Osi tcp ip1 models

© 2007 Cisco Systems, Inc. All rights reserved. ICND1 v1.0—1-1

Building a Simple Network

Understanding the Host-to-Host Communications Model


Understanding Host-to-Host Communications

Older model– Proprietary– Application and combinations software controlled by one

vendor Standards-based model

– Multivendor software– Layered approach


Why a Layered Network Model?

Standardizes interfaces Facilitates modular engineering Ensures interoperable

technology Accelerates evolution Reduces complexity Simplifies teaching and learning


The Seven Layers of the OSI Model (Cont.)


The Application Layer• Example of the Application layer: File transfer Electronic mail Terminal access Web Browser Network management

– Simple Network Management Protocol

Name management– Domain Name System




The Presentation Layer

• Let’s look at what is happening:

I have a good file now.

I want that file too but in 3DES encryption format


The Presentation Layer

The Presentation ensures that the information that the application layer of one system sends out is readable by the application layer of another system.


The Presentation LayerActions of the Presentation layer: Format of data ( binary, BCD, ASCII…) Data structure ( .doc, .JPEG…) Data encryption ( DES, 3DES…)




The Session Layer


The Session Layer

• The Session layer establishes, manages, and terminates sessions between two communicating hosts.




The Transport Layer• The Transport layer can guarantee that packets are received.


The Transport Layer

• The Transport layers segments and reassembles ( lặp ráp ) data into a data stream


The Transport Layer

• Connectionless transmission• Connection-oriented transmission

• The three-way handshake

• Flow control

• Acknowledgement

• Windowing


The Transport LayerConnectionless transmissions

• Let’s look at what happens:

LocalPost Office

DestinationPost Office

Post Office system


The Transport LayerConnectionless transmissions(cont)

LocalPost Office


Post Office system

Host A

Internet

Local Router

Destination Router


The Transport LayerConnectionless transmissions(cont)

• User Datagram Protocol (UDP) is an example of connectionless protocol

• Applications that use UDP to send their data information is DNS, TFTP, SNMP….


The Transport LayerConnection-oriented transmissions

• Let’s look at what happens:

LocalPost Office


Post Office system


The Transport LayerConnection-oriented transmissions(cont)

LocalPost Office


Post Office system

Host A

Internet

Local Router

Destination Router


The Transport LayerConnection-oriented transmissions (cont)

• Transmission Control Protocol (TCP) is an example of connection-oriented protocol

• Applications that use TCP to send their data information is DNS, FTP, HTTP, HTTPs, SMTP, POP3, TELNET, SSH, …


The Transport Layerthe three-way handshake

• In connection-oriented transmission, both the sender and receiver have to establish the session.

• It is called three-way handshake


The Transport Layerthe three-way handshake (cont)

• Let’s look at what happens:• In the three-way handshake process, when Host A (sender) want to establish a session with Host B (receiver), it first send to the receiver a synchronize segment.

• Host B (receiver) after examine the synchronize packet from Host A, if agree, it will send acknowledgement synchronize segment to Host A.

Synchronize (Can I talk to you ?)

Ack (Yes), Synchronize ( Can I talk to you ?)

• Host A after receives the synchronize segment from Host B, it will send an acknowledgement segment to Host B to acknowledge to connection.

Ack (Yes)

Connection Established

Data Transfer(send segments)


The Transport layerFlow Control

• Once data transfer is in progress, congestion can occur for two reasons.


The Transport layerFlow Control (cont)

• First, the sending device might be able to generate traffic faster than the network can transfer it.



• The second reason is that multiple devices need to send data to the same destination.



• When datagram arrive too quickly for a device to process, it temporarily stores them in memory.

data

data



• If the datagrams are part of a small burst, this buffering solves the problem.

data

data



• However, if the traffic continues at this rate, the device eventually exhausts its memory and must discard additional datagrams that arrive.

datadata

datadata



• Instead of losing the data, the transport function can issue a “not ready” indicator to the sender.

datadata

datadata



datadata

datadata



• After the receiving device has processed sufficient segments to free space in its buffer, the receiver sends a “ready transport “ indicator –which is like a go signal.

datadata

datadata

go

Transport



go

Transport


The Transport LayerAcknowledgement

• The transport layer provide a reliable service regardless of the quality of the underlying network


The Transport LayerAcknowledgement (cont)

data

data


The Transport LayerWindowing• Acknowledging every data segment, however, has its drawback

(điều trở ngại).

data

• If the sender has to wait for an acknowledgement of each data segment, the throughput will be very low.

data


The Transport LayerWindowing (cont)

Sender

TCP

Receiver

TCP

You and I will use window size of 1 ?I agree

Send 1Ack 2

Send 2Ack 3


I agree

The Transport LayerWindowing (cont)

• Now let’s examine an example with windows size of 3.

Sender

TCP

Receiver

TCP

You and I will use window size of 3 ?

Send 1Send 2Send 3

Ack 4

Send 4

Send 6Send 5

Ack 5

Send 5

Ack 7






Ethernet Frame Structure


MAC Address Components


MAC Addresses


The Seven Layers of the OSI Model


Data Data Data

Data Stream

Data Stream Data Stream

Data

Data IP Header 1IP Header 1IP Header 1

IP Header 1IP Header 1Frame Header IIP Header 1Frame Header I IP Header 1Frame Header I IP Header 1

IP Header 1 Data

Data Data Data

Data Stream Data Stream

Application

Presentation

Session

Transport

Network

Data Link

Physical

Application

Presentation

Session

Transport

Network

Data Link

Physical


Defines four layers Uses different names for Layers 1

through 3 Combines Layers 5 through 7 into

single application layer

TCP/IP Stack


TCP/IP Stack vs. the OSI Model


Data Encapsulation


Summary

The OSI reference model defines the network functions that occur at each layer.

The information sent on a network is referred to as data or data packets. If one computer wants to send data to another computer, the data must first be packaged by a process called encapsulation.

When the remote device receives a sequence of bits, the physical layer at the remote device passes the bits to the data link layer for manipulation. This process is referred to as de-encapsulation.


Summary (Cont.)

TCP/IP is now the most widely used protocol for a number of reasons, including its flexible addressing scheme, its usability by most operating systems and platforms, its many tools and utilities, and the need to use it to connect to the Internet.

The components of the TCP/IP stack are the network access, Internet, transport, and application layers.

The OSI model and the TCP/IP stack are similar in structure and function, with correlation at the physical, data link, network, and transport layers. The OSI model divides the application layer of the TCP/IP stack into three separate layers.


Osi tcp ip1 models

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