Presentation on theme: "ROUTING TECHNIQUES IN WIRELESS SENSOR NETWORKS: A SURVEY."— Presentation transcript:
ROUTING TECHNIQUES IN WIRELESS SENSOR NETWORKS: A SURVEY
Outline Background Classification of Routing Protocols Data Centric Protocols Flooding and Gossiping SPIN Directed Diffusion Rumor Routing
Background Sensor nodes Small, wireless, battery powered Energy, bandwidth constrained Data sensing, relaying, aggregating No global addressing scheme Sink nodes More powerful nodes Usually gateway to wired networks Data collecting and processing
Goal So at network layer, it is highly desirable to find methods for energy efficient route discovery and relaying of data from the sensor nodes to the BS so that the life time of the network is maximized.
Data-centric Protocols The ability to query a set of sensor nodes Attribute-based naming Data aggregation during relaying For example: Flooding & Gossiping SPIN Directed Diffusion Rumor Routing
Flooding & Gossiping In flooding, sensor broadcasts packets to all its neighbors till dst reached or packets' ttl == 0 In gossiping, sensor sends packets to a randomly selected neighbor which does the same
Flooding & Gossiping(cont.) Pros Simple No routing, no state maintenance Cons Implosion Overlap Resource blindness Delay in Gossiping
SPIN – Sensor Protocols for Information via Negotiation Metadata negotiation done before transmitting the actual data. 3-way handshake: ADV, REQ, DATA Event-driven
SPIN(cont.) Pros Solve the classic problems Topological changes are localized Cons No guarantee on the delivery of data
Directed Diffusion Sink node floods named “interest” with larger update interval Sensor node sends back data via “gradients” Sink node then sends the same “interest” with smaller update interval Query-driven
Directed Diffusion (cont) Pros On demand route setup Each node does aggregation and caching, thus good energy efficiency and low delay Cons Query-driven, not a good choice for continuous data delivery Extra overhead for data matching and queries
Rumor Routing A trade-off between Query & Event flooding An agent, a long-lived packet, is generated when events happen The agent propagate the event to distant nodes
Rumor Routing (cont) Pros Avoid query flooding Cons Performs well only when # of events is small Overhead to maintain agents and event-tables
Hierarchical Routing Protocols When sensor density increases single tier networks cause Gateway overloading Increased latency Large energy consumption Clustered Network allow coverage of large area of interest and additional load without degrading the performance
Hierarchical Routing Protocols Idea Partition the entire network into regions or clusters. Select one or more nodes as the cluster head. The routing is nodes -> cluster head A -> cluster head B -> cluster head C -> nodes The routing between cluster heads and the routing within a cluster may follow different protocols (EGP-BGP and IGP- OSPF). Issues resolved: Energy wasted in collision, collision avoidance, idle-listening Achieves Better scalability Removes the load to less powerful nodes
The LEACH Protocol Low-Energy Adaptive Clustering Hierarchy. Distributed cluster formation technique that enables self-organization of large numbers of nodes.
LEACH - Setup Set up phase Cluster Head (CH) selection (random + rotating) ADV Join REQ TDMA SCH prepared by CH (no collisions and reduced energy consumption)
LEACH - Steady State Broken into frames, where nodes send their data to the cluster head at most once per frame during their allocated transmission slot. Once the cluster head receives all the data, it performs data aggregation.
PEGASIS Power-Efficient GAthering in Sensor Information Systems. The key idea in PEGASIS is to form a chain among the sensor nodes so that each node will receive from and transmit to a close neighbor. Well, what was so bad in LEACH except for a bad name...
PEGASIS - Concept Be Greedy! Align with the one that has the max signal strength, form a near-optimal chain. Communicate with neighbors only. But who takes care of communicating to BS?
PEGASIS - Leader The main idea in PEGASIS is for each node to receive from and transmit to close neighbors and take turns being the leader for transmission to the BS. Nodes take turns transmitting to the BS (i mod N node in round i out of N nodes shall transmit to BS).
Passing the buck... Token passing approach
The TEEN Protocol Threshold sensitive Energy Efficient sensor Network protocol. Proactive Protocols (LEACH) The nodes in this network periodically switch on their sensors and transmitters, sense the environment and transmit the data of interest. Reactive Protocols (TEEN) The nodes react immediately to sudden and drastic changes in the value of a sensed attribute.
TEEN - Functioning At every cluster change time, the cluster-head broadcasts to its members Hard Threshold (HT) This is a threshold value for the sensed attribute. It is the absolute value of the attribute beyond which, the node sensing this value must switch on its transmitter and report to its cluster head. Soft Threshold (ST) This is a small change in the value of the sensed attribute which triggers the node to switch on its transmitter and transmit.
TEEN - Hard Threshold The first time a parameter from the attribute set reaches its hard threshold value, the node switches on its transmitter and sends the sensed data. The sensed value is stored in an internal variable in the node, called the sensed value (SV).
TEEN - Soft Threshold The nodes will next transmit data in the current cluster period, only when both the following conditions are true: The current value of the sensed attribute is greater than the hard threshold. The current value of the sensed attribute differs from SV by an amount equal to or greater than the soft threshold.
TEEN - Drawback If the thresholds are not reached, the user will not get any data from the network at all and will not come to know even if all the nodes die-Adaptive Periodic TEEN This scheme practical implementation would have to ensure that there are no collisions in the cluster.
GPSR: GREEDY PERIMETER STATELESS ROUTING FOR WIRELESS NETWORKS
GPSR Overview Routing Protocol that uses positions of routers and a packet’s destination to make packet forwarding decisions GPSR keeps state only about the local topology (for only a single hop) The word “Stateless” is not meant literally but refers to small, purely local state GPSR scales better in per-router state than shortest- path and ad-hoc routing protocols GPSR finds correct new route quickly under frequent topology changes
Algorithm’s Key Ideas “The position of a packet’s destination and positions of the candidate next hops are sufficient to make correct forwarding decisions, without any other topological information.” “Routing protocol that rely on end-to-end state concerning the path, face scaling challenge with increasing number of routers & rate of change of topology (mobility).” “GPSR generates routing protocol traffic independent of the length of the routes through the network, therefore generates a constant, low volume protocol messages as mobility increases,”
GPSR Modes Modes Nominal: Greedy Forwarding Special : Perimeter Forwarding Greedy Forwarding Uses only information about router’s immediate neighbors Forwarding node makes locally optimal greedy choice of the packet’s next hop
Greedy Forwarding Example Follows successive closer geographic hops, until the destination is reached
Perimeter Forwarding Used in the region where Greedy forwarding fails. There are topologies in which the only route to a destination requires a packet move temporarily farther in geometric distance from the destination Special mechanism (right hand rule) is used in such special situation
Perimeter Forwarding Example Right Hand Rule: x receives a packet from y, and forwards it to its first neighbor counterclockwise about itself, z When Greedy Forwarding Fails. x is a local maximum in geographic proximity to D w and y are farther from D
Perimeter Forwarding Example D is the destination; x is the node where the packet enters perimeter mode; forwarding hops are solid arrows; the line xD is dashed. GPSR forwards packets along the face intersected by the line xD x forwards the packet to the first edge counterclockwise about x form the line xD, follows right hand rule thereafter
Planarized Graphs The RNG graph. For edge(u; v) to be included, the shaded lune must contain no witness w. The GG graph. For edge(u; v) to be included, the shaded circle must contain no witness w.
GPSR Operation GPSR combines greedy forwarding on full network graph and perimeter forwarding in planarized network graphs All nodes maintain neighbor table, which stores the address and location of their single-hop radio neighbors The table provides all states required for forwarding decisions
GPSR Operation All packets are marked initially as greedy mode Upon receiving a greedy-mode packet, a node searches its neighbor table geographically closest to the packet’s destination. If the neighbor is closer to the destination, it forwards the packet to the neighbor. If no neighbor is closer, the packet is marked into perimeter mode.
GPSR Operation In perimeter mode, the packet is forwarded using a simple planner graph The packet is forwarded to progressively closer faces of the planner graph using the right hand rule In perimeter node, the GPSR records the location where greedy failed, and the first edge a packet crosses on a new face When the destination is not reachable, the packet will tour unsuccessfully around the entire face as no intersection with xD is detected Upon traversing on the face second time, the repetition is detected to correctly drop the packet
Algorithm Evaluation Matrices Packet delivery success rate Fraction of applications’ packets delivered successfully by the routing algorithm Routing protocol overhead Per-node state: storage required at each node Protocol message cost: number of protocol packets sent by the routing algorithm Optimality of path lengths taken by data packets
Packet Delivery Success Rate GPSR with varying beacon intervals, B, compared with Dynamic Source Routing (DSR). 50 nodes GPSR delivers a slightly greater fraction of packets successfully than DSR Pause time is the time duration for which all nodes hold the same positions at waypoints. The mobility model used is the random way point model which generates waypoints at random.
Routing Protocol Overhead Total routing protocol packets sent network-wide during the simulation for GP R with varying beacon intervals, B, compared with DSR. 50 nodes. GPSR offers greater savings in routing protocol overhead
Packet Delivery Success Rate Packet Delivery Success Ra t e. F o r G P S R with B = 1.5 compared with DSR. 50, 112, a n d 200 node s. GPSR delivers 97% of its packets along optimal-length paths vs. 84.9% for DSR
Routing Protocol Overhead Total routing protocol packets sent network-wide during the simulation for GPSR with B = 1.5 compared with DSR. y axis log-scaled. 50, 112, and 200 nodes. GPSR generates drastically less routing protocol traffic w.r.t. to DSR
Summary GPSR routing algorithm uses geography to achieve small per-node route state, small routing protocol message complexity, and extremely robust packet delivery GPSR generates routing protocol traffic independent of the length of the routes through the network, therefore generates a constant, low volume protocol messages as mobility increases GPSR performs better than DSR. GPSR keeps states proportional to no. of neighbors; DSR keeps sates proportional to product of no of routes learned and route length in hops. Besides Hierarchy and Caching, Geography is leverages for scaling routing