# DTN and Non-DTN Routing Protocols for Inter-CubeSat Communications: A comprehensive survey
## 4 DTN Routing Protocols in Disjointed Satellite Networks
### DTN Quota-Based Techniques
In another similar work in [64], the proposed multiple spraying technique divides the deadline time span for a message to be delivered to its destination into multiple smaller periods. Every single period will contain the Spray and Wait phase and each message is associated with Time-To-Live (TTL) as a deadline to consider the minimum possible Wait phase. Thus, a limited number of replicas are injected for the Wait phase to start and, if no acknowledgment is received at the end of the Wait phase, the algorithm injects more replicas to raise the delivery probability. Similarly, the Utility-based Distributed routing algorithm with Multi-copies (UDM) allows for a source node to deliver multi-copies to a fixed number of its adjacent nodes [65]. After that, these intermediate nodes forward the message copies to nodes with a higher probability of encountering the destination node according to the utility function. The UDM algorithm varies from Spray and Wait in two main aspects. Firstly, instead of using direct routing to deliver the packet to the destination after injecting a finite number of replicas into the Spray phase, predicted routing that is based on a utility function is used. Secondly, UDM incorporates some buffer control techniques to handle packet congestion. Resultantly, the UDM can provide reduced overheads with a reasonable delivery delay when compared with Epidemic and Spray and Wait algorithms. In Reference [66], a Multi-Copy Spray Routing (MCSR) protocol was proposed. MCSR uses the same concept of wisely spraying a finite number of replicas at the first stage, but then forwards the message to its destination in the second phase while using the single-copy forwarding technique. Using this strategy, MCSR can form an equilibrium by reducing the number of replicas of flooding-based algorithms and reducing the extensive delay produced by single-copy forwarding algorithms. More recently, [PERSON] [68] proposed a heuristic-based algorithm that forwards the limited replicas to nodes that have a larger number of encounters with other nodes in their history, as this implies that these nodes also have a higher probability of encountering the destination nodes. However, under these circumstances, if the destination node is isolated and in a low node density area, the packet might never be delivered. [PERSON] [44] proposed a heuristic-based algorithm that gives more weight to the nodes that encounter particular destinations to overcome this problem. Hence, if a node has a low frequency of encounters with other nodes, but has evidenced several encounters with a destination, that node is allocated a higher weighting to receive more replicas of packets that were associated with that destination. In another more recent work by [69], Adaptive Message Replication Technique (AMRT) that fits onto quota protocols was proposed. AMRT assigns different numbers of replicas to each generated packet based on the congestion that exists amongst the sender's neighbours. In Reference [47], a Mobility Based Routing Protocol (MBRP) was introduced to assess encountered nodes according to their logged mobility patterns to forward a restricted number of packet copies. Inthe case of disjointed space-time graph, the MBRP uses mobility patterns to evaluate encountered nodes reachability, unlike history-based routing protocols, which uses prior encounters for future contact estimation. While some quota-based algorithms only rely on retrieved information from the space-time graph for data routing in networks with mobile nodes, Reference [67] developed Multi-copy Forwarding in Cyclic (MFC) MobiSpace for DTNs with periodic mobility. This MFC extends the Expected Minimum Delay (EMD) that was originally proposed by the authors for a single-copy forwarding scenario [70], where the network is modelled as a state-space graph before an optimal stopping technique is used to extract the extended EMD.