6lowpan G. Mulligan
Internet-Draft Proto6
Intended status: Standards Track C. Williams
Expires: September 9, 2010 D. Huo
ZTE USA
March 8, 2010
Mobility Considerations for 6LoWPAN
draft-williams-6lowpan-mob-02.txt
Abstract
There has been discussion recently within the 6LoWPAN community
regarding mobile usage scenarios. Mobility considerations is
required for the deployment of SmartGrids. The mobility analysis for
SmartGrid and 6lowpan deployment is required to ensure proper
performance for the mobile usage cases. Also, mobility in 6LoWPAN
sensor networks may present unique challenges to the 6LoWPAN
architecture. Hence it is best to have mobility as a consideration
upfront rather than an after thought in the development of 6LoWPAN
milestones. This document provides a mobility perspective to the
6LoWPAN sensor network architecture.
Status of this Memo
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Framework . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Extensions of the PAN Framework . . . . . . . . . . . . . 6
3.2. Global reachability and changing connectivity . . . . . . 8
4. Changing connectivity points of attachments . . . . . . . . . 10
5. Security of the mobile access network . . . . . . . . . . . . 12
5.1. Mobile security for the extended PAN . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative references . . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction
The Internet Protocol (IP) is rapidly becoming a more popular for
interoperable End-to-End Smart Grid Networks. Therefore, it is
important to understand the different uses of the IP suite in
Internet networking technologies for existing and emerging Smart Grid
applications. 6lowpan will be a central component of SmartGrids. The
IETF 6LoWPAN working group was formed in 2004 to address the
challenge of enabling wireless IPv6 communication over the newly
standardized IEEE 802.15.4 low-power radio for devices with limited
space, power and memory, such as sensor nodes. IEEE 802.15.4 radio
links, coupled with the interoperability and ubiquity of IP, will
lead to exciting new deployment scenarios for these low-power
networks. Sensor wireless networks will be integrated into wired
and/or wireless fixed infrastructure. The integration of these
sensor networks with the Internet and wireless infrastructure
networks increases the network capacity, coverage area and
application domains. Such an integration requires that 6LoWPAN
networks handle mobility scenarios.
Mobility in 6LoWPAN networks for SmartGrid and other usage scenarios
is being examined because users that are interested in sensor data
will not always be stationary. In addition, mobile users will need
to inject a sensor query into the 6LoWPAN network while they are
mobile. Mobile users will also need to retrieve a sensor response
from the 6LoWPAN network while they are mobile.
It has also been shown that sensor mobility can be exploited to
compensate for the lack of sensors and improve network coverage.
[MOBCOVERAGE] It has also been shown that mobility helps with
localization requirements by wireless sensor applications that depend
on nodes accurately determining their locations [MOBLOCAL].
Moreover, there has been a desire to deploy sensors mounted on mobile
platforms such as automobiles and planes.
The requirement for mobility and 6lowpan networks can be seen in
usage scenarios for Mobile Command, Control and Collaboration
systems: Public Safety Applications, Military Applications, Civilian
Applications, Educational Centers, Urban security protection system
("Secure Model City" initiatives) ?Commercial and Residential
Security Protection Systems, Metropolitan Mobile and Fixed Networks,
and Smart Grids (Traffic and Power).
Mobility will also play a role in the future interconnection
framework for 6LoWPAN networks as it is expected that internetworking
will not necessarily be limited to a way to transport information
from and to remote hosts. The foreseen degree of integration between
sensor networks may reach upper levels of the protocol stack, where
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one network may offer services to others (including communication
services). In such a setting, even 6LoWPAN sensor network components
may be heterogeneous, consisting of sensors with varied
functionalities, capabilities and interconnection requirements.
Currently, wireless sensor networks are beginning to be deployed at
an accelerated pace. It is not unreasonable to expect that in the
near future, many segments of the world will be covered with wireless
sensor networks that will be accessible via the Internet.
Integration of wireless sensor networks with wireless local area
networks and the Internet, while being important, comes with
connectivity and security issues.
What the authors have concluded through their extensive prototyping
and deployment, it is best to have mobility as a consideration
upfront rather than an after thought in the development of 6LoWPAN
milestones. This document provides a mobility perspective to the
6LoWPAN sensor network architecture.
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2. Terminology
See RFC3753 [RFC3753]for mobility terminology used in this document.
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3. Framework
3.1. Extensions of the PAN Framework
In practical deployment scenarios, 6LowPAN networks may not be
isolated independent PANs. A personal network will be logical
networks, defined by appropriate security associations. In practice
personal networks will have potential huge geographical and
topological span. Personal networks will consists of both ad-hoc and
infrastructure networks. It will be user centric with the PAN (i.e.,
Core PAN) as the central entity. An extension of the PAN framework
is provided in the diagram below.
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Extensions of the PAN Concept:
(Personal Network)
Local Foreign Devices Remote personal Devices
| | |
| | |
| ***********|*******|**
| * +-------|-----+ | *
* | V | | *
**********|********** * | Home Network| | *
* +------|----+ * *********** +-------------+ | *
* |Smart |Bldg | * * / | *
* | 0 V | * * / ************|**
* | 0 | * * / * |
* +-----------+ * +------------*----------------*----+ |
* * | * * | |
* | ***************** ************|***
* | | Interconnecting Structure | | *
* \ |(Internet, WLAN, 3G, Ad-hoc, etc) | +----|-+*
* | | | | V |*
* | | |-|Corp |*
* | | ****** | Network|*
* +-*----*---------------------------+ +------+*
* * * *****
* (user) ***** * ___ *
* +-------------+ * * /___ *****
* | Core PAN | * * +-----------+ +--------------+ *
* | 0 | *_____ * | PAN |__ |Vehicular Area| *
* | 0 0 | * /___*__| 0 | /__ | Network | *
* | 0 | * * | 0 0 | | 0 | *
* +-------------+ * * +--------\--+ +/-------------+ *
* * * \ / *
********************** **************\*****/******************
\ /
\ /
|
Remote Foreign Devices
Figure 1
In this extended PAN framework a diverse personal network is
presented. The illustration local foreign devices in a smart
building which are only accessed through the user's core PAN. No
direct permanent connectivity is provided to these devices. The
diagram also illustrates a PAN connected to a 3G network as well as a
vehicular area network of sensors. Individual sensor nodes from the
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PAN and Vehicular Area network may join and change PANs. Remote
foreign devices may be accessed either by the Core PAN directly
connecting to these ad-hoc networks or through the interconnecting
structure. The corporate and home network are connected to the
Interconnecting structure and may have remote personal devices. The
extension of the PAN framework presented shows a diverse and huge
geographical and topological span with a mobility presence various
aspects of the architecture.
3.2. Global reachability and changing connectivity
6LoWPAN networks may require to be fully integrated into a dynamic
mobile heterogeneous framework for ensuring global reachability to
the individual 6LoWPAN nodes
Sensor networks share several characteristics of ad-hoc scenarios in
that sensor nodes are capable of receiving and forwarding packets to
their peers. However, tiny sensor devices may have more stringent
processing power, memory and energy constraints than other types of
ad hoc networks. These constraints generally imply the need for a
hierarchical ad-hoc network structure in which low-tier sensor nodes
connect to the Internet via one or more levels of gateway devices.
In this draft, we assume that each autonomous network of wireless
sensor devices will have one gateway device. This gateway device is
responsible for media conversion (from 802.15.4 to another link layer
technology, such as 802.11, and vice versa) and for route advertising
to the outside world, which may be a wireless local area network
connected to the Internet.
There will be deployment scenarios where 6LoWPAN networks have
persistent connectivity to the outside world via its gateway device.
At the same time, there may be deployment scenarios that require that
a 6LoWPAN network change its point of attachment to the outside world
from an IP perspective. This may occur, for example, when a sensor
network is part of a moving vehicle which may roam from one wireless
local area network to another wireless local area network with
different IP network prefixes. By the same token, an autonomous
sensor network may be deployed in a location with no wireless (or
wired) local area networks. In this case, its connectivity to the
outside world, when it exists, will be intermittent. Also, the
intermittent connectivity to the Internet may have different
characteristics each time they occur. For example, connectivity of
the 6LoWPAN network to the internet may be realized via an agent
(e.g., a vehicle) which features a satellite interface. At different
points in time, different agents may provide connectivity functions;
in which case the point of attachment of the sensor network may
correspond to a different IP address prefix. Note that the two
scenarios depicted above are equivalent from an IP connectivity point
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of view. In the first scenario, the sensor network moves from one
access network to another. In the second scenario, agents with
different IP addresses provide access functions to a stationary
sensor network. In either case, the IP address of the point of
attachment will change over time.
Here, the requirement is to provide global reachability to the
6LoWPAN nodes no matter where the correspondent peers are located,
and no matter what their point of attachment is. The 6LoWPAN nodes
must still be reachable with their originally prescribed IPv6
addresses.
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4. Changing connectivity points of attachments
Mobility is a fundamental characteristic of a wireless network with
mobile users, and it is therefore anticipated that future networks
will provide mobility support as an integrated and ubiquitous
service. Mobility scenarios anticipated in future networks include
simple end-user migration from one subnetwork to another (as in
cellular or WLAN hot-spot services), as well as more complex mobility
patterns involving movement of radio routers and sensor network
clusters. Collections of sensor networks must be reachable as they
move across different wireless domains. Scalable and accurate
indirection schemes need to be devised to allow for this
functionality.
Mobile IPv6 network mobility (NEMO) [RFC3963] defines a process that
enables Mobile Networks to attach to different points in the
Internet. The protocol is an extension of Mobile IPv6 and allows
session continuity for every node in the Mobile Network as the
network moves. Use of NEMO will enable all 6LoWPAN nodes to be
accessible, no matter what the current point of attachment to the
wide area IP network is.
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Diagram of NEMO and 6LoWPAN integration is provided. [RFC4944] ,
e.g.,
(Nodes in the 6LoWPAN network)
* * * ... * * *
6LoWPAN
network
|
|
+-------------+
| NEMO Client |
+-------------+
|
|
+--------------------+
|Access Network (AR) |
+--------------------+
|
+-------------------+
| Internet |
+-------------------+
|
|
+---------------+
| Correspondent |
| Node |
+---------------+
Figure 2
The NEMO client integration enables the sensor application residing
on some correspondent node provides global reachability to the
6LoWPAN nodes even when the access network for the 6LoWPAN network
changes.
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5. Security of the mobile access network
6LoWPAN networks may be deployed remotely in non-traditional
scenarios. Access networks for these 6LoWPAN networks may be
intermittently available, and their IP address prefixes may change
over time. This means that the IP layer has new requirements to be
able to provide access to these 6LoWPAN networks via changing access
networks and to do so in a secure manner.
5.1. Mobile security for the extended PAN
IPv6 nodes use the Neighbor Discovery protocol (ND) [RFC2461] to
discover other nodes on the link, to determine the link-layer
addresses of other nodes on the link, to find routers, and to
maintain reachability information about the paths to active
neighbors. If proper authentication mechanisms are not in place,
straight use ND in sensor networks may introduce security
vulnerabilities. The IETF has created the Secure Neighbor Discovery
Protocol (SeND) [RFC3971] to provide authentication services for the
ND. SeND may be used as a solution between the NEMO client residing
in the Sensor network and the access network which will have a SeND
service for providing authenticated NEMO autoconfiguration. In this
solution, NEMO with SeND may provide a means by which the access
network is properly authorized to connect to the sensor network.
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Diagram of NEMO, SEND and 6LoWPAN integration is provided. [RFC3971]
, e.g.,
(Nodes in the 6LoWPAN network)
* * * ... * * *
6LoWPAN
network
|
|
+---------+
| NEMO & |
| SEND |
+---------+
|
|
+--------------------+
|Access Network (AR) |
| With SEND |
+--------------------+
|
+-------------------+
| Internet |
+-------------------+
|
|
+---------------+
| Correspondent |
| Node |
+---------------+
Figure 3
Authentication process specified in SeND may involve the use of
server infrastructure for certificate management purposes. It may be
impractical to have a server infrastructure in place for
authentication in the deployment scenarios discussed in this draft.
Therefore, the Cryptographically Generated Addresses (CGA) [RFC3972]
option of SeND may be a useful tool for 6LoWPAN networks in providing
authentication services.
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6. Security Considerations
Security assumptions for stationary 6LoWPAN networks are inadequate
for scenarios whereby mobility is introduced. Mobile users injecting
sensor queries into the 6LoWPAN network while they are mobile pose
new security considerations. This is also true when mobile users are
retrieving sensor responses from the 6LoWPAN network while they are
mobile. Privacy and authentication is also an area for mobile
security analysis. For example, privacy between the 6LoWPAN network
point of attachment and the local area access network may be
established using IPsec. More security analysis is required.
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7. Conclusion
Practical deployment scenarios require mobility of both individual
sensor nodes but also connectivity points for the PANs. Mobility as
an architectural consideration for 6LowPAN must be consider upfront
rather than an after thought in the development of 6LoWPAN
milestones. Finally, techniques developed for other mobile networks
may not be applicable in all usage cases, as in these networks power
conservation is not a requirement.
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8. Acknowledgement
Acknowledgement of Derya Cansever for his input and contributions to
initial discussion on mobility for sensors.
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9. References
9.1. Normative references
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998.
[RFC3753] Manner, J. and M. Kojo, "Mobility Related Terminology",
RFC 3753, June 2004.
[RFC3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
Thubert, "Network Mobility (NEMO) Basic Support Protocol",
RFC 3963, January 2005.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, September 2007.
9.2. Informative References
[MOBCOVERAGE]
Liu, B., Brass, P., Dousse, O., Nain, P., and D. Towsley,
"Mobility Improves Coverage of Sensor Networks", Mobihoc
2005, Proceedings of MobiHoc 2005, May 2005.
[MOBLOCAL]
Hu, L. and D. Evans, "Localization for Mobile Sensor
Networks", MobiCom 2004, Tenth Annual International
Conference on Mobile Computing and Networking,
September 2004.
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Authors' Addresses
Geoff Mulligan
Proto6
Consultant
Colarodo Springs, CO 80901
USA
Phone: 719.593.2992
Email: geoff@proto6.com
Carl Williams
ZTE USA
Consultant
Palo Alto, CA 94306
USA
Phone: +1.650.279.5903
Email: carlw@mcsr-labs.org
David Huo
ZTE USA
33 Wood Ave S
Metuchen, NJ 08840
USA
Phone: +1.732.632.9880
Email: david.huo@zteusa.com
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