Computer Network in Computer Science Engineering, Study Guides, Projects, Research of Computer Networks

Download Computer Network in Computer Science Engineering and more Study Guides, Projects, Research Computer Networks in PDF only on Docsity!

Program Name :B.Tech

Semester :ECE 6th Sem

Course Name: Computer Network

Course Code:EC 602

Facilitator Name: Megha Dewan

Topic Name:- Introduction to OSI Layer

Contents of Topic: Behrouz A. Forouzan

Learning Outcome: Students get to know about basics of

Computer Network

UNIT No. 1

2-1 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.

Topics discussed in this section:

Sender, Receiver, and Carrier

Hierarchy

2. 4

Figure 2.1 Tasks involved in sending a letter

2. 5

ISO is the organization.

OSI is the model.

Note

2. 7

Figure 2.2 Seven layers of the OSI

model

2. 8

Figure 2.4 An exchange using the OSI

model

2.

2-3 LAYERS IN THE OSI MODEL

In this section we briefly describe the functions of each

layer in the OSI model.

Topics discussed in this section:

Physical Layer

Data Link Layer

Network Layer

Transport Layer

Session Layer

Presentation Layer

Application Layer

2.

The physical layer is responsible for movements of

individual bits from one hop (node) to the next.

Note

2. 13

• Physical characteristics of interfaces and medium. The

physical layer defines the characteristics of the interface

between the devices and the transmission medium. It also

defines the type of transmission medium.

• Representation of bits. The physical layer data consists of a

stream of bits (sequence of Os or 1s) with no interpretation.

To be transmitted, bits must be encoded into signals--

electrical or optical. The physical layer defines the type of

encoding (how Os and I s are changed to signals).

Other responsibilities of the Physical layer

Physical topology. The physical topology defines how devices

are connected to make a network. Devices can be connected by

using a mesh topology (every device is connected to every other

device), a star topology (devices are connected through a central

device), a ring topology (each device is connected to the next,

forming a ring), a bus topology (every device is on a common

link), or a hybrid topology (this is a combination of two or more

topologies).

Transmission mode. The physical layer also defines the

direction of transmission between two devices: simplex, half-

duplex, or full-duplex. In simplex mode, only one device can

send; the other can only receive. The simplex mode is a one-way

communication. In the half-duplex mode, two devices can send

and receive, but not at the same time. In a full-duplex (or simply

duplex) mode, two devices can send and receive at the same time.

Other responsibilities of the Physical layer

Figure 2.6 Data link

layer

2. 17

Figure 2.7 Hop-to-hop

delivery

2. 19

Other responsibilities of the data link layer

Framing. The data link layer divides the stream of bits

received from the network layer into manageable data units

called frames.

Physical addressing. If frames are to be distributed to

different systems on the network, the data link layer adds a

header to the frame to define the sender and/or receiver of

the frame. If the frame is intended for a system outside the

sender's network, the receiver address is the address of the

device that connects the network to the next one.

Flow control. If the rate at which the data are absorbed by

the receiver is less than the rate at which data are produced

in the sender, the data link layer imposes a flow control

mechanism to avoid overwhelming the receiver.