29
Addressing the Challenges of Web Data Transport Venkata N. Padmanabhan Microsoft Research UW Whistler Retreat December 1998
Add
ress
ing
the
Cha
lleng
es o
fW
eb D
ata
Tra
nspo
rt
Ven
kata
N. P
adm
anab
han
Mic
roso
ft R
esea
rch
UW
Whi
stle
r R
etre
atD
ecem
ber
1998
Out
line
•C
halle
nges
•So
lutio
ns–
TC
P Se
ssio
n
–Fa
st S
tart
•O
ngoi
ng a
nd F
utur
e W
ork
The
Big
Pic
ture
Inte
rnet
Ser
ver
Sate
llite
Cab
le
Mod
emC
lien
t
Cli
ent
Ser
ver
Goa
l: T
rans
fer
data
fro
m s
erve
rs to
clie
nts
effi
cien
tly
Why
is th
is h
ard?
#1: M
ultip
le in
depe
nden
t com
pone
nts
#2: B
urst
y da
ta tr
ansf
ers
#3: A
cces
s ne
twor
k ch
arac
teri
stic
s
#1: M
ultip
le I
ndep
ende
nt C
ompo
nent
s
Inte
rlea
ved
data
str
eam
⇒ u
ndes
irab
le c
oupl
ing
Imag
e #1
Imag
e #2
stal
l
Imag
e #1
Imag
e #2
Con
curr
ent d
ata
stre
ams
⇒ c
ompe
titio
n
#2: B
urst
y D
ata
Tra
nsfe
rs
Latency
Ban
dwid
th
Tel
net
Bul
k
Web
•D
ownl
oad
time
sens
itive
to la
tenc
y &
ban
dwid
th
•Sh
ared
net
wor
k ⇒
nee
d to
pro
be b
efor
e us
e
Pro
bing
for
ban
dwid
th r
equi
res
time
#1: H
ow to
avo
id c
ompe
titio
n an
dco
uplin
g?•
HT
TP/
1.0
–av
oids
cou
plin
g bu
t not
com
petit
ion
•P-
HT
TP
[PM
94]
–av
oids
com
petit
ion
but n
ot c
oupl
ing
•T
CP
Con
trol
Blo
ck I
nter
depe
nden
ce [
T97
]–
avoi
ds c
oupl
ing
–av
oids
com
petit
ion
at th
e tim
e of
initi
aliz
atio
n bu
tno
t bey
ond
TC
P Se
ssio
n
Dec
oupl
e se
rvic
e m
odel
fro
m tr
ansp
ort a
lgor
ithm
s
Send
erR
ecei
ver
App
licat
ion
App
licat
ion
TC
P Se
ssio
n
TC
PT
CP
TC
PT
CP
TC
PT
CP
Send
er-s
ide
chan
ges
⇒ e
asy
to d
eplo
y in
crem
enta
lly
TC
P Se
ssio
n
TC
P se
ssio
n co
mpo
nent
s
•In
tegr
ated
con
gest
ion
cont
rol
•C
onne
ctio
n sc
hedu
ling
•In
tegr
ated
loss
rec
over
y
Flex
ible
gra
nula
rity
of
inte
grat
ion
(def
ault:
hos
t-pa
ir)
Con
gest
ion
Con
trol
and
Sch
edul
ing
Key
idea
: how
muc
h da
ta, n
ot w
hat d
ata
•U
nifi
ed c
onge
stio
n w
indo
w c
ontr
ols
amou
nt o
fse
ssio
n-w
ide
outs
tand
ing
data
•W
indo
w g
row
th a
nd s
hrin
kage
not
tied
to th
enu
mbe
r of
con
nect
ions
•D
ecou
ple
conn
ectio
n sc
hedu
ling
from
cong
estio
n co
ntro
l
Com
petin
g T
CP
Con
nect
ions
Tim
e (s
econ
ds)
Data transferred (KB)
4 co
ncur
rent
co
nnec
tions
1.5
Mbp
s/50
ms
emul
ated
link
Com
petit
ion
lead
s to
inco
nsis
tent
per
form
ance
0
20406080100
120
140
02
46
Shar
ing
with
TC
P Se
ssio
n
Tim
e (s
econ
ds)
Data transferred (KB)
BSD
/OS
impl
emen
tatio
n
4 co
ncur
rent
conn
ectio
ns
1.5
Mbp
s/50
ms
emul
ated
link
Shar
ing
lead
s to
mor
e co
nsis
tent
per
form
ance
020406080100
120
140
02
46
Inte
grat
ed L
oss
Rec
over
y
21
32
1Se
rver
Clie
nt1
21
2
4
2
Key
idea
: use
pac
ket o
rder
ing
info
rmat
ion
acro
ssco
nnec
tions
to im
prov
e da
ta-d
rive
n lo
ss r
ecov
ery
dupl
icat
e ac
kla
ter
ack
Perf
orm
ance
# cl
ient
s
Download time per client (sec)
Serv
er a
nd c
lient
s co
nnec
ted
via
1.5
Mbp
s/50
ms
link
4 co
ncur
rent
10
KB
tran
sfer
s be
twee
nse
rver
and
eac
h cl
ient
2-3X
red
uctio
n in
dow
nloa
d tim
e
0246810121416
04
812
1620
inde
pend
ent T
CP
conn
ectio
ns
TC
P se
ssio
n
Pack
et L
oss
# cl
ient
s
# packet losses / timeouts
2X r
educ
tion
in p
acke
t los
ses
due
to in
tegr
ated
con
gest
ion
ctrl
.10
X r
educ
tion
in ti
meo
uts
due
to in
tegr
ated
loss
rec
over
y.
04080120
160
200
04
812
1620
inde
pend
ent T
CP
conn
ectio
ns
TC
P se
ssio
n
2X b
ette
r
L L10
X b
ette
r
TT
L: l
oss
T: t
imeo
ut
Sum
mar
y of
TC
P Se
ssio
n
Key
idea
: sep
arat
ion
of T
CP
func
tion
alit
y
Adv
anta
ges
over
inde
pend
ent T
CP
conn
ectio
ns
•Fe
wer
pac
ket l
osse
s
•B
ette
r lo
ss r
ecov
ery
•M
ore
cont
rol o
ver
sche
dulin
g of
dat
a st
ream
s
Adv
anta
ges
over
P-H
TT
P
•N
o co
uplin
g be
twee
n co
ncur
rent
dat
a st
ream
s
•N
ot ti
ed to
spe
cifi
c ap
plic
atio
n
•C
hang
es c
onfi
ned
to s
ende
r si
de
Ban
dwid
th P
robi
ng in
TC
P
•Sl
ow-s
tart
pro
bing
–ex
pone
ntia
l gro
wth
in c
onge
stio
n w
indo
w s
tart
ing
with
a s
ize
of o
ne s
egm
ent
–ac
k cl
ocki
ng a
void
s bu
rstin
ess
•L
inea
r pr
obin
g
•W
hen
is s
low
-sta
rt p
robi
ng in
itiat
ed?
–up
on c
onne
ctio
n st
art u
p
–up
on r
esta
rt a
fter
an
idle
per
iod
•H
ow d
oes
it im
pact
late
ncy?
–n-
segm
ent t
rans
fer
⇒ a
t lea
st lo
g n
RT
Ts
#2: H
ow to
red
uce
cost
of
prob
ing?
•P-
HT
TP
[PM
94]
–av
oid
repe
ated
pro
bing
for
com
pone
nts
of a
sin
gle
Web
pag
e bu
t not
acr
oss
page
s
•4K
slo
w-s
tart
[A
FP98
]
•R
ate-
base
d Pa
cing
[V
H97
]–
smoo
th o
ut u
sing
est
imat
e of
con
nect
ion
rate
–bu
t the
est
imat
e co
uld
itsel
f be
sta
le
TC
P Fa
st S
tart
Bas
ic id
ea:
use
cach
ed n
etw
ork
para
met
ers
tore
duce
the
cost
of
prob
ing
•R
euse
mos
t rec
ent s
ucce
ssfu
l win
dow
siz
e–
slow
-sta
rt ⇒
old
cwnd
/2, l
inea
r ph
ase
⇒ o
ldcw
nd-1
•E
stim
ate
conn
ectio
n’s
rate
as
cwnd
/srt
t
•B
reak
up
larg
e bu
rst i
nto
max
burs
t-si
zed
burs
ts
32
1Se
rver
Clie
nt5
23
1
54
6
46
Dyn
amic
s of
Fas
t Sta
rt
05101520253035
01
23
0
1020304050
01
23
FS TC
P
FS TC
P
Con
gest
ion
win
dow
(K
B)
Sequ
ence
num
ber
(KB
)
Dat
a tr
ansf
er o
ver
Dir
ecPC
sat
ellit
e ne
twor
k
0.95
2.60
Tim
e (s
ec)
Tim
e (s
ec)
Rob
ustn
ess
of F
ast S
tart
Goa
l: F
ast s
tart
sho
uld
help
whe
n ca
ched
info
isva
lid b
ut n
ot h
urt w
hen
it is
sta
le
Stud
ies
indi
cate
that
ava
ilabl
e ba
ndw
idth
is o
ften
stab
le f
or s
ever
al m
inut
es [
P97,
BSS
K97
]
But
we
need
to g
uard
aga
inst
sta
lene
ss
•Pr
otec
ting
othe
rs
•Pr
otec
ting
ones
elf
Prot
ectin
g O
ther
s
•E
nabl
es c
ontr
ol o
n tim
e sc
ale
fine
r th
an R
TT
•A
void
s po
tent
ial c
onge
stio
n co
llaps
e
R
F
S
F
in-p
rofi
le
out-
of-p
rofi
le
Pro
tect
oth
ers
from
ove
r-ag
gres
sive
fast
sta
rt
Pref
eren
tially
dro
p fa
st s
tart
pac
kets
(ex
cept
fir
st o
ne)
Prot
ectin
g O
nese
lf
Pro
tect
one
self
from
con
sequ
ence
s of
bur
st lo
ss
Qui
ckly
det
ect a
nd a
bort
fai
led
fast
sta
rt a
ttem
pt
•Fi
ne-g
rain
ed r
eset
tim
er d
urin
g fa
st s
tart
pha
se–
tied
to th
e fa
st T
CP
tim
er (
200
ms)
•If
res
et ti
mer
exp
ires
, abo
rt f
ast s
tart
–re
set c
wnd
to o
ne s
egm
ent,
initi
ate
slow
sta
rt
–no
oth
er c
onge
stio
n co
ntro
l pen
altie
s•
ssth
resh
not
hal
ved,
RT
O n
ot b
acke
d of
f
•A
bort
als
o w
hen
mul
tiple
loss
es w
ithin
RT
T
Impa
ct o
f St
alen
ess
on O
nese
lf
Abo
rtin
g fa
st s
tart
in c
ase
of f
ailu
re p
reve
nts
sign
ific
ant p
erfo
rman
ce d
egra
datio
n1.5
Mbp
s50
ms
051015202530
02
46
810
# o
f co
mp
etin
g b
ulk
tra
nsf
ers
Download Time (seconds)
TC
PFS FS
-CO
AR
SEFS
-NO
-AB
OR
T
Impa
ct o
f St
alen
ess
on O
ther
s
Prio
rity
dro
ppin
g si
gnif
ican
tly d
ecre
ases
adv
erse
impa
ct o
n co
mpe
ting
traf
fic
2150
2200
2250
2300
2350
2400
2450
2500
2550
1920
2122
2324
25
Tim
e (s
ec)
Segment #
FS FS w
/o P
-Dro
p
Asy
mm
etri
c A
cces
s N
etw
ork
•Pr
oble
m: u
pstr
eam
dat
a pa
cket
s bl
ock
acks
–R
TT
can
bec
ome
very
larg
e
•Po
ssib
le s
olut
ion:
ack
s-fi
rst s
ched
ulin
g [B
PK97
]–
but R
TT
can
stil
l be
larg
e du
e to
the
pack
et in
tran
smis
sionW
WW
W
Serv
erC
lient
WW
EE
EE
E
Impa
ct o
f B
idir
ectio
nal T
raff
ic
Fast
sta
rt h
elps
eve
n th
ough
the
inhe
rent
RT
T is
not l
arge
051015202530
FIF
OA
cks-
firs
t
TC
PF
S
Download Time (seconds)
175
KB
pag
edo
wnl
oad
over
10 M
bps/
28.8
Kbp
sne
twor
k
Sum
mar
y an
d C
oncl
usio
ns
•T
CP
Sess
ion
–de
coup
les
serv
ice
mod
el f
rom
tran
spor
t alg
orith
ms
–en
able
s co
ncur
renc
y w
ithou
t com
petit
ion
•Fa
st S
tart
–ex
ploi
ts d
iffe
rent
iate
d se
rvic
es to
com
plem
ent e
nd-
to-e
nd c
ontr
ol w
ith f
aste
r tim
e-sc
ale
cont
rol
–im
prov
es b
andw
idth
util
izat
ion
in th
e co
mm
on c
ase
–av
oids
ris
k of
per
form
ance
deg
rada
tion
in th
e w
orst
case
Con
clus
ions
•Fa
st s
tart
is r
obus
t–
sign
ific
ant b
enef
it (2
X)
in f
avor
able
con
ditio
ns
–lit
tle p
erfo
rman
ce d
egra
datio
n in
adv
erse
con
ditio
ns•
prio
rity
dro
ppin
g, q
uick
det
ectio
n of
fai
led
fast
sta
rt
•R
educ
ed la
tenc
y he
lps
both
clie
nts
and
serv
ers
–cl
ient
: fas
ter
dow
nloa
ds
–se
rver
: res
ourc
es f
reed
up
mor
e qu
ickl
y
•Si
gnif
ican
t ben
efit
with
new
acc
ess
netw
orks
–sa
telli
te, c
able
mod
em
–pr
ovid
es p
ath
for
incr
emen
tal d
eplo
ymen
t
