1. Introduction Computer Networks

2. Objectives of Today’s Lecture
Lecture Objectives
Objectives of Today’s Lecture
In this Lecture, you will learn about a Computer Networks and there goals. You will learn Different types of computer network like PAN, LAN, WAN, MAN and Internet and there division by scale. You will also get familiar with protocols and what is Layer Architecture, history of Open Systems Interconnection (OSI) Model, OSI Reference Model. You will also be introduced to 7 Layers of OSI Reference Model, TCP/IP Reference Model:. By the end of this lecturer, you should be able to:
What is Computer Network and Its Types.
What is Layer Architecture?
What is OSI Reference Model and what are the 7 layer of OSI Models.
Working and responsibilities of each layer works.
Devices working on each layer
What TCP/IP Reference Model
Difference between OSI and TCP/IP Models

3. What is Computer Network
A large number of separate but interconnected computers to share the resources’ are known as computer networks. OR
A computer network, often simply referred to as a network, is a collection of computers and devices interconnected by communications channels that facilitate communications among users and allows users to share resources.

4. What is Computer Network
The goal of computer network is as follows:
Resource Sharing
Physical Resources - Printers,
Storages like tape backup systems
Information/Date
High Reliability
Saving Money

5. Types of Network Personal Area Networks(PAN) Local Area Network(LAN)
Metropolitan Area Networks (MAN)
Wide Area Networks(WAN)

6. Personal Area Networks (PAN)
Types of Network
Personal Area Networks (PAN)
PANs (Personal Area Networks) let devices communicate over the range of a person.

7. Local Area Network(LAN)
Types of Network
Local Area Network(LAN)
A LAN is a privately owned network that operates within and nearby a single building like a home, office or factory.

8. Metropolitan Area Networks (MAN)
Types of Network
Metropolitan Area Networks (MAN)
A MAN (Metropolitan Area Network) covers a city. The best-known examples of MANs are the cable television networks available in many cities.

9. Wide Area Networks(WAN)
Types of Network
Wide Area Networks(WAN)
A WAN (Wide Area Network) spans a large geographical area, often a country or continent.

10. Types of Network
Internet
A collection of interconnected networks is called an internetwork or internet.
The Internet uses ISP networks to connect enterprise networks, home networks, and many other networks.

11. What’s the Internet: “nuts and bolts” view
Types of Network
What’s the Internet: “nuts and bolts” view
smartphone PC
server
wireless
laptop
millions of connected computing devices:
hosts = end systems
running network apps
mobile network
global ISP
regional ISP
home
network
institutional
communication links
fiber, copper, radio, satellite
transmission rate: bandwidth
wired
links
wireless
Packet switches: forward packets (chunks of data)
routers and switches
router 11

12. Classification of Networks By Scale
Types of Network
Classification of Networks By Scale

13. Data Communication Type
Simplex: Data travel one way, Examples are PA system in school, Radio.
Half duplex: Data communication in either direction but not simultaneously, Examples are CB-radio, Walky Talky.
Full duplex: They travel to both direction at once, Examples are Telephone, Mobile.

14. Network Topology
Network Topology
It is the physical interconnection of the elements (node) of a computer network’s LAN is one example of the physical or logical topology.

15. Types of Network Topology
Bus: Each machine is connected to a single bus.
Star: Each machine is connected to a central hub with a point-to-point connection.

16. Types of Network Topology
Ring: Each computer is connected to the network in a closed loop.
Mesh: That is fully connected to each other.
Tree: It is also known as Hierarchical Network , Is connected to one or more another nodes.

17. Protocol
Protocol
A protocol is an agreement between the communicating parties on how communication is to proceed. A set of layers and protocols is called a network architecture.

18. Organization of air travel
Protocol
Organization of air travel
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
a series of steps

19. Layering of airline functionality
Protocol
Layering of airline functionality
ticket (purchase)
baggage (check)
gates (load)
runway (takeoff)
airplane routing
departure
airport
arrival
intermediate air-traffic
control centers
ticket (complain)
baggage (claim
gates (unload)
runway (land)
ticket
baggage
gate
takeoff/landing
layers: each layer implements a service
via its own internal-layer actions
relying on services provided by layer below

20. Reference Models OSI Reference Model TCP/IP Reference Model

21. OSI Reference Model
OSI Reference Model
International standard organization (ISO) established a committee in 1977 to develop an architecture for computer communication.
Open Systems Interconnection (OSI) reference model is the result of this effort.
In 1984, the Open Systems Interconnection (OSI) reference model was approved as an international standard for communications architecture.
Term “open” denotes the ability to connect any two systems which conform to the reference model and associated standards.

22. OSI Reference Model
OSI Reference Model
The OSI model is now considered the primary Architectural model for inter-computer communications.
The OSI model describes how information or data makes its way from application programmes (such as spreadsheets) through a network medium (such as wire) to another application programme located on another network.
The OSI reference model divides the problem of moving information between computers over a network medium into SEVEN smaller and more manageable problems .
This separation into smaller more manageable functions is known as layering.

23. OSI Reference Model: 7 Layers

24. OSI Reference Model
OSI Reference Model
The process of breaking up the functions or tasks of networking into layers reduces complexity.
Each layer provides a service to the layer above it in the protocol specification.
Each layer communicates with the same layer’s software or hardware on other computers.
The lower 4 layers (transport, network, data link and physical —Layers 4, 3, 2, and 1) are concerned with the flow of data from end to end through the network.
The upper four layers of the OSI model (application, presentation and session—Layers 7, 6 and 5) are orientated more toward services to the applications.
Data is Encapsulated with the necessary protocol information as it moves down the layers before network transit.

25. Physical Layer The lowest layer, 1st in the OSI reference model .
The physical layer is concerned with transmitting raw bits over a communication channel.
It’s sends bits and receive bits only into the value of 0 and 1.
It actually communicate direct with the various type of communication media.
Hub works on Physical layer.

26. OSI Reference Model
Data Link Layer
The main task of the data link layer is to transform a raw transmission facility into a line that appears free of undetected transmission errors to the network layer.
It accomplishes this task by having the sender break up the input data into data frames.
Switch and bridge work on Data link layer

27. OSI Reference Model
Network Layer
Key design issue is determining how packets are routed from source to destination.
Routes can be based on static tables that are ''wired into'' the network and rarely changed.
Router work on network layer

28. OSI Reference Model
Transport Layer
The basic function of the transport layer is to accept data from above,
split it up into smaller units if need be,
pass these to the network layer,
and ensure that the pieces all arrive correctly at the other end.

29. OSI Reference Model
Session Layer
The session layer allows users on different machines to establish sessions between them.
Sessions offer various services, including dialog control, token management, and synchronization.

30. OSI Reference Model
Presentation Layer
It is responsible for data translation and code formatting.
This layer is essentially a translator and provides coding and conversion function.
A successful data transfer technique is to adapt the data into a standard format before transmission.

31. OSI Reference Model
Application Layer
Supplying services to application procedures such as or file transfer) that are outside the OSI model.
That make the spot where user actually communicate to the computer.
The layer actually comes into play when its apparent that access to the network is going to needed soon .

32. The TCP/IP Reference Model
OSI Reference Model
The TCP/IP Reference Model

33. OSI Reference Model
TCP/IP Model
The ARPANET was a research network sponsored by the DoD (U.S. Department of Defense). It eventually connected hundreds of universities and government installations, using leased telephone lines.
When satellite and radio networks were added later, the existing protocols had trouble interworking with them.
The ability to connect multiple networks in a seamless way was one of the major design goals.
This architecture later became known as the TCP/IP Reference Model, after its two primary protocols. It was first described by Cerf and Kahn (1974), and later refined and defined as a standard in the Internet community (Braden, 1989).
The design philosophy behind the model is discussed by Clark (1988).

34. Transport Layer (TCP/UDP)
OSI Reference Model
TCP/IP Model
Application Layer
Application programs using the network
Transport Layer (TCP/UDP)
Management of end-to-end message transmission,
error detection and error correction
Network Layer (IP)
Handling of datagrams : routing and congestion
Data Link Layer
Management of cost effective and reliable data delivery,
access to physical networks
Physical Layer
Physical Media

35. Encapsulation and Decapsulation
OSI Reference Model
Encapsulation and Decapsulation
Encapsulation: When data moves from upper layer to lower level of TCP/IP protocol stack (outgoing transmission) each layer includes a bundle of relevant information called a header along with the actual data.
Decapsulation: The reverse process of encapsulation (or decapsulation) occurs when data is received on the destination computer. As the data moves up from the lower layer to the upper layer of TCP/IP protocol stack (incoming transmission), each layer unpacks the corresponding header and uses the information contained in the header to deliver the packet to the exact network application waiting for the data.

36. Encapsulation and Decapsulation
OSI Reference Model
Encapsulation and Decapsulation
When a car is built in a factory, one person doesn't do all the jobs, rather it's put into a production line and as the car moves through, each person will add different parts to it so when it comes to the end of the production line, it's complete and ready to be sent out to the dealer.
One important piece of information to keep in mind is that data flows 2 ways in the OSI model, DOWN (data encapsulation) and UP (data decapsulation).

37. Encapsulation and Decapsulation
OSI Reference Model
Encapsulation and Decapsulation
source
message M
application
transport
network
link
physical
segment Ht M Ht
datagram Ht Hn M Hn
frame Ht Hn Hl M
link
physical
switch
destination
network
link
physical Ht Hn M M
application
transport
network
link
physical Ht Hn Hl M Ht Hn M Ht M Ht Hn M
router Ht Hn Hl M

38. Encapsulation and Decapsulation
OSI Reference Model
Encapsulation and Decapsulation

39. History of Computer Networks (Internet)

40. 1961-1972: Early packet-switching principles
History
: Early packet-switching principles
1961: Kleinrock - queueing theory shows effectiveness of packet-switching
1964: Baran - packet-switching in military nets
1967: ARPAnet conceived by Advanced Research Projects Agency
1969: first ARPAnet node operational
1972:
ARPAnet public demo
NCP (Network Control Protocol)
first host-host protocol
first program
ARPAnet has 15 nodes

41. 1972-1980: Internetworking, new and proprietary nets
History
: Internetworking, new and proprietary nets
1970: ALOHAnet satellite network in Hawaii
1974: Cerf and Kahn - architecture for interconnecting networks
1976: Ethernet at Xerox PARC
late70’s: proprietary architectures: DECnet, SNA, XNA
late 70’s: switching fixed length packets (ATM precursor)
1979: ARPAnet has 200 nodes

42. 1980-1990: new protocols, a proliferation of networks
History
: new protocols, a proliferation of networks
1983: deployment of TCP/IP
1982: smtp protocol defined
1983: DNS defined for name-to-IP-address translation
1985: ftp protocol defined
1988: TCP congestion control
new national networks: Csnet, BITnet, NSFnet, Minitel
100,000 hosts connected to confederation of networks

43. 1990, 2000’s: commercialization, the Web, new apps
History
1990, 2000’s: commercialization, the Web, new apps
early 1990’s: ARPAnet decommissioned
1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)
early 1990s: Web
hypertext [Bush 1945, Nelson 1960’s]
HTML, HTTP: Berners-Lee
1994: Mosaic, later Netscape
late 1990’s: commercialization of the Web
late 1990’s – 2000’s:
more killer apps: instant messaging, P2P file sharing
network security to forefront
est. 50 million host, 100 million+ users
backbone links running at Gbps

44. 2005-present ~750 million hosts Smartphones and tablets
History
2005-present
~750 million hosts
Smartphones and tablets
Aggressive deployment of broadband access
Increasing ubiquity of high-speed wireless access
Emergence of online social networks:
Facebook: soon one billion users
Service providers (Google, Microsoft) create their own networks
Bypass Internet, providing “instantaneous” access to search, emai, etc.
E-commerce, universities, enterprises running their services in “cloud” (eg, Amazon EC2)