6LoWPAN
Overview, Assumptions, Problem
Statement & Goals
(draft-kushalnagar-lowpan-goals-assumptions-00)
Nandu Kushalnagar & Gabriel Montenegro
Overview of LoWPAN
• A simple low throughput wireless network
comprising typically low cost and low power
devices
• Devices in the network typically work together to
connect the physical environment to real world
applications, e.g., wireless sensors networks
• Common topologies include – star, mesh, and
combinations of star and mesh
• The Phy and MAC layers conform to IEEE
802.15.4-2003 standard
LoWPAN architecture
Typical applications
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Equipment health monitoring
Environment monitoring
Security
Home
Building automation
6LoWPAN characteristics
• Small packet size
• 16-bit short or IEEE 64-bit extended media
access control addresses
• Low bandwidth. (250/40/20 kbps)
• Topologies include star and mesh
• Low power, typically battery operated
• Relatively low cost
• Networks are ad hoc & devices have limited
accessibility and user interfaces
• Inherently unreliable due to nature of devices in
the wireless medium
Assumptions
• Devices conform to IEEE 802.15.4-2003
standard
• Devices “typically” send small amounts of
data
• Typically “constrained” devices
(computing, power, cost, memory, etc)
Problems
• No method exists to make IP run over IEEE 802.15.4
networks
– Worst case .15.4 PDU 81 octets, IPv6 MTU requirements 1280
octets
• Stacking IP and above layers “as is” may not fit within
one 802.15.4 frame
– IPv6 40 octets, TCP 20 octets, UDP 8 octets + other layers
(security, routing, etc) leaving few bytes for data
• Not all adhoc routing protocols may be immediately
suitable for LoWPAN
– DSR may not fit within a packet, AODV needs more memory, etc
• Current service discovery methods “bulky” for LoWPAN
– Primarily XML based that needs computing, more memory, etc
• Limited configuration and management necessary
• Security for multi hop needs to be considered
Goals
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Define adaptation (frag/reassembly) layer to match
IPv6 MTU requirements
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Specify methods to do IPv6 stateless address auto
configuration
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Specify/use header compression schemes.
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Specify implementation considerations and best
methods of an IPv6 stack
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Methods for meshing on LoWPAN below IP*
Not currently in charter
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Use/adapt network management technologies for
LoWPANs
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Specify encoding/decoding (or perhaps new protocols)
for device discovery mechanisms
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Document LoWPAN security threats
BACKUP
Overview of LoWPAN
• A simple low cost wireless network of devices that have limited
power and relaxed throughput requirements.
• Conforms to IEEE 802.15.4-2003
• Typical usages of LoWPAN networks are –
– Networking transducers (sensing & actuation, eg. smart sensors –
Such usages may need in network processing)
– Networking simple controls (home controls)
– Networking complex controls (light & switch & motion sensor)
• Standards based Phy and MAC exist for LoWPAN networks viz.,
IEEE802.15.4 and *possibly* IEEE802.15.3
• Topologies that are commonplace today include – star, mesh, and
combinations of star and mesh
• Today LoWPAN’s are already becoming a reality
LoWPAN - A different *beast* of networks compared to
traditional networks !
Challenges of LoWPAN
Impact
Analysis
Addressing
Routing
Security
Network
management
Low power
(1-2 years lifetime on
batteries)
Storage
limitations, low
overhead
Periodic sleep
aware routing,
low overhead
Simplicity (CPU
usage), low
overhead
Periodic sleep aware
management, low
overhead
Low cost
(<$10/unit)
Stateless address
generation
Small or no
routing tables
Ease of Use,
simple
bootstrapping
Space constraints
Low bandwidth
(<300kbps)
Compressed
addresses
Low routing
overhead
Low packet
overhead
Low network
overhead
High density
(<2-4? units/sq ft)
Large address
space – IPv6
Scalable and
routable to *a
node*
Robust
Easy to use and
scalable
IP network interaction
Address routable
from IP world
Seamless IP
routing
Work end to end
from IP network
Compatible with
SNMP, etc
Subtleties of IEEE 802.15.4
• Small packet size – 128 byte including
MAC, 103 bytes of payload
• Uses 64 bit MAC addresses, but has
provisions for 16 bit short addresses
• Support for multiple topologies
• Supports AES block cypher in several
modes (AES-CCM-64 mandatory)
• Data rates between 20kbps to 250kbps
• Range between 10m to 30m
Why IP?
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Most of the IP based technologies
already exist, well known and proven to
be working.
The pervasive nature of IP networks
allows use of existing infrastructure.
Intellectual property conditions for IP
networking technology is either more
favorable or at least better understood
than proprietary and newer solutions.
Why IPv6?
• Pros –
– More suitable for higher density (futuristically 2 orders of
magnitude larger than traditional networks)
– Statelessness mandated
– No NAT necessary (adds extra cost to the cost prohibitive WSN)
– Possibility of adding innovative techniques such as
location aware addressing
• Cons
– Larger address width (Having efficient address compression
schemes may alleviate this con)
– Complying to IPv6 node requirements (IPSec is mandated)
Why not IPv4?
• Limited address space
• NAT functionality needs gateways, etc
leads to more cost
• Statelessness not mandated
• Gab/Geoff …. any more ideas?
Goals
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Protocol data units may be as small as 81 bytes, far below IP and above
In all cases, reuse existing protocols before creating new ones
Address mismatch between MTU sizes of LoWPAN’s and IPv6
Support stateless auto configuration of IPv6 addressing (location aware?)
Specify header compression (use of existing and/or new techniques eg.
header reconstruction, header short circuiting, etc)
Define security mechanisms, security configuration and bootstrapping
Specify network management (SNMP?)
Specify routing suitable for LoWPAN networks (MANET?, topology
aware, Below L3 or above L3?, etc)
Specify methods to enable and disable IPv6 over LoWPAN.
Specify hooks within routing layer to enable in network processing
Specify light weight discovery mechanisms
Specify any changes needed for L3 + layers
Specify implementation considerations and BKM’s of an IPv6 stack
Drafts of 6LoWPAN
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Define a *shim* layer below IP
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Fragmentation/Reassembly to satisfy IPv6 MTU of 1280 bytes
Routing including mesh
Header compression mechanisms
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Header configuration to enable/disable IPv6
Define a IPv6 LoWPAN Profile
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Address IPv6 node requirements
Define
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Header reconstruction for intra PAN communication
Header short circuiting
L2/L3 interface mechanism
Appropriate security services
Routing considerations
Network management with SNMP
Implementation considerations
Miscellaneous (may be subsequent drafts)
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Hooks from L3 for in network processing (especially critical for WSN)
Transport layer (UDP / TCP)
Security configuration
Light weight discovery mechanisms
More?