NET331_Ch2x

NETWORK MODELS

T.Najah

Al_Subaie

Kingdom of Saudi Arabia

Prince Norah
bint

Abdul
Rahman

University

College of Computer Since and Information System

NET331

Chapter
2


LAYERED TASKS


OSI Model


TCP/IP Model


Layered Tasks


We use the concept of layers in our daily life. As an
example, let us consider two friends who
communicate through postal mail.


The process of sending a letter to a friend would be
complex if there were no services available from
the post office.


Tasks Involved in Sending a Letter


The OSI Model


Established in
1947
,


the International Standards Organization (ISO) is a
multinational body dedicated to worldwide
agreement on international standards.



An ISO standard that covers all aspects of network
communications is the Open Systems Interconnection
(OSI) model.


It was first introduced in the late
1970
s.


Note


ISO is the organization.


OSI is the model.


Seven layers of the OSI model

The OSI Model


ISO model is not a protocol. It is a model for
understanding and designing a network
architecture.


It shows how to facilitate communication between
different system without requiring changes to the
logic of the underlying hardware and software.

The OSI Model


It is a layered framework for the design of network
systems that allows communication between all
types of computer systems.


Consists of seven separated but related layers.


Each layer defines a part of the process of moving
information across a network

Layered Architecture


Each layer groups the networking functions that had
related uses.


Each layer uses the services provided by the layer
just below it.


Between machines, the corresponding layers are
communicated using a set of protocols.


Peer to Peer processes.



The interaction between layers in the
OSI model

The philosopher
-
translator
-
secretary
architectu

Interfaces Between Layers


Each interface defines the information and services
a layer must provide for the layer above it.


Interfaces allows the specific implementation of the
layer’s functionality to be changed or replaced
without requiring changes to the surrounding layers.

An exchange using the OSI model

Organization of the Layer


At the sender:



each layer adds a header or possibly a trailer.


At the receiver:


each layer removes its corresponding header or trailer
and performs the appropriate actions.


When the message reaches layer
7
(application
layer) , the message is in a form appropriate to the
applications.

Encapsulation


The data portion of a packet at level N
-
1
carries
the whole packet ( data and header/ trailer) from
level N.

Layers in the OSI Model.


We briefly describe the functions of each layer in
the OSI model
.


Physical Layer


Data Link Layer


Network Layer


Transport Layer


Session Layer


Presentation Layer


Application Layer


Physical Layer


The physical layer is responsible for movements
of individual bits from one hop (node) to the
next.


Physical Layer


It is also concerned with:


Physical characteristics of interfaces and medium.


Representation of bits.


Data rate.


Synchronization of bits.


Line configuration.


Physical topology.


Transmission mode.


Data Link Layer


The data link layer (DLL) is responsible for
moving frames from one hop (node) to the
next.




Data Link Layer


Data Link Layer


It is also concerned with:


Framing.


Data units in DLL.


Physical addressing


Adding header to define header/receiver of the frame.


Flow control


To avoid overwhelming the receiver.


Error control


A set of mechanisms to keep a reliable transmission.


Access control


To control the traffic in the link.


Hop
-
to
-
hop delivery by the DLL


Network Layer


The network layer is responsible for the

delivery of individual packets from the source
host to the destination host.


Network Layer

Source
-
to
-
Destination Delivery

Transport Layer


The transport layer is responsible for the delivery

of a message from one process to another.

Transport Layer

Transport Layer


It is also concerned with:


Service point addressing.


Segmentation and reassembly.


Connection control.


Flow control.


Error control.


Process to Process Delivery by the
Transport Layer

Session Layer


The session layer is responsible for dialog

control and synchronization.


Its functionalities:


Dialog control.


Synchronization.


Session Layer

Presentation Layer


The presentation layer is responsible for
translation, compression, and encryption.

Presentation Layer

Application Layer


The application layer is responsible for

providing services to the user.

Application Layer

Summary of Layers

TCP/IP Reference Model


the TCP/IP protocol suite is made of five layers:


physical,


data link,



network,



transport,


application.

TCP/IP and OSI model