Internet of Things 2017/2018

Transcription

1 Internet of Things 2017/2018 IoT (Wireless) Networks Johan Lukkien John Carpenter,

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3 What are IoT networks? Guiding questions What is the role of IP? What techniques are used in wireless communications? techniques for media sharing techniques for reducing energy use Which standards are considered? 3

4 Some IoT protocol stacks DTLS/UDP (security) The IoT Architectural Framework, Design Issues and Application Domain, Gordana Gardasˇevic et al. 4

5 Physical organization IP The IEEE local area networks Techniques for medium sharing Techniques for energy reduction Wide area IoT-oriented initiatives Metrics Overview 5

6 General architecture Generic Physical organization IEEE e (WiMAX) 3G, 4G IEEE 802.3, (ethernet) IEEE (WiFi) IP-based network with wide-area coverage, wireless or wired and powerful servers AN IoT infrastructure: static ambient nodes attaching to clusters in lowest layer AN AN MN MN MN MN MN MN = AN = mobile node /network ambient node / network Moving clusters of nodes with sensing capability but often with limited resources e.g. single person moving around with sensors 6

7 Taxonomy Middle layer Multi hop Single hop (no hop) Bottom layer (ambient infra structure) (access points) Multi hop Single hop (no hop) Most general case: moving clusters through ambient infra structure ad-hoc networks Moving nodes connecting to ambient infra structure Moving clusters connecting to access points ad-hoc networks Moving nodes connecting to access points 7

8 Examples Middle layer Multi hop Single hop (no hop) Bottom layer (ambient infra structure) (access points) Multi hop vehicle to vehicle Single hop (no hop) phone vehicle to infra structure user wearing cluster of sensors connected to phone sensor in low power mesh network vehicle to infra structure user wearing sensors connected to phone laptop / wifi 8

9 Physical organization IP The IEEE local area networks Techniques for medium sharing Techniques for energy reduction Wide area IoT-oriented initiatives Metrics Overview 9

10 Layered protocols: OSI( 83) reference model Physical: sends bits on medium (i.e. standardizes the electrical, mechanical, and signalling interfaces) MAC / Data link: manages medium access, detects and corrects errors in frames; deliver frames on one-hop medium Network: send packets from sender to receiver machines using multihop routing Transport: breaks messages into packets; delivery guarantees; multiplexing ports typical frame structure payload 10

11 The hour glass of IP The essence of IP, and its success a unified protocol and naming (addressing) scheme to enable communication between any pair of devices all layer breaking or application knowledge is banned from lower layers until the transport layer it is only about exchanging bits: semantics only at endpoints Recent standardization towards application protocols (HTTP, CoAP) standardizes application structures diverse applications divergence COAP/UDP, HTTP/UDP, HTTP/TCP transport layer (UDP,TCP/IP) network layer IP convergence diverse physical layers 11

12 The essence of IoT Is IoT so much different? a unified protocol and naming (addressing) scheme to enable communication between any pair of devices things that contain embedded networked electronics, of course IP to every thing 12

13 IP to Every Thing? IP connectivity comes with hidden assumptions endpoints are active, reachable by IP packets Devices cannot always guarantee this passive nodes, when there is no device to power wirelessly battery-less nodes duty cycling, or off-time planning incapability to process IP IP-Zigbee bridge zigbee (non-ip) domain Legacy may prevent IP to endpoints existing networks, without capability to use IP Bridging light applications to the IP domain, Bui, Lukkien et. al., ICCE 2011 Need technology to solve this (discussed later) 13

14 Example: which (IP) protocols occur in a lighting network? Connectivity: 6LoWPAN (= adaptation for IP/ ), UDP, TCP [sometimes] RPL, RIP, MPL: routing, multicasting DTLS: packet based security Application Trickle: application protocol for dissemination to all devices in a network RESTful style REST plus HTTP methods CoAP constrained application protocol DNS-SD using mdns, or CoAP directory: for service discovery M2M protocols, e.g. MQTT/TCP Courtesy of Dee Denteneer 14

15 Example application: intelligent outdoor lighting Testbed in Achtse Barrier specialized communication stack, based Real-time, local behavior light setting based on movement sensors Collect data about movements in the street Simulate lighting strategies using those data 15

16 Physical organization IP The IEEE local area networks Techniques for medium sharing Techniques for energy reduction Wide area IoT-oriented initiatives Metrics Overview 16

17 How do end points communicate? 17

18 Networking approaches Physical neighbors: Shared medium or Point-to-point In case of physical separation switching (layer 2) connecting networks (layer 3) multiple interfaces for some nodes Packet oriented Full connectivity by (intelligent) flooding send packet to everyone recursively routing series of hops shared medium point to point 18

19 Wired: Wired or wireless admits nodes to be powered through the network as well, e.g. Power over Ethernet (PoE) no real need for very low resource devices (except power) difficult to scale to large numbers forbids mobility Wireless: typical for really large numbers of devices installed at difficult to reach locations required for mobility is an inherently unreliable medium can still either be battery powered or connected to mains from bloomberg.com 19

20 Wired Wireless Battery Mains Energy limitations will determine uptime communication behavior and protocols. In principle, the wire could be used for power; and at least for waking up nodes No real need for low resources except cost and energy; this class captures regular office/home infra structure devices Energy limitations will determine uptime, communication behavior and protocols; nodes must manage their sleeping behavior; nodes can be mobile Wireless is there for convenience (absence of other infra - outdoors) and for connecting to mobile wireless nodes; powerful wireless protocols can be used, always on 20

21 The LANs Taken from Wikipedia (Nov. 2017) 21

22 The LANs Taken from Wikipedia (Nov. 2017) Important for IoT: the 3 group (ethernet, PoE) the 11 group ( WiFi ) the 15 group (wireless PAN) Within IEEE x: Bluetooth, BT LE 4x: PHY/MAC layer for ZigBee, 6LoWPAN, Thread, WirelessHART, MiWi ContikiMAC, 6Tisch 22

23 The LANs Taken from Wikipedia (Nov. 2017) Important for IoT: the 3 group (ethernet, PoE) the 11 group ( WiFi ) the 15 group (wireless PAN) Within IEEE x: Bluetooth, BT LE 4x: PHY/MAC layer for ZigBee, 6LoWPAN, Thread, WirelessHART, MiWi ContikiMAC, 6Tisch Within the IEEE LANs: 11p: ITS 11e: QoS 11s: meshing 11ah: low power, low interference (HaLow) 23

24 Overview Physical organization IP The IEEE local area networks Techniques for medium sharing Techniques for energy reduction Wide area IoT-oriented initiatives Metrics 24

25 Shared medium A shared medium can be a wire or bus, but also a wireless connection standards must address this sharing, avoiding destructive interference wired: typically, bus protocols Wireless communication is intrinsically subject to errors received signal is the energy collected over time can always be disturbed by an external party (a different protocol family in same frequency), or by another neighbor than the sender quality depends on environment properties (e.g. reflections) Wireless communication is energy-hungry, particularly when compared to the energy used by embedded processors Standards must address the unreliability, sharing and energy use 25

26 What techniques are applied for wireless? FDMA: multiple channels (frequency division multiple access) channel hopping with synchronization e.g (Bluetooth), 6tisch, cell formation / independent domains e.g. 3/4G, IEEE (WiFi) TDMA: division in timeslots (time division multiple access) timeslots with schedules, time synchronization e.g. WirelessHART, DECT, IEEE in superframe mode in combination with cell formation Master-Slave e.g. an access point as master beacon-based signaling e.g. IEEE (WiFi), Bluetooth, IEEE CSMA: try before you cry (carrier sense multiple access) Clear Channel Assessment: Aloha with collision avoidance, detection or resolution e.g. IEEE (ZigBee): random distribution of retries with priority e.g. IEEE e (WiFi + QoS) CDMA (code division multiple access, as in 4G) concurrent access of the medium with coded packets admits decoding even with interference Regulation duty cycle restrictions (e.g. 1% per station) frequency assignment 26

27 FDMA (FDM) Use FDMA for several independent point-to-point channels Use FDMA for increasing reliability, e.g., isolation to a quiet channel multiple transceivers frequency hopping, avoiding crowded frequencies (6tisch, Bluetooth) together with timeslots (TDMA) OFDM: coding using multiple frequencies from internet source 27

28 CSMA/CD CSMA/CD: (fully distributed) protocol for sharing a wired medium, using the following algorithm: sense carrier, wait until it is ready (i.e., free) transmit and monitor for collision upon collision: transmit jam signal until minimum frame size (time) has been reached update counters and check for maximum retransmit backoff random time (dependent on # collisions) continue with sensing carrier complete transmission Used in (shared medium) ethernet (which is obsolete) 28

29 CSMA/CR CSMA/CR: (fully distributed) protocol for sharing a wired medium, using the following algorithm: sense carrier, wait until it is ready transmit and monitor for detecting a collision. upon collision: priority-based choice which station continues upon loss (low priority): resume sensing carrier upon win (high priority): continue transmission complete transmission Used in CAN (in-vehicle bus). Millions of deployments. 29

30 CSMA/CA: (fully distributed) protocol for sharing a (wireless) medium, using the following algorithm: sense carrier when active: back-off for a random period and retry for a given maximum number of trials when not active: send message; wait for ack ack received: ok CSMA/CA no ack received: transmission failed (e.g. collision), retry (up to maximum) Collisions: are due to unfortunate timing or to hidden nodes In wireless networks, collisions cannot be detected by the sending node (major difference with wired) discovered by absence of ACK Back-off time: increases with number of retries 30

31 CSMA: Hidden stations, unicast and broadcast Wireless communication has a limited range collisions can occur between nodes in the same range (NN) or two nodes that cannot see each other disturb a third one (HN) In case of unicast: sender warns its neighbors using an RTS signal receiver responds, and warns its neighbors by responding with CTS confirm receipt using an ACK (with immediate feedback) In case of broadcast this does not work (neither ACK nor CTS) don t know the receivers, in general 31

32 Beacons Beacons are periodic packet broadcasts beacons enforce a globally slotted structure of the medium access superframe, beacon interval the beacon sender has the role of master of the medium (during the superframe) the beacon describes the structure of the period until the next beacon, and how nodes have to behave in that period from overhearing a beacon a node understands next beacon time, when it is (allowed) to transmit and which protocol to use, when to change frequency clock synchronization is required, and the beacon may be used for this from IEEE

33 IEEE beacons CAP: contention access period CSMA/CA CFP: contention free period (assigned slots) GTS: Guaranteed Time Slot BI: Beacon Interval 16 equal time slots SD: Superframe duration shorter than BI to admit duty cycling, or the superframe of another station 33

34 Example: IEEE IEEE MAC protocols are generally CSMA/CA Original IEEE MAC: infra structure mode vs ad-hoc mode infra structure: all communication via an access point Distributed Coordination Function + RTS/CTS just CSMA/CA no prioritization Point Coordination Function (in infrastructure mode only) beaconing (access point is master) Contention-free part of the superframe: AP polls the stations Contention period: DCF no further classing of stations or traffic 34

35 QoS extensions to IEEE IEEE e TXOP: (transmission opportunity) contention-free period (CFP) to be given to stations EDCA: Enhanced Distributed Channel Access fully distributed probabilistic flow prioritization access categories: settings of the MAC to be associated with a group of flows with the same characteristics 36

36 Initial waiting time series of packets Initial waiting time 37

37 EDCA Parameters for a backoff process in access control class q: AIFSN q : initial wait time TXOPLimit q : max. #packets sent arbitration inter frame space transmission opportunity limit [0..CWmin q, CW q, CWmax q ]: contention window contention window minimum, current, maximum RetryLimit q : #trials before giving up Further relevant parameters SIFS: mandatory wait aslottime: time unit short inter frame space AIFS = SIFS + AIFSN x aslottime 38

38 EDCA algorithm, very roughly 1. Select a number of backoff slots in variable bc uniformly from an interval [0..CW] there is some debate if this backoff is there only after contention was observed 2. wait for the channel to be idle for AIFS; only then downcount bc 3. suspend this downcounting upon the media being active; upon resume wait AIFS first 4. when bc reaches 0 transmit frame wait for ack if this does not arrive, double the size of the interval and retry (exponential backoff) 5. after RetryLimit trials: drop the frame 6. after the first succesful frame: transmit available frames until TXOPLimit has been reached or frames run out 39

39 Effects of parameters During contention, the behavior of competing processes (hence, stations) becomes more synchronized A process with a lower AIFS: gets to downcount its bc more often A process with a lower CWMin / CWMax: has its bc reach 0 faster A process with a higher TXOP: gets to send larger messages (more frames) Hence, there are two mechanisms: gain control: even possible to define priorities in this way retain control 42

40 TDMA (time division multiple access) Divide time into fixed periods (slots) and assign transmission slots to stations typically, two-level hierarchy: slots and frames (group of slots) admits slot-based interaction between stations within a frame tricky with multiple cells (hidden nodes) needs multiple frequencies potentially wasteful as not all slots are used Requires time synchronization Requires a master for managing the assignment Both wired and wireless from wikipedia 43

41 Wired Wireless Shared medium Point to point CSMA/CD: coax ethernet CSMA/CR: CAN TDMA token passing: profibus Master/Slave: ethercat (,profibus) Switched ethernet: PoE Common way to set up larger networks using switches and routers MA/CA: (pure) Aloha CSMA/CA: Wifi, Zigbee TDMA: Wireless Hart Master/Beaconing: Wifi, Zigbee FDMA + channel hopping: bluetooth (low energy), 6tisch CDMA: virtual point to point (4G), Chirp Spread Spectrum UWB FDMA Dedicated frequencies for long-haul transport: satellite 44

42 Overview Physical organization IP The IEEE local area networks Techniques for medium sharing Techniques for energy reduction Wide area IoT-oriented initiatives Metrics 45

43 Energy, in low capacity environment Radio communication is a major contributor to energy consumption don t use it Applied techniques (combinations, need support at multiple layers) asymmetry low-power nodes are 1 hop away from well-powered infra control the transmit / receive power trade connectivity for energy duty cycle switch node or radio on and off periodically demand driven event driven control of radio (wakeup radio (IEEE ba), or push mode) with asymmetry push / pull strategies let the low power partner always be the one that takes initiative trade power for range and throughput special network technologies, special physical layers 46

44 Duty Cycling Strict interpretation: station switches on radio with a certain frequency and for a certain time Problem: how to meet each other Options: strict time synchronization energy expensive sender initiated send wakeup sufficiently often to guarantee reception wakeup = packet or wakeup = rendez-vous time receiver initiated switch transceiver on sufficiently long to guarantee meeting the sender or enforce exchange: send receive request (similar as above) asymmetry: one party always on (question: useful for both send and receive?) Guclu, Ozcelebi, Lukkien, Dependability Analysis of Asynchronous Radio Duty Cycling Protocols, ICCCN

45 Example for IEEE e CSL (CSL: Coordinated Sampled Listening) Broadcast: transmit rendez-vous sufficiently often for all receivers to see it Unicast: tune-in to the periodic behavior of the receiver to reduce overhead include acknowledge Guclu, Ozcelebi, Lukkien, Dependability Analysis of Asynchronous Radio Duty Cycling Protocols, ICCCN

46 Consider a low-resource node: Asymmetry and event driven 1. upon observing an event it wants to report it (push by node) 2. it may need information for its work (pull by node) 3. the environment of the node may want to send it information, updates or other (push by environment) 4. the environment may want to have information from the node (pull by environment) Solutions: 3,4: map to time driven behavior: align communication with periodic synchronization of the node with its environment keep alive plus handling pending request inevitably, this introduces a delay, particularly for 4. 1,2; provide always-on environment for demand driven radio control to reduce latency; can also map to time driven behavior of the node 49

47 Overview Physical organization IP The IEEE local area networks Techniques for medium sharing Techniques for energy reduction Wide area IoT-oriented initiatives Metrics 50

48 Outdoor Wired No common infra structure available; some initiatives via light poles or other relatively dense infra Wireless City WiFi 4G/5G: LTE adaptation, LongRange low power WAN technologies Indoor Standard wired infra structure using UTP, fiber, switches, bridges and routers WiFi Bluetooth IEEE based technologies 51

49 Typical tradeoffs are among communication range, data rate, transceiver power and spectrum usage As a rule of thumb, Tradeoffs Increasing range decreases data rate (fix power, use modulation that can be demodulated farther away) Increasing range increases power use (fix modulation and data rate) Increasing power increases data rate (can go to higher modulation with the same error rate) increasing spectrum usage (spreading) increases range and decreases power Note: sketched dependencies are not automatic but require changes in encoding and modulation schemes. Outdoor IoT: long range, low data rate, low power 52

50 Long range: LoRaWAN Picture from LoRa whitepaper on lora-alliance.org 53

51 LoRaWAN (Long Range Wireless WAN), by LoRa Alliance topology: star, IP-connected (L2, act as transparent bridge) gateways single-hop wireless towards sensors physical layer: CHIRP, spread spectrum, wideband (Semtech patent) distinct frequencies Aloha based MAC (just send) bitrate: Adaptive Data Rate, managed by gateway, 0.3kbps 50kbps trading range for bitrate Long range: LoRaWAN device types class A one uplink, two downlink packets device initiated, aloha-like class B: add extra scheduled receive slots class C: always on services geolocation Identification and security Unique Network key (EUI64), ensure security on network level Unique Application key (EUI64) ensure end to end security on application level Device specific key (EUI128) 54

52 From link-labs site Scalability, up to 120 All gateways and nodes use the same channels for all transmissions. Time on air can be quite long. (up to 2 seconds) All uplink transmissions are uncoordinated (Pure Aloha) All gateway transmissions (Acknowledgement and downlink traffic) take the gateway off the air, unbeknownst to nodes trying to transmit. SX1301 based LoRa gateways have only 8 receiver modems to process simultaneous traffic. Improvements Frequency Block Hopping Dynamic Transmit Power and Spreading Factor Selection Synchronous Uplink Slotting Variable Uplink/Downlink Time Boundary Compressed Acknowledgements Quality of Service Listen before talk 55

53 LTE (4G), by 3GPP LTE IoT network: Integrated with the normal 4G network LTE-M(TC) machine type communication end-point negotiated wakeup scheme extended discontinuous repetition, DRX small 1.4MHz assigned bandwidth fraction simplifies receivers Narrowband LTE-MTC further limit the bandwidth to 200KHz 200kpbs down/144kpbs up NB-IoT DSSS (direct-sequence spread spectrum less complex receivers interferes with regular LTE, in principle Since October 2016, NB-IoT is actually deployed 56

54 New low power WAN: NB-FI WAVIoT: Narrowband Fidelity starting at 8bps (!) Further similar issues as LoRa trade range for data rate has some APIs and protocols some sample installations, Seems to make the standard error of implementing the entire OSI stack rather than connecting to IP 57

55 from (November 2017, unverified) 58

56 Physical organization IP The IEEE local area networks Techniques for medium sharing Techniques for energy reduction Wide area IoT-oriented initiatives Metrics Overview 59

57 Metrics (which is how to judge all this) throughput number of bytes per time unit for a station: bytes per interval latency or delay jitter time difference in initiation of a transmission and the start of the receipt consists of processing delay, transmission delay and queueing delay variations in timing, e.g. delay jitter, throughput jitter fairness, ability to prioritize fairness: bound on delay in access to a transmission channel or fair share in competition overhead scalability as utilization increasing the amount of communication increasing # stations e.g. CSMA/CA scales badly when increasing # stations while TDMA scales well as dimensioning predictability reliability LoRaWan can scale the number of gateways with the number of low-power nodes e.g. resilience agains interference power range 60

58 Qualitative metrics +: improves (e.g. Latency + means improves (reduces) Latency) -: makes worse o: no effect/not applicable 61

59 What are IoT networks? Guiding questions What is the role of IP? What techniques are used? techniques for media sharing techniques for reducing energy use Which standards are considered? 62