Effective Cache based Policies in Wireless Sensor Networks: A Survey <s> Figure 4. Cluster formation and query path <s> We describe two small and portable TCP/IP implementations fulfilling the subset of RFC1122 requirements needed for full host-to-host interoperability. Our TCP/IP implementations do not sacrifice any of TCP's mechanisms such as urgent data or congestion control. They support IP fragment reassembly and the number of multiple simultaneous connections is limited only by the available RAM. Despite being small and simple, our implementations do not require their peers to have complex, full-size stacks, but can communicate with peers running a similarly light-weight stack. The code size is on the order of 10 kilobytes and RAM usage can be configured to be as low as a few hundred bytes. <s> BIB001 </s> Effective Cache based Policies in Wireless Sensor Networks: A Survey <s> Figure 4. Cluster formation and query path <s> Previous research on transport layer protocols for wireless sensor ::: networks (WSNs) has focused on designing protocols specifically ::: targeted for sensor networks. Most sensor networks applications, ::: however, are only useful when connected to an external network. The ::: deployment of TCP/IP in WSNs would enable direct connection between ::: the WSN and external TCP/IP networks. However, TCP performs badly in ::: wireless environments both in terms of throughput and energy ::: efficiency. To overcome these problems in WSNs we have designed ::: Distributed TCP Caching. This mechanism greatly enhances TCP ::: performance by caching TCP segments on the nodes in the sensor network ::: and locally retransmitting lost segments. Our simulations ::: demonstrate that with these enhancements TCP performs well enough to ::: be useful in wireless sensor networks. <s> BIB002 </s> Effective Cache based Policies in Wireless Sensor Networks: A Survey <s> Figure 4. Cluster formation and query path <s> In a wide range of applications, such as detecting environmental hazards, monitoring remote terrain and even monitoring customer behavior, wireless sensor networks (WSNs) are playing an important role. Due to the limited energy in each node, a lot of attention has been paid on improving energy efficiency. In this paper, we first propose an energy-efficient waiting caching (EEWC) algorithm to improve the data-centric (DC) transport control protocol by cutting down traffic flow. Second, we deploy networked predictive controller (NPC) to shorten network delay. Thus, the energy consumption can be reduced accordingly. We also analyze the proposed algorithm. Finally, we conduct extensive simulation experiments to evaluate the performance of the proposed algorithm. <s> BIB003
Since this scheme provides an efficient way to multicasting, it can be utilized in WSNs. Although multicasting is supported but the data cache placement scheme utilizes Steiner points which becomes bottleneck as multicast to various subscribers consumes data from the same node and this makes the Steiner points to die soon. The network could be considered in the form of cluster as shown in figure 4 BIB003 . Clusters are made with very few nodes and each cluster has a head BIB003 which is not supposed to sense any data. The function of cluster head is just to process and manage the data between clusters. At a time only two nodes can be active, one is the cluster head and the other one is sensing the data. The energy consumption of head node becomes very high as compared to the other node in the cluster so the role of head node is played in turn to utilize energy consumption in an efficient manner. First Base Station sends query to the sink and then sink to cluster head H1. Then H1 sends this query to the H2 and N1 and so on. When the leaf node N5 sent the data to the H5 , H5 sends it directly to the H4, while H4 is waiting there for the N4 to sense data and send it to the H4.when H4 receives data from N4 it aggregates it with the data from H5 and then sends it to the H3. H3 will again apply the same process as H4. without giving way to form it. The routing of data is assumed to be in single hop between two cluster heads, which is not possible for every case unless they are in coverage area of each other which is quite often. In wireless environment TCP is not a good performer. But connecting the WSN to the outside world through internet makes it usable in various monitoring applications. An optimization in TCP BIB002 has been proposed by the Dunkels et al. and the scheme could perform well in WSNs. Distributed TCP Caching (DTC) tries to avoid end-to-end retransmission and uses segment caching to provide this. Instead of end-to-end transmission this scheme uses local retransmissions for the lost acknowledgements. A major problem with this scheme is that the last node or the nodes closest to the Base Station may runs out of energy. DTC takes care about this issue by distributing the load in the network. Before applying TCP into the WSN some changes has to be done so that WSN becomes usable. Some of the proposed works are as follows: A Spatial IP addressing should be used that uses spatial location information to provide semi-unique IP addresses to sensor nodes. The TCP header overhead can be reduced by using compression techniques for WSNs. For routing, application overlays network can be used to perform data-centric routing and data aggregation for TCP/IP sensor networks. As the size of sensor nodes are too small, TCP/IP stack may proves heavy for the nodes to deal with. But BIB001 has shown that µIP implementation of the TCP/IP stack can run only 8-bit microcontroller and works under a few bytes of RAM. TCP was designed for wired networks where bit errors are usually not there. Any packets drop is concluded as the congestion in the network. But in wireless networks, bit errors are usual and TCP can misinterpret them as congestion in the network and slow down the sending window, even when network is not congested. As TCP uses end-to-end retransmission, all the nodes in the path of communication in wireless sensor network have to forward the same packet which consumes energy. So a local retransmission is a good idea to avoid above problem. The node which will be selected for retransmission should be located nearer to the receiver. DTC implements this feature and requires no change in the sensor nodes and receiver. Only intermediate nodes have to deal with this. It is assumed that nodes have only single location to store TCP segment. More precisely a node can store only one TCP segment due to less storage space. The figure 5 shows how DTC algorithm works. DTC calculates when the packet is lost in the transmission and cache the lost packet in the node when it gets lost. DTC does a Packet Loss Detection, by storing the largest segment of the packet during forwarding in the cache, and relies on link level acknowledgements to detect the packet drop. If there is no feedback from the next node, the node locked the data in the cache. This data is not allowed to overwrite with further segment number of the packets.