Protocols — Set 7

Correct Answer: B. Reliable and connection-oriented

• **Reliable and connection-oriented** = TCP (Transmission Control Protocol) establishes a dedicated connection between sender and receiver before data flows, then verifies every packet arrived intact — if any packet is lost, TCP requests a re-transmission automatically. • **Three-way handshake** — TCP opens every session with a SYN → SYN-ACK → ACK exchange, guaranteeing both sides are ready before a single byte of real data is sent. • TCP is the backbone of web browsing (HTTP/HTTPS), email delivery, and file transfers — anywhere data integrity matters more than raw speed. • 💡 Option A (Fast but unreliable) describes UDP, not TCP; Option C (Only for video) is wrong because TCP is a general-purpose protocol used across many application types; Option D (Broadcast only) is wrong because TCP is a unicast, point-to-point protocol and does not support broadcasting.

Correct Answer: C. 443

• **Port 443** = HTTPS (HyperText Transfer Protocol Secure) is permanently assigned to port 443 by IANA; all encrypted web traffic travels through this port so that servers and firewalls can immediately identify it as secure browsing traffic. • **TLS encryption layer** — HTTPS wraps standard HTTP inside TLS (Transport Layer Security), which is the reason a dedicated port separate from plain HTTP's port 80 is needed. • When you visit a site whose URL begins with "https://", your browser automatically connects on port 443 without you needing to type the number. • 💡 Option A (20) is the FTP data-transfer port, used for file transfers not web browsing; Option B (80) is the port for plain, unencrypted HTTP traffic; Option D (110) is the POP3 port used for downloading emails from a mail server.

Correct Answer: B. DHCP

• **DHCP** = Dynamic Host Configuration Protocol automatically leases an IP address, subnet mask, default gateway, and DNS server addresses to any device that joins the network — no manual configuration required from the user. • **Lease-based system** — DHCP does not assign addresses permanently; it issues them for a set time (the lease period), then renews or reassigns them, which helps conserve the limited pool of available IP addresses. • Your home Wi-Fi router doubles as a DHCP server, typically handing out addresses in the 192.168.x.x range to every phone, laptop, or smart TV that connects. • 💡 Option A (DNS) translates domain names like google.com into IP addresses but does not assign your device's own IP; Option C (FTP) is a file-transfer protocol with no role in address assignment; Option D (SMTP) handles outgoing email and has nothing to do with network addressing.

Correct Answer: B. Sending emails

• **Sending emails** = SMTP (Simple Mail Transfer Protocol) is the standard protocol mail servers use to relay outgoing messages from a sender's mail client to the recipient's mail server, working over port 25 (server-to-server) or port 587 (client-to-server). • **Push-only protocol** — SMTP only pushes mail outward; it cannot retrieve messages from a mailbox. Separate protocols, POP3 or IMAP, are needed to read received mail. • Every time you click "Send" in Gmail, Outlook, or any other email client, the application hands your message to an SMTP server that then routes it across the internet. • 💡 Option A (Downloading files) is the role of FTP or HTTP, not SMTP; Option C (Watching videos) uses streaming protocols such as RTSP or HLS delivered over HTTP; Option D (Searching the web) is handled by HTTP/HTTPS between your browser and the web server.

Correct Answer: A. ICMP

• **ICMP** = Internet Control Message Protocol is used by the "ping" utility to send an Echo Request message to a target host; if the host is reachable, it replies with an Echo Reply, confirming the network path is functional. • **Error-reporting role** — Beyond ping, ICMP also delivers network error messages such as "Destination Unreachable" and "Time Exceeded," which the traceroute tool uses to map the path packets take across the internet. • ICMP operates at the Network Layer (Layer 3) of the OSI model and does not use port numbers, making it distinct from TCP and UDP. • 💡 Option B (TCP) establishes reliable data connections but is not the protocol behind the ping diagnostic tool; Option C (HTTP) is a web application protocol for fetching web pages; Option D (SNMP) is used for monitoring and managing network devices like routers and switches, not for simple reachability tests.

Correct Answer: C. Network Layer

• **Network Layer (Layer 3)** = IP (Internet Protocol) operates here, where it assigns logical IP addresses to packets and determines the best path to route each packet from source to destination across multiple interconnected networks. • **Routers are Layer 3 devices** — Unlike switches (Layer 2) that forward frames using MAC addresses within a single network, routers read IP addresses at Layer 3 to forward packets between different networks worldwide. • IPv4 and IPv6 are both Network Layer protocols; IPv6 was introduced to overcome the address exhaustion of the 32-bit IPv4 address space. • 💡 Option A (Physical Layer) handles raw bit transmission over cables and wireless signals, with no concept of addresses; Option B (Data Link Layer) uses MAC addresses for local frame delivery on the same network segment; Option D (Transport Layer) is where TCP and UDP operate, managing end-to-end communication and port numbers.

Correct Answer: B. UDP

• **UDP** = User Datagram Protocol is preferred for real-time gaming because it sends packets without waiting for acknowledgement — this eliminates the retransmission delays that would cause noticeable lag, making the game feel responsive even on imperfect networks. • **No connection overhead** — UDP is connectionless, meaning it skips the three-way handshake and error-checking round trips of TCP, cutting latency to the bare minimum needed for smooth, frame-by-frame gameplay. • Online games handle minor packet loss in their own application code (e.g., predicting player position), so the reliability TCP offers is unnecessary overhead at the protocol level. • 💡 Option A (TCP) guarantees delivery but its retransmission mechanism introduces variable delay that is unacceptable in real-time games; Option C (FTP) is a file-transfer protocol with no role in live gameplay data exchange; Option D (POP3) is an email-retrieval protocol entirely unrelated to gaming.

Correct Answer: A. NTP

• **NTP** = Network Time Protocol synchronises a device's clock with reference time servers (which ultimately trace back to atomic clocks) with an accuracy of a few milliseconds, keeping all networked computers on a consistent, universal time. • **Stratum hierarchy** — NTP uses a layered "stratum" system: stratum-0 devices are atomic clocks, stratum-1 servers connect directly to them, and your computer typically syncs with a stratum-2 or stratum-3 public server over the internet. • Accurate time is critical for SSL certificate validity, log correlation in security investigations, database transactions, and Kerberos authentication — all of which break if clocks drift by more than a few minutes. • 💡 Option B (DNS) resolves domain names to IP addresses and has no timekeeping function; Option C (DHCP) assigns IP addresses to devices on a network, not time; Option D (ARP) maps IP addresses to MAC addresses within a local network and is completely unrelated to clock synchronisation.

Correct Answer: C. IMAP syncs across devices, POP3 usually downloads and deletes

• **IMAP syncs across devices, POP3 usually downloads and deletes** = IMAP (Internet Message Access Protocol) keeps all emails stored on the server and mirrors changes — read, deleted, or moved — across every device in real time, while POP3 (Post Office Protocol 3) typically downloads messages to one device and removes them from the server. • **Server-side vs. local storage** — With IMAP, your inbox lives on the mail server, so logging in from a phone, tablet, or computer always shows the same up-to-date view; POP3 ties your inbox to whichever single device downloaded the messages. • IMAP operates on port 143 (or 993 for encrypted IMAPS), whereas POP3 uses port 110 (or 995 for POP3S). • 💡 Option A (POP3 is faster) is misleading — POP3 may feel faster on a single device but it is inferior for multi-device use; Option B (IMAP is only for sending mail) is incorrect because IMAP is purely a receiving/syncing protocol, and SMTP handles sending; Option D (IMAP is older) is wrong because POP3 (1984) predates IMAP (1986), making POP3 the older protocol.

Correct Answer: C. HTTP

• **HTTP** = HyperText Transfer Protocol is the foundation of data communication on the World Wide Web; it defines how a browser (client) sends requests to a web server and how the server sends back HTML pages, images, and other resources. • **Request-response model** — HTTP follows a stateless request-response cycle: the client sends a GET or POST request, the server responds with a status code (e.g., 200 OK) and the requested content, then the connection closes unless HTTP Keep-Alive is used. • The secure version, HTTPS, layers TLS encryption over HTTP and has become the default for virtually every website to protect user data from interception. • 💡 Option A (FTP) transfers files between computers but is not the general protocol for browsing web pages; Option B (SMTP) handles outgoing email, not web-page delivery; Option D (SNMP) is used by network administrators to monitor and manage routers, switches, and servers — it has no role in delivering web content to browsers.