Network Working Group S. Burleigh
Internet-Draft JPL, Calif. Inst. of Technology
Intended status: Standards Track F. Templin
Expires: November 6, 2021 The Boeing Company
May 5, 2021
Bundle Protocol Extended Class of Service (ECOS)
draft-burleigh-dtn-ecos-00
Abstract
This document describes an extension to the Delay-Tolerant Networking
(DTN) Bundle Protocol (BP) that marks bundles with class-of-service
designators. The class-of-service designators are an "ordinal"
number that provides fine-grained prioritization of bundles, a
"critical" flag, flags that explicitly request "timely" or "assured"
convergence-layer transmission (or both), and an optional QoS tag.
Requirements Language
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].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on November 6, 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. ECOS Block Format . . . . . . . . . . . . . . . . . . . . . . 3
3. Processing . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Bundle Origination . . . . . . . . . . . . . . . . . . . 5
3.2. Bundle Forwarding . . . . . . . . . . . . . . . . . . . . 6
3.3. Bundle Delivery . . . . . . . . . . . . . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. Normative References . . . . . . . . . . . . . . . . . . . . 8
Appendix A. Congestion Experienced . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
This document describes an extension to the Delay-Tolerant Networking
(DTN) Bundle Protocol (BP) that marks bundles with class-of-service
designators. The Bundle Protocol version 7 (BPv7) base specification
[I-D.ietf-dtn-bpbis] defines no class of service designators, while
its predecessor Bundle Protocol version 6 (BPv6) [RFC5050] defined a
single designator for a bundle's class of service:
o Priority, a value in the range 0 through 2, with higher values
indicating greater urgency: 0 = "bulk", 1 = "normal", 2 =
"expedited". Priority level 3 is reserved for future use.
For some applications, such as space flight and tactical unmanned air
vehicle operations, additional variations in class of service may be
required:
o Many more levels of priority may be needed, enabling more fine-
grained control over the precedence of user-selected application
data types in the progress of bundles through the network.
o A way of indicating emergency ("critical") traffic may be needed.
Emergency traffic is not merely high-priority: it is so important
that the user is willing to incur the network overhead of
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transmitting the bundle along every potential route to its
destination, rather than only on the route that would normally be
selected as the "best" route according to the applicable routing
value function. This expedient ensures that the bundle arrives at
its destination in the least possible time, regardless of how
accurately the routing system reckons end-to-end latency on any
given route: the bundle arrives by whatever turns out to be the
fastest route, as well as by all others.
o There may be a need to request explicitly that all nodes
forwarding the bundle use convergence-layer protocols that either
always do or always don't perform retransmission upon detected
loss of data. This designation may be important for bundles
carrying application data for which timeliness of delivery is
known to be more important than certainty, or vice versa. In some
cases, retransmitted "old data" may be a waste of bandwidth that
could instead be used to convey new data of greater value, or the
out-of-order arrival of retransmitted data may degrade the
usefulness of streaming data such as audio or video.
o There may be a need for an opaque "QoS tag" that can be used by
the application to pass a variety of transmission control
parameters to the convergence-layer protocol.
The Extended Class of Service (ECOS) extension block for BPv7 is
designed to provide these class of service designators.
2. ECOS Block Format
The ECOS block conforms to sections 4.3.2 and 4.4 of
[I-D.ietf-dtn-bpbis], where the block SHALL be represented as a CBOR
array with 5 elements (i.e., since CRC type is 0). The ECOS block is
constrained as follows:
o Block type code is TBD. (See "IANA Considerations" below.)
o Block number is coded as discussed in Section 4.1 of
[I-D.ietf-dtn-bpbis].
o Per Section 4.2.4 of [I-D.ietf-dtn-bpbis], block processing
control flags are next encoded as a CBOR unsigned integer. The
following block processing control flag MUST be set to 1:
* Bit 0 - block must be replicated in every fragment.
The setting of other block processing control flags, where not
mandated by the Bundle Protocol specification, is an
implementation matter.
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o CRC type is set to 0 as discussed in Section 4.2.1 of
[I-D.ietf-dtn-bpbis].
o Block-type-specific data is represented as a single definite-
length CBOR byte string containing a 16-bit Flags field, an 8-bit
Priority field and (optionally) a 32-bit QoS Tag field.
The first field of the Block-type-specific data is a 16-bit Flags
byte. The bits of the flags signify the following conditions:
o The 0x0001 bit, if True, indicates that the bundle is "critical":
the bundle protocol agent is requested to forward one copy of the
bundle along every path that might get it to its destination.
o The 0x0002 bit, if True, indicates an explicit preference that
delivery of the bundle be timely and in order: the bundle protocol
agent is requested to forward the bundle on a "best-effort" basis,
without retransmission.
o The 0x0004 bit, if True, indicates that the Ordinal Number field
of this ECOS block (the byte immediately following the Flags) is
followed by a numeric QoS Tag field.
o The 0x0008 bit, if True, indicates an explicit preference that
delivery of the bundle be assured even if out of order: the bundle
protocol agent is requested to forward the bundle reliably, with
retransmission as necessary.
o The 0x0010 bit, if True, means "BSSP required".
o The 0x0020 bit, if True, means "BIBE required".
o The 0x0040 bit, if True, means "(BIBE) Custody Transfer required".
o Bits 0x0080 through 0x2000 are reserved for future use. For the
purpose of this specification, they are set to 0 on transmission
and ignored on recepition (future specifications may define new
settings and interpretations).
o Bits 0x4000 and 0x8000 are reserved as Congestion Experienced (CE)
indications. For the purpose of this specification, they are set
to 0 on transmission and ignored on recepition (future
specifications may define new settings and interpretations).
Note that both the 0x0002 and 0x0008 bits might be set for a given
bundle. This indicates an explicit preference that delivery of the
bundle be timely and in-order if possible but in any case assured, as
in a bundle streaming service: whenever loss is detected in "best-
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effort" transmission, the lost data are retransmitted for eventual
out-of-order delivery in background.
The Flags field is followed by an 8-bit Priority field with the most
significant 2 bits containing a Service Class value as follows:
o 00 = bulk
o 01 = normal
o 10 = expedited
o 11 is reserved for future use.
The remaining 6 bits of the Priority field encode an unsigned Ordinal
Number value in the range 0-63. For a bundle whose Service Class is
2 ("expedited"), the Ordinal Number indicates the relative priority
of this bundle among all other expedited bundles: Ordinal Number
value 63 indicates greater urgency than value 62, and so on. For a
bundle whose Service Class is not 2, the Ordinal Number value has no
significance.
If the 0x0004 bit of the Flags field is True, the third field of the
block data is a numeric QoS Tag value. The significance of the QoS
Tag is an implementation matter. Notionally, the QoS Tag is intended
to be used to convey quality-of-service information to the
convergence-layer protocol adapter. The bundle protocol agent's
response to a QoS Tag whose significance is unknown is an
implementation matter.
3. Processing
3.1. Bundle Origination
At the time a bundle is sourced it MAY contain one ECOS block. When
a bundle contains an ECOS block, the ECOS block MUST precede the
payload block and it MUST be the only ECOS block in the bundle.
The manner in which the application issuing the block communicates
the values of the ECOS block data fields to the bundle protocol agent
is an implementation matter.
If the ECOS block contains a QoS Tag field, then the 0x0004 bit of
the block's Flags field MUST be set to 1 (True) and the QoS Tag MUST
be a numeric value. Otherwise the 0x0004 bit of the block's Flags
field MUST be set to 0 (False) and the QoS Tag field is omitted.
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The Priority field of the ECOS block MUST contain a 2-bit Service
Class value followed by a 6-bit Ordinal Number unsigned integer in
the range 0-63.
3.2. Bundle Forwarding
This section applies only to nodes at which procedures for processing
ECOS blocks are implemented. When a node at which such procedures
are not implemented receives a bundle that contains one or more ECOS
blocks, those blocks must be processed as prescribed in the Bundle
Protocol specification.
When a received bundle contains multiple ECOS blocks or contains a
single ECOS block that is invalid (that is, one that violates one or
more of the provisions of section 3.1 above), all ECOS blocks in the
bundle MUST be ignored and SHOULD be deleted.
At the time a bundle that has no valid single ECOS block is received
from a neighboring node, the bundle protocol agent MAY insert an ECOS
block into the bundle. The values of the block data fields of such
an ECOS block are an implementation matter, provided that they
conform to this specification.
The forwarding of a bundle that contains a valid ECOS block, whether
locally sourced or received from another bundle protocol agent or
locally inserted upon reception from another bundle protocol agent,
MUST comply with the following rules:
1. If the 0x0001 bit of the ECOS block's Flags field is set to 1,
then exactly one copy of the bundle SHOULD be forwarded to every
neighboring node that has some plausible prospect of being able
to forward the bundle toward its final destination without
returning it to the local node, a determination that is a matter
left to the bundle protocol agent's route computation mechanism;
also, the bundle MUST be queued for transmission as if its
Service Class were 2 ("expedited") and its Ordinal Value were 63,
regardless of the actual values of these fields. Each "critical"
bundle MUST be forwarded *at most once* by each bundle protocol
agent; that is, critical bundles MUST NOT be reforwarded in
response to custody refusals, the expiration of custody transfer
timers, the presence of a routing loop in the network, or any
other condition, because such reforwarding could result in
unbounded bundle transmission explosions. The manner in which
this constraint is enforced is an implementation matter. One
possible approach is to manage a list of the IDs and expiration
times of all critical bundles received, removing bundles from the
list only as the associated expiration times are reached; since
"critical" bundles should be issued rarely, managing such a list
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should not be a severe processing burden. Note that a bundle
protocol agent MAY choose to handle a critical bundle as non-
critical traffic and forward it on only a single path, but
ignoring the "critical" flag may put network assets as risk and
should be avoided unless necessary to preserve the continued
operation of the bundle protocol agent.
2. If the 0x0002 bit of the ECOS block's Flags field is set to 1,
then the bundle protocol agent SHOULD forward the bundle by
invoking an adapter for a convergence layer protocol that does
NOT perform retransmission of data lost in transit. If the
bundle protocol agent has no access to such a convergence layer
adapter then this flag may be ignored, but in that case
application data units may arrive out of transmission order at
the destination (possibly degrading application performance) and/
or transmission bandwidth may be wasted on unnecessary
retransmission, reducing the effective throughput of the network.
3. If the 0x0008 bit of the ECOS block's Flags field is set to 1,
then the bundle protocol agent SHOULD forward the bundle by
invoking an adapter for a convergence layer protocol that DOES
perform retransmission of data lost in transit. If the bundle
protocol agent has no access to such a convergence layer adapter
then this flag may be ignored, but in that case application data
units may not arrive at the destination, possibly degrading
application performance.
4. If both the 0x0002 bit and the 0x0008 bit of the ECOS block's
Flags field are set to 1, then the bundle protocol agent SHOULD
forward the bundle by invoking an adapter for a convergence layer
protocol that functions as a bundle streaming service: whenever
loss is detected in "best-efforts" transmission, the lost data
are retransmitted for eventual out-of-order delivery in
background. If the bundle protocol agent has no access to such a
convergence layer adapter then this flag may be ignored, but in
that case application performance may be degraded.
5. If the bundle's Service Class is 2 (expedited), then the bundle
protocol agent MUST forward this bundle only after forwarding all
other bundles that are to be forwarded to the same node with
Service Class 2 and have explicit or implicit ordinal value that
is higher than or equal to the ECOS block's ordinal value.
Moreover, the bundle protocol agent MUST forward this bundle
before forwarding any other bundle that is to be forwarded to the
same node and either (a) has Service Class 2 and an explicit or
implicit ordinal value lower than the ECOS block's Ordinal Number
field or (b) has Service Class less than 2. An implicit ordinal
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value is the value for a bundle that has no valid ECOS block;
that value is 0.
The valid ECOS block of a received bundle that is to be forwarded to
another node MUST NOT be deleted from the bundle.
3.3. Bundle Delivery
When a bundle that contains an ECOS block is delivered to its final
destination, the values of ECOS block fields MAY be provided to the
application but otherwise have no impact on bundle delivery
procedures.
4. IANA Considerations
The IANA is requested to allocate a codepoint TBD for the Extended
Class of Service (ECOS) block in the Bundle Block Type registry
defined in [I-D.ietf-dtn-bpbis] and with reference to this
specification. The registration should appear as follows:
+----------+-------+-----------------------------+---------------+
| Bundle | Value | Description | Reference |
| Protocol | | | |
| Version | | | |
+----------+-------+-----------------------------+---------------+
| 7 | TBD | Extended Class of Service | [RFCXXXX] |
5. Security Considerations
Clearly the injection of bundles with the "critical" flag set to True
could increase the impact of a denial of service attack. As with all
such attacks, the best available defense is to require the use of
BPsec [I-D.ietf-dtn-bpsec] on all received bundles.
6. Normative References
[I-D.ietf-dtn-bpbis]
Burleigh, S., Fall, K., and E. J. Birrane, "Bundle
Protocol Version 7", draft-ietf-dtn-bpbis-31 (work in
progress), January 2021.
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[I-D.ietf-dtn-bpsec]
III, E. J. B. and K. McKeever, "Bundle Protocol Security
Specification", draft-ietf-dtn-bpsec-27 (work in
progress), February 2021.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC5050] Scott, K. and S. Burleigh, "Bundle Protocol
Specification", RFC 5050, DOI 10.17487/RFC5050, November
2007, <https://www.rfc-editor.org/info/rfc5050>.
Appendix A. Congestion Experienced
Section 2 of this specification reserves two ECOS flag bits as
Congestion Experienced (CE) indications and mandates their values be
set to 0. Further study on whether BPv7 would benefit from CE
indications can therefore be conducted in parallel with the
progression of this specification.
Authors' Addresses
Scott Burleigh
JPL, Calif. Inst. of Technology
4800 Oak Grove Drive, m/s 301-490
Pasadena, CA 91109
USA
Phone: +1 818 393 3353
Email: Scott.C.Burleigh@jpl.nasa.gov
Fred Templin
The Boeing Company
P.O. Box 3707
Seattle, WA 98124
USA
Phone: +1 425 802-9039
Email: fltemplin@acm.org
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