## 3 Generic Routing Solutions
### Generic Routing Solutions vs. LLN Requirements
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Routing** & **Routing** & **Routing** & **Loss** & **Control** & **Link** & **Node** \\
**Category** & **Protocol** & **State** & **Response** & **Cost** & **Cost** & **Cost** \\ \hline \multirow{4}{*}{LSRPs} & OSPF [36] & No & No & No & Yes & No \\  & LS-IS [39] & No & No & No & Yes & Yes \\  & OISRv2 [49] & No & * & * & Yes & Yes \\  & TBRPF [51] & No & Yes & No & Yes & * \\ \hline \multirow{4}{*}{DVRPs} & RIP[59] & Yes & No & Yes & * & No \\  & AODV [64] & Yes & No & Yes & No & No \\  & DYMO [67] & Yes & * & Yes & * & * \\  & DSR [69] & No & Yes & Yes & No & No \\ \hline \hline \end{tabular}  
* Yes: has satisfied the criterion; No: has not satisfied the criterion; *: need improvements.  
\end{table} 
Table 2: Generic routing protocols assessment for LLNs. As shown in Table 2, the first four protocols, LSRPs, passed the link cost criterion but failed or needed improvement to pass other criteria. LSRPs passed the link cost because these protocols take into consideration the link quality during path selection. In LSRPs, each node must learn the complete network topology map, which leads to large-size routing tables that scale linearly with the growth of network size. Therefore, LSRPs failed to satisfy the routing state criterion. The presence of routing information and topology changes in LSRPs can cause them to fail the control cost criterion. This is because this information needs to be propagated throughout the network, leading to an increase in control overheads. OLSRv2 [49] may have the potential to reduce control overhead to an acceptable level by using the Fisheye routing technique. However, there is no specification of how to accomplish the Fisheye technique; thus, OLSRv2 needs improvement in the control cost criterion. OSPF and IS-IS require advertising and responding to any loss or changes in the link, i.e., link failure, even if the link is not actively used. As a result, OSPF and IS-IS failed to pass the loss response criterion. In contrast, OLSRv2 makes the triggered updates optional; thus, only some links' changes are advertised. This raises a problem in topology consistency, as some links may fail but are not advertised through the network. Therefore, OLSRv2 received a \"*\" in the loss response criterion as it needs improvement. The TBRPF only advertises and responds to link failure in the active paths, so it passed the loss response criterion. OSPF does not consider other routing metrics related to the node itself, such as remaining energy or memory size, during path selection, and so fails the node cost criterion. On the other hand, IS-IS and OLSRv2 provide the option of using other node metrics besides the link metric and, therefore, pass the node cost criterion. TBRPF provides a way to use additional metrics, such as node metrics, but without a specification policy on how to use these additional metrics. Therefore, TBRPF received \"*\" on the node cost criterion as TBRPF needs improvement to pass this requirement. The remaining protocols, DVRPs, satisfied the control cost criterion but failed most of the other criteria. RIP passed the control cost criterion because it uses triggered updates for advertising topology changes in active links. The remaining DVRPs are on-demand protocols where nodes generate control traffic only when they need to send data packets and pass the control cost criterion. A routing table of AODV and DYMO contains only the paths for communicating nodes in the network and thus passes the routing state criterion. RIP also passes the routing state criterion because, for each node, the routing table size can be scaled to the number of destinations instead of the number of nodes in the network. In contrast, even though DSR uses source routing, each node stores the source paths for all the destinations in addition to a blacklist of all unidirectional neighbour links; thus failing the routing state criterion. RIP and AODV propagate changes in the links even if they are not actively used and fail the loss response criterion.