Курсы английского
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Z-MAC – Local Frames
Z-MAC – Local Frames
Experimental Setup – Single Hop
Experimental Setup – Single Hop
Experimental Setup – Single Hop
Experimental Setup – Single Hop
Experimental Setup - Testbed
Experimental Setup - Testbed
Experimental Setup - Testbed
Experimental Setup - Testbed
Z-MAC – Single-Hop Throughput
Z-MAC – Single-Hop Throughput
Z-MAC – Two-Hop Throughput
Z-MAC – Two-Hop Throughput
Z-MAC – Two-Hop Throughput
Z-MAC – Two-Hop Throughput
DRAND Performance Results – Run Time
DRAND Performance Results – Run Time
DRAND Performance Results – Run Time
DRAND Performance Results – Run Time
DRAND Performance Results – Run Time
DRAND Performance Results – Run Time
DRAND Performance Results – Run Time
DRAND Performance Results – Run Time
DRAND Performance Results – Message Count and Number of Slots
DRAND Performance Results – Message Count and Number of Slots
DRAND Performance Results – Message Count and Number of Slots
DRAND Performance Results – Message Count and Number of Slots
DRAND Performance Results – Message Count and Number of Slots
DRAND Performance Results – Message Count and Number of Slots
Multi Hop Results – Throughput
Multi Hop Results – Throughput
Fairness (two hop)
Fairness (two hop)
Multi Hop Results – Energy Efficiency (KBits/Joule)
Multi Hop Results – Energy Efficiency (KBits/Joule)
Z-MAC – Performance Results – Energy
Z-MAC – Performance Results – Energy
Multi Hop Results
Multi Hop Results
Z-MAC – Performance Results – Latency
Z-MAC – Performance Results – Latency
Introduction Basic goal of WSN – “Reliable data delivery consuming
Introduction Basic goal of WSN – “Reliable data delivery consuming
Introduction Basic goal of WSN – “Reliable data delivery consuming
Introduction Basic goal of WSN – “Reliable data delivery consuming
Introduction Basic goal of WSN – “Reliable data delivery consuming
Introduction Basic goal of WSN – “Reliable data delivery consuming
Introduction Basic goal of WSN – “Reliable data delivery consuming
Introduction Basic goal of WSN – “Reliable data delivery consuming
LPL – Check Interval
LPL – Check Interval
S-MAC – Design
S-MAC – Design
Clear Channel Assessment
Clear Channel Assessment
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Z-MAC: Hybrid MAC for Wireless Sensor Networks

содержание презентации «Z-MAC: Hybrid MAC for Wireless Sensor Networks.ppt»
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1Z-MAC: Hybrid MAC for Wireless Sensor 27Frame Exchange. 1.33. 1.39. Time
Networks. Manesh Aia, Ajit Warrier, Synchronization. 0.28. 0.036. Total
Jeongki Min, Injong Rhee Department of energy: 7.22 J – 0.03% of typical battery
Computer Science North Carolina State (2500mAh, 3V).
University. 28Multi Hop Results – Throughput.
2CSMA Protocols. When are they useful? 29Fairness (two hop).
When are they a bad idea? Can TDMA be a 30Multi Hop Results – Energy Efficiency
better solution? Why? Why not? (KBits/Joule).
3Effective Throughput CSMA vs. TDMA. 31Question?
Channel Utilization. TDMA. CSMA. # of 32Conclusion. Z-MAC combines the
Contenders. strength of TDMA and CSMA High throughput
4Z-MAC: Basic Objective. Channel independent of contention. Robustness to
Utilization. MAC. CSMA. TDMA. Z-MAC timing and synchronization failures and
Combine best of both Eliminate worst of radio interference from non-reachable
both. Can you do hybrid contention neighbors. Always falls back to CSMA.
resolution? Low Contention. High Compared to existing MAC It outperforms
Contention. High. Low. Low. High. B-MAC under medium to high contention.
5ZMAC - Basic Idea. Use a base TDMA Achieves high data rate with high energy
schedule Node transmissions scheduled on efficiency.
specific slots Allow non-owners of slots 33Z-MAC – Local Frames. Label is the
to 'steal' the slot from owners Provided assigned slot, number in parenthesis is
owners are not transmitting Stealing done maximum slot number within two hops. 5(5).
through competition (CSMA) Possible to After DRAND, each node needs to decide on
guarantee High channel efficiency and fair frame size. Conventional wisdom –
(quality of service). Synchronize with rest of the network on
6Z-MAC: Basic components. Scalable Maximum Slot Number (MSN) as the frame
Efficient TDMA Scheduling Priority-based size. Disadvantage: MSN has to broadcasted
Contention Resolution Fairness Energy across whole network. Unused slots if
efficient and low overhead time sync neighbourhood small, e.g. A and B would
Robust implementation Time synchronization have to maintain frame size of 8, in spite
errors. Radio interferences from of having small neighbourhood.
unreachable nodes. 34Z-MAC – Explicit Contention
7DRAND – Algorithm. Radio Interference Notification. forward. forward. discard.
Map. 1. 0. 3. 2. DRAND slot assignment. 0. discard. C experiences high contention C
1. Input Graph. broadcasts one-hop ECN message to A, B, D.
8DRAND – Algorithm – Successful Round. A, B not on routing path (C->D->F),
Step II – Receive Grants. Step I – so discard ECN. D on routing path, so it
Broadcast Request. Step III – Broadcast forwards ECN as two-hop ECN message to E,
Release. Step IV – Broadcast Two Hop F. Now, E and F will not compete during
Release. Request. Grant. Grant. Release. C's slot as Non-Owners. A, B and D are
Two Hop Release. eligible to compete during C's slot,
9Z-MAC – Reserving Slots. Time Frame albeit with lesser priority as Non-Owners.
Rule (TF Rule) Let node i be assigned to Thick Line – Routing Path Dotted Line –
slot si, and let number of nodes within ECN Messages.
two hop neighbourhood be Fi then i's time 35Z-MAC – Performance Results. Setup
frame is set to be 2a, where positive Single-hop, Two-hop and Multi-hop topology
integer a is chosen to satisfy condition experiments on Mica2 motes. Comparisons
2a-1 <= Fi < 2a – 1 In other words, with B-MAC, default MAC of Mica2, with
i uses the si-th slot in every 2a time different backoff window sizes. Metrics:
frame (i's slots are L * 2a + si, for all Throughput, Energy, Latency, Fairness.
L=1,2,3,...). E.g., 5 neighbors, you 36Z-MAC – Performance Results –
choose a = 3, and your slots are 1,9,17, … Throughput, Fairness. Setup – Single-Hop
10Z-MAC – Local Frames. 20 Mica2 motes equidistant from a sink All
11Z-MAC – Transmission Control. Slot nodes send as fast as they can –
Ownership If current timeslot for me, then throughput, fairness measured at the sink.
I am Owner All other neighbouring nodes Before starting, made sure that all motes
are Non-Owners. Low Contention Level – are within one-hop.
Nodes compete in all slots, albeit with 37Z-MAC – Energy Experiments. Setup 10
different priorities. Before transmitting: nodes within single cell sending to one
if I am the Owner – take backoff = sink Find optimum (lowest) energy to get a
Random(To) else if I am Non-Owner – take given throughput at the sink.
backoff = To + Random(Tno) after backoff, 38Z-MAC – Performance Results – Energy.
sense channel, if busy repeat above, else 39Z-MAC – Latency Experiments. Source.
send. Switches between CSMA and TDMA Sink. Setup 10 nodes in a chain topology.
automatically depending on contention Source at one end transmits 100 byte
level. packets at rate of 1 packet/10 s towards
12Z-MAC – Transmission Control. Time sink at the other end. Packet arrival time
Slots. 1. 0. 0. 2. A(0). B(1). Owner observed at each intermediate node,
Backoffs. Non-Owner Backoffs. Ready to average per-hop latency calculated and
Send, Start Random(To) Backoff. After then reported for different duty cycles.
Backoff, CCA Idle. Ready to Send, Start To 40Multi Hop Results.
+ Random(Tno) Backoff. After Backoff, CCA 41Multi Hop Results.
Busy. 42Z-MAC – Performance Results – Latency.
13Z-MAC – LCL. 2(2). 0(2). 1(2). Time 43Q & A. Z-MAC – a Hybrid MAC for
Slots. 1. 0. 0. 2. A(0). B(1). Collision Wireless Sensor Networks. Thank you for
at C. Problem – Hidden Terminal Collisions your participation.
Although LCL effectively reduces 44Agenda Introduction Wireless Sensor
collisions within one hop, hidden terminal Network (WSN) MAC Layer Design principles
could still manifest itself when two hops Basic Idea Distributed TDMA Scheduling
are involved. (DRAND) TDMA Scheduling DRAND Performance
14Z-MAC – HCL. 2(2). 0(2). 1(2). Time Results Z-MAC B-MAC (LPL, CCA) Performance
Slots. 1. 0. 0. 2. A(0). B(1). High Comparisons.
Contention Level If in HCL mode, node can 45Introduction Basic goal of WSN –
compete in current slot only if: It is “Reliable data delivery consuming minimum
owner of the slot OR It is one-hop power”. Diverse Applications Low to high
neighbour to the owner of the slot. Slot data rate applications Low data rate
in HCL, sleep till next time slot. Periodic wakeup, sense and sleep High data
Collisions still possible here. rate (102 to 105 Hz sampling rate) In
15Z-MAC – Explicit Contention fact, many applications are high rate
Notification. ECN Informs all nodes within Industrial monitoring, civil
two-hop neighbourhood not to send during infrastructure, medial monitoring,
its time-slot. When a node receives ECN industrial process control, fabrication
message, it sets its HCL flag. High plants (e.g., Intel), structural health
contention detected by lost ACKs or monitoring, fluid pipelining monitoring,
congestion backoffs. ECN Suppression HCL and hydrology. Pictures by Wei Hong, Rory
flag is soft state, so reset periodically O’connor, Sam Madden.
Nodes need to resend ECN if high 46LPL – Check Interval. Too small Energy
contention persists. wasted on Idle Listening Too large Energy
16Performance Results. DRAND and ZMAC wasted on packet transmission (large
have been implemented on both NS2 and on preamble) In general, longer check
Mica2 motes (Software can be downloaded interval is better.
from: 47MAC Energy Usage. Four important
http://www.csc.ncsu.edu/faculty/rhee/expor sources of wasted energy in WSN: Idle
/zmac/index.html). Listening (required for all CSMA
17Experimental Setup – Single Hop. protocols) Overhearing (since RF is a
Single-Hop Experiments: Mica2 motes broadcast medium) Collisions (Hidden
equidistant from one node in the middle. Terminal Problem) Control Overhead (e.g.
All nodes within one-hop transmission RTS/CTS or DATA/ACK).
range. Tests repeated 10 times and 48Existing approaches. Hybird (CSMA +
average/standard deviation errors TDMA) SMAC by Ye, Heidemann and Estrin @
reported. USC Duty cycled, but synchronized over
18Z-MAC – Two-Hop Experiments. Sink. macro time scales for neighbor
Sources. Sources. Setup – Two-Hop Dumbbell communication CSMA+Duty Cycle+LPL BMAC by
shaped topology Transmission power varied Polastre, Hill and Culler @ UC Berkeley
between low (50) and high (150) to get Duty cycled, but Low power listen - clever
two-hop situations. Aim – See how Z-MAC way reducing energy consumption (similar
works when Hidden Terminal Problem to aloha preamble sampling).
manifests itself. 49S-MAC – Design. Listen Period
19Experimental Setup - Testbed. 40 Mica2 Sleep/Wake schedule synchronization with
sensor motes in Withers Lab. Wall-powered neighbors Receive packets from neighbors
and connected to the Internet via Ethernet Sleep Period Turn OFF radio Set timer to
ports. Programs uploaded via the Internet, wake up later Transmission Send packets
all mote interaction via wireless. Links only during listen period of intended
vary in quality, some have loss rates up receiver(s) Collision Handling
to 30-40%. Assymetric links also present RTS/CTS/DATA/ACK.
(14-->15). 50S-MAC – Design. Schedules can differ,
20Z-MAC – Single-Hop Throughput. Z-MAC. prefer neighboring nodes to have same
B-MAC. schedule. Border nodes may have to
21Z-MAC – Two-Hop Throughput. High maintain more than one schedule.
Power. Low Power. Z-MAC. Z-MAC. B-MAC. 51B-MAC: Basic Concepts. Keep core MAC
B-MAC. simple Provides basic CSMA access Optional
22Conclusion. CSMA: - low channel link level ACK, no link level RTS/CTS CSMA
utilization at high loads, - but good for backoffs configurable by higher layers
dynamic load. TDMA - utilizes the channel Carrier sensing using Clear Channel
for high, stable load - but poor with Assessment (CCA) Sleep/Wake scheduling
unpredictable traffic MAC protocol needed using Low Power Listening (LPL).
for best of both worlds ZMAC performs 52Clear Channel Assessment. Before
fractional slot reservations, rest TDMA transmission – take a sample of the
Slot owners have greater priority in own channel If the sample is below the current
slots Others steal an empty slot noise floor, channel is clear, send
opportunistically (using CSMA) DRAND immediately. If five samples are taken,
deficiencies stay. Heavy initialization and no outlier found => channel busy,
(what if frequent topology changes). take a random backoff Noise floor updated
23Questions? when channel is known to be clear e.g.
24DRAND – Algorithm – Unsuccessful just after packet transmission.
Round. Step II – Receive Grants from A,B,D 53Low Power Listening. Similar to ALOHA
but Reject from E. Step I – Broadcast preamble sampling Wake up every
Request. Step III – Broadcast Fail. Grant. Check-Interval Sample Channel using CCA If
Request. Reject. Grant. Fail. no activity, go back to sleep for
25DRAND Performance Results – Run Time. Check-Interval Else start receiving packet
Single-Hop. Multi-Hop (Testbed). Round Preamble > Check-Interval.
Time – Single-Hop. Multi-Hop (NS2). 54Low Power Listening. Longer Preamble
26DRAND Performance Results – Message => Longer Check Interval, nodes can
Count and Number of Slots. Multi-Hop sleep longer At the same time, message
(NS2). Number of Slots Assigned – delays and chances of collision also
Multi-Hop (NS2). Single Hop. increase Length of Check Interval
27Overhead (Hidden cost). Operation. configurable by higher layers. Carrier
Average (J). StdDev. Neighbor Discovery. sense.
0.73. 0.0018. DRAND. 4.88. 3.105. Local
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Z-MAC: Hybrid MAC for Wireless Sensor Networks

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