Internet DRAFT - draft-burleigh-bpv7
draft-burleigh-bpv7
Delay-Tolerant Networking Research Group S. Burleigh
Internet Draft JPL, Calif. Inst. Of Technology
Intended status: Informational June 6, 2014
Expires: December 2014
Proposed Revised Bundle Protocol
draft-burleigh-bpv7-00.txt
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Abstract
This Internet Draft presents a proposed modification to the Bundle
Protocol Specification, including notes on the rationale underlying
some of the proposed changes.
Table of Contents
1. Introduction...................................................4
2. Conventions used in this document..............................6
3. Service Description............................................6
3.1. Definitions...............................................6
3.2. Implementation Architectures.............................12
3.2.1. Bundle protocol application server..................13
3.2.2. Peer application nodes..............................13
3.2.3. Sensor network nodes................................13
3.2.4. Dedicated bundle router.............................13
3.3. Services Offered by Bundle Protocol Agents...............14
4. Bundle Format.................................................14
4.1. Self-Delimiting Numeric Values (SDNVs)...................14
4.2. Bundle Processing Control Flags..........................16
4.3. Block Processing Control Flags...........................18
4.4. Identifiers..............................................19
4.4.1. Node number.........................................19
4.4.2. Service number......................................19
4.4.3. Group number........................................20
4.4.4. Endpoint ID.........................................20
4.5. Formats of Bundle Blocks.................................23
4.5.1. Primary Bundle Block................................25
4.5.2. Canonical Bundle Block Format.......................27
4.5.3. Bundle Payload Block................................28
4.6. Extension Blocks.........................................29
4.6.1. Current Custodian...................................29
4.6.2. Destination EID.....................................30
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4.6.3. Previous Node Number................................30
4.6.4. Payload CRC.........................................30
4.6.5. Bundle Age..........................................30
4.6.6. Forwarding Anomaly..................................31
5. Bundle Processing.............................................32
5.1. Generation of Administrative Records.....................32
5.2. Bundle Transmission......................................33
5.3. Bundle Dispatching.......................................34
5.4. Bundle Forwarding........................................34
5.4.1. Forwarding Contraindicated..........................37
5.4.2. Forwarding Failed...................................37
5.5. Bundle Expiration........................................38
5.6. Bundle Reception.........................................38
5.7. Local Bundle Delivery....................................40
5.8. Bundle Fragmentation.....................................40
5.9. Application Data Unit Reassembly.........................42
5.10. Custody Transfer........................................42
5.10.1. Custody Acceptance.................................43
5.10.2. Custody Release....................................43
5.11. Custody Transfer Success................................43
5.12. Custody Transfer Failure................................44
5.13. Bundle Deletion.........................................44
5.14. Discarding a Bundle.....................................45
5.15. Canceling a Transmission................................45
5.16. Polling.................................................45
6. Administrative Record Processing..............................45
6.1. Administrative Records...................................45
6.1.1. Bundle Status Reports...............................46
6.1.2. Custody Signals.....................................50
6.1.3. Reopen Signals......................................52
6.1.4. Multicast Petitions.................................53
6.2. Generation of Administrative Records.....................55
6.3. Reception of Custody Signals.............................55
6.4. Reception of Reopen Signals..............................55
6.5. Generation and Handling of Multicast Petitions...........55
7. Services Required of the Convergence Layer....................57
7.1. The Convergence Layer....................................57
7.2. Summary of Convergence Layer Services....................57
8. Security Considerations.......................................57
8.1. Security considerations of BP basic multicast............59
9. IANA Considerations...........................................60
10. Conclusions..................................................61
11. References...................................................61
11.1. Normative References....................................61
11.2. Informative References..................................61
12. Acknowledgments..............................................62
Appendix A. For More Information.......Error! Bookmark not defined.
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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
utility of the protocol, to the extent that it has been judged
suitable for some network operations and eventual commercialization.
[It has also, as expected, exposed a number of opportunities for
making the protocol simpler, more capable, and easier to use. This
Internet Draft presents a proposed revision of the Bundle Protocol
Specification, including notes on the rationale underlying some of
the proposed changes.
[Amended original "Introduction" text from RFC-5050 follows. Notes
on rationale are enclosed in square brackets, like these last three
paragraphs. Appendix A contains a summary of the more significant
differences between this specification and RFC-5050.]
This document describes version 7 of the Delay Tolerant Networking
(DTN) "bundle" protocol (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 sits
at the application layer of some number of constituent internets,
forming a store-and-forward overlay network. Key capabilities of BP
include:
. Custody-based retransmission
. Ability to cope with intermittent connectivity
. Ability to take advantage of scheduled, predicted, and
opportunistic connectivity (in addition to continuous
connectivity)
. Late binding of overlay network endpoint identifiers to
underlying internet 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 the "native" internet protocols for
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communications within a given internet. Note that "internet" in the
preceding is used in a general sense and does not necessarily refer
to TCP/IP.
The interface between the common bundle protocol and a specific
internetwork protocol suite is termed a "convergence layer adapter".
Figure 1 shows three distinct transport and network protocols
(denoted T1/N1, T2/N2, and T3/N3).
+-----------+ +-----------+
| BP app | | BP app |
+---------v-| +->>>>>>>>>>v-+ +->>>>>>>>>>v-+ +-^---------+
| BP v | | ^ BP v | | ^ BP v | | ^ BP |
+---------v-+ +-^---------v-+ +-^---------v-+ +-^---------+
| Trans1 v | + ^ T1/T2 v | + ^ T2/T3 v | | ^ Trans3 |
+---------v-+ +-^---------v-+ +-^---------v + +-^---------+
| Net1 v | | ^ N1/N2 v | | ^ N2/N3 v | | ^ Net3 |
+---------v-+ +-^---------v + +-^---------v-+ +-^---------+
| >>>>>>>>^ >>>>>>>>>>^ >>>>>>>>^ |
+-----------+ +-------------+ +-------------+ +-----------+
| | | |
|<--- An internet --->| |<--- An internet --->|
| | | |
Figure 1: The Bundle Protocol Sits at the Application Layer of the
Internet Model
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.
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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 the DTN bundle
protocol, 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 usable. Each bundle
comprises a sequence of two or more "blocks" of protocol data, which
serve various purposes. Multiple instances of the same bundle (the
same unit of DTN protocol data) might exist concurrently in
different parts of a network -- possibly in different
representations and/or 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 of some bundle in the network that is in that node's local
memory.
Bundle payload - A bundle payload (or simply "payload") is the
application data whose conveyance to the bundle's destination is the
purpose for the transmission of a given bundle. The terms "bundle
content", "bundle payload", and "payload" are used interchangeably
in this document. The "nominal" payload for a bundle forwarded in
response to a bundle transmission request is the application data
unit whose location is provided as a parameter to that request. The
nominal payload for a bundle forwarded in response to reception of
that bundle is the payload of the received bundle.
Fragment - A fragment is a bundle whose payload block contains a
fragmentary payload. A fragmentary payload is either the first N
bytes or the last N bytes of some other payload -- either a nominal
payload or a fragmentary payload -- of length M, such that 0 < N <
M.
Bundle node - A bundle node (or, in the context of this document,
simply a "node") is any entity that can send and/or receive bundles.
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In the most familiar case, a bundle node is instantiated as a single
process running on a general-purpose computer, but in general the
definition is meant to be broader: a bundle node might alternatively
be a thread, an object in an object-oriented operating system, a
special-purpose hardware device, etc. Each bundle node has three
conceptual components, defined below: a "bundle protocol agent", a
set of zero or more "convergence layer adapters", and an
"application agent".Bundle protocol agent - The bundle protocol
agent (BPA) of a node is the node component that offers the BP
services and executes the procedures of the bundle protocol. The
manner in which it does so is wholly an implementation matter. For
example, BPA functionality might be coded into each node
individually; it might be implemented as a shared library that is
used in common by any number of bundle nodes on a single computer;
it might be implemented as a daemon whose services are invoked via
interprocess or network communication by any number of bundle nodes
on one or more computers; it might be implemented in hardware.
Convergence layer adapters - A convergence layer adapter (CLA) sends
and receives bundles on behalf of the BPA, utilizing the services
of some 'native' internet protocol stack that is supported in one of
the internets within which the node is functionally located. As
such, every CLA implements its own thin layer of protocol,
interposed between BP and the "top" protocol of the underlying
native internet protocol; this "CL protocol" may only serve to
multiplex and de-multiplex bundles to and from the underlying top
protocol, or it may offer additional CL-specific functionality. The
manner in which a CLA sends and receives bundles is wholly an
implementation matter, exactly as described for the BPA. The
definitions of CLAs and CL protocols are beyond the scope of this
specification.
Application agent - The application agent (AA) of a node is the node
component that utilizes the BP services to effect communication for
some purpose. The application agent in turn has two elements, an
administrative element and an application-specific element. The
application-specific element of an AA constructs, requests
transmission of, accepts delivery of, and processes application-
specific application data units; the only interface between the BPA
and the application-specific element of the AA is the BP service
interface. The administrative element of an AA constructs and
requests transmission of administrative records (including status
reports and custody signals), and it accepts delivery of and
processes any custody signals that the node receives. In addition to
the BP service interface, there is a (conceptual) private control
interface between the BPA and the administrative element of the AA
that enables each to direct the other to take action under specific
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circumstances. In the case of a node that serves simply as a
"router" in the overlay network, the AA may have no application-
specific element at all. The application-specific elements of other
nodes' AAs may perform arbitrarily complex application functions,
perhaps even offering multiplexed DTN communication services to a
number of other applications. As with the BPA, the manner in which
the AA performs its functions is wholly an implementation matter; in
particular, the administrative element of an AA might be built into
the library or daemon or hardware that implements the BPA and the
application-specific element of an AA might be implemented either in
software or in hardware.
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 single text string, called a "bundle endpoint ID"
(or, in this document, simply "endpoint ID"; endpoint IDs are
described in detail in Section 4.4.4 below). The special case of an
endpoint that never contains more than one node is termed a
"singleton" endpoint. Singletons are the most familiar sort of
endpoint, but in general the endpoint notion is meant to be broader.
For example, the nodes in a sensor network might constitute a set of
bundle nodes that identify themselves by a single common endpoint ID
and thus form a single bundle endpoint. *Note* too that a given
bundle node might identify itself by multiple endpoint IDs and thus
be a member of multiple bundle endpoints. The final destination of
every bundle is an endpoint, which may or may not be singleton. The
original source of every bundle is a singleton endpoint.
Transmission - A transmission is an attempt by a node's bundle
protocol agent 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 response to a transmission request issued by the
node's application agent. The minimum reception group of an endpoint
may be any one of the following: (a) ALL of the nodes registered in
an endpoint that is permitted to contain multiple nodes (in which
case forwarding to the endpoint is functionally similar to
"multicast" operations in the Internet, though possibly very
different in implementation); (b) ANY N of the nodes registered in
an endpoint that is permitted to contain multiple nodes, where N is
in the range from zero to the cardinality of the endpoint (in which
case forwarding to the endpoint is functionally similar to "anycast"
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operations in the Internet); 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). The
nature of the minimum reception group for a given endpoint can be
determined from the endpoint's ID (again, see Section 4.4 below):
for some endpoint ID "schemes", the nature of the minimum reception
group is fixed - in a manner that is defined by the scheme - for all
endpoints identified under the scheme; for other schemes, the nature
of the minimum reception group is indicated by some lexical feature
of the "scheme-specific part" of the endpoint ID, in a manner that
is defined by the scheme. Any number of transmissions may be
concurrently undertaken by the bundle protocol agent of a given
node.
Forwarding - When the bundle protocol agent of a node determines
that a bundle must be "forwarded" to a node (either a node that is a
member of the bundle's destination endpoint or 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.
Registration - A registration is the state machine characterizing a
given node's membership in a given endpoint. Any number of
registrations may be concurrently associated with a given endpoint,
and any number of registrations may be concurrently associated with
a given node. Any single registration must at any time be in one of
two states: Active or Passive. A registration always has an
associated "delivery failure action", the action that is to be taken
when a bundle that is "deliverable" (see below) subject to that
registration is received at a time when the registration is in the
Passive state. Delivery failure action must be one of the following:
. defer "delivery" (see below) of the bundle subject to this
registration until (a) this bundle is the least recently
received of all bundles currently deliverable subject to this
registration and (b) either the registration is polled or else
the registration is in the Active state; or
. "abandon" (see below) delivery of the bundle subject to this
registration.
An additional implementation-specific delivery deferral procedure
may optionally be associated with the registration. While the state
of a registration is Active, reception of a bundle that is
deliverable subject to this registration must cause the bundle to be
delivered automatically as soon as it is the least recently received
bundle that is currently deliverable subject to the registration.
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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.
Delivery - Upon reception, the processing of a bundle that has been
sent to a given node depends on whether or not the receiving node is
registered in the bundle's destination endpoint. If it is, and if
the payload of the bundle is non-fragmentary (possibly as a result
of successful payload reassembly from fragmentary payloads,
including the original payload of the received bundle), then the
bundle is normally "delivered" to the node's application agent
subject to the registration characterizing the node's membership in
the destination endpoint. A bundle is considered to have been
delivered at a node subject to a registration as soon as the
application data unit that is the payload of the bundle, together
with the value of the bundle's "Acknowledgement by application is
requested" flag and any other relevant metadata (an implementation
matter), has been presented to the node's application agent in a
manner consistent with the state of that registration and, as
applicable, the registration's delivery failure action.
Deliverability, Abandonment - A bundle is considered "deliverable"
subject to a registration if and only if (a) the bundle's
destination endpoint is the endpoint with which the registration is
associated, (b) the bundle has not yet been delivered subject to
this registration, and (c) delivery of the bundle subject to this
registration has not been abandoned. To "abandon" delivery of a
bundle subject to a registration is simply to declare it no longer
deliverable subject to that registration; normally only
registrations' registered delivery failure actions cause deliveries
to be abandoned.
Deletion, Discarding - A bundle protocol agent "discards" a bundle
by simply ceasing all operations on the bundle and functionally
erasing all references to it; the specific procedures by which this
is accomplished are an implementation matter. Bundles are discarded
silently; i.e., the discarding of a bundle does not result in
generation of an administrative record. "Retention constraints" are
elements of the bundle state that prevent a bundle from being
discarded; a bundle cannot be discarded while it has any retention
constraints. A bundle protocol agent "deletes" a bundle in response
to some anomalous condition by notifying the bundle's report-to node
of the deletion (provided such notification is warranted; see
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Section 5.13 for details) and then arbitrarily removing all of the
bundle's retention constraints, enabling the bundle to be discarded.
Custody - A node "takes custody" of a bundle when it retains a copy
of the bundle for some period, forwarding and possibly re-forwarding
the bundle as appropriate, and destroys that copy only when custody
of that bundle is formally "released". Custody of a bundle may only
be taken if the destination of the bundle is a singleton endpoint. A
"custodial node" (or "custodian") of a bundle is a node that has
taken custody of the bundle and has not yet released that custody.
To "accept custody" upon receiving a bundle is to take custody of
the bundle and announce the new custodian to all current custodians
of the bundle. Custody may only be released when either (a)
notification is received that some other node has accepted custody
of the same bundle; (b) notification is received that the bundle has
been delivered at the (sole) node registered in the bundle's
destination endpoint; (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. 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.
The custody transfer mechanism in BP is primarily intended as a
means of optimizing recovery from forwarding failures. When a route
takes a bundle to a node from which it cannot be forwarded to the
application, BP must recover from this error: it can "return" the
bundle back toward some node that can forward it along some
different path in the network, or else it can just send a small
"signal" bundle back to such a node, in the event that this node has
retained a copy of the bundle ("taken custody") and is therefore
able to re-forward the bundle without receiving a copy. Custody
transfer sharply reduces the network traffic required for recovery
from forwarding failures, at the cost of increased buffer occupancy
and state management at the custodial node.
Note that custodial re-forwarding can also be initiated by
expiration of a timer prior to reception of a custody acceptance
signal. Since the absence of a custody acceptance signal might be
caused by failure to receive the bundle, custody transfer can
additionally serve as an automated retransmission mechanism.
Because custody transfer's only remedy for loss of any part of a
bundle is retransmission of the entire bundle (not just the lost
portion), custody transfer is a less efficient automated
retransmission mechanism than the reliable transport protocols that
are typically available at the convergence layer; configuring the
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network to use reliable convergence-layer protocols between nodes is
generally the best means of ensuring bundle delivery at the
destination node(s). But there are some use cases (typically
involving unidirectional links) in which custody transfer in BP may
be a more cost-effective solution for reliable transmission between
two BP agents than operating a retransmission protocol at the
convergence layer.
Embargo - Forwarding failures are not just operational anomalies;
they may also convey information about the network, i.e., a
forwarding failure may indicate a sustained lapse in forwarding
capability. Since forwarding a bundle to a dead end wastes time and
bandwidth, the bundle protocol agent may choose to manage such a
lapse by imposing a temporary "embargo" on subsequent forwarding
activity that is similar to the forwarding attempt that has been
seen to fail. Because the lapse may indeed be temporary, the agent
may elect to test it periodically by forwarding a single "probe"
bundle in deliberate violation of the embargo; upon notification
that a probe bundle was accepted for forwarding, the agent may lift
the embargo.
For bundles that are subject to custody transfer, custody transfer
failure provides a basis for imposing an embargo. For non-custodial
bundles, forwarding failure is detected upon arrival of a "returned"
bundle containing a Forwarding Anomaly block that explains why the
bundle could not be forwarded. The resulting embargo may be tested
by attachment of a "Probe" Forwarding Anomaly block to a bundle that
is forwarded in deliberate violation of the embargo. Notice that
the probe bundle was accepted for forwarding is provided in a
"Reopen signal" administrative record, enabling the embargo to be
lifted.
Embargoes are an optional mechanism. Procedures for determining
when and how to impose, enforce, and lift an embargo are an
implementation matter.
3.2. Implementation Architectures
The above definitions are intended to enable the bundle protocol's
operations to be specified in a manner that minimizes bias toward
any particular implementation architecture. To illustrate the range
of interoperable implementation models that might conform to this
specification, four example architectures are briefly described
below.
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3.2.1. Bundle protocol application server
A single bundle protocol application server, constituting a single
bundle node, runs as a daemon process on each computer. The daemon's
functionality includes all functions of the bundle protocol agent,
all convergence layer adapters, and both the administrative and
application-specific elements of the application agent. The
application-specific element of the application agent functions as a
server, offering bundle protocol service over a local area network:
it responds to remote procedure calls from application processes (on
the same computer and/or remote computers) that need to communicate
via the bundle protocol. The server supports its clients by creating
a new (conceptual) node for each one and registering each such node
in a client-specified endpoint. The conceptual nodes managed by the
server function as clients' bundle protocol service access points.
3.2.2. Peer application nodes
Any number of bundle protocol application processes, each one
constituting a single bundle node, run in ad-hoc fashion on each
computer. The functionality of the bundle protocol agent, all
convergence layer adapters, and the administrative element of the
application agent is provided by a library to which each node
process is dynamically linked at run time. The application-specific
element of each node's application agent is node-specific
application code.
3.2.3. Sensor network nodes
Each node of the sensor network is the self-contained implementation
of a single bundle node. All functions of the bundle protocol agent,
all convergence layer adapters, and the administrative element of
the application agent are implemented in simplified form in
Application-Specific Integrated Circuits (ASICs), while the
application-specific element of each node's application agent is
implemented in a programmable microcontroller. Forwarding is
rudimentary: all bundles are forwarded on a hard-coded default
route.
3.2.4. Dedicated bundle router
Each computer constitutes a single bundle node that functions solely
as a high-performance bundle forwarder. Many standard functions of
the bundle protocol agent, the convergence layer adapters, and the
administrative element of the application agent are implemented in
ASICs, but some functions are implemented in a high-speed processor
to enable reprogramming as necessary. The node's application agent
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has no application-specific element. Substantial non-volatile
storage resources are provided, and arbitrarily complex forwarding
algorithms are supported.
3.3. Services Offered by Bundle Protocol Agents
The bundle protocol agent of each node is expected to provide the
following services to the node's application agent:
. 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
Each bundle shall be a concatenated sequence of at least two block
structures. The first block in the sequence must be a primary bundle
block, and no bundle may have more than one primary bundle block.
Additional bundle protocol blocks of other types may follow the
primary block to support extensions to the bundle protocol, such as
the Bundle Security Protocol [SBSP]. Exactly one of the blocks in
the sequence must be a payload block. The last block in the sequence
must have the "last block" flag (in its block processing control
flags) set to 1; for every other block in the bundle after the
primary block, this flag must be set to zero.
4.1. Self-Delimiting Numeric Values (SDNVs)
The design of the bundle protocol attempts to reconcile minimal
consumption of transmission bandwidth with:
. extensibility to address requirements not yet identified, and
. scalability across a wide range of network scales and payload
sizes.
A key strategic element in the design is the use of self-delimiting
numeric values (SDNVs). The SDNV encoding scheme is closely adapted
from the Abstract Syntax Notation One Basic Encoding Rules for sub-
identifiers within an object identifier value [ASN1]. An SDNV is a
numeric value encoded in N octets, the last of which has its most
significant bit (MSB) set to zero; the MSB of every other octet in
the SDNV must be set to 1. The value encoded in an SDNV is the
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unsigned binary number obtained by concatenating into a single bit
string the 7 least significant bits of each octet of the SDNV. The
following examples illustrate the encoding scheme for various
hexadecimal values.
0xABC : 1010 1011 1100
is encoded as
{1 00 10101} {0 0111100}
= 10010101 00111100
0x1234 : 0001 0010 0011 0100
= 1 0010 0011 0100
is encoded as
{1 0 100100} {0 0110100}
= 10100100 00110100
0x4234 : 0100 0010 0011 0100
= 100 0010 0011 0100
is encoded as
{1 000000 1} {1 0000100} {0 0110100}
= 10000001 10000100 00110100
0x7F : 0111 1111
= 111 1111
is encoded as
{0 1111111}
= 01111111
Figure 2: SDNV Example
Note: Care must be taken to make sure that the value to be encoded
is (in concept) padded with high-order zero bits to make its bitwise
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length a multiple of 7 before encoding. Also note that, while there
is no theoretical limit on the size of an SDNV field, the overhead
of the SDNV scheme is 1:7, i.e., one bit of overhead for every 7
bits of actual data to be encoded. Thus, a 7-octet value (a 56-bit
quantity with no leading zeroes) would be encoded in an 8-octet
SDNV; an 8-octet value (a 64-bit quantity with no leading zeroes)
would be encoded in a 10-octet SDNV (one octet containing the high-
order bit of the value padded with six leading zero bits, followed
by nine octets containing the remaining 63 bits of the value). 148
bits of overhead would be consumed in encoding a 1024-bit RSA
encryption key directly in an SDNV. In general, an N-bit quantity
with no leading zeroes is encoded in an SDNV occupying ceil(N/7)
octets, where ceil is the integer ceiling function.
Implementations of the bundle protocol may handle as an invalid
numeric value any SDNV that encodes an integer that is larger than
(2^64 - 1).
An SDNV can be used to represent both very large and very small
integer values. However, SDNV is clearly not the best way to
represent every numeric value. For example, an SDNV is a poor way to
represent an integer whose value typically falls in the range 128 to
255. In general, though, we believe that SDNV representation of
numeric values in bundle blocks yields the smallest block sizes
without sacrificing scalability.
4.2. Bundle Processing Control Flags
The bundle processing control flags field in the primary bundle
block of each bundle is an SDNV; the value encoded in this SDNV is a
string of bits used to invoke selected bundle processing control
features. The significance of the value in each currently defined
position of this bit string is described here. Note that in the
figure and descriptions, the bit label numbers denote position (from
least significant ('0') to most significant) within the decoded bit
string, and not within the representation of the bits on the wire.
This is why the descriptions in this section and the next do not
follow standard RFC conventions with bit 0 on the left; if fields
are added in the future, the SDNV will grow to the left, and using
this representation allows the references here to remain valid.
2 1 0
7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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|Status Report|Class of Svc.| General |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Bundle Processing Control Flags Bit Layout
The bits in positions 0 through 13 of the value of the bundle
processing control flags SDNV are flags that characterize the bundle
as follows:
0 -- Bundle is a fragment.
1 -- Application data unit is an administrative record.
2 -- Bundle must not be fragmented.
3 -- Custody transfer is requested.
4 -- Destination endpoint is a singleton.
5 -- Acknowledgement by application is requested.
6 -- Bundle is critical.
7 -- Best-efforts forwarding is requested.
8 -- Reliable forwarding is requested.
9 -- Flow label is present.
10 - Payload CRC block is present.
11-13 -- Reserved for future use.
The bits in positions 15 through 20 are used to indicate the
bundle's class of service. They constitute a seven-bit priority
field indicating the bundle's priority, a value from 0 to 127, with
higher values being of higher priority (greater urgency). Within
this field, bit 20 is the most significant bit.
The bits in positions 21 through 27 are status report request flags.
These flags are used to request status reports as follows:
21 -- Request reporting of bundle reception.
22 -- Request reporting of custody acceptance.
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23 -- Request reporting of bundle forwarding.
24 -- Request reporting of bundle delivery.
25 -- Request reporting of bundle deletion.
26 -- Reserved for future use.
27 -- Reserved for future use.
If the bundle processing control flags indicate that the bundle's
application data unit is an administrative record, then the custody
transfer requested flag must be zero and all status report request
flags must be zero. If the custody transfer requested flag is 1,
then the source node requests that every receiving node accept
custody of the bundle. If the bundle's source endpoint ID is
"dtn:none" (see below), then the bundle is not uniquely identifiable
and all bundle protocol features that rely on bundle identity must
therefore be disabled: the bundle's custody transfer requested flag
must be zero, the "Bundle must not be fragmented" flag must be 1,
and all status report request flags must be zero.
4.3. Block Processing Control Flags
The block processing control flags field in every block other than
the primary bundle block is an SDNV; the value encoded in this SDNV
is a string of bits used to invoke selected block processing control
features. The significance of the values in all currently defined
positions of this bit string, in order from least significant
position in the decoded bit string (labeled '0') to most significant
(labeled '5'), is described here.
0
6 5 4 3 2 1 0
+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+
Figure 4: Block Processing Control Flags Bit Layout
0 - Block must be replicated in every fragment.
1 - Transmit status report if block can't be processed.
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2 - Delete bundle if block can't be processed.
3 - Last block.
4 - Discard block if it can't be processed.
5 - Block was forwarded without being processed.
6 - Reserved for future use.
For each bundle whose primary block's bundle processing control
flags (see above) indicate that the bundle's application data unit
is an administrative record, the "Transmit status report if block
can't be processed" flag in the block processing flags field of
every other block in the bundle must be zero.
The 'Block must be replicated in every fragment' bit in the block
processing flags must be set to zero on all blocks that follow the
payload block.
4.4. Identifiers
4.4.1. Node number
Each bundle node has - as a permanent, immutable property of that
node - an assigned number which uniquely identifies the node within
the network in which it operates. Every node must have exactly one
node number. Every BP node number is an integer in the range 0 to
(2**63 - 1). No node may be identified by node number zero; node
number zero is used to signify "no node".
Note that a node's number is not an address; node numbers have no
intrinsic topological significance. A node number is simply a name
that is written in numerals, for bit-efficient (binary)
representation in transmission and processor-efficient
representation in protocol operations. No node number can occupy
more than nine (9) octets when represented as an SDNV, and any node
number can always be stored in a 64-bit integer for the purposes of
a BP implementation.
A registry of node numbers ("CBHE node numbers") is managed by IANA
per RFC-7116 [RFC7116].
4.4.2. Service number
A BP service number notionally functions as a de-multiplexing token.
When the bundle payload is a protocol data unit of some protocol
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that has its own de-multiplexing identifiers, the service number may
function in a manner similar to that of the protocol number in an IP
packet, characterizing the encapsulated protocol; alternatively, the
service number may function in a manner similar to that of the port
number in a UDP datagram.
Service numbers enable inbound bundles' application data units to be
de-multiplexed to instances of application functionality that are
designed to process them, so that effective communication
relationships can be developed between bundle producers and
consumers.
Every service number is an integer in the range 0 to (2**63 - 1).
Node number zero is used to signify "BP administrative records".
A registry of service numbers ("CBHE service numbers") is managed by
IANA per RFC-7116 [RFC7116].
4.4.3. Group number
Each BP multicast group is identified by a multicast group number.
Multicast group numbers may be used as the destination numbers of
bundles for which the destination endpoint is not a singleton
endpoint, as indicated by a value of zero in the "Destination
endpoint is a singleton" bundle processing flag.
Every group number is an integer in the range 0 to (2**63 - 1). No
BP multicast group may be identified by group number zero; group
number zero is used to signify that the destination endpoint ID of
the bundle is explicitly encoded in the bundle's destination-EID
extension block.
4.4.4. Endpoint ID
The sources and destinations of bundles are bundle endpoints,
identified by text strings termed "endpoint IDs" (see Section 3.1).
Each endpoint ID conveyed in any bundle block takes the form of a
Uniform Resource Identifier (URI; [URI]). As such, each endpoint ID
can be characterized as having this general structure:
< scheme name > : < scheme-specific part, or "SSP" >
The scheme identified by the < scheme name > in an endpoint ID is a
set of syntactic and semantic rules that fully explain how to parse
and interpret the SSP. The set of allowable schemes is effectively
unlimited. Any scheme conforming to [URIREG] may be used in a bundle
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protocol endpoint ID. In addition, a single additional scheme is
defined by the present document:
. The "dtn" scheme, which is used at minimum in the
representation of the null endpoint ID "dtn:none". The
forwarding of a bundle to the null endpoint is never
contraindicated, and the minimum reception group for the null
endpoint is the empty set. The other syntactic and semantic
rules that explain how to construct, parse and interpret the
SSP of a URI in the "dtn" scheme are beyond the scope of this
specification and, at the time of this writing, are not
formally defined.
Note that, although the endpoint IDs conveyed in bundle blocks are
expressed as 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]).
While EIDs, being human-readable, are convenient for the purposes of
the human users and managers of a delay-tolerant network, they
consume appreciable transmission bandwidth and are not convenient
for the purposes of computer software:
. As they may be arbitrarily lengthy, they must be stored in
memory regions of appropriate size which typically must be
dynamically allocated. As such, operations on them always risk
failure due to insufficiency of remaining available memory.
Moreover, failure to release such a memory region when the EID
occupying it is no longer needed (however this is determined)
may result in a "memory leak" that permanently reduces
remaining available memory for future operations on EIDs.
. Storing, retrieving, and comparing character strings is
significantly more time-consuming than storing, retrieving, and
comparing numeric values in most computer architectures.
Fortunately, for most purposes it is not necessary for BP
implementations to operate directly on EIDs. This is because the
text of nearly every EID string is implicit in the information
carried in other fields of the bundle. This implicit text can
easily be rendered explicit when EIDs must be exposed to users and
network managers.
The EID that identifies the source of a bundle is a URI in the "ipn"
scheme defined in RFC-6260 [RFC6260]:
ipn:NN.SS
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where NN is the bundle's source node number and SS is the bundle's
source service number. Note that when NN is zero, the bundle's
source is anonymous.
The EID that identifies the "report-to" endpoint of a bundle (the
endpoint that is the destination of all bundle status reports
produced in the course of conveying the bundle to its destination)
is similarly a URI in the "ipn" scheme:
ipn:NN.0
where NN is the bundle's report-to node number. The service number
in this EID is zero, which is the service number reserved for all
bundle administrative record exchange. Note that when NN is zero,
the report-to EID is "ipn:0.0" which is functionally equivalent to
"dtn:none".
The EID that identifies a "current custodian" endpoint of a bundle
(an endpoint that is a destination of Custody Accepted and Custody
Refused signals produced in the course of conveying the bundle to
its destination) is similarly a URI in the "ipn" scheme:
ipn:NN.0
where NN is the bundle's current custodian node number as noted in a
current custodian extension block. The service number in this EID
is again zero, for the same reason. NN should never be zero in this
case: if there is no current custodian then the current custodian
extension block should be omitted from the bundle.
The EID that identifies the destination of a bundle is more complex
to compose, as it depends on the nature of the bundle's destination.
. If the value of the bundle's "Destination endpoint is a
singleton" bundle processing flag is 1, then the bundle's
"forwarding mode" is "basic unicast". The EID that identifies
the destination of the bundle is a URI in the "ipn" scheme:
ipn:NN.SS
where NN is the bundle's destination number interpreted as a node
number and SS is the bundle's destination service number. Note that
when NN is zero the destination EID indicates that the bundle is to
be delivered at no nodes; such an EID is functionally equivalent to
"dtn:none".
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. Otherwise, the bundle's destination is not a singleton
endpoint. If the bundle's destination number is zero, then the
bundle's forwarding mode is undefined and the EID that
identifies the destination of the bundle is carried explicitly,
as a text string, in the bundle's destination-EID extension
block. In this case the bundle's destination service number is
irrelevant and must be set to zero.
. Otherwise, the bundle's forwarding mode is "basic multicast".
The EID that identifies the destination of the bundle is a URI
in the "imc" scheme defined later in this document:
imc:NN.SS
where NN is the bundle's destination number interpreted as a
multicast group number and SS is the bundle's destination service
number.
4.5. Formats of Bundle Blocks
This section describes the formats of the primary block and payload
block. 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 [SBSP]) may require
that BP implementations conforming to those protocols construct and
process additional blocks.
The format of these two basic BP blocks is shown in Figure 5 below.
Primary Bundle Block
+----------------+----------------+----------------+---------------+
| Version | Block length | CRC |
+----------------+----------------+----------------+---------------+
| Bundle Processing flags (*) | [Flow label (*)] |
+----------------+----------------+----------------+---------------+
| Destination number (*) | Destination service number (*) |
+----------------+----------------+----------------+---------------+
| Source node number (*) | Source service number (*) |
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+----------------+----------------+----------------+---------------+
| Report-to node number (*) | Creation timestamp time (*) |
+----------------+----------------+----------------+---------------+
| Creation Timestamp sequence number (*) |
+---------------------------------+--------------------------------+
| Lifetime (*) | [Fragment offset (*)] |
+----------------+----------------+--------------------------------+
| [Total application data unit length (*)] |
+----------------+----------------+--------------------------------+
Bundle Payload Block
+----------------+----------------+----------------+---------------+
| Block type |Block number (*)| Proc. flags (*)| Blk length(*) |
+----------------+----------------+----------------+---------------+
/ Bundle payload (variable) /
+------------------------------------------------------------------+
Figure 5: Basic Bundle Block Formats
(*) Notes:
The bundle processing control ("Proc.") flags field in the Primary
Bundle Block is an SDNV and is therefore of variable length. A two-
octet SDNV is shown here for convenience in representation.
The block length field of the Primary Bundle Block is an SDNV and is
therefore of variable length. A four-octet SDNV is shown here for
convenience in representation.
The destination number, destination service number, source node
number, source service number, report-to node number, creation
timestamp time, and lifetime fields in the Primary Bundle Block are
SDNVs and are therefore of variable length. Two-octet SDNVs are
shown here for convenience in representation.
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The Creation Timestamp sequence number field in the Primary Bundle
Block is an SDNV and is therefore of variable length. A four-octet
SDNV is shown here for convenience in representation.
The flow label field of the Primary Bundle Block is present only if
the Flow Label flag in the block's processing flags byte is set to
1. It is an SDNV and is therefore of variable length; a two-octet
SDNV is shown here for convenience in representation.
The fragment offset field of the Primary Bundle Block is present
only if the Fragment flag in the block's processing flags byte is
set to 1. It is an SDNV and is therefore of variable length; a two-
octet SDNV is shown here for convenience in representation.
The total application data unit length field of the Primary Bundle
Block is present only if the Fragment flag in the block's processing
flags byte is set to 1. It is an SDNV and is therefore of variable
length; a four-octet SDNV is shown here for convenience in
representation.
The block processing control flags ("Proc. flags") field of the
Payload Block is an SDNV and is therefore of variable length. A one-
octet SDNV is shown here for convenience in representation.
The block length ("Blk length") field of the Payload Block is an
SDNV and is therefore of variable length. A one-octet SDNV is shown
here for convenience in representation.
4.5.1. Primary Bundle Block
The primary bundle block contains the basic information needed to
route bundles to their destinations. The fields of the primary
bundle block are:
Version: A 1-byte field indicating the version of the bundle
protocol that constructed this block. The present document describes
version 0x07 of the bundle protocol.
Block Length: a 1-byte field that contains the aggregate length (in
bytes) of all remaining fields of the primary block. Note that,
although most fields of the primary bundle block are variable-length
SDNVs, the lengths of all of these SDNVs are in practice limited;
this ensures that the total length of the primary block cannot
exceed 255.
CRC: a 2-byte field that contains a CRC16 value computed over the
concatenation of all bytes of the primary block (for this purpose
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the CRC field is itself populated with the value zero), the block-
type-specific data of the Destination EID extension block (if
present), and the block-type-specific data of the Payload CRC
extension block (if present), in that order.
[The proposed limit on the maximum length of the primary bundle
block simplifies parsing: bundle parsing logic can be certain that
all critical information needed to begin bundle ingestion - possibly
even to forward the bundle immediately - can be acquired by reading
at most the first 255 bytes of the bundle. The fixed locations and
lengths of the first three fields also simplify CRC computation
somewhat, making BP implementation in FPGAs or ASICs less expensive.
Finally, note that all fields of the primary block are immutable;
none will ever change at any point on the bundle's end-to-end path.
This is intended to simplify canonicalization in the management of
bundle security protocol blocks.]
Bundle Processing Control Flags: The Bundle Processing Control Flags
field is an SDNV that contains the bundle processing control flags
discussed in Section 4.2 above.
Destination number: The Destination number field contains
information that (as noted in 4.4.4 above) may form a part of the
endpoint ID of the bundle's destination, i.e., the endpoint
containing the node(s) at which the bundle is to be delivered.
Destination service number: The Destination service number field
contains information that (as noted in 4.4.4 above) may form a part
of the endpoint ID of the bundle's destination.
Source node number: The Source node number field contains the node
number of the node from which the bundle was initially transmitted.
Source service number: The Source service number field contains the
service number of the endpoint ID of the bundle's nominal source.
Report-to node number: The Report-to node number field contains the
node number of the node 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 SDNVs that,
together with the source node number and (if the bundle is a
fragment) the fragment offset and payload length, serve to identify
the bundle. The first SDNV of the timestamp is the bundle's creation
time, while the second is the bundle's creation timestamp sequence
number. Bundle creation time is the time -- expressed in seconds
since the start of the year 2000, on the Coordinated Universal Time
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(UTC) scale [UTC] -- at which the transmission request was received
that resulted in the creation of the bundle. Sequence count is the
latest value (as of the time at which that transmission request was
received) of a monotonically increasing positive integer counter
managed by the source node's bundle protocol agent that may be reset
to zero whenever the current time advances by one second. For nodes
that lack accurate clocks, 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 either case, a source Bundle Protocol
Agent must never create two distinct bundles with the same source
endpoint ID and bundle creation timestamp. The combination of source
node number and bundle creation timestamp therefore serves to
identify a single transmission request, enabling it to be
acknowledged by the receiving application (provided the source node
number is not zero).
Lifetime: The lifetime field is an SDNV 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 bundle's age exceeds
its lifetime, bundle nodes need no longer retain or forward the
bundle; the bundle may be deleted from the network.
Fragment Offset: If the Bundle Processing Control Flags of this
Primary block indicate that the bundle is a fragment, then the
Fragment Offset field is an SDNV indicating the offset from the
start of the original application data unit at which the bytes
comprising the payload of this bundle were located. If not, then the
Fragment Offset field is omitted from the block.
Total Application Data Unit Length: If the Bundle Processing Control
Flags of this Primary block indicate that the bundle is a fragment,
then the Total Application Data Unit Length field is an SDNV
indicating the total length of the original application data unit of
which this bundle's payload is a part. If not, then the Total
Application Data Unit Length field is omitted from the block.
4.5.2. Canonical Bundle Block Format
Every bundle block of every type other than the primary bundle block
comprises the following fields, in this order:
. Block type code, expressed as an 8-bit unsigned binary integer.
Bundle block type code 1 indicates that the block is a bundle
payload block. Block type codes 2 through 11 are defined as
noted later in this specification. Block type codes 192
through 255 are not defined in this specification and are
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available for private and/or experimental use. All other values
of the block type code are reserved for future use.
. Block number, an unsigned integer expressed as an SDNV. 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, an unsigned integer expressed
as an SDNV. The individual bits of this integer are used to
invoke selected block processing control features.
. Block data length, an unsigned integer expressed as an SDNV.
The Block data length field contains the aggregate length of
all remaining fields of the block, i.e., the block-type-
specific data fields.
. Block-type-specific data fields, whose format and order are
type-specific and whose aggregate length in octets is the value
of the block data length field. All multi-byte block-type-
specific data fields are represented in network byte order.
+----------------+----------------+----------------+---------------+
| Block type |Block number (*)| Proc. Flags (*)| Blk length(*) |
+----------------+----------------+----------------+---------------+
/ Block body data (variable) /
+------------------------------------------------------------------+
Figure 6: Block Layout
4.5.3. Bundle Payload Block
The fields of the bundle payload block are:
Block Type: The Block Type field is a 1-byte field that indicates
the type of the block. For the bundle payload block, this field
contains the value 1.
Block Number: The Block Number field is an SDNV that contains the
unique identifying number of the block. The block number of the
bundle payload block is always zero.
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Block Processing Control Flags: The Block Processing Control Flags
field is an SDNV that contains the block processing control flags
discussed in Section 4.3 above.
Block Length: The Block Length field is an SDNV that contains the
aggregate length of all remaining fields of the block - which is to
say, the length of the bundle's payload.
Payload: The Payload field contains the application data carried by
this bundle.
That is, bundle payload blocks follow the canonical format of the
previous section. The block body data for payload blocks is the
application data carried by the bundle.
4.6. 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.
Whenever a bundle is forwarded that contains one or more extension
blocks that could not be processed, the "Block was forwarded without
being processed" flag must be set to 1 within the block processing
flags of each such block. For each block flagged in this way, the
flag may optionally be cleared (i.e., set to zero) by another node
that subsequently receives the bundle and is able to process that
block; the specifications defining the various extension blocks are
expected to define the circumstances under which this flag may be
cleared, if any.
The extension blocks of the Bundle Security Protocol (block types 2,
3, and 4) are defined separately in the Bundle Security Protocol
specification (work in progress).
The following extension blocks are defined in the current document.
4.6.1. 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 an SDNV containing the node number of
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the custodian. The bundle MAY contain one or more occurrences of
this type of block.
4.6.2. Destination EID
The Destination EID block, block type 6, contains the bundle's
explicit destination EID. This EID may be a URI of any registered
scheme. Procedures for forwarding a block to the endpoint
identified in the destination EID block are beyond the scope of this
specification; it is expected that they will be defined in future
specifications. If the bundle's "Destination endpoint is a
singleton" bundle processing flag is zero and the bundle's
destination number is zero, then the bundle MUST contain exactly one
(1) occurrence of this type of block; otherwise, the bundle MUST NOT
contain any Destination EID block.
4.6.3. Previous Node Number
The Previous Node Number block, block type 7, identifies the node
that forwarded this bundle to the local node; its block-type-
specific data is an SDNV containing the number of that node. If the
local node is the source of the bundle, then the bundle MUST NOT
contain any Previous Node Number block. Otherwise the bundle MUST
contain one (1) occurrence of this type of block if it contains no
Bundle Authentication Block (block type 2, as described in the
Bundle Security Protocol specification) and otherwise MUST NOT
contain any Previous Node Number 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.
4.6.4. Payload CRC
The Payload CRC block, block type 8, contains a CRC32 value computed
over the entire payload of an original, non-fragmented block. The
bundle may contain at most one (1) occurrence of this type of block.
4.6.5. Bundle Age
The Bundle Age block, block type 9, 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 SDNV containing the age of the bundle (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) in seconds. If the bundle's creation time is zero, then
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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.
4.6.6. Hop Count
The Hop Count block, block type 10, contains two SDNVs, hop limit
and hop count, in that order. It is mainly intended as a safety
mechanism, a means of removing bundles from the network that can
never be delivered due to an error in network configuration: a
bundle may 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. A bundle MAY contain at
most one (1) occurrence of this type of block.
4.6.7. Forwarding Anomaly
The Forwarding Anomaly block, block type 11, contains a one-byte
reason code indicating something unusual about the forwarding of
this block. The bundle may contain at most one (1) occurrence of
this type of block. The reason codes that may be conveyed in a
Forwarding Anomaly block are given in Figure 7 below.
+---------+--------------------------------------------+
| Value | Meaning |
+=========+============================================+
| 0x00 | Bundle is a Probe, testing an embargo. |
+---------+--------------------------------------------+
| 0x01 | Reserved for future use. |
+---------+--------------------------------------------+
| 0x02 | Reserved for future use. |
+---------+--------------------------------------------+
| 0x03 | Reserved for future use. |
+---------+--------------------------------------------+
| 0x04 | Depleted storage. |
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+---------+--------------------------------------------+
| 0x05 | Destination endpoint ID unintelligible. |
+---------+--------------------------------------------+
| 0x06 | No known route to destination from here. |
+---------+--------------------------------------------+
| 0x07 | No timely contact with next node on route. |
+---------+--------------------------------------------+
| 0x08 | Block unintelligible. |
+---------+--------------------------------------------+
| (other) | Reserved for future use. |
+---------+--------------------------------------------+
Figure 7: Forwarding Anomaly Reason Codes
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. That is, supplementary DTN
protocol specifications (including, but not restricted to, the
Bundle Security Protocol [SBSP]) may require that additional
measures be taken at specified junctures in these procedures. Such
additional measures shall not override or supersede the mandated
bundle protocol procedures, except that they may in some cases make
these procedures moot by requiring, for example, that
implementations conforming to the supplementary protocol terminate
the processing of a given incoming or outgoing bundle due to a fault
condition recognized by that protocol.
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
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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 one case, the deletion of a bundle for which
custody transfer is requested. In all other cases, the decision on
whether or not to generate a requested status report is left to the
discretion of the bundle protocol agent. Mechanisms that could
assist in making such decisions, such as pre-placed agreements
authorizing the generation of status reports under specified
circumstances, are beyond the scope of this specification.
Notes on administrative record terminology:
. A "bundle reception status report" is a bundle status report
with the "reporting node received bundle" flag set to 1.
. A "custody 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. o
A "bundle deletion status report" is a bundle status report
with the "reporting node deleted the bundle" flag set to 1.
. A "Succeeded" custody signal is a custody signal with the
"custody transfer succeeded" flag set to 1.
. A "Failed" custody signal is a custody signal with the "custody
transfer succeeded" flag set to zero.
. 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 forwarding mode of the bundle must be basic
unicast as described in 4.4 above. If, moreover, custody acceptance
by the source node is required, then either the bundle protocol
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agent must commit to accepting custody of the bundle -- in which
case processing proceeds from Step 2 -- or else the request cannot
be honored and all remaining steps of this procedure must be
skipped. The bundle protocol agent must not commit to accepting
custody of a bundle if the conditions under which custody of the
bundle may be accepted are not satisfied.
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 number of the bundle must be either the node number
assigned to the node of which the BPA is a component or else zero,
indicating that the source of the node is anonymous.
Step 3: Processing proceeds from Step 1 of Section 5.4.
5.3. Bundle Dispatching
The steps in dispatching a bundle are:
Step 1: If the bundle's destination endpoint is an endpoint of which
the node is a member, the bundle delivery procedure defined in
Section 5.7 must be followed.
Step 2: Processing proceeds from Step 1 of Section 5.4.
5.4. Bundle Forwarding
The steps in forwarding a bundle are:
Step 1: The retention constraint "Forward pending" must be added to
the bundle, and the bundle's "Dispatch pending" retention constraint
must be removed.
If the bundle has a Hop Count block:
. If the current value of the hop count in this block is greater
than or equal to the value of the hop limit, then forwarding
failure MAY be declared. In that case, the Forwarding Failed
procedure defined in Section 5.4.2 MUST be followed; the
remaining steps of Section 5 are skipped at this time.
. Otherwise, the value of the hop count in this block MUST be
increased by 1.
Step 2: The bundle protocol agent must determine whether or not
forwarding is contraindicated for any of the reasons listed in
Figure 12. In particular:
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. The bundle protocol agent must determine which node(s) to
forward the bundle to. If the forwarding mode of the bundle is
basic multicast then the bundle is to be forwarded to all
neighboring nodes that are members of the multicast group
identified by the bundle's destination number, excluding the
node from which the bundle was received (if not created
locally). Otherwise 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 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:
o If the "Bundle is critical" flag (in the bundle processing
flags) is set to 1, then ALL nodes that have some
plausible prospect of forwarding the bundle to its
destination node(s) SHOULD be selected for this purpose.
o Any node on which an "embargo" has been imposed that would
apply to the source node and destination endpoint of this
bundle normally SHOULD NOT be selected. However, this
restriction SHOULD be relaxed in the event that the agent
determines that it is time to revisit the possible
suitability of this node as a forwarder; when this is the
case, a Forwarding Anomaly block with reason code Probe
MUST be attached to the bundle.
o If the agent 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. If
both the "Best-efforts forwarding requested" and the "Reliable
forwarding is requested" bundle processing flags are set to 1,
then all selected CLAs MUST be for bundle streaming CL
protocols such as the Bundle Streaming Service Protocol (work
in progress). Otherwise, if only the "Reliable forwarding is
requested" bundle processing flag is set to 1, then all
selected CLAs MUST be for reliable protocols such as TCP/IP.
Otherwise, if only the "Best-efforts forwarding requested"
bundle processing flag is set to 1, then all selected CLAs MUST
be for best-efforts protocols such as UDP/IP. Otherwise, any
available CLAs may be selected. 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 appropriate convergence layer adapters to use in
forwarding this bundle, then forwarding is contraindicated.
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Step 3: If forwarding of the bundle is determined to be
contraindicated for any of the reasons listed in Figure 12, then the
Forwarding Contraindicated procedure defined in Section 5.4.1 must
be followed; the remaining steps of Section 5 are skipped at this
time.
Step 4: If the bundle's custody transfer requested flag (in the
bundle processing flags field) is set to 1, then the custody
transfer procedure defined in Section 5.10.2 must be followed.
Step 5: If the bundle has a Forwarding Anomaly block with reason
code indicating that the bundle is a Probe:
. The bundle protocol agent MUST generate a Reopen signal citing
the bundle's source and destination endpoints, destined for the
sender of the bundle (as noted in the Previous Node block or
Bundle Authentication Block).
. If an embargo has been imposed at the local node that would
apply to the source node and destination endpoint of this
bundle, then the "Probe" Forwarding Anomaly block SHOULD be
retained in the bundle; otherwise the Probe block SHOULD be
removed from the bundle.
Step 6: 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 is to be sent by each
convergence layer adapter is an implementation matter. Note that:
. The order in which convergence layer adapters send bundles
SHOULD normally conform to the priority indicated in each
bundle's bundle processing control flags field: all bundles of
priority 255 should be sent before all bundles of priority 254
and so on.
. But if the "Flow label is present" flag in the bundle
processing control flags is set to 1 then (a) the SDNV
immediately following the bundle processing control flags MUST
be interpreted as a flow label value and (b) that flow label
value may identify overriding procedures for determining the
order in which convergence layer adapters must send bundles.
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
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the bundle was received (or, if the local node is the source of
the bundle, created).
Step 7: 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 for some
reason are:
Step 1: The bundle protocol agent must determine whether or not to
declare failure in forwarding the bundle for this reason. Note: this
decision is likely to be influenced by the reason for which
forwarding is contraindicated.
Step 2: If forwarding failure is declared, then the Forwarding
Failed procedure defined in Section 5.4.2 MUST be followed.
Otherwise, (a) if the bundle's custody transfer requested flag (in
the bundle processing flags field) is set to 1, then the custody
transfer procedure defined in Section 5.10 MUST be followed; (b)
when -- at some future time - the forwarding of this bundle ceases
to be contraindicated, processing proceeds from Step 5 of Section
5.4.
5.4.2. Forwarding Failed
The steps in responding to a declaration of forwarding failure for
some reason are:
Step 1: If the bundle's custody transfer requested flag (in the
bundle processing flags field) is set to 1, custody transfer failure
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must be handled. The bundle protocol agent MUST handle the custody
transfer failure by generating a "Failed" custody signal for the
bundle, destined for the bundle's current custodian(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 requested flag (in the bundle
processing flags field) is set to 0, then the bundle protocol agent
SHOULD forward the bundle back to the node that sent it, as
identified by the Previous Node block or Bundle Authentication
Block. If the bundle protocol agent elects to do this, a Forwarding
Anomaly block MUST be inserted into the bundle, containing a reason
code corresponding to the reason for which forwarding was determined
to be contraindicated.
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 5.13 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; 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
5.13 MUST be followed.
5.6. Bundle Reception
The steps in processing a bundle received from another node are:
Step 1: The retention constraint "Dispatch pending" must be added to
the bundle.
Step 2: If the "request reporting of bundle reception" flag in the
bundle's status report request field is set to 1, then a bundle
reception status report with reason code "No additional information"
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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 5.13 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 the block must be
discarded, then the bundle protocol agent must set to 1 the
"Block was forwarded without being processed" flag in the block
processing flags of the block.
Step 4: If the bundle's custody transfer requested flag (in the
bundle processing flags field) is set to 1 and the bundle has the
same source node number, creation timestamp, and (if the 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 "Failed" custody signal for this bundle with reason code
"Redundant reception", destined for this bundle's current custodian,
and removing this bundle's "Dispatch pending" retention constraint.
Step 5: If the bundle has a Forwarding Anomaly block with any reason
code other than Probe, then the bundle has been returned to sender
as impossible to forward, for the indicated reason. The bundle
protocol agent MAY impose an "embargo" on the forwarding of bundles
to the sending node that are determined (in an implementation-
specific manner) to have source node and destination endpoint that
are similar to those of the received bundle.
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Step 6: 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.
. If the bundle's custody transfer requested flag (in the bundle
processing flags field) is set to 1, custodial delivery must be
reported. The bundle protocol agent must report custodial
delivery by generating a "Succeeded" custody signal for the
bundle, destined for the bundle's current custodian(s).
5.8. Bundle Fragmentation
It may at times be necessary for bundle protocol agents to reduce
the sizes of bundles in order to forward them. This might be the
case, for example, if a node to which a bundle is to be forwarded is
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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 number 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
bundle that was fragmented. Note that the payloads of fragments
resulting from different fragmentation episodes, in different
parts of the network, may be overlapping subsets of the
original bundle's payload.
. The bundle processing flags in the primary block of each
fragment must differ from those of the bundle that is being
fragmented, in that they must indicate that the bundle is a
fragment, and both fragment offset and total application data
unit length must be provided at the end of each fragment's
primary bundle block. The CRC computed for the primary block
of each fragment will necessarily be different from that of the
bundle that is being fragmented.
. The primary blocks of the fragments will differ from that of
the fragmented bundle as noted above.
. The payload blocks of fragments will differ from that of the
fragmented bundle as noted above.
. If the bundle being fragmented is not a fragment or is the
fragment with offset zero, then all extension blocks of the
bundle being fragmented MUST be replicated in the fragment
whose offset is zero.
. Each extension block whose "Block must be replicated in every
fragment" flag, in the block processing flags, is set to 1 MUST
be replicated in every fragment.
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. Beyond these rules, replication of extension blocks in the
fragments is an implementation matter.
. If the local node had taken custody 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 number 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.
. For 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 take custody of that bundle.
. The BPA must then release custody of all fragments 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 route to the destination.
5.10. Custody Transfer
The decision as to whether or not to accept custody of a bundle is
an implementation matter that may involve both resource and policy
considerations; however, if the bundle protocol agent has committed
to accepting custody of the bundle (as described in Step 1 of
Section 5.2), then custody must be accepted.
If the bundle protocol agent elects to accept custody of the bundle,
then it must follow the custody acceptance procedure defined in
Section 5.10.1.
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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 1 of Section 5.6),
then this report should be generated by simply turning on the
"Reporting node accepted custody of bundle" flag in that earlier
report's status flags byte.
The bundle protocol agent must generate a "Succeeded" custody signal
for the bundle, destined for the bundle's current custodian(s).
The bundle protocol agent must assert the new current custodian for
the bundle. It does so by inserting a new Current Custodian
extension block whose value is the node number of the local node or
by changing the value of an existing Current Custodian extension
block to the local node number.
The bundle protocol agent may set a custody transfer countdown timer
for this bundle; upon expiration of this timer prior to expiration
of the bundle itself and prior to custody transfer success for this
bundle, the custody transfer failure procedure detailed in Section
5.12 must be followed. The manner in which the countdown interval
for such a timer is determined is an implementation matter.
The bundle should be retained in persistent storage if possible.
5.10.2. Custody Release
When custody of a bundle is released, the "Custody accepted"
retention constraint must be removed from the bundle and any custody
transfer timer that has been established for this bundle must be
destroyed.
5.11. Custody Transfer Success
Upon receipt of a "Succeeded" custody signal at a node that is a
custodial node of the bundle identified in the custody signal,
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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 that bundle when either (a) that node's custody transfer timer
for that bundle (if any) expires or (b) a "Failed" custody signal
for that bundle is received at that node.
Upon determination of custody transfer failure, the action taken by
the bundle protocol agent is implementation-specific and may depend
on the nature of the failure. For example, if custody transfer
failure was inferred from expiration of a custody transfer timer or
was asserted by a "Failed" custody signal with the "Depleted
storage" reason code, the bundle protocol agent might choose to re-
forward the bundle, possibly on a different route (Section 5.4).
Receipt of a "Failed" custody signal with the "Redundant reception"
reason code, on the other hand, might cause the bundle protocol
agent to release custody of the bundle and to revise its algorithm
for computing countdown intervals for custody transfer timers. In
any case, the bundle protocol agent MAY impose an "embargo" (as in
Step 5 of 5.6 above) on the forwarding of bundles to the node to
which the bundle had been sent.
5.13. Bundle Deletion
The steps in deleting a bundle are:
Step 1: If the retention constraint "Custody accepted" currently
prevents this bundle from being discarded, then:
. Custody of the node 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.
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5.14. Discarding a Bundle
As soon as a bundle has no remaining retention constraints it may be
discarded.
5.15. Canceling a Transmission
When requested to cancel a specified transmission, where the bundle
created upon initiation of the indicated transmission has not yet
been discarded, the bundle protocol agent must delete that bundle
for the reason "transmission cancelled". For this purpose, the
procedure defined in Section 5.13 must be followed.
5.16. Polling
When requested to poll a specified registration that is in the
Passive state, the bundle protocol agent must immediately deliver
the least recently received bundle that is deliverable subject to
the indicated registration, if any.
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. Four
types of administrative records have been defined to date: bundle
status reports, multicast petitions, reopen signals, and custody
signals.
Note that supplementary DTN protocol specifications may require that
BP implementations conforming to those protocols construct and
process additional administrative records.
Every administrative record consists of a four-bit record type code
followed by four bits of administrative record flags, followed by
record content in type-specific format. Record type codes are
defined as follows:
+---------+--------------------------------------------+
| Value | Meaning |
+=========+============================================+
| 0001 | Bundle status report. |
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+---------+--------------------------------------------+
| 0010 | Custody signal. |
+---------+--------------------------------------------+
| 0011 | Reopen signal. |
+---------+--------------------------------------------+
| 0100 | Multicast petition. |
+---------+--------------------------------------------+
| (other) | Reserved for future use. |
+---------+--------------------------------------------+
Figure 8: Administrative Record Type Codes
+---------+--------------------------------------------+
| Value | Meaning |
+=========+============================================+
| 0001 | Record is for a fragment; fragment |
| | offset and length fields are present. |
+---------+--------------------------------------------+
| (other) | Reserved for future use. |
+---------+--------------------------------------------+
Figure 9: Administrative Record Flags
The contents of the various types of administrative records are
described below.
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,
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including notices of receipt, custody transfer, forwarding, final
delivery, and deletion. They are transmitted to the Report-to
endpoints of bundles.
+----------------+----------------+----------------+---------------+
| Status Flags | Reason code | Fragment offset (*) (if
+----------------+----------------+----------------+---------------+
present) | Fragment length (*) (if present) |
+----------------+----------------+----------------+---------------+
| Source node number of bundle X (*) |
+----------------+----------------+----------------+---------------+
| Copy of bundle X's Creation Timestamp time (*) |
+----------------+----------------+----------------+---------------+
| Copy of bundle X's Creation Timestamp sequence number (*) |
+----------------+----------------+----------------+---------------+
Figure 10: Bundle Status Report Format
(*) Notes:
The Fragment Offset field, if present, is an SDNV and is therefore
variable length. A three-octet SDNV is shown here for convenience in
representation.
The Fragment Length field, if present, is an SDNV and is therefore
variable length. A three-octet SDNV is shown here for convenience in
representation.
The Source Node Number and Creation Timestamp fields replicate the
Source Node Number and Creation Timestamp fields in the primary
block of the subject bundle. As such they are SDNVs (see Section
4.5.1 above) and are therefore variable length. Four-octet SDNVs are
shown here for convenience in representation.
The fields in a bundle status report are:
Status Flags: A 1-byte field containing the following flags:
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+----------+--------------------------------------------+
| Value | Meaning |
+==========+============================================+
| 00000001 | Reporting node received bundle. |
+----------+--------------------------------------------+
| 00000010 | Reporting node accepted custody of bundle. |
+----------+--------------------------------------------+
| 00000100 | Reporting node forwarded the bundle. |
+----------+--------------------------------------------+
| 00001000 | Reporting node delivered the bundle. |
+----------+--------------------------------------------+
| 00010000 | Reporting node deleted the bundle. |
+----------+--------------------------------------------+
| 00100000 | Unused. |
+----------+--------------------------------------------+
| 01000000 | Unused. |
+----------+--------------------------------------------+
| 10000000 | Unused. |
+----------+--------------------------------------------+
Figure 11: Status Flags for Bundle Status Reports
Reason Code: A 1-byte field explaining the value of the flags in the
status flags byte. The list of status report reason codes provided
here is neither exhaustive nor exclusive; supplementary DTN protocol
specifications (including, but not restricted to, the Bundle
Security Protocol [SBSP]) may define additional reason codes. Status
report reason codes are defined as follows:
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+---------+--------------------------------------------+
| Value | Meaning |
+=========+============================================+
| 0x00 | No additional information. |
+---------+--------------------------------------------+
| 0x01 | Lifetime expired. |
+---------+--------------------------------------------+
| 0x02 | Forwarded over unidirectional link. |
+---------+--------------------------------------------+
| 0x03 | Transmission canceled. |
+---------+--------------------------------------------+
| 0x04 | Depleted storage. |
+---------+--------------------------------------------+
| 0x05 | Destination endpoint ID unintelligible. |
+---------+--------------------------------------------+
| 0x06 | No known route to destination from here. |
+---------+--------------------------------------------+
| 0x07 | No timely contact with next node on route. |
+---------+--------------------------------------------+
| 0x08 | Block unintelligible. |
+---------+--------------------------------------------+
| (other) | Reserved for future use. |
+---------+--------------------------------------------+
Figure 12: Status Report Reason Codes
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Fragment Offset: If the bundle fragment bit is set in the status
flags, then the offset (within the original application data unit)
of the payload of the bundle that caused the status report to be
generated is included here.
Fragment length: If the bundle fragment bit is set in the status
flags, then the length of the payload of the subject bundle is
included here.
Source Node Number of Subject Bundle: A copy of the source node
number of the bundle that caused the status report to be generated.
Creation Timestamp of Subject Bundle: A copy of the creation
timestamp of the bundle that caused the status report to be
generated.
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.
Custody signals have the following format.
Custody signal regarding bundle 'X':
+----------------+----------------+----------------+---------------+
| Status | Fragment offset (*) (if present) |
+----------------+----------------+----------------+---------------+
| Fragment length (*) (if present) |
+----------------+----------------+----------------+---------------+
| Source node number of bundle X (*) |
+----------------+----------------+----------------+---------------+
| Copy of bundle X's Creation Timestamp time (*) |
+----------------+----------------+----------------+---------------+
| Copy of bundle X's Creation Timestamp sequence number (*) |
+----------------+----------------+----------------+---------------+
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Figure 13: Custody Signal Format
(*) Notes:
The Fragment Offset field, if present, is an SDNV and is therefore
variable length. A three-octet SDNV is shown here for convenience in
representation.
The Fragment Length field, if present, is an SDNV and is therefore
variable length. A four-octet SDNV is shown here for convenience in
representation.
The Source Node Number and Creation Timestamp fields replicate the
Source Node Number and Creation Timestamp fields in the primary
block of the subject bundle. As such they are SDNVs (see Section
4.5.1 above) and are therefore variable length. Four-octet SDNVs are
shown here for convenience in representation.
The fields in a custody signal are:
Status: A 1-byte field containing a 1-bit "custody transfer
succeeded" flag followed by a 7-bit reason code explaining the value
of that flag. Custody signal reason codes are defined as follows:
+---------+--------------------------------------------+
| Value | Meaning |
+=========+============================================+
| 0x00 | No additional information. |
+---------+--------------------------------------------+
| 0x01 | Reserved for future use. |
+---------+--------------------------------------------+
| 0x02 | Reserved for future use. |
+---------+--------------------------------------------+
| 0x03 | Redundant (reception by a node that is a |
| | custodial node for this bundle). |
+---------+--------------------------------------------+
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| 0x04 | Depleted storage. |
+---------+--------------------------------------------+
| 0x05 | Destination endpoint ID unintelligible. |
+---------+--------------------------------------------+
| 0x06 | No known route destination from here. |
+---------+--------------------------------------------+
| 0x07 | No timely contact with next node on route. |
+---------+--------------------------------------------+
| 0x08 | Block unintelligible. |
+---------+--------------------------------------------+
| (other) | Reserved for future use. |
+---------+--------------------------------------------+
Figure 14: Custody Signal Reason Codes
Fragment offset: If the bundle fragment bit is set in the status
flags, then the offset (within the original application data unit)
of the payload of the bundle that caused the custody signal to be
generated is included here.
Fragment length: If the bundle fragment bit is set in the status
flags, then the length of the payload of the subject bundle is
included here.
Source Node Number of Subject Bundle: A copy of the source node
number of the bundle that caused the custody signal to be generated.
Creation Timestamp of Subject Bundle: A copy of the creation
timestamp of the bundle to which the signal applies.
6.1.3. Reopen Signals
Reopen signals are administrative records that enable the lifting of
forwarding embargoes at upstream nodes. They are transmitted to the
nodes that were the senders of bundles containing Forwarding Anomaly
blocks with reason code "Probe".
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Reopen signals have the following format.
Reopen signal signaling acceptance of Probe bundle 'X':
+----------------+----------------+----------------+---------------+
| Source node number of bundle X (*) |
+----------------+----------------+----------------+---------------+
/ Bundle X's Destination EID (variable; NULL-terminated) /
+----------------+----------------+----------------+---------------+
Figure 15: Reopen Signal Format
(*) Notes:
The Source Node Number field replicates the Source Node Number field
in the primary block of the subject bundle. As such it is an SDNV
(see Section 4.5.1 above) and therefore variable length. A four-
octet SDNV is shown here for convenience in representation.
The fields in a Reopen signal are:
Source Node Number of Subject Bundle: A copy of the source node
number of the probe bundle that caused the Reopen signal to be
generated.
Destination EID of Subject Bundle: An explicit representation (a
NULL-terminated character string) of the destination endpoint ID of
the probe bundle that caused the Reopen signal to be generated.
6.1.4. Multicast Petitions
Multicast petitions are administrative records that govern the
propagation of bundles within multicast groups. They are
expressions of interest, or lapse of interest, in bundles destined
for specified multicast groups, identified by "imc"-scheme endpoint
IDs.
IPN multicast forwarding is configured by the propagation of
petitions through a single spanning tree structured as an overlay
upon the nodes of a single DTN-based network. Each node must have
accurate current information identifying all of its "kin" in the
tree, i.e., the nodes that are its parent and all of its children.
Mechanisms for propagating information about nodes' kinship
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relations in a multicast spanning tree are beyond the scope of this
specification.
Every immediate relative of a given node in the multicast tree MUST
be a "neighbor" of that node in the topology of the underlying BP-
based network; that is, each node must be able to exchange bundles
directly, by means of some convergence-layer protocol, with each of
its immediate relatives. This is because loop-free BP basic
multicast petition forwarding procedures requires that the identity
of the immediate relative that sends each received bundle be known
with certainty; no such information can be provided when a bundle is
forwarded by an intermediary non-kin node.
Each multicast petition is transmitted to all (and only) nodes that
are the "kin" of the local node (that is, parent (if any) and all
children (if any)) within the global basic multicast spanning tree
that encompasses all nodes of the network - except that a petition
is never sent back to a node from which it was received.
Multicast petitions have the following format.
+----------------+----------------+----------------+---------------+
| Interest flag | Multicast group number (*) |
+----------------+----------------+----------------+---------------+
Figure 16: Multicast Petition Format
(*) Notes:
The Multicast Group Number field is an SDNV (see Section 4.5.1
above) and therefore variable length. A three-octet SDNV is shown
here for convenience in representation.
The fields in a multicast petition are:
Interest Flag: An indication of the nature of the petition. A value
of 1 indicates that the node sending the petition is now interested
in bundles destined for the indicated multicast group. A value of 0
indicates that the node sending the petition is now no longer
interested in bundles destined for the indicated multicast group.
Multicast Group Number: The number that identifies the multicast
group in which a new expression of interest or disinterest is being
transmitted.
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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 have
the Fragment flag set and must contain the fragment offset and
fragment length fields. The value of the fragment offset field must
be the value of the referenced bundle's fragment offset, and the
value of the fragment length field must be the length of the
referenced bundle's payload.
Step 2: A request for transmission of a bundle whose payload is this
administrative record must be presented to the bundle protocol
agent.
6.3. Reception of Custody Signals
For each received custody signal that has the "custody transfer
succeeded" flag set to 1, the administrative element of the
application agent must direct the bundle protocol agent to follow
the custody transfer success procedure in Section 5.11.
For each received custody signal that has the "custody transfer
succeeded" flag set to 0, the administrative element of the
application agent must direct the bundle protocol agent to follow
the custody transfer failure procedure in Section 5.12.
6.4. Reception of Reopen Signals
For each received reopen signal, the administrative element of the
application agent must direct the bundle protocol agent to lift any
existing embargo pertaining to the forwarding node, source node, and
destination endpoint identified in the signal.
6.5. Generation and Handling of Multicast Petitions
Node join and leave BP basic multicast groups by registering and
unregistering in endpoints formed in the "imc" URI scheme:
registering in any "imc" endpoint for multicast group N (regardless
of service number) causes the node to be a member of multicast group
N, and unregistering from all "imc" endpoints for group N terminates
the nodes membership in group N.
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When a node joins an IMC multicast group, it MUST send a petition
with interest flag value 1, citing the number of that group, to each
of its immediate relatives (parent and children) in the multicast
tree.
When a node leaves an IMC multicast group, it MUST send a petition
with interest flag value 0, citing the number of that group, to each
of its immediate relatives in the multicast tree.
When the administrative element of a node's application agent
receives a petition in a bundle whose bundle ID timestamp (creation
time and sequence number) is greater than the bundle ID timestamp of
the most recently accepted petition regarding the same multicast
group sent by the same immediate relative in the multicast tree, the
petition is considered a "current" petition. Otherwise, the
petition is considered not current and MUST be ignored. This
prevents the propagation of obsolete petition information when
bundles arrive out of transmission order.
When the administrative element of a node's application agent
receives a current petition with interest flag value 1 it MUST:
. Note that the node from which the petition was received has an
interest in bundles destined for the indicated group.
. Forward the petition to each of its immediate relatives in the
multicast tree except the node from which the petition was
received, UNLESS either the receiving node is a member of the
indicated group or one or more other immediate relatives'
interest in bundles destined for the indicated group is
currently noted. In the latter case, the petition MAY (but need
not) be forwarded.
When the administrative element of a node's application agent
receives a current petition with interest flag value 0 it MUST:
. Note that the node from which the petition was received now has
no interest in bundles destined for the indicated group.
. Forward the petition to each of its immediate relatives in the
multicast tree except the node from which the petition was
received, UNLESS either the receiving node is a member of the
indicated group or one or more other immediate relatives'
continued interest in bundles destined for the indicated group
is currently noted. In the latter case, the petition MUST NOT
be forwarded.
When a new immediate relative (parent or child) in the multicast
tree is added for some node, that node MUST send to the new relative
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a petition with interest value 1 for each multicast group in which
either (a) the node itself is a member or (b) interest is currently
noted by one or more of the node's other immediate relatives.
When any one of a node's immediate relatives in the multicast tree
is removed, that node MUST send to every remaining immediate
relative a petition with interest flag value 0 for each multicast
group in which (a) the node itself is not a member and (b) the
removed relative was interested but no other immediate relative is
currently interested.
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;
. discarding each bundle-conveying data unit of the convergence
layer protocol that the convergence layer protocol determines
was corrupted in transit; and
. 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 [SBSP]) may expect convergence layer adapters that
serve BP implementations conforming to those protocols to provide
additional services.
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
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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 [SBSP]; an informative overview of this
architecture is provided in [SECO].
The bundle protocol has been designed with the notion that it will
be run over networks with scarce resources. For example, the
networks might have limited bandwidth, limited connectivity,
constrained storage in relay nodes, etc. Therefore, the bundle
protocol must ensure that only those entities authorized to send
bundles over such constrained environments are actually allowed to
do so. All unauthorized entities should be prevented from consuming
valuable resources.
Likewise, because of the potentially long latencies and delays
involved in the networks that make use of the bundle protocol, data
sources should be concerned with the integrity of the data received
at the intended destination(s) and may also be concerned with
ensuring confidentiality of the data as it traverses the network.
Without integrity, the bundle payload data might be corrupted while
in transit without the destination able to detect it. Similarly, the
data source can be concerned with ensuring that the data can only be
used by those authorized, hence the need for confidentiality.
Internal to the bundle-aware overlay network, the bundle nodes
should be concerned with the authenticity of other bundle nodes as
well as the preservation of bundle payload data integrity as it is
forwarded between bundle nodes.
As a result, bundle security is concerned with the authenticity,
integrity, and confidentiality of bundles conveyed among bundle
nodes. This is accomplished via the use of three independent
security-specific bundle 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.
The Bundle Authentication Block (BAB) ensures the authenticity and
integrity of bundles on a hop-by-hop basis between bundle nodes. The
BAB allows each bundle node to verify a bundle's authenticity before
processing or forwarding the bundle. In this way, entities that are
not authorized to send bundles will have unauthorized transmissions
blocked by security-aware bundle nodes.
Additionally, to provide end-to-end bundle authenticity and
integrity, the Block Integrity Block (BIB) is used. The BIB allows
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any security-enabled entity along the delivery path to ensure the
integrity of the bundle's payload.
Finally, 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.
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 as they transit
intermediate nodes, removal of blocks that do not have their
'Discard block if it can't be processed' flag in the block
processing control flags set to 1 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.
8.1. Security considerations of BP basic multicast
Reliability and consistency: none of the BP endpoints identified by
the URIs of the IMC scheme are guaranteed to be reachable at any
time, and the identity of the processing entities operating on those
endpoints is never guaranteed by the Bundle Protocol itself. Bundle
authentication as defined by the Bundle Security Protocol is
required for this purpose.Malicious construction: malicious
construction of a conformant IMC-scheme URI is limited to malicious
selection of group number. That is, a maliciously constructed IMC-
scheme URI could be used to direct a bundle to an endpoint whose
member nodes might be damaged by the arrival of that bundle. In
that case (and indeed in all bundle processing) the node that
receives a bundle should verify its authenticity and validity before
operating on it in any way.
Back-end transcoding: the limited expressiveness of URIs of the IMC
scheme effectively eliminates the possibility of threat due to
errors in back-end transcoding.
Rare IP address formats: not relevant, as IP addresses do not appear
anywhere in conformant IMC-scheme URIs.
Sensitive information: because IMC-scheme URIs are used only to
represent the identities of Bundle Protocol endpoints, the risk of
disclosure of sensitive information due to interception of these
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URIs is minimal. Examination of IMC-scheme URIs could be used to
support traffic analysis; where traffic analysis is a plausible
danger, bundles should be conveyed by secure convergence-layer
protocols that don't expose endpoint IDs.
Semantic attacks: the simplicity of IMC-scheme URI syntax minimizes
the possibility of misinterpretation of a URI by a human user.
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.
Provisional registration (per [URIREG]) for a URI scheme for CBHE is
requested, with the string "imc" as the suggested scheme name, as
follows.
URI scheme name: "imc".
Status: provisional.
URI scheme syntax:
This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234], including the core ABNF syntax rule for DIGIT
defined by that specification.
imc-uri = "imc:" ipn-hier-part
imc-hier-part = group-nbr nbr-delim service-nbr ; a path-rootless
group-nbr = 1*DIGIT
nbr-delim = "."
service-nbr = 1*DIGIT
None of the reserved characters defined in the generic URI syntax
are used as delimiters within URIs of the IPN scheme.
URI scheme semantics: URIs of the IPN scheme are used as endpoint
identifiers in the Delay-Tolerant Networking (DTN) Bundle Protocol
(BP) [RFC5050] as described in 2.1 above.
Encoding considerations: URIs of the IMC scheme are encoded
exclusively in US-ASCII characters.
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Applications and/or protocols that use this URI scheme name: the
Delay-Tolerant Networking (DTN) Bundle Protocol (BP) [RFC5050].
Interoperability considerations: as noted above, URIs of the IPN
scheme are encoded exclusively in US-ASCII characters.
10. Conclusions
This document is offered as a "strawman" first draft for a Bundle
Protocol specification standard. Comments are welcome.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", RFC 3986, STD 66,
January 2005.
[URIREG] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
Registration Procedures for New URI Schemes", RFC 4395, BCP 115,
February 2006.
11.2. Informative References
[ARCH] V. Cerf et. al., "Delay-Tolerant Network Architecture", RFC
4838, April 2007.
[ASN1] "Abstract Syntax Notation One (ASN.1), "ASN.1 Encoding Rules:
Specification of Basic Encoding Rules (BER), Canonical Encoding
Rules (CER) and Distinguished Encoding Rules (DER)," ITU-T Rec.
X.690 (2002) | ISO/IEC 8825- 1:2002", 2003.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
[RFC5050] Scott, K., and S. Burleigh, "Bundle Protocol
Specification", RFC 5050, November 2007.
[RFC5234] Crocker, D., and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC6260] Burleigh, S., "Compressed Bundle Header Encoding (CBHE)",
RFC 6260, May 2011.
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[RFC7116] Scott, K., and M. Blanchet, "Licklider Transmission
Protocol (LTP), Compressed Bundle Header Encoding (CBHE), and Bundle
Protocol IANA Registries", RFC 7116, February 2014.
[SBSP] Birrane, E., "Streamlined Bundle Security Protocol
Specification", draft-irtf-dtnrg-sbsp-01, May 2014.
[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.
12. Acknowledgments
This work is 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 Intel Research, Stephen Farrell of Trinity College
Dublin, Peter Lovell of SPARTA, Inc., Manikantan Ramadas of Ohio
University, and Howard Weiss of SPARTA, Inc. New material in the
adapted specification was contributed by Ed Birrane of the Johns
Hopkins University Applied Physics Laboratory.
This document was prepared using 2-Word-v2.0.template.dot.
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Appendix A. Summary of Revisions
This specification differs from RFC-5050 in a number of ways. The
revisions that seem to the author to be most significant are listed
below:
. Amplify the discussion of custody transfer. Move current
custodian to an extension block, of which there can be multiple
occurrences (providing possible support for the MITRE idea of
multiple concurrent custodians, from several years ago); define
that block in this spec.
. Add the notion of "embargoes", i.e., what do you do when a
route unexpectedly goes bad for a while? This entails adding
another extension block (Forwarding Anomaly) and another
administrative record (Reopen Signal).
. Incorporate the Compressed Bundle Header Encoding [RFC6260]
concepts into the base specification: nodes are explicitly
identified by node numbers, and operations that pertain to
nodes are described in terms of node numbers rather than
endpoint IDs.
. Add basic ("imc") multicast to the BP spec. This entails
adding another administrative record, Multicast Petition.
. Add Destination EID extension block for destinations that can't
be expressed in "ipn"-scheme and "imc"-scheme URIs. Define it
in this spec.
. Incorporate the "Extended Class of Service" features into the
base specification.
. Restructure the primary block, making it immutable. Add CRC.
Remove the dictionary.
. Add optional Payload CRC extension block, defined in this spec.
. Add block ID number to canonical block format (to support
streamlined Bundle Security Protocol).
. Add bundle age extension block, defined in this spec.
. Define two other extension blocks in this spec: previous node
number, hop count.
. Clean up a conflict between fragmentation and custody transfer
that Ed Birrane pointed out.
. Remove "DTN time" values from administrative records.
Nanosecond precision will not be meaningful among nodes whose
clocks are not closely synchronized, and absent that feature
the administrative record's bundle creation time suffices to
indicate the time of occurrence of the reported event.
. Note that CL protocols are supposed to discard data that they
find to have been corrupted.
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Appendix B. 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) 2014 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
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