Routing in 6LoWPAN

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Transmission of IPV6 packets over LoWPAN devices was considered nearly impossible once because the MTU of IPV6 packets is 1280 bytes which is much larger than the MTU of IEEE 802.15.4 data link layer (127 bytes). So 6LoWPAN implements an adaptation layer between data link layer and network layer to support transmission of IPV6 packets over 802.15.4 . Main purpose of the adaptation layer is to fragment and reassemble the IPV6 packets. Routing in 6LOWPAN can be divided into two categories based on the decision taken either on adaptation layer or on the network layer.

If the routing decision is taken under the adaptation layer it is Mesh Under.
If the routing decision is taken on the network layer it is Route Over.


Mesh Under:

          In mesh under scheme, routing and forwarding are performed at link layer . To send a packet to a particular destination,the EUI 64 bit address or the 16 bit address is used and sent to the neighbour node  so that it can reach to the destination. An IP packet sent by the network layer is fragmented by the adaptation layer into number of fragments . These fragments travel independently and reach the destination and at the destination the adaptation layer reassemble them into the IP packet and give it to the network layer. In case if any fragment is lost,all the fragments should again be retransmitted to the destination.


Route Over
    
      In Route Over Scheme all routing decisions are taken on the network layer. The IP routing supports the forwarding of packets with the help of IP routing tables and IPV6 hop-by -hop options . IP packet is   fragmented the adaptation layer into a number of packets and sent to the next hop. At the next hop all these fragments are reassembled by the adaptation layer and sent to the network layer. At the network layer it checks whether the packet is to it or not , if not it will transmit to the next hop according to the routing table. If one or more fragments is missing or lost then all the fragments has to be retransmitted at one hop distance.


 Conclusion

 In case of total delay mesh under scheme is better when compared to the route over.
whereas if it is noisy environment then it is better to go for route over.

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