UNIT 2: Mobile and Wireless Technologies & Security Models - Short Notes

I. Wireless Network Technologies & Standards

A. 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).

• Core Architecture Components:

  • Access Point (AP): Central hub that bridges wireless and wired networks.

  • Station (STA): Client device (laptop, phone) with wireless NIC.

  • Basic Service Set (BSS): A single AP and its associated STAs.

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

[!TIP] Exam Focus: Distinguish BSS (single AP) from ESS (multiple APs). AP is mandatory in infrastructure mode.

Evolution of Wi-Fi Standards (IEEE 802.11 Family)

• Trend Implications: Progression from single-user to multi-user (MU-MIMO, OFDMA), wider channels, higher modulation (QAM), shift to 5/6 GHz for capacity. Focus moved from peak speed to network efficiency, capacity, and IoT support.

Security Mechanisms:

• WEP (Wired Equivalent Privacy): Broken, uses RC4 with static key.

• WPA/WPA2: Uses TKIP (WPA) and CCMP/AES (WPA2) with 802.1X authentication.

• WPA3: Latest, uses SAE (Simultaneous Authentication of Equals) for stronger password protection, mandatory forward secrecy.

B. Wireless Personal Area Network (WPAN)

• Definition: Short-range (<10m, typically) wireless network for interconnecting devices centered on an individual's workspace.

• Distinguishing Characteristics:

  | Feature | WPAN | WLAN | WMAN | WWAN | | :--- | :--- | :--- | :--- | :--- | | Range | ~1-10 m | ~10-100 m | ~1-5 km | km to global | | Data Rate | Low to Medium | Medium to High | Medium to High | Low to Medium | | Topology | Star (piconet) | Star (BSS/ESS) | Point-to-Multipoint | Cellular | | Typical Use | Device pairing (headset, keyboard) | Internet access, LAN | Metropolitan broadband | Mobile voice/data |

• Key Technologies:

  • Bluetooth: Piconet (1 master, up to 7 active slaves), Scatternet (multiple interconnected piconets). Uses FHSS in 2.4 GHz.

  • Zigbee (IEEE 802.15.4): Low-power, low-data-rate, supports mesh networking. Used in IoT, home automation.

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

C. Wireless Metropolitan Area Network (WMAN) / Broadband Wireless Access

• WiMAX (IEEE 802.16)

  • Physical Layer:

    • Modulation: OFDM (for downlink) and OFDMA (for uplink/downlink in scalable versions). SC-FDMA for uplink in some profiles.

    • Frequency Bands: Operates in both licensed (2.3/2.5/3.5 GHz) and unlicensed (5.8 GHz) bands.

    • Channelization: Flexible channel bandwidths (1.25 MHz to 20 MHz).

  • Architecture:

    • Base Station (BS): Fixed infrastructure providing coverage.

    • Subscriber Station (SS): Customer-premises equipment (CPE).

    • Connection is typically point-to-multipoint.

  • Comparison with Wi-Fi:

    | Aspect | WiMAX | Wi-Fi (802.11) | | :--- | :--- | :--- | | Primary Goal | Metropolitan-area broadband access (last-mile) | Local-area LAN access | | Range | Up to 50 km (line-of-sight) | ~100 m (indoor) | | QoS | Strong, built-in (for voice/video) | Basic (WMM), less robust | | Mobility | Designed for limited mobility (nomadic) | Designed for stationary/slow mobility |

D. Wireless Mesh Networks

• Definition: A network of mesh routers and mesh clients where nodes cooperate to relay data. Forms a multi-hop topology.

• Architecture:

  • Mesh Routers: Form the backbone, have routing functionality, often mains-powered.

  • Mesh Clients: End-user devices that may or may not have routing capability.

• Concept of Multi-hop Relay:

  • Data travels from source to destination via one or more intermediate nodes (routers).

  • Process: Source → Relay Node 1 → Relay Node 2 → ... → Destination.

  • Significance:

    1. Extended Coverage: Reaches areas beyond single-hop radio range.

    2. Reliability & Self-Healing: Multiple paths exist; if one node fails, traffic reroutes.

    3. Network Robustness: No single point of failure.

    4. Scalability: Can cover large areas without wired backhaul to every node.

E. Mobile Ad Hoc Networks (MANETs)

• Definition: Infrastructure-less, self-configuring network of mobile nodes connected wirelessly. Nodes act as both hosts and routers.

• Key Challenges: Dynamic topology, limited bandwidth/battery, hidden terminal problem, security vulnerabilities (no central authority).

• Routing Protocol Classification:

  | Class | Principle | Overhead | Latency | Example Protocols | | :--- | :--- | :--- | :--- | :--- | | Proactive (Table-Driven) | Maintains up-to-date routes to all nodes via periodic updates. | High (constant control traffic) | Low (route available on-demand) | DSDV, OLSR | | Reactive (On-Demand) | Discovers routes only when needed via route request floods. | Low (no periodic updates) | High (discovery delay) | AODV, DSR | | Hybrid | Combines both. Uses proactive within a local zone, reactive outside. | Medium | Medium (low intra-zone, high inter-zone) | ZRP (Zone Routing Protocol) |

[!TIP] Exam Focus: Link overhead vs. latency trade-off. Proactive = high overhead/low latency. Reactive = low overhead/high latency.

II. Cellular & Mobile Network Generations

A. 2.5G / 2.75G: General Packet Radio Service (GPRS)

• Key Features:

  • Introduced packet-switched domain alongside existing circuit-switched GSM.

  • "Always-on" connection (no call setup per session).

  • Higher data rates (~40-100 kbps) than circuit-switched data (CSD).

  • Charging based on data volume, not time.

• Architecture:

  • SGSN (Serving GPRS Support Node): Tracks mobile station location, handles authentication, packet routing/forwarding within its service area.

  • GGSN (Gateway GPRS Support Node): Gateway to external packet networks (Internet, corporate LAN). Assigns IP addresses, performs address translation.

  • Interfaces: Gb (BTS to SGSN), Gn (SGSN to GGSN), Gi (GGSN to external network).

• Role: Enabled practical mobile data services (email, WAP browsing, early mobile internet).

B. 3G: Universal Mobile Telecommunication System (UMTS)

• Core Objectives: Higher data rates (2 Mbps indoor, 384 kbps outdoor), multimedia support (video calls), global roaming.

• Architecture:

  • UTRAN (UMTS Terrestrial Radio Access Network):

    • Node B: Base station (equivalent to BTS in GSM).

    • RNC (Radio Network Controller): Controls multiple Node Bs, handles radio resource management, handovers.

  • Core Network (CN): Evolved from GSM. Contains MSC (circuit-switched voice), SGSN, GGSN (packet-switched data).

• Key Technologies:

  • W-CDMA (Wideband CDMA): Primary air interface for UMTS (5 MHz bandwidth).

  • CDMA2000: Alternative 3G standard (e.g., 1xRTT, EV-DO), primarily in North America/Korea.

C. 4G: Long-Term Evolution (LTE)

• Key Features & Benefits:

  • All-IP Network: No circuit-switched domain. Voice is VoIP (VoLTE).

  • Flat Architecture: Removes RNC. eNodeB (evolved Node B) connects directly to EPC (Evolved Packet Core).

  • High Throughput & Low Latency: Peak rates ~100 Mbps (mobile), 1 Gbps (stationary). Latency < 10 ms.

  • Spectral Efficiency: Uses OFDMA (downlink) and SC-FDMA (uplink) for better efficiency in high-data-rate, multi-user scenarios.

  • Flexible Bandwidth: Supports 1.4 to 20 MHz carrier aggregation.

  • Seamless Mobility: Optimized for high-speed mobility (trains, cars).

D. 3G vs. 4G (LTE) Comparison

III. Mobility Management & IPv6

A. Mobile IP (MIP)

• Core Concepts:

  • Home Agent (HA): Router in home network, maintains binding of MN's Home Address (HoA) to Care-of Address (CoA). Tunnels packets.

  • Foreign Agent (FA): Router in visited network (MIPv4 only). Provides CoA (FA-CoA) and forwards tunneled packets.

  • Care-of Address (CoA): Temporary IP address in visited network. Types: Foreign Agent CoA (FA-CoA) or Co-located CoA (CoA assigned to MN itself).

  • Tunneling: Encapsulating original packet (with HoA as src/dst) inside a new packet (with HA as src, CoA as dst) for delivery to MN.

• Key Differences: Mobile IPv4 vs. Mobile IPv6

  | Feature | Mobile IPv4 | Mobile IPv6 | | :--- | :--- | :--- | | Address Architecture | HoA & FA-CoA (or CoA). Triangular Routing common. | HoA & CoA (always Co-located). Route Optimization fundamental. | | Tunneling Mechanism | IP-in-IP (Protocol 4) or Minimal Encapsulation. | IPv6-in-IPv6 encapsulation or Routing Header (Type 2) for route optimization. | | Foreign Agent (FA) | Mandatory (provides CoA, services). | Optional/Not Used (MN gets its own CoA via SLAAC/DHCPv6). | | Route Optimization | Requires extensions (MIPv4 RO). Triangular routing default (HA always intercepts). | Built-in via Binding Updates to Correspondent Node (CN). | | Security | Relies on IPsec (optional). | Uses IPsec (mandatory for MIPv6 signaling) or other secure mechanisms. | | Header Overhead | 20-40 bytes (IP-in-IP). | 40 bytes (IPv6 hdr) + possible Routing Header. |

[!TIP] Exam Focus: MIPv6 eliminates FA, uses Co-located CoA, and has inherent route optimization. Triangular routing is a key drawback of MIPv4.

B. Encapsulation Headers in Mobility

• Purpose: To allow the Home Agent (HA) to tunnel packets destined for the Mobile Node's (MN) Home Address (HoA) to its current Care-of Address (CoA) in a foreign network.

• Compare Encapsulation Headers: IPv4 vs. IPv6

  | Aspect | IPv4 Encapsulation | IPv6 Encapsulation | | :--- | :--- | :--- | | Outer Header | New IPv4 header (src=HA, dst=CoA). | New IPv6 header (src=HA, dst=CoA). | | Inner Header | Original IPv4 packet (src=CN, dst=HoA). | Original IPv6 packet (src=CN, dst=HoA). | | Protocol Field | Outer header Protocol = 4 (IP-in-IP). | Outer header Next Header field indicates encapsulation (typically 41 for IPv6-in-IPv6) or Routing Header. | | Optimization | Minimal encapsulation (removes outer IP options). | Routing Header (Type 2): Allows CN to send directly to CoA after learning binding, bypassing HA. | | Key Difference | Simple IP-in-IP tunneling. | Supports tunnel mode (like IPv4) and route optimization via Routing Header. |

IV. Security Models & Application Layer

A. Military Security Models

• Primary Objectives: Enforce confidentiality, integrity, and availability within a hierarchical command structure (e.g., military, government).

• Role of Hierarchical Command Structures:

  • Access decisions are based not just on clearance (confidentiality) but also on "need-to-know" and chain of command.

  • Models like Bell-LaPadula enforce *-property (no write down, no read up) which aligns with hierarchical secrecy levels.

  • Biba Model enforces integrity levels (no write up, no read down), applicable to command integrity.

  • The hierarchy defines domains of control; a subject at a higher level can command/read subjects/objects at lower levels, but not vice-versa, maintaining command integrity and secrecy.

[!TIP] Bell-LaPadula = Confidentiality (Simple Security *, *-property). Biba = Integrity (Simple Integrity, *-integrity).

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

• Definition: Attack aimed at disrupting availability of a service or resource for legitimate users.

• In Wireless Context:

  • Jamming: Transmitting noise on the channel to disrupt physical/MAC layer.

  • MAC Layer Exhaustion: Flooding with RTS/CTS or authentication requests to drain battery/starvation.

  • Network Layer Attacks: Routing table overflow (MANETs), malicious route disruption.

  • Battery Drain Attacks: Forcing target to perform expensive operations (e.g., repeated authentication, collision generation).

• General Mitigation: Rate limiting, intrusion detection, filtering, using spread spectrum (FHSS/DSSS) against jamming.

C. E-Commerce & Electronic Payment Systems

• E-Commerce:

  • Definition: Buying and selling goods/services over electronic networks (primarily Internet).

  • Transformation of Business:

    • B2B (Business-to-Business): Streamlined supply chains, e-procurement.

    • B2C (Business-to-Consumer): Online retail (Amazon), 24/7 availability, global reach.

    • C2C (Consumer-to-Consumer): eBay, Etsy (peer-to-peer sales).

    • Reduced transaction costs, personalized marketing, new business models (subscriptions, freemium).

• Electronic Payment Systems:

  • Types: Credit/Debit cards (online), E-wallets (PayPal, Google Pay), Cryptocurrencies (Bitcoin), Bank transfers.

  • Security Requirements: Confidentiality (encryption), Authentication (of parties), Integrity (no tampering), Non-repudiation (proof of transaction).

  • Protocol Example: SET (Secure Electronic Transaction): Uses dual signatures (links order & payment), public key cryptography, but complex and not widely adopted.

D. TCP over Wireless Networks

• Challenges Impacting TCP:

  • High Bit Error Rate (BER): Causes packet loss → TCP interprets as congestion → reduces window unnecessarily (spurious timeout).

  • Variable/High Latency: ACKs delayed → TCP timeout triggers, reducing throughput.

  • Frequent Disconnections: Breaks connection, requires slow start from scratch.

  • Asymmetric Links: Downlink often much faster than uplink; ACK bottleneck.

• Solutions/Enhancements:

  • TCP Reno/NewReno: Fast retransmit/recovery (standard improvements).

  • Snoop Protocol: Local retransmission at base station (or access point). Caches packets, retransmits lost packets locally before MN's TCP times out. Does not break end-to-end semantics.

  • Mobile TCP (M-TCP): Splits connection. Fixed host ↔ Base Station uses standard TCP. Base Station ↔ MN uses a lightweight, reliable protocol. When MN disconnects, base station buffers data and freezes window, avoiding slow start on reconnection.

  • Indirect TCP (I-TCP): Splits TCP connection into two separate connections (fixed host ↔ FA, FA ↔ MN). FA acts as a proxy. Breaks end-to-end semantics but hides wireless loss from fixed host.

V. Additional Technologies

A. Radio Frequency Identification (RFID)

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

• Components:

  • Tag: Microchip + antenna (passive, active, semi-passive).

  • Reader: Transmits RF signal, receives tag response.

  • Middleware: Filters/aggregates data from readers.

  • Database: Stores tag ID and associated object info.

• Principle of Operation & Data Transmission:

  • Inductive Coupling (LF/HF, 125-134 kHz & 13.56 MHz): Magnetic field between reader and tag coils. Short range (<1m). Used for access control, animal tags.

  • Electromagnetic Coupling (UHF, 860-960 MHz & 2.45 GHz): Reader emits RF waves. Passive tag uses backscatter modulation: Tag's antenna impedance is changed by the chip, reflecting/scattering the reader's signal to transmit data back. Reader-to-tag: Modulated RF (provides power & clock). Tag-to-reader: Backscatter (load modulation).

  • Active Tags: Have battery, transmit own signal (longer range, higher cost).

[!TIP] Exam Focus: Key distinction: Passive tags use backscatter for tag-to-reader communication and get power from reader's signal. Active tags have their own power source.

UMTS (Cross-Reference from Section II.B):

• Short Note: UMTS is the 3G standard for GSM evolution. Key features: W-CDMA air interface (5 MHz), UTRAN (Node B + RNC), and evolved core network (SGSN/GGSN). Enabled mobile multimedia (video calls) with higher data rates (384 kbps outdoor) and global roaming. Architecture separates radio access (UTRAN) from core network, paving way for LTE's flat architecture.