Internet DRAFT - draft-bormann-6lowpan-roadmap
draft-bormann-6lowpan-roadmap
6LoWPAN Working Group C. Bormann
Internet-Draft Universitaet Bremen TZI
Intended status: Standards Track April 13, 2013
Expires: October 15, 2013
6LoWPAN Roadmap and Implementation Guide
draft-bormann-6lowpan-roadmap-04
Abstract
6LoWPAN is defined in RFC 4944 in conjunction with a number of
specifications that are currently nearing completion. The entirety
of these specifications may be hard to understand, pose specific
implementation problems, or be simply inconsistent.
The present guide aims to provide a roadmap to these documents as
well as provide specific advice how to use these specifications in
combination. In certain cases, it may provide clarifications or even
corrections to the specifications referenced.
This guide is intended as a continued work-in-progress, i.e. a long-
lived Internet-Draft, to be updated whenever new information becomes
available and new consensus on how to handle issues is formed.
Similar to the ROHC implementation guide, RFC 4815, it might be
published as an RFC at some future time later in the maintenance
curve of the specifications.
This document does not describe a new protocol or attempt to set a
new standard of any kind - it mostly describes good practice in using
the existing specifications, but it may also document emerging
consensus where a correction needs to be made.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on October 15, 2013.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
2. 6LoWPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Optional components of 6LoWPAN . . . . . . . . . . . . . 3
2.2. 6LoWPAN MIB work . . . . . . . . . . . . . . . . . . . . 4
3. 6LoWPAN family . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. 6LoWPAN over Bluetooth Low Energy (BT-LE) . . . . . . . . 4
3.2. 6LoWPAN over DECT Ultra Low Energy (DECT-ULE) . . . . . . 5
3.3. 6LoWPAN over G.9959 (lowpanz) . . . . . . . . . . . . . . 5
4. 6LoWPAN MTU . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. PAN identifiers in IPv6 addresses . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
(To be written - for now please read the Abstract.)
1.1. Terminology
This document is a guide. However, it might evolve to make specific
recommendations on how to use standards-track specifications.
Therefore: The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
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"OPTIONAL" in this document are to be interpreted as described in RFC
2119. They indicate requirement levels for compliant 6LoWPAN
implementations [RFC2119]. Note that these keywords are not only
used where a correction or clarification is intended; the latter are
explicitly identified as such.
The term "byte" is used in its now customary sense as a synonym for
"octet".
2. 6LoWPAN
What is a 6LoWPAN?
The term, originally just the name of the IETF Working Group (WG)
that created the specifications, nowadays refers to a specific way of
building IP-connected wireless networks for embedded use cases. The
6LoWPAN core specifications are:
o [RFC4944], as updated by
o [RFC6282] and
o [RFC6775].
While [RFC4944] defines 6LoWPAN specifically for IEEE 802.15.4
networks, 6LoWPAN concepts have been applied to other PHY/MAC layers.
6LoWPANs MAY use additional protocols, such as [RFC6550] for routing,
or [I-D.ietf-core-coap] for application data transfer. However, the
"6LoWPANness" of a network is caused by adherence to the core
specifications.
2.1. Optional components of 6LoWPAN
Additional sub-protocols are being discussed in the IETF that may
become optional protocols in 6LoWPANs.
For instance, [I-D.bormann-6lowpan-ghc] defines an extension to
[RFC6282] that enables header compression of additional headers and
header-like protocols, including ICMPv6 and RPL.
One other recent proposal, in a much more nascent stage, that may be
of interest to application designers targeting link layers with small
frame sizes is Adaptation Layer Fragmentation Indication (ALFI),
[I-D.bormann-intarea-alfi].
The present document will track these sub-protocols and be amended
once the sub-protocols reach formal status in the IETF.
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2.2. 6LoWPAN MIB work
For management of 6LoWPAN networks, a MIB is being proposed in
[I-D.schoenw-6lowpan-mib]. Besides the usual SMIv2 MIB format that
directly enables management access via SNMP, this draft also
demonstrates a JSON format using a version of the MIB translated into
YANG [RFC6020] as defined in [RFC6643] and made available using the
JSON representation defined in [I-D.lhotka-netmod-yang-json]. This
may facilitate using CoRE protocols for management access
[I-D.ersue-constrained-mgmt], reducing the number transfer protocols
that need to be implemented on a constrained node.
3. 6LoWPAN family
In addition to the support for IEEE 802.15.4 provided by [RFC4944],
additional PHY/MAC layers outside IEEE 802.15.4 (or even 802.15) are
being addressed by 6LoWPAN technology.
E.g., [I-D.ietf-6lowpan-btle] applies 6LoWPAN technology to Bluetooth
Low Energy ("Bluetooth Smart"). As this has passed both 6LoWPAN
Working-Group and IETF Last Call and has received one round of IESG
consideration (now waiting for the allocation of a number from the
BT-SIG), it is becoming part of the "6LoWPAN family" as a companion
specification to [RFC4944], if not part of the (IEEE 802.15.4
focused) term 6LoWPAN itself.
At an earlier stage of work, [I-D.mariager-6lowpan-v6over-dect-ule]
aims to define 6LoWPAN technology for DECT ULE (Ultra Low Energy),
which might become another companion spec to [RFC4944]. Similarly,
[I-D.brandt-6man-lowpanz] is a first draft defining 6LoWPAN
technology for the ITU-T G.9959 radio.
In the further evolution of the 6LoWPAN family, we have to be careful
what changes apply to all members of the family, and which are PHY/
MAC specific.
3.1. 6LoWPAN over Bluetooth Low Energy (BT-LE)
[I-D.ietf-6lowpan-btle] similarly specifies the combination of
o [RFC4944], as updated by
o [RFC6282] and
o [RFC6775].
as the basis for IPv6 over BT-LE, removing a couple of features from
[RFC4944] as they are covered by or become unnecessary in BT-LE:
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o Mesh header
o Fragmentation
3.2. 6LoWPAN over DECT Ultra Low Energy (DECT-ULE)
[I-D.mariager-6lowpan-v6over-dect-ule] is stabilizing in parallel to
the base documents that are maturing within ETSI. While silicon is
already available, complete systems with final firmware (and thus
stable specs) are expected within 2012.
3.3. 6LoWPAN over G.9959 (lowpanz)
[I-D.brandt-6man-lowpanz] was recently discussed at IETF86 in Orlando
and will soon receive an update based on this discussion. The G.9959
radio used in this specification operates in various regionally
available frequencies around 900 MHz ("sub-GHz") and is best known
for its use in the Z-Wave suite of products. As with BT-LE, this MAC
layer already defines a Segmentation and Reassembly (SAR) layer, so
packets larger than the G.9959 MAC PDU can be transmitted without the
need for [RFC4944] fragmentation. Similarly, MAC layer mesh
forwarding is available for G.9959 already.
4. 6LoWPAN MTU
IPv6 defines a minimal value for the "Minimum Transmission Unit",
MTU, of 1280 bytes. This means that every IPv6 network must be able
to transfer a packet of at least 1280 bytes of IPv6 headers and data
without requiring fragmentation.
A common Internet MTU is 1500 bytes (motivated by the Ethernet MTU).
The gap between 1280 and 1500 allows tunneling protocols to insert
headers on the way from the source of a packet to a destination
without breaking the overall MTU of the path. As various tunneling
protocols do indeed insert bytes, it is unwise to simply assume an
end-to-end MTU of 1500 bytes even with the current dominance of
Ethernet. Path MTU discovery [RFC1981] [RFC4821] has been defined to
enable transport protocols to find an MTU value better than 1280
bytes, but still reliably within the MTU of the path being used.
Path MTU discovery places, however, additional strain on constrained
nodes, which therefore may want to stick with an MTU of 1280 bytes
for all IPv6 applications.
6LoWPAN was designed as a stub network, not requiring any tunneling.
As IEEE 802.15.4 packets are rather small (127 bytes maximum at the
physical layer, minus MAC/security and adaptation layer overhead),
1280 bytes was already considered a somewhat large packet size.
Therefore, the 6LoWPAN network MTU was simply set at the minimum size
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allowable by IPv6, 1280 bytes, although the 6LoWPAN fragmentation
mechanism is able to support packets with total lengths (including
the initial IPv6 header) of up to 2047 bytes.
As a more recent development, some modes of operation of the RPL
protocol [RFC6550] do indeed operate by tunneling data packets
between RPL routers. Maintaining the MTU visible to applications at
1280 therefore requires making a larger MTU available to the tunnels.
6LoWPAN routers that employ RPL therefore MUST support a more
appropriate MTU between routers that make use of tunneling between
them. [The specific MTU value is TBD, to be chosen between 1280 and
2047 based on RPL considerations that need to be added to this
document.]
5. PAN identifiers in IPv6 addresses
[RFC4944] incorporates PAN identifiers in IPv6 addresses created from
16-bit MAC addresses, in a somewhat awkward way (one of the 16 bits
needs to be cleared to enable the U/L bit.).
As the use of PAN identifiers in 6LoWPAN networks has since become
less and less meaningful, [RFC6282] provides specific support only
for interface IDs of the form 0000:00ff:fe00:XXXX, i.e. PAN
identifiers of zero. (Other forms can be supported by creating
sufficiently long pieces of compression context information for each
non-zero PAN identifier; however there is a limited number of context
elements and each consumes space in all nodes of a 6LoWPAN.)
It is therefore RECOMMENDED to employ a PAN identifier of zero with
6LoWPAN.
(While this discussion is specific to IEEE 802.15.4 networks, the
recommendation to build short addresses in a way that enables
[RFC6282] compression may apply to other PHY/MAC technologies as
well.)
6. IANA Considerations
This document has no actions for IANA.
7. Security Considerations
(None so far; this section will certainly grow as additional security
considerations beyond those listed in the base specifications become
known.)
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8. Acknowledgements
(The concept for this document is borrowed from [RFC4815], which was
invented by Lars-Erik Jonsson. Thanks!)
9. References
9.1. Normative References
[I-D.brandt-6man-lowpanz]
Brandt, A. and J. Buron, "Transmission of IPv6 packets
over ITU-T G.9959 Networks", draft-brandt-6man-lowpanz-00
(work in progress), February 2013.
[I-D.ietf-6lowpan-btle]
Nieminen, J., Savolainen, T., Isomaki, M., Patil, B.,
Shelby, Z., and C. Gomez, "Transmission of IPv6 Packets
over BLUETOOTH Low Energy", draft-ietf-6lowpan-btle-12
(work in progress), February 2013.
[I-D.mariager-6lowpan-v6over-dect-ule]
Mariager, P. and J. Petersen, "Transmission of IPv6
Packets over DECT Ultra Low Energy", draft-mariager-
6lowpan-v6over-dect-ule-02 (work in progress), May 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, September 2007.
[RFC6282] Hui, J. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
September 2011.
[RFC6775] Shelby, Z., Chakrabarti, S., Nordmark, E., and C. Bormann,
"Neighbor Discovery Optimization for IPv6 over Low-Power
Wireless Personal Area Networks (6LoWPANs)", RFC 6775,
November 2012.
9.2. Informative References
[I-D.bormann-6lowpan-ghc]
Bormann, C., "6LoWPAN Generic Compression of Headers and
Header-like Payloads", draft-bormann-6lowpan-ghc-06 (work
in progress), March 2013.
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[I-D.bormann-intarea-alfi]
Bormann, C., "Adaptation Layer Fragmentation Indication",
draft-bormann-intarea-alfi-03 (work in progress), March
2013.
[I-D.ersue-constrained-mgmt]
Ersue, M., Romascanu, D., and J. Schoenwaelder,
"Management of Networks with Constrained Devices: Problem
Statement, Use Cases and Requirements", draft-ersue-
constrained-mgmt-03 (work in progress), February 2013.
[I-D.ietf-core-coap]
Shelby, Z., Hartke, K., and C. Bormann, "Constrained
Application Protocol (CoAP)", draft-ietf-core-coap-14
(work in progress), March 2013.
[I-D.lhotka-netmod-yang-json]
Lhotka, L., "Modeling JSON Text with YANG", draft-lhotka-
netmod-yang-json-01 (work in progress), April 2013.
[I-D.schoenw-6lowpan-mib]
Schoenwaelder, J., Sehgal, A., Tsou, T., and C. Zhou,
"Definition of Managed Objects for IPv6 over Low-Power
Wireless Personal Area Networks (6LoWPANs)", draft-
schoenw-6lowpan-mib-03 (work in progress), February 2013.
[RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
for IP version 6", RFC 1981, August 1996.
[RFC4815] Jonsson, L-E., Sandlund, K., Pelletier, G., and P. Kremer,
"RObust Header Compression (ROHC): Corrections and
Clarifications to RFC 3095", RFC 4815, February 2007.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, March 2007.
[RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the
Network Configuration Protocol (NETCONF)", RFC 6020,
October 2010.
[RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R.,
Levis, P., Pister, K., Struik, R., Vasseur, JP., and R.
Alexander, "RPL: IPv6 Routing Protocol for Low-Power and
Lossy Networks", RFC 6550, March 2012.
[RFC6643] Schoenwaelder, J., "Translation of Structure of Management
Information Version 2 (SMIv2) MIB Modules to YANG
Modules", RFC 6643, July 2012.
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Author's Address
Carsten Bormann
Universitaet Bremen TZI
Postfach 330440
Bremen D-28359
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
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