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

Hoc Wireless LANs

Shiann-Tsong Sheu and Tzu-fang Sheu

IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL 19. NO. 10. OCT.

2001

Presented: Nov. 1 2001

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Outline Introduction DBASE protocol Throughput analysis Performance evaluation Conclusions

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Idea concepts The bandwidth allocation/sharing/extension

protocol (DBASE) approach is proposed to support multimedia traffic over ad hoc networks.

The basic concept is that each time real time station transmits packet it will also declare and reserve the needed bandwidth at the next contention free period (CFP).

Every rt-station collects this information and then calculates its actual bandwidth at the next cycle.

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Introduction As the speed and capacity of wireless

LAN increases, so dose the demand for improving quality of service for real-time multimedia applications.

The MAC is one of the most important issue to efficiently use wireless channel.

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Assumptions The wireless channel is error-free.

The propagation delay and state transition time are ignored.

There are no hidden terminals and all stations in a WLAN can hear each other.

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DBASE protocol For non-rt-stations, access method is

the same with the conventional DCF. For rt-stations, access method contains

all of the following procedures: - Reservation - Allocation - Sharing - Extension

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Skeleton diagram

RBT: Real time Backoff timeDBT: Data Backoff time

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Access approaches

nrt-session

Dmax

Abbreviations- ReSerVation Table (RSVT)- Sequence ID (SID) and Active counter (AC)- Dmax interval- Reservation Frame (RF)- Contention Free Period Generator(CFPG)

RF frame all rt-sessions’ MAC address Packet length Traffic type

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Reservation procedure Every rt-session needs build and

maintain a RSVT.

RF must be sent in the time stamp t+Dmax if there is any session recorded in the RSVT.

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Reservation procedure(cont’d)

nrt

rt

rt

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Reservation procedure(cont’d) Collision resolution for rt-stations: - P-persistent The rt-backoff time is defined as:

If collision occurs, rt-station will retransmit the RTS in next slot with probability P, and in next backoff range in probability 1-P.

The next backoff time is defined as:

( , )* _RBT rand c d Slot time

( 1, )* _RBTP rand c d Slot time

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Reservation procedure(cont’d)

Normal transmission

c d( , )* _RBT rand c d Slot time

P

1 - P

After collision

c+1 d

( 1, )* _RBTP rand c d Slot time

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Allocation procedure Each station can only reserve the bandwidth less

than average bandwidth requirement (ABR). Retransmission approach.

Next Degree

Extension Flag(used in extension procedure)

Raise Degree(used in extension procedure)

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Sharing procedure This procedure is to reallocate residual

bandwidth for the overloaded rt-stations.

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Extension procedure This procedure to solve the

circumstance that the burst traffic arrives just after a rt-station has issued the ND for the next cycle.

Extension Flag (EF) and Raise Degree (RD) are used here!

Reschedule the SID in the beginning of the CFP.

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Extension procedure(cont’d)

Next Current Raise

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Extension procedure(cont’d)

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Extension procedure(cont’d)

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Retransmission scheme

RTM: Retransmission Mapping frame

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Throughput analysis Model for rt-station (P-persistent):

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Throughput analysis(cont’d) Model for nrt-station:

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Throughput analysis(cont’d) After the analysis, the normalized

saturation throughput S is as:

.E time used for successful trans in repetition periodS

E length of a new repetition period

rt rt rt nrt nrtpayload S payload S payloadE T P E T P E T

RTP DTP

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Performance evaluation Traffic models and parameters for CBR

and VBR are in Table II and Table III, respectively.

Goodput and packet delay dropped probability (PDDP)

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Performance evaluation (cont’d)

The estimated saturation capacity of the system can up to 112 sessions for CBR and up to 39 sessions for VBR

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Performance evaluation(cont’d)

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Performance evaluation(cont’d)

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Conclusions The DBASE approach is proposed to support

multimedia traffic over ad hoc networks. The RF frame would be a heavy overhead

when lots of rt-stations recorded on it. The circumstance that the information in PF

may influence to the neighbor BSS. The DBASE approach really likes the PCF!!