GTU 3150710 Computer Networks (CN) Summer 2023 Solved Paper & Solutions

A Computer Network is an interconnection of two or more autonomous computing devices linked by communication media (cables, fiber, wireless) and protocols to exchange data and share hardware/software resources.

Primary Types of Computer Networks:

• PAN (Personal Area Network): Covers personal workspace within $\approx 10\text{ meters}$ (e.g., Bluetooth connection between smartphone and smartwatch).
• LAN (Local Area Network): Spans a single room, office, or university campus ($100\text{ m} - 1\text{ km}$) with very high data rates of $100\text{ Mbps} - 10\text{ Gbps}$ (e.g., College lab Ethernet/Wi-Fi).
• MAN (Metropolitan Area Network): Covers an entire town or city ($5\text{ km} - 50\text{ km}$), typically operated by cable TV providers or municipal utilities.
• WAN (Wide Area Network): Spans countries and continents using telecom fiber backbones and satellite links (e.g., The global Internet).

2. Queuing Delay ($d_{\text{queue}}$):

• The duration a packet waits in the router output buffer queue before being scheduled for transmission onto the physical link.
• Highly dependent on traffic intensity ($I = \frac{L \cdot a}{R}$). If buffer is full, packet drop occurs.
• Typical Value: Microseconds to milliseconds.

3. Transmission Delay ($d_{\text{trans}}$):

• The time required to push (pump) all packet bits onto the communication medium.
• Formula:

where $L$ = packet length in bits, and $R$ = transmission link rate (bandwidth) in bits per second (bps).

4. Propagation Delay ($d_{\text{prop}}$):

• The time taken for a physical bit to travel from the start of the physical wire to the destination router interface.
• Formula:

where $d$ = physical distance between routers, and $s$ = propagation speed of light in the medium (approx. $2 \times 10^8\ \text{m/s}$ in copper/fiber).

1. Star Topology

• Design: All devices connect directly to a central networking hub, switch, or router via dedicated point-to-point links.
• Advantages: Easy installation and maintenance; single device failure does not affect the rest of the network; easy fault isolation.
• Disadvantages: Single point of failure (if central switch fails, entire network crashes); higher cabling requirements than bus.

2. Bus Topology

• Design: All devices share a single linear backbone communication cable (the "bus"). Terminators are attached at both ends to absorb signal reflection.
• Advantages: Minimal cabling required; cost-effective for small networks.
• Disadvantages: Backbone cable break halts the whole network; heavy packet collisions under high traffic; difficult to isolate faults.

3. Ring Topology

• Design: Devices form a continuous circular loop. Each node has exactly two neighbors. Data circulates sequentially using Token Passing.
• Advantages: Orderly network access with zero packet collisions due to token passing; performs well under heavy load.
• Disadvantages: Unidirectional ring fails completely if any single node or cable breaks; high transmission latency for large loops.

4. Mesh Topology

• Design: Every device is connected to every other device via dedicated point-to-point channels.

• Advantages: Maximum fault tolerance and redundancy; no traffic congestion; excellent data privacy and security.
• Disadvantages: Extremely expensive cabling and complex I/O hardware port requirements.

5. Tree (Hierarchical) Topology

• Design: Hierarchical star networks branched off a central root bus or master switch.
• Advantages: High scalability; easy management and departmental isolation.
• Disadvantages: Root switch dependency; heavy cabling.

6. Hybrid Topology

• Combines two or more basic topologies (e.g., Star-Ring or Star-Bus) to balance cost, reliability, and coverage in large enterprise networks.

The World Wide Web (WWW) is a global hypermedia information system running on top of the Internet that allows documents and multimedia resources to be interconnected via hyperlinks and accessed using HTTP/HTTPS.

3-Tier Web Architecture:

1. Client Tier (Presentation): Web browsers (Chrome, Firefox) that render HTML/CSS and execute JavaScript to interact with the user.
2. Web / Application Server Tier (Logic): Web servers (Nginx, Apache, Node.js) that process client HTTP requests, handle business logic, and generate dynamic responses.
3. Database Tier (Storage): Relational (MySQL, PostgreSQL) or NoSQL databases that securely store and retrieve persistent application data.

• Core Standards: URLs (global resource addressing), HTTP/HTTPS (stateless transport), and HTML (document structure).

1. Scheme / Protocol (http, https, ftp):

• Identifies the protocol used by client and server to transfer data. Web traffic predominantly uses HTTPS (HTTP over TLS encryption).

2. Host / Domain Name (unfoldprep.com or IP address 192.168.1.1):

• The human-readable name or numerical IP address identifying the physical/cloud server hosting the resource, resolved by DNS.

3. Port Number (:80, :443, :8080):

• The logical networking port on the host machine. Defaults to port 80 for HTTP and 443 for HTTPS.

4. Path (/papers/gtu/be-computer/sem-5/):

• The hierarchical file-system or routing path on the server pointing to the exact requested resource.

5. Query String (?subject=3150710&season=summer):

• Key-value parameter pairs preceded by a question mark (?) and separated by ampersands (&), passing dynamic inputs to the web application.

6. Fragment Identifier (#q1, #solution):

• Preceded by a hash (#), points directly to an internal bookmark or anchor within the HTML document without requiring a fresh server roundtrip.

1. GET:

• Retrieves data/representation from the specified resource.
• Properties: Safe, Idempotent, and Cacheable. Does not modify server state; parameters are sent in the URL query string.

2. POST:

• Submits data to the server to create a new resource or process an entity (e.g., submitting a contact form, uploading a file).
• Properties: Non-idempotent (sending multiple times creates multiple duplicate resources). Payload is contained in the request body.

3. PUT:

• Replaces the entire target resource with the uploaded payload, or creates the resource if it does not exist at that specific URI.
• Properties: Idempotent (calling it 10 times results in the same final state as calling it once).

4. DELETE:

• Deletes the specified resource at the target URI.
• Properties: Idempotent. Subsequent calls return 404 Not Found or 200 OK.

5. HEAD:

• Identical to GET, but the server returns only the response headers without the response message body.
• Use Case: Checking resource validity, expiration headers, or file size (Content-Length) without downloading the entire payload.

6. PATCH:

• Applies partial modifications to an existing resource (unlike PUT which replaces the entire object).

7. OPTIONS:

• Requests communication options and allowed HTTP verbs supported by the web server for that URI (critical for Cross-Origin Resource Sharing / CORS preflight).

Flow Control vs Error Control

Comparison: IPv4 vs IPv6

Symmetric vs Asymmetric Key Cryptography