# DTN and Non-DTN Routing Protocols for Inter-CubeSat Communications: A comprehensive survey
## 3 Routing Protocols in Connected CubeSat network
### Single-Layer Routing for Satellite Networks
Iterative optimization methods are applied due to the NP-hardness of the mixed-integer linear programming problem. The results of the FSA algorithm suggested that the simulated annealing method outperformed the other regular link assignment methods. DT-DVTR and FSA algorithms are both connection-oriented routing protocols that consider their network topology based on the predetermined satellite motion calculations. However, neither are efficient in sudden \begin{table}
\begin{tabular}{p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Node and** **Topology-Based Algorithms** & **Network Type** & \begin{tabular}{c} **Topology** \\ **Information** \\ \end{tabular} & **Decision Criteria** & \
\begin{tabular}{c} **Resources** \\ **Consumption** \\ \end{tabular} &
\begin{tabular}{c} **Links** \\ **Recovery** \\ \end{tabular} \\ \hline dv-dvrt [20] & Connection-oriented & Predictable/off-line & Link metric & High & No \\ \hline fsa [21] & Connection-oriented & Predictable/off-line & Link metric & High & No \\ \hline cerm [22] & Connection-oriented & Predictable/off-line & Link metric & High & No \\ \hline elb [23] & Connection-oriented & Predictable/dynamic & Link metric /congestion & High & Yes \\ \hline cal-lsn [24] & Connection-oriented & Predictable/dynamic & Link metric & High & Yes \\ \hline par [25] & Connectionless & Predictable/dynamic/Mesh-grid & Historical Info/Link metric & High & Yes \\ \hline epar [25] & Connectionless & Predictable/dynamic/Mesh-grid & Historical Info/Link metric & High & Yes \\ \hline ddra [26] & Connectionless & Predictable/dynamic/Mesh-grid & Link metric & High & Yes \\ \hline dra [35,36] & Connectionless & Predictable/logical locations/Mesh-grid & Node info & Low & No \\ \hline laor [37] & Connectionless & Predictable/dynamic/Mesh-grid & Node info & High & No \\ \hline dodr [38] & Connectionless & Predictable/dynamic/Mesh-grid & Node info & Medium & Yes \\ \hline lca [39] and lcpr [40] & Connectionless & Predictable/logical locations/Mesh-grid & Node info & Low & No \\ \hline lrs [41] & Connection & Predictable/dynamic/Mesh-grid/MSN & Node info/zone info & Medium & No \\ \hline slsr [42] & Connectionless & Predictable/dynamic/Mesh-grid/MSN & Node/topology info & Medium & Yes \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Single-layer routing algorithms. changes in the topology, because they do not have regular routing table updates. Compact Explicit Multipath Routing (CEMR) is a multipath routing technique for mobile satellite networks [22]. In a similar fashion to the DT-DVTR and FSA algorithms, CEMR models the dynamic topology of the satellite network as a series of discrete-time static topologies. However, CEMR introduces the concept of a compact path identifier (PathID), which includes the ISL identifiers of all hops along the path to the destination. This technique allows for all of the nodes in the path to transmit their packets based on the embedded information in the PathID. A PathID verification process is also implemented in CEMR to regularly evaluate the precision of the PathID. Thus, CEMR can provide lower overheads when compared with other previous source multipath routing or Multiprotocol Label Switching (MPLS) techniques [43]. Contrary to the traditional LEO satellite routing techniques, CEMR considers propagation delay as well as queuing delay as a routing cost metric. Besides this, the possibility of forwarding data over multiple separate paths causes CEMR to provide load balancing, minimize overall delay, and improve throughput. However, packet loss is not considered to be detected for the next hop. An Explicit Load Balancing (ELB) is a multi-hop routing algorithm proposed to solve the load balancing issue in congested mobile satellite networks [23]. The basic idea of ELB is that adjacent satellites can exchange their congestion status to minimize the load on the congested satellite and select an alternative path with less traffic.