## 3 QoS Aware MAC Protocols for WMSNs  
Designing energy efficient MAC protocols to coordinate the transmission of large amount of sensory data and to meet the stringent QoS requirements for WMSNs is a very challenging task. First of all, although duty cycling of radio is a common MAC layer practice to save energy, extra caution should be taken when applying the same technique for MAC protocols in WMSNs due to the dynamic and bursty nature of multimedia traffic. Secondly, in order to guarantee the high data rate needed to transmit the large volume of data, MAC protocols should be designed to be able to minimize collisions, especially in times of transmission of real-time video data. Thirdly, due to the coexistence of heterogeneous types of traffic, a prioritization and service differentiation mechanism is required to allow earlier access to the wireless medium for higher priority traffics.  
In this section we investigate energy efficient MAC protocols which can provide QoS guarantees by means of prioritization and service differentiation. We summarize the surveyed MAC protocols in Table 2.  
Figure 7: Characteristics and Requirements of WMSNs Presented as Unibody.  
\begin{table}
\begin{tabular}{l l l l l l l l l} \hline \hline
**Protocols** & **EQ-MAC** & **[PERSON] et al. [40]** & **Diff-MAC** & **MQ-MAC** & **IH-MAC** & **AMPH** & **PA-MAC** \\ \hline
**MAC** & hybrid & & & & hybrid of & hybrid of & \\  & of CSMA/CA & CSMA/CA & CSMA/CA & IEEE 802.15.4 & CSMA/CA and & CSMA/CA and & IEEE 802.15.4 \\  & and TDMA & & & TDMA & & TDMA & \\ \hline
**Synchronization** & global, precise & not required & not required & local, precise & local, loose & global, precise & global, precise \\
**QoS guarantee** & delay & throughput, delay & reliability, delay & reliability, delay & delay & reliability, delay & throughput, delay \\ \hline
**Prioritization** & traffic types & traffic types, & traffic types, & traffic types, packet & traffic types & traffic types, & traffic types & traffic types \\
**schemes** & traffic types & traffic types & traveled hop count & lifetime & traffic types & traffic types & traffic types \\ \hline
**Service** & dynamic slot & & adaptive & adaptive & & & \\  & allocation & contention & window, dynamic & slot allocation, & & contention & & \\  & allocation & window, dynamic & duty cycle, weighted & adaptive contention & window, dynamic & & \\  & duty cycle & fair queuing & window & slot allocation & slot allocation & & \\ \hline
**Scalability** & poor & good & good & medium & medium & poor & poor \\ \hline
**Adaptation to** & good & medium & medium & poor & good & good & poor \\
**dynamic traffics** & & medium & medium & low & low & low & high \\ \hline
**Collision rate** & low & medium & medium & low & low & low & high \\ \hline
**Fairness** & poor/yes & medium/no & good/no & medium/no & medium/no & good/no & medium/no \\ \hline
**Energy efficiency** & good & medium & medium & good & medium & poor & good \\ \hline
**Message passing** & no & no & yes & no & no & yes & no \\ \hline
**Clustered** & yes & no & no & yes & yes & no & no \\ \hline
**Year** & 2008 & 2008 & 2011 & 2015 & 2013 & 2014 & 2016 \\ \hline \hline \end{tabular}
\end{table}
Table 2: A comparison of surveyed MAC protocols.