## 5 Conclusions  
WBSN is a technology that can provide a paradigm shift towards proactive management by focusing on prevention and early detection of different diseases. It can revolutionize the next generation healthcare issues and reduce healthcare costs. Designing routing protocols for WBSNs is a challenging task due to unique in-body and on-body constraints. In this paper, first we discussed the architecture of Wireless Body Sensor Networks (WBSNs) and then the routing issues and challenges of WBSNs. We have provided a comprehensive review of existing routing protocols specifically designed for WBSNs. Based on their nature and structure, the routing protocols have been classified as QoS-aware routing protocols, temperature-aware routing protocols, cluster-based routing protocols, postural-movement-based routing protocols and cross-layered routing protocols. We have critically analyzed each routing protocol by comparing its relative performance against other state-of-the-art schemes and have identified the relative strengths and weaknesses of each routing protocol.  
Different routing challenges in WBSNs are being considered in different categories of routing protocols, but still a lot of work needs to be done. The proposed QoS-aware routing protocols consider the nature of vital sign-related data of patients and other required quality of service parameters but they  
\begin{table}
\begin{tabular}{l l l l l l l} \hline \hline \multirow{2}{*}{**Protocol**} & \multicolumn{6}{c}{**Characteristics**} \\ \cline{2-7}  & **Goal** & **Mobility** & **Metrics** & **Avg. Delay** & **PDR** & **Energy Cons.** \\ \hline WASP & To decrease PLR, & & & & & \\ (2006) & \begin{tabular}{l} To decrease PLR, \\ energy consumption, \& \\ end-to-end delay & No & \begin{tabular}{l} Hop count \\ and routing \\ \end{tabular} & 324 & \multirow{2}{*}{100\%} & \multirow{2}{*}{Medium} \\ CICADA & To reduce end-to-end & & & & \\ (2007) & \begin{tabular}{l} Delay and energy \\ consumption \\ \end{tabular} & Yes & \begin{tabular}{l} Hop count \\ and routing \\ \end{tabular} & \begin{tabular}{l} \textless{}0.3 \\ milli-seconds \\ \end{tabular} & N/A & Low \\ TICOSS & To improve IEEE & & & & \\ (2007) & 802.15.4 standard & Yes & \begin{tabular}{l} Hop count \\ and routing \\ \end{tabular} & N/A & Over 92\% & Low \\ Biocomm \& & & & & & \\ Biocomm-D & \
\begin{tabular}{l} To optimize the overall \\ performance of the \\ network \\ \end{tabular} & No &
\begin{tabular}{l} Node temp, \\ hop count, \\ and delay \\ \end{tabular} & Medium & 75–100\% & Medium \\ \hline \hline \end{tabular}
\end{table}
Table 5: Cross-layered routing protocols.  
do not consider the postural-movements of the human body or the thermal effects of implanted bio-medical sensor nodes. The routing protocols that consider the postural-movements of the human body don't consider the temperature rise issue and data-centric quality of service issues. While the routing protocols that considers the temperature rise issue due to antenna radiation absorption and power consumption of sensor node circuitry but they do not take care of other routing issues.  
The future routing protocols for WBSNs should provide energy efficient and reliable communication among heterogeneous types of bio-medical sensor nodes in real-time applications. They should also take care of latency, reliability, mobility, thermal-effects and energy consumption. Similarly, more accurate and efficient network architectures should be developed for better routing in WBSNs.