Chapter 1: Application Layer
1 mark
Q. What is address resolution?
Answer: Mapping a name to an address or an address to a name is called address resolution.
Q. What are the different data structures supported by FTP?
Answer: FTP allows three different data structures namely file structure, record structure and page structure.
Q. Which file types can be transferred on FTP ?
Answer: The FTP can transfer ASCII file, EBCDIC file or image file. ASCII file is default format for text files. If one of two machines uses EBCDIC encoding, the EBCDIC file can be transferred using EBCDIC encoding. The image file is default format for transferring binary files.
Q. What is DNS?
Answer: DNS, or Domain Name System, is a system that translates human-readable domain names (like www.example.com) into IP addresses, which computers use to identify and locate each other on the internet. It acts as a directory for the internet, making it easier for users to access websites and services using familiar names instead of numerical IP addresses.
Q. Write a short note on SMTP.
Answer:
SMTP, or Simple Mail Transfer Protocol, is a standard communication protocol used for sending and relaying electronic mail (email) messages over the internet. It serves as the foundation for the email delivery process, enabling the transfer of messages from a sender's email client to a recipient's mail server. It is a TCP/IP protocol that specifies how computers exchange electronic mail.
The Mail transfer is done by MTA or message transfer agents. SMTP uses commands and response to transfer messages between MTA client and MTA server. Commands are sent by client to server which consists of a keyword followed by zero or more arguments. Responses are sent from server to client which is a three digit code. SMTP facilitates message transfer, relaying, error handling and notifications, security and message formating.
Q. What is generic domain?
Answer: A generic domain, is a category of domain names in the Domain Name System (DNS) that consists of common and widely recognized terms. Generic domains have broader applicability and are not tied to a particular geographic location. Example: .com (commercial), .org (Organizations/ Non-profit ), etc
Q. What is address resolution? Explain recursive and iterative resolution in DNS.
Answer: Mapping a name to an address or an address to a name is called as address resolution.
Recursive Resolution:
1) The client's DNS resolver sends a query to its designated DNS server.
2) The DNS server, if it doesn't have the answer, contacts other DNS servers on behalf of the client, obtaining the answer through multiple steps.
3) The final answer is returned to the client's DNS resolver, which then forwards it to the client. The client's resolver might also cache the answer for future use.
Iterative Resolution:
1) The client's DNS resolver sends a query to its designated DNS server.
2) The DNS server, if it doesn't have the answer, returns the best information it has to the client's resolver. It also provides a referral to other DNS servers.
3) The client's resolver continues the process, sending queries to the referred DNS servers step by step, until it obtains the final answer or reaches an authoritative server that provides the required information.
Q. What are the services provided by user agent?
Answer: The services provided by user agent are as follows:
1) Composing Message: It helps user compose or create an email by providing a template on the screen.
2) Reading Messages: It checks each mail and provides one line summary of every received email.
3) Replying to Messages: It allows the user to reply to original sender or to reply all recipients of the messages.
4) Forwarding Messages: It allows the receiver to forward the message with or without extra comments third party.
5) Handling Mail Boxes: It creates two mail boxes, inbox and outbox. Inbox keeps all the received emails until they are deleted by the user and outbox keeps the sent emails until user deletes them.
Q. Explain hierarchial name space.
Answer:
Flat Name Space:
1) In a flat name space, items are assigned names without any grouping or hierarchy. All names are stored in a single directory.
2) Each entity receives a unique name, but as the number of entities grows, searching for specific items becomes inefficient due to the lack of structure.
3) This approach lacks organization, making it challenging to manage and locate items efficiently, especially in larger systems.
Hierarchical Name Space:
1) In a hierarchical name space, names are organized in a tree structure with various levels, reflecting categories or domains.
2) The hierarchy includes top-level domains, subdomains, and so on. This arrangement simplifies management and navigation by narrowing down the scope of the search.
3) Users navigate through levels to find resources, aiding in efficient organization and retrieval of items, particularly in complex systems.
Q. Write a short note on SMTP.
Answer:
SMTP, or Simple Mail Transfer Protocol, is a standard communication protocol used for sending and relaying electronic mail (email) messages over the internet. It serves as the foundation for the email delivery process, enabling the transfer of messages from a sender's email client to a recipient's mail server. It is a TCP/IP protocol that specifies how computers exchange electronic mail.
Q. What is difference between SMTP, POP and IMAP?
Answer: SMTP is a push protocol which pushes the message from client to server so it is used in first and second stage of mail delivery.
Third stage needs pull protocol from receiver to mail server, so they need MAA (message access agents) which is POP and IMAP. These both retrieve mails at receiver's side.
Q. What is POP3?
Answer: Post office protocol is an application layer internet standard protocol used by local email clients to retrieve email from remote sever over tcp ip connection.
Q. What is IMAP4?
Answer: Internet mail access protocol is similar to POP3 but more compelx and more powerful. It provides following functions:
1) user can check email header before downloading
2) use can search email contents before downloading
3) User can partially download email
4) use can create, delete or rename mailboxes.
5) use can create hierarchy of mailboxes in folder for storage.
Q. Give difference between IMAP4 and POP.
Answer:
| Aspect | POP | IMAP |
|---|---|---|
| Client Support | Typically single client | Supports multiple clients |
| Offline Access | Messages accessed offline | Accessible online and offline |
| Search Facility | Limited search features | Robust email search |
| Message Deletion | Can delete from server | Retains messages on server |
| Storage Space Mgmt | Local device management | Centralized server storage |