# SDN-OpenFlow Topology Discovery: An Overview of Performance Issues
## 3 Recent SDN Topology Discovery Performance Studies
### Link Discovery Improvement Algorithms
#### 3.1.1 Periodic
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Proposal** & **Methodology** & **Location of Logic** & **Operation Mode** & **Advantage** & **Disadvantage** \\ \hline \multirow{4}{*}{OFPDv2} & \multirow{2}{*}{\begin{tabular}{c} Merge Packet\_In messages \\ from each port to each \\ SDN-Switch \\ \end{tabular} } & \multirow{2}{*}{Controller} & \multirow{2}{*}{Periodic} & (1) Reducing CPU overhead. (2) Reducing the bandwidth overhead on the control & & It works periodically, and this may introduce \\  & & & & & channel. & unnecessary \\ \hline \multirow{4}{*}{sOFTDP} & \multirow{4}{*}{\begin{tabular}{c} Triggering topology \\ discovery service by link \\ failure events monitored by \\ Bidirectional Forwarding \\ Detection \\ \end{tabular} } & \multirow{4}{*}{Switches} & \multirow{4}{*}{Event} & (1) Reduce learning time. (2) Reduce adaptation time. (3) Reduce CPU overhead. & It restricts the controller’s ability to collect statistical data on discovery traffic \\ \hline \multirow{2}{*}{ForCES} & \multirow{2}{*}{\begin{tabular}{c} Delegating the logic of \\ topology discovery to the \\ SDN-Switches. \\ \end{tabular} } & \multirow{2}{*}{Switches} & \multirow{2}{*}{Event} & (1) Reduce the learning time of link changes. & It is only applicable for ForCES as a \\  & & & & southbound API. \\ \hline \multirow{4}{*}{ESLD} & \multirow{4}{*}{\begin{tabular}{c} Reducing messages between \\ the SDN-Controller and \\ the SDN-Switches for topology \\ by restricting the sending \\ discovery packets to only \\ SDN-Switch ports connected \\ to switches and not to hosts. \\ \end{tabular} } & \multirow{4}{*}{Controller} & \multirow{4}{*}{Periodic} & (1) Reducing CPU overhead. (2) Reducing the bandwidth overhead. & Port classification consumes more \\  & & & & overhead. & messages \\ \hline \multirow{4}{*}{SLDP} & \multirow{4}{*}{\begin{tabular}{c} A new packet format was \\ used for topology discovery \\ messages with a random \\ source MAC address. \\ \end{tabular} } & \multirow{4}{*}{Controller} & \multirow{4}{*}{Periodic} & (1) Reducing CPU overhead. (2) Reducing the bandwidth overhead. & Increases Flow\_Mod messages to enable \\ \hline \multirow{4}{*}{TEDP-S} & \multirow{4}{*}{\begin{tabular}{c} Reducing messages between \\ the SDN-Controller and \\ SDN-Switches by sending \\ only one discovery packet to \\ the root SDN-Switch. \\ \end{tabular} } & \multirow{4}{*}{Controller and \multirow{4}{*}{Periodic}} & (1) Reducing CPU overhead. (2) Reducing the bandwidth overhead on the \\  & & & & overhead. & Increasing CPU overhead on the \\ \hline \multirow{4}{*}{TEDP-H} & \multirow{4}{*}{\begin{tabular}{c} Offloading the process of \\ discovering the topology from SDN-Controller to the \\ root SDN-Switch. \\ \end{tabular} } & \multirow{4}{*}{Controller and \multirow{4}{*}{Periodic}} & (1) Reducing CPU overhead. (2) Reducing the bandwidth overhead. & Increasing CPU overhead on the \\  & & & & overhead. & ND-Switches. \\ \hline \multirow{4}{*}{SDN-RDP} & \multirow{4}{*}{\begin{tabular}{c} Sharing network state \\ management between \\ multiple SDN-Controllers. \\ \end{tabular} } & \multirow{4}{*}{Controller} & \multirow{4}{*}{Periodic} & (1) Reducing the number of \\  & & & messages. & Manual \\ \cline{1-1}  & & & (2) Reducing the computation \\ \cline{1-1}  & & & time. & \\ \hline \multirow{4}{*}{GTOP} & \multirow{4}{*}{\begin{tabular}{c} Improve topology discovery \\ process in PCE to be as \\ OpenFlow \\ \end{tabular} } & \multirow{4}{*}{\begin{tabular}{c} PCE and \\ Switches \\ \end{tabular} } & \multirow{4}{*}{Periodic} & (1) Reduce link failures (2) Reduce updating times & Legacy domain \\ \hline \multirow{4}{*}{SONT} & \multirow{4}{*}{\begin{tabular}{c} Test-signal mechanism to \\ detect network links \\ \end{tabular} } & \multirow{4}{*}{Controller and \\  & & & & (1) Reduce updating times \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1} HDDP & \begin{tabular}{c} A lightweight agent and \\ network exploration model \\ based on flooding \\ \end{tabular} } & \multirow{4}{*}{Controller and \begin{tabular}{c} \\ Switches \\ \end{tabular} } & \multirow{4}{*}{Periodic} & (1) Support different type of \\  & & & & networks & \\ \cline{1-1}  & & & & & messages \\ \hline \multirow{4}{*}{eTDP} & \multirow{4}{*}{\
\begin{tabular}{c} Distributed topology \\ discovery process on layer 2 \\ and uses shortest control \\ paths \\ \end{tabular} } & \multirow{4}{*}{Switches} & \multirow{4}{*}{Periodic} & (1) Reduce discovery time & Back to traditional \\  & & & and cost & networks \\ \hline \multirow{4}{*}{TDP} & \multirow{4}{*}{
\begin{tabular}{c} Rely on network partitioning \\ and using a timer to send \\ topology discovery packets \\ \end{tabular} } & \multirow{4}{*}{Wireless nodes} & \multirow{4}{*}{Periodic} & (1) Reducing send packets (2) Reduce topology & Suitable for tree \\  & & & & (2) Reduce topology \\ \cline{1-1}  & & & discovery energy & only \\ \hline \hline \end{tabular}
\end{table}