OE ae Les pepe 11.) Define Domain Name Space (DNS). What are the three domains of the domain name space? Expjai, DATA COMMUNICATION AND COMPUTER NETWORKS [JNTU, HYDERABAD, PART-B WITH SOLUTIONS 5.1 DOMAIN NAME SPACE Answer : Model Papers at Domain Name Space The domain name space isa structure where the names are defined in an inverted tree with the root atthe top, comprising of only 128 levels (level 0 — level 127). It was designed in order to have hierarchical structure @ o) The three domains of the domain name space are, (a) | Label (©) Domain name (© Domain, Root Challenger a ay Figure: Domain Name Space Label In the tree, e@th node has a unique label. A Label isa string of maximum 63 reed cacg ics ately wee lum 63 characters. The root label at the root node Domain Name Each node in a tree is represented by the domain name which can be defined as the separated by a dot (). It is always defined by starting from the node up to the root node of the tree, ST sent econgant null label, which isthe label ofthe root node. Thus, the last character of domain name isa dot). There are two types of domain names. They are, @ Fully Qualified Domain Name (FQDN). e. Gi) Partially Qualified Domain Name (PQDN). (Fully Qualified Domain Name (FQDN) ‘The FQDN is defined as the label that is terminated by a ull sting. Thus, i 5 name tat comprises the fill name of host. The DNS server reemgnizns ante me tO tis ame ‘Example: Challengercaresia.edu Look for the SIA GROUP LocorAserver to MTA client. Each command pene n se Toth ema nitrates oe don. The list of responses with ther descrinas Ee eee o i if code gives the status of the system or help reply This code is used to get the help messages. (i) 220 This code is used when the services are ready. fi) 221 ee order to close the services of 20 pe is used once the request commands are (wv) 251 This code describes that if the user is non local, still the server can forward the mail message. (wil) 354 ‘This code is used in order to initiate the mail input again. (vill) 421 ‘This code describes that the services are unavailable. (x) 430 ‘This code describes that the mailbox is unavailable. ® 481 “This code describes thatthe command is terminated de to the occurrence of local error. ee, ee ee 503 This code descri of sequence. 504 This code describes that the commands are not implemented during the short period of time. ww) es that the received command is out (vi) 550 “This code describes that the command is rejected for its ‘execution due to unavailability of the mailbox. (vii) (xvii) $51 ‘This code describes that the user is non local. (xix) $52 This code describes that the requested action is terminated due to the over loaded storage. (ay 553 ‘This code describes that the requested action is not considered due to the improper specification of the mail address and name. (xxi) 554 ‘This code describes that the mail transaction is failed due to the occurrence of errors. 18. How POP works? What are the advantages of IMAP over POP? Answer = PoP3 Post Office Protocol, version 3 (POP3) can be specified ‘as one of the simplest message access protocol. It demands installation of POP3 software not just on client machine but also on the server machine. ‘The following figure shows the architectural view of ‘communication taking place between a POP3 client and s POP3 ‘mail server.a FIP operates in peo modes, Ste oF panne modes 1 aceive axed. tbe client sends the IP address along with the por nuaer on which the cont Iter 1 the server machone ‘which thed establishes the TCP connection. In passive the cheat ean"t accept the incoming TCP connection ‘behind the firewall. Here, the IP address and port sumber are received fa response to the PASV command sent by the client to the server max hone “The data transfer using FTP can occur in one of the following three modes, Block Mode “The incoming data is broken down into several blocks “which are then forwarded over the TCP connection. Stream Mode "in this mode, all the incoming data is transmitted as a . stream. This leaves the entire processing over the TCP rather than on the FTP. No end-Sete GUMMMUNIGATION ANU COMPUTER NETWORKS LINTU-HYDERABAD Wile Type (i) Binary/Image Mod ——— Three types of files can be transferred over the data ‘Sonnection in FTP They are, @ ASCH file (W_tmage Binary file and Gi) BBCDIC tite, Data Structure ‘Taree types of data structures can be used for transferring files over the data connection in FTP. They are, @ File structure format, in which a file is represented as a ‘continuous stream of bytes. Record structure format, in which a fle is divided into a ‘mumber of records, This format is possible only for the Text files, ‘Page structure format, in which a file is divided into a ‘number of pages. Each page is associated with a page ‘number and a page header and is stored or accessed in random or a sequential manner. ‘Transmission Mode z ‘Three types of file transmission modes can be used for transferring files over the data connection in FTP. They are, (Stream mode (4) Block mode and mode storing a file differ from retrieving a file? What kind of file types can FTP transfer? Answer Fille Storage A file is stored by the clients on a server's (that is remotely situated) current directory by using STOR (put) ‘command. This STOR command causes the server to recognize and accept data or files being transferred and to store the data. ‘the file transferred does not exists on the server then a new file is created. On the other hand, ifthe file already exists with the same name, then its contents are replaced by the new file's content, File Retrieval ‘A file is retrieved from the current directory of host ‘that is remote to the client, by using RETR (put) command, ‘This invocation of this command results in establishing a data connection between host and the client, Thereafter, the requested file is transferred to the client from the server. w@ Gd, ‘Types of Files Being Transferred FTP can transfer different types of files such as, @ ASCH Fite ‘This mode is usually applied to the textual data. Here, the data is first converted from the sending host’s ‘character representation to the 8-bit ASCII format prior to its transmission and later it is converted back to the receiving host’s character representation, if needed, However, this method is not suitable for the files ‘containing data other than the plain text. Here, the data is transmitted byte-by machine. The receiver receives and stores data in the manner in which it was received (ili) ~~ EBCDIC Mode This mode is used for transferring the plain tex the hosts employing character sets in EBCDIC fon, i 5.6 www poy Q21, Discuss the architecture of WWW. Answer : Model Papert ato Architecture of WWW World Wide Web (WWW) is a storage place of information present across the globe which is interlinked wity a network commonly called internet. It offers features like flexibility, portability and user convenience. It w announced by CERN (European Laboratory Physics) as a system that is capable of managing the resources required for scientific research and are distributed over muliple locations. Modern WWW acts as the distributed client-server service where the requests generated from the clients are sened by the servers. Clients use web browsers for this purpose. The Places where the requested services reside are called as sites ‘websites, These websites carry documents called webpages and links to other documents or web pages. For instance, consider the below figure, initially Figure: Architecture of WWW In the above figure, the client wants to access ® documents that exist on website-1, tn this case, client gener request through browser. The request carries the address of ‘Website and web pages known as Uniform Resource Loa? (URL). A connection is established between client and se" and the requested document is returned to the client. 1F ‘document web page consists of references to website thee ™ client forwards a request to the website-? and the docunes® web pages an that website are also accessed.5.16 DATA COMMUNICATION AND ComPUTER NETWORKS [JNTU-HYDERABAD] Protocols Used in URL, The URL is-an open ended scheme that allows the browsers to use multiple protocols to fetch different types of resourves, ‘The seven most common protocols used in URLS are, 1 2 3. File 4, Ss z é a 6, 7. Telnet, 1 HTTP TRA TTP is an acronym for Hyper Text Transfer Protocol and has been in use with WWW since 1990, ‘The first version, HTTP. allowed forthe transfer ofraw data across the Internet. HTTP 1.0 evalved to provide messages in Multipurpose {nvemet Mail Extension (MIME) types. MIME includes different types of data like image files or audio files not possible with earlier version ). The latest version is HTTPS where security is taken extra care ‘ie communication between browser(client ) and server is defined by the HTTP. The same protocol is used in intranet also( intranet is Internet only, but used within organization), 2 FTP FTP (File Transfer Protocol) is used to access files by FTP. FTP is a standard intemet protocol through which internet users can upload files from theit computers to a website or download files from a website to theit PC's 3. File Tezbrotoeol is used to read or write the contents of file (i. ecess afl) present ona local filing system as awe page. f Performs similar fle access operations as that of the HTTP but does not require a server, as files ave present ata local filing system, 4. News News protocol is used to access news articles as a web page, The news protocol provides two schemes, (Defines a news group that is used to access a pre-configured news site, Gi)_Defines how a specific news article is accessed using an identifier for that news article 5. Gopher [hs mailto protocl is used for sending an e-mail via the web browsers, Clicking a mailto-tink i designed to trigger application that open’ yg the Ung ater aed begin new e-mail message. This is done by clicks onthe “OPEN button and then specifying the URL. in the following format, ‘mailto: Email address of the recipientSx DATA COMMUNICATION AND COMPUTER NETWORKS [JNTU-HYDERABAD} (Wi) Active Documents = ‘eS Astive documents are the documents that contain a PrORTaM or a script in it Which are executed at the client site Example a user wants fo run a program which is based on animated graphics, he/she has to carry out the execution of this program ‘atthe client site. To perform this execution, initially a browser Sends a request for an active document. Then, a copied docurnens ‘or script is transferred by the server to the browser to run the program at the client side ‘Active documents can be developed either by using an Java Aj ‘which the script has to be download and executed at the client site, Client Server a Client request for a copy of program Client Server [ Hesse | oss pplets which follows bytecode format or by JavaScripts in Sending a copy of the program Client Server Program W Wl Program Dee Running the program and creating the document 7 *.Q26. Explain in brief about the static web document. Figure (1: Request is Sent from Client to Server Web document ‘Chet ‘Sener ‘Figure (2): Server Sends the Response to the Client ‘An example of the static web documents is HTML.5.19 ——— imu a HIME (Hypertext a, language ad is irecty interme AteMEE) 8 the Preted by » Hy fodes (tags) that can be embedded ve wees tables ant lists within thy Common Tags tn HTML angi IRC used to create rowser. The HT ML ext and the text ¢ ML provides Gu nd develop web pages. The HTML is not a compiled ‘lactuments are also called Web Pages, HTML comes with special ‘an be linked (called hyperlinks) to other Web Pages. We ean include environment for user's input HEX HT a monty Used NTMI Ta ‘ ane HTM HTML ee is placed at the ‘start as well as at the end of ‘every HTML page, The “sl which resides between these tags forms the head, title and body of the HTML program, Wis compulsory that every HTML program should have ana een | SHTML> atthe start as well as at the end of the document - 2. | Mholds the head information of the HTML code (i.e.,) title, link, meta are| a Mei Stine of the tags that appears in the head region of the html document. 3. | The title whieh is displayed at the title bar of the html document is Provided using