Routing in Sensor Networks

–Routing means carrying data packets from a source node to a destination node (usually called sinks in sensor networks terminology) –Such routing paths helps to create energy-efficient data dissemination paths between sources (sensors) and sinks (global processing unit or human interface devices) –Two kinds of routing: single-path and multi-path –Since energy efficiency is the most essential factor, routing algorithms must be robust to failures and secure against the compromised and malicious nodes to ensure data delivery without impacting the lifetime of the network Why Routing?

–Probabilistic algorithm and makes packet forwarding decisions based on localized information –Based on a tree-like topology rooted at the sink of the network –Uses forward approach to contribute to end-to-end reliability –Avoids packet loss by sending multiple packets of the single event –Three sources of packets loss expected:  Isolated link  Patterned node failures  Malicious or misbehaving nodes Algorithm for Robust Routing in Volatile Environments (ARRIVE) [Karlof+, 2002]

Terminology –Event: Identified by [SourceID, EventID] –Level: Each node has unique level indicating distance from source to sink (in terms of hops) –Parents: Nodes one level closer to the sink –Neighbors: Nodes on the same level and be able hear each other –Push: Push packet to one of the neighbors –Forward: Forward packet to one of the parents –Forwarding Probability: Included in the packet header and used to probabilistically select whether to push or forward –Reputation History: Each node keeps this information for each of its parents and neighbors –Convergence: Prevents multiple packets of the same event being sent to same source of failure ARRIVE [Karlof+, 2002]

–Achieves diversity in paths in two ways:  Upon receiving a packet, the next hop is selected probabilistically based on link reliability and node reputation  When more than two or more packets of the same event are processed, these packets are ensured to follow different outgoing links –Takes advantage of passive participation and needs to be used cautiously –Each nodes keeps the following information:  Level  Neighbors list  Parents list  Reputation history of neighbors and parents  Convergence history of specific events ARRIVE [Karlof+, 2002]

Assumptions –The networks is assumed to be dense enough that sufficient multiplicity of paths between sources and sink for algorithm to perform well –The network is almost considered as a static network –Sensors are considered to have a low per-node cost –Routes used by the packets are unlikely to be optimal due to the probabilistic nature of the algorithm –Messages flow from nodes to sink, not the other way around –There is only one sink available Performance Metrics –Event delivery ratio –Three other metrics measuring the cost of deploying ARRIVE ARRIVE [Karlof+, 2002]

Algorithm Description –Bread first search rooted at sink is used to initialize level, parents, neighbors state information at each node –When a nodes hears a packets, it checks to see if the packet is addressed for it –If so, threshold processing takes place. Nodes are filtered by their reputation and convergence history of the neighbors and parents –A decision needs to be made to either to choose to forward the packet to a parent or push it to one of its neighbors with the probability value found in the packet header. This is randomly determined by the forwarding probability function P r (f). –Each node is weighed by their reputation. The destination is randomly selected from the rest of the nodes (since bad reputation nodes are eliminated) –If the the packet is forwarded to one of the parents, P r (f) is not changed; however, its value is increased ARRIVE [Karlof+, 2002]

Algorithm for Robust Routing in Volatile Environments (ARRIVE) [Karlof+, 2002] Figure 0: Overview of ARRIVE Adapted from [Karlof+ 2002]

Advantages: –High end-to-end reliability –Provides security by eliminating the compromised or malicious nodes –By using multiple paths to forward the same event, the probability of the event reaching sink is increased and this also ensures to avoid packets being forwarded to the same broken link – Reputation history assists in establishing a reliable path ARRIVE [Karlof+, 2002]

Disadvantages: –Extra power consumption for inactive nodes (passive listeners) are not considered –Better mechanism to take care problems caused by passive listening –There is only one sink, packets are sent from sources to sink and not the other way around –Sensor may have storage problems due to maintaining information about its neighbors and parents (reputation history) –Maintaining multiple paths requires more resources ARRIVE [Karlof+, 2002]

Suggestions/Improvements/Future Work: –Beneficial to measure how much passive listening affects energy use –Nodes can be mobile during the simulation instead of static –If there is a significant mobility, state information should be updated using a better mechanism than flooding –Explanation of how multiple packets are generated –How much redundant data is sufficient to optimize the network –Energy-awareness needs to be taken into consideration –Possibly use energy level parameter in the decision making –Include probabilistic analysis of the algorithm –Study the tradeoff the communication cost of ARRIVE vs. its robustness –Consider load balancing issues such that nodes near the sink deplete their resources sooner than nodes farther away –Lack of quantitative analysis of passive participation for security reasons –Experiment with larger number of events ARRIVE [Karlof+, 2002]

Preliminaries  Each node has its neighbor list, and an events table, with forwarding information to all the events it knows.  After a node witnesses an event, an agent may be created, which is a long-lived packet and travels around the network. Each agent contains an events table, including the routing information for all events it knows.  Since an event happens in a zone, composed of several or many nodes, it’s possible more than one agents are created from the zone and moving in the network. Rumor Routing Algorithm for Sensor Networks [Braginsky+ 2002]

Algorithm Description  When a node observes an event, it will add the event to its event table and may also create an agent  An agent will travel in the network and its routing table will be updated if there is a shorter path to an event within the routing table of the node it is visiting  In a similar way, the routing table of the currently visited node will be updated if its route to an event is more costly than the agent’s  Any node may generate a query for a particular event. If it knows the route to the event, it will transmit the query. Otherwise, the query will be sent in a random direction, and this continues until the query reach a node which has a route to the event Rumor Routing Algorithm for Sensor Networks [Braginsky+ 2002]

Adapted from [Braginsky+ 2002] Rumor Routing Algorithm for Sensor Networks [Braginsky+ 2002]

Adapted from [Braginsky+ 2002] Rumor Routing Algorithm for Sensor Networks [Braginsky+ 2002] Figure 3: The agent modifies the exist path (left) to a more optimal one (right)

Advantages:  Deliver queries to events in large networks with less average cumulative hops and lower energy requirements than simple flooding.  The algorithm can handle node failure gracefully, degrading its delivery rate linearly with the number of failed nodes. Rumor Routing Algorithm for Sensor Networks [Braginsky+ 2002]

Disadvantages:  The path found by the agent sometimes is not the shortest and could be unavailable if one of the links of the path is broken.  The agent may carry lots of routing information of events even some events have disappeared.  No hints from the paper about the number of agents which should be created from the event zone.  Can the nodes make a query for an event if no such event is existing in the network?  It seems that each event should have an id, but no information is provided in the paper.  Optimization is not considered Rumor Routing Algorithm for Sensor Networks [Braginsky+ 2002]

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