This document provides an overview of computer network layers and protocols. It discusses the OSI reference model and its seven layers - physical, data link, network, transport, session, presentation, and application layer. It describes the functions of each layer and some examples of protocols used. The document also covers topics like connection-oriented vs connectionless services, network architectures, and network goals of communication and resource sharing.

1. 1
COMPUTER NETWORKS
Network layers and protocols
Lecture.1
Assis.lect.Arwa sahib
By: Dr.Eng.Mohammed i.Shujaa
2020-2021

2. Application
By:Dr.Eng.Muhamed.Shujaa 2
Physical
Source
1. Computer Networks, AndrewS.
Tanenbaum
2. www.cisco.com
3. www.novell.com
4. www.rad.com
5. www.3com.com
Data Link
Network
Transport
Session
Presentation

3. Application
By:Dr.Eng.Muhamed.Shujaa 3
Physical
INTRODUCTION
Presentation
Session
Network
Data Link
Transport

4. NETWORK GOALS
By:Dr.Eng.Muhamed.Shujaa 4
1 Physical
7 Application
The two main benefits of networking computers are…
Communications
Information can be distributed very quickly, such as
email and video conferencing.
Saving Money
Resources such as information, software, and
hardware can be shared.
CPUs and hard disks can be pooled together to
create a more powerful machine.
2 Data Link
3 Network
4 Transport
5 Session
6 Presentation

5. NETWORK ARCHITECTURES
By:Dr.Eng.Muhamed.Shujaa
7 Application
1 Physical
5
A set of layers and protocols is called the network
architecture.
.1 Protocol Hierarchies
Networks are organized as layers to reduce design
complexity. Each layer offers services to the higher
layers. Between adjacent layers is an interface.
Services – connection oriented and
connectionless.
Interface – defines which primitives and services
the lower layer will offer to the upper layer.
Primitives – operations such as request, indicate,
response, confirm.
2 Data Link
3 Network
4 Transport
5 Session
6 Presentation

6. NETWORK ARCHITECTURES
By:Dr.Eng.Muhamed.Shujaa 6
Application
2. Design Issues for the Layers(functions(
• Mechanism for connection establishment
• Rules for data transfer
• Error control
• Fast sender swamping a slow receiver
• Inability of processes to accept long messages
• Routing in the case of multiple paths
Network
Data Link
Physical
Transport
Session
6 Presentation

7. Network Protocols
By:Dr.Eng.Muhamed.Shujaa 7
• Protocol: is a format order of messages sent and
received among the net entities and action takenon msgs
transmission receipt.
Protocol process:
• The format or structure of themessage
• The process by which networking devices shareinformation
about pathways with othernetworks
• How and when error and systemmessages are passed
between devices
• The setup andtermination of data transfer sessions

8. Layering In Networked
Computing
By:Dr.Eng.Muhamed.Shujaa 8
• OSIModel (open system interconnection)
• TCP/IPModel
• Protocols at eachlayer

9. Learning outcomes
• Understand the need of layeringin Networkedcomputing
• Understand the OSImodel and the TCP/IPmodel
– Understand the function protocols and their
role at each layer.
• TCPprotocol
• UDPprotocol
• Understand the role of header in communication betweenlayers
• Understand how data sent from one host arrive to thetarget host.
By:Dr.Eng.Muhamed.Shujaa 9

10. What is Layering in Networked
Computing?
By:Dr.Eng.Muhamed.Shujaa 10
– Breaksdown communication into smaller, simplerparts.

11. Why alayered
model?
By:Dr.Eng.Muhamed.Shujaa 11
– Easierto teach communicationprocess.
– Speedsdevelopment, changesin one layer doesnot
affect how the other levelsworks.
– Allows different hardware and software towork
together.
– Reducescomplexity

12. What is “THEMODEL?”
By:Dr.Eng.Muhamed.Shujaa 12
• Commonly referred to asthe OSIreferencemodel.
• TheOSImodel
– is atheoretical blueprint that helps usunderstandhow
data gets from one user’s computer toanother.
– It is also amodel that helps develop standards so thatall
of our hardware and software talks nicely to eachother.
– It aids to provide an organized structure for hardware and
software developers to follow, to insure there productsare
compatible with current and future technologies.

13. 7 LayerOSIModel
• Q.Why useareference model?
– Servesasan outline of rules for how protocols canbe used to allow
communication betweencomputers.
– Eachlayer hasits own function and provides support to other
layers.
• Q.What are Other reference models are inuse.
– Most well known is the TCP/IPreferencemodel.
– Wewill compare OSIand TCP/IPmodels
• Ascomputing requirements increased, the network modeling hadto
evolve to meet ever increasing demandsof larger networks and
multiple venders.
13
• Problems and technology advancesalso added to the demandsfor
changesin network modeling.
By: Dr.Eng.Muhamed.Shujaa

14. Evolution of the 7-Layers
By:Dr.Eng.Muhamed.Shujaa 14
• SingleLayerModel - First Communication Between Computer Devices
– Dedicated copper wire or radiolink
– Hardware & software inextricablyintertwined
– Singlespecification for all aspects ofcommunication
1
DEVICEA DEVICE B
Hardware
&
Software
Hardware
&
Software

15. Evolution of the 7-Layers
By:Dr.Eng.Muhamed.Shujaa 15
• Two LayerModel
– Problem: Applications were being developed torun over ever-increasing
number of media/signalingsystems.
– Solution: Separateapplication aspects from technical (signaling and routing)
aspects
– Application Layer:Concerned with user interface, file accessand file transfer
Application
Technical
Standards
Application
Technical
Standards

16. Evolution of the7-Layers
By:Dr.Eng.Muhamed.Shujaa 16
• Four Layer Model - Network connectivity inherently requires travel over
intermediate devices (nodes)
• Technical Standards Level divided into Network, Data-link and Physical
Layers 1
Application
Network
Data-Link
Physical
Application
Network
Data-Link
Physical

17. Evolution of the7-Layers
By:Dr.Eng.Muhamed.Shujaa 17
Physical Layer
–Describes physical aspects of network: cards, wires, etc
–Specifies interconnect topologies and devices
Network Layer
–Defines a standard method for operating between nodes
–Address scheme is defined (IP)
–Accounts for varying topologies
Data-Link
–Works with Network Layer to translate logical addresses (IP) into hardware
addresses (MAC) for transmission
–Defines a single link protocol for transfer between two nodes(DLC protocol)
DLC:Data link controlprotocol

18. Evolution of the7-Layers
By:Dr.Eng.Muhamed.Shujaa 18
1
• Five Layer Model – Increase Quality of Service(QOS)
•Variable levels of data integrity in network
•Additional data exchanges to ensure connectivity over worstconditions
•Became the Transport Layer
Application
Transport
Network
Data-Link
Physical
Application
Transport
Network
Data-Link
Physical

19. Application
Session
Transport
Network
Data-Link
Physical
Application
Session
Transport
Network
Data-Link
Physical
By:Dr.Eng.Muhamed.Shujaa 19

20. Evolution of the 7-Layers
By:Dr.Eng.Muhamed.Shujaa 20
• The Seven Layer OSI Model - Addition of Management andSecurity
– Standardizing notation or syntax for application messages (abstract syntax)
1
– Set of encoding rules (transfer syntax)
– Became the Presentation Layer
Application
Presentation
Session
Transport
Network
Data-Link
Physical
Application
Presentation
Session
Transport
Network
Data-Link
Physical

21. What EachLayerDoes
By:Dr.Eng.Muhamed.Shujaa 21
2

22. By:Dr.Eng.Muhamed.Shujaa 22

23. By:Dr.Eng.Muhamed.Shujaa 23

24. By:Dr.Eng.Muhamed.Shujaa 24

25. OSI REFERENCE MODEL
By:Dr.Eng.Muhamed.Shujaa 25
7 Application
The Open Systems Interconnection is the model
developed by the International Standards Organization.
Benefits-Advantage
• Interconnection of different systems (open)
• Not limited to a single vendor solution
Negative Aspect (disadvantage(
• Systems might be less secure
• Systems might be less stable
1 Physical
2 Data Link
3 Network
4 Transport
5 Session
6 Presentation

26. OSI REFERENCE MODEL
By:Dr.Eng.Muhamed.Shujaa 26
Application
1. Physical Layer
a)Convert the logical 1’s and 0’s coming from
layer 2 into electrical signals.
b)Transmission of the electrical signals over a
communication channel.
Main topics:
• Transmission mediums
• Encoding
• Modulation
• RS232 and RS422 standards
• Repeaters
• Hubs (multi-port repeater)
Physical
Data Link
Network
Transport
Session
Presentation

27. OSI REFERENCE MODEL
By:Dr.Eng.Muhamed.Shujaa 27
Application
Physical
2. Data Link Layer
a)Error control to compensate for the
imperfections of the physical layer.
b)Flow control to keep a fast sender from
swamping a slow receiver.
Main topics:
• Framing methods
• Error detection and correction methods
• Flow control
• Frame format
• IEEE LAN standards
• Bridges
• Switches (multi-port bridges)
Data Link
Network
Transport
Session
Presentation

28. OSI REFERENCE MODEL
By:Dr.Eng.Muhamed.Shujaa 28
Application
Physical
3. Network Layer
a) Controls the operation of the subnet.
b) Routing packets from source to destination.
c) Logical addressing.
Main topics:
• Internetworking
• Routing algorithms
• Internet Protocol (IP) addressing
• Routers
Data Link
Network
Transport
Session
Presentation

29. OSI REFERENCE MODEL
By:Dr.Eng.Muhamed.Shujaa 29
Application
Physical
4. Transport Layer
a) Provides additional Quality of Service.
b) Heart of the OSI model.
Main topics:
• Connection-oriented and connectionless services
• Transmission Control Protocol (TCP)
• User Datagram Protocol (UDP)
•ACK
Data Link
Network
Transport
Session
Presentation

30. OSI REFERENCE MODEL
By:Dr.Eng.Muhamed.Shujaa 30
Application
Physical
5. Session Layer
a)Allows users on different machines to establish
sessions (dialogue) between them.
b)One of the services is managing dialogue
control.
c) Token management.
d) Synchronization.
Data Link
Network
Transport
Session
Presentation

31. OSI REFERENCE MODEL
By:Dr.Eng.Muhamed.Shujaa 31
Application
Physical
6. Presentation Layer
a)Concerned with the syntax and semantics of the
information.
b) Preserves the meaning of the information.
c) Data compression.
d) Data encryption.
Data Link
Network
Transport
Session
Presentation

32. OSI REFERENCE MODEL
By:Dr.Eng.Muhamed.Shujaa 32
Application
Physical
7. Application Layer
a) Provides protocols that are commonly needed.
Main topics:
• File Transfer Protocol (FTP)
• HyperText Transfer Protocol (HTTP)
• Simple Mail Transfer Protocol (SMTP)
• Simple Network Management Protocol (SNMP)
• Network File System (NFS)
• Telnet
Data Link
Network
Transport
Session
Presentation

33. SERVICES
By:Dr.Eng.Muhamed.Shujaa 33
Physical
Application
Each layer provides services to the layer above it.
1. Terminologies (scientific words means)
Entities – active elements in each layer (e.g.
process, intelligent I/O chip).
Peer Entities – entities in the same layer on
different machines.
Service Provider – Layer N.
Service User – Layer N + 1.
Service Access Points – places where layer N + 1
can access services offered by layer N.
Data Link
Network
Transport
Session
Presentation

34. SERVICES
By:Dr.Eng.Muhamed.Shujaa 34
Physical
Application
2. Connection-Oriented and Connectionless
Connection-Oriented – before data is sent, the
service from the sending computer must establish
a connection with the receiving computer.
Connectionless – data can be sent at any time by
the service from the sending computer.
Q: Is downloading a music file from the Internet
connection-oriented or connectionless?
Q: Is email connection-oriented or connectionless?
Data Link
Network
Transport
Session
Presentation

35. SERVICES
By:Dr.Eng.Muhamed.Shujaa 35
Application
4 Transport
4 Transport
3. Service Primitives
Request – entity wants the service to do some
work
Indicate – entity is to be informed about an event
Response – entity responds to an event
Confirm – entity is to be informed about its request
Sending Computer Receiving Computer
1. request 4. confirm 2. indicate 3. response
3 Network 3 Network
Physical
Data Link
Network
Transport
Session
Presentation