Notes On Chapter 32 -- The Internet Of Things

• 32.1 Introduction
  
  
  • Internet of Things (IoT)
  • Communication among machines
  • Machine to machine (M2M)
  • Motivation
  • A wireless technology
  
  
• 32.2 Embedded Systems
  
  
  • IoT refers to communication among computers embedded in devices. Most computers are embedded systems.
  • Using IoT, one may implement amenities such as home automation.
    
    
  • 32.2.1 Embedded Systems In The Smart Grid
    
    
    • Electric devices could schedule work based on knowledge off the Internet regarding the cost of power at different times.
    
    
  • 32.2.2 Embedded Online Security Systems
    
    
    • Security devices can be programmed to send a message when something unusual happens, turn on lights, video, and so forth.
    • There can be a sophisticated rule-based response to various contingencies.
    
    
  • 32.2.3 Embedded Systems In Retail
    
    
    • Retail systems could recognize traits of people and display targeted advertisements.
    • Product placement decisions could be based on monitoring the behavior of customers.
  
  
• 32.3 Choosing A Network Technology
  
  
  • Issues include bandwidth, mobility, power consumption, and battery life.
  • No single network technology is best.
  
  
• 32.4 Energy Harvesting
  
  
  • Battery replacement can be expensive.
  • Extracting energy from the surrounding environment is a possible alternative.
  • It could involve using energy from repeated actions.
  
  
• 32.5 Low Power Wireless Communication
  
  
  • WiFi design does not emphasize power conservation.
  • Use of low power runs the risk of loss of range and susceptibility to interference.
  • Thus design of low power networks must be done with care.
  
  
• 32.6 Mesh Topology
  
  
  • One way to make a low-power network is to use a mesh topology.
  • To compensate for limited range, devices forward packets.
    
    
    
    
  • Mesh networks self-organize using broadcasts to find neighbors, and cooperating to discover routes.
  • Orphans or islands could be problematic.
  
  
• 32.7 The ZigBee Alliance
  
  
  • The ZigBee Alliance is a consortium of network equipment vendors.
  • They maintain specs for low-cost, energy efficient mesh networks, especially for smart grids.
  • www.zigbee.org
  • Where possible, ZigBee incorporates existing standards, which facilitates interoperation with existing networks.
  
  
• 32.8 802.15.4 Radios And Wireless Mesh Networks
  
  
  • The resulting network design has very small packet size, low data rate, and short range.
    
    
    
    
  • However, it conforms well to the key design criterion: low power, and situations in which the amount of data to be transferred is small.
  
  
• 32.9 Internet Connectivity And Mesh Routing
  
  
  • Embedded systems typically have very limited computational power and storage.
  • Nodes are designed to rely on cloud services accessed through a border router connected to the Internet.
  • It's important for nodes to have routes to the border router.
  • Nodes use a breadth-first form of distance vector routing, starting with the border router, to compute a best path to the border router for each device.
    
    
    
    
  • Measuring incoming signal strength does not tell the signal strength in the opposite direction.
  • ZigBee includes a Mesh Link Establishment (MLE) protocol that devices use to determine how well their neighbors are able to receive their transmissions. ("Do you read me? I read you five by five.")
  
  
• 32.10 IPv6 In A ZigBee Mesh Network
  
  
  • ZigBee is 'based' on IPv6, but IPv6 requires an MTU of at least 1280 octets, while the MTU of ZigBee is 127 octets.
  • The workaround is an extra layer of protocols between IPv6 and the underlying MAC protocols - IPv6 over Low Power Wireless Personal Area Networks (6LoWPAN)
  • The adaptation layer aka shim layer accepts a datagram, divides it into pieces, and sends them one at a time across a link.
  • The protocol is not end-to-end, like fragmentation. The adaptation layer at the next hop reassembles and passes the result to IPv6.
  • There is a special version of IPv6 Neighbor Discovery for use with ZigBee: 6LoWPAN-ND, which deals with the fact that a single broadcast does not necessarily reach all nodes.
  • Nodes register their addresses with the border router, which takes care of rejecting duplicate addresses.
  
  
• 32.11 The ZigBee Forwarding Paradigm
  
  
  • Nodes in a ZigBee use Routing Protocol For Low Power And Lossy Networks (RPL).
  • The assumptions underlying the use of RPL are that a) the topology of the network will change infrequently, and b) nodes may not have enough memory to store a complete routing table.
  • RPL does not send frequent updates or converge on routes rapidly.
  • Under RPL, nodes inform the border router about the mesh topology, and the border router computes a tree of routes for all nodes. (Destination Oriented Directed Acyclic Graph (DODAG))
  • When it has a datagram from the Internet to forward into the mesh, the border router computes a route and sends it along that route using a source-route header on an encapsulating IPv6 datgram.
  
  
  
  
• 32.12 Other Protocols In The ZigBee Stack
  
  
  • The figure shows other protocols.
  • TLS and PANA are for security.
  • mDNS and DNS-SD are for accessing DNS.
  
  
  
  
• 32.13 Summary