Remote Sensor Networks MAC Layer Professor Jack Stankovic University of Virginia 2006Slide 2
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 laterSlide 3
WSN Architecture – MAC?Slide 4
Ad Hoc Wireless Sensor Networks Reality – Irregular Multi-cast 2 6 information 6 2Slide 5
Outline 802.11 DCF (fundamental viewpoints) S-MAC (quickly) B-MAC Multi-Channel MACSlide 6
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 - MMACSlide 7
TDMA on Wired Network A B C B A Repeat Cycle 0 1 2 3 Time (Slots) Scales?Slide 8
TDMA in Wireless Network B D E A C/D? C B A/E Time Disadvantages? WSN Issues? Advancements?Slide 9
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 DataSlide 10
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 RTSSlide 11
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 DataSlide 12
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 RTSSlide 13
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 pointSlide 15
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 RangeSlide 16
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 RangeSlide 17
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 RangeSlide 18
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 vitalitySlide 19
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 hubsSlide 20
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)Slide 21
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 consciousSlide 22
Duty Cycle Example Preamble Stay alert W rest W Node here needs to send parcel Nodes wakeful and hear preface W = awaken their radioSlide 23
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 issueSlide 24
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 partSlide 25
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 issueSlide 26
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 stackSlide 27
B-MAC Configurable ( Key Feature !) Small center Factor out usefulness and open to higher layers Can be custom fitted to various sorts of systemsSlide 28
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 balancedSlide 29
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 vitalitySlide 30
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 PacketSlide 31
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 TimeSlide 32
B-MAC If Not Clear on CCA Listen Use a blockage backoff time (if none gave utilize a default)Slide 33
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 restSlide 34
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 consciousSlide 35
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.Slide 36
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 parametersSlide 37
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 ACKsSlide 38
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 controlSlide 39
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 anySlide 40
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 MintRouteSlide 41
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 operationsSlide 42
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 channelSlide 43
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 controlSlide 44
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 WSNSlide 45
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 FreqSlide 46
Negotiate on default recurrence
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