COMPUTER NETWORKS For COMPUTER SCIENCE COMPUTER NETWORKS . Syllabus Concept of layering. LAN technologies (Ethernet). Flow and error control techniques. IPv4/IPv6, routers and routing algorithms (distance vector, link state). TCP/ UDP and sockets, congestion control. Application layer protocols (DNS, SMTP, POP, FTP, HTTP). Network security: authentication, basics of public key and private key cryptography, digital signatures and certificates, firewalls. Basics of Wifi & switching, Digital signals. ANALYSIS OF GATE PAPERS Exam Year 1 Mark Ques. 2 Mark Ques. Total 2003 2 3 8 2004 3 4 11 2005 5 2 15 2006 1 5 11 2007 2 6 14 2008 1 4 9 2009 - 5 10 2010 2 3 8 2011 2 2 6 2012 3 3 9 2013 3 2 7 2014 Set-1 2 3 8 2014 Set-2 3 2 7 2014 Set-3 3 3 9 2015 Set-1 4 2 8 2015 Set-2 2 3 8 2015 Set-3 2 3 8 2016 Set-1 2 4 10 2016 Set-2 3 4 11 2017 Set-1 2 3 8 2017 Set-2 1 2 5 2018 3 4 7 © Copyright Reserved by Gateflix.in No part of this material should be copied or reproduced without permission CONTENTS Topics Page No 1. ISO OSI PHYSICAL LAYER, LAN TECHNOLOGIES 1.1 Introduction 1.2 Computer Networks 1.3 Design Issues of Layers 01 1.4 Network Hardware 01 1.5 Network Topology 01 1.6 Transmission Mode 02 1.7 Reference Models 0703 1.8 Functions of the Layer 07 1.9 TCP/IP References Model 1 1.10 Comparison of OSI and TCP/IP Reference Models 108 1.11 Physical Layer 0 1.12 Transmission Media 2 1.13 Coaxial Cable 13 1.14 Optical Fiber 13 1.15 Maximum Date Rate of the Channel 16 1.16 Communication Satellite 17 1.17 Access Algorithms 19 1.18 Manchester Encoding 219 1.19 LMR (Last Minute Revision) 221 Gate Questions 22 2 2. DATALINK LAYER AND SWP 4 2.1 Introduction 2.2 Data Link Layer Design Issue 2.3 Error Detection Correction 335 2.4 Error Correcting Codes 435 2.5 Data Link Protocols 59 2.6 IEEE LAN Standards 0 2.7 LLC Protocol 0 2.8 ALOHA 54 2.9 IEEE 802.3 and Ethernet 55 2.10 LMR (Last Minute Revision) 57 Gate Questions 59 62 3. NETWORK AND TRANSPORT LAYER 66 3.1 Introduction 3.2 Switching Networks 3.3 Congestion Control 76 76 83 © Copyright Reserved by Gateflix.in No part of this material should be copied or reproduced without permission 3.4 Bridges 3.5 Internetworking Devices 3.6 IP Addressing 87 3.7 Inter Networking Protocol (IPv4) Format 89 3.8 IPv6 Addressing 96 3.9 Routing Protocol 98 3.10 Introduction to Transport Layer 992 3.11 Duties of the Transport Layer 1002 3.12 Connection 105 3.13 OSI Transport Protocol 10 3.14 Addressing 10 3.15 Multihomed Device 106 3.16 Subnetting and Supernetting 108 3.17 IP Datagrams and Routing 111 3.18 Internet Protocol 113 Gate Questions 114 116 4. APPLICATION LAYER AND NETWORK SECURITY 129 4.1 Session Layer 4.2 Presentation Layer 4.3 Application Layer 154 4.4 Digital Signatures 155 4.5 Firewalls 163 4.6 Standard Common Applications 165 4.7 POP3 (Post Office Protocol) 166 4.8 IMAP (Interactive Mail Access Protocol) 1662 4.9 DMSP (Distributed Mail System Protocol) 1712 4.10 LMR (Last Minute Revision) 17 Gate Questions 117 172 74 ASSIGNMENT QUESTIONS 1 90 © Copyright Reserved by Gateflix.in No part of this material should be copied or reproduced without permission 1 ISO, OSI PHYSICAL LAYER, LAN TECHNOLOGY 1.1 INTRODUCTION A Network is a set of devices (often referred to as nodes) connected by media links. A node can be a computer, printer, or any other devices capable of sending and / or receiving data generated by other nodes on the network. The links connecting the devices are called communications channels. E.g. fiber optic link, satellite link. 1.2 COMPUTER NETWORKS Computer network means an interconnected collection of autonomous computers capable of having interconnections with each other. Computer network are generally organized as a series of layers or levels, each one built upon the one below it. 1.2.1 DESIGN ISSUES OF LAYERS Every layer needs a mechanism for identifying senders and receivers. A mean should be there for a process on one machine to specify with whom it wants to talk. Design decisions should concern the rules for data transfer. It can either be simplex or half- duplex or full – duplex communication. Error control is an important issue and any error – detecting or correcting codes must be known on both ends of the connections. Protocol that make explicit for the receiver to allow the pieces to be put back together properly. An issue that occurs at every level is how to keep, a fast sender from swapping a slow receiver with data. Issue that allows an arbitrarily long message to get accepted by the processes is, when there are multiple paths between source and destination, a route must be chosen. Sometimes this decision spilt over two or more layers. 1.3 NETWORK HARDWARE The physical devices that are used to establish and maintain the network are said to be Network Hardware. In addition to computers, Network hardware includes NIC, Hub, Switch, Router, Bridge and Gateway. Network Interface Card: It gives minimum eligibility for the nodes to be in networks. It can exist in either H/w or S/w form. It operates typically at Physical Layer. Repeater: It works like amplifier, i.e. It convert weak digital signal in to strong digital signal. It Operates at Physical Layer. Hub: It is a broadcasting device. Hence it stands for Hybrid Universal Broadcast. It operates at Physical and Data link Layers. There are 2 types of hubs: Active and Passive. Passive Hub is Just a Hub but Active hub can do repeater functionality also. © Copyright Reserved by Gateflix.in No part of this material should be copied or reproduced without permission Switch: It is a Uni casting device. There are two switch configurations: 2-layer and 3- layer. 2- Layer switch operates at Data link layer and 3-layer switch operates at Network layer. Router: It is to calculate the optimal route among network nodes. It operates at network and transport layers. Bridge: It is a forwarding device, used to connect two or more LANs or network segments. It operates at Data Link Layer. There are 3 types of bridges: Simple, Learning and Multi Port. Gateway: It is used as intermediate between two or more dissimilar networks. It is capable to convert one protocol format to another. It operates at all the layers. NOTE: Network Hardware, further discussed in detail in Chapter 4. 1.4 TYPES OF COMPUTER NETWORKS 1.4.1 LOCAL AREA NETWORKS (LAN) Local area networks (LAN) are privately – owned networks within a single building or campus of up to a few kilo meters in size e.g. Networks within IIT campus. 1.4.2 METROPOLITAN AREA NETWORK (MAN) Metropolitan area network (MAN) is basically a bigger version of a LAN and can support both data and voice. It covers a group of nearby corporate offices or a city and might be either private or public. E.g. Network connecting all IITs 1.4.3 WIDE AREA NETWORK (WAN) Wide area network (WAN) spans large geographical area, often a country or continent. It contains a collection of machines intended for running user programs. In most wide area network, the subnet consists of two distinct components: transmission lines and switching elements. Transmission lines move bits between machines. They can be made of copper wire, optical fiber, or even radio links. Switching elements are specialized computers that connect three or more transmission lines. When data arrive on an incoming line, the switching element must choose an outgoing line on which to forward them. These switching computers have been called by various names in the past; the name router is now most commonly used. 1.4.4 SYSTEM AREA NETWORKS (SAN) Another kind of network that we need to be aware of is SANs (system area networks). SANs are usually confined to a single room and connect the various components of a large computing system. For example, HiPPI (High Performance Parallel Interface) and Fiber Channel are two common SAN technologies used to connect massively parallel processors to scalable storage server and data vaults. (Because they often connect computers to © Copyright Reserved by Gateflix.in No part of this material should be copied or reproduced without permission storage servers, SANs are sometimes defined as storage area network s). e.g. Organization connected worldwide. 1.4.5 LINE CONFIGURATION Line configuration refers to the way two or more communication devices attach to link. There are two possible line configurations: i) Point- to - Point A point–to–point line configuration provides a dedicated link between two devices. ii) Multi point A multiport line configuration is one in which more than two specific devices share a single link. 1.5 NETWORK TOPOLOGY Topology refers to the way a network is laid out, either physically or logically. Two or more devices connect to a link, and then these two or more links form a topology. The topology of a network is the geometric representation of the relationship of all the links and linking devices (usually called nodes) to each other. Topology is the relative status of the devices to be linked. It can either be peer- to –peer, where the devices share the link equally or primary – secondary, where one devices controls traffic and the others must transmit through it.