# 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.

![img](/lectures/acn/img/d.png)

(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

![img](/lectures/acn/img/e.png)

### 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.
