McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 ATM (Asynchronous Transfer Mode) Cell Relay protocol designed by the ATM Forum and adopted by the ITU-T.

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

ATM(Asynchronous Transfer Mode)

Cell Relay protocol designed by the ATM Forum and adopted by the ITU-T

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Design Goals & Challenges

• To optimize the use of high-data-rate transmission media (Optical fiber)

• Need for a system that can interface with existing systems

• Need for a design that can be implemented inexpensively so that cost would not be a barrier to adoption

• The system must be able to work with and support the existing telecommunications hierarchies (local loops, local providers, long distance carriers and so on)

• The system must be connection-oriented to ensure accurate and predictable delivery.

• T move as many of the functions to hardware as possible.

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Multiplexing Using Different Packet Sizes

X – data packet

A, B, C - audio or video packet

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Multiplexing Using Cells

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

ATM Multiplexing

Cell networking

Cell – a small data unit of fixed sizeCell network uses the cell as the basic unit of data exchange

Advantage Predictability & uniformity – less delay

Interleaving – makes it possible to handle real-time transmissions

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Architecture of an ATM Network

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

TP, VPs, and VCs

Transmission path – physical connection (wire, cable, satellite) between an end point & a switch or between switches, divided into several VPs(set of all highways that directly connects two cities)

Virtual path – provides a connection or set of connections between two switches. (highway)

Virtual circuits – logically connects two points together, source and destination (lanes of a highway.)

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Example of VPs and VCs

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Connection Identifiers

Virtual connection is defined by a pair of numbers : the VPI and the VCI

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Virtual Connection Identifiers in UNIs and NNIs

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

An ATM Cell

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

2 Types of Connection

1. PVC- like a leased line2. SVC Setup shown at

the figure The actual mechanism depends on the network layer

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Two Types of Switches

• VP switch – route the cell using only the VPI- most of the switches in a typical network

• VPC – routes the cell using VPIs & VCIs– Allows hierarchical routing– Switches at the boundaries of the network, those that

interact directly with the end point devices

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Routing with a VP Switch

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

A Conceptual View of a VP Switch

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Routing with a VPC Switch

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

A Conceptual View of a VPC Switch

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Switch Fabrics

• Crossbar switch

• Knockout switch

• Banyan switch

• Batcher banyan switch

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Crossbar Switch

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Knockout Switch

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

A Banyan Switch

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Part I

Example of Routing in a Banyan Switch (a)

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Part II

Example of Routing in a Banyan Switch (b)

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Batcher-Banyan Switch

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

ATM Layers

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

ATM Layers in End-Point Devices and Switches

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

AAL Types• AAL1

– supports applications that transfer information at constant bit rates such as video & voice

– Allows ATM to connect existing digital telephone networks such as DS-3 or E-1– Applications: real time voice and video

• AAL2– Intended to support variable bit-rate applications– Applications: compressed voice, video, or data

• AAL3/4– AAL3 – intended to support connection-oriented data services– AAL4 – intended to support connectioness services– Applications: X.25 & TCP/IP

• AAL5– Simple and efficient adaptation layer (SEAL) – Assumes that all cells belonging to a single message travel sequentially– Applications: point-to-point internetwork transmissions

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

AAL Types

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

AAL1

CSI – for signaling purposes – not yet clearly defined

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

AAL2SAR – 45 bytes

Header – 1 byte- 1 bit – CSI CS identifier- 3 bits – SC sequence count – modulo 8, for

ordering and end-to-end flow and error control- 4 bits – IT information type – identify the data

segment as falling at the beginning , middle or end of the message

Trailer – 2 bytes- 6 bits – LI length indicator – used with the final segment of a message (to know the length of data in the final

cell – how mush is data, how much is padding)- 10 bits – CRC – for the entire data unit

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

AAL3/4

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Header & Trailer at CS

Note: each field added in CS is in byte• T – 0• BT – for sync, & identifies the first cell• BA – tells the receiver how much buffer size is

needed for the coming data• AL – to make the rest of the trailer 4 bytes long• ET – for sync• L – indicates the length of the data unit

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Header & Trailer at SAR

• ST (segment type)– beginning, middle, end of message or single-segment message

• SC (sequence count)– for end-to-end error and flow control

• MID (mux id) – Identifies cells coming from different data, flows & multiplexed on

the same virtual connection

• LI (length indicator) – used with the final segment of a message, identified by ST (to know

the length of data in the final cell – how mush is data, how much is padding)

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

AAL5

UU – left to the discretion of the userT – reserved but not yet definedL – how much of the message is data, how much is padding

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

ATM Layer

ATM layer provides routing, traffic management, switching and multiplexing services

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

ATM Header

CLP – for congestion control

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Payload Type (PT) Fields

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Service Classes

Constant bit rate – real time audio& video servicesVariable bit rate ( real time & nonreal time) – audio & video that use

compression techniqueAvailable bit rate – bursty data, delivers cell at a minimum rateUnspecified bit rate – does not guarantee anything

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Service Classes and Capacity of Network

of the network

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

QoS

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

User Related Attributes

• Sustained cell rate (SCR) – Average cell rate over a long time interval

• Peak Cell rate (PCR)– Sender’s maximum cell rate

• Minimum Cell Rate– Minimum cell rate acceptable to the sender

• Cell variation delay tolerance (CVDT)– Measure of the variation in cell transmission times– Ex. CVDT = 5ns, it means that the difference between the min &

max delays in delivering the cells should not exceed 5ns

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Network Related Attributes

• Cell loss ratio (CLR) – Fraction of cells lost

• Cell transfer delay (CTD)– Average time needed for a cell to travel from source

to destination

• Cell delay variation (CDV)– Difference between the CTD max and CTD min

• Cell error ratio (CER)– Fraction of cells delivered in ratio

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

ATM WAN Routers with 2 stacksof protocol