## 5 Protocol Comparison
\begin{table}
\begin{tabular}{l|l l l l l l l l l} \hline \multirow{3}{*}{**Protocol**} & \multicolumn{6}{c}{**Metrics of Comparison**} \\ \cline{2-10}  & \begin{tabular}{l} **Lifetime** \\ **Improvement** \\ **Mechanism** \\ \end{tabular} & \begin{tabular}{l} **Node or Link** \\ **Disjoint** \\ \end{tabular} & \begin{tabular}{l} **Number** \\ **of paths** \\ \end{tabular} & \begin{tabular}{l} **Network** \\ **Structure** \\ \end{tabular} & \begin{tabular}{l} **Application** \\ **Type** \\ \end{tabular} & \begin{tabular}{l} **QoS** \\ **Connectivity** \\ \end{tabular} & \
\begin{tabular}{l} **Network** \\ **Monbility** \\ \end{tabular} &
\begin{tabular}{l} **Location** \\ **Awareness** \\ \end{tabular} \\ \hline
**M-MPR-SF [41]** & Multi-path & Braided & N/S & Location- & Event-Driven & No & Yes & No & Yes \\  & & (_Meshed_) & & Based & & & & & \\
**AGEM [14]** & Multi-path & Link- Disjoint & N/S & Location- & Event-Driven & Yes & No & Yes _Only_ & Yes \\  & & & Based & & & & & _Sensors_ & \\
**MSMRP [42]** & Multi-path \& & Node- Disjoint & 2 & Flat & N/S & No & No & No \\  & Power Control & & & & & & & \\
**EBMRR [43]** & Multi-path & Node- Disjoint & K (\(k\geq 2\)) & Flat & Event-Driven & No & Yes & No & No \\
**REER [15]** & Multi-path & Node- Disjoint & K (\(k\geq 2\)) & Flat & Query-Driven & No & Yes & No & No \\ \hline \end{tabular}
\end{table} 
Table 2: Comparison of multi-path routing protocols. In AGEM protocol [14], for example, each node checks the location information of its neighboring nodes in route construction phase to find the best neighbor for greedy forwarding mechanism. According to greedy method, a neighboring node having maximum progress on the virtual line between the source and the sink is the best candidate to be chosen as the next hop. The power control mechanisms from Section 4.4 are compared in Table 3 based on the following criteria:  
* _Lifetime improvement mechanism_: This field shows that which kind of mechanism for lifetime improvement is used in each protocol. All algorithms in Table 3 only use power control scheme, except EECA [16] which uses power control and multi-path mechanisms simultaneously to prolong the network lifetime. * _Power adjustment technique_: This field indicates the manner by which, two neighboring nodes collaborate with each other to compute the minimum transmission power level needed for data forwarding. In some algorithms [17], a configuration packet is used to adjust in-network nodes' transmitter power level. The other protocols [16, 18, 19] try to calculate some parameters such as RSSI, LQI, and margin field and attach them to data packets or ACK messages and relay them to the corresponding neighboring node. By using these parameters the sensor nodes are capable to adjust their transmitter power level efficiently. * _Location awareness_: Nodes' coordinates can be one of parameters used for computing the distance between two nodes and the energy needed for data transmission along that link. There are two [16, 17] algorithms in which all nodes are location aware. * _Network structure_: This field is discussed before (in Table 1). It seems the algorithm proposed in [17] can be applied in all multi-hop sensor-to-sink networks while the others are employed in flat [18] or geographic [16] routing protocols. * _Proposed routing_: Some mechanisms [17] only focus on the power control schemes, while others provide joint power control and routing protocols [16]. * _Application Type_: The algorithms proposed in [18] and [19] are employed in time-driven application while the others could be applied in event-driven routing methods. * _Mobility_: None of the protocols in Table 3 was proposed for mobile environments.