notes/docs/lectures/acn/02_MANET_and_DTN.md

Mobile Ad Hoc Networks (MANETs)

• An infrastructure-less network formed by mobile wireless nodes
• Nodes in MANET can communicate via single or multi-hop approach (due to absence of centralised network infrastructure)
• Nodes operate as clients, routers and servers at the same time to forward packets
• The mobility of nodes results in frequent and unpredictable changes in network topology

One of the core features of a MANET node is the ability to autonomously connect to other nodes and configure itself for data transmission over the network.

MANET Routing

• Mobile wireless nodes create a temporary connection between them to forward data
• Because some nodes may not be cooperative or faulty, they may drop/compromise packets
• Typically routing is split into route discovery and actual data transmission.
  • Nodes have to self organise in order to route.

(green boxes is route chosen)

The source has a limited range of nodes it can detect, it cannot send it direct to the destination as it doesn't know where the destination is. Hops are decided by communication protocols.

Proactive MANETs

• Also known as table driven routing protocol
• Nodes in the network maintain a comprehensive routing information of the network
  • This is done by spreading network status information to nodes and tracking changes in network topology - think the network is constantly pinged
  • These status updates can slow the network with the traffic
• Useful if the network is not that large

Reactive MANETs

• Also known as on-demand routing
• Network nodes only store information of paths to destination nodes
• Nodes delay the search for routes to new destinations in order to reduce communication overheads
  • i.e. if a route is found between A and B, this route will be stored and not recalculated
• May be slower, as a shorter path may not be used

Hybrid MANETs

• Hybrid protocols combine the advantages of proactive and reactive protocols to reduce traffic overheads and route discovery delays

Table showing all different protocols of MANETs

Delay/Disconnection Tolerance

Traditional MANET routing protocols like DSR and AODV (both reactive) cannot work in intermittent infrastructure-less environments because they require a complete path from source to destination for communication.

• Messages get dropped at intermediate nodes when the link to the next hop is none existent in MANETs
• DTNs expand MANETs to allow more intermittent and sparse connections of nodes caused by node mobility or low transmission range.

Store-carry-forward Paradigm

• DTN routing protocols allow forwarding of messages by using a 'store-carry-forward' approach.
  • messages are stored by nodes and moved in hops throughout the network until messages reach their destination
  • This approach is used by DTN routing protocols to increase the probability of message delivery.

DTN Protocol Classifications

Flooding based

• Flooding based routing protocols spread a message and have multiple copies of the message in the network.
• This is done to increase the probability of messages reaching their destination and also decrease the time of delivery

Forwarding based

• Forwarding based routing protocols gather information about the nodes in a network to select the best path to forward messages with the aim of enhancing message delivery networks with limited resources.