6LoWPAN(Introduction, Problem Statement &

Goals)

Nandakishore KushalnagarIntel Corporation

What is LoWPAN?• LoWPAN is a wireless network comprising low power (small batteries

for months or even years) and low cost (<$10) devices • Typical usages of LoWPAN networks are –

– Networking transducers (sensing & actuation, eg. smart sensors – Such usages may need in network processing)

– Networking simple controls (light & switch)– Networking complex controls (light & switch & motion sensor)

• Standards based Phy and MAC exist for LoWPAN networks viz., IEEE802.15.4 and *possibly* IEEE802.15.3b

• Topologies that are commonplace today include – star, mesh, and combinations of star and mesh

• Today LoWPANs are already becoming a reality

LoWPAN - A different *beast* compared to traditional networks !

Challenges of LoWPAN

Space constraintsEase of Use, simple bootstrapping

Small or no routing tables

Stateless address generation

Low cost

(<$10/unit)

Periodic sleep aware management, low overhead

Simplicity (CPU usage), low overhead

Periodic sleep aware routing, low overhead

Storage limitations, low overhead

Low power

(1-2 years lifetime on batteries)

Compatible with SNMP, etc

Work end to end from IP network

Seamless IP routing

Address routable from IP world

IP network interaction

Easy to use and scalable

RobustScalable and routable to *a node*

Large address space – IPv6

High density

(<2-4? units/sq ft)

Low network overheadLow packet overhead

Low routing overhead

Compressed addresses

Low bandwidth (<300kbps)

Network management

SecurityRoutingAddressingImpact

Analysis

Subtleties of IEEE 802.15.4

• Small packet size –

– Max MAC frame size: 127 bytes

– Max MAC payload: 102 bytes

– With security (worst case): 81 bytes• 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 authenticated encryption mandatory)• Data rates from 20kbps to 250kbps• Range from 10m to 30m

Other potential LoWPAN standards

• IEEE 802.15.3b a.k.a. UWB supporting higher bit rate emerging

• Maybe others ?

• In all cases, when possible reuse existing protocols before creating new ones

• Address mismatch between MTU sizes of LoWPANs and IPv6• Support stateless auto configuration of IPv6 addressing (and

perhaps other schemes like location-aware, etc)• Specify header compression (use existing and/or new techniques

such as header reconstruction, header short circuiting, etc)• Define security model, mechanisms, configuration procedures

and bootstrapping• Specify network management (SNMP?)• Specify routing suitable for LoWPAN networks (MANET?,

topology aware, Below L3 and/or above L3?, etc)• Specify methods to enable and disable IPv6 over LoWPAN. • Specify hooks between L3 and higher layers?• Specify lightweight discovery mechanisms• Specify requirements and potential changes at L3 and above

(e.g., issues with reliable data transfer)• Specify implementation considerations and best common

practices of an IPv6 stack

Goals of 6LoWPAN

Why IP?

• 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

– IEEE 64 bit address subsumed into IPv6 address

• 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• Not as compressible

• NAT functionality needs gateways, etc leads to more cost

• Statelessness not mandated

Backup

Drafts of 6LoWPAN

• Define a *shim* layer below IP– Fragmentation/Reassembly to satisfy IPv6 MTU of 1280 bytes– Routing including mesh– Header compression mechanisms

• Header reconstruction for intra PAN communication• Header short circuiting

– Header configuration to enable/disable IPv6• Define a IPv6 LoWPAN Profile

– Address IPv6 node requirements– Define

• L2/L3 interface mechanism• Appropriate security services• Routing considerations• Network management with SNMP• Implementation considerations

• Miscellaneous (may be subsequent drafts)– Hooks from L3 for in network processing (especially critical for WSN)– Transport layer (UDP / TCP)– Security configuration– Light weight discovery mechanisms– More?