Master of Computer Applications (MCA)

Paper Code: MCA-106Paper Title: Computer Networks & Internet ConceptInternal Assignment No. 2

Section-A

(i) Define IEEE 802.3(CSMA/CD).IEEE 802.3is aworking groupand a collection ofIEEEstandards produced by the working group defining thephysical layeranddata link layer'smedia access control(MAC) of wiredEthernet. This is generally alocal area networktechnology with somewide area networkapplications. Physical connections are made between nodes and/or infrastructure devices (hubs,switches,routers) by various types of copper orfiber cable.802.3 is a technology that supports theIEEE 802.1network architecture.802.3 also define LAN access method usingCSMA/CD.Short forCarrierSenseMultipleAccess /CollisionDetection,a set of rules determining hownetworkdevicesrespond when two devices attempt to use adata channelsimultaneously (called a collision). StandardEthernetnetworks use CSMA/CD to physically monitor the traffic on the line at participating stations. If no transmission is taking place at the time, the particular station can transmit. If two stations attempt to transmit simultaneously, this causes a collision, which is detected by all participating stations. After a random time interval, the stations that collided attempt to transmit again. If another collision occurs, the time intervals from which the random waiting time is selected are increased step by step. This is known as exponential back off.CSMA/CD is a type ofcontentionprotocol. Networks using the CSMA/CD procedure are simple to implement but do not have deterministic transmission characteristics. The CSMA/CD method is internationally standardized in IEEE802.3 and ISO 8802.3.

(ii) What is TCP/IP and UDP?TCP (Transmission ControlProtocol) is a standard that defines how to establish and maintain a network conversation via whichapplication programscan exchange data. TCP works with the Internet Protocol (IP), which defines how computers sendpackets ofdatato each other. Together, TCP and IP are the basic rules defining the Internet. TCP is defined by the Internet Engineering Task Force (IETF) in the Request for Comment (RFC) standards document number 793.TCP is aconnection-orientedprotocol, which means a connection is established and maintained until theapplication programsat each end have finished exchangingmessages. It determines how to break application data into packets thatnetworkscan deliver, sends packets to and accepts packets from the network layer, managesflow control, andbecause it is meant to provide error-free data transmissionhandles retransmission of dropped or garbled packets as well as acknowledgement of all packets that arrive. In theOpen Systems Interconnection(OSI) communication model, TCP covers parts of Layer 4, theTransport Layer, and parts of Layer 5, theSession Layer.Abbreviation ofTransmission Control Protocol,and pronounced as separate letters. TCP is one of the mainprotocolsinTCP/IPnetworks. Whereas theIPprotocol deals only withpackets, TCP enables twohoststo establish a connection and exchange streams of data. TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent.

UDP- UDP (User Datagram Protocol) is a communications protocol that offers a limited amount of service when messages are exchanged between computers in a network that uses the Internet Protocol (IP). UDP is an alternative to the Transmission Control Protocol (TCP) and, together with IP, is sometimes referred to as UDP/IP. Like the Transmission Control Protocol, UDP uses the Internet Protocol to actually get a data unit (called adatagram) from one computer to another. Unlike TCP, however, UDP does not provide the service of dividing a message into packets (datagrams) and reassembling it at the other end. Specifically, UDP doesn't provide sequencing of the packets that the data arrives in. This means that the application program that uses UDP must be able to make sure that the entire message has arrived and is in the right order. Network applications that want to save processing time because they have very small data units to exchange (and therefore very little message reassembling to do) may prefer UDP to TCP. The Trivial File Transfer Protocol (TFTP) uses UDP instead of TCP.

(iii) Define IP?

Definition - What doesIP Networkmean?An IP network is a communication network that uses Internet Protocol (IP) to send and receive messages between one or more computers. As one of the most commonly used global networks, an IP network is implemented in Internet networks, local area networks (LAN) and enterprise networks. An IP network requires that all hosts or network nodes be configured with the TCP/IP suite.

The Internet is the largest and best known IP network.Each host is assigned a unique logical IP address, which distinguishes it from other nodes and helps initiate data communication with other hosts. IP network communication occurs when a host sends a data packet to another host by addressing its IP address. Similarly, the recipient identifies the sender by its IP address.Moreover, an IP network requires that all connected devices - such as servers, switches, routers and other devices - be configured with the TCP/IP suite and have a valid IP address to perform any network communication.TheInternet Protocol(IP) is the principalcommunications protocolin theInternet protocol suitefor relayingdatagramsacross network boundaries. Itsroutingfunction enablesinternetworking, and essentially establishes theInternet.IP has the task of deliveringpacketsfrom the sourcehostto the destination host solely based on theIP addressesin the packetheaders. For this purpose, IP defines packet structures thatencapsulatethe data to be delivered. It also defines addressing methods that are used to label the datagram with source and destination information.Historically, IP was theconnectionlessdatagram service in the originalTransmission Control Programintroduced byVint CerfandBob Kahnin 1974; the other being the connection-orientedTransmission Control Protocol(TCP). The Internet protocol suite is therefore often referred to as TCP/IP.

(iv) What is Firewall? And Write the types of Firewall.

A firewall is a system designed to prevent unauthorizedaccessto or from a privatenetwork. Firewalls can be implemented in bothhardwareandsoftware, or a combination of both. Firewalls are frequently used to prevent unauthorizedInternetusers from accessing private networks connected to the Internet, especiallyintranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specifiedsecuritycriteria.

Conceptually, there are two types of firewalls:1.Network layer2.Application layer3.2.1 Network layer firewallsThese generally make their decisions based on the source, destination addresses and ports (see AppendixC for a more detailed discussion of ports) in individual IP packets. A simple router is the ``traditional'' network layer firewall, since it is not able to make particularly sophisticated decisions about what a packet is actually talking to or where it actually came from. Modern network layer firewalls have become increasingly sophisticated, and now maintain internal information about the state of connections passing through them, the contents of some of the data streams, and so on. One thing that's an important distinction about many network layer firewalls is that they route traffic directly though them, so to use one you either need to have a validly assigned IP address block or to use a ``private internet'' address block[3]. Network layer firewalls tend to be very fast and tend to be very transparent to users.

Figure 1:Screened Host Firewall

In Figure1, a network layer firewall called a ``screened host firewall'' is represented. In a screened host firewall, access to and from a single host is controlled by means of a router operating at a network layer. The single host is a bastion host; a highly-defended and secured strong-point that (hopefully) can resist attack.

Figure 2:Screened Subnet Firewall

Example Network layer firewall: In figure2, a network layer firewall called a ``screened subnet firewall'' is represented. In a screened subnet firewall, access to and from a whole network is controlled by means of a router operating at a network layer. It is similar to a screened host, except that it is, effectively, a network of screened hosts.3.2.2 Application layer firewallsThese generally are hosts running proxy servers, which permit no traffic directly between networks, and which perform elaborate logging and auditing of traffic passing through them. Since the proxy applications are software components running on the firewall, it is a good place to do lots of logging and access control. Application layer firewalls can be used as network address translators, since traffic goes in one ``side'' and out the other, after having passed through an application that effectively masks the origin of the initiating connection. Having an application in the way in some cases may impact performance and may make the firewall less transparent. Early application layer firewalls such as those built using the TIS firewall toolkit, are not particularly transparent to end users and may require some training. Modern application layer firewalls are often fully transparent. Application layer firewalls tend to provide more detailed audit reports and tend to enforce more conservative security models than network layer firewalls.(v) What is Virus? and Write the various types of Viruses.What are computer viruses and its types?

Computer Viruses are malicious software programs that damage computer program entering into the computer without the permission of the users, and also run against the wishes of the users. They are replicated by themselves. Viruses are so dangerous and malicious that they can be automatically copied and pasted from memory to memory over and over; the transmitting power is too much quick from network to network that can simply hang smoothly running computer, sometimes damage the important programs of the computer. Viruses are very dangerous program can go on their activities automatically and can do a great loss of the users.

All of the users of the computer dont like computer virus and also dont like to hear of it. But its a great mistake. You need to know much about the viruses as they are the enemies of your computer. The clear knowledge of the enemies will protect you from upcoming harm committed by the enemies.It is quite impossible to give the proper information about the types of viruses. The types of viruses are changing day by day. Therefore on the basis of their origin, hiding, damaging types, operating system etc their types as follows:

Boot Sector Virus:Boot sector virus infects the boot sector on floppy disks, hard disks and other bootable media like DVD or CD. The examples of boot sector viruses are Form, Michelangelo, and Stoned.

Macro Virus:A macro virus is an original individual amongst thetypes of computer virus, and contaminates the macros inside a pattern. As soon as you release a spreadsheet or word processing text, the macro virus gets into typical pattern. The examples of Macro viruses are Relax, Babbles, and Melissa.

Companion Viruses:Companion viruses are as same as direct action types or resident types. They are companion viruses as because sometimes they get into the method and accompany the other existing files. The example of accompany viruses are Asimov.1539, Terax.1069.

Section-BQ.1. Explain the media access control.In the seven-layerOSI modelofcomputer networking,media access control(MAC)data communication protocolis a sub layer of thedata link layer(layer 2). The MAC sub layer provides addressing andchannel accesscontrol mechanisms that make it possible for severalterminalsor network nodes to communicate within amultiple access network that incorporates a shared medium, e.g. anEthernetnetwork. The hardware that implements the MAC is referred to as amedia access controller.The MAC sub layer acts as an interface between thelogical link control(LLC) sub layer and the network'sphysical layer. The MAC layer emulates a full-duplex logical communication channel in a multi-point network. This channel may provide unicast,multicastorbroadcastcommunication service.TheMediaAccessControlLayer is one of two sublayers that make up the Data Link Layer of theOSImodel. The MAC layer is responsible for moving datapacketsto and from oneNetwork Interface Card(NIC) to another across a sharedchannel.In the Open Systems Interconnection (OSI) model of communication, the Media Access Control layer is one of two sublayers of the Data Link Control layer and is concerned with sharing the physical connection to the network among several computers. Each computer has its own uniqueMAC address.Ethernetis an example of aprotocolthat works at the Media Access Control layer level.Functions performed in the MAC sub layerAccording to IEEE Std 802-2001 section 6.2.3 "MAC sub layer", the primary functions performed by the MAC layer are:[1] Frame delimiting and recognition Addressing of destination stations (both as individual stations and as groups of stations) Conveyance of source-station addressing information Transparent data transfer of LLC PDUs, or of equivalent information in the Ethernet sub layer Protection against errors, generally by means of generating and checking frame check sequences Control of access to the physical transmission mediumIn the case ofEthernet, according to 802.3-2002 section 4.1.4, the functions required of a MAC are:[2] receive/transmit normal frames half-duplex retransmission and back off functions append/check FCS (frame check sequence) inter frame gap enforcement discard malformed frames prepend(tx)/remove(rx) preamble, SFD (start frame delimiter), and padding half-duplex compatibility: append(tx)/remove(rx) MAC address

Q.2.Explain the following in brief:(A) SMTP (B) FTP (C) DHCP (D) URLANS.(A) SMTP hort forSimpleMailTransferProtocol,aprotocolfor sendinge-mailmessages betweenservers. Most e-mail systems that send mail over theInternetuse SMTP to send messages from one server to another; the messages can then be retrieved with ane-mail clientusing eitherPOPorIMAP. In addition, SMTP is generally used to send messages from a mail client to a mail server. This is why you need to specify both the POP or IMAP server and the SMTP server when youconfigureyour e-mailapplication. Simple Mail Transfer Protocol(SMTP) is anInternet standardforelectronic mail(e-mail) transmission. First defined byRFC 821in 1982, it was last updated in 2008 with theExtended SMTPadditions byRFC 5321- which is the protocol in widespread use today.SMTP by default usesTCPport25. The protocol for mail submission is the same, but uses port 587. SMTP connections secured bySSL, known asSMTPS, default to port 465 (nonstandard, but sometimes used for legacy reasons).Although electronicmail servers and other mail transfer agentsuse SMTP to send and receive mail messages, user-level client mail applications typically use SMTP only for sending messages to a mail server forrelaying. For receiving messages, client applications usually use eitherPOP3orIMAP.Although proprietary systems (such asMicrosoft ExchangeandLotus Notes/Domino) andwebmailsystems (such asHotmail,GmailandYahoo! Mail) use their own non-standard protocols to access mail box accounts on their own mail servers, all use SMTP when sending or receiving email from outside their own systems.

(B) FTP TheFile Transfer Protocol(FTP) is a standardnetwork protocolused to transfercomputer filesfrom onehostto another host over aTCP-based network, such as theInternet.FTP is built on aclient-serverarchitecture and uses separate control and data connections between the client and the server.[1]FTP users may authenticate themselves using aclear-textsign-in protocol, normally in the form of a username and password, but can connect anonymously if the server is configured to allow it. For secure transmission that protects the username and password, and encrypts the content, FTP is oftensecuredwithSSL/TLS(FTPS).SSH File Transfer Protocol(SFTP) is sometimes also used instead, but is technologically different.The first FTP client applications werecommand-line applicationsdeveloped beforeoperating systemshadgraphical user interfaces, and are still shipped with most Windows,Unix, andLinuxoperating systems.[2][3]Many FTP clients and automation utilities have since been developed for desktops, servers, mobile devices, and hardware, and FTP has been incorporated into productivity applications, such asWeb page editors.(C) DHCP TheDynamic Host Configuration Protocol(DHCP) is a standardizednetwork protocolused onInternet Protocol(IP) networks for dynamically distributing network configuration parameters, such asIP addressesfor interfaces and services. With DHCP, computers request IP addresses and networking parameters automatically from a DHCP server, reducing the need for anetwork administratoror a user to configure these settings manually.Computers use the Dynamic Host Configuration Protocol for requesting Internet Protocol parameters from a network server, such as anIP address. The protocol operates based on theclient-server model. DHCP is very common in all modern networks[1]ranging in size fromhome networksto largecampus networksand regionalInternet service providernetworks. Most residential network routers receive a globally unique IP address within the provider network. Within a local network, DHCP assigns a local IP address to devices connected to the local network.When a computer or other networked device connects to a network, the DHCP client software in its operating system sends abroadcastquery requesting necessary information. Any DHCP server on the network may service the request. The DHCP server manages a pool of IP addresses and information about client configuration parameters such asdefault gateway,domain name, thename servers, andtime servers. On receiving a request, the server may respond with specific information for each client, as previously configured by an administrator, or with a specific address and any other information valid for the entire network, and the time period for which the allocation (lease) is valid. A host typically queries for this information immediately afterbooting, and periodically thereafter before the expiration of the information. When an assignment is refreshed by the client computer, it initially requests the same parameter values, but may be assigned a new address from the server, based on the assignment policies set by administrators.(D) URL Auniform resource locator(URL)is a reference to aresourcethat specifies the location of the resource on acomputer networkand a mechanism for retrieving it. A URL is a specific type ofuniform resource identifier(URI).[1]although many people use the two terms interchangeably.[2]A URL implies the means to access an indicated resource, which is not true of every URI.[2][3]URLs occur most commonly to reference web pages (http), but are also used for file transfer (ftp), email (mailto), database access (JDBC), and many other applications.Mostweb browsersdisplay the URL of a web page above the page in anaddress bar. A typical URL has the formhttp://www.example.com/index.html, which indicates the protocol type (http), the domain name, (www.example.com), and the specific web page (index.html).The Uniform Resource Locator was standardized in 1994[4]byTim Berners-Leeand the URI working group of theInternet Engineering Task Force(IETF) as an outcome of collaboration started at the IETF Living Documents"Birds of a Feather"session in 1992.[5][6]The format combines the pre-existing system ofdomain names(created in 1985) withfile pathsyntax, whereslashesare used to separatedirectoryandfilenames. Conventions already existed where server names could be prepended to complete file paths, preceded by a double-slash (//).Berners-Lee later regretted the use of dots to separate the parts of thedomain namewithinURIs, wishing he had used slashes throughout.[7]For example,http://www.example.com/path/to/namewould have been writtenhttp:com/example/www/path/to/name. Berners-Lee has also said that, given the colon following theURI scheme, the two slashes before the domain name were also unnecessary.