09-ATM Pricinple-20090724-A

HUAWEI TECHNOLOGIES CO., LTD.

www.huawei.com

11.Dec,2006

HUAWEI Confidential

Security Level: Internal Use Only

xxxx ATM PrincipleISSUE2.0

HUAWEI TECHNOLOGIES CO., LTD. Page 2HUAWEI Confidential

The Asynchronous Transfer Mode (ATM) principle has dominated the telecom network for a long time as a mainstream datacom technology. Nowadays, the IP technology prevails over the telecom network. It is time for us to unveil the ATM principle thoroughly.


Upon the completion of the course, you can:

Describe the ATM cell

Master the VP switching and the VC switching

Master the ATM switching

Master the service type of the ATM


Chapter 1Chapter 1 ATM OverviewATM Overview

Chapter 2 ATMChapter 2 ATM ConceptsConcepts

Chapter 3 ATMChapter 3 ATM Protocol StacksProtocol Stacks

Chapter 4 ATMChapter 4 ATM Service and PropertiesService and Properties


What Is ATM?

ATM is an asynchronous transfer mode with cell as its unit. Asynchronism indicates that the information or cell flow from any user needs not to be periodical.

ATM integrates the advantages of the circuit switching and the packet switching. It carries various information media and communication services in a single backbone network, guarantees QoS, and meets the needs of the real-time service and non-real time service.


Differences Between ATM, Circuit Switching and Packet Switching

Circuit Switching

Connection oriented

Timeslot-oriented switching, line resources monopolization

Packet Switching

Connectionless oriented

Switching packets, sharing line resources

ATM : Asynchronous Transfer Mode

Connection oriented

Packet switching


Setup

Setup

Setup

Setup

Connectionless Network and Connection-Oriented ATM Network

Connectionless networkConnectionless, segment-by-segment forwarding The packet is too long and of unfixed length.The QoS of the network cannot be guaranteed.

Connection-oriented ATM network

Connection oriented, forwarding at high speed

The cell has a fixed length about 53 bytes

The QoS of the network can be guaranteed.


Organizations for Establishing the ATM Standards

ITU-T

Absorbs itself in standardizing ATM on the public network. Its representative

standards include the Q.2931/Q.2971, BISUP, and I.610.

ATM Forum

Absorbs itself in standardizing ATM on the private network and promoting the

ATM products and usage. Its representative standards include the UNI3.1,

UNI4.0, ILMI, PNNI, MPOA, VTOA, LANE, and TM4.0.

IETF

Absorbs itself in standardizing the IP over ATM and solving the bottleneck of

traditional routers. Its representative standards include the RFC1483,

RFC1577, IP Switch, and MPLS.


Chapter 1 ATM OverviewChapter 1 ATM Overview





ATM Cell StructureGFC：Generic flow control (only valid in the UNI interface)VPI/VCI：Virtual path identifier/virtual channel identifierPT：Payload typeCLP：Cell lose priorityHEC：Header error identifier

ATM UNI UNI Cell ATM NNINNI Cell

48-byte load48-byte load

GFC (4)GFC (4)VPI (8)VPI (8)

VCI (16)VCI (16)

PTIPTI CLPCLP

HECHEC

48-byte load48-byte load

VPI (12)VPI (12)

VCI (16)VCI (16)

PTIPTI CLPCLPHECHEC


The VPI and the VCI are only locally valid.

ATM Connection

Virtual channel connection

Virtual path connection

VP switching

VCswitching

VC switching

NNI NNI

VPI = 2 VCI = 44

VPI = 1 VCI = 40

VPI = 3 VCI = 44

VPI = 4 VCI = 50

UNIUNI

AB C D

E


ATM virtual channel connection (VCC)

A VP contains VCs.A VCC contains VPs.

VC is the logical channel between the ATM nodes.

Virtual Channel (VC)

Virtual channel （ VC）

E3OC-3OC-12

Virtual path (VP)

Virtual path (VP)

The virtual identifier VPI/VCI.

VP and VC


VCI 1 VCI 2 VCI 3 VCI 4

VPI 2VPI 2VPI 3VPI 3VPI 1VPI 1

VPI 2VPI 2

VPI 3VPI 3

VPI 5

VPI 1VPI 1

VPI 4

Port 1

Port 2

Port 3

VCI 1VCI 2

VCI 1VCI 2

VP switching

VC switching

VCI 3

VCI 4

VCI 1

VCI 2

VP Switching and VC Switching


ATM Switching

ATM switching

PPHHYY

AATTMM

Port 3

PPHHYY

AATTMM

Port 4

PortPort VPIVPI VCIVCI

33 11 5151

44 33 3939

ATM layer

ATM switching

PPHHYY

AATTMM

Port 1

PPHHYY

AATTMM

Port 2

PortPort VPIVPI VCIVCI

11 22 3737

22 11 5151

ATM layer

PPHHYY

AATTMM

AAAALL

PPHHYY

AATTMM

AAAALL

VPI = 2 VCI = 37

VPI = 3 VCI = 39

NNI

UNI

UNI


ATM Connection Modes

PVC (permanent virtual channel): The NMS sets up

PVCs. Whether any service passes or any

terminal device is accessed, the PVCs are

always enabled till they are released by NMS.

PVCs are just like lease lines in the telephony

network.

SVC (switching virtual channel) ： SVCs are set up and released by signaling. They are just like subscriber lines in the telephony network.







Reference Model of ATM Stacks

3 planes: user plane, control plane, and management plane

3 layers: physical layer, ATM layer, and ATM adaptation layer

Upper layer Upper layer

ATM layer

Physical layer

Control plane User plane

Management plane

ATM adaptation layer Layer-management

Plane-management


Functions of the ATM Layers

Convergence sublayer

Segmentation and reassembly cells

AAL

Generic traffic controlForm and pick up cell headersInterpret the VPI/VCI of cellsMultiplex and demultiplex cells

ATM layer

Decouple the cell rate, form/check the HEC sequence, delimitate cells, adapt/form/ restore the transmission frames.

Bit timing, physical media.

Voice cells

Video cells Data cells

Physical layer

TC

PM

SAR

CS


AAL Types and B-ISDN Service

Voice, video and circuit emulation service

Packet video Data Application

ATMservice

类AAL Type 1 Type 2 Type 3/4 Type 5

ATM layer

Physical layer

ATMnetwork


Flow for Processing the ATM CellsVoice, video, data, and images

AAL ＋ ATM

ATM cell

Transmission processing

ATM cell

ATM cell Frame header and overhead

Physical medium processing

Frame to be transmitted

Physical interface


AAL

ATM

PH

IP

RFC1483

AAL

ATM

PH

Ethernet

RFC1483

Data Service on the ATM Network

RFC1483B encapsulation RFC1483R encapsulation







ATM Service Types

Constant bit rate (CBR) Constant bit rate service

Variable bit rate-real time (rt-VBR) Variable bit rate-real time service

VBR-non real time (nrt-VBR) VBR-non real time service

Unspecified bit rate (UBR) Unspecified bit rate service

Available bit rate (ABR) Available bit rate service


Traffic ParametersPCR Peak cell rate

SCR Sustainable cell rate

MCR Minimum cell rate

MBS Maximum burst size


CBR Service

Overhead

QoSTraffic parameter

Low High

Tolerance

1 byte

5-byte header

47-byte payload

Cell variationCell loss

PCR

Real time video and voice


VBR Service


Low High

Tolerance

Cell variation (NRT)Cell variation (RT)

PCR

SCR

MBSCell loss

Packet voice and video


UBR Service

Public WAN


Low High No guaranty of QoS

Tolerance

Cell lossCell variation


ABR Service

LAN

Overhead

. No celloverhead

. Uses congestionfeedbackinstead

5-byteheader

48-bytepayload


Low High

PCR

MCR

Tolerance

Cell loss Cell variation


Questions

What are the functions of each byte in the ATM cell header?

How does the ATM switch switches the ATM cells？ What services can the AAL1 and the AAL5 adapt respectively？ What packets do the RFC1483B and the RFC1483R protocol encapsulate

respectively？

谢谢www.huawei.com

09-ATM Pricinple-20090724-A

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