# Mobile Ad Hoc Networks (MANETs)

- An infrastructure-less network formed by mobile wireless nodes
- Nodes in a MANET can communicate via a single- or multi-hop approach (due to the 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 be uncooperative or faulty, they may drop or compromise packets
- Typically routing is split into **route discovery** and **actual data transmission**.
    - Nodes have to self-organise in order to route.

![img](img/d.png)

(The green boxes show the chosen route.)

The source has a limited range of nodes it can detect. It cannot send data directly 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 protocols
- Nodes in the network maintain comprehensive routing information about 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 about 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 the different MANET protocols:

![img](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 non-existent in MANETs
- DTNs expand MANETs to allow more intermittent and sparse connections between 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 they 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 in networks with limited resources.