CS Free MCQ Bank

[ Option B ]

Emails were originally designed to send only ASCII (American Standard Code for Information Interchange) text, meaning simple English letters, digits, and symbols. But over time, people needed to send images, audio, video, documents, and text in other languages (Non-ASCII).

To solve this, an additional standard was developed called MIME (Multipurpose Internet Mail Extensions). It works with existing email protocols like SMTP, POP, or IMAP and allows emails to carry different types of content.
Besides supporting non-ASCII text, MIME also allows multiple parts in a single email, enabling attachments and formatted text. When we attach a photo or a PDF in an email, MIME encodes that file into a format (like Base64) that can be sent as plain text through SMTP. The receiver’s email client then decodes it back to the original file.

[ Option D ]

When we use email, different protocols handle the sending and receiving of messages. SMTP (Simple Mail Transfer Protocol) is used for sending emails from one server to another, while POP (Post Office Protocol) is designed to download emails from the server to a single device, usually removing them from the server afterward. 

In contrast, IMAP (Internet Message Access Protocol) allows users to access, manage, and organize their emails directly on the mail server, keeping messages synchronized across multiple devices such as phones, laptops, and tablets.

[ Option B ]

The Domain Name System (DNS) is like the phonebook of the internet. It helps us convert easy-to-remember domain names into numerical IP addresses that computers use to communicate. DNS makes browsing the internet simple and user-friendly.
There are two types of DNS lookups:
Forward Lookup: This converts a domain name to an IP address using A or AAAA records.
Reverse Lookup: This converts an IP address back to a domain name using a PTR (Pointer) record. It helps in verification, logging, and network troubleshooting.

[ Option D ]

The Address Resolution Protocol (ARP) is used for finding the MAC address that corresponds to a given IP address within a Local Network.
When a device wants to communicate with another device on the same network, it needs the MAC address (Physical Address) of the destination device to actually send the data.
ARP helps in this process by broadcasting a request with the target IP address to all devices on the network. Only the device with the matching IP responds with its MAC address, enabling the sender to Map the IP Address to the correct MAC Address.

[ Option C ]

HDLC (High-Level Data Link Control) is a Layer-2 (Data Link Layer), bit-oriented (it treats the transmitted data as a stream of bits) protocol formalized by ISO. It supports reliable framing, Error Detection (CRC) for reliable communication and operates commonly in point-to-point links (Router-to-Router).

[ Option C ]

SMTP (Simple Mail Transfer Protocol) is used to send email from one computer (Mail Server) to another over the internet. Whenever you send an email, SMTP is responsible for transferring your message from the sender’s server to the receiver’s server.
The SMTP operates over TCP, commonly on port 25, ensuring reliable delivery of messages across networks.

[ Option D ]

In Internet communication, different protocols and standards are used for specific purposes.

[ Option D ]

When a client (web browser) sends a request to a web server using the HTTP (Hypertext Transfer Protocol), the server responds with a status code. These codes tell whether the request was successful, redirected, failed, or caused an error. HTTP status codes are divided into five main categories:

Status code 400 in the HTTP protocol means "Bad Request". This error occurs when the server cannot process a request because the client has sent data that is invalid, malformed, or cannot be understood.

[ Option D ]

DNS (Domain Name System) works like the “PHONEBOOK OF THE INTERNET”. It takes a human-readable domain name like www.surakuacademy.com and finds the corresponding numerical IP address (like 46.28.45.103) so that computers can locate and connect to the correct server. Without DNS, users would have to remember and type IP addresses instead of easy names.

What DNS Does:

• When you type a website name in the browser, DNS receives that name.
• It looks up its database (DNS servers) to find the correct IP address.
• It returns that IP address to your device.
• Your device then uses the IP address to connect to the correct web server.

[ Option C ]

NAV (Network Allocation Vector) is a virtual carrier sensing mechanism used in Wi-Fi (IEEE 802.11) networks as part of the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) protocol.
It acts as a timer that indicates how long the wireless medium will be busy based on the duration information contained in MAC frame headers.

• It helps devices know how long the medium will be busy.
• This is part of CSMA/CA, which Wi-Fi uses to avoid collisions.
• Devices check NAV before sending data.

[ Option B ]

In Automatic Repeat reQuest (ARQ) protocols, sequence numbers are used to keep track of frames sent and received, ensuring that lost or out-of-order frames can be identified and retransmitted correctly. Each ARQ protocol imposes limits on the sender and receiver window sizes to avoid ambiguity caused by sequence number.

Stop-and-Wait ARQ is the simplest protocol. In this method, the sender transmits only one frame at a time and waits for an acknowledgment before sending the next frame. Consequently, both the sender and receiver windows are limited to 1, resulting in a window pair of (1, 1).

Go-Back-N ARQ allows the sender to transmit multiple frames before receiving acknowledgments. To prevent confusion when sequence numbers wrap around, the sender’s window size must be 2ⁿ – 1, where n is the number of bits in the sequence field. For a 5-bit sequence number, this gives a sender window of 31, while the receiver window remains 1, producing the window pair (31, 1).

Selective Repeat ARQ allows both sender and receiver to maintain windows that support individual acknowledgment and retransmission of frames. To avoid ambiguity, both sender and receiver windows must be limited to 2ⁿ⁻¹. With a 5-bit sequence number, this results in 16 for both sender and receiver windows, giving the pair (16, 16).

[ Option B ]

Each URL starts with a scheme name (like http, https, mailto, ftp, etc.), which defines the protocol or method used to handle the request. Different schemes are used for different purposes, such as opening a web page, sending an email, or streaming a video.