Bi 7

ATM Networks

Why ATM?

BISDN Reference Model

ATM Layer

ATM Adaptation Layer

Chapter 9

ATM Networks

Why ATM?

The Integrated Services Vision

Mang in thoai ban u ton tng t

Truyn dn & Chuyn mach

Chuyn dn sang phn loi ton s

1960s: truyn dn mang loi chuyn sang s

1970s: chuyn mach chuyn thnh s

Vong thu bao t khach hng n mang vn con l tng t

Tm nhin cho Dich vu tich hp:

Mang cn phai s t u cui n u cui

Mang cn h tr tt ca cac dich vu: telephone, data, video

Ba giai phap cho Integrated Services Network

ISDN in 1980s

ATM/BISDN in 1990s

Internet in 2000s

Basic rate interface (BRI): 2B+D

BRI

PRI

BRI

PRI

Circuit-

switched

network

Private channel-

switched network

Signaling

network

Packet-

switched

networks

Integrated Services Digital

Network (ISDN)

Primary rate interface (PRI): 23B+D

ISDN:

Integrated access

to end-to-end digital communication services

through a standard set of user-to-network interfaces

Network consisted of separate networks for voice, data, signaling

B=64 kbps

D=16 kbps

Broadband ISDN

BISDN: Mt single universal network mm deo co th cung cp tt ca cac dich vu ngi dung

ISDN khng ap ng c: nhu cu cn 10s to 100s Mbps cho kt ni LAN v digital TV

Synchronous Transfer Mode (kt ni nx64 kbps) ban u c ky vong BISDN, nhng

Asynchronous Transfer Mode (ATM) c chon

Multiplexing & switching framework

connection-oriented virtual circuits

fixed-length packets, cells, with short headers

u im cua ATM

C s ha tng mang v quan ly c n gian hoa do s dung mt ch duy nht cho mang

Ky vong s dung LAN, MAN, v WAN

Kha nng quan ly bng thng rng rai

SONET-like grooming capabilities, but at arbitrary bandwidth granularities

ATM khng bi gii han bi tc v c ly

50-600 Mbps for ATM

Cac thuc tinh QoS cua ATM cho phep vn chuyn voice, data, va video, vi vy lm cho ATM phu hp cho mang a dich vu

Pham vi ky vong cua ATM

Tt ca thng tin truyn bi mang x ly cac cell 53bytes

Co th m rng v tc

Giai phap chuyn mach lm vic LAN, MAN, hoc WAN

ATM fibre backbone

Wide Area Network (WAN)

supercomputer

wireless

interface

wireless

interface

multimedia

terminal

local area

network

(LAN)

User information Network header

5 bytes 48 bytes

video

server

data

base

ATM

Adaptation

Layer

ATM

Adaptation

Layer

ATM Network

Video Packet Voice Video Packet Voice

ATM Networking

AAL chuyn Thng tin thanh Cells

A/D AAL

Voice

s1 , s2 Digital voice samples

cells

AAL Data

Bursty variable-length

packets

cells

A/D AAL

Video

Compression

compressed

frames picture

frames

cells

Thit lp kt ni thit lp knh ao bng cach t pointers trong cac bang trn ng qua mang

Tt ca cac cells cho mt kt ni i theo mt ng Header xac inh kt ni Cells xp hng ch c truyn tai cac ATM switches & multiplexers Co th truyn dich vu CBR v VBR thng qua thoa thun trong qua

trinh thit lp kt ni Phm cht tr v mt mat co th thoa thun trc khi thit lp kt ni

Cell-Switching Virtual Circuit

Switches

Cells

Destination

Source

Cells

Cells

Cells

Switch thc hin oc bang v inh tuyn

ATM switches co th thc hin nh s dung b nh chia se, Bang kt ni chia se, hoc c cu a tng t inh tuyn

ATM Switching

2

3

N

1

Switch

N

1

5

6

video

video

voice

data

25

32

32

61

75

67

39

67

N

1

3

2

video 75

voice

data

video

32

25 32

61

39

67

67

1

2

N

1

2

N

Lu lng packet ghep cac ng u vo

Tach ra tai cac input port

Chuyn tip ti output port

Multiplexing in ATM Switches

Call Admission Control da trn Traffic Descriptors & QoS Reqts

Cell streams c giam sat tai User Network Interface

Cell Enqueueing Policy, Cell Transmission Scheduling, Flow Control

Generalized Processor Sharing, Weighted Fair Queueing, etc.

Multiplexing Gain

Cell Multiplexing implies Delay, Jitter, Loss

VCs

with

different TDs

&

different

QoS reqts

ATM Support for Multiple QoS Levels

Chapter 9

ATM Networks

BISDN Reference Model

M hinh tham chiu BISDN

User Plane: truyn tai user information; flow control;

error recovery

Control Plane: thit lp, quan ly, v ngt kt ni

Layer Management Plane: quan ly cac thc th lp & OAM

Plane Management: quan ly tt ca cac planes

Physical Layer

ATM Layer

ATM Adaptation Layer

Higher Layers

User Plane Control Plane

Management Planes

Layer M

an

ag

em

en

t P

lan

e M

an

ag

em

en

t

Y nghia cua Plane

Ba loai mang logic tham gia vo vic phn phi cac dich vu truyn thng

User Network: truyn tai thng tin ngi dung

Control (Signaling) Network: mang ban tin bao hiu thit lp, duy tri v ngt kt ni

Management Network: mang thng tin quan ly: thng tin giam sat, bao canh v s liu thng k s dung

Mt tp giao thc ring, goi l plane, c inh nghia cho mt trong ba mang ny

ATM Adaptation Layer

(AAL)

ATM Network Layer

Physical Layer

Higher Layers

ATM Adaptation Layer

(AAL)

ATM Network Layer

Physical Layer

Higher Layers

ATM Network Layer

Physical Layer

USER NETWORK USER

ATM Layered Architecture

ATM Layered Architecture

ATM Adaptation Layer

Giao din chun ti cac lp cao hn

Thc hin cac chc nng phi hp

Lm vic E2E gia cac h thng u cui

Phn oan thnh cells v tai rap

ATM Layer Truyn tai Cells

Tao/Tach Cell-Header

Dich (translation) VPI/VCI

Cell multiplexing/demultiplexing

iu khin lung v tc nghen

Physical Layer

Chuyn i Cell stream / bit stream

Truyn dn s

ATM Adaptation Layer

(AAL)

ATM Network Layer

Physical Layer

Higher Layers

Cac giao din ATM

X

X

X

X

X

X

X

X

X

Private

UNI

Public

UNI

NNI

Private

NNI

Private

ATM

network

Public

UNI B-ICI

Public ATM

network A

Public ATM

network B

UNI: User-Network Interface

NNI: Network-Network Interface

B-ICI: Broadband Inter-carrier i/f

ATM Physical Layer

TC Sublayer:

Cell Delineation

Kim tra li Header

Cell Rate Decoupling

(Insertion of Idle Cells)

Ring cho PMD

PMD Sublayer:

Line code

Connectors

Tai s dung cac chun cua lp vt ly hin tai

Transmission

convergence

(TC)

sublayer

Physical medium

dependent

(PMD) sublayer

Private UNI Physical Layers

UTP = Unshielded twisted pair STP = Shielded twisted pair

MMF = Multimode fiber SMF = Single-mode pair

STS = Synchronous Transport Signal

Frame format Bit rate Media

Cell stream 25.6 Mbps UTP-3

STS-1 51.84 Mbps UTP-3

FDDI 100 Mbps MMF

STS-3c, STM-1 155.52 Mbps UTP-3, UTP-5, STP,

SMF, MMF coaxial

pair

Cell stream 155.52 Mbps MMF, STP

STS-12, STM-4 622.08 Mbps SMF, MMF

Public UNI Physical Layers

Frame format Bit rate Media

DS-1 1.655 Mbps Twisted pair

DS-3 44.736 Mbps Coaxial

STS-3c, STM-1 155.52 Mbps SMF

E-1 2.048 Mbps Twisted pair

Coaxial

E3 34.368 Mbps Coaxial

J2 6.312 Mbps Coaxial

Chapter 9

ATM Networks

ATM Layer

ATM Layer

Lin quan n truyn theo th t cac cells qua kt ni mang

Kt ni ATM im-Ni-im: mt chiu hoc hai chiu

Point-to-Multipoint: mt chiu

Permanent Virtual Connections (PVC): cac kt ni di han cung cp bng thng gia cac im u cui trong mt mang ATM

Switched Virtual Connections (SVC): kt ni ngn han thit lp nhm ap ng cho cac yu cu cua khach hng

Virtual Channel Connections: virtual circuit

Virtual Path Connections: tp hp cua mt s kt ni ao (VPC) ATM Header cha thng tin v kt ni ao: 8-bit Virtual Path Identifier 16-bit Virtual Channel Identifier

ATM Virtual Connections

Virtual paths

Virtual channels

Tai sao cell co 53 Bytes?

Anh hng cua tr vo cac packet thoai co tac ng ti vic la chon kich thc cell

Tr tao goi ln ln theo kich c cell

@64kbps: packetization delay = cell size * 125 sec

Nu tr qua lu, cn s dung thit bi trit ting vong

Europe co cac ng truyn ngn v khng cn s dung b trit ting vong, vi vy xut s dung 32 byte payload

U.S. s dung cac ng truyn di v cn s dung cac b trit, vi vy, xut s dung 64 byte payload

Thoa hip: 48 byte payload

The ATM Cell

GFC-undefined

UNI cells has GFC field

NNI cells allocate these 4 bits to VPI; 4096 VPs

GFC (4 bits) VPI (4 bits)

VPI (4 bits) VCI (4 bits)

VCI (8 bits)

VCI (4 bits) PT (3 bits) CLP

(1 bit)

HEC (8 bits) AT

M c

ell

he

ad

er

Payload

(48 bytes)

Virtual Path Identifier

8-bits: 256 VC bundles

Virtual Channel Identifier

16 bits: 65,536 VCs/VP

Payload Type Indicator

Bit 3: data vs. OAM cell

Bit 2: Congestion indication in

data cells

Bit 1: Carried transparently

end-to-end; Used in AAL5

Cell Loss Priority

if 1, cell can be discarded by

network

Header Error Check

The HEC only covers the 5 bytes of the header to protect

against cell misdelivery

Since VPI/VCI changes at every switch, HEC must be

recomputed

HEC used for cell delineation

Two modes: Header Error Detection / Correction

Generating Polynomial: g(x)=x8+ x2+ x+ 1

The pattern 01010101 is XORed to r(x); keeps idle cells

from having HEC=0 and preventing cell delineation

The pattern 01010101 is XORed to r(x) in received

header prior to error checking

ATM Permanent Virtual

Connections

Quan tri mang thit lp bng nhn cng cac bang VPI/VCI tai cac switches v terminals

Thi gian thit lp kt ni lu, cac kt ni keo di

ATM

Switch

ATM

Switch

Operator at

Network Control Center

ATM Switched Virtual

Connections

Terminals v switches s dung VPI/VCI xac inh trc thit lp kt ni ng, theo yu cu

Giao thc bao hiu c s dung trao i vi h thng x ly cuc goi

ATM

Switch

ATM

Switch

Traffic Contract

Trong qua trinh thit lp kt ni, ngi dung v mang thoa thun hai tp tham s cho mi kt ni

Traffic descriptor: ngi dung xac inh lu lng mong mun mang chuyn giup

QoS requirements: ngi dung xac inh loai phm cht mang yu cu bi cac cell

Traffic Contract

Ngi dung cn tun theo traffic descriptor

Mang cn chuyn cell theo cam kt QoS

Cac tham s QoS

Sau tham s QoS

Ba tham s khng c thoa thun trong qua trinh thit lp kt ni:

Cell error ratio: ti l cell c chuyn bi li

Cell mis-insertion ratio: s cells trung binh/second bi chuyn nhm

Severely errored cell block ratio: M hay nhiu hn trong s N cells bi mt, li, hay chuyn nhm

Negotiable QoS Parameters

D0 Peak-to-Peak CDV

Dmax

pro

babili

ty d

ensity o

f cell

dela

y

Cell Loss Ratio (CLR): ti l cells bi mt

Xac inh bi u tin buffer

Cell Transfer Delay (CTD): thoa thun maximum delay Dmax: 1- of cells co tr it hn Dmax

Xac inh bi cell scheduling

Cell Delay Variation (CDV): Peak-to-Peak variation: Dmax-D0

Traffic Descriptors

Peak Cell Rate: tc cells/second mt ngun khng c phep vt

Sustainable Cell Rate: tc cell trung binh do ngun tao ra trong mt khoang thi gian di

Maximum Burst Size: s cell lin tip cc ai mt ngun co th phat tai tc peak cell rate (PCR)

Minimum Cell Rate: tc cell trung binh cells/second, ngun lun c phep truyn

Cell Delay Variation Tolerance: bin ng cell delay cho phep (tolerated) cho mt kt ni cho trc.

CBR VBR

real-time

VBR non-real-time

ABR UBR

Cell Loss

Rate

Cell Transfer

Delay

Cell Delay

Variation

Traffic

Descriptors

Flow Control

specified

specified

specified

unspecified

unspecified

unspecified

PCR/CDVT PCR/CDVT

SCR/BT

PCR/CDVT

& others PCR/CDVT

no yes no

CBR = Constant Bit Rate

VBR = Variable Bit Rate

ABR = Available Bit Rate

UBR = Unspecified Bit Rate

PCR = Peak Cell Rate

CDVT = Cell Delay Variation Tolerance

SCR = Sustainable Cell Rate

BT = Burst Tolerance

Cell transfer services provided by ATM Network

ATM Service Categories

Multiplexing & QoS Guarantees

ATM provides per-connection QoS guarantees

Many cell flows are multiplexed onto a common stream, so how are guarantees delivered?

CBR: scheduler must ensure transmission opportunities are regularly available for each connection

Real-time VBR: expect some multiplexing gain from combining VBR flows; however need to meet delay and loss requirements

Non-real-time VBR: can attempt higher multiplexing gains, subject only to loss requirement

UBR: no guarantees, but excellent performance at light traffic

ABR: some degree of guarantee: low CLR if source responds to network feedback; MCR can be negotiated

Traffic Contract & Call Admission

Control

Traffic contract: bao gm loai dich vu ATM, traffic descriptors, yu cu QoS

Connection admission control (CAC) xac inh xem mt yu cu kt ni co th c chp nhn hay khng

Mi switch trn ng cn xac inh xem no co th chp nhn thm lung mi trong khi vn am bao cam kt vi cac lung hin tai; nu co th, phn b ti nguyn cho lung mi

CAC khng c tiu chun hoa, tuy thuc vo nh cung cp dich vu

Cho phep mc overbooking thu c multiplexing gain khac nhau

Tinh cc khac nhau cho cac dich vu cung cp

Policing, Traffic Shaping, and

Congestion Control

am bao v QoS chi co y nghia khi ngi dung tun theo connection contract

Usage parameter control (UPC) l qua trinh cng ch thoa thun lu lng tai UNI Generic Cell Rate Algorithm co th s dung cho UPC; lin quan

n thut toan leaky-bucket Non-conforming cells co th bi anh du (CLP=1) hoc loai bo

Traffic shaping: ngun co th s dung TS am bao lu lng cua no tun theo connection contract Co th s dung Token bucket

Congestion control Cac cell co CLP=1 bi loai bo trc khi xay ra tc nghen Cac kt ni ABR phai ap ng vi thng tin phan hi tc nghen

nhn c t mang

Chapter 9

ATM Networks

ATM Adaptation Layer

ATM Adaptation Layer AAL: giao thc E2E dung phi hp dich vu truyn tai cell do

mang ATM cung cp theo yu cu cua application classes xac inh

Bao gm chuyn i cells v ngc lai, v cac chc nng phi hp b sung nh khi phuc inh thi, truyn tai tin cy

ITU inh nghia cac loai dich vu sau

Class

End-to-End

Timing

Bit Rate

Connection

Mode

A B C D

required not required

constant variable

connection-oriented connectionless

Class A = circuit emulation

Class B = variable bit-rate video

Class C & D = packet transmission

Cu trc giao thc AAL

AAL co hai lp con:

Segmentation & Reassembly Phn oan PDUs thnh cell

payloads; Tai rap PDUs t cell payloads nhn c

Convergence Common Part: packet

framing v error detection yu cu bi tt ca AAL users

Specific Part: cac chc nng phu thuc vo yu cu ring cua AAL user classes

ATM

Higher Layers

Segmentation

and

Reassembly

Sublayer

AAL

Layer

Convergence

Sublayer

Common Part

Service Specific

Convergence

Sublayer

AAL1

Higher layer User data stream

Convergence

sublayer

SAR sublayer

ATM layer

CS PDUs

SAR PDUs

ATM Cells

47 47 47

1 47 1 47 1 47

H H H

5 48

H

5 48

H

5 48

H

b1 b2 b3

Cung cp truyn dn CBR

AAL2

Truyn dn co hiu qua bng thng cac dich vu tc thp, lu lng packet ngn vi yu cu tr thp

B sung thm lp multiplexing th 3 cho cu truc VP/VC cua ATM, vi vy cac low-bit-rate users co th chia se mt kt ni ATM.

AAL

2

ATM cells

Low bit rate

Short voice packets

Mobile

switching

office

AAL2

Higher layer This example

assumes 24 byte

packets

Common part

convergence

sublayer

SAR sublayer

ATM layer

1 47

5 48

H

P3

Service specific

convergence

sublayer

P2 P1

Assume null

1 47

3 24 3 24 3 24

PAD

5 48

H

Add 3-byte

header to each

user packet

Segment into SAR

PDUs

H H H

AAL3/4

Why 3 / 4 ?

AAL3: Truyn dn d liu connection-oriented

AAL4: Truyn dn d liu connectionless Tt ca packet connectionless s dung cung mt VPI/VCI tai UNI

Multiplexing ID (MID) dung phn bit connectionless packets

AAL3 v AAL4 kt hp thnh AAL co th dung cho truyn dn connection-oriented hay connectionless

AAL3/4 cho phep nhiu ngi dung c ghep knh va ghep xen (interleaved) trong cung ATM VC

Message mode: ban tin cua mt ngi s dung phn oan thnh ATM payloads

Stream mode: mt hoc nhiu ban tin phn oan thnh ATM payloads v phn phi khng cn chi ra phn inh

Assured mode: phn phi ban tin khng li

Non-Assured mode: ban tin co th c phn phi co li hoc khng co li

Higher layer

Common part

convergence

sublayer

SAR sublayer

ATM layer

Service specific

convergence

sublayer

Information

Assume null

T PAD

User message

Pad message to

multiple of 4 bytes.

Add header and trailer.

Each SAR-PDU

consists of 2-byte

header, 2-byte trailer,

and 44-byte payload.

H

4 4

2 44 2 2 44 2 2 44 2

Information

AAL 3/4

Higher layer

Common part

convergence

sublayer

SAR sublayer

ATM layer

PTI = 0

Service specific

convergence

sublayer

48

(1)

Information

T PAD

Information

48

(0)

48

(0)

PTI = 0 PTI = 1

AAL5

n gian hn than AAL3/4

48 bytes payload

Truyn tng packet cho VCI

PTI in ATM

header indicates

last cell for a

given packet

Examples: Voice and Video

Voice

AAL1 for individual PCM

voice calls

AAL1 with structured

transfer for nx64 kbps

AAL2 for low-bit-rate

cellular voice

AAL5 for inexpensive

voice

CBR MPEG2 Video

Timing recovery at AAL

or at MPEG systems

layer?

Error detection &

correction at which

layer?

Timing recovery at

MPEG2 systems level

and AAL5 over CBR

ATM was selected

Example: ATM & ADSL

IP over PPPoE frames segmented by AAL5 into ATM cells at

ADSL modem

ATM cells flow through DSLAM and ATM network to Internet

Service Provider

ISP

AD

SL

AT

M

DSL Access Mux

User Premise Central Office

Telephone

Switch Telephone

Network

ATM

Network

IP

PPPoE

AAL5

ATM

ADSL

splitter

splitter Subscriber

loop