One document matched: draft-irtf-dtnrg-bundle-spec-04.txt
Differences from draft-irtf-dtnrg-bundle-spec-03.txt
Delay Tolerant Networking Research Group K. Scott
Internet Draft The MITRE Corporation
<draft-irtf-dtnrg-bundle-spec-04.txt>
November 2005 S. Burleigh
Expires: May 2006 Jet Propulsion Laboratory
Bundle Protocol Specification
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she
becomes aware will be disclosed, in accordance with Section 6 of BCP
79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This document was produced within the IRTF's Delay Tolerant
Networking Research Group (DTNRG). See http://www.dtnrg.org for more
information.
Abstract
This document describes the end-to-end protocol, header formats, and
abstract service description for the exchange of messages (bundles)
in Delay Tolerant Networking (DTN).
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [1].
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Table of Contents
1. Introduction..........................................3
2. Service Description...................................4
2.1 Definitions...........................................4
2.2 Implementation architectures..........................8
2.3 Services offered by bundle protocol agents............9
3. Bundle Format........................................10
3.1 Canonical Bundle Header Format.......................10
3.2 Bundle Processing Flags..............................10
3.3 Header Processing Flags..............................11
3.4 Self-Delimiting Numeric Values (SDNV)................11
3.5 Endpoint IDs.........................................12
3.6 Formats of Bundle Headers............................13
3.6.1 Primary Bundle Header................................15
3.6.2 Bundle Payload Header................................18
4. Bundle Processing....................................18
4.1 Generation of administrative records.................19
4.2 Bundle transmission..................................19
4.3 Bundle dispatching...................................20
4.4 Bundle forwarding....................................20
4.4.1 Forwarding Contraindicated...........................21
4.4.2 Forwarding Failed....................................22
4.5 Bundle expiration....................................22
4.6 Bundle reception.....................................23
4.7 Local bundle delivery................................23
4.8 Bundle Fragmentation.................................24
4.9 Application Data Unit Reassembly.....................25
4.10 Custody transfer.....................................26
4.10.1 Custody acceptance...................................26
4.10.2 Custody release......................................27
4.11 Custody transfer success.............................27
4.12 Custody transfer failure.............................27
4.13 Bundle deletion......................................28
4.14 Discarding a bundle..................................28
4.15 Canceling a transmission.............................28
4.16 Polling..............................................28
4.17 Acknowledging an application data unit...............28
5. Administrative record processing.....................29
5.1 Administrative records...............................29
5.1.1 Bundle Status Reports................................29
5.1.2 Custody Signals......................................33
5.2 Generation of administrative records.................35
5.3 Reception of custody signals.........................36
6. Services Required of the Convergence Layer...........36
6.1 The Convergence Layer................................36
6.2 Summary of Convergence Layer Services................36
7. Security Considerations..............................37
8. IANA Considerations..................................38
9. Normative References.................................38
10. Informative References...............................38
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1. Introduction
This document describes version 4 of the Delay Tolerant
Networking (DTN) "bundle" protocol (BP). Delay Tolerant Networking
is an end-to-end architecture providing communications in and/or
through highly stressed environments. Stressed networking
environments include those with intermittent connectivity, large
and/or variable delays, and high bit error rates. To provide its
services, BP sits at the application layer of some number of
constituent internets, forming a store-and-forward overlay network.
Key capabilities of BP include:
o Custody-based retransmission
o Ability to cope with intermittent connectivity
o Ability to take advantage of scheduled, predicted, and
opportunistic connectivity (in addition to continuous
connectivity)
o Late binding of overlay network endpoint identifiers to
constituent internet addresses
For descriptions of these capabilities and the rationale for the DTN
architecture, see [2] and [8]. [3] contains a tutorial-level
overview of DTN concepts.
BP's location within the standard protocol stack is as shown in
Figure 1. BP uses the 'native' internet protocols for communications
within a given internet. Note that 'internet' in the preceding is
used in a general sense and does not necessarily refer to TCP/IP.
The interface between the common bundle protocol and a specific
internetwork protocol suite is termed a "convergence layer adapter".
Figure 1 shows three distinct transport and network protocols
(denoted T1/N1, T2,N2, and T3/N3).
+-----------+ +-----------+
| BP app | | BP app |
+---------v-| +->>>>>>>>>>v-+ +->>>>>>>>>>v-+ +-^---------+
| BP v | | ^ BP v | | ^ BP v | | ^ BP |
+---------v-+ +-^---------v-+ +-^---------v-+ +-^---------+
| Trans1 v | + ^ T1/T2 v | + ^ T2/T3 v | | ^ Trans3 |
+---------v-+ +-^---------v-+ +-^---------v + +-^---------+
| Net1 v | | ^ N1/N2 v | | ^ N2/N3 v | | ^ Net3 |
+---------v-+ +-^---------v + +-^---------v-+ +-^---------+
| >>>>>>>>^ >>>>>>>>>>^ >>>>>>>>^ |
+-----------+ +------------+ +-------------+ +-----------+
| | | |
|<-- An internet --->| |<--- An internet --->|
| | | |
Figure 1: The bundle protocol sits at the application layer of the
Internet model.
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This document describes the format of the protocol data units (called
bundles) passed between entities participating in BP communications.
The entities are referred to as "bundle nodes". This document does
not address:
o Operations in the convergence layer adapters that bundle nodes
use to transport data through specific types of internet.
(However, the document does discuss the services that must be
provided by each adapter at the convergence layer.)
o The bundle routing algorithm.
o Mechanisms for populating the routing or forwarding information
bases of bundle nodes.
2. Service Description
2.1 Definitions
Bundle A bundle is a protocol data unit of the DTN bundle protocol.
Multiple instances of the same bundle (the same unit of DTN protocol
data) might exist concurrently in different parts of a network -
possibly in different representations - in the memory local to one or
more bundle nodes and/or in transit between nodes. In the context of
the operation of a bundle node, a bundle is an instance of some
bundle in the network that is in that node's local memory.
Bundle payload A bundle payload (or simply "payload") is the
application data whose conveyance to the bundle's destination is the
purpose for the transmission of a given bundle. The terms "bundle
content", "bundle payload", and "payload" are used interchangeably in
this document. The "nominal" payload for a bundle forwarded in
response to a bundle transmission request is the application data
unit whose location is provided as a parameter to that request. The
nominal payload for a bundle forwarded in response to reception of
that bundle is the payload of the received bundle.
Fragment A fragment is a bundle whose payload header contains a
fragmentary payload. A fragmentary payload is either the first N
bytes or the last N bytes of some other payload either a nominal
payload or a fragmentary payload of length M, such that 0 < N < M.
Bundle node A bundle node (or, in the context of this document,
simply a "node") is any entity that can send and/or receive bundles.
In the most familiar case a bundle node is instantiated as a single
process running on a general-purpose computer, but in general the
definition is meant to be broader; a bundle node might alternatively
be a thread, an object in an object-oriented operating system, a
special-purpose hardware device, etc. Each bundle node has three
conceptual components, defined below: a "bundle protocol agent", a
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set of zero or more "convergence layer adapters", and an "application
agent".
Bundle protocol agent The bundle protocol agent (BPA) of a node is
the node component that offers the BP services and executes the
procedures of the Bundle Protocol. The manner in which it does so is
wholly an implementation matter. For example, BPA functionality
might be coded into each node individually; it might be implemented
as a shared library that is used in common by any number of bundle
nodes on a single computer; it might be implemented as a daemon whose
services are invoked via inter-process or network communication by
any number of bundle nodes on one or more computers; it might be
implemented in hardware.
Convergence layer adapters A convergence layer adapter (CLA) sends
and receives bundles on behalf of the BPA, utilizing the services of
some 'native' internet protocol that is supported in one of the
internets within which the node is functionally located. The manner
in which a CLA sends and receives bundles is wholly an implementation
matter, exactly as described for the BPA.
Application agent The application agent (AA) of a node is the node
component that utilizes the BP services to effect communication for
some purpose. The application agent in turn has two elements, an
administrative element and an application-specific element. The
application-specific element of an AA constructs, requests
transmission of, accepts delivery of, and processes application-
specific application data units; the only interface between the BPA
and the application-specific element of the AA is the BP service
interface. The administrative element of an AA constructs and
requests transmission of administrative records (status reports and
custody signals), and it accepts delivery of and processes any
custody signals that the node receives; in addition to the BP service
interface, there is a (conceptual) private control interface between
the BPA and the administrative element of the AA that enables each to
direct the other to take action under specific circumstances. In the
case of a node that serves simply as a "router" in the overlay
network, the AA may have no application-specific element at all; the
application-specific elements of other nodes' AAs may perform
arbitrarily complex application functions, perhaps even offering
multiplexed DTN communication services to a number of other
applications. As with the BPA, the manner in which the AA performs
its functions is wholly an implementation matter; in particular, the
administrative element of an AA might be built into the library or
daemon or hardware that implements the BPA, and the application-
specific element of an AA might be implemented either in software or
in hardware.
Bundle endpoint A bundle endpoint (or simply "endpoint") is a set
of zero or more bundle nodes that all identify themselves for BP
purposes by some single text string, called a "bundle endpoint ID"
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(or, in this document, simply "endpoint ID"; endpoint IDs are
described in detail in 3.5 below). The special case of an endpoint
that never contains more than one node is termed a "singleton"
endpoint; every bundle node must be a member of at least one
singleton endpoint. Singletons are the most familiar sort of
endpoint, but in general the endpoint notion is meant to be broader.
For example, the nodes in a sensor network might constitute a set of
bundle nodes that identify themselves by a single common endpoint ID
and thus form a single bundle endpoint. **Note** too that a given
bundle node might identify itself by multiple endpoint IDs and thus
be a member of multiple bundle endpoints.
Forwarding - When the bundle protocol agent of a node determines that
a bundle must be "forwarded" to an endpoint, it causes the bundle to
be sent to all of the nodes that the bundle protocol agent currently
believes are in the "minimum reception group" of that endpoint. The
minimum reception group of an endpoint may be any one of the
following: (a) ALL of the nodes registered in an endpoint that is
permitted to contain multiple nodes (in which case forwarding to the
endpoint is functionally similar to "multicast" operations in the
Internet, though possibly very different in implementation); (b) ANY
N of the nodes registered in an endpoint that is permitted to contain
multiple nodes, where N is in the range from zero to the cardinality
of the endpoint (in which case forwarding to the endpoint is
functionally similar to "anycast" operations in the Internet); (c)
THE SOLE NODE registered in a singleton endpoint (in which case
forwarding to the endpoint is functionally similar to "unicast"
operations in the Internet). The nature of the minimum reception
group for a given endpoint can be determined from the endpoint's ID
(again, see 3.5 below): for some endpoint ID "schemes", the nature of
the minimum reception group is fixed - in a manner that is defined by
the scheme - for all endpoints identified under the scheme; for other
schemes, the nature of the minimum reception group is indicated by
some lexical feature of the "scheme-specific part" of the endpoint
ID, in a manner that is defined by the scheme.
Registration A registration is the state machine characterizing a
given node's membership in a given endpoint. Any number of
registrations may be concurrently associated with a given endpoint,
and any number of registrations may be concurrently associated with a
given node. Any single registration must at any time be in one of
two states: Active, Passive. A registration always has an associated
"delivery failure action", the action that is to be taken when a
bundle that is "deliverable" (see below) subject to that registration
is received at a time when the registration is in the Passive state.
Delivery failure action must be one of the following:
o defer "delivery" (see below) of the bundle subject to this
registration until (a) this bundle is the least recently
received of all bundles currently deliverable subject to this
registration and (b) either the registration is polled or else
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the registration is in Active state;
o "abandon" (see below) delivery of the bundle subject to this
registration.
An additional implementation-specific delivery deferral procedure may
optionally be associated with the registration. While the state of a
registration is Active, reception of a bundle that is deliverable
subject to this registration must cause the bundle to be delivered
automatically as soon as it is the least recently received bundle
that is currently deliverable subject to the registration. While the
state of a registration is Passive, reception of a bundle that is
deliverable subject to this registration must cause delivery of the
bundle to be abandoned or deferred as mandated by the registration's
current delivery failure action; in the latter case, any additional
delivery deferral procedure associated with the registration must
also be performed.
Delivery Upon reception, the processing of a bundle that has been
sent to a given node depends on whether or not the receiving node is
registered in the bundle's destination endpoint; if it is, and if the
payload of the bundle is non-fragmentary (possibly as a result of
successful payload reassembly from fragmentary payloads, including
the original payload of the received bundle), then the bundle is
normally "delivered" to the node's application agent subject to the
registration characterizing the node's membership in the destination
endpoint. A bundle is considered to have been delivered at a node
subject to a registration as soon as the application data unit that
is the payload of the bundle, together with relevant metadata (an
implementation matter), has been presented to the node's application
agent in a manner consistent with the state of that registration and,
as applicable, the registration's delivery failure action.
Deliverability, Abandonment A bundle is considered "deliverable"
subject to a registration if and only if (a) the bundle's destination
endpoint is the endpoint with which the registration is associated,
(b) the bundle has not yet been delivered subject to this
registration, and (c) delivery of the bundle subject to this
registration has not been abandoned. To "abandon" delivery of a
bundle subject to a registration is simply to declare it no longer
deliverable subject to that registration; normally only
registrations' registered delivery failure actions cause deliveries
to be abandoned.
Deletion, Discarding A bundle protocol agent "discards" a bundle by
simply ceasing all operations on the bundle and functionally erasing
all references to it; the specific procedures by which this is
accomplished are an implementation matter. Bundles are discarded
silently, i.e., the discarding of a bundle does not result in
generation of an administrative record. "Retention constraints" are
elements of bundle state that prevent a bundle from being discarded;
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a bundle cannot be discarded while it has any retention constraints.
A bundle protocol agent "deletes" a bundle in response to some
anomalous condition by notifying the bundle's report-to endpoint of
the deletion (provided such notification is warranted; see 4.13 for
details) and then arbitrarily removing all of the bundle's retention
constraints, enabling the bundle to be discarded.
Transmission A transmission is a sustained effort by a node's
bundle protocol agent to cause a bundle to be sent to all nodes in
the minimum reception group of some endpoint (which may be the
bundle's destination or may be some intermediate forwarding endpoint)
in response to a transmission request issued by the node's
application agent. Any number of transmissions may be concurrently
undertaken by the bundle protocol agent of a given node.
Custody To "accept custody" upon forwarding a bundle is to commit
to retaining a copy of the bundle - possibly re-forwarding the bundle
when the necessity to do so is determined - until custody of that
bundle is "released". Custody of a bundle whose destination is a
singleton endpoint is released when either (a) notification is
received that some other node has accepted custody of the same
bundle, (b) notification is received that the bundle has been
delivered at the (sole) node registered in the bundle's destination
endpoint, or (c) the bundle is explicitly deleted for some reason,
such as lifetime expiration; the condition(s) under which custody of
a bundle whose destination is not a singleton endpoint may be
released are not defined in this specification. To "refuse custody"
of a bundle is to decide not to accept custody of the bundle. A
"custodial node" of a bundle is a node that has accepted custody of
the bundle and has not yet released that custody. A "custodian" of a
bundle is a singleton endpoint whose sole member is one of the
bundle's custodial nodes.
2.2 Implementation architectures
The above definitions are intended to enable the bundle protocol's
operations to be specified in a manner that minimizes bias toward any
particular implementation architecture. To illustrate the range of
interoperable implementation models that might conform to this
specification, four example architectures are briefly described
below.
a) Bundle protocol application server
A single bundle protocol application server, constituting a single
bundle node, runs as a daemon process on each computer. The daemon's
functionality includes all functions of the bundle protocol agent,
all convergence layer adapters, and both the administrative and
application-specific elements of the application agent. The
application-specific element of the application agent functions as a
server, offering bundle protocol service over a local area network:
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it responds to remote procedure calls from application processes (on
the same computer and/or remote computers) that need to communicate
via the bundle protocol. The server supports its clients by creating
a new (conceptual) node for each one and registering each such node
in a client-specified endpoint; the conceptual nodes managed by the
server function as clients' Bundle Protocol service access points.
b) Peer application nodes
Any number of bundle protocol application processes, each one
constituting a single bundle node, run in ad-hoc fashion on each
computer. The functionality of the bundle protocol agent, all
convergence layer adapters, and the administrative element of the
application agent is provided by a library to which each node process
is dynamically linked at run time; the application-specific element
of each node's application agent is node-specific application code.
c) Sensor network nodes
Each node of the sensor network is the self-contained implementation
of a single bundle node. All functions of the bundle protocol agent,
all convergence layer adapters, and the administrative element of the
application agent are implemented in simplified form in ASICs, while
the application-specific element of each node's application agent is
implemented in a programmable microcontroller. Forwarding is
rudimentary: all bundles are forwarded on a hard-coded default route.
d) Dedicated bundle router
Each computer constitutes a single bundle node that functions solely
as a high-performance bundle forwarder. Many standard functions of
the bundle protocol agent, the convergence layer adapters, and the
administrative element of the application agent are implemented in
ASICs, but some functions are implemented in a high-speed processor
to enable reprogramming as necessary. The node's application agent
has no application-specific element. Substantial non-volatile
storage resources are provided, and arbitrarily complex forwarding
algorithms are supported.
2.3 Services offered by bundle protocol agents
The bundle protocol agent of each node is expected to provide the
following services to the node's application agent:
a) commencing a registration (registering a node in an endpoint);
b) terminating a registration;
c) switching a registration between Active and Passive state;
d) transmitting a bundle to an identified bundle endpoint;
e) canceling a transmission;
f) polling a registration that is in passive state;
g) delivering a received bundle;
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h) acknowledging receipt of a bundle's contents.
3. Bundle Format
Each bundle shall be a concatenated sequence of at least two bundle
header structures. The first header in the sequence must be a
primary bundle header, and no bundle may have more than one primary
bundle header. Additional bundle protocol headers of other types may
follow the primary header to support extensions to the Bundle
Protocol, such as the Bundle Security Protocol. At most one of the
headers in the sequence may be a payload header. The last header in
the sequence must have the "last header" flag (in its header
processing control flags) set to 1; for every other header in the
bundle after the primary header, this flag must be set to zero.
3.1 Canonical Bundle Header Format
Every bundle header of every type other than the primary bundle
header comprises the following elements, in this order:
o Header type code, expressed as an 8-bit unsigned binary
integer. Bundle header type code 1 indicates that the header
is a bundle payload header. All other values of the header
type code are reserved for future use.
o Header processing control flags, a set of eight 1-bit flag
values.
o Header data length, an unsigned integer expressed as an SDNV
(explained below). The Header data length field contains the
aggregate length of all remaining fields of the header, i.e.,
the header-type-specific data fields.
o Header-type-specific data fields, whose format and order are
type-specific and whose aggregate length in octets is the value
of the header data length field. All multi-byte header-type-
specific data fields are represented in network byte order.
3.2 Bundle Processing Flags
The following Boolean processing control flags are present only in
the bundle processing control flags byte of the primary bundle header
of each bundle:
00000001 - Bundle is a fragment.
00000010 - Application data unit is an administrative record.
00000100 - Bundle must not be fragmented.
00001000 - Custody transfer is requested.
00010000 - Destination endpoint is a singleton.
00100000 - Reserved for future use.
01000000 - Reserved for future use.
10000000 - Reserved for future use.
If the bundle processing control flags indicate that the bundle's
application data unit is an administrative record, then the custody
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transfer requested flag must be zero. If the custody transfer
requested flag is 1 then the sending node requests that the receiving
node accept custody of the bundle.
3.3 Header Processing Flags
The following Boolean processing control flags are present in the
header processing control flags byte of every bundle header other
than the primary bundle header of each bundle:
00000001 - Header must be replicated in every fragment.
00000010 - Transmit status report if header can't be processed.
00000100 - Discard bundle if header can't be processed.
00001000 - Last header.
00010000 - Reserved for future use.
00100000 - Reserved for future use.
01000000 - Reserved for future use.
10000000 - Reserved for future use.
For each bundle whose primary header's bundle processing control
flags (see above) indicate that the bundle's application data unit is
an administrative record, the "Transmit status report if header can't
be processed" flag in the header processing flags element of every
other header in the bundle must be zero.
3.4 Self-Delimiting Numeric Values (SDNV)
The design of the bundle protocol attempts to reconcile minimal
consumption of transmission bandwidth with:
o extensibility to address requirements not yet identified, and
o scalability across a wide range of network scales and payload
sizes.
A key strategic element in the design is the use of self-delimiting
numeric values (SDNVs). The SDNV encoding scheme is closely adapted
from the Abstract Syntax Notation One [ASN1] scheme for encoding
Object Identifier Arcs. An SDNV is a numeric value encoded in N
octets, the last of which has its most significant bit (MSB) set to
zero; the MSB of every other octet in the SDNV must be set to 1. The
value encoded in an SDNV is the unsigned binary number obtained by
concatenating into a single bit string the 7 least significant bits
of each octet of the SDNV.
The following examples illustrate the encoding scheme for various
hexadecimal values.
0xABC : 1010 1011 1100
is encoded as
{100 1010 1} {0 011 1100}
= 10010101 00111100
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0x1234 : 0001 0010 0011 0100
= 1 0010 0011 0100
is encoded as
{10 1 0010 0} {0 011 0100}
= 10100100 00110100
0x4234 : 0100 0010 0011 0100
= 100 0010 0011 0100
is encoded as
{1000000 1} {1 00 0010 0} {0 011 0100}
= 10000001 10000100 00110100
0x7F : 0111 1111
= 111 1111
is encoded as
{0 111 1111}
= 01111111
Note: Care must be taken to make sure that the value to be encoded is
(in concept) padded with high-order zero bits to make its bitwise
length a multiple of 7 before encoding. Also note that, while there
is no theoretical limit on the size of an SDNV field, the overhead of
the SDNV scheme is 1/8-th of the bitwise length of the value to be
encoded. In order to encode an 64-bit numeric value, an SDNV field
of 9 octets is required. 128 bits of overhead would be consumed in
encoding a 1024-bit RSA encryption key directly in an SDNV.
An SDNV can be used to represent both very large and very small
integer values. However, SDNV is clearly not the best way to
represent every numeric value. For example, an SDNV is a poor way to
represent an integer whose value typically falls in the range 128 to
255. In general, though, we believe that SDNV representation of
numeric values in bundle headers yields the smallest bundle header
sizes without sacrificing scalability.
3.5 Endpoint IDs
The destinations of bundles are bundle endpoints, identified by text
strings termed "endpoint IDs" (see section 2.1). Each endpoint ID
conveyed in any bundle header takes the form of a Uniform Resource
Identifier (URI; [RFC3986]). As such, each endpoint ID can be
characterized as having this general structure:
<scheme name>:<scheme-specific part, or "SSP">
As used for the purposes of the bundle protocol, neither the length
of a scheme name nor the length of an SSP may exceed 1023 bytes.
Bundle headers cite a number of endpoint IDs for various purposes of
the bundle protocol. Many, though not necessarily all, of the
endpoint IDs referred to in the headers of a given bundle are
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conveyed in the "dictionary" byte array in the bundle's primary
header. This array is simply the concatenation of any number of
null-terminated scheme names and SSPs.
"Endpoint ID references" are used to cite endpoint IDs that are
contained in the dictionary; all endpoint ID citations in the primary
bundle header are endpoint ID references, and other bundle headers
may contain endpoint ID references as well. Each endpoint ID
reference is an ordered pair of 16-bit unsigned integers:
o The offset, within the dictionary, of the first character of
the referenced endpoint ID's scheme name.
o The offset, within the dictionary, of the first character of
the referenced endpoint ID's SSP.
This encoding enables a degree of header compression: when the source
and report-to of a bundle are the same endpoint, for example, the
text of that endpoint's ID may be cited twice yet appear only once in
the dictionary.
The scheme identified by the <scheme name> in an endpoint ID is a set
of syntactic and semantic rules that fully explain how to parse and
interpret the SSP. The set of allowable schemes is effectively
unlimited. Any scheme conforming to [RFC2717] may be used in a
bundle protocol endpoint ID. In addition, a single additional scheme
is defined by the present document:
o The "dtn" scheme, which is used at minimum in the
representation of the null endpoint ID "dtn:none". The
forwarding of a bundle to the null endpoint is never
contraindicated, and the minimum reception group for the null
endpoint is the empty set.
Note that, although the endpoint IDs conveyed in bundle headers are
expressed as URIs, implementations of the BP service interface may
support expression of endpoint IDs in some internationalized manner
(e.g., IRIs; see RFC 3987).
3.6 Formats of Bundle Headers
This section describes the formats of the primary header and payload
header. Rules for processing these headers appear in section 4 of
this document.
Note that supplementary DTN protocol specifications (including, but
not restricted to, the Bundle Security Protocol) may require that BP
implementations conforming to those protocols construct and process
additional headers.
The format of the two basic BP headers is shown in Figure 2 below.
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Primary Bundle Header
+----------------+----------------+----------------+----------------+
| Version | Proc. Flags | COS Flags | SRR Flags |
+----------------+----------------+----------------+----------------+
| [Header length (*)] |
+----------------+----------------+---------------------------------+
| Destination scheme offset | Destination SSP offset |
+----------------+----------------+----------------+----------------+
| Source scheme offset | Source SSP offset |
+----------------+----------------+----------------+----------------+
| Report-to scheme offset | Report-to SSP offset |
+----------------+----------------+----------------+----------------+
| Custodian scheme offset | Custodian SSP offset |
+----------------+----------------+----------------+----------------+
| |
+ Creation Timestamp (8 bytes) +
| |
+---------------------------------+---------------------------------+
| Lifetime |
+----------------+----------------+----------------+----------------+
| Dictionary length (**) |
+----------------+----------------+----------------+----------------+
| Dictionary byte array (variable) |
+----------------+----------------+---------------------------------+
| [Fragment offset (***)] |
+----------------+----------------+---------------------------------+
| [Total application data unit length (****)] |
+----------------+----------------+---------------------------------+
Bundle Payload Header
+----------------+----------------+----------------+----------------+
| Header type | Proc. Flags | Header length(*****) |
+----------------+----------------+----------------+----------------+
| |
| Bundle Payload (variable) |
| |
/ /
/ /
| |
+-------------------------------------------------------------------+
Figure 2: Bundle header formats.
Notes:
(*) The header length field of the Primary Bundle Header is an SDNV
and is therefore variable-length. A four-octet SDNV is shown here
for convenience in representation.
(**) The dictionary length field of the Primary Bundle Header is an
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SDNV and is therefore variable-length. A four-octet SDNV is shown
here for convenience in representation.
(***) The fragment offset field of the Primary Bundle Header is
present only if the Fragment flag in the header's processing flags
byte is set to 1. It is an SDNV and is therefore variable-length; a
four-octet SDNV is shown here for convenience in representation.
(****) The total application data unit length field of the Primary
Bundle Header is present only if the Fragment flag in the header's
processing flags byte is set to 1. It is an SDNV and is therefore
variable-length; a four-octet SDNV is shown here for convenience in
representation.
(*****) The header length field of the Payload Header is an SDNV and
is therefore variable-length. A two-octet SDNV is shown here for
convenience in representation.
3.6.1 Primary Bundle Header
The primary bundle header contains the basic information needed to
route bundles to their destinations. The fields of the primary
bundle header are:
Version. A 1-byte field indicating the version of the bundle
protocol that constructed this header. The present document
describes version 0x04 of the bundle protocol.
Bundle Processing Control Flags. The Bundle Processing Control Flags
field is a 1-byte field that contains the bundle processing
control flags discussed in section 3.2 above.
Class of Service Flags. The COS Flags byte consists of two (2) bits
of priority followed by six (6) bits that are reserved for
future use. The two-bit priority field indicates the bundle's
priority, with higher values being of higher priority: 00 =
bulk, 01 = normal, 10 = expedited, 11 is reserved for future
use.
Status Report Request Flags. The status report request flags
indicate the source node's requests for bundle status report
generation. If the bundle processing control flags indicate
that the bundle's application data unit is an administrative
record, then all status report request flags must be zero.
The interpretation of the status report request flags is as
follows.
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Table 1: Status Report Request Flag Meanings
+---------+--------------------------------------------+
| Value | Meaning |
+=========+============================================+
| 0x00 | No status reports requested. |
+---------+--------------------------------------------+
| 0x01 | Request reporting of bundle reception. |
+---------+--------------------------------------------+
| 0x02 | Request reporting of custody acceptance. |
+---------+--------------------------------------------+
| 0x04 | Request reporting of bundle forwarding. |
+---------+--------------------------------------------+
| 0x08 | Request reporting of bundle delivery. |
+---------+--------------------------------------------+
| 0x10 | Request reporting of bundle deletion. |
+---------+--------------------------------------------+
| 0x20 | Request acknowledgement by application. |
+---------+--------------------------------------------+
| 0x40 | Unused. |
+---------+--------------------------------------------+
| 0x80 | Unused. |
+---------+--------------------------------------------+
Header Length. The Header Length field is an SDNV that contains the
aggregate length of all remaining fields of the header.
Destination Scheme Offset. The Destination Scheme Offset field
contains the offset within the dictionary byte array of the
scheme name of the endpoint ID of the bundle's destination,
i.e., the endpoint containing the node(s) at which the bundle
is to be delivered.
Destination SSP Offset. The Destination SSP Offset field contains
the offset within the dictionary byte array of the scheme-
specific part of the endpoint ID of the bundle's destination.
Source Scheme Offset. The Source Scheme Offset field contains the
offset within the dictionary byte array of the scheme name of
the endpoint ID of the bundle's nominal source, i.e., the
endpoint nominally containing the node from which the bundle
was initially transmitted.
Source SSP Offset. The Source SSP Offset field contains the offset
within the dictionary byte array of the scheme-specific part
of the endpoint ID of the bundle's nominal source.
Report-to Scheme Offset. The Report-to Scheme Offset field contains
the offset within the dictionary byte array of the scheme name
of the ID of the endpoint to which status reports pertaining
to the forwarding and delivery of this bundle are to be
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transmitted.
Report-to SSP Offset. The Report-to SSP Offset field contains the
offset within the dictionary byte array of the scheme-specific
part of the ID of the endpoint to which status reports
pertaining to the forwarding and delivery of this bundle are
to be transmitted.
Custodian Scheme Offset. The "current custodian endpoint ID" of a
primary bundle header identifies an endpoint whose membership
includes the node that most recently accepted custody of the
bundle upon forwarding this bundle. The Custodian Scheme
Offset field contains the offset within the dictionary byte
array of the scheme name of the current custodian endpoint ID.
Custodian SSP Offset. The Destination SSP Offset field contains the
offset within the dictionary byte array of the scheme-specific
part of the current custodian endpoint ID.
Creation Timestamp. The creation timestamp is an 8-byte field that,
together with the source endpoint ID and (if applicable) the
fragment offset, serves to identify the bundle. The high-
order four bytes of the timestamp are the bundle's creation
time while its low-order four bytes are the bundle's creation
timestamp sequence number. Bundle creation time is the time -
expressed in seconds since the start of the year 2000, on the
Coordinated Universal Time (UTC) scale [7] - at which the
transmission request was received that resulted in the
creation of the bundle. Sequence count is the latest value
(as of the time at which that transmission request was
received) of a monotonically increasing positive integer
counter managed by the source node's bundle protocol agent
that may be reset to zero whenever the current time advances
by one second. A source Bundle Protocol Agent must never
create two distinct bundles with the same source endpoint ID
and bundle creation timestamp. The combination of source
endpoint ID and bundle creation timestamp therefore serves to
identify a single transmission request, enabling it to be
acknowledged by the receiving application.
Lifetime. The four-byte lifetime field indicates the time at which
the bundle's payload will no longer be useful, encoded as a
number of seconds past the creation time. When the current
time is greater than the creation time plus the lifetime,
bundle nodes need no longer retain or forward the bundle; the
bundle may be deleted from the network.
Dictionary Length. The Dictionary Length field is an SDNV that
contains the length of the dictionary byte array.
Dictionary. The Dictionary field is an array of bytes formed by
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concatenating the null-terminated scheme names and SSPs of all
endpoint IDs referenced by any fields in this Primary Header
together with, potentially, other endpoint IDs referenced by
fields in other TBD DTN protocol headers. Its length is given
by the value of the Dictionary Length field.
Fragment Offset. If the Bundle Processing Control Flags of this
Primary header indicate that the bundle is a fragment, then
the Fragment Offset field is an SDNV indicating the offset
from the start of the original application data unit at which
the bytes comprising the payload of this bundle were located.
If not, then the Fragment Offset field is omitted from the
header.
Total Application Data Unit Length. If the Bundle Processing Control
Flags of this Primary header indicate that the bundle is a
fragment, then the Total Application Data Unit Length field is
an SDNV indicating the total length of the original
application data unit of which this bundle's payload is a
part. If not, then the Total Application Data Unit Length
field is omitted from the header.
3.6.2 Bundle Payload Header
The fields of the bundle payload header are:
Header Type. The Header Type field is a 1-byte field that indicates
the type of the header. For the bundle payload header this
field contains the value 1.
Header Processing Control Flags. The Header Processing Control Flags
field is a 1-byte field that contains the header processing
control flags discussed in section 3.3 above.
Header Length. The Header Length field is an SDNV that contains the
aggregate length of all remaining fields of the header which
is to say, the length of the bundle's payload.
Payload. The application data carried by this bundle.
4. Bundle Processing
The bundle processing procedures mandated in this section and in
section 5 govern the operation of the Bundle Protocol Agent and the
Application Agent administrative element of each bundle node. They
are neither exhaustive nor exclusive. That is, supplementary DTN
protocol specifications (including, but not restricted to, the Bundle
Security Protocol) may require that additional measures be taken at
specified junctures in these procedures. Such additional measures
shall not override or supersede the mandated bundle protocol
procedures, except that they may in some cases make these procedures
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moot by requiring, for example, that implementations conforming to
the supplementary protocol terminate the processing of a given
incoming or outgoing bundle due to a fault condition recognized by
that protocol.
4.1 Generation of administrative records
All initial transmission of bundles is in response to bundle
transmission requests presented by nodes' application agents. When
required to "generate" an administrative record (a bundle status
report or a custody signal), the bundle protocol agent itself is
responsible for causing a new bundle to be transmitted, conveying
that record. In concept, the bundle protocol agent discharges this
responsibility by directing the administrative element of the node's
application agent to construct the record and request its
transmission as detailed in section 5 below; in practice, the manner
in which administrative record generation is accomplished is an
implementation matter, provided the constraints noted in section 5
are observed.
Notes on administrative record terminology:
a. A "bundle reception status report" is a bundle status report with
the "reporting node received bundle" flag set to 1.
b. A "custody acceptance status report" is a bundle status report
with the "reporting node accepted custody of bundle" flag set to 1.
c. A "bundle forwarding status report" is a bundle status report with
the "reporting node forwarded the bundle" flag set to 1.
d. A "bundle delivery status report" is a bundle status report with
the "reporting node delivered the bundle" flag set to 1.
e. A "bundle deletion status report" is a bundle status report with
the "reporting node deleted the bundle" flag set to 1.
f. An "acknowledgement status report" is a bundle status report with
the "acknowledged by application" flag set to 1.
g. A "Succeeded" custody signal is a custody signal with the "custody
transfer succeeded" flag set to 1.
h. A "Failed" custody signal is a custody signal with the "custody
transfer succeeded" flag set to zero.
i. The "current custodian" of a bundle is the endpoint identified by
the current custodian endpoint ID in the bundle's primary header.
4.2 Bundle transmission
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The steps in processing a bundle transmission request are:
Step 1: If custody transfer is requested for this bundle transmission
and, moreover, custody acceptance by the source node is required,
then either the bundle protocol agent must commit to accepting
custody of the bundle in which case processing proceeds from
Step 2 - or else the request cannot be honored and all remaining
steps of this procedure must be skipped.
Step 2: Transmission of the bundle is initiated. An outbound bundle
must be created per the parameters of the bundle transmission
request, with current custodian endpoint ID set to the null
endpoint ID "dtn:none" and with the retention constraint "Dispatch
pending". The source endpoint ID of the bundle must be either the
ID of an endpoint of which the node is a member or else the null
endpoint ID "dtn:none".
Step 3: Processing proceeds from Step 1 of section 4.3.
4.3 Bundle dispatching
The steps in dispatching a bundle are:
Step 1: If the bundle's destination endpoint is an endpoint of which
the node is a member, the bundle delivery procedure defined in 4.7
must be followed.
Step 2: Processing proceeds from Step 1 of section 4.4.
4.4 Bundle forwarding
The steps in forwarding a bundle are:
Step 1: The retention constraint "Forward pending" must be added to
the bundle, and the bundle's "Dispatch pending" retention
constraint must be removed.
Step 2: The bundle protocol agent must determine whether or not
forwarding is contraindicated for any of the reasons listed in
Table 5. In particular:
o The bundle protocol agent must determine which endpoint(s) to
forward the bundle to. The bundle protocol agent may choose
either to forward the bundle directly to its destination
endpoint (if possible) or else to forward the bundle to some
other endpoint(s) for further forwarding. The manner in which
this decision is made may depend on the scheme name in the
destination endpoint ID but in any case is beyond the scope of
this document. If the agent finds it impossible to select any
endpoint(s) to forward the bundle to, then forwarding is
contraindicated.
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o Provided the bundle protocol agent succeeded in selecting the
endpoint(s) to forward the bundle to, the bundle protocol agent
must select the convergence layer adapter(s) whose services
will enable the node to send the bundle to the nodes of the
minimum reception group of each selected endpoint. The manner
in which the appropriate convergence layer adapters are
selected may depend on the scheme name in the destination
endpoint ID but in any case is beyond the scope of this
document. If the agent finds it impossible to select
convergence layer adapters to use in forwarding this bundle,
then forwarding is contraindicated.
Step 3: If forwarding of the bundle is determined to be
contraindicated for any of the reasons listed in Table 5, then the
Forwarding Contraindicated procedure defined in 4.4.1 must be
followed; the remaining steps of section 4 are skipped at this
time.
Step 4: If the bundle's custody transfer requested flag (in the
bundle processing flags field) is set to 1 then the custody
transfer procedure defined in section 4.10 must be followed.
Step 5: For each endpoint selected for forwarding, the bundle
protocol agent must invoke the services of the selected
convergence layer adapter(s) in order to effect the sending of the
bundle to the nodes constituting the minimum reception group of
that endpoint. Determining the time at which the bundle is to be
sent by each convergence layer adapter is an implementation
matter.
Step 6: When all selected convergence layer adapters have informed
the bundle protocol agent that they have concluded their data
sending procedures with regard to this bundle:
o If the "request reporting of bundle forwarding" flag in the
bundle's class of service field is set to 1, then a bundle
forwarding status report must be generated, destined for the
bundle's report-to endpoint ID. If the bundle has the
retention constraint "custody accepted" and all of the nodes
in the minimum reception group of the endpoint selected for
forwarding are known to be unable to send bundles back to this
node, then the reason code on this bundle forwarding status
report must be "forwarded over unidirectional link"; otherwise
the reason code must be "no additional information".
o The bundle's "Forward pending" retention constraint must be
removed.
4.4.1 Forwarding Contraindicated
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The steps in responding to contraindication of forwarding for some
reason are:
Step 1: The bundle protocol agent must determine whether or not to
declare failure in forwarding the bundle for this reason. Note:
this decision is likely to be influenced by the reason for which
forwarding is contraindicated.
Step 2: If forwarding failure is declared, then the Forwarding Failed
procedure defined in 4.4.2 must be followed. Otherwise, (a) if
the bundle's custody transfer requested flag (in the bundle
processing flags field) is set to 1 then the custody transfer
procedure defined in section 4.10 must be followed; (b) when - at
some future time - the forwarding of this bundle ceases to be
contraindicated, processing proceeds from Step 5 of 4.4.
4.4.2 Forwarding Failed
The steps in responding to a declaration of forwarding failure for
some reason are:
Step 1: If the bundle's custody transfer requested flag (in the
bundle processing flags field) is set to 1, custody transfer
failure must be handled. Procedures for handling failure of
custody transfer for a bundle whose destination is not a singleton
endpoint are not defined in this specification. For a bundle
whose destination is a singleton endpoint, the bundle protocol
agent must handle the custody transfer failure by generating a
"Failed" custody signal for the bundle, destined for the bundle's
current custodian; the custody signal must contain a reason code
corresponding to the reason for which forwarding was determined to
be contraindicated. (Note that discarding the bundle will not
delete it from the network, since the current custodian still has
a copy.)
Step 2: If the bundle's destination endpoint is an endpoint of which
the node is a member, then the bundle's "Forward pending"
retention constraint must be removed. Otherwise the bundle must
be deleted: the bundle deletion procedure defined in 4.13 must be
followed, citing the reason for which forwarding was determined to
be contraindicated.
4.5 Bundle expiration
A bundle expires when the current time is greater than the bundle's
creation time plus its lifetime as specified in the primary bundle
header. Bundle expiration may occur at any point in the processing
of a bundle. When a bundle expires, the bundle protocol agent must
delete the bundle for the reason "lifetime expired": the bundle
deletion procedure defined in 4.13 must be followed.
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4.6 Bundle reception
The steps in processing a bundle received from another node are:
Step 1: The retention constraint "Dispatch pending" must be added to
the bundle.
Step 2: If the "request reporting of bundle reception" flag in the
bundle's class of service field is set to 1, then a bundle
reception status report with reason code "No additional
information" must be generated, destined for the bundle's report-
to endpoint ID.
Step 3: If any header in the bundle cannot be processed:
o If the header processing flags in the header indicate that a
status report must be generated in this event, then a bundle
reception status report with reason code "Header
unintelligible" must be generated, destined for the bundle's
report-to endpoint ID.
o If the header processing flags in that header indicate that
the bundle must be discarded in this event, then the bundle
protocol agent must delete the bundle for the reason "Header
unintelligible": the bundle deletion procedure defined in 4.13
must be followed. Otherwise, processing proceeds from Step 4.
Step 4: If the bundle's custody transfer requested flag (in the
bundle processing flags field) is set to 1 and the bundle has the
same source endpoint ID, creation timestamp, and fragment offset
as another bundle that (a) has not been discarded and (b)
currently has the retention constraint "Custody accepted", custody
transfer redundancy must be handled; otherwise, processing
proceeds from Step 5. Procedures for handling redundancy in
custody transfer for a bundle whose destination is not a singleton
endpoint are not defined in this specification. For a bundle
whose destination is a singleton endpoint, the bundle protocol
agent must handle custody transfer redundancy by generating a
"Failed" custody signal for this bundle with reason code
"Redundant reception", destined for this bundle's current
custodian, and removing this bundle's "Dispatch pending" retention
constraint.
Step 5: Processing proceeds from Step 1 of section 4.3.
4.7 Local bundle delivery
The steps in processing a bundle that is destined for an endpoint of
which this node is a member are:
Step 1: If the received bundle is a fragment, the application data
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unit reassembly procedure described in 4.9 must be followed. If
this procedure results in reassembly of the entire original
application data unit, processing of this bundle (whose
fragmentary payload has been replaced by the reassembled
application data unit) proceeds from Step 2; otherwise the
retention constraint "Reassembly pending" must be added to the
bundle and all remaining steps of this procedure are skipped.
Step 2: Delivery depends on the state of the registration whose
endpoint ID matches that of the destination of the bundle:
o If the registration is in the Active state, then the bundle
must be delivered subject to this registration (see 2.1 above)
as soon as all previously received bundles that are
deliverable subject to this registration have been delivered.
o If the registration is in the Passive state, then the
registration's delivery failure action must be taken (see 2.1
above).
Step 3: As soon as the bundle has been delivered:
o If the "request reporting of bundle delivery" flag in the
bundle's class of service field is set to 1, then a bundle
delivery status report must be generated, destined for the
bundle's report-to endpoint ID. Note that this status report
only states that the payload has been delivered to the
application agent, not that the application agent has
processed that payload.
o If the bundle's custody transfer requested flag (in the bundle
processing flags field) is set to 1, custodial delivery must
be reported. Procedures for reporting custodial delivery for
a bundle whose destination is not a singleton endpoint are not
defined in this specification. For a bundle whose destination
is a singleton endpoint, the bundle protocol agent must report
custodial delivery by generating a "Succeeded" custody signal
for the bundle, destined for the bundle's current custodian.
4.8
Bundle Fragmentation
It may at times be necessary for bundle protocol agents to reduce the
sizes of bundles in order to forward them. This might be the case,
for example, if the endpoint to which a bundle is to be forwarded is
accessible only via intermittent contacts and no upcoming contact is
long enough to enable the forwarding of the entire bundle.
The size of a bundle can be reduced by "fragmenting" the bundle. To
fragment a bundle whose payload is of size M is to replace it with
two "fragments" new bundles with the same source endpoint ID and
creation timestamp as the original bundle whose payloads are the
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first N and the last (M N) bytes of the original bundle's payload,
where 0 < N < M. Note that fragments may themselves be fragmented,
so fragmentation may in effect replace the original bundle with more
than two fragments. (However, there is only one 'level' of
fragmentation, as in IP fragmentation.)
Any bundle whose primary header's bundle processing flags do NOT
indicate that it must not be fragmented may be fragmented at any
time, for any purpose, at the discretion of the bundle protocol
agent.
Fragmentation shall be constrained as follows:
o The concatenation of the payloads of all fragments produced by
a fragmentation must always be identical to the payload of the
bundle that was fragmented. Note that the payloads of
fragments resulting from different fragmentation episodes, in
different parts of the network, may be overlapping subsets of
the original bundle's payload.
o The bundle processing flags in the primary header of each
fragment must be modified to indicate that the bundle is a
fragment, and both fragment offset and total application data
unit length must be provided at the end of each fragment's
primary bundle header.
o All fragments must contain the same headers as the original
bundle, except that (a) the primary headers of the fragments
will differ from that of the fragmented bundle as noted above,
(b) the payload headers of fragments will differ from that of
the fragmented bundle, and (c) any header whose header
processing flags do NOT indicate that the header must be
replicated in every fragment should be replicated only in the
fragment whose fragment offset is zero.
4.9 Application Data Unit Reassembly
If the concatenation as informed by fragment offsets and payload
lengths - of the payloads of all previously received fragments with
the same source endpoint ID and creation timestamp as this fragment,
together with the payload of this fragment, forms a byte array whose
length is equal to the total application data unit length in the
fragment's primary header, then:
o This byte array the reassembled application data unit must
replace the payload of this fragment.
o The "Reassembly pending" retention constraint must be removed
from every other fragment whose payload is a subset of the
reassembled application data unit.
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Note: reassembly of application data units from fragments occurs at
destination endpoints as necessary; an application data unit may also
be reassembled at some other endpoint on the route to the
destination.
4.10 Custody transfer
The conditions under which a node may accept custody of a bundle
whose destination is not a singleton endpoint are not defined in this
specification.
The decision as to whether or not to accept custody of a bundle whose
destination is a singleton endpoint is an implementation matter which
may involve both resource and policy considerations; however, if the
bundle protocol agent has committed to accepting custody of the
bundle (as described in Step 1 of 4.2) then custody must be accepted.
If the bundle protocol agent elects to accept custody of the bundle,
then it must follow the custody acceptance procedure defined in
4.10.1.
4.10.1
Custody acceptance
Procedures for acceptance of custody of a bundle whose destination is
not a singleton endpoint are not defined in this specification.
Procedures for acceptance of custody of a bundle whose destination is
a singleton endpoint are defined as follows.
The retention constraint "Custody accepted" must be added to the
bundle.
If the "request custody acceptance reporting" flag in the bundle's
class of service field is set to 1, a custody acceptance status
report must be generated, destined for the report-to endpoint ID of
the bundle. However, if a bundle reception status report was
generated for this bundle (step 1 of 4.6) then this report should be
generated by simply turning on the "Reporting node accepted custody
of bundle" flag in that earlier report's status flags byte.
The bundle protocol agent must generate a "Succeeded" custody signal
for the bundle, destined for the bundle's current custodian.
The bundle protocol agent must assert the new current custodian for
the bundle. It does so by changing the current custodian endpoint ID
in the bundle's primary header to the endpoint ID of one of the
singleton endpoints in which the node is registered. This may entail
appending that endpoint ID's null-terminated scheme name and SSP to
the dictionary byte array in the bundle's primary header, and in some
case it may also enable the (optional) removal of the current
custodian endpoint ID's scheme name and/or SSP from the dictionary.
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The bundle protocol agent may set a custody transfer countdown timer
for this bundle; upon expiration of this timer prior to expiration of
the bundle itself and prior to custody transfer success for this
bundle, the custody transfer failure procedure detailed in section
4.12 must be followed. The manner in which the countdown interval
for such a timer is determined is an implementation matter.
The bundle should be retained in persistent storage if possible.
4.10.2
Custody release
Procedures for release of custody of a bundle whose destination is
not a singleton endpoint are not defined in this specification.
When custody of a bundle is released, where the destination of the
bundle is a singleton endpoint, the "Custody accepted" retention
constraint must be removed from the bundle and any custody transfer
timer that has been established for this bundle must be destroyed.
4.11 Custody transfer success
Procedures for determining custody transfer success for a bundle
whose destination is not a singleton endpoint are not defined in this
specification.
Upon receipt of a "Succeeded" custody signal at a node that is a
custodial node of the bundle identified in the custody signal, where
the destination of the bundle is a singleton endpoint, custody of the
bundle must be released as described in 4.10.2.
4.12 Custody transfer failure
Procedures for determining custody transfer failure for a bundle
whose destination is not a singleton endpoint are not defined in this
specification. Custody transfer for a bundle whose destination is a
singleton endpoint is determined to have failed at a custodial node
for that bundle when either (a) that node's custody transfer timer
for that bundle (if any) expires or (b) a "Failed" custody signal for
that bundle is received at that node.
Upon determination of custody transfer failure, the action taken by
the bundle protocol agent is implementation-specific and may depend
on the nature of the failure. For example, if custody transfer
failure was inferred from expiration of a custody transfer timer or
was asserted by a "Failed" custody signal with the "Depleted storage"
reason code, the bundle protocol agent might choose to re-forward the
bundle, possibly on a different route (section 4.4). Receipt of a
"Failed" custody signal with the "Redundant reception" reason code,
on the other hand, might cause the bundle protocol agent to release
custody of the bundle and to revise its algorithm for computing
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countdown intervals for custody transfer timers.
4.13 Bundle deletion
The steps in deleting a bundle are:
Step 1: If the retention constraint "Custody accepted" currently
prevents this bundle from being discarded, and the destination of
the bundle is a singleton endpoint, then:
o Custody of the node is released as described in 4.10.2.
o A bundle deletion status report citing the reason for deletion
must be generated, destined for the bundle's report-to
endpoint ID.
Otherwise, if the "request reporting of bundle deletion" flag in
the bundle's class of service field is set to 1, then a bundle
deletion status report citing the reason for deletion must be
generated, destined for the bundle's report-to endpoint ID.
Step 2: All of the bundle's retention constraints must be removed.
4.14 Discarding a bundle
As soon as a bundle has no remaining retention constraints it may be
discarded.
4.15 Canceling a transmission
When requested to cancel a specified transmission, where the bundle
created upon initiation of the indicated transmission has not yet
been discarded, the bundle protocol agent must delete that bundle for
the reason "transmission canceled". For this purpose, the procedure
defined in 4.13 must be followed.
4.16 Polling
When requested to poll a specified registration that is in Passive
state, the bundle protocol agent must immediately deliver the least
recently received bundle that is deliverable subject to the indicated
registration, if any.
4.17 Acknowledging an application data unit
When requested to acknowledge to an indicated report-to endpoint the
bundle transmission request identified by an indicated source
endpoint ID and bundle creation timestamp, the bundle protocol agent
must generate an acknowledgement status report for that transmission
request, destined for that report-to-endpoint.
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5. Administrative record processing
5.1 Administrative records
Two types of administrative records have been defined to date: bundle
status reports and custody signals.
Every administrative record consists of a four-bit record type code
followed by four bits of administrative record flags, followed by
record content in type-specific format. Record type codes are
defined as follows:
Table 2: Administrative Record Type Codes
+---------+--------------------------------------------+
| Value | Meaning |
+=========+============================================+
| 0x01 | Bundle status report. |
+---------+--------------------------------------------+
| 0x02 | Custody signal. |
+---------+--------------------------------------------+
| (other) | Reserved for future use. |
+---------+--------------------------------------------+
Administrative record flags are defined as follows:
Table 3: Administrative Record Flags
+---------+--------------------------------------------+
| Value | Meaning |
+=========+============================================+
| 0x01 | Record is for a fragment; fragment |
| | offset and length fields are present. |
+---------+--------------------------------------------+
| (other) | Reserved for future use. |
+---------+--------------------------------------------+
All time values in administrative records are UTC times expressed in
"DTN time" representation. A DTN time consists of a 32-bit number in
network byte order indicating the number of seconds since the start
of the year 2000, followed by a 32-bit number in network byte order
indicating the number of nanoseconds since the start of the indicated
second.
The contents of the various types of administrative records are
described below.
5.1.1 Bundle Status Reports
The transmission of 'bundle status reports' under specified
conditions is an option that can be invoked when transmission of a
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bundle is requested. These reports are intended to provide
information about how bundles are progressing through the system,
including notices of receipt, custody transfer, forwarding, final
delivery, and deletion. They are transmitted to the Report-to
endpoints of bundles.
Format of Bundle Status Report for bundle 'X':
+----------------+----------------+----------------+----------------+
| Status Flags | Reason code | Fragment offset (*) (if
+----------------+----------------+----------------+----------------+
present) | Fragment length (**) (if present) |
+----------------+----------------+----------------+----------------+
|
+ Time of receipt of bundle X (8 bytes, if present) +
|
+----------------+----------------+----------------+----------------+
|
+ Time of custody acceptance of bundle X (8 bytes, if present) +
|
+----------------+----------------+----------------+----------------+
|
+ Time of forwarding of bundle X (8 bytes, if present) +
|
+----------------+----------------+----------------+----------------+
|
+ Time of delivery of bundle X (8 bytes, if present) +
|
+----------------+----------------+----------------+----------------+
|
+ Time of deletion of bundle X (8 bytes, if present) +
|
+----------------+----------------+----------------+----------------+
|
+ Time of acknowledgement of bundle X (8 bytes, if present) +
|
+----------------+----------------+----------------+----------------+
|
+ Copy of bundle X's Creation Timestamp (8 bytes) +
|
+----------------+----------------+----------------+----------------+
| Length of X's source endpoint ID (***) | Source
+----------------+---------------------------------+ +
endpoint ID of bundle X (variable) |
+----------------+----------------+----------------+----------------+
Notes:
(*) The Fragment Offset field, if present, is an SDNV and is
therefore variable-length. A three-octet SDNV is shown here for
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convenience in representation.
(**) The Fragment Length field, if present, is an SDNV and is
therefore variable-length. A three-octet SDNV is shown here for
convenience in representation.
(***) The source endpoint ID length field is an SDNV and is
therefore variable-length. A three-octet SDNV is shown here for
convenience in representation.
The fields in a bundle status report are:
Status Flags. A 1-byte field containing the following flags:
Table 4: Status Flags for Bundle Status Reports
+---------+--------------------------------------------+
| Value | Meaning |
+=========+============================================+
| 0x01 | Reporting node received bundle. |
+---------+--------------------------------------------+
| 0x02 | Reporting node accepted custody of bundle.|
+---------+--------------------------------------------+
| 0x04 | Reporting node forwarded the bundle. |
+---------+--------------------------------------------+
| 0x08 | Reporting node delivered the bundle. |
+---------+--------------------------------------------+
| 0x10 | Reporting node deleted the bundle. |
+---------+--------------------------------------------+
| 0x20 | Acknowledged by application. |
+---------+--------------------------------------------+
| 0x40 | Unused. |
+---------+--------------------------------------------+
| 0x80 | Unused. |
+---------+--------------------------------------------+
Reason code. A 1-byte field explaining the value of the flags in the
status flags byte. The list of status report reason codes
provided here is neither exhaustive nor exclusive;
supplementary DTN protocol specifications (including, but not
restricted to, the Bundle Security Protocol) may define
additional reason codes. Status report reason codes are
defined as follows:
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Table 5: Status Report Reason Codes
+---------+--------------------------------------------+
| Value | Meaning |
+=========+============================================+
| 0x00 | No additional information. |
+---------+--------------------------------------------+
| 0x01 | Lifetime expired. |
+---------+--------------------------------------------+
| 0x02 | Forwarded over unidirectional link. |
+---------+--------------------------------------------+
| 0x03 | Transmission canceled. |
+---------+--------------------------------------------+
| 0x04 | Depleted storage. |
+---------+--------------------------------------------+
| 0x05 | Destination endpoint ID unintelligible. |
+---------+--------------------------------------------+
| 0x06 | No known route to destination from here. |
+---------+--------------------------------------------+
| 0x07 | No timely contact with next node on route.|
+---------+--------------------------------------------+
| 0x08 | Header unintelligible. |
+---------+--------------------------------------------+
| (other) | Reserved for future use. |
+---------+--------------------------------------------+
Fragment offset. If the bundle fragment bit is set in the status
flags, then the offset (within the original application data
unit) of the payload of the bundle that caused the status
report to be generated is included here.
Fragment length. If the bundle fragment bit is set in the status
flags, then the length of the payload of the subject bundle is
included here.
Time of Receipt (if present). If the bundle-received bit is set in
the status flags, then a DTN time indicating the time at which
the bundle was received at the reporting node is included
here.
Time of Custody Acceptance (if present). If the custody-accepted bit
is set in the status flags, then a DTN time indicating the
time at which custody was accepted at the reporting node is
included here.
Time of Forward (if present). If the bundle-forwarded bit is set in
the status flags, then a DTN time indicating the time at which
the bundle was first forwarded at the reporting node is
included here.
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Time of Delivery (if present). If the bundle-delivered bit is set in
the status flags, then a DTN time indicating the time at which
the bundle was delivered at the reporting node is included
here.
Time of Deletion (if present). If the bundle-deleted bit is set in
the status flags, then a DTN time indicating the time at which
the bundle was deleted at the reporting node is included here.
Time of Acknowledgement (if present). If the bundle-acknowledged-by-
application bit is set in the status flags, then a DTN time
indicating the time at which the bundle was acknowledged by
the application at the reporting node is included here.
Creation Timestamp of Subject Bundle. A copy of the creation
timestamp of the bundle that caused the status report to be
generated.
Length of Source Endpoint ID. The length in bytes of the source
endpoint ID of the bundle that caused the status report to be
generated.
Source Endpoint ID text. The text of the source endpoint ID of the
bundle that caused the status report to be generated.
5.1.2 Custody Signals
Custody signals are administrative records that effect custody
transfer operations. They are transmitted to the endpoints that are
the current custodians of bundles.
Custody signals have the following format.
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Custody Signal regarding bundle 'X':
+----------------+----------------+----------------+----------------+
| Status | Fragment offset (*) (if present) |
+----------------+----------------+----------------+----------------+
| Fragment length (**) (if present) |
+----------------+----------------+----------------+----------------+
|
+ Time of signal (8 bytes) +
|
+----------------+----------------+----------------+----------------+
|
+ Copy of bundle X's Creation Timestamp (8 bytes) +
|
+----------------+----------------+----------------+----------------+
| Length of X's source endpoint ID (***) | Source
+----------------+---------------------------------+ +
endpoint ID of bundle X (variable) |
+----------------+----------------+----------------+----------------+
Notes:
(*) The Fragment Offset field, if present, is an SDNV and is
therefore variable-length. A three-octet SDNV is shown here for
convenience in representation.
(**) The Fragment Length field, if present, is an SDNV and is
therefore variable-length. A four-octet SDNV is shown here for
convenience in representation.
(***) The source endpoint ID length field is an SDNV and is
therefore variable-length. A three-octet SDNV is shown here for
convenience in representation.
The fields in a custody signal are:
Status. A 1-byte field containing a 1-bit "custody transfer
succeeded" flag followed by a 7-bit reason code explaining the value
of that flag. Custody signal reason codes are defined as follows:
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Table 6: Custody Signal Reason Codes
+---------+--------------------------------------------+
| Value | Meaning |
+=========+============================================+
| 0x00 | No additional information. |
+---------+--------------------------------------------+
| 0x01 | Reserved for future use. |
+---------+--------------------------------------------+
| 0x02 | Reserved for future use. |
+---------+--------------------------------------------+
| 0x03 | Redundant reception (reception by a node |
| | that is a custodial node for this bundle).|
+---------+--------------------------------------------+
| 0x04 | Depleted storage. |
+---------+--------------------------------------------+
| 0x05 | Destination endpoint ID unintelligible. |
+---------+--------------------------------------------+
| 0x06 | No known route to destination from here. |
+---------+--------------------------------------------+
| 0x07 | No timely contact with next node on route.|
+---------+--------------------------------------------+
| 0x08 | Header unintelligible. |
+---------+--------------------------------------------+
| (other) | Reserved for future use. |
+---------+--------------------------------------------+
Fragment offset. If the bundle fragment bit is set in the status
flags, then the offset (within the original application data
unit) of the payload of the bundle that caused the status
report to be generated is included here.
Fragment length. If the bundle fragment bit is set in the status
flags, then the length of the payload of the subject bundle is
included here.
Time of Signal. A DTN time indicating the time at which the signal
was generated.
Creation Timestamp of Subject Bundle. A copy of the creation
timestamp of the bundle to which the signal applies.
Length of Source Endpoint ID. The length in bytes of the source
endpoint ID of the bundle to which the signal applied.
Source Endpoint ID text. The text of the source endpoint ID of the
bundle to which the signal applies.
5.2 Generation of administrative records
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Whenever the application agent's administrative element is directed
by the bundle protocol agent to generate an administrative record
with reference to some bundle, the following procedure must be
followed:
Step 1: The administrative record must be constructed. If the
referenced bundle is a fragment, the administrative record must
have the Fragment flag set and must contain the fragment offset
and fragment length fields; the value of the fragment offset field
must be the value of the referenced bundle's fragment offset, and
the value of the fragment length field must be the length of the
referenced bundle's payload.
Step 2: A request for transmission of a bundle whose payload is this
administrative record must be presented to the bundle protocol
agent.
5.3 Reception of custody signals
For each received custody signal that has the Custody Transfer
Succeeded flag set to 1, the administrative element of the
application agent must direct the bundle protocol agent to follow the
custody transfer success procedure in 4.11.
For each received custody signal that has the Custody Transfer
Succeeded flag set to 0, the administrative element of the
application agent must direct the bundle protocol agent to follow the
custody transfer failure procedure in 4.12.
6. Services Required of the Convergence Layer
6.1 The Convergence Layer
The successful operation of the end-to-end bundle protocol depends on
the operation of underlying protocols at what is termed the
"convergence layer"; these protocols accomplish communication between
nodes. A wide variety of protocols may serve this purpose, so long
as each convergence layer protocol adapter provides a defined minimal
set of services to the bundle protocol agent. This convergence layer
service specification enumerates those services.
6.2 Summary of Convergence Layer Services
Each convergence layer protocol adapter is expected to provide the
following services to the bundle protocol agent:
a) sending a bundle to all bundle nodes in the minimum reception
group of the endpoint identified by a specified endpoint ID
that are reachable via the convergence layer protocol;
b) delivering to the bundle protocol agent a bundle that was sent
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by a remote bundle node via the convergence layer protocol.
The convergence layer service interface specified here is neither
exhaustive nor exclusive. That is, supplementary DTN protocol
specifications (including, but not restricted to, the Bundle Security
Protocol) may expect convergence layer adapters which serve BP
implementations conforming to those protocols to provide additional
services.
7. Security Considerations
The bundle protocol has taken security into concern from the outset
of its design. It was always assumed that security services would be
needed in the use of the bundle protocol. As a result, the bundle
protocol security architecture and the available security services
are specified in an accompanying document, the Bundle Security
Protocol specification [5]; an informative overview of this
architecture is provided in [6].
The bundle protocol has been designed with the notion that it will be
run over networks with scarce resources. For example, the networks
might have limited bandwidth, limited connectivity, constrained
storage in relay nodes, etc. Therefore, the bundle protocol must
ensure that only those entities authorized to send bundles over such
constrained environments are actually allowed to do so. All
unauthorized entities should be prevented from consuming valuable
resources.
Likewise, because of the potentially long latencies and delays
involved in the networks that make use of the bundle protocol, data
sources should be concerned with the integrity of the data received
at the intended destination(s) and may also be concerned with
ensuring confidentiality of the data as it traverses the network.
Without integrity, the bundle payload data might be corrupted while
in transit without the destination able to detect it. Similarly, the
data source can be concerned with ensuring that the data can only be
used by those authorized; hence the need for confidentiality.
Internal to the bundle-aware overlay network, the bundle nodes should
be concerned with the authenticity of other bundle nodes as well as
the preservation of bundle payload data integrity as it is forwarded
between bundle nodes.
As a result, bundle security is concerned with the authenticity,
integrity, and confidentiality of bundles conveyed among bundle
nodes. This is accomplished via the use of three, independent
security specific bundle headers which may be used together to
provide multiple bundle security services or independently of one
another, depending on perceived security threats, mandated security
requirements, and security policies that must be enforced.
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The Bundle Authentication Header (BAH) ensures the authenticity and
integrity of bundles on a hop-by-hop basis between bundle nodes. The
BAH allows each bundle node to verify a bundles authenticity before
processing or forwarding the bundle. In this way, entities that are
not authorized to send bundles will have unauthorized transmissions
blocked by security-aware bundle nodes.
Additionally, to provide "security-source" to "security-destination"
bundle authenticity and integrity, the Payload Security Header (PSH)
is used. A "security-source" may not actually be the origination
point of the bundle but instead may be the first point along the path
that is security-aware and is able to apply security services. For
example, an enclave of networked systems may generate bundles but
only their gateway may be required and/or able to apply security
services. The PSH allows any security-enabled entity along the
delivery path, in addition to the "security-destination" (the
recipient counterpart to the "security-source"), to ensure the
bundles authenticity.
Finally, to provide payload confidentiality, the use of the
Confidentiality Header (CH) is available. The bundle payload may be
encrypted to provide "security-source" to "security-destination"
payload confidentiality/privacy. The CH indicates the cryptographic
algorithm and key IDs that were used to encrypt the payload.
Inclusion of the Bundle Security Protocol in any Bundle Protocol
implementation is RECOMMENDED. Use of the Bundle Security Protocol
in Bundle Protocol operations is OPTIONAL.
8. IANA Considerations
The new Uniform Resource Identifier scheme "dtn", defined by the
Bundle Protocol, will need to be documented.
9. Normative References
[RFC3978] Bradner, S., "IETF Rights in Contributions", BCP 78, RFC
3978, March 2005.
[RFC3979] Bradner, S., "Intellectual Property Rights in IETF
Technology", BCP 79, RFC 3979, March 2005.
[RFC3986] T. Berners-Lee, R. Fielding, L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, Jan
2005.
[RFC2717] Petke, R. and I. King, "Registration Procedures for URL
Scheme Names", BCP 35, RFC 2717, November 1999.
10. Informative References
K. Scott and S. Burleigh Expires - May 2006 [Page 38]
Internet Draft Bundle Protocol Specification November 2005
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997
[2] V. Cerf, et. al., "Delay-Tolerant Network Architecture," work in
progress, draft-irtf-dtnrg-arch-03.txt, July 2005
[3] F. Warthman, "Delay-Tolerant Networks (DTNs): A Tutorial",
Warthman Associates, available from http://www.dtnrg.org
[4] Mills, D., "Network Time Protocol (Version 3) Specification,
Implementation and Analysis", RFC 1305, March 1992
[5] S. Symington, et. al., "Bundle Security Protocol Specification,"
draft-irtf-dtnrg-bundle-security-00.txt, June 2005
[6] S. Farrell, S. Symington, and H. Weiss, "Delay-Tolerant
Networking Security Overview," draft-irtf-dtnrg-sec-overview-
00.txt, September 2005
[7] E. F. Arias and B. Guinot, B., "Coordinated universal time UTC:
historical background and perspectives" in Journιes systemes de
reference spatio-temporels 2004
[8] K. Fall, " A Delay-Tolerant Network Architecture for Challenged
Internets", SIGCOMM 2003
Author's Addresses
Dr. Keith L. Scott Scott C. Burleigh
The MITRE Corporation Jet Propulsion Laboratory
7515 Colshire Drive 4800 Oak Grove Drive
McLean, VA 22102 M/S: 179-206
Telephone +1 (703) 883-6547 Pasadena, CA 91109-8099
FAX +1 (703) 883-7142 Telephone +1 (818) 393-3353
Email kscott@mitre.org FAX +1 (818) 354-1075
Email Scott.Burleigh@jpl.nasa.gov
Please refer comments to dtn-interest@mailman.dtnrg.org. The Delay
Tolerant Networking Research Group (DTNRG) web site is located at
http://www.dtnrg.org.
Intellectual Property Statement
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Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
K. Scott and S. Burleigh Expires - May 2006 [Page 39]
Internet Draft Bundle Protocol Specification November 2005
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
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The IETF invites any interested party to bring to its attention any
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Disclaimer
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
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ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
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Copyright Notice
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgements
The authors gratefully acknowledge the contributions of Dr. Vint Cerf
of MCI, Dr. Kevin Fall and Michael Demmer of Intel Corporation,
Adrian Hooke and Leigh Torgerson of the Jet Propulsion Laboratory,
Stephen Farrell of Trinity College Dublin, and Robert Durst and Susan
Symington of The MITRE Corporation. Thanks to Howard Weiss of
SPARTA, Inc., for the text of section 7 and to Manikantan Ramadas of
Ohio University for most of the text of section 3.4, which is adapted
from the specification for the Licklider Transmission Protocol.
K. Scott and S. Burleigh Expires - May 2006 [Page 40]
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