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Autonomous Networking/notes/4 WSN Routing.md

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+-  routing technique is needed to establish multi-hop communication
+- the routing strategy should ensure
+	- mminimun energy consumption
+	- maximization of the network lifetime
+
+#### Ad Hoc Routing Protocols – Classification
+- **network topology**
+	- flat
+	- hierarchical
+- **which data is used to identify nodes**
+	- arbitrary identifier
+	- the position of a node
+		- can be used to assist in geographical routing problems to decide next hop
+		- scalable and suitable for sensor networks
+
+##### Flat routing protocols
+Three main categories
+
+- Proactive protocols (table driven)
+	- always tries to keep routing data up-to-date
+	- active before tables are actually needed
+		- routes are always already known
+		- more bandwidth and energy usage
+- Reactive protocols
+	- route determined only when needed
+	- operates on demand
+		- when a route is needed, a kind of global search is started
+			- causes delays if routes are not already cached
+- Hybrid protocols
+	- combination of these behaviors
+
+### Destination Sequence Distance Vector (DSDV)
+- based on bellman-ford algorithm
+- proactive protocol
+- add aging information to avoid routing loops
+- on topology change, send incremental route updates
+- unstable route updates are delayed
+
+![[Pasted image 20241011191033.png]]
+
+- to avoid loops, DSDV adds a **sequence number** to each routing table entry which is periodically updated. Routes with higher sequence number are preferred
+
+##### Reactive protocols
+
+### Flooding
+- copies of incoming packets are sent by every link except the one by which the packet is arrived
+- generates a lot of superfluous traffic
+- flooding is a reactive technique, and does not require costly topology maintenance and complex route discovery algorithms
+
+Characteristics:
+- derivery is guaranteed (e grazie al cazzo)
+- one copy will arrive by the quickest possible route (wow)
+
+Drawbacks:
+- implosion: duplicated messages are broadcasted to the same node
+- overlap: if two nodes share the same under observation region, both of them may sense the same stimuli at the same time. As a result, neighbor nodes receive duplicated messages
+- resource blindness (no knowledge about the available resources)
+- does not take into consideration all the available energy resources
+- consumes a lot of energy
+
+### Gossiping
+- nodes send the incoming packages to a randomly selected neighbor
+- avoids implosion, but it takes long to propagate the message
+
+### Dynamic Source Routing (DSR)
+- Source routing: Each data packet sent carries in its header the complete, ordered list of nodes through which the packet will pass
+- The sender can select and control the routes used for its own packets and supports the use of multiple routes to any destination
+- Including the route in the header of each packet, helps other nodes forwarding the packet to cache the routing information for future use
+
+**DSR is composed by two main mechanism:**
+- **Route Discovery**
+	- mechanism by which a node S obtains the route to a destination node D
+	- used only if S doesn't already know the route
+	- every request contains an unique ID and a route record
+		- S sends a broadcast Route Request packet
+		- every node broadcasts the packet (with the same ID) appending their own address to the route record
+		- when D receives the request, it sends a Route Reply back to the initiator S, with a copy of the route record
+			- more than a route can be returned, making the protocol more resistent to changes in network topology
+- **Route Maintenance**
+	-  mechanism by which a node S can detect (while sending a packet to D) if the network topology has changed and the route can't be used anymore
+
+![[Pasted image 20241012174130.png]]
+
+### Ad-hoc On Demand Distance Vector routing (AODV)
+- a mix between DSR and DSDV
+- nodes maintain routing tables
+- sequence numbers added to handle stale caches (when routing info is too old)
+- nodes remember from where a packet came and populate routing tables
+
+We can see it as an improved DSDV, as it minimizes the number of required broadcast by creating routes on a demand basis.
+- if the source node S does not have the route to D, S initiates a path discovery process to locate D
+- the route request is broadcasted to the neighbors
+- when a node receives a broadcast RREQ, it records in their table the address of the neighbor who sent the request
+- when the destination or an intermediate node that can reach the destiation is reached, it replies with a route reply (RREP) packet back to the neighbor from which it first received the RREQ
+- the RREQ is routed back along the reverse path
+- nodes along the path updates their table
+
+![[Pasted image 20241012175224.png]]
+
+## Geographical routing
+- routing tables contain information to which next hop a packet should be forwarded
+- this can be explicitly constructed, or implicitly inferred from physical placement of nodes
+	- by knowing the position of nodes, we can send the packet to a neighbor in the right direction
+	- we can also do *geocasting*: sending to any node in a given area
+	- to map a node ID to the node position we might need a location service
+
+Strategies
+- **Most forward within range r**
+	- send to that neighbor that realizes the most forward progress towards destination, but staying in a range r (quello che stando nel range r si avvicina di più geograficamente parlando)
+- **Nearest node with (any) forward progress**
+	- the opposite as the previous strategy
+	- minimizes transmission power
+- **Directional routing**
+	- choose next hop that is angularly closest to destination (closest to the connecting line to destination)
+	- come se tracciassi una linea tra S e D e prendessi gli hop più vicini alla linea
+	- problem: might result in loops!
+
+#### Dead ends problem
+![[Pasted image 20241012182403.png]]
+
+## Conclusion
+- there are many other protocols
+- the best solution depends on network characteristics
+	- mobility
+	- node capabilities
+- geographic approach allows to save more energy
+- proactive approach is fast, but involves overhead
+- reactive approach generate much less overhead, but it is slower