# Vortex: Network-Driven Opportunistic Routing for Ad Hoc Networks
## 2 Related Works
### Local information-based routing protocols  
The protocols classified into this type do not require network-wide information for route or forwarder selection, and only require local information to perform the routing procedure. DSR [2] and AODV [3], the representative conventional unicast routing protocols for MANET, require route discovery procedures when they do not have valid route information to destination terminals. They also take a single path-based forwarding procedure with the discovered route to the destination terminals. The main difference between the protocols is that DSR manages the end-to-end routes, whereas AODV only manages the \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Local Information-Based Routing**} & \multicolumn{2}{c}{**Network-Wide Information-Based Routing**} \\ \cline{2-5}  & **Route-Based** & **Forwarder-Based** & **Route-Based** & **Forwarder-Based** \\ \hline \multirow{2}{*}{Single path} & DSR [2], FT-AORP [9] & AODV [3], CORA [10] & SOAR [11] 1, CEPRM [8] & \multirow{2}{*}{GeRaF [12] 1} \\ \hline \multirow{2}{*}{Multiple path} & CHORUS [13] 1, CHOR [14] 1, EORB-TP [15] 1 & VORTEX 1, AOMDV-GA [6] & HRAN [16], OxDSR [17] 1 & ExOR [18; 19] 1, LCAR [20] 1, TDICOR [21] 1 \\ \hline \hline \end{tabular}  
* Opportunistic Routing Protocol.  
\end{table} 
Table 1: Routing protocols for multi-hop networks. next or previous forwarder for a designated destination terminal. Some improved routing protocols such as FT-AORP [9], CORA [10], EORB-TP [15], and AOMDV-GA [6] have been proposed aiming to achieve better routing and communication performance. However, the improved protocols are generally designed for a specific field and are not sufficiently applicable to other fields. CHORUS (clustered hierarchical opportunistic routing using stability information) [13] and CHOR (clustered hierarchical opportunistic routing) [14], our previous works, also use local information to form clusters and discover guides for opportunistic forwarding. Note that CHORUS is the former version of CHOR and this paper only explains CHOR. CHOR first assigns two types of clusters, local cluster (LC) and regional cluster (RC). LC and RC are established based on the neighbor terminal degree information and CHOR assigns hierarchy information to each cluster head (CH) based on the clustering results. After the clustering and hierarchization, MANET would have a virtual gradient where CH of RC represents the top of the gradient. CHOR then starts the route discovery procedure in the same way as the conventional discovery procedure. The unique feature of CHOR in the discovery procedure is that CHOR degenerates the collected route information and uses the degenerated route information as a guide for forwarding. Thus, the information contains only the nearest CH information and some rendezvous relay terminals. That is to say, packets forwarded by CHOR basically climb up the gradient toward the rendezvous relay terminals or the CH, and then descend the gradient towards destination terminals. One of the advantages of the above-stated routing protocols is the light and simple routing operation. In other words, it is not necessary for them to gather information from entire networks for the routing procedure, and they also have a certain degree of rapid adaptability to changes in the network environment. However, the simple procedure does not always result in the optimal solution in the sight of comprehensive route management. That is to say, the individual route establishment may fail to use network resources or reuse other routing information efficiently. **Network-wide information-based routing**  
Most ORs make use of network-wide information for the forwarder selection or forwarding decision. Several OR protocols have been proposed and the following ExOR and GeRaF are representative legacy ORs.