Tài liệu Chapter 5: LAN ARCHITECTURE ATHENA . pdf

Introduction © Sending Data ¢ Recognize data ¢ Divide data into manageable chunks ¢ Add information to each chunk Location of data Identify receiver ¢ Add timing and error checkin

Chapter 5: LAN ARCHITECTURE

ATHENA

Objectives

© Identify the seven protocol layers of the

Open System Interconnection (OSI) Reference Model

© Discuss the functional attributes of each

layer of the Open Systems

Interconnection Reference Model

© Understanding Putting Data on the

Cable and Access Methods

Introduction

© Sending Data

¢ Recognize data

¢ Divide data into manageable chunks

¢ Add information to each chunk

Location of data

Identify receiver

¢ Add timing and error checking

® Put data on the network and send it

© Protocols: procedures to send data

ATHENA

Introduction (2)

© To solve the problem of networks being

incom patible and unable to

communicate with each other, the

International Organization for

Standardization (ISO) released the Open

Systems Interconnection (OSI) reference

model in 1984

© First standard to describe architecture

for dissimilar devices to communicate

© Best known and widely used

Open Systems Interconnection

© The OSI model organizes communication

protocols into seven levels:

¢ The Physical Layer

¢ The Data Link Layer e¢ The Network Layer

e The Transport Layer

¢ The Session Layer

¢ The Presentation Layer

¢ The Application Layer

ATHENA

Open Systems Interconnection (2)

Packet Assembly & Disassembly Process

Layer 7: The Application Layer

© Topmost layer

© Window for application processes to access

network services

© User-end interface that support transfer files,

access database, e-mail

© Handles general network access, flow control,

error recovery

ATHENA

Layer 6: The Presentation Layer

© Determines format to be used to exchange data

© Called the network translator

© Responsible for protocol conversion, translating

data, encrypting data

© Manages data compression

© Redirector utility operates at this layer

ATHENA

Layer 5: The Session Layer

© Performs name recognition and allows

two applications on different com puters establish, manage and end a connection

(session)

© Provides synchronization between user

tasks by placing checkpoints in the data

stream

© Implements dialog control between

communicating processes

ATHENA

Layer 4: The Transport Layer

© Ensures packets are delivered error free,

in sequence, no losses or duplication

© Repackages messages, breaking up into

smaller packets

© Unpacks message at receiving end and

sends acknowledgement

© Provides flow control, error handling,

solves transmission problems

ATHENA

Layer 3: The Network Layer

© Addresses messages, translates logical

addresses/names into physical addresses

© Organizes data into packets then

forwards them to their destination

© Determines the best route on the

network based on network conditions,

priority of service

© Manages traffic problems and controls

congestion of data

Layer 2: The Data Link Layer

© Sends data frames from network layer to

physical layer

© Data frame: organized logical structure in

which data can be placed

¢ Simple data frame: Destination ID, Sender ID,

Control, Data, CRC (cyclical redundancy check)

© Provides error free transfer of frames

from one computer to another through

the physical layer

ATHENA

Layer 2: The Data Link Layer (2)

Layer |: Physical Layer

© Responsible for the mechanical, electrical and

procedural characteristics of the transmission (transmit the unstructured raw bit stream over

a physical link)

© Establishes and maintains physical link

between communication computers

© Defines how the cable is attached to the NIC

© Transmit bit (0,1) from one computer to

another

Layer |: Physical Layer (2)

How Networks Send Data

How Networks Send Data (2)

©Large Streams of Data

ATHENA

How Networks Send Data (3)

OWhy network divided data to packets?

« Packets : small chunks/frames of data

How Networks Send Data (4)

How Networks Send Data (5)

© Packets may contain:

¢ Information such as messages

¢ Types of computer control data, commands, service requests

¢ Session control codes (error correction)

ATHENA

How Networks Send Data (6)

How Networks Send Data (7)

How Networks Send Data (9)

How Networks Send Data (10)

¢ Contains error checking component (CRC)

¢ CRCis a mathematical calculation done on

data

ATHENA

How Networks Send Data (11)

© Packet Creation

¢ Begins at Application layer

e As data descends through each layer, more info is added at each layer

ATHENA

How Networks Send Data (12)

Access Methods (2)

© An access method is a Set of rules

defining how acom puter puts data on

and takes off a network cable

© Prevent simultaneous access to the cable

ATHENA

Contention

© Contention means that the computer are

contending for use of the transmission medium (first come, first served)

© Specifications for contention-based

access methods include procedure for how to avoid collisions and what to do if collision occurs

© Contention-based access methods

include:

¢ CSMA/CD

CSMA/ CD

© CSMA/CD is stand for Carrier-Sense

Multiple Access/ Collision Detection

© Multiple access is when two devices

begin to talk at the same time

© Carrier sensing refers to the process ofa

device looking for a clear channel before sending a message

© IEEE 802.3

CSMA/ CD (2)

© Checks the cable for network traffic

¢ Computer listens to the network

e If the network is not busy, that computer can send data

e If the network is busy, the computer refrains from transmitting until the network quiets down

ATHENA

ATHENA

CSMA/CD (4)

© Carrier detection mechanism:

¢ Computers continue to listen to the network

as they transmit

¢ Ifa computer detects another signal that interferes with the signal it Is sending, it

stops transmitting

¢ Both computers then wait a random amount

of time and attempt to retransmit

ATHENA

Summary

© This topic examined:

¢ OSI and seven layers

¢ How network sends data

°® Access Methods

ATHENA