Video-Streaming

for

Fast

Moving

Users

in

Mobile

Networks

The

emergence

of

third-generation

-LRB-

-RRB-

mobile

networks

offers

new

opportunities

for

the

effective

delivery

of

data

with

rich

content

including

multimedia

messaging

and

video-streaming

Provided

that

streaming

services

have

proved

highly

successful

over

stationary

networks

in

the

past

we

anticipate

that

the

same

trend

will

soon

take

place

in

networks

Although

mobile

operators

currently

make

available

pertinent

services

the

available

resources

of

the

underlying

networks

for

the

delivery

of

rich

data

remain

in-herently

constrained

At

this

stage

and

in

light

of

large

numbers

of

users

moving

fast

across

cells

networks

may

not

be

able

to

warrant

the

needed

quality-of-service

requirements

The

support

for

streaming

services

necessitates

the

presence

of

content

or

media

servers

properly

placed

over

the

network

such

servers

essen-tially

become

the

source

for

streaming

applications

Evidently

a

centralized

approach

in

organizing

streaming

content

might

lead

to

highly

congested

media-nodes

which

in

presence

of

moving

users

will

certainly

yield

increased

response

times

and

jitter

to

user

requests

In

this

paper

we

propose

a

workaround

that

enables

networks

to

offer

uninterrupted

video-streaming

services

in

the

presence

of

a

large

number

of

users

moving

in

high-speed

At

the

same

time

we

offer

a

distributed

organization

for

the

network

's

media-servers

to

better

handle

over-utilization

H.

-LSB-

Systems

and

Software

-RSB-

Information

networks

H.

-LSB-

Online

Information

Services

-RSB-

Data

sharing

C.

-LSB-

Distributed

Systems

-RSB-

Distributed

applications

Algorithms

Design

Performance

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to

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all

or

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use

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provided

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are

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made

or

distributed

for

profit

or

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advantage

and

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notice

and

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MobiDE

June

Baltimore

Maryland

USA

Copyright

ACM

The

third

generation

-LRB-

-RRB-

mobile

phone

system

UMTS

enables

better

quality

and

allows

for

more

convenient

use

of

multimedia

messaging

and

video-services

by

offering

higher

bandwidth

and

lower

latency

than

its

GSM

and

GPRS

predecessors

-LSB-

-RSB-

UMTS

furnishes

upto

Mbps

rates

for

indoor

and

upto

for

outdoor

environments

Clearly

much

improvement

in

terms

of

allo-cated

resources

has

been

made

for

the

handling

of

rich

data

including

multimedia

messages

and

video-services

Nevertheless

the

available

resources

still

present

significant

limitations

for

the

scale

up

of

services

when

very

large

number

of

clients

are

present

in

a

cell

of

a

network

Perhaps

the

most

daunting

challenge

comes

from

moving

users

who

access

multimedia

data

and

video

feeds

with

the

help

of

their

mobile

phones

and

PDAs

while

traveling

on

either

private

vehicles

or

mass

transportation

means

such

as

commuter

trains

and

public

busses

Evidently

a

large

number

of

concurrent

connections

soliciting

data

resources

in

a

cell

and

being

handled

in

real-time

pose

significant

capacity

problems

for

the

underlying

network

The

situation

becomes

even

more

challenging

when

users

attempt

to

follow

streaming

sources

while

on

the

move

We

consider

streaming

services

to

be

of

key

importance

as

they

will

ultimately

offer

information

on

demand

for

the

moving

user

in

any

geographic

position

and

at

any

time

In

order

to

facilitate

video

streaming

over

UMTS

networks

a

number

of

issues

have

to

be

addressed

so

that

users

do

not

experience

delays

and

discontinuities

during

playback

The

two

core

aspects

that

require

attention

are

the

variations

of

the

available

bandwidth

as

users

enter

and

leave

cells

as

well

as

the

effective

management

of

handovers

as

roaming

users

attach

to

different

base-stations

along

their

trajectory

The

problem

of

graceful

transition

when

moving

between

base-stations

becomes

more

critical

when

the

users

are

on

high-speed

motorways

In

this

case

handovers

become

more

frequent

and

traffic

load

at

successive

base-stations

may

vary

In

this

paper

we

outline

the

above

emerging

problem

and

propose

a

scheme

that

allows

for

not

only

improved

network

resource

sharing

but

also

for

enhanced

management

of

streaming

sources

to

the

mobile

user

It

is

expected

that

base-stations

are

to

transmit

in

different

bitrates

throughout

the

journey

of

an

individual

as

cells

will

undoubtedly

present

diverse

levels

of

congestion

and

availability

of

connections

When

considering

vehicular

users

in

general

one

can

exploit

the

fact

that

the

user

's

trajectory

can

be

predicted

in

a

satisfactory

manner

An

early

method

to

attain

this

goal

is

to

keep

an

aggregate

history

of

observations

made

regarding

the

movement

of

users

within

each

cell

-LSB-

-RSB-

Based

on

this

information

probability

density

functions

for

the

prediction

for

the

next-cell-to-move

can

be

derived

and

used

Traffic

authorities

imposed

speed

limits

and

road

signals

can

also

assist

in

the

more

accurate

estimation

of

a

user

's

average

speed

In

addition

the

user

's

direction

can

be

predicted

reasonably

well

by

keeping

track

of

her

trajectory

thus

far

Although

a

model

for

precise

prediction

is

beyond

the

scope

of

this

paper

we

can

assume

that

there

are

already

techniques

that

can

offer

a

good

estimation

of

a

moving

user

path

For

instance

an

individual

's

geographic

location

could

be

tracked

with

the

assistance

of

UMTS

Location

Service

-LRB-

LCS

-RRB-

-LSB-

-RSB-

that

can

identify

the

cell

that

a

user

presently

appears

in

If

a

user

is

moving

along

a

highway

one

could

easily

estimate

not

only

the

direction

of

his

movement

but

also

his

average

speed

along

a

given

trajectory

Finally

the

soon

anticipated

incorporation

of

Global

Positioning

System

-LRB-

GPS

-RRB-

receivers

into

mobile

phones

through

A-GPS

features

-LSB-

-RSB-

will

help

in

the

very

accurate

user

positioning

and

extraction

of

their

movement

characteristics

It

is

our

conjecture

that

at

this

stage

simply

knowing

the

overall

direction

of

a

user

's

trajectory

in

conjuction

with

the

highway

that

she

travels

on

can

ensure

timely

video-streaming

and

playout

continuity

for

users

In

our

streaming

environment

there

exist

three

distinct

types

of

synergistic

computing

systems

media-servers

base-stations

and

user

equipment

These

systems

are

organized

in

three

functional

layers

as

Figure

depicts

The

role

of

the

media-servers

is

to

predominantly

manage

content

in

a

highly

distributed

fashion

where

fast

content

retrieval

and

data

resilience

can

be

guaranteed

Base-stations

handle

all

user

initiated

connections

to

the

network

and

through

their

channels

offer

users

requested

data

The

last

tier

of

Figure

consists

of

cellular

phones

and

PDAs

equipped

with

appropriate

video-players

and

featuring

minimal

buffer

capabilities

to

support

streaming

Base

Station

Media

Server

Base

Station

Base

Station

Media

Server

Base

Station

WCDMA

radio

interface

Figure

Three-Tier

Organization

for

Streaming

Provision

Media

and

base-stations

are

internetworked

via

high-speed

wired

links

while

UMTS

offer

wireless

connections

between

user

equipment

and

base-stations

This

distributed

media-server

architecture

provides

for

dividing

of

large

video

streams

into

multiple

segments

-LSB-

-RSB-

A

media-server

initially

retrieves

a

solicited

video

object

either

from

its

storage

units

or

from

another

remote

media-server

In

this

paper

we

take

the

approach

that

instead

of

transmitting

the

entire

object

to

a

single

base-station

we

first

segment

it

and

then

forward

its

segments

to

the

base-stations

along

the

user

's

path

Our

rationale

is

that

an

individual

base-station

handles

only

a

section

of

the

video

file

the

size

of

the

section

in

discussion

is

commensurate

to

the

duration

of

a

user

's

trip

inside

the

cell

Clearly

video-object

segmentation

reduces

both

network

transmission

costs

between

media

and

base-stations

and

start-up

latencies

that

users

experience

upon

cell

entrance

On

the

other

hand

segmentation

might

get

more

complex

if

a

user

remains

longer

in

a

cell

than

her

estimated

time

and

so

she

may

face

delays

in

the

reception

of

frames

We

address

this

issue

by

continual

monitoring

of

both

user

speed

and

position

and

by

doing

so

giving

the

base-station

the

option

to

receive

additional

video

increments

and

sufficiently

feed

a

user

at

all

times

Our

work

requires

minimal

buffer

capabilities

for

mobile

stations

so

that

a

sufficient

number

of

frames

can

be

accommodated

Buffer

presence

assures

that

the

playout

does

not

stop

if

the

base-station

emits

at

lower

bitrate

due

to

network

congestion

We

propose

a

rate

adaptation

scheme

which

allows

a

base-station

to

adjust

its

transmitting

bitrate

at

any

time

according

to

base-station

load

and

the

states

of

the

client-side

buffer

The

UMTS

streaming

class

defines

that

the

bitrate

assigned

to

a

moving

user

is

guaranteed

even

though

it

might

be

less

than

the

maximum

video

bitrate

-LSB-

-RSB-

The

base-station

's

decision

of

accepting

a

video

streaming

session

has

an

impact

on

all

subsequent

base-stations

that

follow

up

on

the

video

delivery

process

While

a

streaming

session

is

in

progress

the

load

of

base-stations-to-service

may

dynamically

change

and

potentially

lead

to

session

drops

Such

drops

are

highly

undesirable

and

we

adopt

a

policy

to

address

this

issue

Our

proposed

scheme

gives

a

base-station

the

opportunity

to

appropriately

alter

the

transmission

bitrate

by

taking

into

account

the

current

base-station

load

and

simultaneously

ensuring

that

the

client

buffer

does

not

starve

The

rest

of

the

paper

is

organized

as

follows

Section

presents

the

overall

system

architecture

and

examines

the

interaction

between

media-servers

and

base-stations

Section

proposes

our

bitrate

adaptation

scheme

and

Section

discusses

the

results

of

our

preliminary

experimentation

Finally

related

work

and

conclusions

can

be

found

in

Sections

and

respectively

The

fast

movement

of

users

via

different

cells

of

the

network

imposes

a

set

of

new

requirements

for

the

entire

video

delivery

system

As

the

user

relocates

rapidly

she

faces

a

high

number

of

handovers

during

her

journey

and

as

a

consequence

a

large

video

stream

has

to

be

fetched

from

different

base-stations

in

order

to

warrant

continuous

playback

As

suggested

earlier

we

assume

the

deployment

of

dedicated

media-servers

which

undertake

both

the

storage

and

distribution

of

video-streams

to

underline

base-stations

It

is

imperative

that

media-servers

base-stations

and

user-equipment

involved

in

a

streaming

session

must

cooperate

in

order

to

guarantee

QoS

for

the

video

reception

of

the

moving

individual

In

this

section

we

outline

our

overall

architecture

discuss

the

content

delivery

process

that

media-servers

carry

out

and

present

specific

algorithms

for

video

segmentation

and

content

distribution

Architecture

The

three

distinct

types

of

cooperative

computing

systems

-LRB-

shown

in

Figure

-RRB-

organized

in

a

multi-tier

architecture

constitute

our

proposed

streaming

environment

We

assume

that

base-stations

communicate

with

the

mobile

stations

through

the

WCDMA

radio

interface

-LSB-

-RSB-

Each

cell

of

the

UMTS

network

is

served

by

a

different

base-station

whose

responsibility

is

to

deliver

the

video

streams

to

its

constituent

mobile

users

A

streaming

service

necessitates

the

use

of

media

servers

that

will

handle

the

storage

and

delivery

of

video

files

-LSB-

-RSB-

Although

we

could

adopt

a

centralized

approach

to

accommodate

the

media

in

delivery

high

contention

and

resource

over-utilization

would

impact

user

request

response

times

greatly

Clearly

a

distributed

approach

that

webs

media-servers

together

is

required

High-speed

wired

communication

means

link

these

servers

and

all

share

required

meta-data

structures

Due

to

incurred

costs

and

the

fact

that

users

move

at

high-speeds

having

a

dedicated

media

server

for

each

base-station

would

be

a

poor

decision

If

the

mobile

user

is

traveling

at

a

speed

of

km/h

and

the

cell

radius

is

km

then

he

will

pass

through

the

given

cell

in

seconds

at

maximum

assuming

an

hexagonal

shape

This

implies

that

the

number

of

frequent

handovers

taking

place

increase

the

interaction

among

media-servers

that

will

have

to

be

involved

throughout

the

streaming

session

Furthermore

in

order

to

avoid

under-utilization

of

media-servers

and

strike

a

balance

in

the

aggregate

use

for

facilitating

streaming

we

group

cells

into

groups

as

Figure

depicts

This

assignment

is

expected

to

happen

in

a

static

manner

although

it

could

be

modified

to

reflect

emerging

new

realities

in

the

core

network

In

this

regard

Figure

shows

a

network

layout

in

which

sets

of

sixteen

cells

are

configured

to

function

as

a

group

In

this

example

the

mobile

user

is

currently

in

a

cell

of

group

A

and

is

heading

towards

group

F

The

media-servers

that

can

be

involved

in

the

delivery

of

video

objects

are

A

D

E

and

F

The

server

A

is

expected

to

interact

with

server

D

D

with

E

and

E

with

F

In

this

chained-fashion

we

anticipate

that

the

media

servers

notify

each

other

about

the

streaming

session

of

the

oncoming

mobile

user

In

addition

the

media-servers

send

and

receive

in

pipelined

fashion

the

video

object

under

transmission

-LRB-

-RRB-

A

B

Figure

Grouping

of

Cells

There

may

be

other

interactions

as

well

For

instance

there

must

be

cooperation

between

media

server

A

and

F

if

the

requested

video

object

is

initially

located

at

F

A

media

server

accepts

video

requests

from

base-stations

residing

in

its

group

if

it

does

not

currently

have

the

object

it

is

responsible

for

locating

using

the

meta

data

structure

and

fetching

it

Due

to

the

location

awareness

of

our

approach

we

assume

that

each

server

predominantly

stores

streams

specific

to

its

own

geographic

area

For

instance

if

the

route

drawn

in

Figure

crosses

a

county

video

clips

with

showing

traffic

conditions

ahead

in

specific

points

may

be

requested

Similarly

in

a

city

setting

such

requests

may

entail

multimedia

location-based

virtual

presentations

Content

Distribution

Provided

that

a

media

server

has

a

video

clip

in

place

a

straightforward

approach

would

be

to

transmit

the

object

into

all

base-stations

operating

in

cells

located

on

or

near-by

the

user

's

trajectory

This

is

not

only

wasteful

in

both

network

and

base-station

resources

but

also

increases

the

user-perceived

playout

latency

Therefore

we

resort

to

using

video

segmentation

-LSB-

-RSB-

-LSB-

-RSB-

in

order

to

reduce

network

transmission

costs

between

the

video-holding

media

server

and

its

subordinates

base-stations

Segmentation

also

decreases

the

start-up

latency

that

users

experience

upon

cell

entrance

The

length

of

a

video-segment

denoted

S

t

sent

to

each

base-station

is

proportional

to

the

average

time

that

the

user

is

expected

to

stay

in

the

specific

cell

The

process

of

segmenting

the

video

streams

into

chunks

of

frames

of

specific

duration

assumes

that

the

media

servers

are

aware

of

the

underlying

cell

configuration

In

particular

a

media-server

has

to

be

aware

of

the

precise

manner

with

which

a

motorway

cuts

across

its

subordinate

cells

the

direction

as

well

as

the

speed

of

moving

users

With

this

data

available

the

media-server

in

discussion

can

approximate

the

time

that

a

user

spends

in

a

cell

For

example

if

a

motorist

moving

at

has

just

entered

a

cell

and

departs

after

traversing

a

km

route

portion

the

server

can

compute

the

duration

of

the

user

's

stay

to

be

at

ap-proximately

seconds

The

media-server

can

capitalize

on

this

very

information

to

appropriately

segment

the

streamed

video

it

only

dispatches

enough

frames

for

a

playout

period

of

seconds

The

duration

of

a

user

's

presence

within

a

cell

may

vary

according

to

speed

changes

with

clearly

lower

speeds

leading

to

elongated

stays

in

the

cell

and

vice

versa

Should

the

speed

be

decreasing

the

base-station

will

ultimately

require

more

frames

from

the

media

server

than

the

number

predicted

once

the

user

appeared

in

the

cell

Such

a

request

constitutes

a

cache

miss

which

will

not

be

noted

by

the

user

if

detected

on

time

and

acted

upon

by

the

coordinating

base-station

Imposing

a

minimum

threshold

in

the

number

of

frames

always

available

for

delivery

at

a

base-station

may

help

overcome

such

cache-misses

Therefore

when

the

number

of

frames

awaiting

transmission

on

a

base-station

falls

below

the

abovementioned

threshold

the

base-station

signals

its

need

for

additional

frames

to

its

overseeing

media-server

should

the

latter

act

upon

this

request

additional

frames

arrive

on

time

at

the

base-station

for

delivery

On

the

other

hand

as

soon

as

a

user

increases

speed

she

will

depart

the

cell

extend

earlier

than

initially

anticipated

The

drawback

here

is

that

the

media-server

has

provided

the

base-station

with

more

frames

than

those

eventually

needed

During

the

handover

process

the

coordinating

media-server

has

to

generate

a

video-fragment

which

in

its

opening

contains

frames

that

have

already

been

transmitted

to

the

previous

base-station

but

not-yet

seen

by

the

user

Our

approach

allows

a

base-station

to

dynamically

alter

the

transmission

bitrate

according

to

its

current

load

Under

light

load

a

base-station

may

opt

to

increase

the

transmission

rate

for

a

specific

video-stream

thus

leading

to

potential

frame

shortage

To

easily

avoid

such

shortage

we

use

the

minimum

allowed

vehicle

speed

to

compute

the

size

of

the

video-segment

S

t

to

be

transported

to

base-stations

S

t

Distance

M

inimumSpeed

-LRB-

-RRB-

In

most

freeways

there

are

authority-posted

limits

for

minimum

allowed

speed

in

each

road

segment

As

media-servers

are

aware

of

the

geographic

area

that

they

serve

such

minimum

speed

rates

are

statically

designated

for

each

cell

in

their

jurisdiction

Evidently

the

video-segment

size

that

we

potentially

use

as

safety

against

frame

shortage

is

S

t

Distance

M

inimumSpeed

Distance

AverageSpeed

-LRB-

-RRB-

Algorithms

and

depict

the

video

segmentation

and

distribution

that

we

follow

in

our

media

distribution

Upon

a

new

video-streaming

request

we

assume

that

the

media-server

can

efficiently

retrieve

the

corresponding

video-file

either

from

local

storage

options

or

remote

servers

via

its

low-latency/high-bandwidth

wired

networking

infrastructure

The

identification

of

the

user

's

current

location

the

precompiled

knowledge

of

the

traveled

distance

within

a

cell

in

conjunction

with

the

minimum

allowed

speed

on

pertinent

highway

segments

permit

for

the

estimation

of

the

maximum

user

stay

S

t

in

a

specific

cell

Subsequently

the

media-server

can

create

the

first

segment

of

frames

needed

for

transmission

via

the

base-station

to

the

requesting

client

The

size

of

a

video-segment

is

given

by

V

P

N

i

F

i

where

F

i

is

the

size

of

the

i-th

frame

and

N

is

the

number

of

frames

in

the

segment

we

can

easily

compute

N

by

multiplying

the

frame-rate

-LRB-

frames/second

-RRB-

with

the

duration

of

stay

in

a

cell

S

t

Algorithm

Video

Segmentation

at

Media-Server

Get

Minimum

User

Speed

MinSpeed

Get

PathLength

in

cell

range

p

last

frame

transmitted

if

-LRB-

New

Session

-RRB-

then

S

t

P

athLength

M

inSpeed

else

Shortage

of

Frames

S

t

P

athLength

M

inSpeed

with

end

if

V

i

P

p

N

i

=p

F

i

where

F

i

is

size

of

i-th

frame

N

F

rameRate

S

t

In

light

of

frame

shortage

our

video-segmentation

algorithm

dispatches

into

the

base-station

with

need

an

increment

of

frames

This

is

defined

as

a

fixed

fraction

of

the

length

of

S

t

in

the

current

cell

-LRB-

line

of

Algorithm

-RRB-

Requests

of

such

increments

may

occur

multiple

times

before

a

motorist

leaves

a

cell

due

to

congestion

A

handover

might

find

a

moving

user

either

serviced

by

a

base-station

in

the

realm

of

the

current

media-server

or

under

the

authority

of

a

completely

new

media-server

along

the

motorist

's

path

In

the

first

case

the

media-server

initiates

the

delivery

of

the

next

video-fragment

to

the

next-base-station

encountered

The

just

departed

base-station

can

help

in

determining

the

appropriate

stream

position

p

from

which

the

segmentation

will

have

to

resume

The

duration

of

the

video-segment

is

computed

anew

using

the

same

algorithm

that

now

takes

into

consideration

the

data

points

from

the

new

cell

Clearly

the

length

of

the

route

as

well

as

designated

minimum

speed

limits

may

be

different

from

those

encountered

in

the

previous

cell

In

the

second

scenario

a

handover

may

force

a

user

to

operate

in

an

entirely

new

group

of

cells

supported

by

a

new

media-server

In

general

the

portion

of

the

not-yet-seen

stream

has

to

be

forwarded

from

the

previous

to

the

new

media-server

unless

the

latter

already

maintains

its

own

copy

If

we

are

not

interested

in

reducing

the

transmission

costs

we

can

transport

the

entire

video

object

to

the

new

media-server

using

the

assumed

high-speed

link

The

media-server

now

in

charge

takes

over

the

session

identifier

of

the

moving

user

and

along

with

user

state

data

from

its

previous

location

can

help

coordinate

the

delivery

of

the

video

in

the

new

cell

To

enhance

coordination

among

media-servers

in

the

highest-level

of

Figure

prefetching

could

be

used

-LSB-

-RSB-

We

could

de-Algorithm

Video

Distribution

from

Media-Server

to

Base-Station

-LRB-

s

-RRB-

while

-LRB-

OutstanindRequests

-RRB-

do

if

New

Session

then

Start

session

-LRB-

user

's

location

video

stream

cell

ID

-RRB-

if

Video

Stream

Not

in

Storage

then

Get

Video

Stream

from

corresponding

Media-Server

end

if

end

if

if

-LRB-

not

-LRB-

Handover

-RRB-

-RRB-

then

Apply

Video

Segmentation

Algorithm

Send

Video-Segment

V

to

Base-Station

else

if

-LRB-

new

Base-Station

within

Media-Server

realm

-RRB-

then

Apply

Video

Segmentation

Algorithm

Send

Segment

V

to

Base-Station

Send

playback

position

p

to

new

Base-Station

else

Send

Video

Stream

to

next

Media-Server

Send

playback

position

p

to

next

Media-Server

end

if

end

if

end

while

ploy

prefetching

of

video-segments

to

media-servers

and/or

base-stations

to

facilitate

playout

continuity

and

minimize

the

start-up

latencies

Users

moving

with

similar

speed

and

nearby

to

the

streaming

user

can

benefit

from

the

already

segmented

video

stream

and

start

the

playout

immediately

Caching

efficiency

is

limited

by

the

fact

that

only

users

with

similar

traveling

behavior

may

use

the

video

segments

We

can

overcome

this

limitation

if

the

starting

point

of

the

video

segment

at

the

next

cell

corresponds

to

users

traveling

at

the

maximum

speed

within

the

current

cell

At

the

same

time

the

total

size

of

the

segment

caters

for

users

that

travel

at

minimum

speed

within

the

next

cell

thus

remaining

longer

in

the

cell

's

range

This

ensures

that

successive

base

stations

hold

a

sufficient

amount

of

frames

to

serve

users

traveling

at

different

speeds

In

this

section

we

propose

a

rate

adaptation

scheme

whose

objective

is

to

better

serve

the

overall

needs

of

fast-roaming

users

More

specifically

we

present

a

mechanism

used

by

base-stations

to

control

the

rate

at

which

they

transmit

video

to

each

user

when

the

cell

becomes

overloaded

and

the

transmission

bitrate

eventually

needs

to

be

decreased

In

light

of

this

reduction

we

seek

ways

to

avoid

discontinuities

in

user

playback

and

cell

bandwidth

over-utilization

lowering

so

the

probability

for

a

session

drop

While

focusing

on

bitrate

management

between

the

second

and

last

tier

of

Figure

we

assume

that

pertinent

video-segment

data

is

available

at

a

base-station

Upon

session

initiation

the

size

Q

of

the

mobile

device

buffer

becomes

known

to

the

managing

base-station

In

general

we

assume

that

a

video-object

is

divided

into

frames

of

constant

duration

Frames

that

belong

to

the

same

file

vary

in

size

depending

on

the

encoding

rate

and

the

scene

content

A

time

domain

perspective

allows

us

to

control

the

transmission

rate

examining

the

time

interval

between

transmission

of

successive

frames

rather

than

their

respective

sizes

If

the

inter-departure

time

corresponds

to

the

rate

instructed

by

the

file

's

frame

rate

Typical

frame

rate

values

are

frames/sec

for

the

PAL

color

Figure

Rate

Adaptation

Modules

within

a

base-station

the

transmission

bitrate

corresponds

to

the

file

's

encoding

bitrate

Alterations

in

the

inter-departure

times

result

in

the

inversely

proportional

changes

in

transmission

bitrate

Let

-LCB-

X

i

k

-RCB-

k

denote

the

departure

process

of

the

video

frames

from

the

base-station

for

the

i-th

user

If

i

k

is

the

departure

time

for

frame

k

X

i

k

i

k

i

k

is

the

inter-departure

interval

for

the

k-th

frame

In

the

absence

of

buffering

capabilities

on

the

mobile

device

the

smoothness

of

-LCB-

X

i

k

-RCB-

is

critical

for

the

smoothness

of

playback

at

the

user

's

end

Thus

the

following

should

hold

P

-LCB-

X

i

k

T

-RCB-

-LRB-

-RRB-

where

T

is

the

inter-departure

interval

specified

by

the

video-object

frame

rate

The

buffer

support

that

we

assume

available

at

the

user-end

enables

the

modification

of

the

-LCB-

X

k

-RCB-

process

reflecting

modifications

to

the

actual

transmitting

bitrate

of

the

base-station

Video

Streaming

modules

are

integral

parts

of

the

base-station

configuration

and

each

such

module

handles

the

transmission

of

a

video-stream

Hence

a

segment

of

a

video-stream

is

assigned

to

an

instance

of

a

Video

Streaming

module

for

final

delivery

to

the

user

's

equipment

A

Rate

Adaptation

-LRB-

RA

-RRB-

element

is

assigned

to

each

user

session

for

the

specified

video

stream

An

RA

is

aware

of

the

user

's

buffer

size

and

is

responsible

for

the

forwarding

of

video

frames

to

the

actual

Transmitter

of

the

base-station

As

information

about

the

station

's

load

is

fed-back

by

the

Transmitter

the

Rate

Adaptation

element

regulates

the

inter-departure

process

of

video

frames

from

the

station

to

a

user

in

a

way

that

preserves

playback

continuity

Figure

depicts

the

interaction

among

these

two

elements

and

the

Transmitter

at

a

base-station

that

serves

k

concurrent

sessions

for

the

same

video-object

The

operation

of

the

Rate

Adaptation

element

is

governed

by

periodic

time

intervals

of

constant

duration

termed

Control

Cycles

Operating

in

the

time

domain

the

module

is

aware

of

the

exact

number

of

frames

the

media

player

at

the

user-end

will

need

over

a

specific

period

of

time

to

ensure

smooth

playback

Let

A

denote

the

duration

of

the

control

cycle

Also

let

Q

A

be

the

occupancy

-LRB-

i.e.

number

of

frames

-RRB-

of

the

buffer

at

the

beginning

of

the

control

cycle

and

N

A

the

number

of

frames

that

will

be

reproduced

at

the

user-end

during

the

control

cycle

Since

N

A

frames

are

requested

tem

that

corresponds

to

an

inter-departure

time

of

msec

and

fps

for

the

NTSC

system

which

corresponds

to

inter-departure

time

of

msec

from

the

media-player

and

Q

A

frames

are

accumulated

the

rate

adapter

needs

only

transmit

N

A

Q

A

frames

at

minimum

over

the

control

cycle

The

video

frame

rate

instructs

that

a

frame

be

transmitted

every

T

A

N

A

mseconds

Each

one

of

the

N

A

Q

A

frames

transmitted

at

minimum

during

the

control

cycle

will

depart

the

base-station

at

longer

intervals

equal

to

T

A

N

A

Q

A

The

initial

inter-departure

time

has

been

spread

by

a

tolerance

factor

-LRB-

-RRB-

where

A

N

A

Q

A

-LRB-

-RRB-

A

N

A

Q

A

N

A

Q

A

-LRB-

-RRB-

The

tolerance

factor

is

a

parameter

of

the

control

cycle

may

turn

negative

only

when

Q

A

N

A

Thus

a

more

specific

definition

of

would

be

Q

A

N

A

Q

A

-LCB-

Q

A

N

A

-RCB-

-LCB-

Q

A

N

A

-RCB-

-LRB-

-RRB-

If

the

RA

element

forwards

frames

at

the

rate

instructed

by

the

tolerance

factor

the

transmission

bitrate

over

the

control

cycle

will

be

equal

to

B

-LRB-

-RRB-

where

B

is

the

encoding

bitrate

of

the

video-stream

A

control

cycle

during

which

the

base-station

transmits

at

the

minimum

bitrate

instructed

by

is

called

a

degraded

cycle

A

degraded

cycle

will

lead

to

zero

buffer

occupancy

at

the

end

of

the

control

cycle

and

the

tolerance

factor

for

the

next

control

cycle

will

be

equal

to

zero

Therefore

no

two

successive

degraded

cycles

may

occur

Non-zero

buffer

occupancy

at

the

beginning

of

a

control

cycle

will

be

present

only

if

the

overall

transmission

rate

over

the

previous

control

cycles

exceeded

B

This

can

be

achieved

if

the

RA

element

forwards

frames

at

a

higher

rate

when

the

station

is

un-derutilized

Let

denote

the

speed-up

factor

the

factor

by

which

the

bitrate

increases

in

this

case

An

expression

for

the

speed-up

factor

may

be

obtained

if

we

consider

that

the

maximum

transmission

bitrate

will

lead

to

a

full

user

buffer

at

the

end

of

the

control

cycle

If

Q

A

is

the

buffer

occupancy

at

the

beginning

of

the

cycle

then

the

station

may

transmit

at

maximum

Q

Q

A

frames

over

the

control

cycle

In

this

case

each

frame

will

be

transmitted

every

A

Q

Q

A

mseconds

with

inter-departure

interval

having

been

decreased

by

A

Q

Q

A

-LRB-

-RRB-

A

N

A

N

A

Q

Q

A

-LRB-

-RRB-

An

upgraded

cycle

will

transmit

at

a

rate

of

B

-LRB-

-RRB-

The

speed-up

factor

may

turn

negative

only

when

the

free

buffer

space

is

less

than

the

frames

that

will

be

played

back

during

the

control

cycle

In

this

case

the

cycle

is

forced

to

operate

in

degraded

mode

so

that

we

can

avoid

buffer

overflow

It

is

clear

that

the

n-th

control

cycle

may

forward

frames

at

a

rate

in

the

range

of

B

max

-LCB-

-LRB-

-RRB-

-LRB-

-RRB-

-RCB-

B

n

B

-LRB-

-RRB-

-LRB-

-RRB-

The

respective

inter-departure

process

-LCB-

X

n

-RCB-

will

be

in

the

range

of

-LRB-

-RRB-

T

-LCB-

X

n

k

-RCB-

max

-LCB-

-LRB-

-RRB-

T

-LRB-

-RRB-

T

-RCB-

-LRB-

-RRB-

The

RA

element

knows

at

any

time

the

exact

number

of

frames

that

have

been

transmitted

to

the

user

and

it

also

knows

the

time

that

has

passed

since

the

session

initiation

which

corresponds

to

the

number

of

frames

the

playback

process

has

consumed

The

difference

between

the

two

values

denotes

the

user

buffer

occupancy

so

no

feedback

mechanism

is

required

as

far

as

the

user

buffer

occupancy

is

concerned

The

algorithm

followed

by

each

Rate

Adaptation

element

in

the

Video

Streaming

module

is

outlined

in

Algorithm

Algorithm

Rate

Adaptation

element

operation

Executed

at

the

beginning

of

every

control

cycle

for

user

i

Q

i

A

F

ramesT

ransmit

i

F

ramesP

layed

i

Q

i

A

-LRB-

F

ramesCycle

Q

i

A

-RRB-

F

ramesCycle

-LRB-

Q

Q

i

A

-RRB-

M

inInterval

i

-LRB-

-RRB-

T

if

then

M

axInterval

i

M

inInterval

i

else

M

axInterval

i

-LRB-

-RRB-

T

end

if

Interval

i

M

inInterval

i

-LRB-

CellLoadP

-RRB-

-LRB-

M

axInterval

i

M

inInterval

i

-RRB-

Since

the

duration

of

the

control

cycle

is

constant

multiple

control

cycles

may

occur

during

a

user

's

presence

in

the

range

of

a

single

cell

depending

on

the

size

of

the

cell

and

the

user

's

speed

We

assume

that

the

each

cell

handover

always

initiates

a

new

control

cycle

Algorithm

allows

for

alteration

in

the

transmission

bitrate

by

providing

upper

and

lower

bounds

-LRB-

i.e.

M

inInterval

i

and

M

ax

Interval

i

-RRB-

to

ensure

the

smoothness

of

the

playout

process

The

choice

of

the

actual

bitrate

within

the

specified

range

at

which

the

base-station

transmits

during

a

control

cycle

is

ultimately

a

function

of

the

station

's

load

at

the

time

This

load

is

continually

estimated

with

the

help

of

the

Transmitter

module

This

feedback

enables

each

Rate

Adaptation

element

to

cater

for

buffer

occupancy

increase

taking

advantage

of

low

system

load

periods

At

the

same

time

by

detecting

high

system

load

the

Rate

Adaptation

element

lowers

the

transmission

bandwidth

allowing

for

more

sessions

to

be

accommodated

while

at

the

same

time

the

playback

process

is

not

distorted

In

order

to

reproduce

and

experiment

with

the

behavior

of

our

proposed

architecture

and

bitrate

adaptation

scheme

we

have

setup

a

simulation

testbed

We

have

assumed

a

user

trajectory

with

duration

of

seconds

The

user

traverses

numerous

cells

of

different

sizes

Each

base-station

is

equipped

with

the

Video

Streaming

module

as

described

earlier

A

Control

Cycle

of

seconds

is

adopted

by

all

elements

The

buffer

size

at

the

user-equipment

is

assumed

to

be

large

enough

to

store

seconds

which

is

readily

met

by

modern

cellular

phones

and/or

PDAs

We

designate

ten

levels

of

base-station

load

with

load

changing

at

random

times

The

maximum

duration

of

each

load

state

is

The

PAL

color

system

is

assumed

for

the

video

being

transmitted

so

the

default

inter-departure

time

for

each

frame

is

set

at

mseconds

At

the

beginning

of

each

control

cycle

the

Rate

Adaptation

element

applies

the

proposed

Algorithm

The

testbed

initially

computes

the

tolerance

and

speed-up

factors

thus

generating

the

acceptable

inter-departure

times

range

The

actual

inter-departure

time

for

the

control

cycle

is

proportional

to

the

station

's

load

at

the

time

If

the

station

is

lightly

loaded

the

minimum

interdeparture

time

-LRB-

maximum

bandwidth

-RRB-

is

applied

Conversely

when

the

base-station

is

heavily

loaded

the

frames

are

forwarded

to

the

transmitter

at

the

minimum

rate

instructed

by

the

maximum

interdeparture

time

For

intermediate

load

levels

an

appropriate

value

from

the

inter-departure

times

range

is

selected

according

to

Algorithm

in

a

uniform

fashion

Figure

shows

the

evolution

of

the

base

stations

load

during

the

user

's

trajectory

over

all

cells

that

the

individual

travels

in

Having

defined

load

of

value

as

normal

load

the

base-station

load

remains

relatively

high

through

the

user

trajectory

with

a

few

very

short

periods

of

low

load

Load

Time

Base

station

load

Figure

Base-station

load

during

user

trajectory

Figure

shows

the

applied

transmission

bitrate

along

with

the

minimum

and

maximum

bitrates

allowed

for

every

control

cycle

The

y-axis

represents

the

percentage

of

the

actual

transmission

bitrate

to

the

video

encoding

bitrate

The

bitrate

is

inversely

proportional

to

the

inter-departure

times

which

are

illustrated

in

figure

If

we

compare

the

curves

of

Figures

and

we

can

easily

establish

that

the

actual

bitrate

applied

is

a

function

of

the

base-station

load

and

the

calculated

allowed

bitrate

range

At

times

of

high

load

the

applied

bitrate

is

closer

to

the

minimum

acceptable

bitrate

and

conversely

at

times

of

light

load

the

applied

bitrate

is

closer

to

the

maximum

acceptable

bitrate

Figure

shows

that

the

interdeparture

times

are

indeed

proportional

to

the

base-station

load

Transmission

bitrate

-LRB-

-RRB-

Time

Transmission

bitrate

Figure

Allowed

transmission

bitrate

limits

and

applied

transmission

bitrate

Interdeparture

time

Time

Frame

interdeparture

time

Figure

Applied

interdeparture

interval

We

show

the

user

buffer

occupancy

throughout

the

trajectory

in

Figure

The

buffer

does

not

starve

at

any

time

suggesting

the

usefulness

of

our

proposed

scheme

The

occupancy

increases

at

times

where

the

base

station

load

falls

below

the

normal

load

Under

overall

higher-than-normal

base-station

load

settings

our

tests

show

that

the

playback

continuity

is

preserved

by

only

taking

advantage

of

relatively

small

periods

of

station

underutilization

to

increase

the

transmission

bitrate

The

range

of

the

acceptable

transmission

rate

includes

the

bandwidth

already

guaranteed

by

the

network

upon

session

acceptance

at

all

times

Therefore

the

network

was

never

forced

to

transmit

at

a

higher-than-agreed

bitrate

At

times

of

station

over-utilization

the

decreased

transmission

bitrate

allows

for

more

calls

to

be

accommodated

significantly

decreasing

the

probability

of

session

drop

Occupancy

Time

Occupancy

Figure

User

buffer

occupancy

A

system

that

adopts

no

rate

adaptation

scheme

would

constantly

require

a

transmission

bitrate

equal

to

the

of

the

video

encoding

bitrate

throughout

the

session

Although

the

bitrate

of

real-time

video

streaming

sessions

is

guaranteed

by

the

UMTS

specifications

at

near-capacity

situations

the

network

would

have

to

either

drop

a

session

or

be

forced

to

transmit

with

lower

bitrate

The

former

case

is

clearly

undesirable

and

the

latter

generates

jitter

effects

for

the

end-user

This

would

happen

even

if

the

station

gets

overloaded

only

for

a

period

of

time

equal

to

the

proposed

scheme

's

control

cycle

duration

Discontinuities

in

the

playback

process

may

be

observed

at

a

system

adopting

the

proposed

rate

adaptation

scheme

as

well

however

only

in

the

case

when

the

base-station

is

constantly

load

saturated

thus

not

allowing

for

any

upgraded

cycles

to

take

place

There

has

been

a

large

amount

of

reported

work

in

related

areas

that

include

caching

for

video

systems

management

of

moving

objects

and

rate

adaptation

for

streaming

systems

on

wired

networks

Data

caching

and

mirroring

has

been

proposed

as

a

way

to

help

the

scalability

of

video

delivery

systems

-LSB-

-RSB-

By

placing

content

closer

to

the

consuming

clients

not

only

network

costs

can

be

curtailed

but

also

the

load

of

streaming

servers

can

be

reduced

Various

aspects

of

the

use

of

proxy

servers

for

video

objects

has

been

examined

in

-LSB-

-RSB-

In

-LSB-

-RSB-

the

segmentation

and

caching

of

streaming

objects

is

proposed

and

the

merging

of

requests

that

are

temporally

related

is

investigated

This

merging

idea

has

been

used

in

-LSB-

-RSB-

to

save

bandwidth

in

light

of

requests

for

the

same

video

object

that

arrive

closely

in

time

The

partial

caching

of

two

successive

intervals

of

a

video

stream

is

proposed

in

-LSB-

-RSB-

as

a

way

to

speed-up

the

serving

of

follow-up

requests

for

the

the

same

video

object

In

-LSB-

-RSB-

the

caching

of

initial

frames

of

a

video

object

is

used

in

a

proxy-setting

to

reduce

startup

latency

In

the

same

direction

the

storage

of

the

bursty

parts

of

a

video-stream

in

a

proxy

is

advocated

in

-LSB-

-RSB-

the

remaining

parts

of

the

video

are

directly

retrieved

from

the

source

helping

significantly

reduce

peak

bandwidth

requirements

in

the

backbone

A

caching

mechanism

for

layered

encoded

multimedia

streams

is

suggested

in

-LSB-

-RSB-

the

objective

of

the

technique

is

to

selectively

deliver

stream

quality

by

differentiating

on

the

client

network

connection

Stream

quality

differentiation

is

also

addressed

in

-LSB-

-RSB-

in

conjuction

with

a

seamless

handoff

mechanism

for

mobile

users

A

formal

spatiotemporal

framework

for

modeling

moving

objects

and

a

query

language

is

discussed

in

-LSB-

-RSB-

Efficient

techniques

for

indexing

moving

objects

in

one

and

two

dimensions

are

proposed

in

-LSB-

-RSB-

while

in

-LSB-

-RSB-

the

trade-offs

for

indexing

schemes

to

answer

interval

rectangle

approximate

nearest-neighbor

approximate

farthest-neighbor

and

convex-hull

queries

are

examined

The

indexing

of

current

and

anticipated

positions

of

moving

objects

in

the

context

of

location

based

services

is

examined

in

-LSB-

-RSB-

Much

work

has

been

also

reported

in

data

broadcast

and

dissemination

over

wireless

networks

during

the

last

decade

-LSB-

-RSB-

Rate

adaptation

for

wired

streaming

systems

has

been

exten-sively

studied

in

-LSB-

-RSB-

These

studies

assume

an

adaptable

video

encoding

system

that

changes

the

encoding

parameters

on

the

fly

based

on

feedback

information

about

the

channel

state

The

notion

of

cycle-based

operation

is

used

in

-LSB-

-RSB-

with

cycles

being

successively

alternating

between

good

and

bad

cycles

Our

work

differs

in

that

it

does

not

require

a

prefetching

period

so

that

an

initial

occupancy

is

built

up

in

the

buffer

before

the

playback

begins

Also

our

algorithm

functions

in

a

graceful

manner

when

the

base-station

load

does

not

allow

for

aggressive

use

of

channel

resources

In

this

paper

we

address

the

problem

of

efficient

video

delivery

in

real-time

to

high-speed

users

roaming

a

network

We

propose

a

network

of

media

servers

handling

the

content

distribution

on

top

of

the

mobile

environment

that

closely

cooperates

with

the

base-stations

and

user-equipment

for

the

provision

of

continuous

video

playout

We

segment

video

streams

into

variable-sized

parts

according

to

the

user

's

speed

and

traversal

path

through

different

cells

In

this

manner

we

minimize

the

transmission

costs

between

media-servers

and

base-stations

as

well

as

the

start-up

latency

experienced

by

users

during

handover

We

adopt

the

use

of

Video

Streaming

modules

along

with

their

Rate

Adaptation

elements

with

the

infrastructure

of

base-stations

to

ensure

smoothness

of

the

playout

process

Preliminary

experimentation

results

through

simulation

show

that

the

proposed

scheme

rapidly

adapts

to

changes

in

load

conditions

at

base-stations

thus

minimizing

the

probability

of

buffer

starvation

or

even

session

drops

The

low

complexity

of

the

proposed

mechanism

makes

it

suitable

for

real-time

applications

-LSB-

-RSB-

Generation

Partnership

Project

Universal

Mobile

Telecommunication

System/IMT

Spectrum

Technical

Report

UMTS

Forum

-LSB-

-RSB-

Generation

Partnership

Project

Stage

Functional

Specification

of

Location

Services

in

URAN

Technical

Report

-LRB-

TR

version

-RRB-

UMTS

Forum

Technical

Specification

Group

-LRB-

TSG

-RRB-

RAN

Working

Group

-LRB-

-RRB-

-LSB-

-RSB-

Generation

Partnership

Project

Transparent

End-to-End

Packet

Switched

Streaming

Service

-LRB-

PSS

-RRB-

General

Description

-LRB-

Release

-RRB-

Technical

Report

UMTS

Forum

Technical

Specification

Group

Services

and

System

Aspects

-LSB-

-RSB-

S.

Acharya

M.J.

Franklin

and

S.

B.

Zdonik

Balancing

Push

and

Pull

for

Data

Broadcast

In

Proceedimgs

of

SIGMOD

Tucson

AZ

May

-LSB-

-RSB-

P.K.

Agarwal

L.

Arge

J.

Erickson

and

H.

Yu

Efficient

Tradeoff

Schemes

in

Data

Structures

for

Querying

Moving

Objects

In

Annual

European

Symposium

on

Algorithms

-LRB-

ESA

-RRB-

pages

Bergen

Norway

September

-LSB-

-RSB-

D.

Aksoy

M.

Altinel

R.

Bose

U.

Cetintemel

M.

Franklin

J.

Wang

and

S.

Zdonik

Research

in

Data

Broadcast

and

Dissemination

In

Proceedings

of

International

Conf

on

Advanced

Multimedia

Content

Processing

-LRB-

AMCP

-RRB-

Osaka

Japan

November

-LSB-

-RSB-

P.

Cao

E.

W.

Felten

A.

R.

Karlin

and

K.

Li

A

Study

of

Integrated

Prefetching

and

Caching

Strategies

In

Proceedings

of

ACM

SIGMETRICS

Conf.

pages

Ottawa

Canada

May

-LSB-

-RSB-

S.

Chan

and

F.

Tobagi

Caching

schemes

for

distributed

video

services

In

Proceedings

of

the

IEEE

International

Conference

on

Communications

-LRB-

ICC

-RRB-

Vancouver

Canada

June

-LSB-

-RSB-

S.

Choi

and

K.

G.

Shin

Predictive

and

Adaptive

Bandwidth

Reservation

for

Hand-Offs

in

QoS-Sensitive

Cellular

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In

Proceedings

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ACM

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Dan

and

D.

Sitaram

A

Generalized

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In

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Multimedia

Computing

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-LSB-

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Dan

D.

Sitaram

and

P.

Shahabuddin

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Batching

Policies

for

an

On-demand

Video

Server

Multimedia

Systems

-LRB-

-RRB-

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G.

Kollios

and

D.

Gunopulos

and

V.J.

Tsotras

On

Indexing

Mobile

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In

Proceedimgs

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ACM

SIGACT-SIGMOD-SIGART

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on

Principles

of

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-LRB-

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PA

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Hassan

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Atzori

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Krunz

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Technical

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K.A.

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Cai

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Patching

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E.

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IEEE

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on

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R.

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H.

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Handoff

Support

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O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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