🌐 IT4506 Computer Networks (2024)
UCSC BIT | MCQ Solutions with Simple Theory & Examples
ISO's Reference Model
Theory: The OSI (Open System Interconnection) Model was developed by ISO to standardize network communication into 7 layers (Physical, Data Link, Network, Transport, Session, Presentation, Application).
TCP/IP Physical Transmission
Theory: In the TCP/IP model, the Link Layer (or Network Access Layer) handles the physical transmission of data between adjacent network nodes over cables or Wi-Fi.
Connecting Different Networks
Theory: A Gateway connects different networks, especially those using different communication protocols. It acts as a translator between networks.
Dynamic Bandwidth Distribution
Theory: Statistical Multiplexing flexibly distributes bandwidth based on users' current demand. Unlike TDM (fixed slots), it only gives bandwidth to users who actually have data to send.
MAC Sublayer Location
Theory: The Data Link Layer (Layer 2) is divided into the LLC and MAC (Media Access Control) sublayers. MAC handles physical addressing (MAC addresses) and access to the transmission medium.
Data Rate Calculation
Theory: In networking, 1 kbps = 1000 bits/second (not 1024). Therefore, in 1 second, a 1 kbps channel transmits 1000 bits. (Storage uses 1024, but network speeds use 1000).
Purpose of Cookies
Theory: Web browsers store cookies to remember user information, such as login status, preferences, and to track browsing activities for personalized recommendations.
Twisted Pair Cables
Theory: Twisted pair cables are twisted to reduce electromagnetic interference (EMI) and crosstalk. The twisting causes the electromagnetic fields of the two wires to cancel each other out.
ISM Band Frequency
Theory: The 2.4 GHz ISM (Industrial, Scientific, Medical) band is a license-free frequency widely used for Wi-Fi, Bluetooth, and IoT devices.
Nyquist Theorem (Noiseless)
Theory: For a noiseless channel, Max Data Rate = 2 × B × log₂(L). For binary signalling (L=2), log₂(2)=1. So, Rate = 2 × 1000 kHz = 2000 kbps.
Two-Way, One at a Time
Theory: Half-duplex allows data to travel in both directions, but only one direction at a time (like a walkie-talkie). Full-duplex allows simultaneous two-way communication.
Dividing by Frequency Bands
Theory: Frequency Division Multiplexing (FDM) divides the total bandwidth into different frequency bands, giving each user a dedicated frequency channel (like FM radio stations).
Forward Error Correction (FEC)
Theory: FEC adds enough redundant bits during transmission so that the receiver can detect and correct errors locally without asking the sender to retransmit.
Code Rate Calculation
Theory: If a message has m bits and r check bits are added, the total transmitted bits are m + r. The Code Rate (efficiency) is m / (m + r).
Hamming Distance Detection
Theory: A code with a minimum Hamming distance of d can detect up to d - 1 errors. If d = 5, it can detect 5 - 1 = 4 errors.
Parity Bits
Theory: An even parity bit ensures the total number of 1s is even. It can be calculated by taking the XOR of all bits in the message. Parity bits can only detect errors, not correct them.
Purpose of a Checksum
Theory: A checksum is a calculated value sent with data. The receiver recalculates it to verify data integrity. Its primary purpose is to detect errors during transmission.
Slotted ALOHA Vulnerable Period
Theory: In Pure ALOHA, the vulnerable period is 2T. In Slotted ALOHA, time is divided into slots, reducing the vulnerable period to just T (the frame transmission time), making it more efficient.
Management Plane
Theory: The Management Plane enables network administrators to configure devices, monitor performance, view logs, and troubleshoot the network (e.g., using SSH or SNMP).
SDN Component
Theory: In SDN, the Southbound API (like OpenFlow) connects the SDN Controller to the network devices (switches/routers), allowing the controller to program forwarding rules at Layer 3.
Hardware Routing Tables
Theory: Implementing routing in hardware (like TCAM/ASICs) allows the router to keep high-speed links and route packets at link speed without relying on a slower CPU.
ARPANET Name Resolution
Theory: Before DNS was invented, ARPANET used a centralized file called HOSTS.TXT to map computer names to their corresponding IP addresses.
DNS Library Procedure
Theory: The Resolver is the client-side library procedure that takes a domain name (like www.google.com) and queries DNS servers to resolve it into an IP address.
DNS Record Validity
Theory: The TTL (Time To Live) field in a DNS Resource Record indicates how long (in seconds) the record is valid and can be cached by a resolver before it must be refreshed.
Browser Extensions
Theory: A Plug-in is a third-party code module installed as an extension to a web browser to add support for special content or technologies (e.g., old Adobe Flash videos).
Complete Answer Key (Q1–Q25)
| Q | Answer | Key Concept |
|---|---|---|
| 1 | OSI Model | 7-layer model by ISO |
| 2 | Link Layer | TCP/IP physical transmission |
| 3 | Gateway | Connects different protocols |
| 4 | Statistical Mux | Demand-based bandwidth |
| 5 | Data Link | Contains MAC sublayer |
| 6 | 1000 bits | 1 kbps = 1000 bps |
| 7 | Track activities | Cookies store user data |
| 8 | Reduce EMI | Twisting cancels interference |
| 9 | 2.4 GHz | ISM Band (Wi-Fi/Bluetooth) |
| 10 | 2000 kbps | Nyquist: 2 × Bandwidth |
| 11 | Half Duplex | Two-way, one at a time |
| 12 | FDM | Shares by frequency bands |
| 13 | FEC | Detects & corrects errors |
| 14 | m / (m+r) | Code Rate formula |
| 15 | 4 errors | Hamming detect = d - 1 |
| 16 | XOR | Even parity calculation |
| 17 | Detect errors | Checksum purpose |
| 18 | T | Slotted ALOHA vulnerable time |
| 19 | Manage/Monitor | Management Plane |
| 20 | Southbound API | Controller ↔ Switches |
| 21 | Link speed | Hardware routing tables |
| 22 | HOSTS.TXT | Pre-DNS name mapping |
| 23 | Resolver | Domain to IP conversion |
| 24 | TTL | DNS cache lifetime |
| 25 | Plug-in | Browser capability extension |
📚 Important Formulas to Memorize
Maximum Data Rate = 2 × B × log₂(L)
(B = Bandwidth, L = Signal Levels)
Code Rate = m / (m + r)
(m = Data bits, r = Check bits)
Detectable Errors = d - 1
Correctable Errors = ⌊(d - 1) / 2⌋
Pure ALOHA = 2T
Slotted ALOHA = T
❓ Frequently Asked Questions (FAQ)
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