Introduction to TCP/IP and OSI model 1/12/20141Mr. Naresh Sharma, http:\\nareshsir.com.

$: Introduction to TCP/IP and OSI model 1/12/20141Mr. Naresh Sharma, http:\\nareshsir.com.$
Introduction to TCP/IP and OSI model

04/10/23 1Mr. Naresh Sharma, http:\\nareshsir.com

More OSI Info

• Who made up the OSI?

• It was created by the International Organization for Standardization (ISO)


The Open System Interconnection Model (OSI)

• The International Standards Organization (ISO) has developed a universal architecture for computer communications.

• This standard, Known as the open Systems Interconnection model, or OSI model.

• The purpose of OSI is to permit communications among devices made by manufacturers.


OSI Layers

• OSI has seven layers.• Each layer represents a particular function.• It could be, each function is preformed by a

separate piece of hardware or software.• Sometimes, a single program may performed the

functions of several layers.• All layers are necessary for communications to

occur.


OSI Layers

• The ISO-OSI model chooses to divided the function of computer communications into seven layers, though more or fewer could have been chosen.


What is the OSI Reference Model?

• It is a conceptual framework specifying the network functions that occur at each layer

• It is a way of picturing how information travels through networks.


OSI Reference Model (standard)

• Any application process should be able to communicate freely with any any application process in any other computer that supports the same standards…

• The OSI Reference Model shows how this takes place.


OSI Reference Model

• The OSI reference model describes how data makes its way from application programs through a network medium to another application located on another computer on a network


• To accomplish this task data must travel from the application layer to the physical layer on one computer across the network media and from the physical layer to the application layer of another computer

Computer A Computer B


OSI Reference Model Layers

• The Application Layer provides services to application processes (such as electronic mail, file transfer, and terminal emulation) that are outside of the OSI model.

• The application layer identifies and establishes the availability of intended communication partners (and the resources required to connect with them), synchronizes cooperating applications, and establishes agreement on procedures for error recovery and control of data integrity.


OSI Reference Model

• The Presentation Layer ensures that information sent by the application layer will be readable by the application layer of the receiving system.

• The presentation layer is also concerned with the data structures used by programs and therefore negotiates data transfer syntax for the application layer.04/10/23 11Mr. Naresh Sharma, http:\\nareshsir.com

OSI Reference Model

• The Session Layer establishes, manages, and terminates sessions between applications and manages data exchange between presentation layer entities

(Ensures Interhost communication)


OSI Reference Model

• The Transport Layer is responsible for reliable network communication between end nodes.

• The transport layer provides mechanisms for the establishment, maintenance, and termination of virtual circuits, transport fault detection and recover, and information flow control.


OSI Reference Model

• The Network Layer provides connectivity and path selection between two end systems.

• The network layer is the layer at which routing occurs.


OSI Reference Model• The Data Link Layer provides

reliable transit of data across a physical link.

• The data link layer is concerned with – physical addressing, – network topology, – line discipline, – error notification,– ordered delivery of frames, – flow control.


OSI Reference Model

• The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems


OSI Reference Model

Host Layers:}Media Layers:} Control physical delivery of

messages over a network

Provide accurate data delivery between computers


• As data moves down through the layers of the OSI model, headers are added.

Computer A


Computer B

• As data moves up through the layers of the OSI model, headers are removed.


OSI Reference Model

• There are other models by different vendors• Most vendors use the OSI Model• OSI is conceptual other than tangible• Used to educate how networks function at

each layer


What does the OSI Model do?

• It reduces complexity (from one big problem to 7 small ones)

• It standardizes interfaces• It facilitates modular engineering• It assures interoperable technology• Accelerates evolution• Simplifies teaching & learning


Review Time!

• Divide into two groups• Play Jeopardy• Bonus answer is the layer number


OSI Layers • The Lowest layer, Known as physical Layer

or Layer 1,– is responsible for transmission of bits. – Is always implemented by using hardware.– Is encompasses the mechanical, electrical, and

functional interface.– Is the interface to the outside world– using electronic signals as specified by

interface standards.


OSI Layers

• The Data Link Layer, Or Layer 2,– is responsible for ensuring error-free,– reliable transmission of data.– Scrutinizes the bits received to determine if errors

occurred during transmission.– Is able to request retransmission or correction of

any errors using protocols.


OSI Layers

• The Network Layer, or Layer 3,– is responsible for setting up the appropriate

routing of messages throughout a network– is concerned with he types of switching networks

used to route the data• Note:

Physical, Data Link, and Network layers are usually referred to as the lower layers


OSI Layers • The Transport Layer, or Layer 4,

– is responsible for isolating the function of the lower layers from the higher layers

– is responsible for monitoring the quality of the communication channel

– is responsible for selecting the most cost efficient communication service.

– accepts messages from higher layers, and breaks them down into messages that can be accepted by the lower layers


OSI Layers

• The Session Layer, or Layer 5, – is responsible for terminating the connection– requests a logical connection be established based

on the end user’s request– handles any necessary “log-on” and password

procedures.


OSI Layers

• The Presentation Layer, or Layer 6,– provides format and code conversion services– handles any necessary conversion different

character codes; example ASCII-to- EBCDIC


OSI Layers

• The Application Layer or Layer 7,– provides access to the network for the end user– determines the user’s capabilities on the network– some Application Layer software, permit remote

terminal to only access a host computer; other Application Layer software might also permit file transfers.


The TCP/IP Protocol Suite

• The TCP/IP Suite – is a collection of protocols originally designed for

use on an network connecting U.S. government agencies with universities performing research

– specifies protocols at various levels of the OSI model and covers a wide variety of tasks likely to be performed on an open network


Comparison of ISO-OSI Model and the DOD (TCP/IP) Model

Application

Application Presentation

Session

Transport Host-to-Host

Network Internet

Data Link Network Access

Physical

Source: http://starter.sdsu.edu/remote/demo/osi-tcp.html


http://starter.sdsu.edu/remote/demo/osi-tcp.html

LayersHow network hardware and software work together in layered fashion to make communication possible

Each layer covers different network activities , equipment and protocols.


OSI

• Open Systems Interconnection• developed by the International Organization

for Standardization (ISO)• has seven layers• is a theoretical system delivered too late!• TCP/IP is the de facto standard


OSI Layers


Application Provides access to the OSI environment for users and also provides distributed information service

Presentation Provides independence to the application process from difference in data representation (syntax)

Session Provides the control structure for communication between application; establishes, manages ___ terminates connection (session) between cooperating applications.

Transport Provides reliable, transparent transfer data between end points; provides end-to-end error recovery and flow control.

network Provides upper layer with independence from the data transmission and switching technologies used to connect systems; responsible for establishing, maintaining, and terminating connections.

Data Link Provides for the reliable transfer of information across the physical link; sends blocks of data (frames) with the necessary synchronization, error control ,and flow control

Physical Concerned with transmission of unstructured bit stream over physical medium; deals with the mechanical, electrical, functional and procedural characteristics to access the physical


Physical Concerned with transmission of unstructured bit

stream over physical medium Deals with the mechanical, electrical, functional

and procedural characteristics to access the physical medium

• 0,1 – Volt, duration, transmission characteristic directions, connectors pins


Data Link Provides for the reliable transfer of information

across the physical link Sends blocks of data (frames) with the

necessary synchronization, error control and flow control

• Frame, acknowledgment from lost, duplicate• Piggy backing


Network Provides upper layer with independence from the

data transmission and switching technologies used to connect systems

Responsible for establishing, maintaining, and terminating connections.

• Operations of subnet, Packet size• Routing, congestion control• network Addressing• Accounting• Broadcast networks


Transport Provides reliable, transparent transfer of

data between end points Provides end-to-end error recovery and

flow control. Addressing port, connection management Distinctive network connection, multiplexing


Session Provides the control structure for communication

between applications Establishes, manages and terminates

connections (sessions) between cooperating applications.

Dialog management Token Management synchronization


Presentation Provides independence to the application

processes from difference in data representation (syntax)

ASCII , Unicode


Application LayerProvides access to the OSI environment for usersProvides distributed information services.Web browsing (http) E-Mail (smtp)


Need For Protocol Architecture

• data exchange can involve complex procedures, cf. file transfer example

• better if task broken into subtasks• implemented separately in layers in stack

– each layer provides functions needed to perform comms for layers above

– using functions provided by layers below

• peer layers communicate with a protocol04/10/23 45Mr. Naresh Sharma, http:\\nareshsir.com

Key Elements of a Protocol

• syntax - data format• semantics - control info & error handling• timing - speed matching & sequencing


TCP/IP Protocol Architecture

• developed by US Defense Advanced Research Project Agency (DARPA)

• for ARPANET packet switched network• used by the global Internet• protocol suite comprises a large collection of

standardized protocols


Simplified Network Architecture


TCP/IP Layers

• no official model but a working one – Application layer– Host-to-host, or transport layer– Internet layer– Network access layer– Physical layer


Physical Layer

• concerned with physical interface between computer and network

• concerned with issues like:– characteristics of transmission medium– signal levels– data rates– other related matters


Network Access Layer

• exchange of data between an end system and attached network

• concerned with issues like :– destination address provision– invoking specific services like priority– access to & routing data across a network link

between two attached systems• allows layers above to ignore link specifics


Internet Layer (IP)

• routing functions across multiple networks• for systems attached to different networks• using IP protocol• implemented in end systems and routers• routers connect two networks and relays data

between them


Transport Layer (TCP)

• common layer shared by all applications• provides reliable delivery of data• in same order as sent• commonly uses TCP


Application Layer

• provide support for user applications• need a separate module for each type of

application


OSI v TCP/IP


TCP/IP Applications

• have a number of standard TCP/IP applications such as– Simple Mail Transfer Protocol (SMTP)– File Transfer Protocol (FTP)– Telnet


Some TCP/IP Protocols


Introduction to TCP/IP and OSI model 1/12/20141Mr. Naresh Sharma, http:\\nareshsir.com.

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