## 5 WBAN and the Communications Protocol Stack
### Network Layer  
In a traditional WSN context the network layer has to cater for numerous disparate nodes potentially spread over a wide geographical area. Network layer protocols make use of routing algorithms that use multi-hop to route packets to the destination node. In comparison to WSNs, WBAN nodes are mobile, likely to be clustered in specific areas and do not have the same extensive multi-hop requirement as WSNs. In comparison to WSNs, the bandwidth available to WBANs is limited, likely to be shared with other local ISM band devices and is subject to physical layer attributes such as interference, fading, and attenuation due to the specific characteristics of the human body. Existing WSN research at the network layer doesn't fully consider the range of heterogeneous nodes within a WBAN and are generally concerned with energy efficient routing via static nodes rather than the extensive body movements in a WBAN. The required routing algorithm complexity within WBANs is low in comparison to large-scale WSNs where nodes are potentially distributed across large-scale areas. However, the unique factors relating to communicating in and around the human body mean that network layer issues need to form an important part of WBAN protocol design. The standard WBAN architecture of a number of heterogeneous nodes linked to a BCU or sink device often assumes single hop routing where all node communications are transmitted directly to the BCU. [PERSON] _et al._[30] looked at the potential of multi-hop in a UWB based WBAN with an \begin{table}
\begin{tabular}{c c} \hline
**Protocol** & **Protocol Summary** \\ \hline BSN-MAC & Designed to exploit feedback information from nodes to deliver increased energy efficiency. Control algorithm enables the BSN coordinator to adjust parameters in the 802.15.4 superframe structure to avoid idle listening and achieve both energy efficiency and low latency on energy critical nodes. \\ \hline DQ-MAC & Grants immediate access for light traffic loads (behaving as a random access mechanism) and moves to a reservation system for high traffic loads, eliminating collisions for all data transmissions. Delivers energy saving improvements over BSN-MAC and 802.15.4. \\ \hline H-MAC & Exploits heartbeat rhythm to perform time synchronization for TDMA. nodes use heart rate waveform peaks for node synchronization. Nodes can achieve synchronization without having to turn on their radio. Energy cost for time synchronization can be avoided, thereby increasing the lifetime of the network. Limitation of single point of failure. \\ \hline CA-MAC & Adopts different transmission strategies, depending on variation of patient activity, vital life signs or environment status. Protocol incorporates a hybrid mechanism for channel access using TDMA and contention-based model to reduce energy consumption and latency. Demonstrated packet loss rate of 50\% lower than comparable MACs with reasonable tradeoff between reliability and efficiency. \\ \hline Power Efficient MAC & On-demand wakeup radio mechanism. Additional receiver attached to the sensor node operates independently from main node radio to reduce idle listening and reduce power consumption. Model incorporates periodic and emergency traffic scenarios. Offers improvements in terms of power efficiency and delay in single hop scenarios compared to B-MAC, X-MAC, WiseMAC and ZigBee (802.15.4). \\ \hline TaMAC & Adapted to cater for _normal, emergency and on-demand_ traffic types. Main radio deals with normal traffic and second is used for emergency/on-demand traffic. Results showed performance improvements over 802.15.4, WiseMAC and S-MAC. \\ \hline TDMA & Differentiates between normal and urgent traffic using two BAN coordinators. \\ directional MAC & Urgent packets are directed to a secondary BAN coordinator when the node doesn’t have its own guaranteed time slot. \\ \hline \end{tabular}
\end{table} 
Table 3: _Cont_. energy comparison for a transmission from a node located on the back of a patient to a node on the chest.