Asynchronous Transfer Asynchronous Transfer Mode (ATM)Mode (ATM)

Member’s Name:Member’s Name: Chen Sing TiongChen Sing Tiong (KL003676) (L)(KL003676) (L)Cheng Chin Tat Cheng Chin Tat (KL003832)(KL003832)Low Mei EeLow Mei Ee (KL003796)(KL003796)Ng Shook KienNg Shook Kien (KL003795)(KL003795)Pang Yin YeePang Yin Yee (KL003719)(KL003719)

Tan Lay KoonTan Lay Koon (KL003809)(KL003809)Tan Wee KhoonTan Wee Khoon (KL003844)(KL003844)

Yong Yen JenYong Yen Jen (KL003797)(KL003797)

What is ATM?What is ATM?• A transfer mode in which information is organised into cells

• International Telecommunication Union-Telecommunications Standards Section (ITU-T) standard for cell relay wherein information for multiple service types, such as voice, video, or data, is conveyed in small, fixed-size cells.

• Based on the efforts of the ITU-T Broadband Integrated Services Digital Network (B-ISDN) standard. It was originally conceived as a high-speed transfer technology over public networks. – Operates at Layer 2 of the OSI-RM

• Switching technology in WAN backbone network

• Minimal functionality in the network

• Provide faster packet switching

– ATM Layer, common to all services and provides packet transfer capabilities:

• fixed size cells• logical connections

– ATM Adaptation Layer (AAL), that is service dependent:

• supports information transfer protocols not based on ATM, by mapping the information into ATM cells

ObjectivesObjectives

1.1. Explain the cell establishment Explain the cell establishment connection in ATM.connection in ATM.

2.2. Explain the protocol architecture of ATM Explain the protocol architecture of ATM in relation with OSI model.in relation with OSI model.

3.3. ATM cell structure and it effect on the ATM cell structure and it effect on the performance of ATM network.performance of ATM network.

ATM Cell EstablishmentATM Cell Establishment

• When an ATM device wants to establish a connection with another ATM device, it sends a signaling-request packet to its directly connected ATM switch. This request contains the ATM address of the desired ATM endpoint, as well as any Quality of Services parameters required for the connection.

The ATM Connection The ATM Connection Establishment ProcessEstablishment Process

• ATM signaling uses the one-pass method of connection setup. An ATM connection setup proceeds in the following manner:

- Source end system sends a setup message

- Send call proceeding message - Destination end system receives setup message - Send a connect message - Send acknowledge message

The ATM Connection The ATM Connection Establishment Process (Con’t)Establishment Process (Con’t)

• First, source end system sends a setup message

- a setup message is forwarded to the first ATM switch (ingress switch) in the network.

• Send call proceeding message - This switch sends a call proceeding message

and invokes an ATM routing protocol. The signaling request is propagated across the network

The ATM Connection The ATM Connection Establishment Process (Con’t)Establishment Process (Con’t)

• Destination end system receives setup message

- The exit switch (egress switch) that is attached to the destination end system receives the setup message.

• Send a connect message - The egress switch forwards the setup

message to the end system across its UNI, and the ATM end system sends a connect message if the connection is accepted.

The ATM Connection The ATM Connection Establishment Process (Con’t)Establishment Process (Con’t)

• Send acknowledge message - The connect message traverses back

through the network along the same path to the source end system, which sends a connect acknowledge message back to the destination to acknowledge the connection. Data transfer can then begin.

ATM Devices Establish Connections Through the One-Pass Method

ATM Call EstablishmentATM Call Establishment

ATM Protocol ArchitectureATM Protocol Architecture• The ATM architecture is divided into 3 layers:

– ATM Adaptation Layer (AAL)• Convergence Sub-layer (CS)• Segmentation and Reassembly Sub-layer

(SAR) – ATM Layer– Physical Layer (PHY)

• Physical Layer Medium Dependent Sub-layer (PM)

• Transmission Convergence Sub-layer (TC)

ATM vs. OSIATM vs. OSI

Application

Presentation

Session

Transport

Network

Data Link

Physical

OSI Reference Model

B-ISDN Protocol Reference Model

(**) Common for all services

Source: ITU-T; I.371

Functions of B-ISDNFunctions of B-ISDN

Functions of the B-ISDN in relation to the Protocol Reference Model.Source: ITU-T; I.371

B-ISDN and ATMB-ISDN and ATM• B-ISDN is based on ATM (ITU-T et

al:1984-1988)• ATM is used to implement B-ISDN• B-ISDN uses optical fibre• A service requiring transmission

channels capable of supporting rates greater than the primary rate (ITU-T)

Layered ArchitectureLayered Architecture

ATMATM

PHYPHY

AALAAL

ATMATM NetworkNetwork UNIUNIUNIUNI

ATMATM

AALAAL

PHYPHY

• Physical Layer (PHY)• User Network Interface (UNI)• Different AAL Protocols for Different Traffic Types (e.g., data, voice, video)

Cell SwitchingCell Switching

End Station End StationSwitch

VoiceVoice

DataData

VideoVideo

AAAALL

PHY

PHY

ATM

PHY

ATM

PHY

ATM

AAAALL

Voice

Data

Video

Cells

• AAL: Inserts/extracts information into 48 byte payload• ATM Layer: Adds/removes 5 byte header to payload• PHY: Converts to appropriate electrical or optical format

Physical Layer (PHY)Physical Layer (PHY)

Speed MatchingSpeed Matchingand Framingand Framing

CableCablePlantsPlants

Wide Range of Wide Range of SpeedsSpeeds

LAN, MAN, LAN, MAN, WAN WAN CompatibilityCompatibility

Use Existing MediaUse Existing Media

Twisted PairTwisted Pair

CoaxCoax

FiberFiber

TransmissionTransmissionFrameFrame

PHY Sub-layersPHY Sub-layers

• PM:– Transmission medium, bit timing– Probably use existing standards and technology

• TC:– Specific to the PM– Cell delineation (identify beginning of cell)– Cell rate decoupling (inserting empty cells during

idle periods)

Transmission Convergence Transmission Convergence Sub-layer (TC)Sub-layer (TC)

Physical Layer Medium Dependent Physical Layer Medium Dependent Sub-layer (PM)Sub-layer (PM)

ATM LayerATM Layer

• Provide call transfer for all services• Functions:

– Generic Flow Control– Cell header generation/extraction– Cell VPI/VCI translation– Cell MUX/DEMUX

ATM Layer In Minor DetailATM Layer In Minor Detail

}}

48-Byte48-BytePayloadsPayloadsFrom AALFrom AAL 5-Byte Header5-Byte Header

Header Contains Virtual Header Contains Virtual PathPath

and Channel Identifiersand Channel Identifiers

53-Byte Cell53-Byte CellTo Physical LayerTo Physical Layer

•Adds/Removes Header To 48 Byte Payload•Header Contains Connection Identifier (VCI/VPI)•Multiplexes 53 Byte Cells Into Virtual Connections•Sequential Delivery Within A Virtual Connection

Source: ATM Forum

ATM Adaptation Layer (AAL)ATM Adaptation Layer (AAL)• Provide service dependent functions to higher layer

ExamplesClass A:

64 Kbps digital voiceClass B:

Variable bit rate encoded video?

Class C:Frame Relay over ATM

Class D:CCITT I.364 (SMDS) over ATM

AAL continue…AAL continue…• This division leads to four types of services:

– Class A: Constant Bit Rate (CBR) service, connection-oriented, with timing relation

– Class B: Variable Bit Rate (VBR) service, connection-oriented, with timing relation– Class C: VBR, connection-oriented, no

timing relation– Class D: VBR, connection-less, no timing

relation

ATM Adaptation LayerATM Adaptation Layer

48 Bytes48 Bytes

AALAAL TypesTypes11 Circuit EmulationCircuit Emulation

-Constant Bit Rate (CBR) -Constant Bit Rate (CBR)

Low Bit Rate Voice (Real Time)Low Bit Rate Voice (Real Time)

-Variable Bit Rate (VBR)-Variable Bit Rate (VBR)

Time Invariant Data (bursty data)Time Invariant Data (bursty data)

““Simple” Data Simple” Data

22

3/43/4

55

•Provides Mapping Of Applications To ATM Service Of The Same Type•Segments/Reassembles Into 48 Payloads•Hands 48 Bytes Payloads To ATM Layer (4 Bytes to adapt)

AAL Sub-layersAAL Sub-layers• Segmentation and Reassembly (SAR)

– segment data in native format into fixed length ATM cells and vice versa

• Convergence Sub-layer (CS)– error checking, removal of corrupted

cells– service specific

ATM In UseATM In Use

DataDataCellCell

VideoVideoCellCell

VoiceVoiceCellCell

In DetailIn DetailATM Cell Creation TransmissionATM Cell Creation Transmission

AdaptationAdaptationLayerLayer

ATMATMLayerLayer

PhysicalPhysicalLayerLayer

Conversion Conversion to ATM Data to ATM Data Types, 48-Types, 48-

Byte LengthByte Length

Forward Forward Cell Cell

Through Through NetworkNetwork

Add 5-Byte Add 5-Byte HeaderHeader

Convert To Convert To Correct Correct

Electrical Electrical Or Optical Or Optical

FormatFormat

VoiceVoiceCellCell

DataDataCellCell

VideoVideoCellCell

Services

ATM Cell Structure (cont.)ATM Cell Structure (cont.)• Two types of header

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

UNI header octet NNI header

Generic Flow Control Virtual Path Identifier 1 Virtual Path Identifier

Virtual Path Identifier VCI  2Virtual Path Identifier

  VCI 

Virtual Channel Identifier 3 Virtual Channel Identifier

VCI  Payload Type CLP 4 VCI  Payload Type CLP

Header Error Control 5 Header Error Control

ATM Cell StructureATM Cell Structure• fixed size of 53 bytes.

– 5 byte header• Virtual Channel Information (VCI)• Virtual Path Information (VPI)• Payload Type Information (PT)• Cell Loss Priority (CLP)

– 48 bytes information

ATM cell

48 bytes information5 byte header

ATM Cell Structure (cont.)ATM Cell Structure (cont.)• Header Fields:

– Generic Flow Control (GFC)- 4 bits. Used only for flow control protocols on shared medium user access networks. (UNI format only)

– Virtual Path Identifier- 8 (UNI) or 12 bits (NNI). Field constitute a routing field for the network. Allowing for more virtual paths to be supported within the network.

– Virtual Channel Identifier- 16 (UNI) or 20 bits (NNI). Field is used for routing to and from the end user.

ATM Cell Structure (cont.)ATM Cell Structure (cont.)– Payload Type - 3 bits. Used mainly for

Operations and Maintenance purposes.(5th edition, pg 335)

– Cell Loss Priority-1 bit. Used for congestion control purposes.

– Header Error Control (HEC)- 8 bits. Used for header error protection. Allows to correct single bit errors in the header. Also used in the cell delineation process (used to determine on which bit position the cell starts, i.e. cell synchronisation)

ATM CellsATM Cells• Fixed size( 5 octet header and 48 octet

information field)• Small cells reduce queuing delay for high priority

cells• Small cells can be switched more efficiently• Easier to implement switching of small cells in

hardware

ConclusionConclusion•Asynchronous Transfer Mode is the cell relay protocol designed by the ATM forum and adopted by the ITU-T

•The ATM data packet is called cell and composed of 53 bytes

•The cell network is based on permanent virtual circuit routing

•The ATM standard define three layers

AAL

ATM

Physical layer

Conclusion (cont.)Conclusion (cont.)

•ATM can handle or minimize the severity of:

Out of sequence packets

Delay time between packets of a message

Bit errors

•ATM cell have 2 types

UNI

NNI

Questions and AnswersQuestions and Answers(1) What is the definition of ATM?Answer: A transfer mode in which information is

organised into cells; for cell relay wherein information for multiple service types, such as voice, video, or data, is conveyed in small, fixed-size cells.

(2) What is the method used by ATM signaling for setup connection?

Answer: one-pass method

Questions and Answers Questions and Answers (cont.)(cont.)

(3) What are the 3 lower layer of the OSI stack which the ATM specific function ca be found?

Answer: ATM adaptation Layer (AAL),ATM layer, and Physical layer

(4) In AAL, which types of services that required timing between source and definition?

Answer: Class A, and Class B.

Questions and Answers Questions and Answers (cont.)(cont.)

(5) What is the header field consist in UNI ATM cell format?

Answer: GFC, VPI, VCI, PT, CLP and HEC.

(6) What is the 2 types header in ATM cell structure?

Answer: UNI and NNI