ece544lec8dr-qos_2015.pptx

8/18/2019 ECE544Lec8DR-QoS_2015.pptx

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ECE544: Communication Networks-II,Spring 2015

D. Raychaudhuri

Lecture 8 (QoS)

Includes teaching materials from D. Raychaudhuri, L. Peterson


2/65

Toda!s "ecture

• Congestion control in best efortnetworks – Basic rinciles ! "echanis"s – #Q$ %#Q$ congestion &eedback$ 'C$

RD

• Quality*o&*ser+ice (QoS) –

,echanis"s (tra-c shaing$ad"ission control$ reser+ation$riority ueuing)

– RS/ 0ntser+ and Difser+$ R01

– Co"arison to 2', (CBR$ /BR3 2BR)


3/65

Congestion Contro# $ %oS in&acket Networks

• Congestion control 4 reacti+e "ethodsused in best efort networks – acket scheduling at network nodes

– #eedback congestion control• nd*to*end• 5o*by*ho

• QoS control 4 roacti+e "ethods used

&or re"iu" or guaranteed ser+ices6 – Source tra-c shaing ! olicing at entry

oints – riority ueuing and acket dro at routers – nd*to*end reser+ation and ad"ission

control


4/65

Network Congestion•

2ll networks ha+e saturating throughut – Reduction in er&or"ance beyond "a7

caacity

– eed to kee inut load below 9: –

2lso "ust a+oid unstable euilibriu" oint in o+erloadregion

Overload

region

Normal operating

Point (G!

"apacity Limit#ma$

Offered %raffic (G!

%hru%raffic

margin

"ongestion control policies

&nsta'le netor) load

#ta'le netor) load lines

ith congestion control


5/65

%ueue Sc'edu#ing

• 2 ueue scheduler e"loys ;strategies6 – Scheduling discipline6 %hich acket to

ser+e (trans"it) ne7t

– Drop policy 6 %hich acket to dro

ne7t (when reuired)


6/65

(I() %ueuing

• #0#16


7/65

(air %ueuing

• ,ain idea6 – "aintain a searate ueue &or each

=ow currently =owing through router – router ser+ices ueues in Round*

Robin &ashion


8/65

(% i##ustration*lo +

*lo

*lo n

I-P O-P

ariation/ 0eighted *air 1ueuing (0*1!


9/65

Some Comp#ications

• ackets are o& diferent length

• %e really need bit*by*bit round*

robin (RR)• #Q si"ulates bit*by*bit RR

– ot &easible to interlea+e bits>


10/65

*it-+-+it • Single =ow6 suose clock ticks when a bit is

trans"itted. #or acket i6 – i6 length$ 2i ? arri+al ti"e$ Si6 begin trans"it ti"e$ #i6


11/65

*it-+-+it

*lo + *lo

P)t 2+34 units

P)t +2+3 units

P)t 23 units

P)t +23

+ unit

P)t +243

+ unit

"hannel cloc) 2 +2+

P(+,+! 3

P(+,! 3 +

P(+,4! 3 +

P(,+! 3 4

P(,! 3

#tart ith 5(6,6!3 (all p)ts arrive at %3!

*(+,+! 3 +

*(+,! 3 +.7

*(+,4! 3

*(,+! 3 +.7

*(,! 3 .7

*i 3 ma$ (*i2+, 5i! 8 Pi

2+ +2 +24 2


12/65

eig'ted (air %ueuing .(%/

• %eighted #air Queuing (%#Q)6 assign a weightto each =ow – 2ssu"e trans"itting wq bits each ti"e the

router ser+es ueue q (simulate in packet

scheduling) – Control the ercentage o& the links

bandwidth that a =ow will get• 'he bandwidth that =ow q gets (n acti+e ueues

sending data)6

–

∑=

= n

q

q

q

q

w

w

B

+


13/65

Congestion Contro# and Congestion oidance

• 'Cs blindE aroach6 – Detect congestion (loss) a&ter it haens and back of on

ofered rate – 0ncrease load trying to "a7i"iFe utiliFation until loss

occurs

#ourceRate

('ps!

"ongestion detected

(via pac)et loss!

%ime2out

• 2lternati+ely6

– %e can try to redict congestion and reduce rate be&oreackets start being discarded

– 'his is called congestion avoidance


14/65

Congestion Contro# ia

outer (eed+ack• Router has uni


15/65

So#ing t'e (u## %ueues

&ro+#em• Router "onitors the load• Dro (or "ark) ackets be&ore

ueue beco"es &ull (early dro)• 0ntuition6 noti&y senders o& inciient

congestion –

Si"le e7a"le6• 0& len G dro le+el$ dro (or "ark) eachnew acket with a


16/65

andom Ear# etection

.E/• ,oti+ation6

– 5igh bw*delay =ows ha+e large

ueues to acco""odate transientcongestion

– 'C detects congestion &ro" loss *a&ter ueues ha+e built u andincrease delay

• 2i"6 – Hee throughut high and delay low

– 2cco""odate bursts


17/65

andom Ear# etection

.E/• Detect inciient congestion$ allow

bursts

• Hee ower (throughutdelay) high – kee a+erage ueue siFe low

– assu"e hosts resond to lost ackets

• 2+oid window synchroniFation – rando"ly "ark ackets$ instead o&

droing

•

2+oid bias against bursty tra-c


18/65


19/65

E )peration

9inthreshold

9a$threshold

5verage :ueue

length

minthresh ma$thresh

9a$P

+.

5vg length

P(drop!

• 0& 2+gLen I? ,in'hreshold – Queue the acket

• 0& ,in'hreshold I 2+glen I,a7'hreshold – Calculate robability

– Dro the arri+ing ackets with robability

• 0& 2+glen G? ,a7'hreshold – Dro the arri+ing acket

• AveLen = (1-) ! AveLen " !SampleLen

• Count6J o& newly arri+ing ackets thatha+e been ueued (not droed) while2+gLen has been between the twothresholds – Count increases$ increases

– ,ake dro "ore e+enly distributed (2+oidbias against bursty tra-c)

!+-(

!(

!(

TempP count TemP P

ld MinThreshold MaxThresho

ld MinThresho AvgLen MaxP TempP

×−=

−

−×=


20/65

E3p#icit Congestion Contro#

• Router can signal thecongestion by "arkingackets instead o&droing using RD –

Set the C bit (bit K o&the 0 '1S


21/65

%ua#it o Serice

1utline

Realti"e 2lications

0ntegrated Ser+ices

Diferentiated Ser+ices


22/65

ea#time pp#ications

• Reuire deli+er on ti"eE assurances – "ust co"e &ro" inside the network – 7a"le alication (audio) – sa"le +oice once e+ery A;us – each sa"le has a play#ack time –

ackets e7erience +ariable delay in network – add constant &actor to layback ti"e6 play#ack point – Nse initial bufering delay to co"ensate Oitter$ but

result in longer end*to*end delay

+icrophone

Speaker

Sampler , A Dcon!erter

-uffer,D A


23/65

a+ack *uer

S e . u e n c e n u m

" e r

Packetgeneration

/et0ork

dela1

-uffer

Pla1"ack

Time

Packet

arri!al


24/65

E3amp#e istri+ution o

e#as

'

2

*

P a c k e t s

3 #

)$3 )43 )&3 ))3

'5$ 2$$'$$5$

Dela1 milliseconds#


25/65

pp#ication reuirements $ Serices C#asses

• Diferent alication reuire"ents – lastic6 no restrict delay reuire"ents$ traditional data – Real*ti"e6 delay bound$ Oitter$ loss

• Loss6 intolerant or tolerant to so"e loss• Delay6 adati+e (e.g. lengtheningshortening the silence between

words$ laying back +ideo a little slower$ etc) or not adati+e• Data rate6 adati+e (e.g. reduce +ideo uality by co"ressing +ideo

"ore) or not adati+e• Diferent alication reuire"ents?Gdiferent ser+ice

classes (not only best efort any"ore)• 2 network that can ro+ide these diferent le+els o& ser+ice is

said to suort QoS – 0ntegrated ser+ice6


26/65

Ta3onom o app#ications

5pplications

;lasticReal2%ime

Loss, delay

tolerantIntolerant

Interactive

Non2adaptiveadaptive Non2adaptive

Delay

adaptive

Rate

adaptive

Rate

adaptive

5synchronous

Interactive2'ul)


27/65

Components o Integrated Sericesarc'itecture

• Flowspec: information of the ow traccharacteristics and its service

•

Reservations (includes reser+ation signalingrotocol)• Admission control based on =ow descrition and

current load• Scheduling to "eet the reser+ation

• Trac shaping at edges to


28/65

Tpes o guarantees

• 2bsolute bound on delay and Oitter

• 2bsolute bound on delay only

• Statistical bound on delay

• o uantitati+e delay bound butad"ission control and re&erential

treat"ent• one


29/65

Internet serice c#asses proposed +IET(

• 9uaranteed ser+ice –


30/65

)eriew o mec'anisms

• #low seci


31/65

(#owspecs

• 'sec6 describes the =ows tra-ccharacteristics

• Rsec6 describes the ser+icereuested &ro" the network


32/65

Traic S'aping

• 'ra-c shaing6 control tra-c in order tocon&or" to the tra-c contract by delayingackets to "eet certain criteria. – 'o oti"iFe or guarantee er&or"ance (lower

latency$ higher usable bandwidth)

– co""only alied at the network edges to controltra-c entering the network$ but can also be aliedby the tra-c source or in the network

• 'oken bucket – tokens are laced in bucket at rate r – i& bucket


33/65

Traic &o#icing• 'ra-c olicing6 router "onitors the =ow tra-c

&or con&or"ity with a tra-c contract – Dro or tag the ackets not con&or"ing to the 'Sec

that used to "ake the reser+ation – to en&orce co"liance with that contract

• 'oken bucket – tokens are laced in bucket at rate r – i& bucket


34/65

Token +ucket i#ter

• Described by ; ara"eters6 – token rate r6 rate o& tokens laced in the

bucket

– bucket deth B6 caacity o& the bucket

• 1eration6 – tokens are laced in bucket at rate r

–

i& bucket


35/65

Token +ucket operation

to)ens

Pac)et

overflo

to)ens

to)ens

Pac)et

;nough to)ens

pac)et goes through,

to)ens removed

Not enough

to)ens 2 ait for

to)ens to

accumulate


36/65

T* c'aracteristics

• 1n the long run$ rate is li"ited to r

• 1n the short run$ a burst o& siFe B

can be sent at eak data rate• 2"ount o& tra-c entering at

inter+al ' is bounded by6

– tra-c ? B @ r'• 0n&or"ation use&ul to ad"ission

algorith"


37/65

Token +ucket specs


38/65

dmission contro#

• %hen new =ow reuest arri+es$look at Rsec and 'sec and

decide whether to ad"it or reOect – Can it ro+ide the desired ser+ice

reuested by the =ow$ gi+en thecurrently a+ailable resources without

causing any re+iously ad"itted =owto recei+e worse ser+ice that agreedP

• ot olicing


39/65

eseration protoco#: S6&

&pper layer protocols and applications

IP

Lin) layer modules

I"9P IG9P R#PIP service interface

Lin) layer service interface


40/65

S6&• Nsed on connectionless networks

• Relies on so&t state6 reser+ations"ust be re&reshed and do not ha+eto be e7licitly deleted

• 2i"s to suort "ulticast asefecti+ely as unicast =ows * "cast

as good candidates &or real*ti"e$ and are heterogeneous

• Recei+er*oriented aroach


41/65

*asic message tpes

• 2'5 "essage

• RS/ "essage

• C1#0R,2'01"essage – generated only uon reuest

– unicast to recei+er when RS/

reaches node with established state• '2RD1% "essage

• RR1R "essage (i& ath or RS/

&ails)


42/65

7aking a reseration

• Recei+ers "ake reser+ation

• Be&ore "aking a reser+ation$

recei+er "ust know6 – tye o& tra-c sender will send ('sec)

– ath the senders ackets will &ollow

• Both can be acco"lished bysending 2'5 "essages by thesender


43/65

&T8 messages• 2'5 "essages carry senders 'sec

and sent &ro" the sender to the recei+er

• Record the ath &ro" the sender to the

recei+er in the 2'5 "essage• Recei+ers send RS/ "essages that

&ollow re+erse ath and setureser+ations

• 0& reser+ation cannot be "ade$ user getsan error


44/65

&T8 and ES6 messages

R

#ender +

#ender

receiver +

receiver

R R

R

P5%=

P5%= R;#

R;#

R;# (merged!


45/65

Sot State• 2llow increasing or decreasing the le+el o&

resource reser+ation• 2dat to link or router &ailure and toology

changes – Routing rotocol "akes routing changes$ RS/adOusts reser+ation state

– 0n absence o& route or "e"bershi changes$eriodic 2'5 and RS/ "sgs re&resh

established reser+ation state – %hen change$ new 2'5 "sgs &ollow new ath$

new RS/ "sgs set reser+ation – on*re&reshed state ti"es out auto"atically


46/65

outer 'and#ing o ES6

messages• 0& new reuest reOected$ send error

"essage

• 0& ad"itted6 – install acket


47/65

&acket c#assiing and

sc'edu#ing• ach arri+ing acket "ust be6

– classied6 associated with the

alication reser+ation• 7a"ining u to


48/65

S6& and mu#ticast

• Reser+ations &ro" "ultile recei+ers &ora single sender are "erged together atbranching oints

• Reser+ations &or "ultile senders "aynot be added u6 – audio con&erence$ not "any talk at sa"e

ti"e – Diferent reser+ation styles6

• Reser+e resources &or all seakers• Reser+e resources &or any n seakers• Reser+e resources &or seakers 2 and B only


49/65

S6& ersus T7 .%92;1/•

RS/ – recei+er generates reser+ation – so&t state (re&reshti"eout) – searate &ro" route establish"ent –

QoS can change dyna"ically – recei+er heterogeneity

• 2', – sender generates connection reuest –

hard state (e7licit delete) – concurrent with route establish"ent – QoS is static &or li&e o& connection – uni&or" QoS to all recei+ers


50/65

T7 Serice CategoriesT7 Serice Categories

•

CBR – Constant Bit Rate

– Continuous =ow o& data with tight bounds on delay and delay+ariation

• rt*/BR –

Real*'i"e /ariable Bit Rate – /ariable bandwidth with tight bounds on delay and delay

+ariation

• nrt*/BR – on*Real*'i"e /ariable Bit Rate

– /ariable bandwidth with tight bound on cell loss

• NBR – Nnseci


51/65

ierentiated Serices

.iSer/• 2nalogy6 – airline ser+ice$


52/65

ierentiated Serices .cont/• Di+ide tra-c into a s"all nu"ber o&

classes and allocates resource on a er*class basis$ instead o& indi+idual =ows – Scalable

– o need &or reser+ations6 Oust "arkackets• .g. acket "arking can be done at

ad"inistrati+e boundaries be&ore

inOecting ackets into network – Signi


53/65

I& iSer

• 0 ackets carry M*bitser+ice code oints(DSC) – otentially suort

M*diferent classes o&ser+ices

– 0n i"le"entation$the nu"ber o& DSCs

used in a network is"uch s"aller$ e.g.si"le two*classnetwork

Version HLen TOS Length

Ident Flags Offset

TTL Protocol Checksum

SourceAddr

DestinationAddr

Options !aria"le# Pad!aria"le#

$ % & '( ') *'

Data

•

'oS


54/65

iSer

• %here and how to set the DSC +alue – 5ost set DSC based on knowledge o& alication

reuire"ents – Router at an ad"inistrati+e boundary set DSC

according to a certain olicy• %hat does a router do when it recei+es a

acket "arked with a certain DSC – Routers "a DSC to er*ho*beha+ior (5B) – 5Bs can be standard or local –

Standard 5Bs include• De&ault6 o secial treat"ent or best efort• 7edited &orwarding (#)6 should be &orwarded with

low delay and loss• 2ssured &orwarding (2#)6 ,ultile classes$ each class

with "ultile dro re&erence


55/65

E3pedited (orwarding .E(/

• 2 router should &orward the # acketswith "ini"al delay and low loss

• 'o i"le"ent$ ut all # ackets in a

dedicated # ueue and ensure that thearri+al rate o& ackets to the ueue isless than the ser+ice rate – Con


56/65

ssured (orwarding .(/

• 2 set o& 2# 5Bs is de


57/65

n E3amp#e iSer NetworkImp#ementation

• Suort 'wo*tye DifSer+ –re"iu" (e7edited) ser+ice6 (tye )

• Nser sends within ro


58/65

&remium traic #ow

first hoprouter

internalrouter

'order router

host

'order router

I#P

"ompany 5

&nmar)ed

pac)et flo

Pac)ets in premium

flos have 'it setPremium pac)et flo

restricted to R 'ytes-sec


59/65

2-+it dierentiated serice

• Nse recedence


60/65

"ea router input unctiona#it

"lear

5 > P 'its

Pac)et

classifier

9ar)er +

9ar)er N

*orarding

engine5rriving

pac)et


61/65

7arkers to imp#ement two dierentserices

0ait for to)en #et P 'it

Pac)et

input

Pac)et

output

Drop on overflo

P service

%est if

to)en#et 5 'it

to)en

No to)en

Pac)et

input

Pac)et

output

5 service


62/65

outer output interace or two-+itarc'itecture

• ; ueues6 ackets on higher riority ueue

• Lower riority ueue i"le"ents RD 0n or1utE sche"e (R01)

P2'it set?

If 52'it set

incr 5@cnt

=igh2priority 1

Lo2priority 1

If 52'it set

decr 5@cntRIO :ueue

management

Pac)ets out

yes

no


63/65

*order router input interace &roi#e 7eters

5rriving

pac)et

Is pac)et

mar)ed?

%o)en

availa'le?

%o)en

availa'le?

"lear 52'it

Drop pac)et

*orarding

engine

5 set

P set

to)en

to)en

Not mar)ed

no

no

• 2t border routers$ ro


64/65

ed wit' In or )ut .I)/• Si"ilar to RD$ but with two searate robability cur+es•

5as two classes$ 0nE and 1utE (o& ro


65/65

Toda!s 8omework• Chater M

*M.A th ed

*M.;*M.

*M.

Due A

ece544lec8dr-qos_2015.pptx

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