1. What Are the Responsibilities of Application Layer?

UNIT-5 APPLICATIONS

Applications - DNS- SMTP – WWW –SNMP- Security –threats and services - DES- RSA- web

security -SSL

2-Marks with answer

1. What are the responsibilities of Application Layer?

The Application Layer enables the user, whether human or software, to access thenetwork. It provides user interfaces and support for services such as e-mail, shared databasemanagement and other types of distributed information services

oNetwork virtual Terminal

oFile transfer, access and Management (FTAM)

oMail services

oDirectory Services

2. What is Encapsulation and De-capsulation ?

To send a message from one application program to another, the TCP/UDP protocolencapsulates and de-capsulate messages.

3. What is DNS?

Domain name service is the method by which Internet address in mnemonic formsuch assun.it.ac.in are converted into the equivalent numeric IP address such as 134.220.4.1

4. What is Fully Qualified Domain Name?

If a label is terminated by a null string is called a Fully Qualified Domain Name.

5. What is Generic Domains?

Generic domain define registered hosts according to their generic behaviour. Each

node in the tree defines a domain, which is an index to the domain name space database

Eg.com – Commercial organizations

edu - Educational institutions

gov - Government institutions

6. What is simple mail transfer protocol?

The TCP/IP protocol that supports electronic mail on the internet is called SimpleMail Transfer Protocol (SMTP). It is a system for sending messages to other computer usersbased on email addresses.

7. What is User Agent?

A user Agent is defined in SMTP, but the implementation details are not. The UA isnormally a program used to send and receive mail.

8. What do you mean by File transfer protocol?

It is a standard mechanism provided by the internet for copying a file from one hostto another

9. What are the two types of connections in FTP?

FTP establishes two connections between the hosts.

Control connection

Open connection

One connection isused for data transfer, the other for control information. The controlconnection uses very simple rules of communication. The data connectionneeds more complex rules due to the variety of data types transferred.

10. Define HTTP.

It is used mainly to access data on the World Wide Web. The protocol transfer data inthe form of plaintext, hypertext, audio, video and so on.

11. What are the types of messages in HTTP transaction?

The types of messages in HTTP transaction are

Request messages

Response messages

12. What are the parts of a browser?

The parts of a browser are

A controller

A client program

Interpreter

13. Name the four aspects of security.

Privacy: The sender and the receiver expect confidentiality.

Authentication: The receiver is sure of the sender’s identity and that animposter has not sent the message.

Integrity: The data must arrive at the receiver exactly as it was sent.

Non-Reputation: The receiver must able to prove that a received messagecame from a specific sender.

14. Define Cryptography.

The science and art of manipulating messages to make them secure.

15, Define authentication.

It means that the receiver is sure of the sender identity.

16. What do you mean by encryption?

The process of converting plain text to cipher text.

17. Define Privacy

It means that sender and receiver expect confidentiality.

18. What do you mean by Symmetric key cryptography?

In Symmetric key cryptography both the parties will use the same key.

19. What are steps to transfer a mail message?

The steps in transferring a mail message are

a) Connection establishment

b) Mail transfer

c) Connection termination

20. What is POP?

Post Office Protocol, version3 (POP3) and Internet Mail Access Protocol version4(IMAP4) are protocol used by a mail server in conjunction with SMTP to receive and holdmail for hosts.

21. Discuss the three main division of the domain name space.

Generic domains

Country domains

Inverse domain.

Generic domain: Define registered hosts according to their generic behavior,uses generic suffixes.

Country domain: Uses two characters to identify a country as the last suffix.

Inverse domain: Finds the domain name given the IP address.

22. What is the difference between a user agent (UA) and a mailtransfer agent (MTA)?

The UA prepares the message, creates the envelope, and puts themessage in the envelope. The MTA transfers the mail across the Internet.

23. How does MIME enhance SMTP?

MIME is a supplementary protocol that allows non-ASCII data to besent through SMTP. MIME transforms non-ASCII data at the sendersite to NVT ASCII data and deliverers it to the client SMTP to be sentthrough the Internet.

The server SMTP at the receiving side receives the NVT ASCII data and

delivers it to MIME to be transformed back to the original data.

24. Why is POP needed for electronic messaging?

Workstations interact with the SMTP host, which receives the mail onbehalf of every host in the organization, to retrieve messages by using aclient-server protocol such as Post Office Protocol, version 3(POP3).Although POP3 is used to download messages from the server, the SMTP

client still needed on the desktop to forward messages from the workstationuser to its SMTP mail server.

25. Give the format of HTTP request message.

• Request line
• Headers
• A Blank line
• Body (Present only in some messages)

26. Give the format of HTTP response message.

• Status line
• Headers
• A Blank line
• Headers
• Body (Present only in some messages)

27. Define CGI.

CGI is a standard for communication between HTTP servers andexecutable programs. It is used in crating dynamic documents.

28. Define Jitter

Variation in network latency. Large jitter has a variant impact on thequality of video & audio applications.

29. Write down the three types of WWW documents.

Static: Fixed-content documents that are created and stored in a server.

Dynamic: Created by web server whenever a browser requests thedocument.

Active: A program to be run at the client side.

30. Define digital signature.

Digital signature is a method to authenticate the sender of a message.It is similar to that of signing transactions documents when you do businesswith a bank. In network transactions, you can create an equivalent of anelectronic or digital signature by the way you send data.

31. Define substitution & transposition encryption.

Substitutional: A character level encryption in which each character isreplaced by another character in the set.

Transpositional: A Character level encryption in which the characters

retain their plaintext but the position of the character changes.

32. Distinguish secret key from public key.

In secret key, the same key is used by both parties. The sender usesthis key and an encryption algorithm to encrypt data; the receiver uses thesame key and the corresponding decryption algorithm to decrypt the data.

In public key, there are two keys: a private key and a public key. Theprivate key is kept by the receiver. The public key is announced to thepublic.

33. What are the advantages & disadvantages of public keyencryption?

Advantages:

a) Remove the restriction of a shared secret key between two entities. Hereeach entity can create a pair of keys, keep the private one, and publiclydistribute the other one.

b) The no. of keys needed is reduced tremendously. For one million users tocommunicate, only two million keys are needed.

Disadvantages:

If you use large numbers the method to be effective. Calculating the ciphertext using the long keys takes a lot of time. So it is not recommended forlarge amounts of text.

34. Mention the advantages & disadvantages of secret key

encryption.

Advantages:

Secret Key algorithms are efficient: it takes less time to encrypt a message.

The reason is that the key is usually smaller. So it is used to encrypt or

decrypt long messages.

Disadvantages:

a) Each pair of users must have a secret key. If N people in world want to

use this method, there needs to be N (N-1)/2 secret keys. For one million

people to communicate, a half-billion secret keys are needed.

b) The distribution of the keys between two parties can be difficult.

21. What is permutation?

Permutation is transposition in bit level.

Straight permutation: The no. of bits in the input and output are preserved.

Compressed permutation: The no. of bits is reduced (some of the bits aredropped).

Expanded permutation: The no. of bits is increased (some bits arerepeated).