ATM(Asynchronous Transfer Mode)

Presented By- Surbhi & Vasundhara

Content: What is ATM Network? ATM Protocol Architecture ATM Devices and the Network Environment ATM network interfaces ATM Cell Format ATM switching operation ATM Service Categories ATM Adaption Layer (AAL 1 to AAL 5) Advantages of ATM Network

What is ATM?• ATM Net = Data Net + Phone Net• Combination of Internet method of communication (packet

switching) and phone companies’ method (circuit switching)• International Telecommunication Union-Telecommunications

Standards Section (ITU-T) standard for cell relay • ATM networks are connection-oriented.• ATM virtual circuit: which is an end-to-end connection that has

defined end points and routes but does not have bandwidth dedicated to it.

• Bandwidth is allocated on demand by the network as users have traffic to transmit

ATM Protocol architecture

ATM Protocol architecture(cont.) ATM cell: fixed size packets for information flow Reduces overhead of processing and space (support high rate) Planes in ATM network: User plane: Provides for user information transfer, along with

associated flow and error control Control plane: Performs call control and connection control

functions Management plane: plane mgmt. & resources management as

per parameter of protocol entities.

ATM Protocol architecture(cont.) Physical layer :

Cells are converted into a bit stream The transmission and receipt of bits on the physical medium are

controlled. ATM cell boundaries are tracked. Cells are packaged into the appropriate types of frames for the

physical medium. Min data rate: 155.52 mbps : Max data rate: 622.08 Mbps

ATM Layer: independent of service demanded (common to all) Deals with AT cell transmission & use of logical connections

ATM Devices and the Network Environment An ATM network is made up of an ATM switch and ATM

endpoints. An ATM switch is responsible for cell transit reads and updates the cell header information and quickly

switches the cell to an output interface towards its destination. Examples of ATM endpoints are workstations, routers, digital

service units (DSUs), LAN switches, and video coder-decoders (Codec’s).

ATM Network Interfaces

ATM network interfaces

UNI(connects ATM end systems (such as hosts and routers) to

an ATM switch )

Public UNI Private UNI

NNI(Connects two ATM switches)

Public UNI Private UNI

ATM Cell Format

Each cell consists of 53 octets Small, fixed-length cells are well suited to transfer voice

and video traffic.

Header (5 Bytes) Payload (48 bytes)

CELL format in ATM Header(UNI)

GFC (4 bits) VPI (4 bits)

VPI (4 bits) VCI (4 bits)

VCI (8 bits)

VCI (4 bits) PT (3 bits) CLP (1 bit)

HEC (8 bits)

ATM cell header

Payload (48 bytes)

Generic Flow Control (GFC)—Provides local functions, such as identifying multiple stations that share a single ATM interface. This field is typically not used and is set to its default value of 0 (binary 0000).

CELL format in ATM Header(UNI)

GFC (4 bits) VPI (4 bits)

VPI (4 bits) VCI (4 bits)

VCI (8 bits)

VCI (4 bits) PT (3 bits) CLP (1 bit)

HEC (8 bits)

ATM cell header

Payload (48 bytes)

Virtual Path Identifier (VPI)—In conjunction with the VCI, identifies the next destination of a cell as it passes through a series of ATM switches on the way to its destination

CELL format in ATM Header(UNI)

GFC (4 bits) VPI (4 bits)

VPI (4 bits) VCI (4 bits)

VCI (8 bits)

VCI (4 bits) PT (3 bits) CLP (1 bit)

HEC (8 bits)

ATM cell header

Payload (48 bytes)

Virtual Channel Identifier (VCI)—In conjunction with the VPI, identifies the next destination of a cell as it passes through a series of ATM switches on the way to its destination.

ATM Logical connection

Two levels of ATM connections:• virtual path connections• virtual channel connections

Indicated by two fields in the cell header:• virtual path identifier VPI(identifies a particular VP link)

• virtual channel identifierVCI (numerical tag

to identifies a particular VC)

Physical Link

Virtual Paths

Virtual Channels

ATM switching operations

CELL format in ATM Header(UNI)

GFC (4 bits) VPI (4 bits)

VPI (4 bits) VCI (4 bits)

VCI (8 bits)

VCI (4 bits) PT (3 bits) CLP (1 bit)

HEC (8 bits)

ATM cell header

Payload (48 bytes)

• Payload Type (PT)—Indicates in the first bit whether the cell contains user data or control data. If the cell contains user data, the bit is set to 0. If it contains control data, it is set to 1.

• The second bit indicates congestion (0 = no congestion, 1 = congestion).

• The third bit indicates whether the cell is the last or not.

CELL format in ATM Header(UNI)

GFC (4 bits) VPI (4 bits)

VPI (4 bits) VCI (4 bits)

VCI (8 bits)

VCI (4 bits) PT (3 bits) CLP (1 bit)

HEC (8 bits)

ATM cell header

Payload (48 bytes)

Cell Loss Priority (CLP)—Indicates whether the cell should be discarded if congestion as it moves through the network.

If the CLP bit equals 1, the cell should be discarded in preference.

CELL format in ATM Header(UNI)

GFC (4 bits) VPI (4 bits)

VPI (4 bits) VCI (4 bits)

VCI (8 bits)

VCI (4 bits) PT (3 bits) CLP (1 bit)

HEC (8 bits)

ATM cell header

Payload (48 bytes)

Header Error Control (HEC)—Calculates checksum only on the first 4 bytes of the header. HEC can correct a single bit error in these bytes, thereby preserving the cell rather than discarding it.

ATM Service CategoriesATM

Service Categories

Real-Time Service

Constant bit rate(CBR)

Real-Time Variable bit rate(rt-VBR)

NON-REAL-TIME service

Non real-time variable bit rate(nrt-

VBR)

Available Bit rate(ABR)

Unspecified BIT

Rate(UBR)

Guaranteed Frame

Rate(GFR)

Tolerance of JITTER matters

here(tight constraints

of delay)

Busty traffic characteristics

(un-tight constraints of

delay)

Fixed rate throughout lifetime of

connection(telephony, video conf)

Time sensitive application

(video compression effect rate)

Data rate varies

Relative low delay and minimal loss cell

(End system have specify peak cell

rate)

FIFO based transmission acc. To

left resources (variable delay and

data rate)

Fair distribution of resources among

ABR sources(if left given to UBR)

Used for IP and Ethernet based sub

networks(sp. For frame based

network)

ATM Adaption layer

Higher Layers

ATM Adaptation Layer (AAL)Convergence Sub layer (CS)

Segmentation and Reassembly Sub layer (SAR)

ATM Layer (ATM) Virtual Channel (VC) Virtual Path (VP)

Physical Layer (PL) Transmission Convergence Sub layer (TC)

Physical Medium Sub layer (PM)

ATM Adaptation Layer Defines the rules for breaking up a higher level protocol data unit

(PDU) into ATM cells for transmission on the network, and for reassembling the PDU at the other end.

Segmentation and reassembly (SAR): breaks data into cells at the sender and reassembles cells into larger data units at the receiver.

Convergence sub layer: adds sequencing and control information to aid SAR process

TCPIP

AALATM

TCPIP

AALATMATM

Network

PDU

PDUCS-header Pad CS-trailer

Cellheader

Cellpayload

SAR-PDUheader

SAR-PDUpayload

SAR-PDUtrailer

SAR-PDUheader

SAR-PDUpayload

SAR-PDUtrailer

Higherlayer

CSlayer

SARlayer

ATMlayer Cell

headerCell

payload

Adaptation Layer : A detailed view

ATM Adaptation Layer

Connectionless Date Transfer

Bit Rate

Connection Mode

Examples of Services

CircuitEmulation

Constant Bit Rate Video and Audio

Constant Variable

Connection Oriented Connectionless

Variable Bit Rate Video and Audio

Connection- oriented Data Transfer

AALTYPE AAL 1 AAL 2

AAL 3/4AAL 5

Class A Class B Class C Class D

Related Not Related

Service

Timing betweenSource andDestination

AAL3/4AAL 5

AAL Type 1 Protocol Supports Class A traffic, i.e., constant bit rate data with specific requirements for

delay, delay jitter, and timing, e.g., PCM voice. Summary of AAL 1 functions

CS Functions Handling of cell delay variation Forward error correction for high quality video and audio Report end-to-end performance status

SAR FUNCTIONS Segmentation and reassembly of user information Sequence numbering Error protection Mapping between CS PDU and SAR PDU

Consists of 1 octet header (PCI) and 47 octets of payload Sequence Number (SN): A 1-bit Convergence Sub layer Indication and 3-bit

sequence count to detect deletion or miss insertion of cells Sequence Number Protection (SNP): 3-bit CRC with even parity for detecting

and correcting SN error

The 4 bit RTS is transferred by the CSI bit in successive SAR-PDU headers with an odd SN (SN = 1, 3, 5, 7)

For P format operations, the CSI value in SAR-PDU headers with an even SN (SN = 0, 2, 4, 6) is set to 1

SN SNP SAR-PDU Payload

4 bits 4 bits 47 Octets

Cyclic Redundancy Check Even Parity

1 bit3 bit

1 bit 3 bits

Convergence Sub layer Indication (CSI)

Sequence Number (SN)

AAL Type 2 protocol Deals with variable bit-rate information Intended for analog applications ,such as video and audio(CBR

not required)

Supports variable bit rate data where there is no timing relationship between source and destination, e.g., X.25, frame relay.

Convergence sublayer divided into two parts: Common Part Convergence Sublayer (CPCS) Service Specific Convergence Sublayer (SSCS)

AAL Type 3/4 protocol

AAL Type ¾ protocol

Types of services provided by AAL ¾ • Connectionless(independent packet) &

connection-oriented(multiple SAR logical connection)• Message mode(cell mode) & stream mode(block

mode)CPCS-PDU payloadCpcs header Cpcs-pdu trailerpad

CPI Btag BAsize AL ETag Length of payload

1 octet1 octet 1 octet 2 octet 2 octet1 octet

CPCS= common part convergence sub layer

SAR= Segmentation & Reassembly

PDU= protocol data unit

CPCS-H= caps header

CPCS-T = cpcs trailer

Sar-H= Sar headerSAR- H = SAR TailerATM-H = Atm headerBOM= beginning of msgCOM = continuation of message

AAL Type 5 Protocol AAL5 is a simple and efficient AAL (SEAL) to perform a subset

of the functions of AAL3/4 The CPCS-PDU payload length can be up to 65,535 octets and

must use PAD (0 to 47 octets) to align CPCS-PDU length to a multiple of 48 octets

CPCS-PDU Payload PAD CPI Length

1 2 40 - 47

CPCS UU

1

CRC-32

PAD PaddingCPCS-UU CPCS User-to-User IndicatorCPI Common Part IndicatorLength CPCS-PDU Payload LengthCRC-32 Cyclic Redundancy Chuck

AAL Type 5 SAR-PDU

PAD CPCS-PDU Trailer

CPCS-PDU

SAR-PDU Payload

CPCS-SDU

SAR-PDU Payload

SAR-PDU Payload

SAR-PDU Payload

SAR-PDU Payload

SAR-PDU SAR-PDU SAR-PDU SAR-PDUSAR-PDU

CPCS-PDU Payload

Advantages of ATM

Dynamic bandwidth for bursty traffic :meeting application needs and delivering high utilization of networking resources

Smaller header with respect to the data to make the efficient use of bandwidth.

Can handle Mixed network traffic very efficiently fixed size cell. Cell network: All data is loaded into identical cells that can be transmitted

with complete predictability and uniformity. Class-of-service support for multimedia traffic allowing applications with

varying throughput and latency requirements to be met on a single network.

Scalability in speed and network size supporting link speeds of (622 Mbps). Common LAN/WAN ATM technology can be used either as a LAN

technology or a WAN technology.

“Thank youfor

being connected”