1. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
Host A
Host B
Application
Data Link
Presentation
Network
Physical
Session
Transport
Physical Medium
Sami S.Al-Wakeel
Sami S.Al-Wakeel

2. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
Application
Data Link
Presentation
Network
Physical
Session
Transport
Physical Medium
Host A
Host B
Interface
Sami S.Al-Wakeel
Sami S.Al-Wakeel

3. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
Application
Data Link
Presentation
Network
Physical
Session
Transport
Physical Medium
Host A
Host B
Protocol
Layer 7 Protocol
Layer 6 Protocol
Layer 5 Protocol
Layer 4 Protocol
Layer 3 Protocol
Layer 2 Protocol
Layer 1 Protocol
Sami S.Al-Wakeel
Sami S.Al-Wakeel

4. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
Application
Data Link
Presentation
Network
Physical
Session
Transport
Physical Medium
Layer 7 Protocol
Layer 1 Protocol
Layer 2 Protocol
Layer 3 Protocol
Layer 4 Protocol
Layer 5 Protocol
Layer 6 Protocol
Layer 6/7 Interface
Layer 5/6 Interface
Layer 4/5 Interface
Layer 3/4 Interface
Layer 2/3 Interface
Layer 1/2 Interface
Host A
Host B
Sami S.Al-Wakeel
Sami S.Al-Wakeel

5. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
Interface: It defines which primitive operations and services the lower layer offers to the upper layer.
Peer: The similar layer on a different machine.
Protocol: It is a set of rules and conventions used by the layer to communicate with similar peer layer in another (remote) system.
The peer processes communicate with each other using a protocol.
A set of layers and protocols is called a network architecture.
Sami S.Al-Wakeel
Sami S.Al-Wakeel

6. The ISO OSI Reference Model
Sami S.Al-Wakeel

7. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
In reality, no data are directly transferred from layer i on one machine to layer i on another machine. Instead, each layer passes data and control information to the layer immediately below it, until the lowest layer is reached. Below layer 1 is the physical medium through which actual communication occurs.
Send-To-Other-side ( )
Get-From-Other-side ( )
Protocol
(Virtual Communication)
Host A
Host B
Layer i
Sami S.Al-Wakeel
Sami S.Al-Wakeel

8. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
Sami S.Al-Wakeel
Sami S.Al-Wakeel

9. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
Host A
Host B
Layer 7 Protocol
Application
Application
Data Link
Presentation
Network
Physical
Session
Transport
Layer 6 Protocol
Presentation
Layer 5 Protocol
Session
Layer 4 Protocol
Transport
Network
Network
Network
Data Link
Data Link
Data Link
Physical
Physical
Physical
Sami S.Al-Wakeel
Sami S.Al-Wakeel

10. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
Information Flow:
Source machine
Destination machine m
Layer 7 Protocol m M M
Layer 6 Protocol M M
Layer 5 Protocol M2 H4 M2 H4
Layer 4 Protocol M2 H4 H3 M2 H4 H3
Layer 3 Protocol M2 H4 H3 H2 T2 M2 H4 H3 H2 T2
Layer 2 Protocol
Sami S.Al-Wakeel
Sami S.Al-Wakeel

11. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
1. The Physical Layer:
It concerns with transmitting raw bits over a communication channel.
Voltage Levels for 0 and 1.
Connectors: Number of bins and purpose of each bin.
Transmission Media.
Attenuation and Distortion.
Analog PSTN Circuits and Digital Leased Circuits.
Sami S.Al-Wakeel
Sami S.Al-Wakeel

12. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
2. The Data Link Layer:
The main task of the data link layer is to take a raw transmission facility and transform it into a line that appears free of transmission errors to the network layer.
Point-to-point error control:
If a frame is destroyed, the data link layer retransmits the frame.
If an acknowledgement frames is lost, a duplicate frame is produced.
Destination
Source
Frame
Acknowledgement
Sami S.Al-Wakeel
Sami S.Al-Wakeel

13. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
2. The Data Link Layer:
Point-to-point flow control:
Some regulation mechanism must be employed to let the transmitter know how much buffer space the receiver has at the moment. This is to prevent a fast transmitter from drowning a slow receiver in data.
Framing:
It creates and recognizes frame boundaries.
STX
Message
ETX
Sami S.Al-Wakeel
Sami S.Al-Wakeel

14. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
3. The Network Layer:
Routing: It determines how packets are routed from source to destination.
Congestion Control: Many packets in the subnet trying to use the same route.
Internetworking: It allows heterogeneous networks to be interconnected.
Accounting Function.
Sami S.Al-Wakeel
Sami S.Al-Wakeel

15. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
4. The Transport Layer:
It acts as interface between the higher application oriented layers and the network dependent protocol layers.
Disassembling and Reassembling: It accepts data from a session layer, split it up to smaller units if needed, pass these to the network layer, and ensure that the pieces all arrive correctly at the other end.
End-to-end error control.
End-to-end flow control.
Sami S.Al-Wakeel
Sami S.Al-Wakeel

16. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
4. The Transport Layer:
It defines Quality of Service (QOS). There are five classes of service ranging from 0, which provides only basic functions needed for connection establishment and data transfer, to class 4, which provides full error and flow control procedures.
It is an end-to-end layer. Lower layers communicate with intermediate nodes.
Sami S.Al-Wakeel
Sami S.Al-Wakeel

17. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
5. The Session Layer:
It allows users on different machines to establish sessions between them.
Interaction Management: The data exchange associated with a dialog may be:
Duplex: Two-way simultaneous.
Half-Duplex: Two-way alternate.
Simplex: One-way.
Synchronization: For lengthy transaction, the user may choose to establish synchronization points associated with the transfer. If a fault develops during a transaction, the dialog may be restarted at an agreed synchronization point.
Sami S.Al-Wakeel
Sami S.Al-Wakeel

18. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
6. The Presentation Layer:
It converts from a code used by a computer to a standard network code. Different computers have different codes for representing characters (e.g., ASCII and EBCDIC), integers (e.g., one’s complement and two’s complements), and so on.
Data Compression.
Data Encryption.
Sami S.Al-Wakeel
Sami S.Al-Wakeel

19. The ISO OSI Reference Model
CHAPTER1
The ISO OSI Reference Model
7. The Application Layer:
The application layer contains a variety of protocols that are commonly needed.
It handles the incompatibilities on the different machines.
Sami S.Al-Wakeel
Sami S.Al-Wakeel

20. Data transmission in OSI Reference Model
CHAPTER1
Data transmission in OSI Reference Model
Application
Data Link
Presentation
Network
Physical
Session
Transport
Receiving Process
Sending Process
Data
Data AH
Data PH
Data SH
Data TH
Data NH
Data DH DT
Bits
Sami S.Al-Wakeel
Sami S.Al-Wakeel