Computer Network

Hem Sagar Pokhrel

Faculty Member, Lecturer

Computer Systems and IT Applications

Prime College

Unit VII

Internet

service

provider

Internet backbone

Broadband

Internet

Interconnection between two or more than two

nodes

Connected using wired or

wireless media.

For communication and resource

sharing purpose.

Each computer or

devices connected on

network is called as

node or host. E.g.

Your laptop, modem,

routers, switch,

smartphones and so

on..

Wired media

(Guided Media)

Twisted Pair Cable

Fiber Optics

Coaxial Cable

Wireless media

(Unguided Media)

Twisted Pair Cable

Fiber Optics

Coaxial Cable

Resource may

be data,

software or

hardware

Introduction to Computer Network

Introduction to Computer Network

Computer network can be defined in various ways:

▪ A collection of computing devices that are connected in various ways in order to communicate and share resources.

▪ In other words, computer network is interconnection between two or more than two computing devices using guided or unguided medias for resource sharing or communication purpose.

▪ It is a telecommunications network that allows computers to exchange data.

▪ The best-known computer network is the internet.

Benefits over standalone computers

1. Distributed Processing Capability

2. Enhance Storage Capability

3. Centralized Security Management

4. Centralized resource access

5. Greater Scalability

6. Robustness

7. Redundancy

Usage of Computer Network

1. Sharing of Resources▪ Hardware sharing e.g. Printer Sharing in college & banking

institutions

▪ Sharing of information e.g. WWW, emails, databases etc.

2. Communication and Entertainment▪ Social network, Internet Calls, VOIP, Online games and so

on..

3. Research, Education and Business▪ Share views, ideas among students and research teams

▪ Online business and marketing (email marketing, Social Media Marketing)

▪ Business may use network for Electronic Data Interchange(EDI), Enterprise Resource Planning(ERP) and Customer Relationship Management etc.

Some Networking Terms

• The generic term node or host refers to any device on a network

• Data transfer rate refers to the speed with which data is moved from one place on a network to another

• Data transfer rate is a key issue in computer networks.

• Computer networks have opened up an entire frontier in the world of computing called the client/server model

• File server A computer that stores and manages files for multiple users on a network

• Web server A computer dedicated to responding to requests (from the browser client) for web pages

Figure: Client/Server interaction

Communication/Transmission MediaGuided/Bounded and Unguided/Unbounded Media

▪All types of communications need some kind of medium.

▪ The information is encoded in a signal that is carried through a medium.▪ Quality depends on the characteristics of the medium.

▪ Two main groups of transmission media, namely the guided/wire medium and the unguided/wireless medium.

▪ For the guided medium, there is a physical path (such as a cable) for electromagnetic wave propagation. E.g. Coaxial Cable, Twisted Pair Cable, Fiber Optics etc.

▪ For the wireless medium, the electromagnetic wave is transmitted through air, water, or vacuum (space). E.g. Microwave communication, Satellite Communication etc.

Communication/Transmission MediaGuided/Bounded and Unguided/Unbounded Media

Types of Computer Network

1. Personal Area Networks (PANs)

2. Local Area Networks (LANs)

3. Metropolitan Area Networks (MANs)

4. Wide Area Networks (WANs)

On the basis of Size and Coverage Area

1. PERSONAL AREA NETWORKS (PANs)

▪ A personal area network (PAN) is a computer network used for communication among computer and different information technological devices close to one person.

▪ Is a small network established for communication between different devices, such as laptops, computers, mobiles, and PDAs.

▪ A pan may include wired and wireless devices.

▪ The reach of a pan typically extends to 10 meters.

Local Area Network(LANs)

▪ A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as a home, school, office building, or closely positioned group of buildings.

▪ Each computer or device on the network is a node.

▪ Wired LANs are most likely based on Ethernet technology.

LAN: Topologies

• Various configurations, called topologies, have been used to administer LANs

• Ring topology A configuration that connects all nodes in a closed loop on which messages travel in one direction

• Star topology A configuration that centers around one node to which all others are connected and through which all messages are sent

• Bus topology All nodes are connected to a single communication line that carries messages in both directions

LAN: Topologies

▪ A bus technology called Ethernet has become the industry standard for local-area networks

Figure: Various network topologies

15-10

Metropolitan Area Network (Wan)

▪ It is relatively larger than LAN and extends across a city or a metropolitan.

▪ It is created by connecting two or more LANs located at different locations in a city.

Wide Area Network(Wans)

▪ A wide area network (WAN) is a computer network that covers a large geographic area such as a city, country, or spans even intercontinental distances.

▪ A WAN uses a communications channel that combines many types of media such as telephone lines, cables, and air waves.

▪ A WAN often makes use of transmission facilities provided by common carriers, such as telephone companies.

▪ One of the most prominent examples of the existing wans is the Internet.

Types of Networks

• Wide-area network (WAN) A network that connects two or more local-area networks over a potentially large geographic distance

Often one particular node on a LAN is set up to serve as a gateway to handle all communication going between that LAN and other networks

Communication between networks is called internetworking

The Internet, as we know it today, is essentially the ultimate wide-area network, spanning the entire globe

Types of Networks

Figure: Local-area networks connected across a distance to create a

wide-area network

So, who owns the Internet?

Well, nobody does. No single person or company owns the Internet or even controls it entirely. As a wide-area network, it is made up of many smaller networks. These smaller networks are often owned and managed by a person or organization. The Internet, then, is really defined by how connections can be made between these networks.

Types of Computer Network

1. Client-server Network

2. Peer-to-peer Network

On the basis of Architecture

Classification of Network

▪ The architecture of a network is a logical design that determines how the devices in the network communicate.

▪ The commonly used architectures for computer networks are:

1. Client-server architecture

2. Peer-to-peer architecture

3. Hybrid architecture

PEER-TO-PEER ARCHITECTURE

▪ On a network built using the peer-to-peer architecture, there is no specific distinction exists between a client and a server.

▪ Any node can provide a service as well as send a request for a service from another node on the network.

▪ The peer-to-peer network architecture allows sharing of resources, data, and users.

▪ Each node on the network has full control over the network resources.

▪ Peer-to-peer network is also called workgroup

▪ No hierarchy among computers all are equal

▪ No administrator responsible for the network

Peer-to-peer

PEER-TO-PEER ARCHITECTURE

24▪ Advantages of peer-to-peer networks:

▪ Low cost

▪ Simple to configure

▪ User has full accessibility of the computer

▪ Disadvantages of peer-to-peer networks:▪ May have duplication in resources

▪ Difficult to uphold security policy

▪ Difficult to handle uneven loading

▪ Where peer-to-peer network is appropriate:▪ 10 or less users

▪ No specialized services required

▪ Security is not an issue

▪ Only limited growth in the foreseeable future

CLIENT-SERVER ARCHITECTURE

▪ On a network built using the client-server architecture, the devices communicate to other devices through a central computer referred to as a server.

▪ The server is a computer with high processing power, which provides services for the other computers on the network.

▪ The client is a terminal that accesses the resources available on a server.

▪ Clients (Workstation)▪ Computers that request network resources or services

▪ Network Servers▪ Computers that manage and provide network resources and

services to clients

▪ Usually have more processing power, memory and hard disk

space than clients

▪ Run Network Operating System that can manage not only

data, but also users, groups, security, and applications on

the network

▪ Servers often have a more stringent requirement on its

performance and reliability

CLIENT-SERVER ARCHITECTURE

Advantages of client/server networks▪ Facilitate resource sharing – centrally

administrate and control

▪ Facilitate system backup and improve fault

tolerance

▪ Enhance security – only administrator can

have access to Server

▪ Support more users – difficult to achieve with

peer-to-peer networks

Disadvantages of client/server networks▪ High cost for Servers

▪ Need expert to configure the network

▪ Introduce a single point of failure to the system

NETWORK TOPOLOGY..

▪ A network topology is the pattern in which nodes (i.e., computers, printers, routers or other devices) are connected to a local area network (LAN) or other network via links (e.g., twisted pair copper wire cable or optical fiber cable).

▪ The pattern of interconnection of nodes in a network is called the Topology. (Physical)

▪ This layout also determines the manner in which information is exchanged within the network. (Logical)

▪ The different types of network topologies that can be used to set up a network are:

1. Bus Topology

2. Star Topology

3. Ring Topology

4. Mesh Topology

5. Tree Topology

6. Hybrid Topology

Network TopologiesLogical and Physical Topologies

▪ Logical topology, or signal topology, is the arrangement of devices on a computer network and how they communicate with one another.

▪ The physical topology is the way you physically lay out the network, like a map. (i.e. structure of how nodes are connected)

▪ logical topology is the way the information flows on the network. (i.e. how information flows)

▪ Usually, the physical and logical topology is the same, but sometimes they can differ.

▪ Simply, topology in general, refers to physical topology in network.

BUS TOPOLOGY

▪ Popular topology for data network.

▪ Single transmission medium onto which various nodes are attached.

▪ Normally coaxial cable is used.

▪ Terminators at both end of BUS absorb signal, removing it from BUS.

▪ Simple and low-cost

▪ A single cable called a trunk (backbone, segment)

▪ Only one computer can send messages at a time

▪ Passive topology - computer only listen for, not regenerate data

Star Topology

▪ The star topology connects nodes over a network using a central control unit called the hub.

▪ You can easily add nodes to a star-based network by attaching the required nodes to the hub.

▪ Setting up a star topology requires a lot of cabling because all the nodes have to connect to the hub.

Ring topology

▪ The ring topology connects the nodes on a network through a point-to-point connection.

▪ Data is accepted from one neighboring node transmitted to other.

▪ Data travels in one direction.

▪ If one of the nodes on the network stops, the entire network stops functioning.

Mesh Topology

▪ Each node is connected to more than one node.

▪ This provide an alternate route mechanism.

▪ Excellent for long distance networking.

▪ Supports back-up and rerouting.

▪ Used in large internetworking environments with stars, rings and buses as nodes .

Tree topology

▪ The tree topology is created where the nodes are connected in a hierarchical manner.

▪ In tree topology, the device at the root is referred to as the parent for all the other nodes or devices in the network.

▪ The nodes below a parent node are referred to as child nodes.

Hybrid Topology

▪ The hybrid topology can be a combination of two or more basic topologies, such as bus, ring, star, mesh, or tree.

▪ Hybrid networks combine more than two topologies, which, in turn, enable you to get advantages of the constituent topologies.

IP Address

▪ IP address is an unique identification numbers that identifies each computer/devices using the Internet Protocol to communicate over a network.

▪ Your computer's IP is like your home's mailing address.

▪ An IP address consists of four numbers called as octet, each of which contains one to three digits, with a single dot (.) called as period separating each number or set of digits.

▪ Each of the four numbers can range from 0 to 255.

▪ Here's an example of what an IP address might look like: 204.132.40.155 where value of each octet ranges from 0 to 255.

▪ In fact, it is a 32-bit number subdivided into four bytes.

▪ This is how your computer sees that IP:

11001100.10000100.00101000.10011011

This addressing scheme is called IP Version 4 i.e. IPV4 scheme.

Network Addresses

• An IP address can be split into• network address, which specifies a specific network

• host number, which specifies a particular machine in that network

An IP address

represented as 4

bytes

CLASSFUL IP ADDRESS CONCEPT

You can determine which class any IP address is in by examining the first 4 bits of the IP address.

Class A addresses begin with 0xxx, or 1 to 126 decimal.

Class B addresses begin with 10xx, or 128 to 191 decimal.

Class C addresses begin with 110x, or 192 to 223 decimal.

Class D addresses begin with 1110, or 224 to 239 decimal.

Class E addresses begin with 1111, or 240 to 254 decimal.

IPV4 Address

Q: Why we are running out of IPV4 Addresses ?

A: IPv4 uses 32 bits for its Internet addresses. That means it can support 2^32 IP addresses in total — around 4.29 billion. That may seem like a lot, but all 4.29 billion IP addresses have now been assigned to various institutions, leading to the crisis we face today.

A new version of IP Address i.e. IPV6

What Next ?

IPV6 Address

▪ Unlike the familiar IPv4 addresses which are 32 bits long, written in decimal, and separated by periods, IPv6 addresses are 128 bits long, written in hexadecimal, and separated by colons.

▪ An example would be like: 3ffe:1900:4545:3:200:f8ff:fe21:67cf

▪ Each alphanumeric set of hexadecimal numbers separated by colon are called as group.

▪ Colons separate 16-bit fields. Leading zeros can be omitted in each field as can be seen above where the field :0003: is written :3:

▪ In addition, a double colon (::) can be used once in an address to replace multiple fields of zeros. ▪ For example:

fe80:0:0:0:200:f8ff:fe21:67cf

can be written

fe80::200:f8ff:fe21:67cf

IPV6 Address

Q: How does IPv6 solve the problem of IPV4?

A: IPv6 utilizes 128-bit Internet addresses. Therefore, it can support 2^128 Internet addresses —340,282,366,920,938,000,000,000,000,000,000,000,000 of them to be exact. That's a lot of addresses, so many that it requires a hexadecimal system to display the addresses. In other words, there are more than enough IPv6 addresses to keep the Internet operational for a very, very long time.

IPV4 Vs IPV6

1. An IPv6 address consists of 128 bits, while an IPv4 address consists of only 32.

2. IPv6 has a lot more usable addresses compared to IPv4. (2^128)3. IPv6 makes the router’s task more simple compared to IPv4.4. IPv6 is better suited to mobile networks than IPv4.5. IPv6 addresses are represented in a hexadecimal, colon-

separated notation, while IPv4 address use the dot-decimal notation.

6. IPv6 allows for bigger payloads than what is allowed in IPv4.7. IPv6 is used by less than 1% of the networks, while IPv4 is still in

use by the remaining 99%.

Advantages of Computer Network

1. Resource Sharing2. Job Sharing 3. Communication4. Centralized Software Management5. Speed6. Cost Reduction7. Interactive Entertainment

Other advantages

1. It enhances communication and availability of information.

2. It allows for more convenient resource sharing.

3. It makes file sharing easier. 4. It is highly flexible. 5. It is an inexpensive system. 6. It increases cost efficiency. 7. It boosts storage capacity.

Disadvantages of Computer Network

1. Expensive to install and manage2. Data Security3. Manager Dependence4. Vulnerable to hackers and viruses5. Social Problems

Disadvantages..

1. It lacks independence. 2. It poses security difficulties. 3. It lacks robustness. 4. It allows for more presence of computer viruses and malware. 5. It requires an expensive set-up.6. It requires an efficient handler.

Phew !