Tài liệu Chapter 5: LAN ARCHITECTURE ATHENA . pdf

ATHENA
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
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Content
~ Introduction
~ Open Systems Interconnection (OSI)
Reference Model
~ How network sends data
~ Access Method
~ Summary
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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

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Introduction (2)
~ To solve the problem of networks being
incompatible 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
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Open Systems Interconnection
~ The OSI model organizes communication
protocols into seven levels:
• The Physical Layer
• The Data Link Layer
• The Network Layer
• The Transport Layer
• The Session Layer
• The Presentation Layer
• The Application Layer
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Open Systems Interconnection (2)
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Packet Assembly & Disassembly Process
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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
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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
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Layer 5: The Session Layer
~ Performs name recognition and allows
two applications on different computers
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
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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
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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
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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
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Layer 2: The Data Link Layer (2)

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Layer 1: 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
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Layer 1: Physical Layer (2)
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How Networks Send Data
~ Two reasons why large chunks of data tie up
network
• Large chunk of data generate a problem traffic
during transmission
• Timely interaction and communication impossible
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How Networks Send Data (2)
~Large Streams of Data
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How Networks Send Data (3)
~Why network divided data to packets?
• Packets : small chunks/frames of data
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How Networks Send Data (4)
~ Special control info sent with each

packet
• Send the original, disassembled data in small
chunks
• Reassemble the data in the proper order at
destination
• Check data for errors
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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)
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How Networks Send Data (6)
~ Packet components:
• Source address
• Data intended for transmission
• Destination address
• Instructions that tell network how to pass
data
• Info for receiving computer on how to
reassemble packets
• Error checking info
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How Networks Send Data (7)
~ Components have three sections:
• Header
• Data
• Trailer

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How Networks Send Data (8)