Wireless Sensor Networks A wireless sensor network (WSN) consists of spatially distributed autonomous sensors to monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants and to cooperatively pass their data through the network to a main location.
Classification Of RoutingProtocols Routing techniques are required for sending data between sensor nodes and the base stations for communication. Routing Protocols can be classified : Based on Mode of functioning and type of target applications into Proactive, Reactive and Hybrid. Based on Participation style of the nodes into as Direct Communication, Flat and Clustering Protocols . Depending on the Network Structure as Hierarchical, Data Centric and Location
Proactive, Reactive and Hybrid In a Proactive Protocol the nodes switch on their sensors and transmitters, sense the environment and transmit the data to a BS through the predefined route. The Low Energy Adaptive Clustering hierarchy protocol (LEACH) utilizes this type of protocol. In Reactive Protocol if there are sudden changes in the sensed attribute beyond some pre-determined threshold value, the nodes immediately react. This type of protocol is used in time critical applications The Threshold sensitive Energy Efficient sensor Network(TEEN) is an example of a reactive protocol.
Hybrid Protocols Incorporate both Proactive and Reactive concepts. They first compute all routes and then improve the routes at the time of routing. Adaptive Periodic TEEN(APTEEN) is an example of Hybrid Protocols.
Direct Communication, Flat and ClusteringProtocols In Direct Communication Protocols, any node can send information to the BS directly. When this is applied in a very large network, the energy of sensor nodes may be drained quickly. Its scalability is very small. SPIN is an example of this type of protocol. In the case of Flat Protocols, if any node needs to transmit data, it first searches for a valid route to the BS and then transmits the data. Nodes around the base station may drain their energy quickly. Its scalability is average. Rumor Routing is an example of this type of protocol.
According to the clustering protocol, the total area is divided into numbers of clusters. Each and every cluster has a cluster head (CH) and this cluster head directly communicates with the BS. All nodes in a cluster send their data to their corresponding Cluster Head. The Threshold sensitive Energy Efficient sensor Network(TEEN) is an example of a clustering protocol.
Data Centric, Hierarchical and Location based Data centric protocols are query based and they depend on the naming of the desired data, thus it eliminates much redundant transmissions. The BS sends queries to a certain area for information and waits for reply from the nodes of that particular region. Depending on the query, sensors collect a particular data from the area of interest. This particular information is only required to transmit to the BS and thus reducing the number of transmissions ◦ SPIN was the first data centric protocol
Hierarchical routing is used to perform energy efficient routing. Higher energy nodes can be used to process and send the information and low energy nodes are used to perform the sensing in the area of interest ◦ examples: LEACH, TEEN, APTEEN Location based routing protocols need some location information of the sensor nodes. Location information can be obtained from GPS signals, received radio signal strength, etc. Using location information, an optimal path can be formed without using flooding techniques. ◦ GEAR is an example of a location based routing protocol.
Flooding Each node Which receives a packet broadcasts it, if the maximum hop count of the packet is not reached. This technique does not require complex topology maintenance . The disadvantages of flooding are : ◦ Implosion ◦ Overlap ◦ Resource Blindness
Gossiping Gossiping is modified version of flooding. The nodes send packets to a randomly selected neighbor to avoid Implosion. The disadvantages of Gossiping are: ◦ It does not guarantee that all the nodes of the network will receive the message. ◦ It takes a long time for a message to propagate throughout the network.
Rumor Routing It is an agent based path creation algorithm. Agents are basically packets which are circulated in the network to establish shortest path to events. They can also perform path optimizations at nodes they visit. When agent finds a node whose path to an event is longer than its own, it updates the node’s routing table. When query is generated at a sink, it is sent on a random walk with the hope that it will find a path leading to the required event. If query Does not find an event path , the sink times out and uses flooding to propagate the
Sequential AssignmentRouting The SAR algorithm creates multiple trees, where the root of each tree is a one-hop neighbor of the sink. Each tree grows toward from the sink and avoids nodes with low throughput or high delay. At the end of procedure, most nodes belong to multiple trees.
SPIN SPIN stands for Sensor Protocol for Information via Negotiation. SPIN uses negotiation and resources adaption to address the deficiencies of flooding. Negotiation reduces overlap and implosion. Meta-data is transmitted instead of row data. SPIN has three types of messages : ADV, REQ and DATA. The simple version of SPIN is shown in
SPINSensor Protocol for Information viaNegotiation
Direct Diffusion Useful where the sensor nodes themselves generate requests/queries for data sensed by other nodes. Each sensor node names its data with one or more attributes and other nodes express their interest depending on these attributes. Data is propagated along the reverse path of the interest propagation. Each path is associated with a gradient that is formed at the time of interest propagation. The gradient corresponding to an interest is derived from the interval/data-rate field specified in the interest. This model uses data naming by attributes and local data transformation to reflect the data centric nature of sensor network operations.
Geographic Hash Table GHT is a system based on data centric storage. GHT hashes keys into geographic co- ordinates and stores a pair at the sensor node nearest to the hash value. The calculated hash value is mapped onto a unique node consistently, so that queries for the data can be routed to the correct node. Data is distributed among nodes such that it is scalable and the storage load is balanced. GHT is more effective in large network
Direct Transmission All sensor nodes transmit their data directly to BS. This is extremely expensive in terms of energy consumed, since the BS may be very far away from some nodes. Nodes must take turns while transmitting to the BS to avoid collision. The media access delay is also large
PEGASIS PEGASIS assumes that all sensor nodes know the location of every other node. Any node has the required transmission range to reach the BS in one-hop, when it is select as a leader. The goals of PEGASIS are as follows : Minimize the distance over which each node transmits. Minimize the broadcasting overhead. Minimize the number of messages that need to be sent to the BS. Distribute the energy consumption equally across all nodes.
PEGASISPower Efficient Gathering for Sensor Information Systems
A greedy algorithm is used to construct a chain of sensor nodes, starting from the node farthest from the BS. At each step, the nearest neighbor which has not been visited is added to the chain. At every node, data fusion is carried out. so, that only one message is passed on from one node to next. The leader finally transmits one message to BS. The delay involved in message reaching the BS is O(N), where N is the total number of nodes in
Binary Scheme This is also a chain-based scheme like PEGASIS. Classifies nodes into different levels. Nodes which receive messages at one level rises to the next level. The number of nodes is halved from one level to the next.
Binary Scheme• In figure aggregated data reaches the BS in 4steps, which is O(log2 N),where N is the number of nodes in the network.
Chain Based Three levelScheme In this scheme chain is constructed as in PEGASIS. The chain is divided into number of groups to space out simultaneous transmission. One node out of each group aggregates data from all group members and rises to the next level. In the second level all nodes are divided into two groups. Third level consist of a message exchange between one node from each group of second level. Finally the leader transmits a single message