PRESENTATION COMPUTER NETWORKS

INTRODUCTION TO NETWORK UNIT 1: INTRODUCTION TO NETWORK

CONTENTS Network Definition Requirements for establishing a Network Network Hardware and Software Network Topologies Uses of Computer Networks OSI Reference Model TCP/IP Reference Model Comparison of OSI & TCP/IP Reference Model

NETWORK DEFINITION “Network is a process where two or more computers are interconnected for data communication and sharing resources.” “Two or more computers connected with the help of data communication devices and transmission media is referred to as Network.”

Requirements for establishing a Network LAN Card – It is a hardware device which allows a computer to be connected to the network. It is a printed circuit board which is installed on one of the expansion slots of the computer and provides a port on the back of the computer to which the network cable is attached. Communication Media – It is divided into two parts: - Wired Media - Wireless Media

NETWORK HARDWARE LAN – LAN stands for Local Area Network. These are privately owned networks which are used in a single building or in a campus or upto few kilometers in size. LAN’s are used to connect personal computers and workstations in companies, offices and factories to share resources and exchange information. LAN provides high speed data communication. MAN – MAN stands for Metropolitan area Network. It interconnects computers within a city. The best known example of MAN is cable television network which is found in the entire city. Networks that share some of the characteristics of both LAN and WAN are referred to as Metropolitan Network. (To be continued)

WAN – WAN stands for Wide Area Network WAN – WAN stands for Wide Area Network. WAN is a network that covers the wide geographical area such as a country, continent or even the whole world. WAN’s are the biggest type of networks available on the earth. Examples of WAN are airline reservation system, internet and banking. In WAN, complex communication protocols are used. NIC – It is a hardware device which allows a computer to be connected to the network. It is a printed circuit board which is established on one of the expansion slots of the computer and provides a port on the back of the computer to which the network cable is established. (To be continued)

NETWORK DEVICES – It includes the following: Router: It is a device which is used to interconnect two or more then two networks. Routers are hardware devices used to direct messages across a network. Routers maintain a routing table i.e used for making decisions about routing the data over the network. The two main functions of router are Routing and Packet Filtering. Repeaters: They connect multiple network segments together. It boosts or amplifies the signal before passing it through the next section of the cable. Repeaters makes the signal travel longer distance. It receives the signal and regenerates it. This allows the distance of network cabling to be extended. (To be continued)

Hub: Hub is a duffer device because it does not know any type of addressing. The main task of Hub is buffering of packets and filtering so that unwanted packets are discarded. Hub is based on bus topology because only one user can communicate at a time. Bridges: These are mainly used to divide a large network into smaller sub networks called segments. It can be used to connect two or more segments of a network that use same communication protocols. Switches: Switches are a device used to connect network devices together. It acts as a central connection point for cables from network devices. When a packet arrives at any of the switch port, it forwards it only to the appropriate part of the intended receiver.

NETWORK SOFTWARE Layers – To reduce complexity, most networks have been organized in layers, each one built upon the one below it. The name of each layer, function of each layer, contents of each layer differ from network to network. Each layer performs a well defined function in networking. The computers on the network work on the fundamental concepts of layers. Communication Protocol & Protocol Hierarchy – For any network to exist, there must be a connection between computers and agreements which are known as protocols. Protocols perform a variety of functions that are necessary for data transmission between computers. Different types of protocols are available and each protocol performs a well defined function. (To be continued)

Design issues for layers: Some of the important design issues that occur in computer network are as follows: - Error Control - Flow Control - Routing - Addressing Connection Oriented & Connectionless service: Connection oriented service guarantees the delivery of the data and also maintains sequencing of packets. Connectionless service is one where no long lasting connection is established between the source and destination. Each packet is routed independently over the lines. (To be continued)

Connection Oriented Service Connectionless Service - Reliable mode of service. - Unreliable mode of service. - Packets arrive at destination is order. - No sequencing of packets is done. - Acknowledgement is required about the delivery of the message. - No acknowledgement is done. - Example: TCP - Example: UDP Ensure error free delivery of packets at destination. - Packets are not guaranteed to be error free. Slow communication. - Fast communication.

Topology Topology means arrangement of computers in a network. It specifies the data paths to be used between two computers on the network. The path taken by data from sender to receiver mainly depends upon the topology of the network. “Topology refers to the way in which end points of a network are linked together.”

TYPES OF TOPOLOGIES Bus Topology: All the nodes are connected to a single cable or a single transmission medium. This transmission medium is known as a “bus”. In bus topology, a cable has two end points one at the start and the other at the end. Star Topology: A special device known as a server is placed in the center of the network and all nodes are connected to the central server and communicate through it. (To be continued)

Mesh Topology: All the computers are directly connected to the rest of the computers in the network with a point to point link. It refers to the network in which a cable runs from every computer to every other computer and there is no chance of data failure. Tree Topology: Allows for expansion of an existing network. In this network, various computers are linked to the main computer in a hierarchical manner. It is the main computer which is at the highest level of hierarchy and sometimes this computer is called “parent”. (To be continued)

Ring Topology: It connects all the computers in the form of a ring i Ring Topology: It connects all the computers in the form of a ring i.e each computer is connected to two or more computers at both ends and the first computer is connected with last computer to complete the ring in the network.

USES OF COMPUTER NETWORKS Sharing Resource sharing Cost reduction Reliability Saving of time Instant messaging USENET Benefit to mobile users E-Commerce E-Mails Flexible working environment Communication speed is increased

OSI REFERENCE MODEL OSI model is the outcome of ANSI working group. This model was invented on 12th Oct. 1979. This model is based on the proposal developed by ISO as the first step towards international standardization of protocols used in various layers. This model was given the name OSI because it deals with connecting open systems i.e systems that are open for communication with other systems. OSI model was invented because when networking was first introduced two computers were not able to properly communicate with each other, so the whole networking process was divided into parts and each part was named as “layer” (To be continued)

Application Layer: Provides the user interface Application Layer: Provides the user interface. When an application on a computer starts communicating with the other computer, the application layer provides the services to user defined application processes. It includes variety of protocols that are commonly needed by the users such as FTP, HTTP, TELNET, SMTP etc. Presentation Layer: is concerned with the syntax and semantics of the information to be transmitted. This This layer provides several facilities to convert data into more meaningful form. It performs transformations such as encryption, decryption, compression, decompression. Security is the main fundamental issue at this layer. (To be continued)

Session Layer: is responsible for establishing, maintaining and terminating a session or connection between the applications. It performs 3 services: - Dialog Control - Token Management - Synchronization Transport Layer: The main purpose of this layer is to accept the data from above, divide the big message into packets is required, pass it to the network layer and to ensure all packets arrive at the other end and in right order. This layer is also responsible for resending the packets if no acknowledgment regarding delivery of the packet has been received. (To be continued)

Network Layer: The main issue at the network layer is routing the packets from source to destination. Routers choose the shortest path to deliver the packet to the destination. If too many packets are present on the same route, then this may lead to congestion and collisions. It is the responsibility of the network layer to manage congestion and to protect the packets from collision. Data Link Layer: The main purpose is to detect and correct errors in the transmitted data. It is responsible for reliable node to node delivery of data. It converts them into frames so that correction and detection can be carried out independently for each frame. (To be continued)

Physical Layer: is concerned with transmitting raw bits in the form of 0 and 1 over a communication channel(unguided and guided). This layer is concerned with dealing with electrical, mechanical and timing interfaces. It is responsible for actual physical connection between the devices. It defines NIC attachment to hardware and how cable is attached to NIC.

TCP/IP REFERENCE MODEL TCP/IP is the outcome of the research work by US-DOD. This model includes a suite of protocols. TCP/IP came into existence in 1970’s. It closely reflects the structure of internet. TCP/IP model says that in the OSI model, there is duplication of functions performed by the layers, which increases number of layers and further adds to complexity. But in TCP/IP model each layer performs a clear and a single function. Following are the layers in TCP/IP model: - Application Layer - Transport Layer - Internet Layer - Host to network layer (To be continued)

- FTP (File Transfer Protocol) - HTTP (Hyper Text Transfer Protocol) Application Layer: This layer provides communication between applications or processes running on different machines. It includes several high level protocols that are used for wide variety for applications: - FTP (File Transfer Protocol) - HTTP (Hyper Text Transfer Protocol) - SMTP (Simple Mail Transfer Protocol) - SNMP (Simple Network Management Protocol) - TELNET (Terminal Network) - DNS (Domain Name System) - DHCP (Dynamic Host Configuration Protocol) - NNTP (Network News Transfer Protocol) - POP3 (Post Office Protocol, Version 3) - RIP (Routing Information Protocol) (To be continued)

Transport Layer: The transport layer of TCP/IP model performs the same function as the transport layer in OSI reference model. It supports end to end communication between source and destination. Two protocols have been defined here: - TCP (Transmission Control Protocol) - UDP (User Datagram Protocol) Internet Layer: The main purpose of this layer is to send packets and travel them independently to the destination. Four protocols have been defined here: - IP (Internet Protocol) - ICMP (Internet Control Message Protocol) - ARP (Address Resolution Protocol) - RARP (Reverse Address Resolution Protocol)

Host to Network layer: TCP/IP has not defined its own standard for this layer. It uses the services of the physical layer and the data link layer of the OSI Reference model. The main purpose of this layer is defining a network and how datagrams are transmitted. It needs the details of the network for correct coding of data being transmitted.

COMPARISON BETWEEN OSI & TCP/IP REFERENCE MODEL TCP/IP Reference Model OSI Reference Model TCP/IP Reference Model 1)OSI Model is a proposal developed by ISO as the 1st step towards international standardization of protocols used in various layers. It was invented by ANSI in 1979. 1) TCP/IP model was created in 1970’s by ARPA for use in developing internet protocols and the structure of internet is closely reflected by TCP/IP model. 2)Services, Interfaces, Protocols are the 3 major fundamental concepts of OSI model. It makes proper distinction between these 3 concepts. 2)TCP/IP has never been able to make proper distinction between Services, Protocols and Interfaces. 3)More complexity due to more number of layers. 3) Less complexity due to less number of layers. (To be continued)

5)OSI model was invented after TCP/IP model was invented. 4)OSI model is not built around any network. It is used as a guidance tool. OSI model is the standard around which the process of networking has been developed. 4)TCP/IP model is considered to be more flexible because TCP/IP protocols are the standard around which internet was developed. 5)OSI model was invented after TCP/IP model was invented. 5)TCP/IP model was invented before OSI model was invented. 6)OSI model supports only connection oriented service in the transport layer. 6)TCP/IP supports both connection oriented as well as connectionless service in the transport layer. 7)OSI model supports both connection oriented as well as connectionless service in the network layer. 7)TCP/IP supports only connectionless service in the network layer. (To be continued)

8)OSI model has defined its own standard configuration for each layer 8)OSI model has defined its own standard configuration for each layer. It does not uses the services of other models. 8)TCP/IP has not defined its own standard configuration for host to network layer. It uses services of physical and data link layer of OSI model. 9)The data link and transport layer performs the function of error control, flow control and buffering. So duplication may lead to confusion. 9)Each layer in TCP/IP model performs a single and a clear function.