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docs/lectures/acn/05_DTN_advanced_protocols.md

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+# DTN Protocols - Advanced
+
+**Rate control** - addresses easing network congestion by controlling the rate of traffic on the network.
+
+**Adaptive forwarding** - to direct traffic away from congestion hot spots.
+
+#### Spray and Focus
+
+* Spray and focus replicates an allowable number of messages from source in the spray phase.
+* **The focus phase allows** each node to forward a copy of its messages to other potential nodes until the messages gets to its destination.
+* The protocol uses a single-copy utility based routing scheme to forward a copy of the message further.
+* Forwarding decisions are made based on **timers** which record the times nodes come in communication range of each other.
+* Node $$A$$ forwards message with destination $$D$$ to node $$B$$ , **if and only if** $$B$$ has a higher potential of delivering the message to $$D$$.
+
+#### SimBet
+
+* A source node with no prior knowledge of the destination node will forward a message to a more central node that has the potential of finding a suitable relay node.
+  * A central node has the ease of connecting other nodes in a network.
+  * This is known as **centrality** a measure of the **structural importance** of a node in a network.
+* A central node uses **similarity and betweenness centrality** to avoid unnecessary information exchange in the entire network.
+* SimBet maintains a single copy of each message in the network to reduce resource overheads.
+
+### Replication Management
+
+Replication Management refers to easing network congestion by managing the amount and frequency that messages are replicated.
+
+* This is particularly notable concern as it is often the replication of messages that leads to congestion in DTNs, with surplus and redundant messages causing wastage within node message buffers.
+
+#### Café
+
+* Congestion Aware Forwarding Algorithm (Café)
+  * Single-copy
+  * Adaptive forwarding techniques - to reduce network congestion by directing traffic away from nodes experiencing congestion to less congested areas of the network.
+  * Uses **Contact Manager** and **Congestion Manager**
+
+**Contact Manager** - deals with nodes forwarding heuristics, updating statistics for each contact such as frequency and duration's.
+
+**Congestion Manager** - focuses on calculating the availability of nodes, keeping and updating a record of information such as the amount of available buffer and delays expected from each contacted node.
+
+#### CafREP
+
+* Congestion Aware Forwarding and Replication (CafREP)
+  * replication-based
+  * builds on Cafe protocol by coalescing the proposed **adaptive forwarding algorithm with an adaptive replication management technique**