1ATM -

All rights reserved. No part of this publication and file may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior written permission of Professor Nen-Fu Huang (E-mail: nfhuang@cs.nthu.edu.tw).

ATM Networks

2ATM -

An Overview of ATM

ATM is Asynchronous Transfer Mode. A technology for multiplexing fixed-length (53

octets) cells from a variety of sources to a variety of remote locations.

Capable of moving data at a wide range of speeds. Capable of handling data from a variety of media

(e.g. voice, video, and data) using a single interface.

ATM is a connection-oriented protocol. Connections are established between ATM service

users, (e.g. a workstation with an ATM interface or a call setup process running on an ATM switch).

3ATM -

An Overview of ATM

Connections can be switched (SVC), or permanent (PVC).

Signaling procedures are used to set up calls(Q.2931).

Permanent connections are established through administrative procedures.

Each ATM connection operates at a certain quality of service (QoS) which is characterized by such parameters as cell loss rate, cell delay, delay jitter, bandwidth, peak rate, average rate, duration, etc.

The QoS is negotiated between the user and the network when the connection is established.

4ATM -

ATM operates on a best effort basis. ATM guarantees that cells will not be misordered. Two types of connections:

Point-to-point Multipoint (Multicast)

Four Types of Services: CBR (Constant Bit Rate) VBR (Variable Bit Rate) ABR (Available Bit Rate) Flow Control, Rate-based, Credit-

based UBR (Unspecific Bit Rate) No Flow control.

Aggregate Bandwidth vs. Shared Medium (Ethernet, Token-Ring, Token-Bus, WLAN).

An Overview of ATM

5ATM -

ATM Network Structure

ATM LAN

ATM

WAN

UNI

UNI

NNI

NNI

UNI: User-Network Interface (UNI 4.0)NNI: Network-Network Interface (PNNI)

UNI

End Station

ATM Switch

ATM Switch

ATM Switch

ATM Switch

ATM Switch

ATM Switch

End Station

End Station

6ATM -

. . .

Fore ASX-200 Newbridge VIVID

DEC

DEC

OC-3c

(OC-3c x 4)(TAXI x 6)

(OC-3c x 12)

(OC-3c x 8)

電通中心（綜二館 7F ）

清大計算機中心 ( 綜二館 3F)

資訊系 2F

資訊系 3F

電機系 4F

WSWWWServers ATM/FDDI

(DEC Alpha Station x 8)

清華大學高速網路實驗平台 (1998)

遠距教學教室

OC-3c

OC-3c

FDDI

FDDI

FOREASX-200

交大計算機中心

SW

T1/T3

OC-3c

T1/T3

NII 網路

OC-3c

(SUN)

(SUN)

WS

WS

電機系 6F

TAXI

(TAXI x4)

VoD Server Clients

VoD Clients, Video Conference

Video Conference

(OC-3c x 12)

FORE ASX-200

FOREASX-200

FOREASX-100

FOREASX-200

高速電腦中心OC-3c

OC-3c

WS

ATM/Ethernet Hub

Ether-Switch

TAXI

ATM/Wireless Bridge

ATM/Wireless Bridge

7ATM -

ATMCellFormat

酬載48 Octets

GFC VPI VCI PTI CLP HEC

4 8 16 3 1 8 位元

酬載48 Octets

VPI VCI PTI CLP HEC

12 16 3 1 8 位元

(a) UNI Cell format

(b) NNI Cell format GFC: Generic Flow Control (4 bits). Used by the

flow control mechanism at the UNI. VPI: Virtual Path Identifier (8 bits). Used for

directing cells within the ATM network. VCI: Virtual Channel Identifier (16 bits). PTI: Payload Type Identifier (3 bits). Identifies

the type of data being carried by the cell. CLP: Cell Loss Priority (1 bit). 1 = low priority. HEC: Header Error Correction (8 bits). Generated

and inserted by the physical layer. For first 4 octets. Correct single-bit errors and detect some Multiple-bit errors.

8ATM -

Cell Multiplexing and Cell Switching Examples

100 200 100 100200

150 150 150 100100

200 200 400 200400

300 300 300

100 100

VPI/VCI OP New VPI/VCI

100 0 100150 2 200

0

1

2

3

0

1

2

3

VPI/VCI OP New VPI/VCI

100 1 300200 2 400

ATM Switch

100

100

200200

200

300300

300

400

400

UTP

UTP

SMF

MMF

UTP

UTP

SMF

MMF

9ATM -

ATM Protocol Stack

Physical Layer (PMD)

ATM Layer

ATM Adaptation Layer

Higher LayersHigher Layers

Control planeUser plane

Management plane

Layer management

Plane managementVirtual Channel Functions

Virtual Path Functions

10ATM -

ATM Layer Service

Transparent transfer of 48-octet data unitDeliver data in sequence on a connectionTwo levels of multiplexingThree types of connections

Point-to-point Point-to-Multipoint Multipoint-to-Multipoint

Transport is best-effortNetwork QoS negotiationTraffic control and congestion control

11ATM -

ATM Layer Functions

Cell multiplexing and switchingCell rate decouplingCell discrimination based on pre-defined

VPI/VCIQuality of Service (QoS)Payload type characterizationGeneric flow controlLoss priority indication and Selective cell

discardingTraffic shaping

12ATM -

Pre-assigned VPI/VCI Values

Unassigned Cell Indication (VPI = 0, VCI = 0)Meta signaling (VCI=1)

Meta signaling is the bootstrap procedure used to establish and release a signaling VC. Not used for PVC setup.

General broadcasting signaling (VCI=2)OAM F4 flow indication -- segment and end-

to-end (VCI=3 and VCI=4)Point-to-Point Signaling (VCI=5)Carriage of Interim Local Management

Interface (ILMI) messages (VPI=0, VCI=16)

13ATM -

Cell Rate Decoupling and Cell Discrimination

Cell Rate Decoupling ATM sending entity adds unassigned cells to the assigned cell stream

in order to adjust to the cell rate acquired by the payload capacity of the physical layer (R).

Cell Discrimination Meta signaling General broadcast signaling Point-to-point Signaling Segment OAM F4 flow cell End-to-end OAM F4 flow cell ILMI message User data

14ATM -

Virtual Channels, Virtual Paths, and the Physical Channel

Virtual PathVirtual ChannelPhysical link

100 100

200 200

300 300

100200

100200300

10203040

Connection (VPI/VCI) =

(100,100),(100,200),(200,100),

(200,200),(200,300),(300,10),

(300,20),(300,30),(300,40)

100/100200/300300/10300/40

100200

100200300

10203040

Virtual PathVirtual Channel

Cell

15ATM -

Virtual Channels

The virtual channel (VC) is the fundamental unit of transport in a B-ISDN. Each ATM cell contains an explicit label in its header to identify the virtual channel.

a Virtual Channel Identifier (VCI)a Virtual Path Identifier (VPI)

A virtual channel (VC) is a communication channel that provides for the transport of ATM cells between two or more endpoints for information transfer.

A Virtual Channel Identifier (VCI) identifiers a particular VC within a particular VP over a UNI or NNI.

A specific value of VCI has no end-to-end meaning.

16ATM -

Virtual Paths

A Virtual Path (VP) is a group of Virtual Channels that are carried on the same physical facility and share the same Virtual Path Identifier (VPI) value.

The VP boundaries are delimited by Virtual Path Terminators (VPT).

AT VPTs, both VPI and VCI are processed. Between VPTs associated with the same VP,

only the VPI values are processed (and translated) at ATM network elements.

The VCI values are processed only at VPTs, and are not translated at intermediate ATM network elements.

17ATM -

Why Virtual Paths and Virtual Channel ?

A B

(1)

VCI OP

(1) 2 (2)

NewVCI

(127) 2 (35)

0 1

255

0 1

255

(2)(3)

(127)(35)

(255)

(208)(254)

(38)

(208) 2 (254)

0

1

255

Assume the identification field contains 8 bits. All used

as VCI. Then the size of the mapping table is 256.VCI OP

(2) 1 (3)

NewVCI

(35) 1 (255) (254) 1 (38)

01

255

18ATM -

Why Virtual Paths and Virtual Channels ?

0

1

7

0

1

7

0

1

7

(0/1)

(7/1)

(1/1)

(1/31)

(0/31)

(0/31)

(7/25)

(1/25)

(7/25)

0 1

31

0 1

31

0 1

31

7

VPI OP

(0) 2 (7)

NewVPI

(1) 2 (0)

0

1 (7) 2 (1)

VPI OP

(7) 1 (1)

NewVPI

(0) 1 (0)

0

1 (1) 1 (7)

7

Assume VPI takes 3 bits and VCI takes 5 bits. Then the size of the mapping table is 8.

19ATM -

Virtual Channels Examples

1A D

1C B

(300,10)

(100,20)(300,20)

(100,10)

(300,10)

(200,20) (200,10)

(100,10)

(100,20)

23

1 2

24

2

VPI/VCI OP

(100,10) 2 (200,10)

NewVPI/VCI

(100,20) 2 (200,20)

VPI/VCI OP

(200,10) 3 (300,20)

NewVPI/VCI

(200,20) 2 (300,10)

VPI/VCI OP

(300,20) 2 (100,20)

NewVPI/VCI

VPI/VCI OP

(200,10) 4 (300,10)

NewVPI/VCI

a

b

c

d

Port (a,1)

Port (c,2)

Port (d,1) Port (b,1)

VPI/VCI OP

(100,10) 4 (200,10)

NewVPI/VCI

Port (b,2)

4

1 (100,20)

VPI/VCI

1 (300,10)

VPI/VCI

1 (300,10)

VPI/VCI

1 (100,10)

VPI/VCI

連線 1 (100,10)

VPI/VCI

輸出連線

2 (100,20)

(200,10)

輸出連線

輸入連線

輸入連線

輸入連線 連線

連線

連線

連線

20ATM -

ATM Adaptation Layers (AAL)

AAL Reference StructureAAL Type 1AAL Type 2AAL Type 3/4AAL Type 5SAAL (Signaling AAL)

21ATM -

AAL Reference Structure

Service Specific CS (SCCS)(may be Null)

Common Part CS (CPCS)

SAR(Common)

AAL

ConvergenceSublayer (CS)

SAR

SAP

SAP

Primitives

Primitives

22ATM -

AAL

AAL

Service Specific Layers

ATM

Transmission Convergence

Sublayer

PMD

Layer

MGMT

...

...

48 byte payloads

add 5 byte header

message

23ATM -

AAL Functions

Functions ParametersError Detection CRC, length, correlation tagsFraming of user data units Payload type/segment typeCell sequence indication Cell sequence count fieldMultiplexing Message ID (MID)Error Correction FEC, retransmissionFlow Control Credit windowTiming Recovery Time stamp

24ATM -

ATM Adaptation Layers (AAL)

In order to carry data units longer than 48 octets in ATM cells, an adaptation layer is needed.

The ATM adaptation layer (AAL) provides for segmentation and reassembly of higher-layer data units and for detection of errors in transmission.

Since the ATM layer simply carries cells without concern for their contents, a number of different AALs can be used across a single ATM interface.

The AAL maps the user, control, or management protocol data units into the information field of the ATM cell and vice versa.

To reflect the spectrum of applications, four service classes have been defined by CCITT.

25ATM -

CCITT Services Classifications

Timing between source and destination

Class A Class B Class C Class D

Required Not required

Bit Rate Constant Variable

Connection

modeConnection oriented Connectionless

CircuitEmulation

Packetizedvoice/video

ConnectionOriented

DataDatagramAttribute

Examples: Class A: 64kbps digital voice Class B: Variable bit rate encoded video Class C: Frame Relay over ATM, File Transfer (Telnet, FTP, TCP),... Class D: IP over ATM, MPOA, ... Class X: Raw Cell Service (e.g., proprietary AAL)

26ATM -

AAL Service Classification

Timing between source and destination

Class A Class B Class C Class D

Required Not required

Bit Rate Constant Variable

Connection

ModeConnection oriented Connectionless

CircuitEmulation

Packetizedvoice/video

ConnectionOriented

DataDatagram

AttributeAAL1 AAL2 SAAL

AAL 5

AAL 4AAL 3

Signalling

(Q.93B)

27ATM -

AAL Types

Five AALs have been accepted for consideration by the CCITT.

AAL 1 is meant for constant-bit-rate services (voice). AAL 2 is meant for variable-bit-rate services with a

required timing relationship between source and destination (audio and video).

AAL 3 was originally meant for connection-oriented variable -bit-rate services without a required timing relationship; it has now been merged with AAL 4.

AAL 3/4 and 5 are meant for connectionless services (e.g. connectionless data).

Only AALs 3/4 and 5 are of interest for IP networking.

28ATM -

AAL 1 (Constant Bit Rate -CBR) Functions

Emulation of DS1 and DS3 Circuits Distribution with forward error correction Handle cell delay for constant bit rate Transfer timing information between source and destination Transfer structure information (structure pointer) Provide indication of unrecoverable lost or errored information

Header SN SNP 47 Octets Payload

SAR PDU

CSI SeqCount EPCRC

1 3 3 1

29ATM -

AAL 2 Protocol Data Unit (PDU)

Header SN IT 47 Octets Payload LI CRC

SAR PDU

ATM PDU

SN: Sequence number

IT: Information Type:BOM,COM,EOM,SSM

Length Indicator

30ATM -

AAL 3/4

The variable bit rate (VBR) adaptation layer, defined in CCITT recommendation I.363, is defined for services (e.g. data) that require bursty bandwidth.

Comprises two sublayers:the convergence sublayer (CS) the segmentation and reassembly

sublayer (SAR)

31ATM -

AAL 3/4 CS and SAR PDU Structures

CS-PDU

Header

4 Octets

CS-PDU User Information <= 65,535 Octets

CS-PDU

Trailer

4 Octets

PAD

0-3

Octets

Common

Part

IndicatorBTag BASize Alignment

CS User Infor.

LengthETag

1 1 2 1 1 2

CPI:00000000 Btag/Etag: Beginning/Ending Tag -- 256 increment counters BAsize: receiving side maximum buffering requirement (>= CPCS-PDU) Pad: make CPCS-PDU on 32-bit boundary AL(Alignment): make trailer 32-bit aligned Length: CPCS-PDU size

32ATM -

AAL 3/4 SAR Sublayer

SAR-PDU

Header

2 Octets

Segmentation Unit ,SAR-PDU Payload 44 Octets

SAR-PDU

Trailer

2 Octets

SAR Type

Length SAR SN

MID SAR-PDU CRC

2 4 1 9 6 10

p

ST: COM(00),BOM(10),EOM(01),SSM(11) SN: Modulo 16 sequence counter P(Priority): 1- Priority CS-PDU, 0- Normal CS-PDU MID (Multiplexing ID) -- Multiplexing multiple CPCS connections on a single ATM connection LI: Length <=44 CRC on Cell Header, SAR-PDU payload and LI

33ATM -

AAL 5 PDU Structure

The Simple and Efficient Adaptation Layer (SEAL), attempts to reduce the complexity and overhead of AAL 3/4.

It eliminates most of the overhead of AAL 3/4.

AAL 5 comprises a convergence sublayer and a SAR sublayer, although the SAR is essentially null.CS-PDU User Information

<= 65,535 Octets

CS-PDU

Trailer

8 Octets

PAD

0-47

Octets

Protocol

Control CRCLength

2 2 4

34ATM -

AAL 5 Segmentation and Reassembly

CPCS-PDU Payload (CPCS-SDU) <= 65,535 Octets

CS-PDU

Trailer

8 Octets

PAD

0-47

Octets

Control CRC-32Length

2 2 4

User SDU

User DataMore= T

User DataMore= T

Data TMore= F

...

Control

CPCS-UU -- CPCS User-to-User Indication

(1 octet). Transparently transfer CPCS user

to user information

CPI -- Common Part Indicator (1 octet). Align

trailer to 64 bits. Possible identification of

layer management message.

48 octets 48 octets

ATM cell ATM cell ATM cell

35ATM -

AAL 5

A datagram is converted to a CS-PDU by adding the pad (if necessary) and trailer.

The CS-PDU is breaked into 48-octet SAR-PDUs and transmitted in an ATM cell.

Since there is no AAL 5 SAR header, an end-of-frame indication in the ATM cell header is required: SDU type of 1 (binary value 0X1) in the PTI field.

The receiver simply concatenates the received cells, watching for the end-of-frame indication.

The higher layer is responsible for ignoring or using the PDUs with CRC errors.

36ATM -

SAAL Structure

Service Specific Coordination Function (SSCF)

Service Specific Connection Oriented Peer-to-Peer Protocol (SSCOP)

Common Part AAL Peer-to-Peer Protocol (CP-AAL)

Service SpecificConvergence Sublayer

Common Part

Peer-to-Peer Message

Peer-to-Peer Message

Primitives

Primitives

37ATM -

SAAL

Reside between Q.93B and ATM Layer.

SAAL is used to provide reliable transport of Q.93B messages between peer Q.93B entities.

SAAL CP-AAL uses AAL5 Common Part Protocol.

SSCOP can be used for any reliable service.

38ATM -

Interconnection with Legacy LANs

LAN EmulationIP-Over-ATMMultiple Protocol Over ATM

(MPOA)IP Switching

39ATM -

Summary of ATM Networks

Switching-Based Network Architecture

Connection-Oriented ProtocolQoS Guaranteed ServicesAggregated BandwidthMultiple Data Rates and

Interfaces