1. by Saltanat Mashirova & Afshin Mahini
Mobile Ad Hoc Network
by Saltanat Mashirova & Afshin Mahini

2. What is a mobile ad hoc network?
- A mobile ad hoc network is a self-configuring infrastructureless network of mobile devices connected by wireless communications.
- Each device in the network is allowed to move independently, forms its own connections to other devices and must forward information notwithstanding of its own use. Therefore, each device must become a router in the network.
- A mobile ad-hoc network (MANET) is an ad-hoc network but an ad-hoc network is not necessarily a MANET.
- If one device needs to communicate to another device in the network, usually a query is sent to following devices along the path to the device queried.
- Topology changes frequently

3. Example network

4. Characteristics of MANET
1. Dynamic Network Topologies - Nodes are free to move arbitrarily, meaning that the network topology, which is typically multi-hop, may change randomly and rapidly at unpredictable times.
2. Bandwidth constrained links - Wireless links have significantly lower capacity than their hardwired counterparts. They are also less reliable due to the nature of signal propagation.
3. Energy constrained operation - Devices in a mobile network may rely on batteries or other exhaustible means as their power source. For these nodes, the conservation and efficient use of energy may be the most important system design criteria.

5. Routing Protocols
- Table driven or proactive routing protocols - Every node in the network has one or more routes to any possible destination in its routing table at any given time
- On demand or reactive routing protocols - Every node in the network obtains a route to a destination on a demand fashion. Reactive protocols do not maintain up-to-date routes to any destination in the network and do not generally exchange any periodic control messages.
- Hybrid routing protocols - Every node acts reactively in the region close to its proximity and proactively outside of that region or zone

6. Table Driven vs On demand

8. Destination-Sequenced Distance Vector
-Based on the Bellman-Ford algorithm
- Developed by C.Perkins and P. Bhagwat in 1994
- Every node maintains a routing table
- all available destinations
- the next node to reach to destination
- the number of hops to reach the destination
-Periodically send table to all neighbors to maintain topology
- Main contribution to solve loop problem
- The main complexity is in generating and maintaining these routing tables

9. Destination-Sequenced Distance Vector
When X receives information from Y about a route to Z
–Let destination sequence number for Z at X be Xs, Ys is sent from Y
–If Xs > Ys, X discards the routing information received from Y
–If Xs = Ys, and if cost of going through Y is smaller than the route known to X, X sets Y as the next hop to Z
–If Xs < Ys, X sets Y as the next hop to Z, and Xs is updated to equal Ys

10. Disadvantages of DSDV
- Wasting of bandwidth because of unnecessary advertising of routing information even if there is no change in the network topology
– DSDV doesn’t support Multi path Routing.
– Time delay is determined hardly for advertisement of routes.
– Hard to maintain routing table for large network. Each and every host in the network should maintain a routing table for advertising. But for larger network this would lead to overhead, which consumes more bandwidth.

11. Dynamic Source Routing
-allows the network to be completely self-organizing and self-configuring, without the need for any existing network infrastructure or administration
- utilizes source routing
-mobile nodes are required to maintain route caches that contain the source routes of which the mobile is aware
- each node can become aware of other nodes in its neighborhood by using local broadcast

12. How DSR works?
- the source node broadcast to the neighbors a route request packet (called RREQ)
- each neighbor either satisfy the RREQ, by sending back a routing reply (RREP), or rebroadcast the RREQ to its own neighbors after increasing the hop_count by one
- RREQ travels from source to many destinations, it automatically sets up the reverse path, from all nodes back to the source

13. DSR Let’s node S wants to send packet to node D
- A receives a packet, and A doesn’t have route to D; so it broadcasts packet after adding its address to source route

14. Limitations of DSR
- Scalability, since the source need to add the IDs of all nodes along the path to the destination which increase the overhead in every data packet sent.
- When a link is broken RouteError packets need to go all the way to the source to inform it about the problem due to this it increase the packet delay time.
- Intermediate node can use outdated routes stored in their cache.
- As mobility increases more links are broken which cause a significant decrease in the packet delivery fraction.

16. References http://ciemcal.org/manet-and-routing-techniques/
file:///Users/saltanat/Desktop/dsr.pdf