Human Computer Interaction (CY-803 (C)) - Unit 2 Short Notes

UNIT 2: Mobile and Wireless Networking Technologies & Security

I. Wireless Network Fundamentals & Standards Evolution

Evolution of Wi-Fi (IEEE 802.11) Standards

Wi-Fi standards, defined by IEEE 802.11, have evolved to meet increasing demands for speed, capacity, and efficiency.

[!TIP] Exam Trend: Questions often ask for implications (e.g., "How did 802.11ac improve capacity?"). Focus on the key technology shift (MIMO → OFDMA) and its impact on spectral efficiency and dense client environments.

Wireless Personal Area Network (WPAN)

• Definition: A short-range wireless network (typically < 10m) for interconnecting personal devices.

• Distinguishing Characteristics vs. Other Wireless Networks:

  • Range: Very short (cm to 10m) vs. WLAN (tens to 100m), WMAN (kms), WWAN (kms to global).

  • Power Consumption: Extremely low, designed for battery-powered devices.

  • Data Rate: Can be high (Bluetooth 5: 2 Mbps) or very low (RFID).

  • Use-Cases: Device synchronization (phone to laptop), peripheral connection (mouse, keyboard), body-area networks, asset tracking.

  • Key Technologies: Bluetooth, Zigbee, Z-Wave, RFID, Infrared (IrDA).

Wireless Local Area Network (WLAN)

• Definition: A local-area network that uses wireless communication (Wi-Fi) to connect devices within a limited area (home, office, campus).

• Key Features:

  • Infrastructure Mode: Devices communicate via a central Access Point (AP). AP connects to wired network (distribution system).

  • Ad-hoc (IBSS) Mode: Peer-to-peer network without an AP; devices communicate directly.

  • Components: Stations (STA) (clients), Access Point (AP), Distribution System (DS) (wired backbone).

  • Services: SSID (network name), authentication (open/WPA2/WPA3), association, roaming.

  [!NOTE] Short Note Focus: Define WLAN, contrast Infrastructure vs. Ad-hoc, list core components (AP, STA).

Wireless Metropolitan Area Network (WMAN) - WiMAX (IEEE 802.16)

• Purpose: Provide broadband wireless access (BWA) over metropolitan areas (up to 50 km), competing with DSL/cable.

• Physical Layer:

  • Modulation: OFDM (downlink) and OFDMA (uplink & downlink for multiple users). OFDMA divides channel into sub-carriers, allocated dynamically.

  • Frequency Bands: Operates in both licensed (2-11 GHz, 10-66 GHz) and unlicensed bands. Licensed bands avoid interference but require spectrum license.

• Key Feature: Supports Non-Line-of-Sight (NLOS) operation in lower bands (2-11 GHz) using OFDM.

Universal Mobile Telecommunication System (UMTS)

• Definition: A 3G mobile cellular system for voice and data, based on GSM core network.

• Architecture:

  • UTRAN (UMTS Terrestrial Radio Access Network): Consists of Node B (base station) and Radio Network Controller (RNC). Node B handles radio transmission; RNC manages radio resources, handovers.

  • Core Network (CN): Circuit-Switched (for voice) and Packet-Switched (for data) domains. Connects to external networks (PSTN, Internet).

• Air Interface: W-CDMA (Wideband Code Division Multiple Access). Uses 5 MHz channels, provides higher data rates (~2 Mbps) than 2G (GPRS).

II. Cellular Mobile Communication Generations & Technologies

Key Differences: 3G vs. 4G Networks

General Packet Radio Service (GPRS)

• Definition: A 2.5G packet-switched overlay on GSM, enabling "always-on" mobile data.

• Key Features & Capabilities:

  • Packet-Switched: Shares radio channels among users, efficient for bursty data (email, web).

  • Always-On: No need to establish a circuit call for each session; IP address assigned on attach.

  • Data Rates: Theoretical up to ~114 kbps (using all 8 timeslots), practical ~40-50 kbps.

  • Enables Mobile Data: Foundation for later EDGE and 3G. Introduced GGSN (Gateway GPRS Support Node) and SGSN (Serving GSN) in core network for routing.

Long-Term Evolution (LTE)

• Definition: A 4G standard (though initial LTE not fully IMT-Advanced) for high-speed wireless broadband.

• Key Features & Benefits:

  • OFDMA (Downlink) & SC-FDMA (Uplink): Efficient spectrum use, flexible bandwidth (1.4-20 MHz).

  • MIMO: Multiple antennas at TX/RX for spatial multiplexing (higher throughput) and diversity (reliability).

  • Flat IP Architecture: Removes RNC, simplifies core to EPC (Evolved Packet Core) with MME, S-GW, P-GW. Reduces latency.

  • Benefits: High throughput (100+ Mbps), low latency (<10 ms air interface), scalable bandwidth, seamless mobility with earlier 3G via CS fallback.

Mobile IP (IPv4 vs. IPv6)

• Core Concepts (Both Versions):

  • Home Agent (HA): Router in home network; maintains binding of MN's home address to care-of address.

  • Foreign Agent (FA - MIPv4 only): Router in visited network; provides care-of address and tunnels packets.

  • Care-of Address (CoA): Temporary IP address of MN in foreign network (could be FA's address or co-located).

  • Tunneling: HA encapsulates packets destined to MN's home address and sends to CoA. FA (or MN itself in MIPv6) decapsulates.

  • Binding Updates: MN informs HA of its current CoA.

[!TIP] Key Difference: MIPv6 eliminates FA and supports native route optimization, reducing latency and HA load. MIPv4 often suffers from triangle routing unless RO is explicitly used.

III. Mobile Ad Hoc and Mesh Networks

Routing Protocols in Ad Hoc Networks

[!NOTE] Exam Focus: For "difference" questions, contrast Proactive (always-updated tables, high overhead) vs. Reactive (on-demand discovery, high latency). Mention AODV and DSDV as classic examples.

Mesh Networks & Multi-Hop Relay

• Concept of Multi-Hop Relay: In a mesh network, a source node may not be in direct range of the destination. Data is forwarded via intermediate relay nodes (each hop is a wireless link). Nodes act as both clients and routers.

• Significance in Mesh Networks:

  • Extended Coverage: Spans large areas without wired infrastructure (community networks, IoT).

  • Increased Reliability & Resilience: Multiple paths exist; if one node/link fails, traffic reroutes (self-healing).

  • Load Balancing: Traffic can be distributed across multiple paths.

  • Scalability: Can grow organically by adding nodes.

  • Applications: Wireless community networks, smart grids, IoT backhauls, disaster recovery.

IV. Core Networking Protocols & Adaptation for Wireless

TCP over Wireless Networks

• Challenges Impacting TCP Performance:

  1. High Bit Error Rate (BER): Wireless links are noisy. Packet loss often due to corruption, not congestion. TCP interprets loss as congestion → unnecessary cwnd reduction.

  2. Variable Latency & Route Changes (Handoffs): Causes spurious timeouts and duplicate ACKs, triggering congestion control.

  3. Frequent Disconnections: Mobile devices move out of coverage → long timeouts → TCP assumes congestion, enters slow start.

  4. Asymmetric Links: Uplink often slower/bottlenecked; ACKs may be delayed or lost.

• Impact: Severe throughput degradation compared to wired networks, especially with high BER/mobility.

• Adaptation Techniques (Brief):

  • TCP-Feedback (TCP-F): Link layer informs TCP about corruption vs. congestion.

  • TCP-Explicit Link Failure Notification (TCP-ELN): Link layer sets a flag in ACK for non-congestion loss.

  • Split Connection Approaches (e.g., Snoop, I-TCP): Break TCP connection at base station/FA. Local retransmissions hide losses from sender.

  • TCP Westwood+: Estimates bandwidth from ACKs, sets cwnd more aggressively after loss.

Encapsulation Headers: IPv4 vs. IPv6

• Purpose of Encapsulation Headers: Used in tunneling (e.g., Mobile IP, VPNs) and mobility support. Outer header routes packet through intermediate tunnel endpoint; inner header is original packet.

• Compare & Contrast Structure:

[!TIP] Key Point: IPv6's elimination of router fragmentation and extension header chain simplifies processing and improves performance in mobile/tunneling scenarios, despite larger base header.

V. Enabling Technologies: RFID & IoT

Radio Frequency Identification (RFID)

• Definition: Technology using electromagnetic fields to automatically identify and track tags attached to objects.

• System Components:

  • Tag (Transponder): Microchip + antenna. Stores ID/data. Classified by power source.

  • Reader (Interrogator): Emits RF signal, receives tag response. Connects to middleware.

  • Middleware: Software that filters/aggregates tag data, interfaces with enterprise apps.

  • Database: Stores tag-associated information.

• Principle of Operation & Data Transmission:

  • Inductive Coupling (LF/HF, 125-134 kHz / 13.56 MHz): Reader's antenna creates magnetic field. Tag's coil induces current (powers passive tag). Near-field communication (cm range). Used for access control, payment cards.

  • Electromagnetic Wave Propagation (UHF, 860-960 MHz; Microwave, 2.45/5.8 GHz): Reader emits EM waves. Tag's dipole antenna receives energy (radiative coupling). Far-field communication (meters). Used for supply chain, inventory.

  • Data Modulation: Tag modulates backscatter of reader's signal (changes antenna impedance) to send data (e.g., ASK, PSK).

  • Tag Powering:

    • Passive: No battery; powered by reader's RF energy. Cheapest, smallest, unlimited life, shortest range.

    • Active: Has battery; actively transmits. Long range (100m+), expensive, limited battery life.

    • Semi-Passive (Battery-Assisted): Battery powers chip, but communication via backscatter. Better range than passive.

VI. Security Models and Threats

Military Security Models

• Primary Objectives (CIA Triad + Extensions):

  1. Confidentiality: Prevent unauthorized disclosure of information.

  2. Integrity: Prevent unauthorized modification of data.

  3. Availability: Ensure timely, reliable access to resources.

  4. Accountability (Non-Repudiation): Actions can be traced to responsible entity (audit trails).

• Role of Hierarchical Command Structures:

  • Enforces centralized policy and chain of command for security decisions.

  • Implements mandatory access control (MAC) based on security clearances and classification levels (e.g., Bell-LaPadula model: "no read up, no write down").

  • Ensures uniform enforcement of security rules across distributed units.

  • Facilitates incident response and accountability through defined reporting lines.

Denial of Service (DoS) / Distributed Denial of Service (DDoS)

• Definition & Objective: Attack aimed at disrupting service availability to legitimate users by overwhelming a target (server, network, application) with malicious traffic or resource exhaustion.

• General Mechanisms in Wireless/Mobile Context:

  • Flooding Attacks: Overwhelms target with bogus requests (e.g., SYN flood in TCP, HTTP flood). In wireless, can target AP or base station control channels.

  • Resource Exhaustion: Consumes finite wireless resources: bandwidth (jamming), battery power (forcing MN to transmit repeatedly), connection state (half-open connections).

  • Jamming: Transmits noise on the same frequency to disrupt physical layer (simple but effective against wireless).

  • Protocol Exploitation: Exploits weaknesses in protocols (e.g., 802.11 deauthentication frames to disconnect clients).

  • DDoS: Attack launched from multiple distributed sources (botnets/zombies), making mitigation harder.

VII. E-Commerce and Electronic Payment Systems

E-Commerce

• Definition: Buying and selling of goods/services, or transmitting funds/data, over electronic networks (primarily the Internet).

• Transformation of Traditional Business:

  • Global Reach: Businesses can access worldwide markets 24/7.

  • Reduced Costs: Lower overhead (physical stores, staff), automated processes.

  • New Business Models: B2B (e.g., Alibaba), B2C (e.g., Amazon), C2C (e.g., eBay), C2B (e.g., freelancing platforms).

  • Personalization & Customer Data: Enables targeted marketing, recommendation systems.

  • Supply Chain Integration: Real-time inventory, just-in-time ordering.

  • Disintermediation/Reintermediation: Removal of traditional middlemen or creation of new digital intermediaries.

Electronic Payment Systems

• Definition: Systems that facilitate financial transactions electronically, without physical cash/checks.

• Role: Enable the settlement of e-commerce transactions securely and efficiently. Bridge buyer, seller, and financial institutions.

• Types:

  • Card-Based: Credit/Debit cards (via payment gateways like Stripe, PayPal).

  • Digital Wallets/E-Wallets: Store payment info (e.g., Apple Pay, Google Pay, PayPal). Use tokenization.

  • Electronic Funds Transfer (EFT/ACH): Direct bank-to-bank transfer (e.g., net banking).

  • Cryptocurrencies: Decentralized digital currencies (e.g., Bitcoin) using blockchain.

• Key Requirements:

  • Security: Encryption (SSL/TLS), authentication (2FA, biometrics), integrity (digital signatures). Prevents fraud, eavesdropping.

  • Privacy: Protects user's financial and personal data from unauthorized parties.

  • Efficiency: Fast transaction processing, low cost, reliability.

  • Acceptability: Widely supported by merchants and users.

  • Anonymity (where applicable): Some systems (cash-like e-cash) offer anonymity.