Wh ti 6L WPAN? What is 6LoWPAN?
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Wh t is What i 6LoWPAN? 6L WPAN? 6LoWPAN makes this possible - Low-power p RF + IPv6 = The Wireless Embedded Internet IPv6 over Low-Power wireless Area Networks (IEEE 802.15.4) Defined by IETF standards - RFC 4919, 4944 IPv6 Stack - draft-ietf-6lowpan-hc and -nd - draft-ietf-roll-rpl Stateless header compression Enables a standard socket API Minimal use of code and memory Direct end-to-end Internet integration - Multiple topology options Reference: 6LoWPAN: The Wireless Embedded Internet, Shelby & Bormann L P N t k Protocols P t l Low Power Network 802.15.4 802.15.1 802.11 802.3 Class WPAN WPAN WLAN LAN Lifetime (days) 100-1000+ 1-7 0.1-5 Powered Capacity 65535 7 30 1024 Bandwidth (kbps) 20-250 720 11,000+ 100,000+ Coverage Range (m) 1-75+ 1-10+ 1-100 185 (wired) Design Goals Low Power, Large Scale, Low Cost L C t Cable Replacement Throughput Throughput P t Protocol l Stacks St k F t Features off 6LowPAN 6L PAN Support for e.g. 64-bit and 16-bit 802.15.4 addressing Useful with low-power link layers such as IEEE 802.15.4, narrowband ISM and power-line communications Efficient header compression - IPv6 base and extension headers, UDP header Network auto-configuration using neighbor discovery Unicast, U i t multicast lti t and db broadcast d t supportt - Multicast is compressed and mapped to broadcast Fragmentation g - 1280 byte IPv6 MTU -> 127 byte 802.15.4 frames Support for IP routing (e.g. IETF RPL) Support for use of link-layer link layer mesh (e (e.g. g 802 802.15.5) 15 5) Benefits B fit off Benefits B fit off 6LoWPAN 6L WPAN gy Technology • The benefits of 6LoWPAN include: – Open, long-lived, reliable standards – Easy y learning-curve g – Transparent Internet integration – Network maintainability – Global scalability – End-to-end E dt d data d t flows fl IP 6 over 802 IPv6 802.15.4 15 4 Challenges Ch ll Fragmentation - IPv6: Minimum MTU(Maximum Transmission Unit) is 1,280 bytes - IEEE 802.15.4: Maximum 127 bytes Head compression - IPv6: 40 bytes compressed IP Header - 802.15.4: effective link payload is 81 bytes Routing g - IPv6: A link is a single broadcast domain short range connections - 802.15.4: a mesh of short-range 21 H d Comparison Header C i Reference: 6LoWPAN: The Wireless Embedded Internet, Shelby & Bormann IP 6 Addressing Add i Example E l IPv6 Reference: 6LoWPAN: The Wireless Embedded Internet, Shelby & Bormann Route-over vs Mesh-under R ti iin 6LoWPAN Routing 6L WPAN 6L WPAN R ti 6LoWPAN Routing Here we consider IP routing (Layer 3 routing) - Routing in 6LoWPAN - Single-interface routing - Simple LowPAN scenario - End-to-End data transmissions Reference: 6LoWPAN: The Wireless Embedded Internet, Shelby & Bormann 6L WPAN Challenges 6LoWPAN Ch ll UDP datagram …, modbus, BacNET/IP, … , HTML, XML, …, ZCL transport header Network packet application payload 40 B + options cls flow len hops NH src IP 16 B Link Layer frame ctrl len src UID dst UID dst IP 16 B Payload 1280 Bytes MIN link payload 128 Bytes MAX • Large IP Address & Header => 16 bit short address / 64 bit EUID • Minimum Transfer Unit => Fragmentation g & Embedded • Short range => Multiple p Hops p chk F Fragmentation t ti IPv6 requires underlying links to support Minimum Transmission Units (MTUs) of at least 1280 bytes The performance of large IPv6 packets fragmented over low-power wireless mesh networks is poor ! - Lost fragments cause whole packet to be retransmitted Low-bandwidth and delay of the wireless channel 6LoWPAN application protocols should avoid fragmentation Compression should be used on existing IP application protocols when used over 6LoWPAN if possible - IP datagram that are too large to fit in a 802.15.4 frame are fragmented into multiple frames g for reassembly y - Self describing 28 R ti in Routing i 6LoWPAN 6L WPAN Based on which layer the routing decision i.e. the data-gram forwarding occurs we can divide routing protocols in 6LoWPAN into two categories: - Mesh Under Routing - No IP routing - Routing within the 6LoWPAN - Route Over Routing - Routing at the IP layer - Utilizing Utili i network-layer t kl capabilities biliti defined by IP Routing at two different layers may be in conflict ki group - IETF ROLL working - Routing Over Low-Power and Lossy networks M h Mesh-under d Scheme S h In mesh-under scheme, routing and forwarding are performed at link layer based on 802 802.15.4 15 4 frame or the 6LoWPAN header header. - Multiple link layer hops are used to complete a single IP hop To send a packet to a particular destination destination, - the EUI 64 bit address or the16 bit short address is used and sent it to a g node to move the p packet closer to the destination. neighbor All fragments of an IP packet can go through route paths and they are gathered at the destination. - All fragments are reached successfully - The adaptation p layer y of the destination node reassembles all fragments g and creates an IP packet. - Any y fragment g missing g in the forwarding gp process - The entire IP packet i.e. all fragments for this IP packet are retransmitted to the destination for recovery. R t Route-over S h Scheme In route-over scheme all routing decisions are taken in the network layer where each node acts as an IP router. - The IP routing supports the forwarding of packets between these links. - The network layer takes decision using the additional encapsulated IP header. An IP packet is fragmented by the adaptation layer, fragments are sent to th nextt hop the h based b d on th the routing ti ttable bl iinformation. f ti - The adaptation layer of the next hop checks received fragments. - All fragments are received successfully, the adaptation layer creates an IP packet from fragments and send it to the network layer. - If there are one or more fragments missing, missing then all fragments are retransmitted to one hop distance. Wh Where Should Sh ld Routing R ti Take T k Place? Pl ? Historically, a number of interesting research initiatives on WSN - Work on Wireless Sensors Network focussed on algorithms. Most work assumed the use of MAC addresses - Layer 2 “routing” (mesh-under routing) Support pp of multiple p PHY/MAC ((heterogeneous g networks)) - IEEE 802.15.4, Low Power Wifi, Power Line Communications (PLC) Use IP to route - Supports multiple PHY/MAC - Moves from mesh mesh-under under (L2) to router-over(L3) router over(L3) Energy cost of IPv6 over IEEE 802.15.4 The Energy Th E Consumption C ti on 6LowPAN T h i l Challenges Technical Ch ll Energy consumption is a major issue (battery powered sensors/actuators) Limited processing power Very dynamic topologies - Link failure (LP RF) - Node failures (triggered or non triggered) - Node mobility (in some environments), Data processing usually required on the node itself Sometimes deployed in harsh environments (e.g. Industrial) Potentially deployed at very large scale Must be self-managed self managed E Energy Profile P fil off a Transmission T i i Datasheet Analysis A A. B B. Power up oscillator & radio (Based on TI CC2420) 20mA C fi Configure radio di C. Clear Channel Assessment, encrypt and load TX buffer 10mA C D E D. Transmit packet E. Switch to rcv mode, listen, receive ACK A B 5 ms 10 ms Reference: http:// www.ti.com/lit/ds/symlink/cc2420.pdf E C ti Analysis A l i Energy Consumption * * Payload ∆ Energy ∆ for fixed payload Reference: David E. Culler, 6LowPAN, IPSO Alliance Th E The Energy C Costt off 6L 6LowPAN PAN Energy cost of communication has five parts - Sleep - Transmission T i i - Receiving - Listening (ready to receive) - Overhearing (packets overhearing form others) The increase in header size to support IP over 802.15.4 802 15 4 results in a small increase in transmit and receive costs. The dominant cost is listening. - Can only receive if transmission happens when radio is on, “listening”. - Preamble sampling, low-power listening and related listen “all the time”, that will pay extra than transmission. - Use TDMA scheduling listen only when necessary. - A Ttransmission Tt i i pair i mustt waitit ffor transmission/listen t i i /li t slot. l t - Clocks must be synchronized. Increase delay to reduce energy consumption. C Conclusion l i 802.15.4 devices have great ability to work within the resource constraints of low-power, low-memory, low-bandwidth devices. 802.15.4 provides open-systems based interoperability among low-power d i devices. 6LowPAN provides interoperability between low-power devices and e isting IP de existing devices, ices using sing ro route-over te o er ro routing ting techniq techniques. es 6LoWPAN turns IEEE 802.15.4 into the next generation, All-IP networks.
