DIT

Dar es Salaam institute of Technology (DIT)

ETU 07420

Switching Systems

Ally, J

jumannea@gmail.com

DIT

Asynchronous Transfer Mode (ATM)

DIT

To provide a high-speed, low delay

multiplexing and switching network to any type of

user traffic, such as voice support, data,or video

applications.

Why do we need a new technology?

DIT

What is ATM?ATM for Telecommunications is Asynchronous

Transfer Mode, (not Automatic Teller Machine!).ATM is a flexible high bandwidth, low delay

network technology that is capable of handling voice, video and data on a single network; and mostly used in the backbone

In general, ATM means that traffic is carried in small, fixed-length packets called cells.

A technology that integrates advantages of circuit switch and packet switch.

ATM can support any type of user services, such as voice, data, or video service.

DIT

ATM Overview

53byte fixed length cell= 5Bytes cell header+48Bytes payload.

ATM must set up virtual connection before communication.

ATM network will confer with terminal on parameter of QoS before the connection is set up.

Contract

5-Bytes Header

48-Bytes Payload

DIT

ATM can provides both CBR and VBR transport

DIT

Connectionless & Connection-oriented

Setup

Setup

SetupSetu

p

Connectionless: Every packet is transferred from different routes, so the receiving order of packets doesn’t possibly depend on the sending order.

Connection-oriented : All packets are transferred from the same route , so the receiving order of packets depends on the sending order. Time delay is fixed.

DIT

ATM Switch Model’s Characteristic Any user’s cell will not be send

periodically, and bandwidth will be shared and statistically multiplexed.

Many types of service can be transferred in the same time and Quality of Service is supported in an ATM network.

Fixed length cell, so switch can be controlled by hardware and high-speed switching is easy to be realized.

DIT

ATM’s Advantage Integration of various services such as voice, image, video, data and

multimedia.

Standardization of network structures and components. This results in cost savings for network providers.

Transmission that is independent of the medium used PDH, SDH, SONET and other media can be used to transport ATM cells.

ATM is scaleable, i.e. the bandwidth can be adapted extremely flexibly to meet user requirements.

Guaranteed transmission quality to match the service required by the user (quality of service, QoS).

DIT

ATM’s Application In Switching:

Traditional Exchange is evolving into Broadband Exchange by ATM’s application

In Transmission: ATM virtual path exchange node and ATM

Add/Drop Multiplexer

In Internet: ATM router applied in IP Switching, Multi-Protocol

Label Switching

DIT

ATM Network Model

UNI

UNI

UNI

PNNI

PNNI

NNI NNI NNI

NNI

NNI

NNI

NNI

ICI Other Network

NNI ： Network Node InterfaceUNI ： User Node InterfaceICI ： Inter-carrier InterfacePNNI ： Private Network Node Interface

DIT

ATM InterfacesThe following ATM interfaces have been defined and standardized Private UNI (user-node interface) –specification of the interface

between a user’s device (e.g. a workstation) and a private ATM switch

Private NNI (network-node interface) –e.g. between private ATM switches needed to support the ATM infrastructure

Public UNI–specification of the interface between the user’s device and a provider of a public ATM service

Public NNI–interface between ATM switches in public carrier networks.

Also referred to as B-ISSI (broadband inter-switching system interface) when applied to the connection between two public

switches of the same carrier Also referred to as B-ICI (broadband inter-carrier interface) when applied to the connection between two carriers networks

DIT

ATM Cell

DIT

ATM Cell GFC ( Generic Flow Control): It is intended for control of a possible

bus system at the user interface and is not used at the moment. VPI ( Virtual Path Identifier): The VPI contains the second part of the

addressing instructions and is of higher priority than the VCI. VCI ( Virtual Channel Identifier): VCI in each case indicates a path

section between switching centers or between the switching center and the subscriber.

PTI ( Payload Type Identifier): Indicates the type of data in the information field.

CLP ( Cell Loss Priority): Determines whether a cell can be preferentially deleted or not in the case of a transmission bottleneck.

HEC ( Header Error Control): Provided in order to control and, to some extent, correct errors in the header data that may occur. The HEC is used to synchronize the receiver to the start of the cell.

DIT

ATM Connection There are two types of ATM connections

Virtual path connections –identified by virtual path identifiers (VPI) Virtual channel connections –identified by a combination of virtual path

and circuit identifiers (VPI and VCI) Virtual channels (VC)

are the basic unit that carry a stream of ATM cells from one user to another are identified by a virtual channel identifier can be configured statically as PVCs (permanent virtual circuits) that are

set up at network configuration time and dynamically as SVCs (switched virtual circuits) that are dynamically configured on-demand

can be bundled together into virtual path connections Virtual paths (VP)

contain one or more virtual channels are identified by a virtual path identifier are routed through a network as a single entity can be used internally for bundling virtual circuits between switches

DIT

Port 1 VPI=2 VCI=37

VPI=3 VCI=39

NNI

UNI

UNI

ATM Cell Switching

ATM Switch

Port VPI VCI 1 2 37 2 1 51

Port 2

Port 1 ATM Switch

Port VPI VCI 1 1 51 2 3 39

Port 2

ATM TerminalUser B

User A

ATM Network Node

Cell and user’s data change each other

VPI=1 VCI=51

ATM Network Node

ATM TerminalCell and user’s data change each other

DIT

Permanent Virtual Channel (PVC): The connections are analogous to leased lines that are switched between certain users. A change can only be made by the network provider. This type of ATM network often forms the initial stage in the introduction of this technology.

Switch Virtual Channel (SVC): Users connected to this type of network can set up a connection to the user of their own choice by means of signaling procedures. This can be compared with the process of dialing a telephone number.

Signaling In ATM

DIT

Types of ATM Virtual ConnectionAccording to the switching mode, ATM Virtual Connection can be classified :

VPC (Virtual Path Connection)

VCC (Virtual Channel Connection)

According to connection establishment, ATM Virtual Connection can be classified:

SVC(Switching Virtual Connection)

PVC(Permanent Virtual Connection)

DIT

UNI cell

VPC and VCCATM terminal A C

ATM network node G UNI cell

NNI cell NNI cellVC

switching

VCC

VPC

VCC

UNI cell UNI cell

B DFor example: When E receives cells from A or B, which would be transferred to C or D, the VPI of these cells would be set to uniform value in E. These cells would be received by G and switched to F by VP switching. Then the cells will be delivered to C or D at F. It means that VPC has been set up between E and F, while VCC has been set up among A, B, C and D.

E F

VP switching

VC switching

DIT

Cells

Voice

Data

Video

Connection oriented Fast packet switching Statistical multiplexer Supports voice, data and video service Provides QoS

Features of ATM

DIT

ATM Protocol Structure Model

USER

SAAL

ATM Layer

Physical Layer

AAL

USERService and signaling of user

Information of user and cell conversion

Cell exchange and multiplexing or demultiplexing

Frame structure physical medium

Impartiblemanagement of all layer

Independent management of every layer

Call connection and Control

User information 、 Flow Control and Error Recovery

Interface ManagementLayer Management

Control interface User interface

DIT

Three Communications Planes The user plane transports the user data for an

application. It uses the physical, ATM and ATM adaptation layers to do this.

The control plane takes care of establishing, maintaining and clearing down user connections in the user plane. The key word here is signaling.

The management plane includes layer management and plane management. Layer management monitors and coordinates the individual layer tasks. Plane management handles monitoring and coordination tasks in the network.

DIT

ATM Sublayer ModelATM Protocol Stack Model OSI Reference Model

User

PMD

TCPHY

ATM

AALCS

SARInterface manage

ment

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data link

1 Physical

DIT

Two sublayers:

Transmission Convergence Sublayer (TC)

transmission frame generation/recovery Processing HEC (Header Error Control) cell delimiting transmission frame adaptation

Physical Medium Dependent Sublayer (PMD)

Link coding Network physical medium

Function of ATM Physical Layer

AAL

ATM

PHY

DIT

Cell switch

Quality of Service

Processing the cell header

Types of payload

Multiplexing /Demultiplexing of different connection cell

Function of ATM Layer

AAL

ATM

PHY

DIT

Support services for user

Segment and reassemble

Complete the change between User-PDU and ATM payload

Function of ATM Adaptation Layer (AAL)

AAL

ATM

PHY

DIT

Function of ATM AAL OverviewFunction of ATM AAL:

Provide a high-speed,

low delay multiplexing

and switching network

to support any type of

user service, such as

voice, data,or video

applications.

ATM Payload

ConstantBit Rate

Data Bursts

Variable Bit Rate

ATM Cell

Multiplexing

AAL SDU

DIT

Types of AAL

In order to support different types of user services, there are five types of AAL. AAL type 1–meets the needs of class A servicesAAL type 2–meets the needs of class B servicesAAL type 3/4-meets the needs of class C and D servicesAAL type 5–meets the needs of class D services

Service type A B C DBit rate constant variable variable variable

Real time YES YES NO NOConnection mode Connection oriented connectionless

AAL AAL1 AAL2 AAL3/4 AAL5

DIT

Service Types of ATM layer CBR (Constant bit rate) Intended to support real-time applications requiring tightly constrained delay variation (e.g. voice, video) VBR-NRT (Variable bit rate-non real time) Intended for non-real-time applications with bursty traffic (e.g. multimedia-email) VBR-RT (VBR-real time) intended for real-time applications with bursty traffic (e.g. compressed video/voice) UBR (Unspecified bit rate) Represents a “best-effort service intended for non-real-time applications that do not require tightly constrained delay or delay variation and are tolerant to cell loss ( widely used today for TCP/IP) ABR (Available bit rate) similar to UBR but enhanced to handle applications that require a minimum bandwidth requirement (e.g. email and file transfer)

DIT

(IP over ATM) IPOA Protocol Stack

ATM network Physical layer

IP address is mapped to PVC or SVC

User application

ATM

AAL

IP

TCP/UDP

ATM

AAL

IP

TCP/UDP

IP packet is transferred to ATM Payload

User application

DIT

TCP/IP ProcessApp DataTCP Header

TCP header App DataIP Header

IP Header TCP Header App DataLLC

SAR-SDU#1 SAR-SDU#2 SAR-SDU#3 SAR-PDU#4 SAR-PDU#5

TCP

IP

SNAP/LLC

AAL5CS

SAR

ATM

PHY

Cell header will be added to SAR-PDU, whose VPI and VCI depends on the map table of IP address to PVC/SVC. Then ,the cells will be sent to Physical Layer.

Perform the transmission of ATM cells via physical media.

LLC IP Header TCP Header App Data PAD CPCS-PDU Tail

DIT

Thanks!

Technology changes but communication lasts.