## 2 Related Work  
Many implementations of body area networks used for body sensor communication have recently been reported in the literature [14-16]. A number of these researches focus mainly on on-body MAC layer issues. The system in [13] uses a slotted multipoint-to-point architecture in which the data from multiple on-body sensors are sent to a sink node in a collision free manner. The transmission slots are synchronized using beacon signals periodically sent out by a pre-designated sink node. The mechanisms reported in [14] involve the use of an on-body adaptation of the standard IEEE 802.15.4/ZigBee based MAC. The work reported in [15,16] investigated on-body MAC-routing cross-layer issues via distributed transmission coordination in the presence of specific routing structures. In [15], the authors presented an energy-efficient slotted MAC in the presence of a Wireless Autonomous Spanning tree Protocol (WASP) that is used for on-body packet routing. The protocol in [16] adopts a similar tree-based cross-layer approach, but is designed specifically for reducing packet delivery delays over an on-body spanning tree. This protocol also handles body mobility by adaptively re-constructing and maintaining the spanning tree used for packet routing. From the on-body routing standpoint, most of the existing WBANs systems adopt star or tree topologies on a connected graph; meaning a physically connected end-to-end path between any pair of on-body sensors is assumed at any given point in time. However, these models do not apply for the targeted DTN routing paradigm in this paper, which handles topology partitioning leading to scenarios in which end-to-end physical connectivity between node pairs may not be present at times. Such partitioning is mainly due to the ultra short range RF transceivers used. The knowledge based strategies are typically for single copy forwarding and they make use of information about connectivity dynamics to make efficient forwarding decisions. The hybrid approaches [14,16,17] combine replication and knowledge based strategies. The general principle behind these approaches is as follows: when a node with a packet to be forwarded encounters another node, the forwarding rule should determine if the packet (or a copy of the packet) should be transferred to that node or it should continue to be buffered. The rule is based on the estimate whether the encountered node is more likely than the forwarding node to visit the destination. The above mechanisms are all applied to networks spanning across local to wide areas, with a few extending all the way up to the inter-planetary scale. The objective of the work described in [18] is to apply the key DTN routing concepts, as identified above, in an ultra short-range body area environment. The challenge is to develop mechanisms for capturing the locality of on-body node movements caused by human postural mobility. WBANs provide efficient communication solutions to ubiquitous healthcare systems. Health monitoring, telemedicine, military, interactive entertainment, and portable audio/video systems are some of the applications where WBANs can be used. [PERSON] _et al_. [19] have presented a comprehensive work on the applications of WBANs in smart healthcare applications, including epileptic seizure warning, glucose monitoring, and cancer detection. In this paper, the authors highlighted a number of projects that enable WBANs to provide unobtrusive long-term healthcare monitoring with real-timeupdates to a health center. [PERSON] _et al_. [20] presented BASNs as systems enabling human-centric sensing for a variety of intriguing applications in healthcare, fitness, and entertainment, but such networks must demonstrate enough value for users to overcome inhibitions related to inconvenience, invasiveness, and general discomfort. Authors described wearable technologies that will \"silently monitor\" heart rhythm, detect irregularities, and alert emergency personnel in the event of a heart attack.