providing delay guarantees in bluetooth rachid ait yaiz and geert heijenk international conference...

Providing Delay Guarantees in Bluetooth

Rachid Ait Yaiz and Geert HeijenkInternational Conference on Distributed Computing Systems Workshops (ICDCSW’03)

Outline

Introduction The Guaranteed Service approach

Implementation of the Guaranteed Service approach in Bluetooth

Evaluation Conclusions

Introduction

Bluetooth uses a polling mechanism to divide bandwidth among the participants

Many polling mechanisms are proposed None of the studied pollers is able to guarant

ee packet delay bounds in its current state This paper presents a polling mechanism

that is able to guarantee delay bounds in an efficient manner

The Guaranteed Service Approach

Guaranteed service guarantees datagrams will arrive within the guaranteed delivery time and will not be discarded due to queue overflows

RFC 2212, IETF

WFQ

token rate, r

bucket size, b

per-flowrate, R

D = b/Rmax

arrivingtraffic


Provides a requested fluid model bandwidth R, then a delay bound dmax dmax can be computed given a requested fluid model bandwidth R by

RprD

R

CM

pRrDR

CM

rp

Rp

R

Mb

d

tottot

tottot

,

,

max

•D: rate-dependent deviation•C:rate-independent deviation

–Ctot and Dtot are the sum of the deviations taken over all network elements in the GS path.

•p:peak rate•r:token rate •b:bucket size •m:minimum policed unit •M:maximum transfer unit


If an application specifies its traffic using a token bucket traffic specification

If the network elements in the GS path export their deviation from the fluid model Provided that Dtot<dmax ,a fluid model service rat

e R can be requested such that a desired delay bound dmax is achieved

Guaranteed service does not control the minimal or average delay of datagrams, merely the maximal queueing delay

Implementation of the Guaranteed Service Approach in Bluetooth

The provisioning of Guaranteed Service in a network requires The source to provide a traffic

specification A desired delay bound Requires the receiver to calculate the

proper bandwidth request


Furthermore Requires the network elements to

compute and export their deviation from the fluid model

Requires a mechanism that transports all specifications and requests between the source,the destination, and the intermediate network elements

Requires the network elements to perform admission control, and to schedule the guaranteed service traffic as promised


In this paper, we focus on the determination of the C and D error terms As the C and D error terms and the

admission control are directly related to the polling mechanism

We restrict ourselves to an ideal radio environment where no transmission errors occur and where retransmissions are not needed

Planning Polls With a Fixed Time Interval

Xi:inter-poll timeSi,j,k(li,j) : Transmission time

Planning Polls With a Fixed Time Interval

A planned poll can be delayed by a period of at most yi

The Guaranteed Service provides the means to communicate this deviation to the requester . we accept this initial delay and propagate it

to the exported error terms

Determining the value of Xi

The transmission of a packet j of flow i will be completed at most a time period xi+yi+lij*xi Initial delay of xi+yi A packet j of flow i will be served within a ti

me period lij*xi


After an initial delay of xi+yi ,all segments of a packet j of flow i are served within a time period Lij/Ri, following must hold

ijiii

ji

ji

i

ijiii

jiiji

MLmR

l

L

x

thusand

MLmR

Lxl

,,

,

,,

,


Poll efficiency єpi,j the average number of bytes per poll

Associated with packet j of flow i also a result of the segmentation policy that is

followed as well as the set of baseband packet types that is allowed to be used.

Minimum poll efficiency of a flow i

)6(minmin

,

,min

, Rix

l

Li

ijiii

pi

ji

ji

MLmp

Determining the value of Yi

If at random one of the planned polls is chosen and executed, all the flows may have to wait for all the other flows Each flow will experience the same large value of yi

maximum time have to wait for is minimized. if Each flow is assigned a priority polls for a particular flow only have to wait for pol

ls for flows that are assigned a higher priority

Exporting C and D Terms

The deviation δFi of the polling mechanism from the fluid model with respect to serving flow i obeys

Then form (6)

Thus Ci= Di=

maxiii sxF

maxmin

ii

pi s

RF i

min

ip max

is

Admission Control

A planned poll should never be delayed by waiting polls for the same flow. Achieved by ensuring that yi<xi

The allowed fluid model bandwidth Ri is inversely proportional to yi

The admission control should reassign the priorities such that all the GS flows, including the new one, comply with (9)

)9(min

i

pi Ry i

Evaluation

Evaluation

For the GS flows,the packet sizes are uniformly distributed Minimum size of 144 bytes, mi=144 byte Maximum size of 176 bytes, Mi=176 byte

For the BE flows the packet sizes are of a fixed size of 176 bytes The sources of flows 5/6, 7/8, 9/10 and 11/12

generate BE traffic at a data rate of 41.6 kbps, 47.2 kbps, 52.8 kbps and 58.4 kbps respectively.

Evaluation

The allowed baseband packet types are DH1 and DH3.

Because of the fixed intervals between packet generations, and because of the packet size distribution The remaining parameters of the token bu

cket specification are

Evaluation

The algorithm used to determine yi gives y1=3.75ms, y2=7.5ms, y3=y4=11.25ms

Thus, get R

bytesCiip

144min msDi 75.3

1600

32

skbytesms

bytes

yR

i

pi

i /8.1225.11

144min

Evaluation

Requested delay bound dmax

msmsskbyte

bytesbytesD

R

CMd tot

tot 75.2875.3/8.12

144176max

Simulation results

Conclusions

This polling mechanism is highly determining with respect to the delay that packets experience in a piconet.

Further Works

The evaluation of the proposed polling mechanisms in a non-ideal radio environment Transmission errors may occur where retra

nsmissions are needed

providing delay guarantees in bluetooth rachid ait yaiz and geert heijenk international conference...

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