SMU MBA IT 3 sem Solved Assignment Computer Networks

Computer Networks

1.    Explain the working of Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Protocol.

CSMA/CD is a set of protocols used to resolve and manage collisions of data that occur during the transfer of data. The CSMA/CD protocol is used in the second layer (data link layer) of the OSI model. Fig shows the working of CSMA/CD in a flowchart:

Simultaneous data transmissions by two nodes or devices degrade the

performance of the Ethernet, resulting in collisions. In such situations,

CSMA/CD is helpful. Data transmitted over the network is referred to as a

frame. Devices are connected through Ethernet technology of LAN uses

CSMA/CD as a base for the transmission of data. Devices on the network

are first connected to cables to access the CSMA/CD protocol.

The device that has to send the data first senses or detects whether the transmitting medium is free or not, with the help of a carrier (a specified level used for the transmission of a frame). If the carrier is detected, then the transmission is delayed until the carrier is terminated and a notification signal is sent to the device, while the non-detection of the carrier signifies that the medium for transmitting the frame is free and the process can proceed.

When the medium is found free, the device transmits the frame. If two or more devices transmit the frames at the same time, collision occurs. Carrier sensing detects for these collisions. This whole process of collision is known as listen while talking. When collision detection occurs, the device transmitting the frames waits for an indefinite period before retransmitting the frames. The process in which devices wait before transmitting frames is known as back off.

The period for which the device waits is decided by a random number that is generated by the collisions counter located on each device. The function of collisions counter is to count the number of frames for which one or more collisions happened when the frames were transmitted.

After a back off, the device involved in collision, broadcasts data again. This whole process is continued till a carrier is not detected or sensed.

If collision is not found in the working of CSMA/CD then transmission of the frame takes place and the process of transmission completes; otherwise, the frame is re-transmitted to the node until the collision counter is cleared.

2.    Write short notes on

a. Coaxial Cables

b. Satellite

c. Microwave

d. Value-added Network

e. Web EDI

Coaxial Cables

Coaxial cables are another type of transmission media having better shielding than twisted-pair media. A coaxial cable has a metal wire in the central axis covered by insulating material. These cables are mainly used in television dish, LANs, and long distance telephone networks. Coaxial cables are shielded in a better way; therefore, they are less prone to noise. The bandwidth of the signal is entirely based on the cable quality.

They can transfer the signals up to 1 GHz. Coaxial cables were widely used for the long distance telephone lines, but now they are largely replaced by fibre optics. However, they still have dominance in cable television and metropolitan area network (MAN).

Satellite

Satellite communication mode transmits and receives the data over the network using a series of satellites in orbits; thereby, allowing for long-range wireless communication. The satellite wireless mode includes satellite television, satellite phones, satellite Internet service, and Global Positioning

System (GPS). Satellite is the most widely used wireless communication medium nowadays. Due to this, satellite communication products, such as

Communications Intelligence (COMINT), are designed keeping the security issue in mind. COMINT provides consumers with intelligence on diplomatic, economic, and scientific developments. Different communication intelligence equipment’s have been designed to provide all security aspects with a secure communication channel. Satellites provide a way to build secure virtual networks. In addition, it enables you to include remote networks in secure virtual networks.

Microwave

Microwave is also used in global transmissions, which use geosynchronous satellite and ground-based dishes to adhere to the line-of-sight requirement. Microwave uses higher transmission for both short distance and global transmission. It can be used to extend the LAN’s using wireless. The limitation of using a microwave is that the transmitter and receiver must be within the line of sight of each other. It can be extremely expensive, but it is less susceptible to signal interference and eavesdropping than radio waves and provides higher bandwidth.

VAN

VAN acts as a regional post office in EDI, which first receives a transaction, verify the to-and-from information, and direct the transaction to the final recipient. VAN provides numerous other services, such as retransmitting documents, providing third party audit information, acting as a gateway for different transmission services, and handling telecommunication supports. organizations even in the cases when both trading parties are using

Internet-based protocols for transferring data.

VANs also help in replacing the certificates in the Applicability Statement 2(AS2) mode of transmission of data. Each mode in the traditional business oriented

AS2 transmission includes a security certificate. When a large number of partners are routed through VAN, the certificates can be replaced more easily. The functionalities of VAN as a transmission medium are as follows:

·         Routes, stores, and delivers EDI messages and provides delivery reports;

·         Examines the EDI messages and specifies the requirements whether or not the messages need extra envelopes for transfer of information; and,

·         Operates using various entities. Due to the services provided by VAN, it is preferably used by business

Web EDI

The Internet employs its own communication protocols for secured transmission of EDI documents over a network. The most commonly used protocols are HTTPS, AS2, and FTP using SSL (FTPS). Web-based EDI or the Web EDI allows an organization to interact with its buyers or suppliers in distant regions, without implementing a complex EDI infrastructure.

In other words, Web EDI helps the small to medium-scale business organizations to receive, create and manage electronic documents using only a Web browser. Web EDI transforms the transmitted data into the EDI format and then forwards the transformed data to the other trading partner.

EDI transactions can be received, edited and forwarded easily by using a Web-based interface, which can be accessed from anywhere.

The Web EDI works on the hub and spoke model, where the major trading partners or Application Servers are the hubs and the smaller partners are the spokes. The trading partners can send EDI messages directly to a web enabled EDI messaging site by using the hub and a Web browser. Web EDI users can interact with VANs without incurring the costs of setting a dedicated VAN connection.

3.    Write short notes on

a. Subnet

b. Super netting

c. Subnet masks

d. Dynamic NAT

e. Domain Name System

Subnets

A network that exists within the Class A, B, or C network is called a subnet. It can also be defined as a network within a network. Subnets are created to extend network IDs by using host bits of one or more Class A, B, or C. Therefore, subnets can have a network ID of any length. All devices that have IP addresses with same prefix are defined as subnets. These are connected to the Internet by using the same shared network. While designing a subnet, always specify the maximum number of subnets that are required and ensure that enough host addresses are available.

Supernetting

Supernetting is defined as the combination of all network routing commands in a single routing table entry. It is commonly called Classless Inter-Domain Routing (CIDR). It is designed to solve the problems such as, wastage of many addresses in the Class addresses.

Supernetting resolves many problems arising because of subnetting, such as, all zeroes, and all ones masks in the IP addresses. Supernetting, like subnetting, can take any number of host IDs. The difference between supernetting and subnetting is that in supernetting, the host and network IDs are merged, while in subnetting the IDs are split. CIDR masks for classes A, B, and C are /8, /16, and /24, respectively.

Subnet Masks

A subnet mask is another 32 bit number defined for identifying a subnetwork. Subnet masks describe the bits associated with the network and host IDs. If an octet in the subnet mask is equal to 1 it refers to the network ID, and if it is equal to zero it refers to the host ID. Subnet masks inform routers about the working of subnetting. The network ID of an IP address is determined when the router has both the IP address and subnet masks. Subnet masks defined with the Class A, B, and C addresses are the default subnet masks.

Network Address Translation

Network Address Translation (NAT) is a method used to convert a local IP address of a system into a global and unique IP address before the transmission of information takes place over an external network (Internet).

NAT technology is used as a firewall. So if computer in a company network uses local address 127.0.0.1 and it has to communicate to internet public address like www.google.com than the request from this computer is passed on by firewall to www.google.com however the IP address by the firewall will be changed (Natted) to public IP address of company. Multiple IP addresses are used internally by an organisation to join several ISDN connections into a single Internet connection. A system on NAT cannot be accessed by external network systems. NAT increases network security by hiding the internal structure of a network from systems outside the network.

DNAT, similar to SNAT, is used in large organisations for mapping private (internal) IP addresses to public (registered) IP addresses. However, unlike SNAT, DNAT maps private IP addresses to a group of registered IP addresses.

Domain Name System

Domain Name System (DNS) is a facility provided by the TCP/IP that allows you to remember only the name of a site instead of a lengthy IP address. It is a client/server based architecture that functions at the Application Layer. Nowadays, the use of Internet services is widespread. The name of a site you type in the address bar is converted into an IP address. Suppose, the DNS utility was not available and you wanted to search for information on any topic from Google. In that case, you had to type 216.239.51.10 instead of typing www.google.com.

4.    a. What is an email? List the advantages of an Email

b. Write the steps to set up a pop-up blocker

E-mail

E-mail is short form for electronic mail, a service that helps you communicate with others on the Internet. Through e-mail, you can communicate with anyone connected to the Internet and possessing an email identification (e-mail id) by sending and receiving electronic messages within seconds. In the starting days of this service, you could only send textual messages. However, today it is possible to send or receive information in different formats ranging from scanned/faxed images to Computer graphics and sound and video files along with your e-mail messages.

Advantages of E-mail

1.       Saves paper and allows you to edit the message easily.

2.       Transmits messages faster than other conventional forms of communication, such as postal service

3.       Sends messages according to the sender’s convenience

4.       Provides space to store incoming and outgoing email messages for future reference.

5.       Enables a user to transmit a single e-mail message to multiple users.

b. Steps to set up pop-up blocker.

1. Click the Tools menu in the Menu Bar of the Internet Explorer window.

2. Now, click the Pop-up Blocker option in the drop-down menu.

3. Click the Pop-up Blocker Settings option in the sub-menu to allow popup windows from any specific website and set the filter level.

4. Type the address of the website pop-up that you want to allow under the Address of website to allow option.

5. Click the Add button.

6. Repeat steps 4 and 5 to add other websites in the Allowed sites box.

7. Next, click the down arrow button below the filter level option to set the filter level.

8. Select an option — High, Medium or Low — as per your preference from the drop-down menu. In our case, we have selected the Low option.

9. Now, click the Close button.

5. Briefly explain the networking applications in government sector

In the government sector, e-governance is part of the networking applications. Electronic governance (e-governance) is the application of IT by the government for providing better facilities or services to its citizens, in an efficient manner. It helps in improving access of citizens to the government services and delivering these services on time. In other words, e-governance is a medium used by the government for interacting with its citizens electronically. E-governance is preferred because it provides the government with a cheap, transparent and easy way of interacting with its people. Therefore, e-governance can be considered as an application of electronics in governance.

·         To provide access to information about political processes, services and choices available to the people.

·         To encourage active participation of citizens by informing, consulting and involving them in various government activities.

·         To satisfy and fulfill the needs of citizens at the front office by simplifying their interaction with several online services.

·         To facilitate speedy, transparent and accountable administration services at the back office.

MCA 21— India’s Prestigious G2B Services Portal

The project named MCA 21 was conceived and implemented by the Ministry of Company Affairs in association with Tata Consultancy Services Limited to provide e-governance in the field of Company Law. This project provides the authorised signatories (stakeholders) or employees of companies, citizens and investors across the country with access to the online services provided by the Ministry of Company Affairs.

National Portal of India

The National Portal of India was developed in order to enable a single window access to information and services that are being provided by various entities of the Indian government. The content of this portal is the result of a combined effort of several ministries and departments of the Government of India, at the central, state or district level. The National

Portal of India is a Mission Mode Project, which lies under the National EGovernance Plan that was designed and maintained by National Informatics Centre (NIC), Department of Information Technology (DIT), Ministry of Communication and Information Technology (MoCIT) and Government of India. The URL of the National Portal of India is www.india.gov.in.

Income Tax Portal

The need for efficient tax collection system has been long felt in India. Therefore, the Income Tax department launched a website in 2002, with the aim to provide information that would help users to pay their income tax as well as solve their queries. Later in 2005-2006, electronic transactions were introduced through the income tax website. Presently, 19 services are

offered through this website. The URL of the income tax portal is www.incometaxindia.gov.in/home.asp.

Consular Passport and VISA Division (Passport Office of India)

Consular Passport and VISA Division, a division of Ministry of External Affairs, is the Indian Passport office for the people of India. It is an executive agency of the Government of India, which is responsible for issuing passports to Indians. Consular Passport and VISA Division portal helps citizens with any tasks or issues related to passports and answer any queries that they may have. The URL of the passport office of India is www.passport.gov.in.

Supreme Court of India

The Supreme Court of India is the highest judicial body in India. It also has a website that contains information related to the cases handled by it and the judgments it has passed. In addition, the website provides case studies, news and e-filing. The URL of the supreme court of India is www.supremecourtofindia.nic.in.

Indian Courts

Indian courts are a bouquet of websites, containing the websites of the Supreme Court and all 21 High Courts, and their branches in India. It offers a single point of access to information related to the Supreme Court or any High Court in India. The URL of the Indian courts is www.indiancourts.nic.in.

Defence Research and Development Organisation

Defence Research and Development Organisation (DRDO) works under the Department of Defence Research and Development of the Ministry of Defence. DRDO is a network of more than 50 laboratories that are involved in developing defence technologies covering various disciplines, including aeronautics, armaments, electronics, combat vehicles, engineering systems, instrumentation, missiles, advanced computing and simulation, special materials, naval systems, life sciences, training, information systems and agriculture. The URL of DRDO is www.drdo.gov.in.

6.    Explore the different models in cloud environment and their examples

Introducing Infrastructure as a Service

Infrastructure as a Service (IaaS) allows you to deliver hardware resources, such as servers, storage space and network, as cloud service to the customers. In addition, operating systems and virtualisation technology are provided to the customers to manage the resources. IaaS delivers computer infrastructure, i.e., the virtualised infrastructural environment as a service to the end users. Clients or customers, instead of investing in hardware or software resources, can simply purchase these resources as the outsourced service. This reduces the problems faced by customers in purchasing and installing these resources in their data centre. For such services, the cloud service providers charge the customers on the utility computing basis. It implies that the customers pay for this service on the basis of the amount of resources being utilised.

Introducing Platform as a Service

Platform as a Service (PaaS) offers the platform on a cloud for the customers and the services are consumed through the Web browser. In PaaS, the service provider offers you an integrated set of software that allows developers to build applications without installing any software for both application development and runtime. PaaS offers all the functionalities required for lifecycle management and provides Web applications on a cloud. When we talk about lifecycle management, we mean managing all the stages of software development, such as planning, designing, testing and deploying.

Introducing Software as a Service

Software as a Service (SaaS) is a software delivery model in which the required software is provided to customers on-demand and the software as well as its associated data is centrally hosted on cloud by a vendor. The software provided as a service is accessed by the customers through the Web browser. Generally, the hosted set of software that can run on a platform as well as infrastructure is provided to the customers, and the service providers charge on the basis of utilisation. When software is provided as a service, the customers are not required to do any development or programming; instead, they can simply configure the software.

Explaining Cloud Elements

Cloud computing solution comprises components such as clients, data centre and distributed servers. Each cloud component has a specific purpose and plays a major role in offering functional cloud-based application.

Clients: This signifies the general computers that you use at your home or in office. For instance, clients can be laptops, tablet computers, PDAs, PCs or mobile phones which access the data available on clouds. In general, clients are those devices that are used by the end users to work with their data available on the cloud.

Data Centre: This refers to the collection of servers on which the applications of the clients are installed or hosted. You can consider data centre as a large room in your office or room filled up with servers. Clients can access applications hosted by a data centre through the Internet. The growth and development in the IT world led to the introduction of virtual servers. This implies that multiple instances of virtual servers can be installed on a single physical server. Note that the count up of the virtual servers that you can install on a single physical server depends on the size and speed of the server.

Distributed Servers: This refers to the collections of servers that are located at geographically distant locations. However, due to the instant accessibility of data, clients assume that these servers are available at a single location. At the same time, due to the distributed nature of servers, cloud service providers have scalability in options and security. To understand how providers have flexibility due to the use of distributed servers, let us consider an example. The Google Cloud service provider has its servers distributed all across the world. Therefore, if a failure of any one of the server takes place, the customers can access the service through another server. Moreover, in terms of scalability, the distributed servers are a better option for service providers because of need of an additional hardware on cloud; the service providers can simply add the hardware on another server to provide it on the cloud.