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6LoWPAN Connectivity Protocols in IoT

Introduction 
  • Low-power Wireless Personal Area Networks over Ipv6.
  • Allows for the smallest devices with limited processing ability to transmit information wirelessly using an Internet protocol.
  • Allows low-power devices to connect to the Internet.
  • Created by the Internet Engineering Task Force (IETF) - RFC 5933 and RFC 4919.
Features of 6LoWPANs
  • Allows IEEE 802.15.4 radios to carry 128-bit addresses of Internet Protocol version 6 (IPv6).
  • Header compression and address translation techniques allow the IEEE 802.15.4 radios to access the Internet.
  • IPv6 packets compressed and reformatted to fit the IEEE 802.15.4 packet format.
  • Uses include IoT, Smart grid, and M2M applications.
Addressing in 6LoWPAN
  • 664-bit addresses : globally unique
  • 16 bit addresses : PAN specific; assigned multicast not supported by 802.15.4
  • IPv6 packets carried as link layer broadcast frames

6LowPAN Packet Format




Header Type : Dispatch Header


  • Dispatch : Initiates communication
  • 0,1 : Identifier for Dispatch Type
  • Dispatch :
          6 bits
          Identifies the next header type
  • Type Specific Header :
          Determined by Dispatch header

Header Type : Mesh Addressing Header



  • 1,0 : ID Mesh Addressing Header
  • V: '0' if originator is 64-bit extended address , '1' if 16-bit address
  • F: '0' if destination is 64-bit addr., '1' if 16-bit addr.
  • Hops Left : decremented by each node before sending to next hop

Header Type : Fragmentation Header




6LoWPAN Routing Considerations
  • Mesh routing within the PAN space.
  • Routing between IPv6 and the PAN domain
  • Routing protocols in use:

          LOADng
          RPL

LOADng Routing

Derived from AODV and extented for use in IoT.
Basic operations of LOADng include :
  • Generation of Route Requests (RREQs) by a LOADng Router (originator) for discovering a route to a destination,
  • Forwarding of such RREQs until they reach the destination LOADng Router,
  • Generation of Route Replies (RREPs) upon receipt of an RREQ by the indicated destination, and unicast hop-by-hop forwarding of these RREPs towards the originator.
  • If a route is detected to be broken, a Route Error (RERR) message is returned to the originator of that data packet to inform the originator about the route breakage.
  • Optimized flooding is supported, reducing the overhead incurred by RREQ generation and flooding.
  • Only the destination is permitted to respond to an RREQ.
  • Intermediate LOADng Routers are explicitly prohibited from responding to RREQs, even if they may have active routes to the sought destination.
  • RREQ/RREP messages generated by a given LOADng router share a single unique , monotonically increasing sequence number.
RPL Routing
  • Distance Vector IPv6 routing protocol for lossy and low power networks.
  • Maintains routing topology using low rate beaconing.
  • Beaconing/link rate increase on detecting inconsistencies (e.g node/link in a route is down).
  • Routing information included in the datagram itself.
  • Proactive : Maintaining routing topology.
  • Reactive : Resolving routing inconsistencies.
  • RPL separates packet processing and forwarding from the routing optimization objective, which helps in Low power Lossy Networks (LLN).
  • RPL supports message confidentiality and integrity.
  • Routing optimization objectives include
          - minimizing energy
          - minimizing latency
          - satisfying constraints (w.r.t. node power, bandwidth, etc.)
  • RPL operations require bidirectional links.
  • In some LLN scenarios, those links may exhibit asymmetric properties.
  • It is required that the reachability of a router be verified before the router can be used as a parent

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