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

A Bandwidth Allocation/Sharing/Extension Protocol A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 for Multimedia Over IEEE 802.11 Ad HocAd Hoc Wireless Wireless

LANsLANs

Παρουσίαση : Τσιπουρίδου ΔέσποιναΠαρουσίαση : Τσιπουρίδου Δέσποινα

Shiann-Tsong Sheu, Tzu-Fang SheuShiann-Tsong Sheu, Tzu-Fang Sheu

Ειδικά θέματα σε Δίκτυα ΕπικοινωνιώνΕιδικά θέματα σε Δίκτυα Επικοινωνιών

PRESENTATION STRUCTUREPRESENTATION STRUCTURE

A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANsA Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs 1 1

IntroductionIntroduction

DBASE Protocol descriptionDBASE Protocol description

Throughput AnalysisThroughput Analysis

Performance EvaluationPerformance Evaluation

ConclusionsConclusions


IntroductionIntroduction

Speed and capacity of Wireless LANs increaseSpeed and capacity of Wireless LANs increase

Demand for improving quality of service (QoS) for real-time Demand for improving quality of service (QoS) for real-time multimedia applicationsmultimedia applications

Already existing protocols : Relatively poor performance Already existing protocols : Relatively poor performance in terms of packet delay, fairness, QoS. in terms of packet delay, fairness, QoS.

In this paper a new DBASE protocol is proposed to In this paper a new DBASE protocol is proposed to support both asynchronous and multimedia traffics over support both asynchronous and multimedia traffics over IEEE 802.11 IEEE 802.11 ad hocad hoc WLAN where no fixed access point WLAN where no fixed access point coordinates accesses.coordinates accesses.


In the proposed protocol :In the proposed protocol :

Time-sensitive Time-sensitive rtrt-packets always have higher priority than -packets always have higher priority than ordinary ordinary nrtnrt-packets in order to meet the delay restrictions.-packets in order to meet the delay restrictions.

A modified CSMA/CA protocol, compatible with IEEE A modified CSMA/CA protocol, compatible with IEEE 802.11 standard, is proposed for this reason.802.11 standard, is proposed for this reason.

The The rtrt-stations transmit their packets during the Contention -stations transmit their packets during the Contention Free Period (CFP) in every superframe.Free Period (CFP) in every superframe.

To support both CBR and VBR services over WLAN, the To support both CBR and VBR services over WLAN, the channel will be dynamically allocated, shared and released.channel will be dynamically allocated, shared and released.


Basic conceptBasic concept : each time a : each time a rtrt-station transmits packet -station transmits packet also declares and reserves the needed bandwidth also declares and reserves the needed bandwidth at the next CFP. at the next CFP.

Every Every rtrt-station collects the mentioned above information-station collects the mentioned above information and calculates its actual bandwidth at the next cycle.and calculates its actual bandwidth at the next cycle.

So :So :

rtrt-stations with light-load “offer” their redundant -stations with light-load “offer” their redundant bandwidth to the overloaded onesbandwidth to the overloaded ones the DBASE schedules the donators at the front the DBASE schedules the donators at the front of the access sequence in CFPof the access sequence in CFP once any donator desires to extend its once any donator desires to extend its bandwidth informs the other bandwidth informs the other rtrt-stations to -stations to recalculate their bandwidth quotarecalculate their bandwidth quota

fair and efficient

bandwidth allocation


DBASE Protocol descriptionDBASE Protocol description

Ad HocAd Hoc Networks : IEEE 802.11 WLAN stations are able to Networks : IEEE 802.11 WLAN stations are able to

communicate directly. Possible : when these stations are communicate directly. Possible : when these stations are

close enough to form a direct connection without preplanning.close enough to form a direct connection without preplanning.

In this section :In this section : We describe the access procedures for transmitting We describe the access procedures for transmitting nrtnrt-packets and -packets and rtrt-packets separately in an -packets separately in an ad hocad hoc network. network.


The frames are divided into three priorities, according to The frames are divided into three priorities, according to the standard.the standard.

Frames of different priorities have to wait different b inter- Frames of different priorities have to wait different b inter- frame spaces (IFSs) before they are transmitted. frame spaces (IFSs) before they are transmitted.

Inter-frame spaces :Inter-frame spaces :

Short IFS (SIFS) : used by immediate control frames, Short IFS (SIFS) : used by immediate control frames, which always have the highest priority which always have the highest priority (clear to send (CTS), ACK)(clear to send (CTS), ACK) Priority IFS (PIFS) : used by Priority IFS (PIFS) : used by rtrt-frames -frames (reservation frame (RF), request to send (RTS)) (reservation frame (RF), request to send (RTS)) DCF IFS (DIFS) : the longest IFS, used by DCF IFS (DIFS) : the longest IFS, used by nrtnrt--framesframes and have the lowest priorityand have the lowest priority


The Access Procedure for Asynchronous Data StationsThe Access Procedure for Asynchronous Data Stations

Basic access method for Basic access method for nrtnrt-stations : based on the -stations : based on the conventional DCF. conventional DCF.

If the medium is detected as an idle duration for a DIFS If the medium is detected as an idle duration for a DIFS period, the period, the nrtnrt-station starts the backoff procedure.-station starts the backoff procedure.

The data The data backoff time (DBT) :backoff time (DBT) :

which b grows exponentially for each retransmission which b grows exponentially for each retransmission attempt and attempt and Slot_time Slot_time is setis set as 20as 20μμs.s.

timeSlotbarandDBT _),(

The DBT counter is decreased when the channel is idle The DBT counter is decreased when the channel is idle and suspended while the medium becomes busy. and suspended while the medium becomes busy. When DBT counter = 0 : the When DBT counter = 0 : the nrtnrt-station transmits its data -station transmits its data packet (or RTS).packet (or RTS).


The Access Procedure for Real-Time StationsThe Access Procedure for Real-Time Stations

Every Every rtrt-station needs-station needs build and maintain a build and maintain a ReSerVation TableReSerVation Table

((RSVTRSVT) which records the information of all ) which records the information of all rtrt- stations that have - stations that have

finished the reservation procedure successfully.finished the reservation procedure successfully.

The information includes :The information includes : the access sequence, the MAC address, the access sequence, the MAC address, the service type and the required bandwidth for each the service type and the required bandwidth for each rtrt-station. -station.

A new A new rtrt-station (STA-station (STARTRT) contents for the medium by first issuing the ) contents for the medium by first issuing the RTS packet to join the RTS packet to join the RSVT RSVT and reserve its needed bandwidth. and reserve its needed bandwidth.

Each Each rtrt-station is equipped with a sequence ID (SID) register and an -station is equipped with a sequence ID (SID) register and an active counter (AC) to maintain the correct access sequence. active counter (AC) to maintain the correct access sequence.


1.1. Reservation ProcedureReservation Procedure

Before starting a session, at time Before starting a session, at time t,t, STA START RT monitors the channel for monitors the channel for

detecting the RF in the interval (detecting the RF in the interval (t, t + Dt, t + Dmaxmax). ).

DDmaxmax : smallest maximal tolerance delay among all multimedia sessions : smallest maximal tolerance delay among all multimedia sessions

RFRF : announces the beginning of CFP, carries information of the number : announces the beginning of CFP, carries information of the number

of active rt-stations and the of active rt-stations and the RSVTRSVT content of the CFPG.content of the CFPG. If none RF frame is detected for a specific interval, STAIf none RF frame is detected for a specific interval, START RT will execute will execute the the

backoffbackoff procedure. Real-time backoff time (RBT) : procedure. Real-time backoff time (RBT) :timeSlotdcrandRBT _),(

When RBT counter = 0 : the When RBT counter = 0 : the rtrt-station transmits its RTS.-station transmits its RTS.


If collision occurs when transmitting the RTS, the If collision occurs when transmitting the RTS, the P-persistentP-persistent scheme is scheme is

used to decide whether the collided stations insist on accessing channel used to decide whether the collided stations insist on accessing channel

in the next Slot_time. in the next Slot_time.

The deferred station recalculates the RBT (RBTP) : The deferred station recalculates the RBT (RBTP) :

timeSlotdcrandRBTP _),1(

To make sure that the repetition cycle will not be longer than DTo make sure that the repetition cycle will not be longer than Dmaxmax we we

define a parameter real-time transmission period (RTP).define a parameter real-time transmission period (RTP).

RTP = CFP + real-time contention periodRTP = CFP + real-time contention period

The propagation delay can be ignored. Ad hoc WLAN composed of The propagation delay can be ignored. Ad hoc WLAN composed of

stations within mutual communication range of each other, able to stations within mutual communication range of each other, able to

communicate to each other directly. communicate to each other directly.


AnAn example of joining a new example of joining a new rtrt-station into the -station into the RSVTRSVT : :


2.2. Allocation ProcedureAllocation Procedure

The RSVT information can be got and updated by the RF frame and by 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).checking the duration field of MAC header in each MAC PDU (MPDU).

The DBASE MAC header format :The DBASE MAC header format :

Each station utilizes the ND (next degree) field to inform other Each station utilizes the ND (next degree) field to inform other stations its demanded bandwidth at the next cycle.stations its demanded bandwidth at the next cycle.


If the bandwidth demand of each If the bandwidth demand of each rtrt-station -station << average bandwidth average bandwidth requirement (ABR), the demanded bandwidth will be allocated. requirement (ABR), the demanded bandwidth will be allocated.

Otherwise, only the average bandwidth quota (AVD) of its multimedia Otherwise, only the average bandwidth quota (AVD) of its multimedia type will be first allocated. Therefore the maximal bandwidth reserved type will be first allocated. Therefore the maximal bandwidth reserved for all active sessions in every CFP : for all active sessions in every CFP :

sessionsactiveallofAVDsCFPmax

If CFP If CFP < < CFPCFPmax max : there is residual bandwidth to be shared by the : there is residual bandwidth to be shared by the overloaded overloaded rtrt-stations!-stations!


Retransmission scheme : Retransmission scheme : After passing the CFP, the CFPG will After passing the CFP, the CFPG will broadcast the retransmission mapping (RTM) frame to inform all broadcast the retransmission mapping (RTM) frame to inform all stations which can retransmit their packetsstations which can retransmit their packets


3.3. Sharing ProcedureSharing Procedure

Before reallocating the residual bandwidth for the overloaded stations, Before reallocating the residual bandwidth for the overloaded stations, every rt-station will first accumulate the spare bandwidth from those every rt-station will first accumulate the spare bandwidth from those whose ND requests are less than AVD. whose ND requests are less than AVD.

CD : required bandwidth degree of a station in the current cycleCD : required bandwidth degree of a station in the current cycle

From CD and AVD of each session we calculate the unit time slots From CD and AVD of each session we calculate the unit time slots (UST) that can be shared (SS) (UST) that can be shared (SS)

Finally, to fairly share the residual bandwidth among overloaded Finally, to fairly share the residual bandwidth among overloaded stations, the proportional approach is used and the actual number of stations, the proportional approach is used and the actual number of reserved unit slot (RS) for each session for the current cycle is reserved unit slot (RS) for each session for the current cycle is calculated. calculated.


4.4. Extension ProcedureExtension Procedure

In the case that the burst traffic arrives just after a station has issued 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 the ND for the next cycle, the 1-bit extension flag (EF) in duration field of each MAC frame is used. of each MAC frame is used.

If the EF is set in the duration field of MPDU the following 4-bit raise 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. degree (RD) will record the renewal demand at the current cycle.

But : But :

RD will not be larger than AVDRD will not be larger than AVD the SS, CD, RS : must be recalculated by the other the SS, CD, RS : must be recalculated by the other rtrt-stations -stations

The transmission instances of sessions with ND < AVD are arranged The transmission instances of sessions with ND < AVD are arranged at the beginning of the CFP by scheduler. at the beginning of the CFP by scheduler.


Examples of DBASE protocolExamples of DBASE protocol


Throughput AnalysisThroughput Analysis

In this section is developedIn this section is developed

a P-persistent model for a P-persistent model for rtrt-stations-stations a non-persistent model for a non-persistent model for nrtnrt-stations -stations

The repetition period consists of The repetition period consists of

the contention free period of reserved the contention free period of reserved rtrt-stations-stations the contention period of new the contention period of new rtrt-stations-stations the contention period of the contention period of nrtnrt-stations -stations


A. P-persistent ModelA. P-persistent Model

The The P-persistent P-persistent model is developed for the contention period of model is developed for the contention period of rtrt-stations-stations


From the previous Markov chain the following probabilities can be From the previous Markov chain the following probabilities can be derived : derived :

PPT_rtT_rt : at least one : at least one rtrt-station transmits its packet : -station transmits its packet :

PPS_rtS_rt : a packet is transmitted successfully : : a packet is transmitted successfully :

ττrt rt : a station transmits in a slot time : a station transmits in a slot time

NNrtrt : the : the rtrt-stations-stations


B. Reservation ModelB. Reservation Model

The reservation model is used to analyze the average number of active The reservation model is used to analyze the average number of active rtrt-stations in the CFP.-stations in the CFP.

The average number of The average number of rtrt-stations in the reservation list is defined by -stations in the reservation list is defined by the state of the following Markov chain the state of the following Markov chain

m : the maximum number of active m : the maximum number of active rtrt-stations -stations


In order to analyze the time length of a contention period spent on In order to analyze the time length of a contention period spent on arrival arrival rtrt-stations contending, two parameters are defined : -stations contending, two parameters are defined :

TTS_rtS_rt : average time that the channel is sensed busy because of : average time that the channel is sensed busy because of a successful transmission a successful transmission

TTC_rtC_rt : average time that the channel is sensed busy by a station : average time that the channel is sensed busy by a station during contention periodduring contention period


So, the length of the period used by So, the length of the period used by rtrt-stations (RP) is :-stations (RP) is :

ξ : ξ : average number of active average number of active rtrt-stations in the CFP-stations in the CFPIIr r : : maximum idle slots in the period of maximum idle slots in the period of rtrt-sessions-sessionsPPS_rt S_rt : the probability that a RTS is transmitted successfully in the : the probability that a RTS is transmitted successfully in the real-time contention period real-time contention period TTHH : time needed to transmit both MAC and PHY headers : time needed to transmit both MAC and PHY headers


C. Nonpersistent ModelC. Nonpersistent Model

The nonpersistent model is developed to analyze the contention period ofThe nonpersistent model is developed to analyze the contention period ofnrtnrt-stations. -stations.

Markov chain model for nonpersistent procedure of Markov chain model for nonpersistent procedure of nrtnrt-stations :-stations :


From the previous Markov chain the following probabilities can be From the previous Markov chain the following probabilities can be derived : derived :

PPT_nrtT_nrt : at least one : at least one nrtnrt-station transmits packet : -station transmits packet :

PPS_rtS_rt : a : a nrtnrt-station-station transmits its packettransmits its packet successfully : successfully :

TTS_nrt S_nrt : average time of a successful transmission and : average time of a successful transmission and TTC_nrtC_nrt : average time of an unsuccessful transmission, sensed by a : average time of an unsuccessful transmission, sensed by a nrtnrt-station-station


Because the cycle is limited by the maximum delay bound (DBecause the cycle is limited by the maximum delay bound (Dmaxmax), the ), the length of asynchronous data transmitting period (DTP) will also be limited : length of asynchronous data transmitting period (DTP) will also be limited :


Finally, the normalized saturation throughput S is defined as : Finally, the normalized saturation throughput S is defined as :

And, according to the previous analysis : And, according to the previous analysis :


Performance EvaluationPerformance Evaluation

A. Traffic ModelsA. Traffic Models

Voice traffic model (CBR) Voice traffic model (CBR)

Video traffic model (VBR)Video traffic model (VBR)

Data traffic model (Poisson process)Data traffic model (Poisson process)

B. Performance Measurements B. Performance Measurements

GoodputGoodput : : the percentage of the time used by both the percentage of the time used by both rtrt- and - and nrtnrt-stations -stations to successfully transmit their pure payload datato successfully transmit their pure payload data

Packet delay dropped probability (PDDP) : Packet delay dropped probability (PDDP) : the fraction of discarded the fraction of discarded rtrt-packets caused by violating the delay bound -packets caused by violating the delay bound


C. Simulation ResultsC. Simulation Results

Relations of the goodput and the data load under different numbers of Relations of the goodput and the data load under different numbers of rtrt-stations and different traffic types individually-stations and different traffic types individually

Goodput up to 80% for VBR traffics

Goodput up to 67% for CBR traffics


The derived PDDPs under different numbers of VBR and CBR The derived PDDPs under different numbers of VBR and CBR rtrt-stations -stations


The derived goodputs and PDDPs under mixed The derived goodputs and PDDPs under mixed rtrt-traffic load in WLAN -traffic load in WLAN

The DBASE protocol can also support heterogeneous The DBASE protocol can also support heterogeneous rtrt-traffic -traffic situations in WLAN situations in WLAN


Comparison of the goodputs derived by DBASE and DCF under Comparison of the goodputs derived by DBASE and DCF under different traffic types, when Ndifferent traffic types, when Nnrtnrt = 10 = 10


Comparison of goodputs and PDDPs of DBASE, DCF and DFS in the Comparison of goodputs and PDDPs of DBASE, DCF and DFS in the interfering environment when PER = 0.1 and Ninterfering environment when PER = 0.1 and Nnrtnrt = 0 = 0


ConclusionsConclusions

The DBASE protocol :The DBASE protocol :

can support multimedia services of either CBR or VBR in can support multimedia services of either CBR or VBR in ad hocad hoc WLAN WLAN

performs very well and much better than the conventional IEEE 802.11 performs very well and much better than the conventional IEEE 802.11 standard with DCFstandard with DCF

achieves up to 90% channel efficiency for only supporting VBR trafficsachieves up to 90% channel efficiency for only supporting VBR traffics

accomplishes very low packet loss probability of rt-packets even though accomplishes very low packet loss probability of rt-packets even though the total traffic load is heavy the total traffic load is heavy

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

Documents

Transcript of A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless...