MAC Protocols CSMA Hidden terminal problem Exposed terminal

MAC Protocols CSMA Hidden terminal problem Exposed terminal problem Solution: CSMA/CA RTS/CTS packets A B B A B B C

CSMA/CA

CSMA/CA

Energy problems Collision Overhearing Idle listening Protocol overhead

Contention based Protocols S-MAC (Listen and Sleep intervals) B-MAC (Preamble based) WiseMAC

B-MAC

Sparse Topology and Energy Management(STEM)

Reservation based protocols Avoids collision by assigning slots to nodes A number of TDMA-based protocols have been developed TRAMA

Traffic Adaptive MAC (TRAMA) No collisions Switches to sleep mode whenever nodes are not transmitting or receiving Time is slotted Depending on nodes information determines the nodes transmission slot No data to transmit -> no slot assigned

TRAMA What is needed to avoid collision?

TRAMA Consists of 4 phases: Neighborbood discovery Traffic information exchange Schedule establishment Data transmission

TRAMA Neighbor protocol (NP) Schedule exchange protocol (SEP) Adaptive exchange algorithm (AEA)

TRAMA Neighbor Protocol NP

TRAMA Schedule Exchange protocol (SEP) Compute the packet rate X Find winning slots in [t, t+X] Create schedule Announce schedule

TRAMA Schedule Exchange protocol (SEP)

TRAMA

Problems

Problems

Problems

Network Layer Responsible for delivering data to destination Many Network layer (Routing) protocols have been proposed Energy consumption Scalable Robustness -…

Routing protocols Data centric Hierarchical Geographical QoS-based

Data centric Instead of “ temperature from node 25” “the area where temp >50 deg.”

Data centric Flooding Whenever a node receives a packet, the node broadcasts the packet Gossiping Whenever a node receives a packet, the node sends to only to one node(randomly selected)

Hierarchical Grouped into clusters One node - cluster head Other nodes – cluster members

August, 2004 Hierarchical LEACH: Low energy adaptive clustering hierarchy PEGASIS PEDAP

August, 2004 LEACH Consists of two phases: SETUP Phase (build routes) STEADY Phase (transfer data) SETUP PHASE: Some nodes are randomly selected as cluster heads (5 % of all nodes) For this example we assume 20 % of nodes are selected as cluster heads (4 out of 20). Cluster head base

August, 2004 LEACH Some nodes are randomly selected as cluster heads (5 % of all nodes) STEADY PHASE: Other nodes transmit to their nearest cluster head. base

August, 2004 LEACH Some nodes are randomly selected as cluster heads (5 % of all nodes) Other nodes transmit to their nearest cluster head. STEADY PHASE: Cluster heads transmit to the base. base

August, 2004 LEACH Periodically selects new cluster heads SETUP phase again base Alternates between SETUP and STEADY phases.

August, 2004 Schemes LEACH: Low energy adaptive clustering hierarchy PEGASIS: PEDAP

August, 2004 Pegasis IDEA: A chain is formed between all nodes. Trying to minimize the length of the chain. Packets are routed over the chain. Each station transmits and receives once. One randomly selected node transmits to the base station. base

August, 2004 Pegasis – How to form the chain Start forming the chain from the furthest point from base. Grow the chain using a greedy approach: At each step, add the closest neighbor of head of chain to the chain. After building the chain, select a random node to transmit to the base (this node will be called as leader). base Leader

August, 2004 Pegasis – Data transmission We will start from two ends of the chain to transmit data Data will collected at the leader node. The leader node will send the final aggregated data to the base base Leader End of chain End of chain

August, 2004 PEDAP PEDAP: Power Efficient Data Gathering and Aggregation Forward data from all sensors to the base over a minimum spanning tree.

August, 2004 PEDAP Computation of MST can be done by using an MST algorithm. One such algorithm is Prim’s algorithm. Add edges to the MST in increasing costs and also make sure that no cycle is formed. base MST Formed

August, 2004 PEDAP: Data transfer phase base S B J I H G F E D C A K Since the energy consumed mostly depends on the distance, PEDAP consumes less energy than others