Internet DRAFT - draft-irtf-dtnrg-ecos
draft-irtf-dtnrg-ecos
Network Working Group S. Burleigh
Internet-DraftJet Propulsion Laboratory, California Institute of Technol
Intended status: Experimental July 01, 2013
Expires: January 02, 2014
Bundle Protocol Extended Class Of Service (ECOS)
draft-irtf-dtnrg-ecos-05
Abstract
This document describes an extension to the Delay-Tolerant Networking
(DTN) Bundle Protocol (BP) that marks bundles with class-of-service
designators beyond those defined for the BP primary block. The
extended 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 flow label.
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 January 02, 2014.
Copyright Notice
Copyright (c) 2013 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 Extension Block Format . . . . . . . . . . . . . . . . . 3
3. Processing . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Bundle Origination . . . . . . . . . . . . . . . . . . . 5
3.2. Bundle Forwarding . . . . . . . . . . . . . . . . . . . . 5
3.3. Bundle Delivery . . . . . . . . . . . . . . . . . . . . . 7
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. Normative References . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
This document describes an extension to the Delay-Tolerant Networking
(DTN) Bundle Protocol (BP) [RFC5050] that marks bundles with class-
of-service designators beyond those defined for the BP primary block.
The bundle protocol specification defines 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 operations, additional
variation 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
transmitting the bundle along every potential route to its
destination, rather than only on the route that would normally be
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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 "flow label" 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 to Bundle Protocol is
designed to provide these additional class of service designators.
2. ECOS Extension Block Format
The ECOS block conforms to sections 4.5.2 and 4.6 of [RFC5050],
constrained as follows:
o Block type code is 19. (See "IANA Considerations" below.)
o 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.
o The block MUST NOT contain any EID references.
o Block data length is 2 + N, where N is zero if the ECOS block
contains no flow label (as described below) and is otherwise the
length of the SDNV in which that flow label is represented.
The block data of the ECOS block comprises at least two and possibly
three fields.
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The first field of the block data is an 8-bit "flags" byte. The bits
of the flags signify the following conditions:
o The 0x01 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 destinaion.
o The 0x02 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-efforts"
basis, without retransmission.
o The 0x04 bit, if True, indicates that the "ordinal" byte of this
ECOS block (the byte immediately following the "flags" byte) is
followed by a numeric "flow label" in SDNV representation.
o The 0x08 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 All other bits of the "flags" byte are reserved for future use.
Note that both the 0x02 and 0x08 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-
efforts" transmission, the lost data are retransmitted for eventual
out-of-order delivery in background.
The "flags" byte is followed by an 8-bit "ordinal" byte, containing
an unsigned "ordinal" number in the range 0-255. For a bundle whose
standard class of service is 2 ("expedited"), the ordinal number
indicates the relative priority of this bundle among all other
expedited bundles: ordinal value 100 indicates greater urgency than
ordinal value 99, and so on. Ordinal value 255 is reserved for
custody signals. For a bundle whose standard class of service is not
2, the ordinal value has no significance.
If the 0x04 bit of the ECOS block's "flags" byte is True, the third
field of the block data is a numeric "flow label" value in SDNV
representation. The significance of the flow label is an
implementation matter. Notionally, the flow label 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
flow label whose significance is unknown is an implementation matter.
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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 flow label, then the 0x04 bit of the
block's "flags" byte MUST be set to 1 (True) and the flow label MUST
be a numeric value represented as a valid SDNV. Otherwise the 0x04
bit of the block's flags byte MUST be set to 0 (False).
The ordinal byte of the ECOS block MUST contain an unsigned integer
in the range 0-255. If the bundle of which the ECOS block is a part
is a custody signal, then the value of the ordinal byte MUST be 255;
otherwise, the value of the ordinal bit MUST be in the range 0-254.
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 0x01 bit of the ECOS block's flags byte is set to 1, then
exactly one copy of the bundle SHOULD be forwarded to every
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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
standard class of service were 2 ("expedited") and its ordinal
value were 254, 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 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 0x02 bit of the ECOS block's flags byte 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 0x04 bit of the ECOS block's flags byte 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 0x02 bit and the 0x04 bit of the ECOS block's flags
byte are set to 1, then the bundle protocol agent SHOULD forward
the bundle by invoking an adapter for a convergence layer
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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 class of service 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 and have got class of service 2 and have explicit or
implicit ordinal byte value that is higher than or equal to the
ECOS block's ordinal byte 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 got
class of service 2 and explicit or implicit ordinal byte value
lower than the ECOS block's ordinal byte value or (b) has got
class of service less than 2. An implicit ordinal byte value is
the ordinal byte 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
This specification allocates a codepoint from the Bundle Block Type
Codes registry defined in [I-D.irtf-dtnrg-iana-bp-registries]. The
additional entry in the Bundle Block Type Codes Registry assigns
value 19 to the Extended Class of Service block and references this
specification.
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 valid Bundle
Authentication Blocks on all received bundles.
6. Normative References
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, January 2005.
[RFC5050] Scott, K. and S. Burleigh, "Bundle Protocol
Specification", RFC 5050, November 2007.
Author's Address
Scott Burleigh
Jet Propulsion Laboratory, California Institute 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
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