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+# COMP-347: Computer Networks
+## Assignment 3
+
+**Student Name:** [Your Name]  
+**Student ID:** [Your Student ID]  
+**Time Spent:** [Hours spent on assignment]  
+**Due:** After completion of Units 6 and 7
+
+---
+
+## Part 1: Short Answer Questions (30%)
+
+### 1.1 Anchor MSC in GSM Networks (5%)
+
+The **Anchor MSC (Mobile Switching Center)** plays a crucial role in GSM (Global System for Mobile Communications) networks, particularly in managing mobile subscriber mobility and maintaining service continuity during handovers.
+
+#### Primary Functions:
+
+#### 1. Home Location Register (HLR) Interface
+- **Subscriber Authentication**: The Anchor MSC maintains the primary connection to the subscriber's HLR, which contains the master copy of subscriber profile data
+- **Service Profile Management**: Stores and manages subscriber service capabilities, restrictions, and supplementary services
+- **Location Management**: Coordinates with the HLR to track the subscriber's current location area and serving MSC
+
+#### 2. Call Routing and Management
+- **Incoming Call Routing**: Acts as the initial point of contact for incoming calls to a mobile subscriber, routing calls to the current serving MSC
+- **Call Continuity**: Ensures seamless call continuation during inter-MSC handovers by maintaining call state information
+- **Billing Coordination**: Centralizes billing records and coordinates charging information across multiple serving MSCs
+
+#### 3. Handover Coordination
+- **Inter-MSC Handover Support**: When a mobile subscriber moves between different MSC coverage areas during an active call, the Anchor MSC coordinates the handover process
+- **Resource Management**: Maintains circuit connections and manages radio resources during complex handover scenarios
+- **Quality Maintenance**: Ensures call quality is preserved during mobility events
+
+#### 4. Visitor Location Register (VLR) Coordination
+- **Registration Management**: Coordinates subscriber registration/deregistration across multiple VLRs as the subscriber roams
+- **Authentication Coordination**: Manages authentication procedures when subscribers roam between different MSC areas
+- **Temporary Identity Management**: Handles Temporary Mobile Subscriber Identity (TMSI) allocation and management
+
+#### 5. Network Optimization Benefits
+- **Reduced HLR Load**: By serving as an intermediary, the Anchor MSC reduces the number of direct HLR queries from multiple serving MSCs
+- **Improved Performance**: Centralized management of subscriber data reduces lookup times and improves call setup performance
+- **Enhanced Mobility**: Provides seamless service as subscribers move between different network areas
+
+#### Operational Scenario:
+When a GSM subscriber roams from their home area to a different MSC area:
+1. The new serving MSC registers the subscriber's presence
+2. The Anchor MSC updates the HLR with the new location information
+3. For incoming calls, the HLR directs calls to the Anchor MSC
+4. The Anchor MSC then routes calls to the current serving MSC
+5. During handovers, the Anchor MSC maintains call state and coordinates resource allocation
+
+**Key Insight**: The Anchor MSC concept enables efficient mobility management in GSM networks by centralizing subscriber management functions while allowing distributed call processing, thereby optimizing both network performance and subscriber experience during roaming scenarios.
+
+### 1.2 LTE Network Characteristics (5%)
+
+**LTE (Long Term Evolution)** represents a significant advancement in cellular network technology, introducing fundamental changes in radio access network architecture and capabilities compared to previous generations.
+
+#### Main Characteristics of LTE Radio Access Networks:
+
+#### 1. All-IP Architecture
+- **Packet-Switched Only**: LTE eliminates circuit-switched voice calls, using Voice over LTE (VoLTE) for all voice communications
+- **Flat Network Architecture**: Simplified network topology with fewer network elements compared to 3G
+- **IP Multimedia Subsystem (IMS)**: Integrated multimedia services delivered over IP
+
+#### 2. OFDMA and SC-FDMA Technologies
+- **Orthogonal Frequency Division Multiple Access (OFDMA)**: Used in downlink for efficient spectrum utilization and multi-user access
+- **Single Carrier FDMA (SC-FDMA)**: Used in uplink to reduce peak-to-average power ratio and improve battery life
+- **Flexible Bandwidth**: Supports 1.4, 3, 5, 10, 15, and 20 MHz channel bandwidths
+
+#### 3. MIMO Technology
+- **Multiple Input Multiple Output (MIMO)**: Uses multiple antennas at both transmitter and receiver
+- **Spatial Multiplexing**: Increases data throughput by transmitting multiple data streams simultaneously
+- **Diversity Gain**: Improves signal reliability in fading environments
+
+#### 4. Advanced Radio Resource Management
+- **Dynamic Resource Allocation**: Real-time allocation of radio resources based on traffic demand and channel conditions
+- **Link Adaptation**: Automatic adjustment of modulation and coding schemes based on channel quality
+- **Inter-Cell Interference Coordination (ICIC)**: Coordinates resource usage between neighboring cells
+
+#### How LTE Differs from Previous Generations:
+
+#### Architecture Differences:
+
+**2G/3G Architecture:**
+- **Circuit-Switched Core**: Separate networks for voice (circuit-switched) and data (packet-switched)
+- **Hierarchical Network**: Multiple network elements (RNC, BSC, MSC)
+- **Voice Priority**: Networks primarily designed for voice services
+
+**LTE Architecture:**
+- **All-IP Core**: Single packet-switched network for all services
+- **Flat Architecture**: Evolved NodeB (eNodeB) directly connects to core network
+- **Data-Centric**: Optimized for high-speed data transmission
+
+#### Performance Improvements:
+
+| Aspect | 3G (UMTS) | LTE |
+|--------|-----------|-----|
+| **Downlink Speed** | Up to 42 Mbps (HSPA+) | Up to 300 Mbps |
+| **Uplink Speed** | Up to 5.7 Mbps | Up to 75 Mbps |
+| **Latency** | 100-500 ms | <10 ms |
+| **Spectral Efficiency** | 1-2 bps/Hz | 3-4 bps/Hz |
+
+#### Key Technological Advances:
+
+#### 1. Radio Interface Evolution
+- **CDMA → OFDMA**: Transition from Code Division to Orthogonal Frequency Division Multiple Access
+- **Advanced Modulation**: Support for 64-QAM and higher-order modulation schemes
+- **Adaptive Antenna Systems**: Beamforming and advanced antenna technologies
+
+#### 2. Protocol Stack Simplification
+- **Reduced Layers**: Streamlined protocol stack compared to 3G
+- **Header Compression**: More efficient header compression techniques
+- **Fast Retransmission**: Hybrid ARQ (HARQ) for rapid error recovery
+
+#### 3. Mobility Management
+- **Seamless Handovers**: Faster handover procedures with minimal service interruption
+- **Inter-RAT Mobility**: Smooth transitions between LTE and legacy networks (2G/3G)
+- **Self-Organizing Networks (SON)**: Automated network optimization and configuration
+
+#### 4. Quality of Service (QoS)
+- **Evolved Packet System (EPS) Bearers**: Fine-grained QoS control for different traffic types
+- **Policy Control**: Dynamic policy enforcement based on subscriber profiles and network conditions
+- **Guaranteed Bit Rate (GBR)**: Service-specific bandwidth guarantees
+
+**Key Insight**: LTE represents a fundamental paradigm shift from circuit-switched, voice-centric networks to an all-IP, data-optimized architecture that provides significantly higher throughput, lower latency, and improved spectral efficiency while supporting seamless multimedia services and enhanced mobility management.
+
+### 1.3 CSMA/CD Protocol (5%)
+
+**CSMA/CD** stands for **Carrier Sense Multiple Access with Collision Detection**, a media access control protocol used in traditional Ethernet networks to manage shared medium access among multiple nodes.
+
+#### How CSMA/CD Works:
+
+#### 1. Carrier Sense (CS)
+- **Listen Before Transmit**: Before transmitting, a node listens to the medium to detect if another transmission is already in progress
+- **Channel Assessment**: If the channel is busy, the node waits until it becomes idle
+- **Persistence Strategy**: Once idle is detected, the node may wait a brief interframe gap before attempting transmission
+
+#### 2. Multiple Access (MA)
+- **Shared Medium**: Multiple nodes share the same physical transmission medium (bus topology)
+- **Contention-Based**: All nodes compete for access to the medium using the same protocol rules
+- **Distributed Control**: No central authority controls medium access; all decisions are made locally by each node
+
+#### 3. Collision Detection (CD)
+- **Simultaneous Transmission Monitoring**: While transmitting, nodes continuously monitor the medium to detect collisions
+- **Signal Comparison**: Compare transmitted signal with received signal to identify interference from other transmissions
+- **Early Abort**: Upon detecting collision, immediately stop transmission to minimize medium occupation time
+
+#### 4. Collision Handling Procedure
+When a collision is detected:
+1. **Jam Signal**: Transmit a 32-bit or 48-bit jam signal to ensure all nodes detect the collision
+2. **Exponential Backoff**: Each involved node waits a random time before retransmitting
+3. **Backoff Algorithm**: Wait time = random(0, 2^n - 1) × slot time, where n = number of consecutive collisions
+4. **Retry Limit**: After 16 consecutive collisions, the frame is discarded
+
+#### Importance of RTT in CSMA/CD:
+
+The **Round-Trip Time (RTT)** is critical for CSMA/CD's proper operation due to the **collision detection window**:
+
+#### 1. Collision Detection Window
+- **Maximum Detection Time**: RTT represents the maximum time needed to detect a collision anywhere on the network
+- **Worst-Case Scenario**: Node A starts transmitting just as Node B (at maximum distance) begins transmission
+- **Signal Propagation**: Time for A's signal to reach B plus time for B's collision signal to return to A
+
+#### 2. Minimum Frame Size Requirement
+- **Frame Transmission Time**: Must be ≥ 2 × propagation delay (RTT)
+- **Collision Detection Guarantee**: Ensures transmitting node can detect collision before finishing frame transmission
+- **Ethernet Standard**: 64-byte minimum frame size ensures collision detection on maximum cable length
+
+#### 3. Network Diameter Limitation
+- **Maximum Cable Length**: RTT limits the physical size of collision domain
+- **Signal Attenuation**: Longer cables increase propagation delay and reduce signal strength
+- **Timing Constraints**: RTT must remain small enough for reliable collision detection
+
+#### 4. Slot Time Calculation
+- **Slot Time**: Basic timing unit = 2 × maximum propagation delay
+- **Backoff Intervals**: Random backoff periods are multiples of slot time
+- **Network Synchronization**: Ensures all nodes use consistent timing for collision avoidance
+
+#### Mathematical Relationship:
+```
+Minimum Frame Time ≥ 2 × (Cable Length ÷ Propagation Speed + Processing Delays)
+```
+
+For traditional Ethernet:
+- Maximum cable length: 2.5 km
+- Propagation speed: ~2×10^8 m/s  
+- RTT: ~25 μs
+- Minimum frame size: 64 bytes (512 bits)
+- Slot time: 512 bit times
+
+#### Protocol Efficiency Impact:
+- **Short RTT**: Allows smaller minimum frames, higher efficiency, larger networks
+- **Long RTT**: Requires larger minimum frames, reduces efficiency, limits network size
+- **Collision Domain**: RTT determines maximum collision domain size
+
+**Key Insight**: RTT is fundamental to CSMA/CD because it defines the collision detection window, determines minimum frame size requirements, and limits the physical extent of collision domains, directly affecting network efficiency and scalability.
+
+### 1.4 CSMA/CA Protocol (5%)
+
+**CSMA/CA** stands for **Carrier Sense Multiple Access with Collision Avoidance**, a media access control protocol primarily used in wireless networks (such as 802.11 Wi-Fi) where collision detection is impractical due to the wireless medium characteristics.
+
+#### How CSMA/CA Works:
+
+#### 1. Carrier Sense (CS)
+- **Physical Carrier Sense**: Listen to the wireless medium to detect ongoing transmissions
+- **Virtual Carrier Sense**: Use Network Allocation Vector (NAV) from RTS/CTS or other control frames
+- **Clear Channel Assessment (CCA)**: Determine if medium is idle before attempting transmission
+- **Energy Detection**: Monitor RF energy levels to identify channel activity
+
+#### 2. Multiple Access (MA)
+- **Shared Wireless Medium**: Multiple stations compete for access to the same radio frequency spectrum
+- **Hidden Terminal Problem**: Stations may not hear each other due to distance or obstacles
+- **Distributed Coordination**: No centralized control; stations coordinate access through distributed algorithms
+
+#### 3. Collision Avoidance (CA)
+Unlike collision detection, CSMA/CA attempts to **prevent collisions** rather than detect them after they occur:
+
+#### Basic CSMA/CA Operation:
+1. **Channel Sensing**: Station senses the medium for a minimum time period (DIFS - Distributed Inter-Frame Space)
+2. **Random Backoff**: If medium is idle, station waits a random backoff time before transmitting
+3. **Transmission**: If medium remains idle after backoff, station transmits the frame
+4. **Acknowledgment**: Receiver sends ACK frame to confirm successful reception
+5. **Retransmission**: If no ACK received, sender assumes collision and retransmits after backoff
+
+#### How Collisions Are Avoided:
+
+#### 1. Random Backoff Mechanism
+- **Contention Window**: Each station selects random backoff time from [0, CW-1] × slot time
+- **Exponential Backoff**: After collision, contention window doubles (CW = CW × 2)
+- **Collision Probability Reduction**: Random timing reduces likelihood of simultaneous transmission
+- **Fairness**: All stations have equal probability of accessing the medium
+
+#### 2. Inter-Frame Spacing (IFS)
+Different frame types use different inter-frame spaces to establish priority:
+- **SIFS (Short IFS)**: Highest priority for ACKs and CTS frames
+- **DIFS (Distributed IFS)**: Standard priority for data frames  
+- **EIFS (Extended IFS)**: Used after corrupted frame reception
+- **Priority Access**: Critical frames get preferential medium access
+
+#### 3. Request-to-Send/Clear-to-Send (RTS/CTS)
+**Optional mechanism for avoiding hidden terminal collisions:**
+
+**RTS/CTS Handshake:**
+1. **RTS Frame**: Sender transmits Request-to-Send to receiver
+2. **CTS Frame**: Receiver responds with Clear-to-Send if medium available
+3. **NAV Setting**: Both RTS and CTS set Network Allocation Vector in other stations
+4. **Data Transmission**: Sender transmits data frame after successful RTS/CTS exchange
+5. **ACK Frame**: Receiver acknowledges data reception
+
+**Benefits:**
+- **Hidden Terminal Solution**: CTS frame alerts hidden terminals about upcoming transmission
+- **Collision Reduction**: Reduces collision probability for large data frames
+- **Bandwidth Reservation**: Virtual carrier sensing reserves medium for transmission
+
+#### 4. Network Allocation Vector (NAV)
+- **Virtual Carrier Sensing**: Maintains timer indicating when medium will be busy
+- **Duration Field**: Frames carry duration information for NAV updates
+- **Medium Reservation**: Stations defer transmission while NAV > 0
+- **Collision Avoidance**: Prevents transmissions that would cause collisions
+
+#### 5. Binary Exponential Backoff
+**Collision Response Mechanism:**
+- **Initial Window**: Start with minimum contention window (CW_min)
+- **Window Doubling**: After each collision, CW = min(CW × 2, CW_max)
+- **Random Selection**: Choose backoff = random[0, CW-1] × slot_time
+- **Window Reset**: Reset CW to CW_min after successful transmission
+
+#### 6. Frame Retry and Timeout
+- **ACK Timeout**: If ACK not received within specified time, assume collision
+- **Retry Limit**: Maximum number of retransmission attempts before frame discard
+- **Exponential Backoff**: Apply backoff algorithm for each retry attempt
+
+#### CSMA/CA vs CSMA/CD Comparison:
+
+| Aspect | CSMA/CA | CSMA/CD |
+|--------|---------|---------|
+| **Medium** | Wireless | Wired |
+| **Collision Handling** | Avoidance | Detection |
+| **Collision Detection** | Not possible | Real-time |
+| **Overhead** | Higher (RTS/CTS, ACK) | Lower |
+| **Efficiency** | Lower due to avoidance | Higher when collisions are rare |
+| **Hidden Terminal** | Addressed by RTS/CTS | Not applicable |
+
+**Key Insight**: CSMA/CA compensates for the inability to detect collisions in wireless media by implementing sophisticated avoidance mechanisms including random backoff, virtual carrier sensing, RTS/CTS handshakes, and prioritized channel access, trading some efficiency for reliability in challenging wireless environments.
+
+### 1.5 Data Link Layer Error Detection/Correction (5%)
+
+The data link layer employs various techniques to handle transmission errors that may occur due to noise, interference, or signal attenuation in communication channels.
+
+## Error Detection Techniques:
+
+#### 1. Parity Check
+- **Single Parity**: Adds one parity bit to detect single-bit errors
+- **Even Parity**: Total number of 1s (including parity bit) is even
+- **Odd Parity**: Total number of 1s (including parity bit) is odd
+- **Limitation**: Cannot detect even numbers of bit errors
+
+#### 2. Checksum
+- **Internet Checksum**: Sum all data words, take 1's complement (used in IP, TCP, UDP)
+- **Fletcher Checksum**: Uses modular arithmetic for improved error detection
+- **Advantages**: Simple implementation, good for random errors
+- **Limitations**: May miss certain systematic error patterns
+
+#### 3. Cyclic Redundancy Check (CRC)
+- **Polynomial-Based**: Uses generator polynomial to create check sequence
+- **Frame Check Sequence (FCS)**: CRC bits appended to frame
+- **Detection Capability**: Detects all single-bit, double-bit, odd number of bits, and burst errors ≤ r bits (where r = degree of generator polynomial)
+- **Common Polynomials**: CRC-16, CRC-32, CRC-CCITT
+- **High Reliability**: Very low probability of undetected errors
+
+#### 4. Two-Dimensional Parity
+- **Block Structure**: Arrange data in rows and columns
+- **Row Parity**: Calculate parity for each row
+- **Column Parity**: Calculate parity for each column
+- **Enhanced Detection**: Can detect and correct single-bit errors, detect some multi-bit errors
+
+## Error Correction Techniques:
+
+#### 1. Forward Error Correction (FEC)
+**Hamming Codes:**
+- **Single Error Correction**: Can correct single-bit errors automatically
+- **Redundancy**: Requires 2^r ≥ m + r + 1 (where m = data bits, r = parity bits)
+- **Syndrome Decoding**: Uses parity check equations to locate error position
+- **Example**: Hamming(7,4) code uses 4 data bits, 3 parity bits
+
+**Reed-Solomon Codes:**
+- **Block Codes**: Operate on symbols rather than individual bits
+- **Burst Error Correction**: Excellent for correcting burst errors
+- **Applications**: Used in CDs, DVDs, QR codes, satellite communications
+- **Capability**: Can correct up to t symbol errors with 2t redundant symbols
+
+#### 2. Convolutional Codes
+- **Continuous Encoding**: Encode data stream continuously using shift registers
+- **Memory**: Output depends on current and previous input bits
+- **Viterbi Decoding**: Maximum likelihood decoding algorithm
+- **Applications**: Widely used in wireless communications, satellite links
+
+#### 3. Turbo Codes
+- **Iterative Decoding**: Uses two or more constituent codes with iterative decoding
+- **Near Shannon Limit**: Approaches theoretical maximum error correction capability
+- **Applications**: 3G/4G cellular networks, satellite communications
+- **Complexity**: Higher computational complexity but superior performance
+
+## Automatic Repeat Request (ARQ):
+
+#### 1. Stop-and-Wait ARQ
+- **Simple Protocol**: Send one frame, wait for ACK before sending next
+- **Positive ACK**: Receiver sends acknowledgment for correctly received frames
+- **Timeout**: Sender retransmits if no ACK received within timeout period
+- **Sequence Numbers**: Prevents duplicate frame acceptance
+
+#### 2. Go-Back-N ARQ
+- **Sliding Window**: Multiple frames can be outstanding
+- **Cumulative ACK**: ACK n acknowledges all frames up to n
+- **Error Recovery**: Retransmit all frames from error point onwards
+- **Efficiency**: Better throughput than stop-and-wait
+
+#### 3. Selective Repeat ARQ
+- **Individual ACK**: Each frame acknowledged individually
+- **Selective Retransmission**: Only retransmit errored frames
+- **Buffer Requirements**: Receiver must buffer out-of-order frames
+- **Optimal Efficiency**: Best throughput but most complex
+
+## Hybrid Techniques:
+
+#### 1. Hybrid ARQ (HARQ)
+- **FEC + ARQ Combination**: Uses error correction with retransmission backup
+- **Type I HARQ**: FEC for error correction, ARQ for error detection
+- **Type II HARQ**: Incremental redundancy - additional parity bits sent on retransmission
+- **Applications**: LTE, 5G, and other modern wireless systems
+
+#### 2. Adaptive Error Control
+- **Dynamic Selection**: Choose error control method based on channel conditions
+- **Channel Quality Feedback**: Adjust redundancy based on measured error rates
+- **Optimization**: Balance between throughput and reliability
+
+## Implementation Considerations:
+
+| Technique | Detection | Correction | Overhead | Complexity | Applications |
+|-----------|-----------|------------|----------|------------|--------------|
+| **Parity** | Limited | No | Low | Very Low | Simple systems |
+| **Checksum** | Good | No | Low | Low | Internet protocols |
+| **CRC** | Excellent | No | Medium | Medium | Ethernet, Wi-Fi |
+| **Hamming** | Good | Single-bit | High | Medium | Memory systems |
+| **Reed-Solomon** | Excellent | Multiple | High | High | Storage, broadcast |
+| **ARQ** | Perfect | Perfect | Variable | Medium | Most data networks |
+
+**Key Insight**: Data link layer error control combines detection techniques (parity, checksum, CRC) with correction methods (FEC, ARQ) to provide reliable data transmission, with the choice of technique depending on channel characteristics, performance requirements, and acceptable complexity trade-offs.
+
+### 1.6 Wi-Fi Network Standards (5%)
+
+Modern Wi-Fi technology encompasses several IEEE 802.11 standards that have evolved to provide higher data rates, improved reliability, and enhanced features for today's wireless networking needs.
+
+## Current Wi-Fi Standards in Industry Use:
+
+### 1. 802.11n (Wi-Fi 4) - 2009
+**Link Characteristics:**
+- **Frequency Bands:** 2.4 GHz and 5 GHz (dual-band)
+- **Channel Bandwidth:** 20 MHz and 40 MHz channels
+- **Data Rates:** Up to 600 Mbps (theoretical maximum)
+- **MIMO Technology:** Up to 4×4 spatial streams
+- **Range:** ~70m indoor, ~250m outdoor
+- **Modulation:** OFDM with up to 64-QAM
+- **Backward Compatibility:** Compatible with 802.11a/b/g
+
+### 2. 802.11ac (Wi-Fi 5) - 2013
+**Link Characteristics:**
+- **Frequency Band:** 5 GHz only
+- **Channel Bandwidth:** 20, 40, 80, and 160 MHz channels
+- **Data Rates:** Up to 6.93 Gbps (theoretical maximum)
+- **MIMO Technology:** Up to 8×8 MU-MIMO (Multi-User MIMO)
+- **Range:** ~35m indoor, ~120m outdoor
+- **Modulation:** OFDM with up to 256-QAM
+- **Beamforming:** Explicit beamforming for improved signal focus
+- **Wave 1 vs Wave 2:** Wave 2 adds MU-MIMO and 160 MHz channels
+
+### 3. 802.11ax (Wi-Fi 6/6E) - 2019/2020
+**Link Characteristics:**
+- **Frequency Bands:** 2.4 GHz, 5 GHz, and 6 GHz (Wi-Fi 6E)
+- **Channel Bandwidth:** 20, 40, 80, and 160 MHz channels
+- **Data Rates:** Up to 9.6 Gbps (theoretical maximum)
+- **MIMO Technology:** Up to 8×8 MU-MIMO (uplink and downlink)
+- **Range:** Similar to 802.11ac but more efficient in dense environments
+- **Modulation:** OFDMA with up to 1024-QAM
+- **Key Features:** OFDMA, Target Wake Time (TWT), BSS Coloring
+
+### 4. 802.11be (Wi-Fi 7) - 2024 (Emerging)
+**Link Characteristics:**
+- **Frequency Bands:** 2.4 GHz, 5 GHz, and 6 GHz (tri-band)
+- **Channel Bandwidth:** Up to 320 MHz channels
+- **Data Rates:** Up to 46 Gbps (theoretical maximum)
+- **MIMO Technology:** Up to 16×16 MU-MIMO
+- **Advanced Features:** Multi-Link Operation (MLO), 4K-QAM modulation
+
+## Detailed Standard Comparison:
+
+| Standard | Year | Frequency | Max Bandwidth | Max Rate | MIMO | Key Features |
+|----------|------|-----------|---------------|----------|------|--------------|
+| **802.11n** | 2009 | 2.4/5 GHz | 40 MHz | 600 Mbps | 4×4 | First MIMO, dual-band |
+| **802.11ac** | 2013 | 5 GHz | 160 MHz | 6.93 Gbps | 8×8 | MU-MIMO, 256-QAM |
+| **802.11ax** | 2019 | 2.4/5/6 GHz | 160 MHz | 9.6 Gbps | 8×8 | OFDMA, 1024-QAM, TWT |
+| **802.11be** | 2024 | 2.4/5/6 GHz | 320 MHz | 46 Gbps | 16×16 | MLO, 4K-QAM |
+
+## Technical Characteristics by Standard:
+
+### Physical Layer Features:
+**802.11n:**
+- **Guard Interval:** 400ns and 800ns options
+- **Frame Aggregation:** A-MSDU and A-MPDU for efficiency
+- **Space-Time Block Coding (STBC):** Improved reliability
+- **Greenfield Mode:** 802.11n-only operation for maximum efficiency
+
+**802.11ac:**
+- **Wider Channels:** 80 MHz and 160 MHz for higher throughput
+- **More Spatial Streams:** Up to 8 spatial streams
+- **Advanced Beamforming:** Standardized explicit beamforming
+- **Downlink MU-MIMO:** Simultaneous transmission to multiple clients
+
+**802.11ax:**
+- **OFDMA:** Orthogonal Frequency Division Multiple Access for efficiency
+- **Uplink MU-MIMO:** Multi-user transmission in both directions
+- **BSS Coloring:** Reduces interference between overlapping networks
+- **Target Wake Time:** Power management for IoT devices
+
+### Industry Applications:
+
+**Enterprise Networks:**
+- **802.11ax:** Predominant choice for new installations
+- **High-Density Environments:** Airports, stadiums, conference centers
+- **OFDMA Benefits:** Better performance with many connected devices
+
+**Home Networks:**
+- **802.11ac:** Still widely deployed in existing installations
+- **802.11ax:** Becoming standard for new home routers
+- **Backward Compatibility:** Support for legacy devices
+
+**IoT and Industrial:**
+- **2.4 GHz Bands:** Better wall penetration and range
+- **Low Power Features:** TWT for battery-powered devices
+- **Mesh Networks:** Wi-Fi 6 mesh systems for whole-home coverage
+
+**Public Wi-Fi:**
+- **6 GHz Band:** Wi-Fi 6E reduces congestion in crowded areas
+- **Higher Capacity:** Support for more simultaneous users
+- **Quality of Service:** Better traffic prioritization
+
+### Performance Characteristics:
+
+**Range Considerations:**
+- **5 GHz vs 2.4 GHz:** 5 GHz offers higher speeds but shorter range
+- **6 GHz Band:** Highest speeds but most limited range
+- **Beamforming:** Improves range and reliability across all modern standards
+
+**Interference Handling:**
+- **Channel Bonding:** Wider channels increase susceptibility to interference
+- **Dynamic Frequency Selection (DFS):** Avoids radar interference on 5 GHz
+- **BSS Coloring:** Wi-Fi 6 feature reduces co-channel interference
+
+**Key Insight:** Modern Wi-Fi standards have evolved from simple OFDM-based systems to sophisticated multi-user, multi-band technologies that optimize spectrum efficiency, reduce latency, and support diverse applications from high-bandwidth streaming to low-power IoT devices, with each generation addressing specific limitations of previous standards while maintaining backward compatibility.
+
+---
+
+## Part 2: Long Answer Questions (70%)
+
+### 2.1 Code Division Multiple Access (CDMA) (15%)
+
+[To be completed]
+
+### 2.2 Two-Dimensional Checksum (15%)
+
+**Given payload:** 1011 0110 1010 1011
+
+[To be completed]
+
+### 2.3 CSMA/CD Ethernet Analysis (20%)
+
+**Given:**
+- 1 Gbps Ethernet
+- 180 m cable with 3 repeaters
+- Propagation speed: 2×10^8 m/sec
+- Frame size: 1,024 bits
+- Backoff intervals: multiples of 512 bits
+- Repeater delay: 20-bit transmission time
+- Post-collision: A draws K=0, B draws K=1
+
+[To be completed]
+
+### 2.4 802.11 RTS/CTS Transmission (10%)
+
+**Given:**
+- 802.11 station with RTS/CTS
+- 1024 bytes of data
+- All other stations idle
+
+[To be completed]
+
+### 2.5 Bluetooth Frame Format Analysis (10%)
+
+[To be completed]
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