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ATM Basis

Applicable to Staff with Skill Certificate Level II or LowerReleased by GU Product Support Dept.

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Version Introduction

References:

1.

2.

Version Date Author Checked by Amendment Record

R1.0 2010-03-01 Lei Haiting *** RNC V3.09.30

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Course Objectives:

To master the basic concepts of ATM switch

To understand the ATM protocol

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Contents

ATM Overview

ATM Basic Knowledge and Concepts

ATM Protocol and Qos

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What Is ATM?Principles and Advantages

• High-speed, low-delay switching technology using short, fixed-size packets called cells

• Cell-switching technique that supports transmission of voice, video, image, and data

• Combines the advantages of circuit switching and packet switching

ATM Advantages:

• Support for multimedia applications

• Cost savings by combining data, voice, and video over a single physical channel

• Single technology spanning local (LAN) and wide area networking (WAN)

• Guaranteed service for time-sensitive applications

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How Does ATM Work?

Transfers information using fixed length cells (53 octets)Routing information stored in cell headerATM switch hardware makes routing decisions

Application

User bits PAD Ctrl/ Length CRC

0-47 4 4 octets 0 to 65,000 octets

ReassemblySegmentation

1 - Cell-based Technology

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How Does ATM Work?

5-byte header

ATM Cell

53 byte

To identify VP

48-byte payload

2 - ATM Cell Format

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ATM Interfaces

Private ATM network

Private UNI

Public UNI

PublicNNI

Private NNI (PNNI)

UNI = User-Network InterfaceNNI = Network-Node InterfaceB-ICI = Broadband Inter-Carrier Interface

Public ATM network

B-ICI

Public ATM network

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Contents

ATM Overview

ATM Basic Knowledge and Concepts

ATM Protocol and Qos

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Structure of ATM Header

GFC VPI

VPI VCI

VCI VCI PTI CLP

HEC

VPI

VPI VCI

VCI

VCI PTI

HEC

UNI (User-Network Interface) NNI (Network-Node Interface)

GFC: general flow controlVPI: virtue path identifierVCI: virtue channel identifier

PT: payload typeCLP: cell loss priorityHEC: header error control

CLP

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ATM Switching Principles

Port 1 VPI=2VCI=37

VPI=3VCI=39

NNI

UNI

UNI

ATM Switching

Port VPI VCI 1 2 37 2 1 51

Port 2

Port 1 ATM Switching

Port VPI VCI 1 1 51 2 3 39

Port 2

ATM TerminalUser B

User A

ATM Network Equipment

User data ATM Cell

User data ATM Cell

VPI=1 VCI=51

ATM Network Equipment

ATM Terminal

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Virtual Connections2 - Virtual Paths and Virtual Channels

Bundles of VCs are switched via Virtual Paths (VPs)

Physical linkVirtual Path

Virtual Channel

Transmission PathVP

VP

VP

VP

VCs

VCs

VCs

VCs

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Virtual Connections3 - Virtual Paths Switching

VC21VC22

VC23VC24

VC25VC24

VC21VC22

VC23VC24

VC25VC24

VP1

VP2

VP3

VP4

VP5

VP6

VP Switch = Cross-connect

VP1

VP6

VP2VP4

VP3VP5

VP Concatenation

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Virtual Connections

VC Switch

VC21VC22

VC21VC22

VC21VC22

VP1

VP4

VP Cross-connect

VC24

VC23

VP6

VP2

VP3

VP2

VP3

VP1

Endpoint of VPC

4 - VC and VP Switching

VP4 VP6

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ATM Connection1 - Permanent Virtual Connections

NetworkManagementSystem

VPI/VCIVPI/VCI VPI/VCI

VPI/VCI

Long setup time (especially with human intervention) means that connections are left active for long periods of time e.g. days, weeksVPI/VCI tables setup in terminals and switches

ATMNetwork

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ATM Connection2 - Switched Virtual Connections

Signaling ChannelVPI/VCI = 0/5

Signaling ChannelVPI/VCI = 0/5

Switch and terminal exchange signaling messages using the predefined signaling channel, VPI/VCI = 0/5

ATMNetwork

2 routing mechanisms:static: Interim Inter Switch Protocol (up to 10 ATM nodes)dynamic: P-NNI (private) or MTP3 (public)

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Contents

ATM Overview

ATM Basic Knowledge and Concepts

ATM Protocol and Qos

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Layered Architecture1 - ATM Forum Model versus OSI

Control plane User plane

Higher layers Higher layers

ATM Adaptation Layer (AAL)

ATM layer

Physical layer

Management plane

OSI Model

Data Link Layer

Physical Layer

Layer Management

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Layered Architecture2 - ITU-T ATM Model

User layer

Physical layer (transmission)

ATM layer (cell format)

AAL

User plane

Management planeControl plane

Class ACBR(circuit emulation)

Signaling and control

Class BVBR(compressed video/audio)

Class CCONS for data(Frame Relay)

Class DCLNS for data(LAN)

AAL 1 AAL 3/4 or AAL 5AAL 2Convergence Sublayer

SAR sublayer

Class XCONS

UBR

Class YCONS

ABR

AAL 5 AAL 5

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Layered Architecture3 - ATM Layers Location

User

Physicallayer

AAL

ATM layer

Higherlayer

Network(Error recovery and flow control)

User

End-to-end

Edge-to-edge

Physicallayer

AAL

ATM layer

Higherlayer

Physicallayer

ATM layer

Physicallayer

ATM layer

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ATM Physical Layer Functions

AAL

ATM Layer

Physical Layer

The Two Sublayers:• Transmission Convergence Sublayer (TC)

Cell rate decoupling HEC sequence gener/verification Cell delineation Transmission frame adaptation Transmission frame gener/recovery

• Physical Medium Sublayer (PMD) Bit timing, Physical medium

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ATM Layer Functions

AAL

ATM Layer

Physical Layer

• Cell Convergence

• Cell Detachment

• VPI/VCI Conversion

• Header Generation and Detachment

• General Flow Control

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ATM Adaptation Layer Functions

AAL

ATM Layer

Physical Layer

The Two Sublayers:

• Segmentation And Reassembly sublayer (SAR)

• Convergence Sublayer (CS)

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AAL-5 Characteristics

Simplification of AAL-3/4SEAL = Simple and Efficient AAL Layer

Less overhead and better error protection below CPCS than AAL-3/4

Used for most connection-oriented and connectionless services

Supports VBR-NRT, UBR and ABR service categories

Main Service Specific Convergence Sublayer:

• FR SSCS for Frame Relay

• SSCOP for signaling (Q.SAAL)

• Can be null, but CPCS is always necessary

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AAL-5 SAR PDU Segmentation

SAR-PDUSAR-PDU

SAR-PDU

SAR-PDU48 octets

CPCS-PDUpayload PAD CPCS-PDU

trailer

CPCS-PDUSAR-PDUpayload

SAR-PDUpayload

SAR-PDUpayload

SAR-PDUpayload

ATM-PayloadHeaderMORE ATM-PayloadHeader

LAST

Payload Type = 1

SegmentationAndReassembly

ATM Layer

UpperLayerProtocol

Common Part Convergence Sublayer adds a Trailer

User Data (connectionless) User Data (connection)

TrailerService Specific Convergence Sublayer adds a Header/Trailer

Header User Data (up to 64 K octets)

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AAL-5 Format of CPCS PDU

User to User indicator(information between CPCS and user)

LgUU

0-47 1 1 2 octets 4 octets

1 to 65535 octets

Lg = Length

CPCS PDU PAD CPI CRC32

Common PartIndicator

Max = 4 octets

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AAL2 - Characteristics

AAL-2 is a multiplexed ATM Adaptation Layer for voice, data, video and signaling

More than one type 2 information stream can be supported on a single ATM connection (multiplexed in a single cell)

Provides for bandwidth efficient transmission of low-rate, short, and variable length packets in delay sensitive applications (VBR-Real Time)

Best for voice over ATM and for compressed speech

AAL-2: Multiple, short packet based user channels over the same ATM connection.

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AAL-2 Cell Packing/Multiplexing

CPS Packets

CPS-PDUs

User 2 Variable Bit-RateUser 3

User 1

Atm Adaptation Layer

ATM Layer

UpperLayerProtocol

ATMCells

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AAL-2 Format of CPS Packet and CPS PDU

CPS PDU payload = 0, 1 or more CPS packetsSNOSF PAD

48 octets

6 bits 4 bits 0 to 44 bits

ParitySequence Number

CPS InformationUUILI

1 to 45/64 octets

6 bits 5 bits

3 octets

CID HEC

User to UserIndicator(information between CPCS and user)

5 bits8 bits

LI = Length Indicator

ChannelIDentifier

HeaderErrorControl

P

OffSetField

1 bit

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ATM Service Categories

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ATM Service Categories- Main Characteristics

ATM AdaptationType

AAL-1 AAL-2 AAL-3/4 AAL-5

ServiceExamples

Constant Bit-Rate:Circuit EmulationSpeechCBR Video

Variable Bit-Rate(Real-Time):Efficient speechVideo-conference

Variable Bit-Rate(Non Real-Time)

TCP/IPFrame RelayLAN

TimingRelationship? Yes Yes No

Bit Rate Constant Variable Variable

Connection mode Connection orientedConnection oriented

Connection-less

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Traffic Contract - Traffic Contract and QoS Parameters

BroadcastVideo

Traffic parameters:• Peak Cell Rate (PCR)• Sustainable Cell Rate (SCR)• Maximum Burst Size (MBS)

Quality of Service:• Cell Transfer Delay (CTD),• Cell Delay Variation (CDV),• Cell Loss Ratio (CLR),• Cell Error Ratio (CER),• Severely Errored Cell Block Ratio

(SECBR),• Cell Misinsertion Rate (CMR).

Traffic Contract

Cell Loss Ratio

Cell Delay Variation (seconds)

Voice

File Transfer

Web Browsing

InteractiveData

InteractiveVideo

CircuitEmulation

10-4 10-3 10-2 10-1 100 101

10-4

10-6

10-8

10-10

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ATM Forum Traffic Management

ATM Layer Service CategoryAttribute

CBR rt-VBR nrt-VBR UBR ABR

Traffic Parameters:

Peak Cell Rate Specified Specified Specified

Sustainable Cell Rate N/A Specified N/A

Min. Cell Rate N/A N/A Specified

QoS Parameters:

Peak-to-peak CDV

Specified UnspecifiedMax. Cell Transfer Delay

Specified Unspecified

Cell Loss Ratio Specified Unspecified

Max. Burst Size N/A Specified N/A

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Course Review

Describe the basic process of ATM switch. Describe the ATM traffic type and Qos parameters.

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