6LoWPAN Tutorial IP on IEEE 802.15.
4 Low-Power Wireless Networks
David E. Culler Jonathan Hui
Arch Rock Corporation
IEEE 802.15.4 The New IP Link
http://www.ietf.org/internet-drafts/draft-ietf-6lowpan-format-12.txt
Please refer to the internet draft / RFCs for definitive reference
1% of 802.11 power, easier to embed, as easy to use.
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THE Question
If Wireless Sensor Networks represent a future of billions of information devices embedded in the physical world,
why dont they run THE standard internetworking protocol?
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The Answer
They should
Substantially advances the state-of-the-art in both domains. Implementing IP requires tackling the general case, not just a specific operational slice
Interoperability with all other potential IP network links Potential to name and route to any IP-enabled device within security domain Robust operation despite external factors
Coexistence, interference, errant devices, ...
While meeting the critical embedded wireless requirements
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High reliability and adaptability Long lifetime on limited energy Manageability of many devices Within highly constrained resources
Many Advantages of IP
Extensive interoperability
Other wireless embedded 802.15.4 network devices Devices on any other IP network link (WiFi, Ethernet, GPRS, Serial lines, )
Established security
Authentication, access control, and firewall mechanisms Network design and policy determines access, not the technology
Established naming, addressing, translation, lookup, discovery Established proxy architectures for higher-level services
NAT, load balancing, caching, mobility
Established application level data model and services
HTTP/HTML/XML/SOAP/REST, Application profiles
Established network management tools
Ping, Traceroute, SNMP, OpenView, NetManager, Ganglia,
Transport protocols
End-to-end reliability in addition to link reliability
Most industrial (wired and wireless) standards support an IP option
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Leverage existing standards, rather than reinventing the wheel
RFC 768 RFC 791 RFC 792 RFC 793 RFC 862 RFC 1101 RFC 1191 RFC 1981 RFC 2131 RFC 2375 RFC 2460 RFC 2463 RFC 2765 RFC 3068 RFC 3307 RFC 3315 RFC 3484 RFC 3587 RFC 3819 RFC 4007 RFC 4193 RFC 4291 UDP - User Datagram Protocol IPv4 Internet Protocol ICMPv4 Internet Control Message Protocol TCP Transmission Control Protocol Echo Protocol DNS Encoding of Network Names and Other Types IPv4 Path MTU Discovery IPv6 Path MTU Discovery DHCPv4 - Dynamic Host Configuration Protocol IPv6 Multicast Address Assignments IPv6 ICMPv6 - Internet Control Message Protocol for IPv6 Stateless IP/ICMP Translation Algorithm (SIIT) An Anycast Prefix for 6to4 Relay Routers Allocation Guidelines for IPv6 Multicast Addresses DHCPv6 - Dynamic Host Configuration Protocol for IPv6 Default Address Selection for IPv6 IPv6 Global Unicast Address Format Advice for Internet Subnetwork Designers IPv6 Scoped Address Architecture Unique Local IPv6 Unicast Addresses IPv6 Addressing Architecture [1980] [1981] [1981] [1981] [1983] [1989] [1990] [1996] [1997] [1998] [1998] [1998] [2000] [2001] [2002] [2003] [2003] [2003] [2004] [2005] [2005] [2006]
Proposed Standard - "Transmission of IPv6 Packets over IEEE 802.15.4 Networks"
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Key Factors for IP over 802.15.4
Header
Standard IPv6 header is 40 bytes [RFC 2460] Entire 802.15.4 MTU is 127 bytes [IEEE ] Often data payload is small
Fragmentation
Interoperability means that applications need not know the constraints of physical links that might carry their packets IP packets may be large, compared to 802.15.4 max frame size IPv6 requires all links support 1280 byte packets [RFC 2460]
Allow link-layer mesh routing under IP topology
802.15.4 subnets may utilize multiple radio hops per IP hop Similar to LAN switching within IP routing domain in Ethernet
Allow IP routing over a mesh of 802.15.4 nodes
Options and capabilities already well-defines Various protocols to establish routing tables
Energy calculations and 6LoWPAN impact
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IEEE 802.15.4 Frame Format
D pan Dst EUID 64 S pan Src EUID 64
Max 127 bytes
Len
preamble
SFD
FCF
DSN
Dst16 Src16
Fchk
Network Header
Application Data
Low Bandwidth (250 kbps), low power (1 mW) radio Moderately spread spectrum (QPSK) provides robustness Simple MAC allows for general use
Many TinyOS-based protocols (MintRoute, LQI, BVR, ), TinyAODV, Zigbee, SP100.11, Wireless HART,
6LoWPAN => IP
Choice among many semiconductor suppliers Small Packets to keep packet error rate low and permit media sharing
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RFC 3189 "Advice for Internet Sub-Network Designers"
Total end-to-end interactive response time should not exceed human perceivable delays Lack of broadcast capability impedes or, in some cases, renders some protocols inoperable (e.g. DHCP). Broadcast media can also allow efficient operation of multicast, a core mechanism of IPv6 Link-layer error recovery often increases end-to-end performance. However, it should be lightweight and need not be perfect, only good enough Sub-network designers should minimize delay, delay variance, and packet loss as much as possible Sub-networks operating at low speeds or with small MTUs should compress IP and transport-level headers (TCP and UDP)
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6LoWPAN Format Design
Orthogonal stackable header format Almost no overhead for the ability to interoperate and scale. Pay for only what you use
IEEE 802.15.4 Frame Format
D pan Dst EUID 64 S pan Src EUID 64
preamble
FCF
DSN
Max 127 bytes
Dst16 Src16 Fchk
SFD
Len
Network Header
HC1 HC2 dsp
Application Data
IETF 6LoWPAN Format Dispatch: coexistence Header compression Mesh (L2) routing
IP
UDP
mhop
HC1
dsp
mhop
dsp
frag frag
HC1 HC1 dsp
Message > Frame fragmentation
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6LoWPAN The First Byte
Coexistence with other network protocols over same link Header dispatch - understand whats coming
IEEE 802.15.4 Frame Format
D pan preamble Dst EUID 64
SFD DSN Len
S pan Dst16 Src16
Src EUID 64 Fchk
FCF
IETF 6LoWPAN Format
Network Header
Application Data
00 01 10 11
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Not a LoWPAN frame LoWPAN IPv6 addressing header LoWPAN mesh header LoWPAN fragmentation header
6LoWPAN IPv6 Header
IEEE 802.15.4 Frame Format
D pan preamble Dst EUID 64
SFD DSN Len
S pan Dst16 Src16
Src EUID 64 Fchk
FCF
Network Header
Application Data
IETF 6LoWPAN Format
01 0 0 0 0 0 1 01 0 0 0 0 1 0
dsp
Uncompressed IPv6 address [RFC2460] HC1 Fully compressed: 1 byte
: derived from link address : derived from link address : zero : UDP, TCP, or ICMP
40 bytes
Source address Destination address Traffic Class & Flow Label Next header
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IPv6 Header Compression
in HC1 byte v6 In 802.15.4 header Link local => derive from 802.15.4 header zero
Link local => derive from 802.15.4 header
http://www.visi.com/~mjb/Drawings/IP_Header_v6.pdf
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uncompressed
HC1 Compressed IPv6 Header
Source prefix compressed (to L2) Source interface identifier compressed (to L2) Destination prefix compressed (to L2) Destination interface identified compressed (to L2) Traffic and Flow Label zero (compressed) Next Header 00 uncompressed, 01 UDP, 10 TCP, 11 ICMP Additional HC2 compression header follows HC1
0 7
Zero or more uncompressed fields follow in order
IPv6 address <prefix64 || interface id> for nodes in 802.15.4 subnet derived from the link address.
PAN ID maps to a unique IPv6 prefix Interface identifier generated from EUID64 or Pan ID & short address
Hop Limit is the only incompressible IPv6 header field
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6LoWPAN: Compressed IPv6 Header
IEEE 802.15.4 Frame Format
D pan preamble Dst EUID 64
SFD DSN Len
S pan Dst16 Src16
HC1
Src EUID 64 Fchk
FCF
IETF 6LoWPAN Format
Network Header
Application Data
01 0 0 0 0 1 0
C o m pr es
HC1
h o w it i s
dsp
uncompressed v6 fields -Non 802.15.4 local addresses -non-zero traffic & flow - rare and optional
se d
se
IP v6
co m
pr es
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6LoWPAN Compressed / UDP
IEEE 802.15.4 Frame Format
D pan preamble Dst EUID 64
SFD DSN Len
S pan Dst16 Src16
Src EUID 64 Fchk
FCF
Network Header
dsp HC1
Application Data
IETF 6LoWPAN Format Dispatch: Compressed IPv6 HC1: IP: UDP:
IP
UDP
Source & Dest Local, next hdr=UDP Hop limit 8-byte header (uncompressed)
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L4 UDP/ICMP Headers (8 bytes)
P + [0..15] P + [0..15]
from 15.4 header
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6LoWPAN Compressed / Compressed UDP
IEEE 802.15.4 Frame Format
D pan preamble Dst EUID 64
SFD DSN Len
S pan Dst16 Src16
Src EUID 64 Fchk
FCF
Network Header
HC1 dsp HC2
Application Data
IETF 6LoWPAN Format Dispatch: Compressed IPv6
IP
UDP
HC1: Source & Dest Local, next hdr=UDP IP: Hop limit UDP: HC2+3-byte header (compressed) source port = P + 4 bits, p = 61616 (0xF0B0) destination port = P + 4 bits
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6LoWPAN / Zigbee Comparison
IEEE 802.15.4 Frame Format
D pan preamble Dst EUID 64
SFD DSN Len
S pan Dst16 Src16
Src EUID 64 Fchk
FCF
Network Header
dsp HC1 HC2
Application Data
IETF 6LoWPAN Format
IP
UDP
S ep APS
Zigbee APDU Frame Format
D ep
fctrl: Frame Control bit fields D ep: Destination Endpoint (like UDP port) clstr: cluster identifier prof: profile identifier S ep: Source Endpoint APS: APS counter (sequence to prevent duplicates) *** Typical configuration. Larger and smaller alternative forms exist.
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fctrl
clstr prof
6LoWPAN Compressed / ICMP
IEEE 802.15.4 Frame Format
D pan preamble Dst EUID 64
SFD DSN Len
S pan Dst16 Src16
Src EUID 64 Fchk
FCF
Network Header
dsp HC1
Application Data
IETF 6LoWPAN Format Dispatch: Compressed IPv6 HC1: IP: ICMP:
IP
ICMP
Source & Dest Local, next hdr=ICMP Hops Limit 8-byte header
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L4 TCP Header (20 bytes)
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6LoWPAN Compressed / TCP
IEEE 802.15.4 Frame Format
D pan preamble Dst EUID 64
SFD DSN Len
S pan Dst16 Src16
Src EUID 64
Max 127 bytes
Fchk
FCF
Network Header
dsp HC1
IETF 6LoWPAN Format Dispatch: Compressed IPv6 HC1: IP: TCP:
IP
TCP
Application Data
Source & Dest Local, next hdr=TCP Hops Limit 20-byte header
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Key Points for IP over 802.15.4
Header overhead
Standard IPv6 header is 40 bytes [RFC 2460] Entire 802.15.4 MTU is 127 bytes [IEEE std] Often data payload is small
Fragmentation
Interoperability means that applications need not know the constraints of physical links that might carry their packets IP packets may be large, compared to 802.15.4 max frame size IPv6 requires all links support 1280 byte packets [RFC 2460]
Allow link-layer mesh routing under IP topology
802.15.4 subnets may utilize multiple radio hops per IP hop Similar to LAN switching within IP routing domain in Ethernet
Allow IP routing over a mesh of 802.15.4 nodes
Localized internet of overlapping subnets
Energy calculations and 6LoWPAN impact
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Fragmentation
All fragments of an IP packet carry the same tag
Assigned sequentially at source of fragmentation
Each specifies tag, size, and position Do not have to arrive in order Time limit for entire set of fragments (60s)
First fragment 11 0 0 0 size tag
Rest of the fragments 11 1 0 0 size tag offset
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6LoWPAN Example Fragmented / Compressed / Compressed UDP
IEEE 802.15.4 Frame Format
D pan preamble Dst EUID 64
SFD DSN Len
S pan Dst16 Src16
Src EUID 64 Fchk
FCF
Network Header
HC1 HC2 dsp Frag 1st
IETF 6LoWPAN Format
Application Data
IP
UDP
Dispatch: Fragmented, First Fragment, Tag, Size Dispatch: Compressed IPv6 HC1: IP: UDP: Source & Dest Local, next hdr=UDP Hop limit HC2+3-byte header (compressed)
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Key Points for IP over 802.15.4
Header overhead
Standard IPv6 header is 40 bytes [RFC 2460] Entire 802.15.4 MTU is 127 bytes [IEEE std] Often data payload is small
Fragmentation
Interoperability means that applications need not know the constraints of physical links that might carry their packets IP packets may be large, compared to 802.15.4 max frame size IPv6 requires all links support 1280 byte packets [RFC 2460]
Allow link-layer mesh routing under IP topology
802.15.4 subnets may utilize multiple radio hops per IP hop Similar to LAN switching within IP routing domain in Ethernet
Allow IP routing over a mesh of 802.15.4 nodes
Localized internet of overlapping subnets
Energy calculations and 6LoWPAN impact
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Mesh Under Header
Originating node and Final node specified by either short (16 bit) or EUID (64 bit) 802.15.4 address
In addition to IP source and destination
Hops Left (up to 14 hops, then add byte) Mesh protocol determines node at each mesh hop
LoWPAN mesh header 10 o f hops left
orig. addr (16/64) final. addr (16/64)
fi ori nal s gi n ho ato rt r s add ho re rt a ss dd res
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6LoWPAN Example Mesh / Compressed / Compressed UDP
IEEE 802.15.4 Frame Format
D pan preamble Dst EUID 64
SFD DSN Len
S pan Dst16 Src16
Src EUID 64 Fchk
FCF
Network Header
HC1 HC2 M o16 f16 dsp
IETF 6LoWPAN Format
Application Data
UDP
IP
Dispatch: Mesh under, orig short, final short Mesh: HC1: IP: UDP: orig addr, final addr Source & Dest Local, next hdr=UDP Hop limit HC2+3-byte header Dispatch: Compressed IPv6
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6LoWPAN Example Mesh / Fragmented / Compressed / UDP
IEEE 802.15.4 Frame Format
D pan preamble Dst EUID 64
SFD DSN Len
S pan Dst16 Src16
Src EUID 64 Fchk
FCF
Network Header
M o16 f16 HC1 HC2 Frag 1st dsp
IETF 6LoWPAN Format
IP
UDP
Application Data
Dispatch: Mesh under, orig short, final short Mesh: orig addr, final addr Dispatch: Fragmented, First Fragment, Tag, Size Dispatch: Compressed IPv6 HC1: IP: UDP:
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Source & Dest Local, next hdr=UDP Hop limit HC2 + 3-byte header
Key Points for IP over 802.15.4
Header overhead
Standard IPv6 header is 40 bytes [RFC 2460] Entire 802.15.4 MTU is 127 bytes [IEEE std] Often data payload is small
Fragmentation
Interoperability means that applications need not know the constraints of physical links that might carry their packets IP packets may be large, compared to 802.15.4 max frame size IPv6 requires all links support 1280 byte packets [RFC 2460]
Allow link-layer mesh routing under IP topology
802.15.4 subnets may utilize multiple radio hops per IP hop Similar to LAN switching within IP routing domain in Ethernet
Allow IP routing over a mesh of 802.15.4 nodes
Localized internet of overlapping subnets
Energy calculations and 6LoWPAN impact
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IP-Based Multi-Hop Routing
IP has always done multi-hop
Routers connect sub-networks to one another The sub-networks may be the same or different physical links
Routers utilize routing tables to determine which node represents the next hop toward the destination Routing protocols establish and maintain proper routing tables
Routers exchange messages using more basic communication capabilities Different routing protocols are used in different situations RIP, OSPF, IGP, BGP, AODV, OLSR,
IP routing over 6LoWPAN links does not require additional header information at 6LoWPAN layer
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IPv6 Address Auto-Configuration
64-bit Prefix 64-bit Suffix or Interface Identifier
EUID - 64 Link Local pan* 00-FF-FE-00 short
802.15.4 Address
PAN* - complement the Universal/Local" (U/L) bit, which is the next-to-lowest order bit of the first octet
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Key Points for IP over 802.15.4
Header overhead
Standard IPv6 header is 40 bytes [RFC 2460] Entire 802.15.4 MTU is 127 bytes [IEEE std] Often data payload is small
Fragmentation
Interoperability means that applications need not know the constraints of physical links that might carry their packets IP packets may be large, compared to 802.15.4 max frame size IPv6 requires all links support 1280 byte packets [RFC 2460]
Allow link-layer mesh routing under IP topology
802.15.4 subnets may utilize multiple radio hops per IP hop Similar to LAN switching within IP routing domain in Ethernet
Allow IP routing over a mesh of 802.15.4 nodes
Localized internet of overlapping subnets
Energy calculations and 6LoWPAN impact
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Energy Efficiency
Battery capacity typically rated in Amp-hours
Chemistry determines voltage AA Alkaline: ~2,000 mAh = 7,200,000 mAs D Alkaline: ~15,000 mAh = 54,000,000 mAs
Unit of effort: mAs
multiply by voltage to get energy (joules)
Lifetime
1 year = 31,536,000 secs 228 uA average current on AA 72,000,000 packets TX or Rcv @ 100 uAs per TX or Rcv 2 packets per second for 1 year if no other consumption
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Energy Profile of a Transmission
Datasheet Analysis 20mA
10mA
Power up oscillator & radio (CC2420) Configure radio Clear Channel Assessment, Encrypt and Load TX buffer Transmit packet Switch to rcv mode, listen, receive ACK
5 ms 10 ms
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Low Impact of 6LoWPAN on Lifetime Comparison to *Raw* 802.15.4 Frame
Energy Cost of Packet Communication vs. Data Size
Energy for fixed payload
*
Max Payload
uAs per Packet
RCV 6LoWPAN Local <= Global RCV 6LoWPAN Local <= Local RCV Raw 802.15.4 TX 6LoWPAN Local => Global TX 6LoWPAN Local => Local TX Raw 802.15.4 0 20 40 60 80 100 120
* fully compressed header * additional 16-byte IPv6 address
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Bytes of Payload
Rest of the Energy Story
Energy cost of communication has four parts
Transmission Receiving Listening (staying ready to receive) Overhearing (packets destined for others)
The increase in header size to support IP over 802.15.4 results in a small increase in transmit and receive costs
Both infrequent in long term monitoring
The dominant cost is listening! regardless of format.
Can only receive if transmission happens when radio is on, listening Critical factor is not collisions or contention, but when and how to listen Preamble sampling, low-power listening and related listen all the time in short gulps and pay extra on transmission TDMA, FPS, TSMP and related communication scheduling listen only now and then in long gulps. Transmission must wait for listen slot. Clocks must be synchronized. Increase delay to reduce energy consumption.
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Conclusion
6LoWPAN turns IEEE 802.15.4 into the next IP-enabled link Provides open-systems based interoperability among lowpower devices over IEEE 802.15.4 Provides interoperability between low-power devices and existing IP devices, using standard routing techniques Paves the way for further standardization of communication functions among low-power IEEE 802.15.4 devices Offers watershed leverage of a huge body of IP-based operations, management and communication services and tools Great ability to work within the resource constraints of lowpower, low-memory, low-bandwidth devices like WSN
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Frequently Asked Questions
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How does 6LoWPAN compare to Zigbee, SP100.11a, ?
Zigbee
only defines communication between 15.4 nodes (layer 2 in IP terms), not the rest of the network (other links, other nodes). defines new upper layers, all the way to the application, similar to IRDA, USB, and Bluetooth, rather utilizing existing standards. Specification still in progress (Zigbee 2006 incompatible with Zigbee 1.0. Zigbee 2007 in progress.) Lacks a transport layer.
SP100.11a
seeks to address a variety of links, including 15.4, 802.11, WiMax, and future narrow band frequency hoppers. Specification is still in the early stages, but it would seem to need to redefine much of what is already defined with IP. Much of the emphasis is on the low-level media arbitration using TDMA techniques (like token ring) rather than CSMA (like ethernet and wifi). This issue is orthogonal to the frame format.
6LoWPAN defines how established IP networking layers utilize the 15.4 link.
it enables 15.4 15.4 and 15.4 non-15.4 communication It enables the use of a broad body of existing standards as well as higher level protocols, software, and tools. It is a focused extension to the suite of IP technologies that enables the use of a new class of devices in a familiar manner.
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Do I need IP for my stand-alone network?
Today, essentially all computing devices use IP network stacks to communicate with other devices, whether they form an isolated stand-alone network, a privately accessible portion of a larger enterprise, or publicly accessible hosts.
When all the devices form a subnet, no routing is required, but everything works in just the same way.
The software, the tools, and the standards utilize IP and the layers above it, not the particular physical link underneath. The value of making it all the same far outweighs the moderate overheads. 6LoWPAN eliminates the overhead where it matters most.
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Will the ease of access with IP mean less security?
No. The most highly sensitive networks use IP internally, but are completely disconnected from all other computers. IP networks in all sorts of highly valued settings are protected by establishing very narrow, carefully managed points of interconnection.
Firewalls, DMZs, access control lists,
Non-IP nodes behind a gateway that is on a network are no more secure than the gateway device. And those devices are typically numerous, and use less than stateof-the-art security technology. 802.15.4 provides built-in AES128 encryption which is enabled beneath IP, much like WPA on 802.11.
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Does using 6LoWPAN mean giving up deterministic timing behavior?
No. Use of the 6LoWPAN format for carrying traffic over 802.15.4 links is orthogonal to whether those links are scheduled deterministically.
Deterministic media access control (MAC) can be implemented as easily with 6LoWPAN as with any other format.
There is a long history of such TDMA mechanisms with IP, including Token Ring and FDDI.
MAC protocols, such as FPS and TSMP, extend this to a mesh. Ultimately, determinacy requires load limits and sufficient headroom to cover potential losses. Devices using different MACs on the same link (TDMA vs CSMA) may not be able to communicate, even though the packet formats are the same.
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Is 6LoWPAN less energy efficient than proprietary protocols?
No. Other protocols carry similar header information for addressing and routing, but in a more ad hoc fashion. While IP requires that the general case must work, it permits extensive optimization for specific cases. 6LoWPAN optimizes within the low-power 802.15.4 subnet
More costly only when you go beyond that link. Other protocols must provide analogous information (at application level) to instruct gateways.
Ultimately, the performance is determined by the quality the implementation.
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With IPs open standards, companies must compete on performance and efficiency, rather than proprietary lock in
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Do I need to run IPv6 instead of IPv4 on the rest of my network to use 6LoWPAN?
No. IPv6 and IPv4 work together throughout the world using 4-6 translation. IPv6 is designed to support billions of non-traditional networked devices and is a cleaner design.
Actually easier to support on small devices, despite the larger addresses.
The embedded 802.15.4 devices can speak IPv6 with the routers to the rest of the network providing 4-6 translation.
Such translation is already standardized and widely available.
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