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