# 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 the 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 reach their destinations.
- 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 when nodes come within communication range of each other.
- 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 $D$.

#### 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 number of message copies and the frequency with which messages are replicated.

- 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.

#### 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.

**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 the Café protocol by coalescing the proposed **adaptive forwarding algorithm with an adaptive replication management technique**