Human Computer Interaction (CY-803 (C)) - Unit 3 Short Notes

UNIT 3: Mobile and Wireless Networking & Security

I. Wireless Access Technologies & Standards

Evolution and Trends of Wi-Fi (IEEE 802.11)

• Historical Progression:

  • 802.11 (1997): Original standard, 2 Mbps at 2.4 GHz.

  • 802.11a (1999): 54 Mbps, 5 GHz band, OFDM modulation.

  • 802.11b (1999): 11 Mbps, 2.4 GHz, DSSS modulation, widely adopted.

  • 802.11g (2003): 54 Mbps, 2.4 GHz, backward compatible with b.

  • 802.11n (2009): MIMO support, up to 600 Mbps, dual-band (2.4/5 GHz).

  • 802.11ac (2013): "Wi-Fi 5", wider channels (160 MHz), MU-MIMO, 5 GHz only, multi-gigabit speeds.

  • 802.11ax (2019): "Wi-Fi 6/6E", OFDMA in 2.4/5/6 GHz, improved efficiency in dense environments, target for IoT.

• Key Trends: Shift to higher frequencies (5/6 GHz) for more spectrum, MIMO/MU-MIMO for spatial multiplexing, OFDMA for efficient multi-user access, focus on density and IoT support over raw speed.

Wireless Personal Area Network (WPAN)

• Definition: A personal area network for interconnecting devices centered around an individual, typically within a range of 10 meters.

• Distinguishing Characteristics:

  • Range: Shortest (cm to 10m) vs. WLAN (100m), WMAN (km), WWAN (global).

  • Power: Very low power consumption.

  • Topology: Often peer-to-peer (ad-hoc) or star (with a hub).

  • Data Rate: Can be high (Bluetooth) or very low (Zigbee).

• Key Technologies:

  • Bluetooth (IEEE 802.15.1): 2.4 GHz, up to 3 Mbps (BR/EDR), 2-100m, for peripherals, PAN.

  • Zigbee (IEEE 802.15.4): 2.4/868/915 MHz, low data rate (250 kbps), very low power, for IoT sensors and control networks.

  • IrDA: Infrared, line-of-sight, very short range, legacy.

WiMAX (IEEE 802.16)

• Physical Layer Architecture: Designed for Broadband Wireless Access (BWA). Uses Orthogonal Frequency Division Multiplexing (OFDM) for the downlink and Orthogonal Frequency Division Multiple Access (OFDMA) for both uplink and downlink in scalable OFDMA (802.16e/m).

• Modulation Techniques:

  • OFDM: Splits channel into many orthogonal sub-carriers, resistant to multipath fading.

  • OFDMA: Allocates subsets of sub-carriers to different users dynamically, enabling flexible bandwidth allocation.

• Frequency Bands:

  • Licensed: 2.3, 2.5, 3.5 GHz bands (requires operator license, used for cellular-like services).

  • License-Exempt: 5.8 GHz band (similar to Wi-Fi, for unregulated deployment).

Wireless Local Area Network (WLAN)

• General Characteristics: Provides wireless connectivity within a local area (building/campus). Based on IEEE 802.11 standards.

• Components & Architecture:

  • Access Point (AP): Central hub, connects wireless clients to wired network.

  • Client/Station (STA): Device with wireless NIC.

  • Basic Service Set (BSS): Single AP + associated clients.

  • Extended Service Set (ESS): Multiple BSSs connected via distribution system (wired LAN).

• Comparison with Wired LANs:

  • Mobility: High vs. fixed.

  • Installation: Easier/cheaper (no cabling) vs. expensive cabling.

  • Security: More vulnerable (airborne signal) vs. physical access control.

  • Reliability: Susceptible to interference, fading vs. stable.

  • Bandwidth: Shared medium, contention-based access vs. dedicated/switched.

Cellular Mobile Technologies (Generations)

• 3G vs. 4G (LTE):

  | Feature | 3G (UMTS) | 4G (LTE) | | :--- | :--- | :--- | | Core Network | Circuit-switched (voice) + Packet-switched (data) | All-IP, packet-switched only | | Air Interface | W-CDMA, CDMA2000 | OFDMA (downlink), SC-FDMA (uplink) | | Peak Data Rate | ~2 Mbps (mobile), ~384 kbps | 100 Mbps (mobile), 1 Gbps (fixed) | | Latency | ~100-500 ms | < 50 ms (user plane) | | Primary Service | Mobile broadband, early smartphones | High-speed mobile broadband, HD video, IoT |

• Universal Mobile Telecommunication System (UMTS):

  • 3G standard based on W-CDMA.

  • Key feature: Separate circuit-switched domain for voice and packet-switched domain for data.

  • Enabled mobile internet browsing and video calling.

• Long-Term Evolution (LTE):

  • Key Features: All-IP core network (EPC), flat architecture (no RNC), OFDMA/SC-FDMA, MIMO, carrier aggregation.

  • Benefits: High throughput, low latency, spectral efficiency, seamless mobility.

• General Packet Radio Service (GPRS):

  • 2.5G technology overlay on GSM.

  • Features: "Always-on" packet data, shared channels (efficient), speeds up to ~114 kbps.

  • Role: Enabled first true mobile internet/email on phones, introduced PDP context for data sessions.

II. Mobile Network Architecture & Protocols

Mobile IP (Internet Protocol)

• Purpose: Enable seamless mobility for IP devices while maintaining a permanent IP address (home address) as they move across networks.

• Core Concepts:

  • Home Agent (HA): Router in home network, tunnels packets to mobile node's current location.

  • Foreign Agent (FA): Router in visited network, provides care-of address and routing services.

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

  • Tunneling: Encapsulation of original IP packet with new outer header (HA -> CoA).

• Mobile IPv4 vs. Mobile IPv6:

  | Aspect | Mobile IPv4 | Mobile IPv6 | | :--- | :--- | :--- | | Address | 32-bit IPv4 | 128-bit IPv6 (no NAT issues) | | Tunneling | IP-in-IP (RFC 2003) or Minimal Encapsulation | IPv6-in-IPv6 (RFC 2473) | | Route Optimization | Optional, complex (via HA or FA) | Mandatory and native (direct route from CN to MN via CoA) | | Agent Discovery | Agent Advertisement/ Solicitation messages | Uses standard IPv6 Neighbor Discovery | | Security | Often requires IPsec | Built-in IPsec support |

Routing in Ad Hoc and Mesh Networks

• Proactive (Table-Driven):

  • Principle: Maintains up-to-date routing tables for all nodes via periodic control messages.

  • Examples: DSDV (Destination-Sequenced Distance-Vector), OLSR (Optimized Link State Routing).

  • Trade-off: Low latency for route setup, high overhead in large/dynamic networks.

• Reactive (On-Demand):

  • Principle: Discovers routes only when needed via route discovery (flooding RREQ) and route maintenance.

  • Examples: AODV (Ad-hoc On-demand Distance Vector), DSR (Dynamic Source Routing).

  • Trade-off: Low overhead in idle networks, high latency during discovery, susceptible to broadcast storms.

• Hybrid:

  • Principle: Combines proactive within local zone and reactive outside.

  • Example: ZRP (Zone Routing Protocol) uses IARP (proactive intra-zone) and IERP (reactive inter-zone).

Mesh Networking Concepts

• Multi-hop Relay:

  • Principle: Nodes act as routers/repeaters. A packet from source to destination may traverse multiple intermediate nodes (hops) if direct link is unavailable or inefficient.

  • Mechanism: Each node forwards packets for others based on routing table or discovery process.

• Significance in Mesh Networks:

  • Extended Coverage: Reaches beyond single-hop radio range.

  • Robustness & Reliability: Multiple paths exist; failure of one node doesn't disconnect network.

  • Self-Healing & Self-Configuration: Nodes can find alternative routes automatically.

  • Scalability: Can grow by adding more nodes as relays.

Network Layer Encapsulation

• Purpose: To carry a packet (e.g., TCP segment) across a network, the network layer adds a header containing addressing and control information (source/dest IP, TTL, etc.). This creates a packet (IPv4) or datagram (IPv6).

• Compare IPv4 vs. IPv6 Headers:

  | Feature | IPv4 Header | IPv6 Header | | :--- | :--- | :--- | | Length | Variable (20-60 bytes) | Fixed (40 bytes) | | Address Size | 32-bit | 128-bit | | Fields | Version, IHL, Type of Service, Total Length, ID, Flags, Fragment Offset, TTL, Protocol, Header Checksum, Source/Dest IP, Options | Version, Traffic Class, Flow Label, Payload Length, Next Header, Hop Limit, Source/Dest IP, Extension Headers | | Checksum | Header checksum (recomputed at each hop) | No header checksum (reliability from lower layers/end-nodes) | | Fragmentation | Done by routers and source | Done only by source; routers don't fragment. | | Options | Variable-length options field | Extension Headers (chainable, processed only by destination/ routers specified) |

III. Security in Mobile & Wireless Environments

Denial of Service (DoS) Attacks

• General Concept: Attack aims to disrupt legitimate service by overwhelming resources (bandwidth, CPU, memory) or exploiting protocol vulnerabilities, making services unavailable.

• Wireless/Mobile Specific Manifestations:

  • Jamming: Transmitting noise on the physical layer to corrupt all signals in a channel.

  • Protocol Layer Attacks:

    • 802.11: Deauthentication/disassociation attacks (forged management frames).

    • TCP: SYN flood, RST attacks to tear down connections.

    • Routing: Exhausting resources via fake route requests/replies in AODV/DSR.

  • Battery Drain: Malicious repeated authentication requests to drain mobile device battery.

  • Challenges: Wireless medium is open, easy to launch attacks anonymously; resource constraints (mobile nodes) make them more vulnerable.

Military-Grade Security Models

• Primary Objectives (CIA Triad +):

  • Confidentiality: Prevent unauthorized disclosure of information.

  • Integrity: Prevent unauthorized modification of information.

  • Availability: Ensure timely and reliable access to resources.

  • Mandatory Access Control (MAC): System-enforced policy where access is based on security labels (e.g., Top Secret, Secret) of subjects and objects, not user discretion.

• Role of Hierarchical Command Structures:

  • Enforces clearance levels and need-to-know principles.

  • Security policy is centralized and non-bypassable.

  • Information flow is strictly controlled downward (from higher to lower clearance levels) or laterally within same level.

  • Prevents unauthorized data aggregation (e.g., a lower-clearance user cannot combine multiple classified fragments).

IV. Mobile Applications, Services & Supporting Technologies

E-commerce

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

• Models:

  • B2B (Business-to-Business): Transactions between companies (e.g., supplier portals).

  • B2C (Business-to-Consumer): Retail to end-users (e.g., Amazon).

  • C2C (Consumer-to-Consumer): Consumer-to-consumer (e.g., eBay, Facebook Marketplace).

  • C2B (Consumer-to-Business): Consumer sells to business (e.g., freelance platforms).

• Transformation of Traditional Business:

  • Global Reach: Removes geographical barriers.

  • 24/7 Availability: Always-open storefronts.

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

  • New Business Models: Subscription services, digital goods, on-demand economy.

  • Data-Driven: Personalized marketing, customer analytics.

  • Supply Chain Integration: Real-time inventory and ordering.

Electronic Payment Systems

• Definition: Technologies that allow financial transactions to be conducted electronically without using cash or checks.

• Categories:

  • Card-Based: Credit/Debit cards (via payment gateways, PCI-DSS compliance).

  • Digital Wallets: Store payment info (e.g., Apple Pay, Google Pay, PayPal), use tokenization.

  • Cryptocurrency: Decentralized digital assets (e.g., Bitcoin), use blockchain.

  • Bank Transfers: Direct electronic funds transfer (EFT, NEFT, RTGS).

• Facilitation of Secure Transactions:

  • Encryption (SSL/TLS): Secures data in transit.

  • Authentication: Multi-factor (password, OTP, biometrics) to verify parties.

  • Transaction Protocols: Secure standards (e.g., SET for cards, blockchain consensus).

  • Tokenization: Replaces sensitive card number with a unique token.

  • Audit Trails: Digital records for dispute resolution.

Radio Frequency Identification (RFID)

• Principle of Operation:

  1. Reader emits radio frequency energy.

  2. Tag (passive/active) receives energy. Passive tags use inductive coupling (near-field) or backscatter (far-field) to reflect/modulate signal.

  3. Tag powers its IC (if passive) and transmits stored data (ID) back to reader.

  4. Reader decodes signal and sends data to back-end system (database/application).

• Data Transmission Mechanism:

  • Passive Tags: No internal power. Powered by reader's signal. Use backscatter: tag changes impedance of its antenna to reflect signal, encoding data.

  • Active Tags: Have battery. Actively transmit signal (like a beacon), longer range.

• Key Components & Frequencies:

  • Components: Tag (chip + antenna), Reader, Antenna, Middleware, Back-end Database.

  • Frequencies:

    • LF (125-134 kHz): Short range, good penetration (animal tagging).

    • HF (13.56 MHz): Medium range, NFC (smart cards, payment).

    • UHF (860-960 MHz): Long range (1-10m), supply chain (EPC Gen2).

    • Microwave (2.45/5.8 GHz): Very long range, vehicle tolling.

V. Transport Layer Adaptation for Wireless Networks

TCP over Wireless Networks

• Challenges Introduced by Wireless Links:

  • High Bit Error Rate (BER): Fading, interference cause packet loss not due to congestion.

  • Variable & High Latency: Handoffs, retransmissions at link layer.

  • Handoffs: Temporary loss of connectivity during movement between APs/cells.

  • Asymmetric Bandwidth: Downlink often much higher than uplink.

• Impact on Standard TCP Congestion Control:

  • TCP interprets all packet loss as congestion.

  • Spurious Timeouts: Long delays mistaken for loss → unnecessary window reduction.

  • Throughput Degradation: Frequent window cuts lead to low utilization of available wireless bandwidth.

• Overview of Adaptation Techniques:

  • Split TCP: Connection split at base station/FA; separate TCPs for wired and wireless segments. Hides wireless losses from sender.

  • TCP Snooping: Local retransmission at base station (link layer recovery) to hide losses from sender.

  • TCP Westwood+: Estimates available bandwidth from ACK arrivals; on loss, sets congestion window based on this estimate, not halving. Better for wireless.

  • Selective Retransmission: Link layer provides selective recovery, not go-back-N.

  • New TCP Variants: TCP Veno, TCP Jersey designed for wireless.