45 lines
2.6 KiB
Markdown
45 lines
2.6 KiB
Markdown
# DTN Protocols - Advanced
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**Rate control** - addresses easing network congestion by controlling the rate of traffic on the network.
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**Adaptive forwarding** - to direct traffic away from congestion hot spots.
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#### Spray and Focus
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- Spray and Focus replicates an allowable number of messages from the source in the spray phase.
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- **The focus phase allows** each node to forward a copy of its messages to other potential nodes until the messages reach their destinations.
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- The protocol uses a single-copy, utility-based routing scheme to forward a copy of the message further.
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- Forwarding decisions are made based on **timers** which record the times when nodes come within communication range of each other.
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- Node $A$ forwards a message with destination $D$ to node $B$, **if and only if** $B$ has a higher potential of delivering the message to $D$.
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#### SimBet
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- 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.
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- A central node has the ease of connecting other nodes in a network.
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- This is known as **centrality**, a measure of the **structural importance** of a node in a network.
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- A central node uses **similarity and betweenness centrality** to avoid unnecessary information exchange in the entire network.
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- SimBet maintains a single copy of each message in the network to reduce resource overheads.
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### Replication Management
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Replication management refers to easing network congestion by managing the number of message copies and the frequency with which messages are replicated.
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- This is a 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.
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#### Café
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- Congestion Aware Forwarding Algorithm (Café)
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- Single-copy
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- Adaptive forwarding techniques - to reduce network congestion by directing traffic away from nodes experiencing congestion to less congested areas of the network.
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- Uses **Contact Manager** and **Congestion Manager**
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**Contact Manager** - deals with nodes' forwarding heuristics, updating statistics for each contact such as frequency and duration.
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**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.
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#### CafREP
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- Congestion Aware Forwarding and Replication (CafREP)
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- replication-based
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- Builds on the Café protocol by coalescing the proposed **adaptive forwarding algorithm with an adaptive replication management technique**
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