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
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