high speed networks lecture 3

High Speed Networks

Lecture 3

Uday Prakash uday3prakash@gmail.com

Content to be covered

• Motivation for ATM• Definition of ATM• Genesis of ATM

Motivations for ATM

• There exist too many networks already.• But each one tailored (designed) for a specific

service requirement.• It is desired to have a single platform capable of

handling all the requirements.• single platform– Better network management– Reduced operational costs– Greater flexibility to network infrastructure

Motivations for ATM

• ATM is developed to fulfill this need.• So, for its realization, it deserves– Single Platform To provide end to end connectivity.

– Universal Platform that integrates different network services.

• Provisioning of Single Platform is called Seamless Networking

Seamless Networking

• Geographical distance between communicating entities must be hidden from end users (including time taken to fetch data from remote server, propagation time,..).

• This response time is different for LANs and WANs.

• ATM answers this problem by providing a common medium of transmission in both LAN and WAN environments.

Seamless Networking

• Generally, WANs provide lower data rates than LANs

• ATM overcome this problem as it is a point-to-point based technology. It has common LAN/WAN transmission medium.

Universal Platform

• Requirement to have a universal platform that can support different types of applications.

• Before ATM, networking fraternity was divided into two factions:1. Telecommunication world

backed by ITU-T.2. Data communication world

backed by IEEE, ISO and IETF

Universal Platform

Telecommunication world• ITU-T• Priority: voice transmission• ISDN paved a digital pipe

for Integrated (Multimedia) services.

• Failure of ISDN to provide Universal Platform, lead to the invention of B-ISDN

Data communication world

• ISO, IETF, IEEE• Priority: Data

transmission• VOIP made voice

transmission comfortable

• ATM was developed to provide a synergy between these two worlds.

Network Failures Vs Successes

Requirements for Success

• Low cost• High Performance Killer Applications• Timely Completion • Management• Interoperability• Coexistence with legacy LANs• Existing Infrastructure is more important than

new technology

ATM-definition

• Asynchronous Transfer Mode• It is the transfer mode in which information is

organized into cells, it is asynchronous in the sense that the recurrence of cells containing information is not periodic.

• Standardized as ITU-T I.113

MUX

`

Wasted bandwidth

ATM

TDM

4 3 2 1 4 3 2 1 4 3 2 1

4 3 1 3 2 2 1

Voice

Data packets

Images

Asynchronous Transfer Mode (ATM)

What in ATM?

ATM • ATM standard (defined by CCITT) is widely accepted

by common carriers as mode of operation for communication – particularly BISDN.

• ATM is a form of cell switching using small fixed-sized packets.

Header Payload

5 Bytes 48 Bytes

Basic ATM Cell Format

Leon-Garcia & Widjaja: Communication Networks

ATM Conceptual ModelFour Assumptions

1. ATM network will be organized as a hierarchy.User’s equipment connects to networks via a UNI (User-

Network Interface).Connections between provided networks are made through

NNI (Network-Network Interface).

2. ATM will be connection-oriented.A connection (an ATM channel) must be established before any cells are sent.

X

X

X

X

X

X

X

X

X

Private UNI

Public UNI

NNI

Private NNI

Private ATM network

Public UNI

B-ICI

Public UNIPublic ATM network A

Public ATM network B

Figure 9.5Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

ATM Connections

• two levels of ATM connections:virtual path connectionsvirtual channel connections

• indicated by two fields in the cell header: virtual path identifier VPI virtual channel identifier VCI

Physical Link

Virtual Paths

Virtual Channels

Figure 7.40

ATM Virtual Connections

Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

ATM Conceptual Model Assumptions (cont.)

3. Vast majority of ATM networks will run on optical fiber networks with extremely low error rates.

4. ATM must supports low cost attachments• This decision lead to a significant decision – to

prohibit cell reordering in ATM networks. ATM switch design is more difficult.

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)

Figure 9.7

UNI Cell Format

Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

2

3

N

1Switch

N

1…

5

6

video 25

video

voice

data

32

32 61

2532

3261

75

67

3967

N1

32

video 75

voice 67

data 39

video 67

Figure 7.38

…

…

ATM Cell Switching

Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

c ATMSw1

ATMSw4

ATMSw2

ATMSw3

ATMDCC

ab

de

VP3 VP5

VP2

VP1

a

bc

deSw = switch

Figure 7.39

Digital Cross ConnectOnly switches virtual paths

Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

25

Plane managem

entManagement plane

Control plane User plane

Physical layer

ATM layer

ATM adaptation layer

Higher layers Higher layers

Layer managem

ent

Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

ATM-layers

Cell Switching and Jitter

References

• Sumit Kasera, “ATM Networks-concepts and Protocols”, 2e, Tata McGraw Hill publications, ISBN-10: 0-07-058353-6.

• Harry Perros, “ATM Networks”.• Leon-Garcia & Widjaja, “ Communication

Networks”.• ATM network Simulatorhttp://w3.antd.nist.gov/Hsntg/req_atm-sim.html.