Chapter 6

OSI Reference Model

Data Communications

1By Chhay Buntha

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.

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 1970s.

Layered Tasks of the OSI ModelChap

ter6

2By Chhay Buntha

Tasks involved in sending a letter.Chap

ter6

3By Chhay Buntha

Chap

ter6

4By Chhay Buntha

ISO is the organization.OSI is the model.

Note

Seven Layers of the OSI ModelChap

ter6

5By Chhay Buntha

The interaction between layersChap

ter6

6By Chhay Buntha

An exchange using the OSI modelChap

ter6

7By Chhay Buntha

Layer1: Physical LayerChap

ter6

8By Chhay Buntha

-Physical Characteristics of interfaces and medium

-Representation of bits: Stream of bits 0s and 1s

-Data Rate

-Synchronization of bits

-Line configuration: Connection

-Physical topology

-Transmission mode: Simplex,Half/Full duplex

Layer2: Data Link LayerChap

ter6

9By Chhay Buntha

-Framing: convert from up layer to frame-Physical addressing: MAC (Media Access Control)-Flow/Error/Access control: Make error free to upper

Layer3: Network LayerChap

ter6

10By Chhay Buntha

Responsible for the source to destination delivery of a packet.

-Routing-Logical addressing: IP Address

Layer4: Transport LayerChap

ter6

11By Chhay Buntha

Responsible for process-to-process delivery of the entire

message:

-Flow/Error control

-Connection control: Connectionless and connection

oriented

Layer4: Transport LayerChap

ter6

12By Chhay Buntha

Layer5: Session LayerChap

ter6

13By Chhay Buntha

Responsible for established the connection between

communication systems

Layer6: Presentation LayerChap

ter6

14By Chhay Buntha

-Translate

-Encryption/Decryption

Layer7: Application LayerChap

ter6

15By Chhay Buntha

Summary of LayersChap

ter6

16By Chhay Buntha

AddressingChap

ter6

17By Chhay Buntha

Four levels of addresses are used in an internet employing

the TCP/IP protocols: physical, logical, port, and specific.

Physical Address: MAC AddressChap

ter6

18By Chhay Buntha

Most local-area networks use a 48-bit (6-byte) physical

address written as 12 hexadecimal digits; every byte (2

hexadecimal digits) is separated by a colon, as shown

below:

07:01:02:01:2C:4B

A 6-byte (12 hexadecimal digits) physical address.

Logical Address: IP AddressChap

ter6

19By Chhay Buntha

An IPv4/IPv6 addresses is a 32/128-bit address that

uniquely and universally defines the connection of a device

(for example, a computer or a router) to the Internet. Figure

below is the sample of IPv4 address.

Port AddressChap

ter6

20By Chhay Buntha

A port address is a 16-bit address represented by one

decimal number as shown.

753A 16-bit port address represented

as one single number.

Special Address:Chap

ter6

21By Chhay Buntha

What is a special address?

- www.google.com

- www.ppiu.edu.kh

- www.dap-news.com

- 127.0.0.0