundle constitutes a byte array. This byte array
may, like any other, be presented to the bundle protocol agent
as an application data unit that is to be transmitted to some
endpoint.
. The original bundle thus forms the payload of an encapsulating
bundle that is forwarded using some other convergence-layer
protocol(s).
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. When the encapsulating bundle is received, its payload is
delivered to the peer application agent administrative element,
which then instructs the bundle protocol agent to dispatch that
original bundle in the usual way.
The purposes for which this technique may be useful (such as cross-
domain security) are beyond the scope of this specification.
The only interface between the BPA and the application-specific
element of the AA is the BP service interface. But between the BPA
and the administrative element of the AA there is a (conceptual)
private control interface in addition to the BP service interface.
This private control interface enables the BPA and the
administrative element of the AA to direct each other to take action
under specific circumstances
In the case of a node that serves simply as a BP "router", the AA
may have no application-specific element at all. The application-
specific elements of other nodes' AAs may perform arbitrarily
complex application functions, perhaps even offering multiplexed DTN
communication services to a number of other applications. As with
the BPA, the manner in which the AA performs its functions is wholly
an implementation matter.
Singletons are the most familiar sort of endpoint, but in general
the endpoint notion is meant to be broader. For example, the nodes
in a sensor network might constitute a set of bundle nodes that
identify themselves by a single common endpoint ID and thus form a
single bundle endpoint. *Note* too that a given bundle node might
identify itself by multiple endpoint IDs and thus be a member of
multiple bundle endpoints.
The destination of every bundle is an endpoint, which may or may not
be singleton. The source of every bundle is a node, identified by
the endpoint ID for some singleton endpoint that contains that node.
The minimum reception group of an endpoint may be any one of the
following: (a) ALL of the nodes registered in an endpoint that is
permitted to contain multiple nodes (in which case forwarding to the
endpoint is functionally similar to "multicast" operations in the
Internet, though possibly very different in implementation); (b) ANY
N of the nodes registered in an endpoint that is permitted to
contain multiple nodes, where N is in the range from zero to the
cardinality of the endpoint; or (c) THE SOLE NODE registered in a
singleton endpoint (in which case forwarding to the endpoint is
functionally similar to "unicast" operations in the Internet).
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The nature of the minimum reception group for a given endpoint can
typically be determined from the endpoint's ID. For some endpoint
ID "schemes", the nature of the minimum reception group is fixed -
in a manner that is defined by the scheme - for all endpoints
identified under the scheme. For other schemes, the nature of the
minimum reception group is indicated by some lexical feature of the
"scheme-specific part" of the endpoint ID, in a manner that is
defined by the scheme.
Any number of transmissions may be concurrently undertaken by the
bundle protocol agent of a given node.
When the bundle protocol agent of a node determines that a bundle
must be forwarded to a node (either to a node that is a member of
the bundle's destination endpoint or to some intermediate forwarding
node) in the course of completing the successful transmission of
that bundle, it invokes the services of a CLA in a sustained effort
to cause a copy of the bundle to be received by that node.
Upon reception, the processing of a bundle that has been received by
a given node depends on whether or not the receiving node is
registered in the bundle's destination endpoint. If it is, and if
the payload of the bundle is non-fragmentary (possibly as a result
of successful payload reassembly from fragmentary payloads,
including the original payload of the newly received bundle), then
the bundle is normally delivered to the node's application agent
subject to the registration characterizing the node's membership in
the destination endpoint.
Whenever, for some implementation-specific reason, a node's BPA
finds it impossible to immediately deliver a bundle that is
deliverable, delivery of the bundle has failed. In this event, the
delivery failure action associated with the applicable registration
must be taken. Delivery failure action MUST be one of the following:
. defer delivery of the bundle subject to this registration until
(a) this bundle is the least recently received of all bundles
currently deliverable subject to this registration and (b)
either the registration is polled or else the registration is
in the Active state; or
. abandon delivery of the bundle subject to this registration.
An additional implementation-specific delivery deferral procedure
MAY optionally be associated with the registration.
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While the state of a registration is Passive, reception of a bundle
that is deliverable subject to this registration MUST cause delivery
of the bundle to be abandoned or deferred as mandated by the
registration's current delivery failure action; in the latter case,
any additional delivery deferral procedure associated with the
registration MUST also be performed.
While the state of a registration is Active, reception of a bundle
that is deliverable subject to this registration MUST cause the
bundle to be delivered automatically as soon as it is the next
bundle that is due for delivery according to the BPA's bundle
delivery scheduling policy, an implementation matter.
Normally only registrations' registered delivery failure actions
cause deliveries to be abandoned.
Custody of a bundle MAY be taken only if the destination of the
bundle is a singleton endpoint. Custody MAY be released only when
either (a) notification is received that some other node has
accepted custody of the same bundle; (b) notification is received
that the bundle has been delivered at the (sole) node registered in
the bundle's destination endpoint; (c) the current custodian chooses
to fragment the bundle, releasing custody of the original bundle and
taking custody of the fragments instead, or (d) the bundle is
explicitly deleted for some reason, such as lifetime expiration.
The custody transfer mechanism in BP comprises two services. For
each bundle either one of the two services, or neither, or both may
be requested.
The "retransmission" service of the custody transfer mechanism
provides a means of recovering from data loss along the path to the
destination node. When the custodian of a bundle forwards that
bundle it SHOULD set a retransmission timer; reception of a
responding custody signal of any kind prior to timer expiration MUST
disable that timer. Upon expiration of that timer, the custodian
MUST re-forward the bundle. When a bundle for which custody has
been taken and retransmission service has been requested arrives at
a node from which it must be forwarded, and that node determines
that it will forward the bundle but will not take custody, the
receiving node SHOULD send a "custody delegation" signal back to the
custodian indicating the next node to which the bundle will be
forwarded together with an estimate of the interval that will elapse
between the time the bundle was received and the time at which it
will be forwarded. This mechanism is intended to facilitate
accurate timeout interval calculation for this bundle.
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The "rerouting" service of the custody transfer mechanism provides a
means of optimizing recovery from forwarding failures. When the
custodian of a bundle forwards that bundle it SHOULD set a rerouting
timer; reception of a responding custody signal of any kind prior to
timer expiration MUST disable that timer. Upon expiration of that
timer, the custodian MUST re-forward the bundle. When a bundle for
which custody has been taken and rerouting service has been
requested arrives at a node from which it must be forwarded, but
that node determines that it will not forward the bundle (and
therefore must not take custody), the receiving node SHOULD send a
custody refusal signal to the current custodian node, alerting the
custodian node to a forwarding anomaly on this route.
When both the retransmission and rerouting services of custody
transfer are requested for some bundle, a single custody transfer
timer SHOULD be shared by both services. Expiration of that timer
has the same effect - re-forwarding of the bundle - regardless of
the services requested.
Computation of the timeout interval for a bundle's custody transfer
timer (i.e., determination of the moment at which a responding
custody signal is expected) is an implementation matter and may be
dynamically responsive to changes in connectivity. In some
environments it may be impossible to compute this interval with
operationally satisfactory accuracy; in such environments the use of
custody transfer services is contraindicated.
Alternatively, when the custody transfer services for a given bundle
are not requested:
. Data loss along the path to the destination node can be
minimized by utilizing reliable convergence-layer protocols
between neighbors on all segments of the end-to-end path. This
approach may make more efficient use of links than custody
transfer because a convergence-layer protocol may perform
finer-grained retransmission than custody transfer does,
retransmitting only the specific portions of a transmitted
bundle that were not received, rather than the entire bundle.
However, in some environments there may be segments of the end-
to-end path for which no reliable convergence-layer protocol is
available; in such environments the use of reliable
convergence-layer protocols wherever possible can minimize the
incidence of data loss.
. Recovery from a forwarding failure can be accomplished by
"returning" the bundle back toward some node for forwarding
along some other path in the network.
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3.3. Services Offered by Bundle Protocol Agents
The BPA of each node is expected to provide the following services
to the node's application agent:
. commencing a registration (registering the node in an
endpoint);
. terminating a registration;
. switching a registration between Active and Passive states;
. transmitting a bundle to an identified bundle endpoint;
. canceling a transmission;
. polling a registration that is in the Passive state;
. delivering a received bundle.
4. Bundle Format
The format of bundles SHALL conform to the Concise Binary Object
Representation (CBOR [RFC7049]).
Each bundle SHALL be a concatenated sequence of at least two blocks,
represented as a CBOR indefinite-length array (major type 4 with
additional info 31). The first block in the sequence (the first
item of the array) MUST be a primary bundle block in CBOR
representation as described below; the bundle MUST have exactly one
primary bundle block. The primary block MUST be followed by one or
more canonical bundle blocks (additional array items) in CBOR
representation as described below. The last such block MUST be a
payload block; the bundle MUST have exactly one payload block. The
last item of the array, immediately following the payload block,
SHALL be a CBOR "break" stop code (major type 7 with additional
information 31).
4.1. BP Fundamental Data Structures
4.1.1. CRC Type
CRC type is an unsigned integer type code for which the following
values (and no others) are valid:
. 0 indicates "no CRC is present."
. 1 indicates "a CRC-16 (a.k.a., CRC-16-ANSI) is present."
. 2 indicates "a standard IEEE 802.3 CRC-32 is present."
CRC type SHALL be represented as a CBOR unsigned integer.
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4.1.2. CRC
CRC SHALL be omitted from a block if and only if the block's CRC
type code is zero.
When not omitted, the CRC SHALL be represented as a CBOR unsigned
integer.
4.1.3. Bundle Processing Control Flags
Bundle processing control flags assert properties of the bundle as a
whole rather than of any particular block of the bundle. They are
conveyed in the primary block of the bundle.
The following properties are asserted by the bundle processing
control flags:
. The bundle is a fragment. (Boolean)
. The bundle's payload is an administrative record. (Boolean)
. The bundle must not be fragmented. (Boolean)
. Custody transfer retransmission service requested for this
bundle. (Boolean)
. Custody transfer rerouting service requested for this bundle.
(Boolean)
. The bundle's destination endpoint is a singleton. (Boolean)
. Acknowledgment by the user application is requested. (Boolean)
. Status time is requested in all status reports. (Boolean)
. The bundle contains a "manifest" extension block. (Boolean)
. Flags requesting types of status reports (all Boolean):
o Request reporting of bundle reception.
o Request reporting of custody acceptance.
o Request reporting of bundle forwarding.
o Request reporting of bundle delivery.
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o Request reporting of bundle deletion.
If the bundle processing control flags indicate that the bundle's
application data unit is an administrative record, then both custody
transfer service requested flags values must be zero and all status
report request flag values must be zero.
If either or both custody transfer service requested flags are 1,
then the source node is requesting that every receiving node accept
custody of the bundle.
If the bundle's source node is omitted (i.e., the source node ID is
the ID of the null endpoint, which has no members as discussed
below; this option enables anonymous bundle transmission), then the
bundle is not uniquely identifiable and all bundle protocol features
that rely on bundle identity must therefore be disabled: both of the
bundle's custody transfer service requested flag values must be
zero, the "Bundle must not be fragmented" flag value must be 1, and
all status report request flag values must be zero.
The bundle processing control flags SHALL be represented as a CBOR
unsigned integer item with additional info 25; the 16-bit unsigned
integer following the item type byte SHALL be a bit field indicating
the control flag values as follows:
. Bit 0 (the high-order bit, 0x8000): reserved.
. Bit 1 (0x4000): reserved.
. Bit 2(0x2000): bundle deletion status reports are requested.
. Bit 3(0x1000): bundle delivery status reports are requested.
. Bit 4(0x0800): bundle forwarding status reports are requested.
. Bit 5(0x0400): custody acceptance status reports are requested.
. Bit 6(0x0200): bundle reception status reports are requested.
. Bit 7(0x0100): bundle contains a Manifest block.
. Bit 8(0x0080): status time is requested in all status reports.
. Bit 9(0x0040): user application acknowledgement is requested.
. Bit 10(0x0020): destination is a singleton endpoint.
. Bit 11(0x0010): custody transfer rerouting is requested.
. Bit 12(0x0008): custody transfer retransmission is requested.
. Bit 13(0x0004): bundle must not be fragmented.
. Bit 14(0x0002): payload is an administrative record.
. Bit 15 (the low-order bit, 0x0001: bundle is a fragment.
4.1.4. Block Processing Control Flags
The block processing control flags assert properties of canonical
bundle blocks. They are conveyed in the header of the block to
which they pertain.
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The following properties are asserted by the block processing
control flags:
. This block must be replicated in every fragment. (Boolean)
. Status report must be transmitted if this block can't be
processed. (Boolean)
. Block must be removed from the bundle if it can't be processed.
(Boolean)
. Bundle must be deleted if this block can't be processed.
(Boolean)
For each bundle whose bundle processing control flags indicate that
the bundle's application data unit is an administrative record, or
whose source node ID is the null endpoint ID as defined below, the
value of the "Transmit status report if block can't be processed"
flag in every canonical block of the bundle must be zero.
The block processing control flags SHALL be represented as a CBOR
unsigned integer item with additional info 24; the 8-bit unsigned
integer following the item type byte SHALL be a bit field indicating
the control flag values as follows:
. Bit 0 (the high-order bit, 0x80): reserved.
. Bit 1 (0x40): reserved.
. Bit 2(0x20): reserved.
. Bit 3(0x10): reserved.
. Bit 4(0x08): bundle must be deleted if block can't be
processed.
. Bit 5(0x04): status report must be transmitted if block can't
be processed.
. Bit 6(0x02): block must be removed from bundle if it can't be
processed.
. Bit 7(the low-order bit, 0x01): block must be replicated in
every fragment.
4.1.5. Identifiers
4.1.5.1. Endpoint ID
The destinations of bundles are bundle endpoints, identified by text
strings termed "endpoint IDs" (see Section 3.1). Each endpoint ID
(EID) is a Uniform Resource Identifier (URI; [URI]). As such, each
endpoint ID can be characterized as having this general structure:
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< scheme name > : < scheme-specific part, or "SSP" >
The scheme identified by the < scheme name > in an endpoint ID is a
set of syntactic and semantic rules that fully explain how to parse
and interpret the SSP. The set of allowable schemes is effectively
unlimited. Any scheme conforming to [URIREG] may be used in a bundle
protocol endpoint ID.
Note that, although endpoint IDs are URIs, implementations of the BP
service interface may support expression of endpoint IDs in some
internationalized manner (e.g., Internationalized Resource
Identifiers (IRIs); see [RFC3987]).
The endpoint ID "dtn:none" identifies the "null endpoint", the
endpoint that by definition never has any members.
Each BP endpoint ID (EID) SHALL be represented as a CBOR array with
additional info 2, indicating that the item is a 2-tuple.
The first item of the array SHALL be the code number identifying the
endpoint's URI scheme [URI], as defined in the registry of URI
scheme code numbers for Bundle Protocol maintained by IANA as
described in Section Error! Reference source not found. [URIREG].
Each URI scheme code number SHALL be represented as a CBOR unsigned
integer.
The second item of the array SHALL be the applicable CBOR
representation of the scheme-specific part (SSP) of the EID, defined
as follows:
. If the EID's URI scheme is "dtn" then the SSP SHALL be
represented as a CBOR text string unless the EID's SSP is
"none", in which case the SSP SHALL be represented as a CBOR
unsigned integer with the value zero.
. If the EID's URI scheme is "ipn" then the SSP SHALL be
represented as a CBOR array with additional info 2, indicating
that the item is a 2-tuple. The first item of this array SHALL
be the EID's node number represented as a CBOR unsigned
integer. The second item of this array SHALL be the EID's
service number represented as a CBOR unsigned integer.
. Definitions of the CBOR representations of the SSPs of EIDs
encoded in other URI schemes are included in the specifications
defining those schemes.
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4.1.5.2. Node ID
For many purposes of the Bundle Protocol it is important to identify
the node that is operative in some context.
As discussed in 3.1 above, nodes are distinct from endpoints;
specifically, an endpoint is a set of zero or more nodes. But
rather than define a separate namespace for node identifiers, we
instead use endpoint identifiers to identify nodes, subject to the
following restrictions:
. Every node MUST be a member of at least one singleton endpoint.
. The EID of any singleton endpoint of which a node is a member
MAY be used to identify that node. A "node ID" is an EID that
is used in this way.
. A node's membership in a given singleton endpoint MUST be
sustained at least until the nominal operation of the Bundle
Protocol no longer depends on the identification of that node
using that endpoint's ID.
4.1.6. DTN Time
A DTN time is an unsigned integer indicating a count of seconds
since the start of the year 2000 on the Coordinated Universal Time
(UTC) scale [UTC]. Each DTN time SHALL be represented as a CBOR
unsigned integer item.
4.1.7. Creation Timestamp
Each creation timestamp SHALL be represented as a CBOR array item
with additional info 2, indicating that the item is a 2-tuple.
The first item of the array SHALL be a DTN time.
The second item of the array SHALL be the creation timestamp's
sequence number, represented as a CBOR unsigned integer.
4.1.8. Fragment ID
Fragment ID SHALL be omitted from the primary block if and only if
the value of the "bundle is a fragment" flag in the bundle
processing control flags is zero.
Otherwise, the bundle's fragment ID SHALL be represented as a CBOR
array with additional info 2, indicating that the item is a 2-tuple.
The first item of this array SHALL be the fragment offset of the
bundle's payload, represented as a CBOR unsigned integer. The
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second item of this array SHALL be the total (original) application
data unit length, represented as a CBOR unsigned integer.
4.1.9. Block-type-specific Data
Block-type-specific data in each block (other than the primary
block) SHALL be the applicable CBOR representation of the content of
the block. Details of this representation are included in the
specification defining the block type.
4.2. Bundle Representation
This section describes the primary block in detail and non-primary
blocks in general. Rules for processing these blocks appear in
Section 5 of this document.
Note that supplementary DTN protocol specifications (including, but
not restricted to, the Bundle Security Protocol [BPSEC]) may require
that BP implementations conforming to those protocols construct and
process additional blocks.
4.2.1. Bundle
Each bundle SHALL be represented as a CBOR indefinite-length array
(major type 4 with additional info 31). The first item of this
array SHALL be the CBOR representation of a Primary Block. Every
other item of the array except the last SHALL be the CBOR
representation of a Canonical Block. The last item of the array
SHALL be a CBOR "break" stop code (major type 7 with additional
information 31).
4.2.2. Primary Bundle Block
The primary bundle block contains the basic information needed to
forward bundles to their destinations.
Each primary block SHALL be represented as a CBOR array (major type
4) with additional info either 8 (if the bundle is not a fragment
and CRC type is zero) or 9 (if the bundle is a fragment or CRC type
is non-zero, but not both) or 10 (if the bundle is a fragment and
CRC-type is non-zero). The items of this array SHALL be as
indicated in Table 1, appearing in the order shown in this table.
+-------------+-----------------+---------------------------------+
| | Item Type Byte | Content Bytes |
| | | |
| | Major | |
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| | Item | Add'l | |
| | Type | Info | |
| Item | 3 bits | 5 bits | Size | Value |
+=============+========+========+======+==========================+
| version | 0 | 7 | n/a | n/a |
+-------------+--------+--------+------+--------------------------+
| bundle | See Section 4.1.3. above |
| processing | | | | |
| control | | | | |
| flags | | | | |
+-------------+--------+--------+------+--------------------------+
| CRC type | 0 | type | n/a | n/a |
| | | code | | |
+-------------+--------+--------+------+--------------------------+
| destination | See Section 4.1.5.1. above |
| EID | | | | |
+-------------+--------+--------+------+--------------------------+
| source node | See Section 4.1.5.2. above |
| ID | | | | |
+-------------+--------+--------+------+--------------------------+
| report-to | See Section 4.1.5.1. above |
| EID | | | | |
+-------------+--------+--------+------+--------------------------+
| creation | See Section 4.1.7. above |
| timestamp | | | | |
+-------------+--------+--------+------+--------------------------+
| lifetime | 0 | as required to contain value |
+-------------+--------+--------+------+--------------------------+
| fragment ID | See Section 4.1.8. above |
+-------------+--------+--------+------+--------------------------+
| CRC | See Section 4.1.2. above |
+-------------+--------+--------+------+--------------------------+
Table 1: Primary Block Data Items
The fields of the primary bundle block are:
Version: An unsigned integer value indicating the version of the
bundle protocol that constructed this block. The present document
describes version 7 of the bundle protocol. Version number SHALL be
represented as a CBOR unsigned integer item.
Bundle Processing Control Flags: The Bundle Processing Control Flags
are discussed in Section 4.1.3. above.
CRC Type: CRC Type codes are discussed in Section 4.1.1. above.
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Destination EID: The Destination EID field identifies the bundle
endpoint that is the bundle's destination, i.e., the endpoint that
contains the node(s) at which the bundle is to be delivered.
Source node ID: The Source node ID field identifies the bundle node
at which the bundle was initially transmitted, except that Source
node ID may be the null endpoint ID in the event that the bundle's
source chooses to remain anonymous.
Report-to EID: The Report-to EID field identifies the bundle
endpoint to which status reports pertaining to the forwarding and
delivery of this bundle are to be transmitted.
Creation Timestamp: The creation timestamp is a pair of unsigned
integers that, together with the source node ID and (if the bundle
is a fragment) the fragment offset and payload length, serve to
identify the bundle. The first of these integers is the bundle's
creation time, while the second is the bundle's creation timestamp
sequence number. Bundle creation time shall be the time - expressed
in seconds since the start of the year 2000, on the Coordinated
Universal Time (UTC) scale [UTC] - at which the transmission request
was received that resulted in the creation of the bundle. Sequence
count shall be the latest value (as of the time at which that
transmission request was received) of a monotonically increasing
positive integer counter managed by the source node's bundle
protocol agent that may be reset to zero whenever the current time
advances by one second. For nodes that lack accurate clocks (that
is, nodes that are not at all moments able to determine the current
UTC time to within 30 seconds), bundle creation time MUST be set to
zero and the counter used as the source of the bundle sequence count
MUST NEVER be reset to zero. In any case, a source Bundle Protocol
Agent MUST NEVER create two distinct bundles with the same source
node ID and bundle creation timestamp. The combination of source
node ID and bundle creation timestamp serves to identify a single
transmission request, enabling it to be acknowledged by the
receiving application (provided the source node ID is not the null
endpoint ID).
Lifetime: The lifetime field is an unsigned integer that indicates
the time at which the bundle's payload will no longer be useful,
encoded as a number of seconds past the creation time. When a
bundle's age exceeds its lifetime, bundle nodes need no longer
retain or forward the bundle; the bundle SHOULD be deleted from the
network. Bundle lifetime SHALL be represented as a CBOR unsigned
integer item.
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Fragment ID: If and only if the Bundle Processing Control Flags of
this Primary block indicate that the bundle is a fragment, the
Fragment ID field as discussed in 4.1.8. above SHALL be present in
the primary block. Fragment offset in the Fragment ID SHALL be an
unsigned integer indicating the offset from the start of the
original application data unit at which the bytes comprising the
payload of this bundle were located. Total Application Data Unit
Length in the Fragment ID SHALL be an unsigned integer indicating
the total length of the original application data unit of which this
bundle's payload is a part.
CRC: If and only if the value of the CRC type field of this Primary
block is non-zero, a CRC SHALL be present in the primary block. The
length and nature of the CRC SHALL be as indicated by the CRC type.
The CRC SHALL be computed over the concatenation of all bytes of the
primary block including the CRC field itself, which for this purpose
SHALL be temporarily populated with the value zero.
4.2.3. Canonical Bundle Block Format
Every block other than the primary block (which blocks are termed
"canonical" blocks) SHALL be represented as a CBOR array (major type
4) with additional info either 5 (if CRC type is zero) or 6
(otherwise). The items of this array SHALL be as indicated in Table
2, appearing in the order shown in this table.
+-------------+-----------------+---------------------------------+
| | Item Type Byte | Content Bytes |
| | | |
| | Major | |
| | Item | Add'l | |
| | Type | Info | |
| Item | 3 bits | 5 bits | Size | Value |
+=============+========+========+======+==========================+
| block type | 0 | as required to contain value |
| code | | | | |
+-------------+--------+--------+------+--------------------------+
| block number| 0 | as required to contain value |
+-------------+--------+--------+------+--------------------------+
| block | See Section 4.1.4. above |
| processing | | | | |
| control | | | | |
| flags | | | | |
+-------------+--------+--------+------+--------------------------+
| CRC type | 0 | type | n/a | n/a |
| | | code | | |
+-------------+--------+--------+------+--------------------------+
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| CRC | See Section 4.1.2. above |
+-------------+--------+--------+------+--------------------------+
| block data | 0 | as required to contain value |
| length | | | | |
+-------------+--------+--------+------+--------------------------+
| block-type- | See Section 4.1.9. above |
| specific | | | | |
| data | | | | |
+-------------+--------+--------+------+--------------------------+
Table 2: Canonical Block Data Items
Every canonical block SHALL comprise the following fields:
. Block type code, an unsigned integer. Bundle block type code 1
indicates that the block is a bundle payload block. Block type
codes 2 through 9 are explicitly reserved as noted later in
this specification. Block type codes 192 through 255 are not
reserved and are available for private and/or experimental use.
All other block type code values are reserved for future use.
. Block number, an unsigned integer. The block number uniquely
identifies the block within the bundle, enabling blocks
(notably bundle security protocol blocks) to explicitly
reference other blocks in the same bundle. Block numbers need
not be in continuous sequence, and blocks need not appear in
block number sequence in the bundle. The block number of the
payload block is always zero.
. Block processing control flags as discussed in Section 4.1.4
above.
. CRC type as discussed in Section 4.1.1 above.
. If and only if the value of the CRC type field of this block is
non-zero, a CRC. If present, the length and nature of the CRC
SHALL be as indicated by the CRC type and the CRC SHALL be
computed over the concatenation of all bytes of the block
including the CRC field itself, which for this purpose SHALL be
temporarily populated with the value zero.
. Block data length, an unsigned integer. The block data length
field SHALL contain the aggregate length of all remaining
fields of the block, i.e., the block-type-specific data fields.
Block data length SHALL be represented as a CBOR unsigned
integer item.
. Block-type-specific data fields, whose nature and order are
type-specific and whose aggregate length in octets is the value
of the block data length field. For the Payload Block in
particular (block type 1), there SHALL be exactly one block-
type-specific data field, termed the "payload", which SHALL be
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an application data unit, or some contiguous extent thereof,
represented as a CBOR byte string (major type 2).
4.3. Extension Blocks
"Extension blocks" are all blocks other than the primary and payload
blocks. Because not all extension blocks are defined in the Bundle
Protocol specification (the present document), not all nodes
conforming to this specification will necessarily instantiate Bundle
Protocol implementations that include procedures for processing
(that is, recognizing, parsing, acting on, and/or producing) all
extension blocks. It is therefore possible for a node to receive a
bundle that includes extension blocks that the node cannot process.
The values of the block processing control flags indicate the action
to be taken by the bundle protocol agent when this is the case.
The following extension blocks are defined in other DTN protocol
specification documents as noted:
. Block Integrity Block (block type 2) and Block Confidentiality
Block (block type 3) are defined in the Bundle Security
Protocol specification (work in progress).
. Manifest Block (block type 4) is defined in the Manifest
Extension Block specification (TBD). The manifest block
identifies the blocks that were present in the bundle at the
time it was created. The bundle MUST contain one (1)
occurrence of this type of block if the value of the "manifest"
flag in the bundle processing control flags is 1; otherwise the
bundle MUST NOT contain any Manifest block.
. The Flow Label Block (block type 6) is defined in the Flow
Label Extension Block specification (TBD). The flow label
block is intended to govern transmission of the bundle by
convergence-layer adapters.
The following extension blocks are defined in the current document.
4.3.1. Current Custodian
The Current Custodian block, block type 5, identifies a node that is
known to have accepted custody of the bundle. The block-type-
specific data of this block is the node ID of a custodian, which
SHALL take the form of an endpoint ID represented as described in
Section 4.1.5.2. above. The bundle MAY contain one or more
occurrences of this type of block.
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4.3.2. Previous Node
The Previous Node block, block type 7, identifies the node that
forwarded this bundle to the local node (i.e., to the node at which
the bundle currently resides); its block-type-specific data is the
node ID of that forwarder node which SHALL take the form of a node
ID represented as described in Section 4.1.5.2. above. If the local
node is the source of the bundle, then the bundle MUST NOT contain
any previous node block. Otherwise the bundle MUST contain one (1)
occurrence of this type of block. If present, the previous node
block MUST be the FIRST block following the primary block, as the
processing of other extension blocks may depend on its value.
4.3.3. Bundle Age
The Bundle Age block, block type 8, contains the number of seconds
that have elapsed between the time the bundle was created and time
at which it was most recently forwarded. It is intended for use by
nodes lacking access to an accurate clock, to aid in determining the
time at which a bundle's lifetime expires. The block-type-specific
data of this block is an unsigned integer containing the age of the
bundle in seconds, which SHALL be represented as a CBOR unsigned
integer item. (The age of the bundle is the sum of all known
intervals of the bundle's residence at forwarding nodes, up to the
time at which the bundle was most recently forwarded, plus the
summation of signal propagation time over all episodes of
transmission between forwarding nodes. Determination of these
values is an implementation matter.) If the bundle's creation time
is zero, then the bundle MUST contain exactly one (1) occurrence of
this type of block; otherwise, the bundle MAY contain at most one
(1) occurrence of this type of block.
4.3.4. Hop Count
The Hop Count block, block type 9, contains two unsigned integers,
hop limit and hop count. A "hop" is here defined as an occasion on
which a bundle was forwarded from one node to another node. The hop
count block is mainly intended as a safety mechanism, a means of
identifying bundles for removal from the network that can never be
delivered due to a persistent forwarding error: a bundle SHOULD be
deleted when its hop count exceeds its hop limit. Procedures for
determining the appropriate hop limit for a block are beyond the
scope of this specification. The block-type-specific data in a hop
count block SHALL be represented as a CBOR array (major type 4) with
additional info 2, indicating that the item is a 2-tuple. The first
item of this array SHALL be the bundle's hop limit, represented as a
CBOR unsigned integer. The second item of this array SHALL be the
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bundle's hop count, represented as a CBOR unsigned integer. A bundle
MAY contain at most one (1) occurrence of this type of block.
5. Bundle Processing
The bundle processing procedures mandated in this section and in
Section 6 govern the operation of the Bundle Protocol Agent and the
Application Agent administrative element of each bundle node. They
are neither exhaustive nor exclusive. Supplementary DTN protocol
specifications (including, but not restricted to, the Bundle
Security Protocol [BPSEC]) may augment, override, or supersede the
mandates of this document.
5.1. Generation of Administrative Records
All transmission of bundles is in response to bundle transmission
requests presented by nodes' application agents. When required to
"generate" an administrative record (such as a bundle status report
or a custody signal), the bundle protocol agent itself is
responsible for causing a new bundle to be transmitted, conveying
that record. In concept, the bundle protocol agent discharges this
responsibility by directing the administrative element of the node's
application agent to construct the record and request its
transmission as detailed in Section 6 below. In practice, the manner
in which administrative record generation is accomplished is an
implementation matter, provided the constraints noted in Section 6
are observed.
Under some circumstances, the requesting of status reports could
result in an unacceptable increase in the bundle traffic in the
network. For this reason, the generation of status reports is
mandatory only in two cases:
. the reception of a bundle containing at least one block that
cannot be processed, for which the value of the "transmit
status report if block could not be processed" block processing
flag is 1, and
. the deletion of a bundle for which either custody transfer
service is requested.
In all other cases, the decision on whether or not to generate a
requested status report is left to the discretion of the bundle
protocol agent. Mechanisms that could assist in making such
decisions, such as pre-placed agreements authorizing the generation
of status reports under specified circumstances, are beyond the
scope of this specification.
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Notes on administrative record terminology:
. A "bundle reception status report" is a bundle status report
with the "reporting node received bundle" flag set to 1.
. A "custody acceptance status report" is a bundle status report
with the "reporting node accepted custody of bundle" flag set
to 1.
. A "bundle forwarding status report" is a bundle status report
with the "reporting node forwarded the bundle" flag set to 1.
. A "bundle delivery status report" is a bundle status report
with the "reporting node delivered the bundle" flag set to 1.
. A "bundle deletion status report" is a bundle status report
with the "reporting node deleted the bundle" flag set to 1.
. "Custody transfer is requested" means that either or both of
the custody transfer services are requested for this bundle.
. A "current custodian" of a bundle is a node identified in a
Current Custodian extension block of that bundle.
5.2. Bundle Transmission
The steps in processing a bundle transmission request are:
Step 1: If custody transfer is requested for this bundle
transmission then the destination MUST be a singleton endpoint. If,
moreover, custody acceptance by the source node is required when
custody is requested (an implementation matter) but the conditions
under which custody of the bundle may be accepted are not satisfied,
then the request cannot be honored and all remaining steps of this
procedure MUST be skipped.
Step 2: Transmission of the bundle is initiated. An outbound bundle
MUST be created per the parameters of the bundle transmission
request, with the retention constraint "Dispatch pending". The
source node ID of the bundle MUST be either the null endpoint ID,
indicating that the source of the bundle is anonymous, or else the
EID of a singleton endpoint whose only member is the node of which
the BPA is a component.
Step 3: Processing proceeds from Step 1 of Section 5.4.
5.3. Bundle Dispatching
The steps in dispatching a bundle are:
Step 1: If the bundle's destination endpoint is an endpoint of which
the node is a member, the bundle delivery procedure defined in
Section 5.7 MUST be followed.
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Step 2: Processing proceeds from Step 1 of Section 5.4.
5.4. Bundle Forwarding
The steps in forwarding a bundle are:
Step 1: The retention constraint "Forward pending" MUST be added to
the bundle, and the bundle's "Dispatch pending" retention constraint
MUST be removed.
Step 2: The bundle protocol agent MUST determine whether or not
forwarding is contraindicated for any of the reasons listed in
Figure 4. In particular:
. The bundle protocol agent MUST determine which node(s) to
forward the bundle to. The bundle protocol agent MAY choose
either to forward the bundle directly to its destination
node(s) (if possible) or to forward the bundle to some other
node(s) for further forwarding. The manner in which this
decision is made may depend on the scheme name in the
destination endpoint ID and/or on other state but in any case
is beyond the scope of this document. If the BPA elects to
forward the bundle to some other node(s) for further forwarding
but finds it impossible to select any node(s) to forward the
bundle to, then forwarding is contraindicated.
. Provided the bundle protocol agent succeeded in selecting the
node(s) to forward the bundle to, the bundle protocol agent
MUST select the convergence layer adapter(s) whose services
will enable the node to send the bundle to those nodes. The
manner in which specific appropriate convergence layer adapters
are selected is beyond the scope of this document. If the agent
finds it impossible to select any appropriate convergence layer
adapter(s) to use in forwarding this bundle, then forwarding is
contraindicated.
Step 3: If forwarding of the bundle is determined to be
contraindicated for any of the reasons listed in Figure 4, then the
Forwarding Contraindicated procedure defined in Section 5.4.1 MUST
be followed; the remaining steps of Section 5 are skipped at this
time.
Step 4: If either or both of the bundle's custody transfer service
requested flags (in the bundle processing flags field) are set to 1,
then the custody transfer procedure defined in Section 5.10 MUST be
followed.
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Step 5: For each node selected for forwarding, the bundle protocol
agent MUST invoke the services of the selected convergence layer
adapter(s) in order to effect the sending of the bundle to that
node. Determining the time at which the bundle protocol agent
invokes convergence layer adapter services is a BPA implementation
matter. Determining the time at which each convergence layer
adapter subsequently responds to this service invocation by sending
the bundle is a convergence-layer adapter implementation matter.
Note that:
. If the bundle contains a flow label extension block then that
flow label value MAY identify procedures for determining the
order in which convergence layer adapters must send bundles,
e.g., considering bundle source when determining the order in
which bundles are sent. The definition of such procedures is
beyond the scope of this specification.
. If the bundle has a bundle age block, then at the last possible
moment before the CLA initiates conveyance of the bundle node
via the CL protocol the bundle age value MUST be increased by
the difference between the current time and the time at which
the bundle was received (or, if the local node is the source of
the bundle, created).
Step 6: When all selected convergence layer adapters have informed
the bundle protocol agent that they have concluded their data
sending procedures with regard to this bundle:
. If the "request reporting of bundle forwarding" flag in the
bundle's status report request field is set to 1, then a bundle
forwarding status report SHOULD be generated, destined for the
bundle's report-to endpoint ID. If the bundle has the retention
constraint "custody accepted" and all of the nodes to which the
bundle was forwarded are known to be unable to send bundles
back to this node, then the reason code on this bundle
forwarding status report MUST be "forwarded over unidirectional
link"; otherwise, the reason code MUST be "no additional
information".
. The bundle's "Forward pending" retention constraint MUST be
removed.
5.4.1. Forwarding Contraindicated
The steps in responding to contraindication of forwarding are:
Step 1: The bundle protocol agent MUST determine whether or not to
declare failure in forwarding the bundle. Note: this decision is
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likely to be influenced by the reason for which forwarding is
contraindicated.
Step 2: If forwarding failure is declared, then the Forwarding
Failed procedure defined in Section 5.4.2 MUST be followed.
Otherwise, (a) if either or both of the bundle's custody transfer
requested flags (in the bundle processing flags field) are set to 1,
then the custody transfer procedure defined in Section 5.10 MUST be
followed; (b) when -- at some future time - the forwarding of this
bundle ceases to be contraindicated, processing proceeds from Step 5
of Section 5.4.
5.4.2. Forwarding Failed
The steps in responding to a declaration of forwarding failure are:
Step 1: If the bundle's custody transfer rerouting service requested
flag (in the bundle processing flags field) is set to 1, custody
transfer failure must be handled. The bundle protocol agent MUST
handle the custody transfer failure by generating a custody signal
of type 1 (custody refusal) for the bundle, destined for the
bundle's current custodian(s); the custody signal MUST contain a
reason code corresponding to the reason for which forwarding was
determined to be contraindicated. (Note that discarding the bundle
will not delete it from the network, since each current custodian
still has a copy.)
If the bundle's custody transfer rerouting service requested flag
(in the bundle processing flags field) is set to 0, then the bundle
protocol agent MAY forward the bundle back to the node that sent it,
as identified by the Previous Node block.
Step 2: If the bundle's destination endpoint is an endpoint of which
the node is a member, then the bundle's "Forward pending" retention
constraint MUST be removed. Otherwise, the bundle MUST be deleted:
the bundle deletion procedure defined in Section 5.14 MUST be
followed, citing the reason for which forwarding was determined to
be contraindicated.
5.5. Bundle Expiration
A bundle expires when the bundle's age exceeds its lifetime as
specified in the primary bundle block. Bundle age MAY be determined
by subtracting the bundle's creation timestamp time from the current
time if (a) that timestamp time is not zero and (b) the local node's
clock is known to be accurate (as discussed in section 4.5.1 above);
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otherwise bundle age MUST be obtained from the Bundle Age extension
block. Bundle expiration MAY occur at any point in the processing
of a bundle. When a bundle expires, the bundle protocol agent MUST
delete the bundle for the reason "lifetime expired": the bundle
deletion procedure defined in Section 5.14 MUST be followed.
5.6. Bundle Reception
The steps in processing a bundle that has been received from another
node are:
Step 1: The retention constraint "Dispatch pending" MUST be added to
the bundle.
Step 2: If the "request reporting of bundle reception" flag in the
bundle's status report request field is set to 1, then a bundle
reception status report with reason code "No additional information"
SHOULD be generated, destined for the bundle's report-to endpoint
ID.
Step 3: For each block in the bundle that is an extension block that
the bundle protocol agent cannot process:
. If the block processing flags in that block indicate that a
status report is requested in this event, then a bundle
reception status report with reason code "Block unintelligible"
SHOULD be generated, destined for the bundle's report-to
endpoint ID.
. If the block processing flags in that block indicate that the
bundle must be deleted in this event, then the bundle protocol
agent MUST delete the bundle for the reason "Block
unintelligible"; the bundle deletion procedure defined in
Section 5.14 MUST be followed and all remaining steps of the
bundle reception procedure MUST be skipped.
. If the block processing flags in that block do NOT indicate
that the bundle must be deleted in this event but do indicate
that the block must be discarded, then the bundle protocol
agent MUST remove this block from the bundle.
. If the block processing flags in that block indicate neither
that the bundle must be deleted nor that that the block must be
discarded, then processing continues with the next extension
block that the bundle protocol agent cannot process, if any;
otherwise, processing proceeds from step 4.
Step 4: If the bundle's custody transfer rerouting service requested
flag (in the bundle processing flags field) is set to 1 and the
bundle has the same source node ID, creation timestamp, and (if the
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bundle is a fragment) fragment offset and payload length 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. The
bundle protocol agent MUST handle custody transfer redundancy by
generating a custody signal of type 1 (custody refusal) for this
bundle with reason code "Redundant reception", destined for this
bundle's current custodian, and removing this bundle's "Dispatch
pending" retention constraint.
Step 5: Processing proceeds from Step 1 of Section 5.3.
5.7. Local Bundle Delivery
The steps in processing a bundle that is destined for an endpoint of
which this node is a member are:
Step 1: If the received bundle is a fragment, the application data
unit reassembly procedure described in Section 5.9 MUST be followed.
If this procedure results in reassembly of the entire original
application data unit, processing of this bundle (whose fragmentary
payload has been replaced by the reassembled application data unit)
proceeds from Step 2; otherwise, the retention constraint
"Reassembly pending" MUST be added to the bundle and all remaining
steps of this procedure MUST be skipped.
Step 2: Delivery depends on the state of the registration whose
endpoint ID matches that of the destination of the bundle:
. If the registration is in the Active state, then the bundle
MUST be delivered subject to this registration (see Section 3.1
above) as soon as all previously received bundles that are
deliverable subject to this registration have been delivered.
. If the registration is in the Passive state, then the
registration's delivery failure action MUST be taken (see
Section 3.1 above).
Step 3: As soon as the bundle has been delivered:
. If the "request reporting of bundle delivery" flag in the
bundle's status report request field is set to 1, then a bundle
delivery status report SHOULD be generated, destined for the
bundle's report-to endpoint ID. Note that this status report
only states that the payload has been delivered to the
application agent, not that the application agent has processed
that payload.
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. If either or both of the bundle's custody transfer service
requested flags (in the bundle processing flags field) are set
to 1, custodial delivery MUST be reported. The bundle protocol
agent MUST report custodial delivery by generating a custody
signal of type 0 (custody acceptance) for the bundle, destined
for the bundle's current custodian(s).
5.8. Bundle Fragmentation
It may at times be advantageous for bundle protocol agents to reduce
the sizes of bundles in order to forward them. This might be the
case, for example, if a node to which a bundle is to be forwarded is
accessible only via intermittent contacts and no upcoming contact is
long enough to enable the forwarding of the entire bundle.
The size of a bundle can be reduced by "fragmenting" the bundle. To
fragment a bundle whose payload is of size M is to replace it with
two "fragments" -- new bundles with the same source node ID and
creation timestamp as the original bundle -- whose payloads are the
first N and the last (M - N) bytes of the original bundle's payload,
where 0 < N < M. Note that fragments may themselves be fragmented,
so fragmentation may in effect replace the original bundle with more
than two fragments. (However, there is only one 'level' of
fragmentation, as in IP fragmentation.)
Any bundle that has any Current Custodian extension block citing any
node other than the local node MUST NOT be fragmented. This
restriction aside, any bundle whose primary block's bundle
processing flags do NOT indicate that it must not be fragmented MAY
be fragmented at any time, for any purpose, at the discretion of the
bundle protocol agent.
Fragmentation SHALL be constrained as follows:
. The concatenation of the payloads of all fragments produced by
fragmentation MUST always be identical to the payload of the
fragmented bundle (that is, the bundle that is being
fragmented). Note that the payloads of fragments resulting from
different fragmentation episodes, in different parts of the
network, may be overlapping subsets of the fragmented bundle's
payload.
. The primary block of each fragment MUST differ from that of the
fragmented bundle, in that the bundle processing flags of the
fragment MUST indicate that the bundle is a fragment and both
fragment offset and total application data unit length must be
provided. Additionally, the CRC of the fragmented bundle, if
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any, MUST be replaced in each fragment by a new CRC computed
for the primary block of that fragment.
. The payload blocks of fragments will differ from that of the
fragmented bundle as noted above.
. If the fragmented bundle is not a fragment or is the fragment
with offset zero, then all extension blocks of the fragmented
bundle MUST be replicated in the fragment whose offset is zero.
. Each of the fragmented bundle's extension blocks whose "Block
must be replicated in every fragment" flag is set to 1 MUST be
replicated in every fragment.
. Beyond these rules, replication of extension blocks in the
fragments is an implementation matter.
. If the local node is a custodian of the fragmented bundle, then
the BPA MUST release custody of the fragmented bundle before
fragmentation occurs and MUST take custody of every fragment.
5.9. Application Data Unit Reassembly
If the concatenation -- as informed by fragment offsets and payload
lengths -- of the payloads of all previously received fragments with
the same source node ID and creation timestamp as this fragment,
together with the payload of this fragment, forms a byte array whose
length is equal to the total application data unit length in the
fragment's primary block, then:
. This byte array -- the reassembled application data unit --
MUST replace the payload of this fragment.
. The BPA MUST take custody of each fragmentary bundle whose
payload is a subset of the reassembled application data unit,
for which custody transfer is requested but the BPA has not yet
taken custody.
. The BPA MUST then release custody of every fragment whose
payload is a subset of the reassembled application data unit,
for which it has taken custody.
. The "Reassembly pending" retention constraint MUST be removed
from every other fragment whose payload is a subset of the
reassembled application data unit.
Note: reassembly of application data units from fragments occurs at
the nodes that are members of destination endpoints as necessary; an
application data unit MAY also be reassembled at some other node on
the path to the destination.
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5.10. Custody Transfer
The decision as to whether or not to accept custody of a bundle is
an implementation matter that may involve both resource and policy
considerations.
If the bundle protocol agent elects to accept custody of the bundle,
then it must follow the custody acceptance procedure defined in
Section 5.10.1.
5.10.1. Custody Acceptance
Procedures for acceptance of custody of a bundle are defined as
follows.
The retention constraint "Custody accepted" MUST be added to the
bundle.
If the "request reporting of custody acceptance" flag in the
bundle's status report request field is set to 1, a custody
acceptance status report SHOULD be generated, destined for the
report-to endpoint ID of the bundle. However, if a bundle reception
status report was generated for this bundle (Step 2 of Section 5.6)
but has not yet been transmitted, then this report SHOULD be
generated by simply turning on the "Reporting node accepted custody
of bundle" flag in that earlier report.
The bundle protocol agent MUST generate a custody signal of type 0
(custody acceptance) for the bundle, destined for the bundle's
current custodian(s).
The bundle protocol agent MUST assert the new current custodian for
the bundle. It does so by deleting all of the bundle's existing
Current Custodian extension blocks and inserting a new Current
Custodian extension block whose value is the node ID of the local
node.
If the value of a custody transfer timer interval for this bundle
can be calculated with operationally satisfactory accuracy, the
bundle protocol agent SHOULD set a custody transfer countdown timer
for the bundle; upon expiration of this timer prior to expiration of
the bundle itself and prior to custody transfer success for this
bundle, the custody transfer failure procedure detailed in Section
5.12 MUST be followed. The manner in which the countdown interval
for such a timer is determined is an implementation matter.
The bundle SHOULD be retained in persistent storage if possible.
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5.10.2. Custody Release
When custody of a bundle is released, the "Custody accepted"
retention constraint MUST be removed from the bundle and any custody
transfer timer that has been established for this bundle SHOULD be
destroyed.
5.11. Custody Transfer Success
Upon receipt of a custody signal of type 0 (custody acceptance) at a
node that is a custodial node of the bundle identified in the
custody signal, custody of the bundle MUST be released as described
in Section 5.10.2.
5.12. Custody Transfer Failure
Custody transfer is determined to have failed at a custodial node
for a given bundle when either (a) that node's custody transfer
timer for that bundle (if any) expires or (b) a custody signal of
type 1 (custody refusal) for that bundle is received at that node.
Upon determination of custody transfer failure due to expiration of
a custody transfer countdown timer, the bundle protocol agent MUST
re-forward the bundle, possibly on a different route (Section 5.4).
Upon determination of custody transfer failure due to reception of a
custody signal of type 1 (custody refusal), the action taken by the
bundle protocol agent is implementation-specific and may depend on
the reason code cited for the refusal. For example, if the custody
signal's reason code was "Depleted storage", the bundle protocol
agent might choose to re-forward the bundle, possibly on a different
route (Section 5.4). If the reason code was "Redundant reception",
on the other hand, this might cause the bundle protocol agent to
release custody of the bundle and to revise its algorithm for
computing countdown intervals for custody transfer timers.
5.13. Custody Transfer Deferral
Upon receipt of a bundle for which custody transfer retransmission
service has been requested, which the bundle protocol agent plans to
forward but for which it elects not to accept custody, the bundle
protocol agent SHOULD generate a custody signal of type 2 (custody
delegation) for the bundle, destined for the bundle's current
custodian(s).
Custody transfer is determined to have been deferred at a custodial
node for given bundle when a custody signal of type 2 (custody
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delegation) for that bundle is received at that node. The action
taken by the bundle protocol agent in this event is implementation-
specific. Notionally, this is an opportunity for the bundle
protocol agent to revise its retransmission timeout interval for
this bundle, based on the information provided in the custody
signal: the next candidate custodian for the bundle is now known,
and the minimum length of time before a custody acceptance signal
will arrive can now be adjusted accordingly.
5.14. Bundle Deletion
The steps in deleting a bundle are:
Step 1: If the retention constraint "Custody accepted" currently
prevents this bundle from being discarded, then:
. Custody of the bundle is released as described in Section
5.10.2.
. A bundle deletion status report citing the reason for deletion
MUST be generated, destined for the bundle's report-to endpoint
ID.
Otherwise, if the "request reporting of bundle deletion" flag in the
bundle's status report request field is set to 1, then a bundle
deletion status report citing the reason for deletion SHOULD be
generated, destined for the bundle's report-to endpoint ID.
Step 2: All of the bundle's retention constraints MUST be removed.
5.15. Discarding a Bundle
As soon as a bundle has no remaining retention constraints it MAY be
discarded, thereby releasing any persistent storage that may have
been allocated to it.
5.16. Canceling a Transmission
When requested to cancel a specified transmission, where the bundle
created upon initiation of the indicated transmission has not yet
been discarded, the bundle protocol agent MUST delete that bundle
for the reason "transmission cancelled". For this purpose, the
procedure defined in Section 5.14 MUST be followed.
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6. Administrative Record Processing
6.1. Administrative Records
Administrative records are standard application data units that are
used in providing some of the features of the Bundle Protocol. Two
types of administrative records have been defined to date: bundle
status reports and custody signals. Note that additional types of
administrative records may be defined by supplementary DTN protocol
specification documents.
Every administrative record consists of:
. Record type code (an unsigned integer for which valid values
are as defined below).
. Record content in type-specific format.
Valid administrative record type codes are defined as follows:
+---------+--------------------------------------------+
| Value | Meaning |
+=========+============================================+
| 1 | Bundle status report. |
+---------+--------------------------------------------+
| 2 | Custody signal. |
+---------+--------------------------------------------+
| (other) | Reserved for future use. |
+---------+--------------------------------------------+
Figure 3: Administrative Record Type Codes
Each BP administrative record SHALL be represented as a CBOR array
(major type 4) with additional info 2 indicating that the item is a
2-tuple.
The first item of the array SHALL be a record type code, which SHALL
be represented as a CBOR unsigned integer.
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The second element of this array SHALL be the applicable CBOR
representation of the content of the record. Details of the CBOR
representation of administrative record types 1 and 2 are provided
below. Details of the CBOR representation of other types of
administrative record type are included in the specifications
defining those records.
6.1.1. Bundle Status Reports
The transmission of "bundle status reports" under specified
conditions is an option that can be invoked when transmission of a
bundle is requested. These reports are intended to provide
information about how bundles are progressing through the system,
including notices of receipt, custody transfer, forwarding, final
delivery, and deletion. They are transmitted to the Report-to
endpoints of bundles.
Each bundle status report SHALL be represented as a CBOR array
(major type 4) with additional info either 6 (if the subject bundle
is a fragment) or 4 (otherwise).
The first item of the bundle status report array SHALL be bundle
status information represented as a CBOR array (major type 4) with
additional info 5. The five items of the bundle status information
array shall provide information on the following five status
assertions, in this order:
. Reporting node received bundle.
. Reporting node accepted custody of bundle.
. Reporting node forwarded the bundle.
. Reporting node delivered the bundle.
. Reporting node deleted the bundle.
Each item of the bundle status information array SHALL be a bundle
status item represented as a CBOR array (major type 4) with
additional info either 2 (if the value of the first item of this
bundle status item is 1 AND the "Report status time" flag was set to
1 in the bundle processing flags of the bundle whose status is being
reported) or 1 (otherwise). The first item of the bundle status
item array SHALL be a Boolean value, indicating whether or not the
corresponding bundle status is asserted, represented as a CBOR
unsigned integer. The second item of the bundle status item array,
if present, SHALL indicate the time (as reported by the local system
clock, an implementation matter) at which the indicated condition
became true for this bundle, represented as a DTN time as described
in Section 4.1.6. above.
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The second item of the bundle status report array SHALL be the
bundle status report reason code explaining the values of the status
flags, represented as a CBOR unsigned integer. Valid status report
reason codes are defined in Figure 4 below but the list of status
report reason codes provided here is neither exhaustive nor
exclusive; supplementary DTN protocol specifications (including, but
not restricted to, the Bundle Security Protocol [BPSEC]) may define
additional reason codes.
+---------+--------------------------------------------+
| Value | Meaning |
+=========+============================================+
| 0 | No additional information. |
+---------+--------------------------------------------+
| 1 | Lifetime expired. |
+---------+--------------------------------------------+
| 2 | Forwarded over unidirectional link. |
+---------+--------------------------------------------+
| 3 | Transmission canceled. |
+---------+--------------------------------------------+
| 4 | Depleted storage. |
+---------+--------------------------------------------+
| 5 | Destination endpoint ID unintelligible. |
+---------+--------------------------------------------+
| 6 | No known route to destination from here. |
+---------+--------------------------------------------+
| 7 | No timely contact with next node on route. |
+---------+--------------------------------------------+
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| 8 | Block unintelligible. |
+---------+--------------------------------------------+
| (other) | Reserved for future use. |
+---------+--------------------------------------------+
Figure 4: Status Report Reason Codes
The third item of the bundle status report array SHALL be the source
node ID identifying the source of the bundle whose status is being
reported, represented as described in Section 4.1.5.2. above.
The fourth item of the bundle status report array SHALL be the
creation timestamp of the bundle whose status is being reported,
represented as described in Section 4.1.7. above.
The fifth item of the bundle status report array SHALL be present if
and only if the bundle whose status is being reported contained a
fragment ID. If present, it SHALL be the subject bundle's fragment
ID represented as described in Section 4.1.8. above.
The sixth item of the bundle status report array SHALL be present if
and only if the bundle whose status is being reported contained a
fragment ID. If present, it SHALL be the length of the subject
bundle's payload represented as a CBOR unsigned integer item.
6.1.2. Custody Signals
Custody signals are administrative records that effect custody
transfer operations. They are transmitted to the nodes that are the
current custodians of bundles.
Each custody signal SHALL be represented as a CBOR array (major type
4) with additional info either 6 (if the subject bundle is a
fragment) or 4 (otherwise).
The first item of the custody signal array SHALL be a signal type
code represented as a CBOR unsigned integer. Valid custody signal
types are defined as follows:
+---------+--------------------------------------------+
| Value | Meaning |
+=========+============================================+
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| 0 | Custody acceptance. The reporting node |
| | commits to supporting the requested custody|
| | transfer service(s). |
+---------+--------------------------------------------+
| 1 | Custody refusal. Applicable only when |
| | rerouting service is requested.
+---------+--------------------------------------------+
| 2 | Custody delegation: the bundle will be |
| | forwarded but custody was not taken. |
| | Applicable only when retransmission |
| | service is requested. |
+---------+--------------------------------------------+
| (other) | Reserved for future use. |
+---------+--------------------------------------------+
Figure 5: Custody Signal Type Codes
The second item of the custody signal array SHALL be additional
information amplifying the signal type code, represented as a CBOR
array (major type 4) with additional info either 2 (if the signal
type is 2) or 1 (otherwise).
When signal type is 0 or 1, the sole item in the additional
information array SHALL be a custody signal reason code, represented
as a CBOR unsigned integer. Valid custody signal reason codes are
defined as follows:
+---------+--------------------------------------------+
| Value | Meaning |
+=========+============================================+
| 0 | No additional information. |
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+---------+--------------------------------------------+
| 1 | Reserved for future use. |
+---------+--------------------------------------------+
| 2 | Reserved for future use. |
+---------+--------------------------------------------+
| 3 | Redundant (reception by a node that is a |
| | custodial node for this bundle). |
+---------+--------------------------------------------+
| 4 | Depleted storage. |
+---------+--------------------------------------------+
| 5 | Destination endpoint ID unintelligible. |
+---------+--------------------------------------------+
| 6 | No known route destination from here. |
+---------+--------------------------------------------+
| 7 | No timely contact with next node on route. |
+---------+--------------------------------------------+
| 8 | Block unintelligible. |
+---------+--------------------------------------------+
| (other) | Reserved for future use. |
+---------+--------------------------------------------+
Figure 6: Custody Signal Reason Codes
When signal type is 2, the first item in the additional information
array SHALL be the node ID of the node to which the reporting node
anticipates forwarding the bundle, represented as described in
Section 4.1.5.2. above, and the second item in this array SHALL be
an estimate of the number of seconds that will have elapsed since
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reception of the bundle before the anticipated forwarding begins,
represented as a CBOR unsigned integer.
The third item of the custody signal array SHALL be the source node
ID identifying the source of the bundle for which custodial activity
is being reported, represented as described in Section 4.1.5.2.
above.
The fourth item of the custody signal array SHALL be the creation
timestamp of the bundle for which custodial activity is being
reported, represented as described in Section 4.1.7. above.
The fifth item of the custody signal array SHALL be present if and
only if the bundle for which custodial activity is being reported
contained a fragment ID. If present, it SHALL be the subject
bundle's fragment ID represented as described in Section 4.1.8.
above.
The sixth item of the custody signal array SHALL be present if and
only if the bundle for which custodial activity is being reported
contained a fragment ID. If present, it SHALL be the length of the
subject bundle's payload represented as a CBOR unsigned integer
item.
6.2. Generation of Administrative Records
Whenever the application agent's administrative element is directed
by the bundle protocol agent to generate an administrative record
with reference to some bundle, the following procedure must be
followed:
Step 1: The administrative record must be constructed. If the
referenced bundle is a fragment, the administrative record MUST
contain the fragment ID and fragment length.
Step 2: A request for transmission of a bundle whose payload is this
administrative record MUST be presented to the bundle protocol
agent.
6.3. Reception of Custody Signals
For each received custody signal that has signal type zero (custody
acceptance), the administrative element of the application agent
MUST direct the bundle protocol agent to follow the custody transfer
success procedure in Section 5.11.
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For each received custody signal that has signal type 1 (custody
refusal), the administrative element of the application agent MUST
direct the bundle protocol agent to follow the custody transfer
failure procedure in Section 5.12.
For each received custody signal that has signal type 2 (custody
delegation), the administrative element of the application agent
MUST direct the bundle protocol agent to follow the custody
delegation procedure in Section 5.13.
7. Services Required of the Convergence Layer
7.1. The Convergence Layer
The successful operation of the end-to-end bundle protocol depends
on the operation of underlying protocols at what is termed the
"convergence layer"; these protocols accomplish communication
between nodes. A wide variety of protocols may serve this purpose,
so long as each convergence layer protocol adapter provides a
defined minimal set of services to the bundle protocol agent. This
convergence layer service specification enumerates those services.
7.2. Summary of Convergence Layer Services
Each convergence layer protocol adapter is expected to provide the
following services to the bundle protocol agent:
. sending a bundle to a bundle node that is reachable via the
convergence layer protocol;
. delivering to the bundle protocol agent a bundle that was sent
by a bundle node via the convergence layer protocol.
The convergence layer service interface specified here is neither
exhaustive nor exclusive. That is, supplementary DTN protocol
specifications (including, but not restricted to, the Bundle
Security Protocol [BPSEC]) may expect convergence layer adapters
that serve BP implementations conforming to those protocols to
provide additional services such as reporting on the transmission
and/or reception progress of individual bundles (at completion
and/or incrementally), retransmitting data that were lost in
transit, discarding bundle-conveying data units that the convergence
layer protocol determines are corrupt or inauthentic, or reporting
on the integrity and/or authenticity of delivered bundles.
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8. Security Considerations
The bundle protocol has taken security into concern from the outset
of its design. It was always assumed that security services would be
needed in the use of the bundle protocol. As a result, the bundle
protocol security architecture and the available security services
are specified in an accompanying document, the Bundle Security
Protocol specification [BPSEC]; an informative overview of this
architecture is provided in [SECO].
The bundle protocol has been designed with the notion that it may be
run over networks with scarce resources. For example, the networks
might have limited bandwidth, limited connectivity, constrained
storage in relay nodes, etc. Therefore, the bundle protocol must
ensure that only those entities authorized to send bundles over such
constrained environments are actually allowed to do so. All
unauthorized entities should be prevented from consuming valuable
resources as soon as practicable.
Likewise, because of the potentially high latencies and delays
involved in the networks that make use of the bundle protocol, data
sources should be concerned with the integrity of the data received
at the intended destination(s) and may also be concerned with
ensuring confidentiality of the data as it traverses the network.
Without integrity, the bundle payload data might be corrupted while
in transit without the destination able to detect it. Similarly, the
data source can be concerned with ensuring that the data can only be
used by those authorized, hence the need for confidentiality.
Internal to the bundle-aware overlay network, the bundle nodes
should be concerned with the authenticity of other bundle nodes as
well as the preservation of bundle payload data integrity as it is
forwarded between bundle nodes.
As a result, bundle security is concerned with the authenticity,
integrity, and confidentiality of bundles conveyed among bundle
nodes. This is accomplished via the use of two independent security-
specific bundle blocks, which may be used together to provide
multiple bundle security services or independently of one another,
depending on perceived security threats, mandated security
requirements, and security policies that must be enforced.
To provide end-to-end bundle authenticity and integrity, the Block
Integrity Block (BIB) is used. The BIB allows any security-enabled
entity along the delivery path to ensure the integrity of the
bundle's payload or any other block other than a Block
Confidentiality Block.
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To provide payload confidentiality, the use of the Block
Confidentiality Block (BCB) is available. The bundle payload, or any
other block aside from the primary block and the Bundle Security
Protocol blocks, may be encrypted to provide end-to-end payload
confidentiality/privacy.
Additionally, convergence-layer protocols that ensure authenticity
of communication between adjacent nodes in BP network topology
SHOULD be used where available, to minimize the ability of
unauthenticated nodes to introduce inauthentic traffic into the
network.
Bundle security MUST NOT be invalidated by forwarding nodes even
though they themselves might not use the Bundle Security Protocol.
In particular, while blocks MAY be added to bundles transiting
intermediate nodes, removal of blocks with the 'Discard block if it
can't be processed' flag set in the block processing control flags
may cause security to fail.
Inclusion of the Bundle Security Protocol in any Bundle Protocol
implementation is RECOMMENDED. Use of the Bundle Security Protocol
in Bundle Protocol operations is OPTIONAL.
9. IANA Considerations
The "dtn" and "ipn" URI schemes have been provisionally registered
by IANA. See http://www.iana.org/assignments/uri-schemes.html for
the latest details.
Registries of URI scheme type numbers, extension block type numbers,
and administrative record type numbers will be required.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC7049] Borman, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, October 2013.
[URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", RFC 3986, STD 66,
January 2005.
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[URIREG] Thaler, D., Hansen, T., and T. Hardie, "Guidelines and
Registration Procedures for URI Schemes", RFC 7595, BCP 35, June
2015.
10.2. Informative References
[ARCH] V. Cerf et al., "Delay-Tolerant Network Architecture", RFC
4838, April 2007.
[BPSEC] Birrane, E., "Bundle Security Protocol Specification", Work
In Progress, October 2015.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
[RFC5050] Scott, M. and S. Burleigh, "Bundle Protocol
Specification", RFC 5050, November 2007.
[SECO] Farrell, S., Symington, S., Weiss, H., and P. Lovell, "Delay-
Tolerant Networking Security Overview", Work Progress, July 2007.
[SIGC] Fall, K., "A Delay-Tolerant Network Architecture for
Challenged Internets", SIGCOMM 2003.
[TUT] Warthman, F., "Delay-Tolerant Networks (DTNs): A Tutorial",
<http://www.dtnrg.org>.
[UTC] Arias, E. and B. Guinot, "Coordinated universal time UTC:
historical background and perspectives" in "Journees systemes de
reference spatio-temporels", 2004.
11. Acknowledgments
This work is freely adapted from [RFC5050], which was an effort of
the Delay Tolerant Networking Research Group. The following DTNRG
participants contributed significant technical material and/or
inputs to that document: Dr. Vinton Cerf of Google, Scott Burleigh,
Adrian Hooke, and Leigh Torgerson of the Jet Propulsion Laboratory,
Michael Demmer of the University of California at Berkeley, Robert
Durst, Keith Scott, and Susan Symington of The MITRE Corporation,
Kevin Fall of Carnegie Mellon University, Stephen Farrell of Trinity
College Dublin, Peter Lovell of SPARTA, Inc., Manikantan Ramadas of
Ohio University, and Howard Weiss of SPARTA, Inc.
This document was prepared using 2-Word-v2.0.template.dot.
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12. Significant Changes from RFC 5050
Points on which this draft significantly differs from RFC 5050
include the following:
. Clarify the difference between transmission and forwarding.
. Amplify discussion of custody transfer. Move current custodian
to an extension block, of which there can be multiple
occurrences (possible support for the MITRE idea of multiple
concurrent custodians, from several years ago); define that
block in this specification.
. Introduce the concept of "node ID" as functionally distinct
from endpoint ID, while having the same syntax.
. Restructure primary block, making it immutable. Add optional
CRC.
. Add optional CRCs to non-primary blocks.
. Add block ID number to canonical block format (to support
streamlined BSP).
. Add bundle age extension block, defined in this specification.
. Add previous node extension block, defined in this
specification.
. Add flow label extension block, *not* defined in this
specification.
. Add manifest extension block, *not* defined in this
specification.
. Add hop count extension block, defined in this specification.
. Clean up a conflict between fragmentation and custody transfer
that Ed Birrane pointed out.
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Appendix A. For More Information
Please refer comments to dtn@ietf.org. The Delay Tolerant Networking
Research Group (DTNRG) Web site is located at http://www.dtnrg.org.
Copyright (c) 2016 IETF Trust and the persons identified as authors
of the code. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, is permitted pursuant to, and subject to the license
terms contained in, the Simplified BSD License set forth in Section
4.c of the IETF Trust's Legal Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info).
Authors' Addresses
Scott Burleigh
Jet Propulsion Laboratory, California Institute of Technology
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
US
Phone: +1 818 393 3353
Email: Scott.Burleigh@jpl.nasa.gov
Kevin Fall
Carnegie Mellon University / Software Engineering Institute
4500 Fifth Avenue
Pittsburgh, PA 15213
US
Phone: +1 412 268 3304
Email: kfall@cmu.edu
Edward J. Birrane
Johns Hopkins University Applied Physics Laboratory
11100 Johns Hopkins Rd
Laurel, MD 20723
US
Phone: +1 443 778 7423
Email: Edward.Birrane@jhuapl.edu
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