1. SENSYS 2003 2006. 9. 7 Presented by Cheolki Lee
Energy-efficient, collision-free medium access control for wireless sensor networks
SENSYS 2003
Presented by Cheolki Lee
가나다라마바사

2. Contents Introduction Related works
TRAMA (TRaffic-Adaptive Medium Access protocol)
Overview of TRAMA
Access modes
Three components of TRAMA
NP (Neighbor Protocol)
SEP (Schedule Exchange Protocol)
AEA (Adaptive Election Algorithm)
Experiments
Conclusions
TRAMA

3. Introduction Nodes in sensor networks Major challenge
Processing and communication capabilities, sensing devices
Deployed in ad-hoc manner
Self-organized
Battery-powered
Recharging is difficult, not cost-effective
Major challenge
Scheduling of transmissions among nodes
Self adaptive to changes in traffic, node state, connectivity
Prolong the battery life of each node
TRAMA

4. Schedules of transmitting
Related works (1/2)
MAC protocols for multi-hop wireless networks
Contention-based protocol
DCF (Distributed Coordination Function ) of the IEEE b
CSMA (Carrier Sense Multiple Access) + 4-way handshake
Energy consumption in an idle state
S-MAC
Overhearing avoidance
Periodic listen and sleep
☞ Probability of collision increases with the offered load
Schedules of transmitting
TRAMA

5. Related works (2/2) Scheduling-based protocol Sohrabi and Potti
Combination of TDMA and FDMA or CDMA
Times slots is wasted
NAMA (Node Activation Multiple Access)
Distributed election algorithm
One transmitter per two-hop neighborhood
Collision-free transmission
No energy conservation mechanism
TRAMA

6. Overview of TRAMA TRAMA (TRaffic-Adaptive Medium Access protocol)
Energy efficient
Collision avoidance
Sleep mode when a node is not the intended receiver
Collision-free channel access
One node within a two-hop neighborhood
Traffic adaptive
Schedules influenced by traffic information
Assumption
A single, time-slotted channel for data/signaling packets
Time is divided into two categories
Random-access periods, scheduled-access periods
Adequate synchronization is attained
TRAMA

7. Time slot organization
Access modes
Random access periods (contention based access)
Nodes transmit only signaling packets by selecting a slot randomly
New nodes can join
Time synchronization can be done
Period length should be ‘7*1.44*N’ (99%)
(N: average num of neighbors in 2-hop distance)
Scheduled access periods
Nodes exchange collision-free data, or schedules
Time slot organization
TRAMA

8. NP (Neighbor Protocol)
Nodes exchange signaling packets
A two-hop topology is gained at each node
Signaling packets
Incremental neighborhood updates
Connectivity between neighbors
Signaling packet header format
TRAMA

9. SEP (Schedule Exchange Protocol) (1/3)
Nodes exchange schedules with neighbors
Schedule generation
SCHEDULE_INTERVAL (ex.100)
‘Winning slots’ in [t, t+SCHEDULE_INTERVAL]
Winning slots between [1000,1100]
-> 1009, 1030, 1033, 1064, 1075, 1098
Intended receivers
Node’s last winning slot
Reserved for broadcasting the nodes’ schedule for the next interval
Schedule packet
‘Intended receivers’ information using bitmap
Zero bitmap
When winning slot go unused (vacant slots)
TRAMA

10. SEP (Schedule Exchange Protocol) (2/3)
Winning slot
Zero bitmap
Schedule packet format
TRAMA

11. SEP (Schedule Exchange Protocol) (2/3)
Data packet header format
Summary of node schedule with every data packet
Size of the bitmap
‘numSlots’
Whether the node is transmitting or giving up the corresponding slot
No intended receiver information
Data packet format
TRAMA

12. AEA (Adaptive Election Algorithm) (1/4)
Decides a transmitter and intended receivers
Priority function
‘Absolute winner’ : highest priority
An absolute winner uses the time slot
All other nodes switch to low-power mode
(u: node identifier, t: time slot)
t=0
t=1
t=2
t=3
t=4
t=5 A 14 23 9 56 3 26 B 33 64 8 12 44 6 C 53 18 57 2
Priorities of node A and its two neighbors B and C
TRAMA

13. AEA (Adaptive Election Algorithm) (2/4)
State of node u is determined by
U’s two-hop neighborhood information
Schedules announced by u’s one hop neighbors
Possible states
TX (transmit)
Highest priority, has data to send
RX (receive)
Intended receiver of the current transmitter
SL (sleep)
Not the intended receiver
TRAMA

14. AEA (Adaptive Election Algorithm) (3/4)
Inconsistency problem
A thinks it can send
B knows that D has higher priority in its 2-hop neighborhood
Absolute winner
Alternative winner
Inconsistency problem
TRAMA

15. AEA (Adaptive Election Algorithm) (4/4)
Definition
Absolute winner : tx(u)
Node with the highest priority in
Alternative winner : atx(u)
Node with the highest priority in one hop neighbors, hidden from tx(u)
Possible transmitter set : PTX(u)
One-hop neighborhood that can transmit without collision
Need contender set : NEED(u)
Subset of PTX(u), data to send
Need transmitter
Node with the highest priority in NEED(u)
TRAMA

16. Experiments (1/5) Setup Protocol parameter Qualnet network simulator
50 nodes are uniformly distributed (500m*500m)
Transmission range of each node : 100m
6 one-hop neighbors, 17 two-hop neighbors on average
Traffic load type
Traffic statistically generated based on a exponentially distributed inter-arrival time
Data gathering applications
Protocol parameter
SCHEDULE_INTERVAL : 100 transmission slot
SMAC setting
SYNC_INTERVAL : 10 sec
Duty cycle : 10%, 50%
TRAMA

17. Average packet delivery ratio for synthetic traffic
Experiments (2/5)
Average packet delivery ratio for synthetic traffic
Schedule-based MACs achieve better delivery
X: Mean interarrival time (in seconds)
Y: Percentage received
Average packet delivery ratio for synthetic traffic
TRAMA

18. Experiments (3/5) Average queuing delay for synthetic traffic
X: Mean interarrival time (in seconds)
Y: Average delay
Average queuing delay
TRAMA

19. Percentage energy savings
Experiments (4/5)
Percentage sleep time for synthetic traffic
X: Mean interarrival time (in seconds)
Y: Percentage sleep time
Percentage energy savings
TRAMA

20. Average sleep interval
Experiments (5/5)
Average sleep interval for synthetic traffic
X: Mean interarrival time (in seconds)
Y: Average length of sleep interval
(in milli-seconds)
Average sleep interval
TRAMA

21. Conclusions TRAMA offers Contributions Significant energy savings
Nodes can sleep for up to 87% of the time
High throughput
Around 40% over S-MAC and CSMA, and 20% over
Contributions
TRAMA is well suited for applications
Not delay sensitive
High delivery
Energy efficiency
TRAMA

22. Appendix(1/2)
TRAMA

23. Appendix(2/2)
TRAMA