Introduction Computer Networks Lecture Objectives of Todays Lecture

Introduction Computer Networks

Lecture 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 understand: • • 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

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.

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

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

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

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.

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.

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

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.

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

Types of Network Classification of Networks By Scale

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.

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.

Network Topology 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.

Network Topology Types of Network Topology Ring: Each computer is connected to the network in a

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.

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

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

Reference Models OSI Reference Model TCP/IP 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.

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.

OSI Reference Model: 7 Layers

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.

OSI Reference Model Physical Layer The lowest layer, 1 st 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.

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

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

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.

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.

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.

OSI Reference Model Application Layer Supplying services to application procedures such as Email 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.

OSI Reference Model The TCP/IP Reference Model

OSI Reference Model TCP/IP Model The ARPANET was a research network sponsored by the Do. D (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).

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

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.

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).

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

OSI Reference Model Encapsulation and Decapsulation

History of Computer Networks (Internet)

History 1961 -1972: 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 e-mail program – ARPAnet has 15 nodes

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

History 1980 -1990: new protocols, a proliferation of networks • • 1983: deployment of TCP/IP 1982: smtp e-mail 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

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 1990 s: 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, P 2 P file sharing • network security to forefront • est. 50 million host, 100 million+ users • backbone links running at Gbps

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 EC 2)