Data
Communication
Networks
Lecture 2
Network Models
Dr/ Amr Wageeh
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.
Protocol Hierarchies or Layering
Network Models
ISO International Standard Organization make
standardization to main task for operation (IEEE)
• OSI Model
An ISO standard that covers all aspects of network
communications is the Open Systems Interconnection (OSI)
model. It was first introduced in the late 1970s.
•TCP/IP Model
Widely used in internet
THE OSI MODEL
The interaction between layers in the OSI model
An exchange using the OSI model
Layered in OSI model
In this section 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 main task of the physical layer is to transmit raw bits over a communication channel.
• The design issues deal with mechanical, electrical, and procedural interfaces, and the
physical transmission medium, which lies below the physical layer.
• The physical layer may be sure that the given stream of bits was encoded and transmitted
Physical Layer
It’s responsible for all Physical properties of the
network :
Cable length.
Cable type.
Transmission mode.
Bit rate.
Synchronization of bits.
Voltage levels.
H/W interface types.
Data link layer
The data link layer is responsible for moving frames from one hop (node) to the next.
•Framing: To create and to recognize frame boundaries – typically by attaching special bit
patterns to the beginning and end of the frame,
•Error Control: To solve the problems caused by damaged, lost or duplicate frames
• Flow Control: To keep a fast transmitter from drowning a slow receiver in data.
• Physical addressing.
Hop to hop delivery
Network layer
The network layer is responsible for the delivery of individual packets from the
source host to the destination host.
•To implement the routing mechanism
• Logical addressing.
• To allow interconnection of heterogeneous networks
Source to destination delivery
Transport layer
The transport layer is responsible for the delivery of a message from one process
to another
• Segmentation and Re-assembler
•Multiplexing/Demultiplexing
•Flow control
•Error Control
Popular TCP/ UDP applications
Reliable process-to-process delivery of a message
Session layer
The session layer is responsible for dialog control and synchronization.
Presentation Layer
This layer is responsible for presenting the data in the proper format .
Translation. Compression. Securing.
Application layer
It’s the S\w on our PCs that is used to represent a user interface to the network &
so aids the user to make applications.
Summary of layers
TCP/IP PROTOCOL SUITE
The layers in the TCP/IP protocol suite do not exactly match those in the
OSI model.
The original TCP/IP protocol suite was defined as having four layers: host-
to-network, internet, transport, and application. However, when TCP/IP is
compared to OSI, we can say that the TCP/IP protocol suite is made of five
layers: physical, data link, network, transport, and application.
TCP/IP and OSI model
Relationship of layers and addresses in TCP/IP
