# Traffic Aware Scheduler for Time-Slotted Channel-Hopping-Based IPv6 Wireless Sensor Networks
## 3 Related Work
### Discussion
\begin{table}
\begin{tabular}{p{56.9 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Scheduler** & **Approach** & **Strong Points** & **Limitations** \\ \hline \multirow{4}{*}{**ALICE [7]**} & \multirow{4}{*}{Static link based} & Separation between upstream and downstream traffic; scheduling of cells changes in time; early drop of packets & Not adaptive, allocates the same amount of cells regardless of traffic load \\ \cline{3-4}  & & \multirow{4}{*}{Static node based} & cells allocated based on the subgraph of a node; increase in average duty cycle even for low traffic & Not adaptive and downward traffic is not supported; duty cycle is directly linked to the size of the routing table \\ \hline \multirow{4}{*}{**PAAS [9]**} & \multirow{4}{*}{Adaptive based on SBS Orchestra} & Reduces the number of Rx cells if traffic load is low & Tx cells are allocated before Rx cells which might lead to packet loss; increase in overhead by extending the size of the DIO message \\ \cline{2-4}  & \multirow{2}{*}{Adaptive with 2 slotframes for unicast traffic} & The size of the unicast slotframes is adjusted based on traffic load & Introduces overhead when nodes communicate the slotframe size \\ \hline \multirow{4}{*}{**ATAS [11]**} & \multirow{4}{*}{Adaptive and packet prioritization} & cells are allocated based on the number of remaining packets in the queue; priority packets are added at the head of the queue & The additional cells are allocated sequentially which might increase collision probability \\ \hline \multirow{4}{*}{**A3 [12]**} & \multirow{4}{*}{Adaptive and fully autonomous} & Sender and receiver allocate cells independently based on traffic load; sender predicts traffic based on remaining packets in the queue; receiver estimates incoming traffic by sampling the channel \\ \cline{3-4}  & & \multirow{4}{*}{Adaptive} & The rank of the node is used to allocate additional cells in case of high traffic & Might allocate not needed cells in case of unbalanced networks \\ \hline \multirow{4}{*}{**MSF [14]**} & \multirow{4}{*}{Adaptive and distributed} & Autonomous cells ensure minimal bidirectional communication; in case of traffic burst, additional cells are allocated through negotiation & Distributed scheduler which might lead to increased complexity in implementation \\ \cline{3-4}  & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Strong points and limitations of discussed schedulers. lower-to-no dropped packets from the queue without creating overhead. In other adaptive schedulers, such as TESLA and MSF, overhead is created each time the nodes need to adapt their schedule. An increase in control traffic overhead not only hinders the transmission of data packets but also leads to an increase in duty cycle. The \(A^{3}\) scheduler avoids these problems by using estimation techniques for matching the number of cells that should be added on both the receiver and sender sides. This approach increases the overhead of CPU because of the computational complexity of the estimation techniques. In all the discussed adaptive approaches, the additional resources are deallocated once they are not needed anymore.