What is a MAC Protocol .


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What is a MAC Protocol. Medium Access ControlCoordinate activities over a common channel (fundamental topic of numerous solutions)Test channel to check whether busyIf occupied, waitIf not occupied, transmitIf crash, back off and attempt again later. WSN Architecture
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Slide 1

Remote Sensor Networks MAC Layer Professor Jack Stankovic University of Virginia 2006

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What is a MAC Protocol Medium Access Control Coordinate activities over a common channel (essential subject of numerous arrangements) Test channel to check whether occupied If occupied, hold up If not occupied, transmit If crash, back off and attempt again later

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WSN Architecture – MAC?

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Ad Hoc Wireless Sensor Networks Reality – Irregular Multi-cast 2 6 information 6 2

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Outline 802.11 DCF (fundamental viewpoints) S-MAC (quickly) B-MAC Multi-Channel MAC

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Types of MAC Protocols Contention Based 802.11b DCF (CSMA) S-MAC , T-MAC, Z-MAC and B-MAC (just for WSN) Scheduled Based TDMA , NAMA, TRAMA Multi-Channel - MMAC

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TDMA on Wired Network A B C B A Repeat Cycle 0 1 2 3 Time (Slots) Scales?

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TDMA in Wireless Network B D E A C/D? C B A/E Time Disadvantages? WSN Issues? Advancements?

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802.11 DCF RTS A B CTS Main Parts Sense channel – if not occupied transmit Send Request to Send (RTS) – incorporate what amount of time is required for transmission – a component of the length of the message Clear to Send (CTS) – incorporate (rehash) what amount of time is required Send Data Packet Data

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802.11 DCF RTS A B CTS Main Parts Sense channel – if not occupied transmit If occupied then do an irregular backoff in a window before attempting again Data Interval is time opened (e.g., 10 openings) Use counter (pick counter esteem in window) Wait until channel is clear and begin decrementing the counter the length of channel stays sit without moving If channel is/gets occupied then stop counter until free When counter = 0 attempt RTS

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802.11 DCF RTS A B CTS Main Parts If RTS is lost Detected by no CTS Consider this clog Then twofold the length of the window Data

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802.11 DCF RTS A B CTS Main Parts Inter-outline separating 4 diverse between casing spacings Enables every parcel to have an alternate need when fighting for the channel Data ACK SIFS PIFS DIFS EIFS CTS/ACK Increasing long of hold up DIFS RTS

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802.11b

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802.11 DCF ATIM A B ATIM-ACK Main Parts Power Saving Mode – snooze mode C ATIM Window Time Beacon All hubs conscious in ATIM window An and B remain alert amid whole signal interim If hub does not send or get ATIM it enters Doze mode until next reference point

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802.11 DCF RTS A B CTS Example – no simultaneousness Sense channel – if not occupied transmit RTS C reacts with CTS Data B sends to C A hears RTS D hears CTS – Both An and D know to sit tight and for to what extent A B C D B\'s Range C\'s Range

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802.11 DCF RTS A B CTS Hidden Terminal Problem Use same case ( B sends to C ) D can\'t hear B so imagine a scenario where it transmits before C sends a CTS Data A B C D B\'s Range C\'s Range

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802.11 DCF RTS A B CTS Exposed Terminal Problem B sends to A C needs to send to D, yet is forestalled on the grounds that it heard that B is transmitting Data A B C D B\'s Range C\'s Range

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Design - Fn(Types of Traffic) Classical MACs improve for the general case and for discretionary examples and workloads WSN Local Uni/communicate Nodes to sink (maybe all in one bearing) Periodic or uncommon (burst correspondence) Must consider vitality

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What Makes a Good MAC for WSN Low power operation Effective crash evasion Simple execution, little code and RAM measure Efficient channel usage at low and high information rates Reconfigurable by system conventions Tolerant to evolving RF/organizing conditions Scalable to expansive quantities of hubs

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Energy Consumption Idle Listening (biggest sum) Due to impacts Protocol overhead (control bundles) Overhearing (a hub gets parcels not bound for it – could have been sleeping)

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Idle Listening When will a hub get a bundle. Listen 100% of the time. Costly! Three Schemes Schedule (like S-MAC) Wake-up bundle – utilize vitality in parcel Use obligation cycle in CSMA and a long preface Node gets up intermittently and listens for prelude; if introduction there, it remains conscious

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Duty Cycle Example Preamble Stay alert W rest W Node here needs to send parcel Nodes wakeful and hear preface W = awaken their radio

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S-MAC Node\'s radio is snoozing amid the latent piece of edge Active part: speak with neighbors and send any messages lined amid the uninvolved/rest time Active Passive/Sleep 115 ms 885 ms Clock float of say 500 microsecs is not an issue

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S-MAC At every dynamic period, hubs trade adjust information After SYNC period, information can be sent utilizing RTS-CTS If a hub catches a RTS-CTS it dozes, yet will conscious a brief span after the neighbor has transmitted to promptly send its own particular information NOTE: All correspondence is pressed into the dynamic part

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S-MAC End result: Trades sparing vitality for less throughput and more prominent idleness Good for what kind of movement examples? Light movement When dormancy not an issue

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B-MAC CSMA Improves over S-MAC Better bundle conveyance rates Higher Throughput Lower Latency Less vitality utilization Adaptive prelude testing plan to diminish obligation cycle and minimize sit out of gear examining Moves MAC works up the stack

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B-MAC Configurable ( Key Feature !) Small center Factor out usefulness and open to higher layers Can be custom fitted to various sorts of systems

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B-MAC – 4 Capabilities Clear channel appraisal (CCA) Packet backoff Link layer acks Low power tuning in (LPL) Via an interface these 4 things can be balanced

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B-MAC CCA Determine if the channel is clear How Ambient commotion changes over the long run Use weighted moving normal of tests when the channel is attempted to be sit without moving Use 5 to 10 tests Note: 802.15.4 utilizations 1 test Subject to numerous false alerts (i.e., convention conceives that clamor is a parcel) Wastes vitality

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B-MAC Listen (is there a genuine parcel coming?) Check 5 tests If exception spike well beneath limit then this is not a bundle A genuine parcel would have an excess of vitality to have such a "negative" spike If no anomaly, then this is a bundle THR Real Packet

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B-MAC Interface – turn CCA off/on OFF - > execute a planning convention above B-MAC (e.g., you know when the channel is sit out of gear or busy)(such as TDMA) ON - > When prepared to send there is an underlying backoff time Caller can set that time, else a default After the underlying backoff, run CCA listen Wake Up Ready to Send Backoff CCA Listen Time

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B-MAC If Not Clear on CCA Listen Use a blockage backoff time (if none gave utilize a default)

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B-MAC At collector (no parcel to send) Node awakens Turns on radio Listens If it hears an introduction/parcel it remains conscious to get approaching parcel After bundle arrives it does a reversal to rest If no parcel was gotten after a timeout then simply about-face to rest

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B-MAC At sender CCA is utilized to check whether channel is clear At beneficiary CCA is utilized to check whether channel is dynamic and thus this recipient needs to remain conscious

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B-MAC LPL (low power tuning in) Duty go the radio through occasional inspecting 100 ms Uses CCA No. of tests Of radio flag Idle listening is characterized as being alert and examining when nothing is being sent.

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B-MAC Preamble length is coordinated to the interim that the channel is checked for action Check each 100 ms then preface must be no less than 100 ms Wake up, tune in, identify movement, get the prelude, get the message Wake up, tune in… … ..nothing, about-face to rest B-MAC Interface Check interim and introduction length are parameters

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B-MAC Optional connection layer ACK If on , there will be an ACK sent for each bundle Note: you can settle on a parcel by parcel premise in the event that you need ACK or not Why is this valuable? High need parcels need ACK Sensing repetition – may not require ACKs

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B-MAC Analytical Model for Energy Consumption (see paper if intrigued) E = E(Transmit) + E(Receive) + E(Listen) + E(Data Sampling) + E(Sleeping) E(Listen) can be lessened by means of MAC layer Plus decrease crashes, max time in rest Lower transmit control

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B-MAC Other focuses to make (about paper) No RTS/CTS (no misuse of vitality) Consider (little information) bundle sizes!!!! Small scale benchmarks Typical needs/operations (see what they consider normal for a MAC convention) You may need to characterize miniaturized scale benchmarks for your venture, assuming any

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B-MAC Analytical model is approved (sum up) Interesting tradeoffs shown Compare against condition of-workmanship S-MAC in genuine execution Workload: Run genuine Surge application (observing sort application) – incorporate BMAC and MintRoute

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B-MAC See Figure 1 – Interfaces for BMAC in nesC Table 1 – code and information sizes Table 2 – Time and current utilization for different send/rcv operations

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Single Channel MAC (up to now) Example – Mica2 Motes Choose either 433MHz OR 916MHz as recurrence channel Implies ONE channel Requires ONE handset for every hub Entire framework keeps running with this single recurrence channel

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Multi-Channel MAC N handsets per hub – costly Example with 2 for every hub RTS/CTS F1 Control Channel A B F2 Data Channel half of transfer speed for control

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More Transceivers 2 handsets for each hub 1 for control 1 for information and reuse the control channel amid information transmission stage N handsets Expensive and shape calculate Solutions not that commonsense for WSN

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Multi-Channel MAC Can you have multi-channel MAC with single handset per hub? YES the length of that handset can progressively move between frequencies Time Different hubs can Transmit at the same time Negotiate For Freq. On Default Freq

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Negotiate on default recurrence

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