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Παρουσίαση : Τσιπουρίδου Δέσποινα

A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs. Shiann-Tsong Sheu, Tzu-Fang Sheu. Ειδικά θέματα σε Δίκτυα Επικοινωνιών. Παρουσίαση : Τσιπουρίδου Δέσποινα. PRESENTATION STRUCTURE. Introduction DBASE Protocol description

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Παρουσίαση : Τσιπουρίδου Δέσποινα

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  1. A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc WirelessLANs Shiann-Tsong Sheu, Tzu-Fang Sheu Ειδικά θέματα σε Δίκτυα Επικοινωνιών Παρουσίαση : Τσιπουρίδου Δέσποινα

  2. PRESENTATION STRUCTURE • Introduction • DBASE Protocol description • Throughput Analysis • Performance Evaluation • Conclusions A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 1

  3. Introduction • Speed and capacity of Wireless LANs increase Demand for improving quality of service (QoS) for real-time multimedia applications • Already existing protocols : Relatively poor performance in terms of packet delay, fairness, QoS. • In this paper a new DBASE protocol is proposed to support both asynchronous and multimedia traffics over IEEE 802.11 ad hoc WLAN where no fixed access point coordinates accesses. A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 2

  4. In the proposed protocol : • Time-sensitive rt-packets always have higher priority than ordinary nrt-packets in order to meet the delay restrictions. • A modified CSMA/CA protocol, compatible with IEEE 802.11 standard, is proposed for this reason. • The rt-stations transmit their packets during the Contention Free Period (CFP) in every superframe. • To support both CBR and VBR services over WLAN, the channel will be dynamically allocated, shared and released. A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 3

  5. Basic concept : each time a rt-station transmits packet • also declares and reserves the needed bandwidth • at the next CFP. • Every rt-station collects the mentioned above information • and calculates its actual bandwidth at the next cycle. • So : • rt-stations with light-load “offer” their redundant bandwidth to the overloaded ones • the DBASE schedules the donators at the front of the access sequence in CFP • once any donator desires to extend its bandwidth informs the other rt-stations to recalculate their bandwidth quota fair and efficient bandwidth allocation A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 4

  6. DBASE Protocol description Ad Hoc Networks : IEEE 802.11 WLAN stations are able to communicate directly. Possible : when these stations are close enough to form a direct connection without preplanning. In this section : We describe the access procedures for transmitting nrt-packets and rt-packets separately in an ad hoc network. A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 5

  7. The frames are divided into three priorities, according to the standard. • Frames of different priorities have to wait different b inter- frame spaces (IFSs) before they are transmitted. • Inter-frame spaces : • Short IFS (SIFS) : used by immediate control frames, which always have the highest priority (clear to send (CTS), ACK) • Priority IFS (PIFS) : used by rt-frames (reservation frame (RF), request to send (RTS)) • DCF IFS (DIFS) : the longest IFS, used by nrt-frames and have the lowest priority A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 6

  8. The Access Procedure for Asynchronous Data Stations • Basic access method for nrt-stations : based on the • conventional DCF. • If the medium is detected as an idle duration for a DIFS • period, the nrt-station starts the backoff procedure. • The data backoff time (DBT) : which b grows exponentially for each retransmission attempt and Slot_time is setas 20μs. • The DBT counter is decreased when the channel is idle • and suspended while the medium becomes busy. • When DBT counter = 0 : the nrt-station transmits its data • packet (or RTS). A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 7

  9. The Access Procedure for Real-Time Stations • Every rt-station needsbuild and maintain a ReSerVation Table • (RSVT) which records the information of all rt- stations that have • finished the reservation procedure successfully. • The information includes :the access sequence, the MAC address, • the service type and the required bandwidth for each rt-station. • A new rt-station (START) contents for the medium by first issuing the • RTS packet to join the RSVT and reserve its needed bandwidth. • Each rt-station is equipped with a sequence ID (SID) register and an • active counter (AC) to maintain the correct access sequence. A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 8

  10. Reservation Procedure • Before starting a session, at time t, START monitors the channel for detecting the RF in the interval (t, t + Dmax). Dmax : smallest maximal tolerance delay among all multimedia sessions RF : announces the beginning of CFP, carries information of the number of active rt-stations and the RSVTcontent of the CFPG. • If none RF frame is detected for a specific interval, START will execute the backoff procedure. Real-time backoff time (RBT) : When RBT counter = 0 : the rt-station transmits its RTS. A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 9

  11. If collision occurs when transmitting the RTS, the P-persistent scheme is used to decide whether the collided stations insist on accessing channel in the next Slot_time. • The deferred station recalculates the RBT (RBTP) : • To make sure that the repetition cycle will not be longer than Dmax we define a parameter real-time transmission period (RTP). RTP = CFP + real-time contention period • The propagation delay can be ignored. Ad hoc WLAN composed of stations within mutual communication range of each other, able to communicate to each other directly. A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 10

  12. Anexample of joining a new rt-station into the RSVT : A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 11

  13. Allocation Procedure The RSVT information can be got and updated by the RF frame and by checking the duration field of MAC header in each MAC PDU (MPDU). The DBASE MAC header format : • Each station utilizes the ND (next degree) field to inform other stations its demanded bandwidth at the next cycle. A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 12

  14. If the bandwidth demand of each rt-station < average bandwidth requirement (ABR), the demanded bandwidth will be allocated. • Otherwise, only the average bandwidth quota (AVD) of its multimedia type will be first allocated. Therefore the maximal bandwidth reserved for all active sessions in every CFP : If CFP < CFPmax : there is residual bandwidth to be shared by the overloaded rt-stations! A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 13

  15. Retransmission scheme : After passing the CFP, the CFPG will broadcast the retransmission mapping (RTM) frame to inform all stations which can retransmit their packets A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 14

  16. Sharing Procedure • Before reallocating the residual bandwidth for the overloaded stations, every rt-station will first accumulate the spare bandwidth from those whose ND requests are less than AVD. • CD : required bandwidth degree of a station in the current cycle • From CD and AVD of each session we calculate the unit time slots (UST) that can be shared (SS) • Finally, to fairly share the residual bandwidth among overloaded stations, the proportional approach is used and the actual number of reserved unit slot (RS) for each session for the current cycle is calculated. A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 15

  17. Extension Procedure In the case that the burst traffic arrives just after a station has issued the ND for the next cycle, the 1-bit extension flag (EF) in duration field of each MAC frame is used. • If the EF is set in the duration field of MPDU the following 4-bit raise degree (RD) will record the renewal demand at the current cycle. • But : • RD will not be larger than AVD • the SS, CD, RS : must be recalculated by the other rt-stations • The transmission instances of sessions with ND < AVD are arranged at the beginning of the CFP by scheduler. A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 16

  18. Examples of DBASE protocol A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 17

  19. A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 18

  20. A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 19

  21. Throughput Analysis In this section is developed • a P-persistent model for rt-stations • a non-persistent model for nrt-stations The repetition period consists of • the contention free period of reserved rt-stations • the contention period of new rt-stations • the contention period of nrt-stations A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 20

  22. A. P-persistent Model The P-persistent model is developed for the contention period of rt-stations A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 21

  23. From the previous Markov chain the following probabilities can be derived : PT_rt : at least one rt-station transmits its packet : PS_rt : a packet is transmitted successfully : τrt : a station transmits in a slot time Nrt : the rt-stations A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 22

  24. B. Reservation Model The reservation model is used to analyze the average number of active rt-stations in the CFP. • The average number of rt-stations in the reservation list is defined by the state of the following Markov chain m : the maximum number of active rt-stations A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 23

  25. In order to analyze the time length of a contention period spent on arrival rt-stations contending, two parameters are defined : • TS_rt : average time that the channel is sensed busy because of a successful transmission • TC_rt : average time that the channel is sensed busy by a station during contention period A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 24

  26. So, the length of the period used by rt-stations (RP) is : ξ : average number of active rt-stations in the CFP Ir : maximum idle slots in the period of rt-sessions PS_rt : the probability that a RTS is transmitted successfully in the real-time contention period TH : time needed to transmit both MAC and PHY headers A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 25

  27. C. Nonpersistent Model The nonpersistent model is developed to analyze the contention period of nrt-stations. Markov chain model for nonpersistent procedure of nrt-stations : A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 26

  28. From the previous Markov chain the following probabilities can be derived : PT_nrt : at least one nrt-station transmits packet : PS_rt : a nrt-stationtransmits its packetsuccessfully : TS_nrt : average time of a successful transmission and TC_nrt : average time of an unsuccessful transmission, sensed by a nrt-station A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 27

  29. Because the cycle is limited by the maximum delay bound (Dmax), the length of asynchronous data transmitting period (DTP) will also be limited : A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 28

  30. Finally, the normalized saturation throughput S is defined as : And, according to the previous analysis : A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 29

  31. Performance Evaluation A. Traffic Models • Voice traffic model (CBR) • Video traffic model (VBR) • Data traffic model (Poisson process) B. Performance Measurements • Goodput : the percentage of the time used by both rt- and nrt-stations to successfully transmit their pure payload data • Packet delay dropped probability (PDDP) : the fraction of discarded rt-packets caused by violating the delay bound A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 30

  32. C. Simulation Results Relations of the goodput and the data load under different numbers of rt-stations and different traffic types individually Goodput up to 80% for VBR traffics Goodput up to 67% for CBR traffics A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 31

  33. The derived PDDPs under different numbers of VBR and CBR rt-stations A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 32

  34. The derived goodputs and PDDPs under mixed rt-traffic load in WLAN The DBASE protocol can also support heterogeneous rt-traffic situations in WLAN A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 33

  35. Comparison of the goodputs derived by DBASE and DCF under different traffic types, when Nnrt = 10 A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 34

  36. Comparison of goodputs and PDDPs of DBASE, DCF and DFS in the interfering environment when PER = 0.1 and Nnrt = 0 A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 35

  37. Conclusions The DBASE protocol : • can support multimedia services of either CBR or VBR in ad hoc WLAN • performs very well and much better than the conventional IEEE 802.11 standard with DCF • achieves up to 90% channel efficiency for only supporting VBR traffics • accomplishes very low packet loss probability of rt-packets even though the total traffic load is heavy A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 36

  38. ΤΕΛΟΣ

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