Computer Networks UNIT - 1 Student Handout UNIT – 1 Introduction to Computer Networks © Dept.s of CSE & IT, PEC For the internal circulation in Pragati Engineering College only Page 1 Soma Sekhar T.
UNIT - 1 Computer Networks Student Handout Introduction Computer Network “an interconnected collection of autonomous computers”. Two computers are said to be interconnected if they are able to communicate and exchange information. If one computer can forcibly start, stop or control another one, the computers are not autonomous. Computer Networks are mainly used where there is a need for resource sharing and communication. Basic Terminology Network host a computer connected to any type of data network. A network host can host information resources as well as application software for providing network services. Data network an electronic communications process that allows for the orderly transmission and receptive of data, such as letters, spreadsheets, and other types of documents. There are two basic types of data networks 1. The private data network is essentially a local network that is designed to allow for the transmission of data between the various departments within a given entity, such as a company. 2. In contrast to the private data network, the public data network will be widely accessible to both residential and corporate clients of a given carrier network. Subnet1 the collection of routers and communication lines that moves data from the source host to the destination host. Transmission the process of sending, propagating and receiving information over a physical transmission medium (either wired or wireless). Network Medium The physical channel used for transmission in the network. Protocol a set of rules which is used by computers to communicate with each other across a network. A protocol can also be defined as “the rules governing the syntax, semantics, and synchronization of communication”. For proper communication both source and destination hosts must use the same protocol2. IP address a numerical label that is assigned to devices participating in a computer network for communication between its nodes. An IP address is used to uniquely identify a device in the network. A typical IP address looks like 18.104.22.168. It may also be known as a logical address. MAC address is a unique identifier assigned to most network adapters or network interface cards (NICs) by the manufacturer for identification. It may also be known as an Ethernet Hardware Address (EHA), hardware address, adapter address, or physical address. Internetworking connecting two or more computer networks via gateways. The result is called an internetwork or simply an internet3. Firewall a part of a computer system or network that is designed to block unauthorized access while permitting authorized communications. 1 The concept of subnet mentioned here is different from Subnetting in IP addresses. Different protocols may be used by source and destination hosts when there is a protocol translator in between. 3 This internet is different from the Internet, which is the worldwide huge network. 2 © Dept.s of CSE & IT, PEC For the internal circulation in Pragati Engineering College only Page 2 Soma Sekhar T.
UNIT - 1 Computer Networks Student Handout Proxy a server that acts as an intermediary for requests from clients seeking resources from other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource, available from a different server. The proxy server evaluates the request according to its filtering rules. DNS the Domain Name System translates human-friendly computer hostnames (domain names) into IP addresses. The Internet a global system of interconnected computer networks to serve billions of users worldwide. It is a network of networks that consists of millions of private and public, academic, business, and government networks of local to global scope that are linked by a broad array of electronic and optical networking technologies. The Internet carries a vast array of information resources and services. World Wide Web (WWW / W3) /The Web the Web is one of the services that runs on the Internet. It is a collection of interconnected documents and other resources, linked by hyperlinks and URLs. Switching Devices / Internetworking Devices Repeater receives signal from input channel, increases the strength of the signal, removes the unwanted noise and transmits the signal on to the output channel. Hub a device for connecting multiple devices together and thus making them act as a single network segment. Hub receives signal from one channel and forwards it to all other channels connected to the hub. (A multiport repeater) Three different types of hubs exist: 1. Passive A hub which does not need an external power source, because it does not regenerate the signal and therefore falls as part of the cable 2. Active (Passive Hub + Repeater) A hub which regenerates the signal and therefore needs an external power supply 3. Intelligent (Active Hub + error detection) A hub which provides error detection (e.g. excessive collisions) and also does what an active hub does Switch unlike hub; switch forwards the signal only on to the channel where destination host is present. The devices mentioned above are for connecting devices with in a network, where as devices mentioned below are for connecting two or more networks together to form an internet. © Dept.s of CSE & IT, PEC For the internal circulation in Pragati Engineering College only Page 3 Soma Sekhar T.
Computer Networks UNIT - 1 Student Handout Router & Bridge Both the devices are used for connecting networks together. But the only difference is Router uses IP addressing scheme where as Bridge uses MAC addressing scheme. Brouter a network bridge and a router combined in a single product. Gateway a network node equipped for interfacing with another network that uses different protocols. The devices mentioned before gateway are operative only when the networks they are connecting uses same protocols. Where as a Gateway can also operate between the networks that uses different protocols. Gateway acts as a protocol translator. Types of Communication Simplex communication that occurs in one direction only Half-Duplex communication in both directions, but only one direction at a time (not simultaneously) Full-Duplex communication in both directions, and, unlike half-duplex, allows this to happen simultaneously. Types of Transmission Unicast the sending of messages to a single destination host Multicast the delivery of information to a group of destinations simultaneously Broadcast transmitting a packet that will be received by every device on the network Directed Broadcast the message is broadcasted to all the nodes in some other network. Limited Broadcast the message is broadcasted to all the nodes in same network. Anycast data is routed to the nearest or best destination Evolution of Computer Networks and the Internet Feb 28th, 1992 © Dept.s of CSE & IT, PEC For the internal circulation in Pragati Engineering College only Page 4 Soma Sekhar T.