path: root/generated/NOTES.md

# COMP-347: Computer Networks - Final Exam Study Notes

**Based on:** Computer Networking: A Top-Down Approach, 8th Edition  
**Course Units:** 1-7 covering all major networking concepts  
**Prepared for:** Final Examination

---

## Table of Contents

1. [Unit 1: Introduction to Computer Networks](#unit-1-introduction-to-computer-networks)
2. [Unit 2: Application Layer](#unit-2-application-layer)
3. [Unit 3: Transport Layer](#unit-3-transport-layer)
4. [Unit 4: Network Layer - Data Plane](#unit-4-network-layer---data-plane)
5. [Unit 5: Network Layer - Control Plane](#unit-5-network-layer---control-plane)
6. [Unit 6: Link Layer and LANs](#unit-6-link-layer-and-lans)
7. [Unit 7: Wireless and Mobile Networks](#unit-7-wireless-and-mobile-networks)
8. [Key Formulas and Calculations](#key-formulas-and-calculations)
9. [Protocol Comparison Tables](#protocol-comparison-tables)
10. [Common Exam Topics](#common-exam-topics)

---

## Unit 1: Introduction to Computer Networks

### 1.1 What is the Internet?

**Key Concepts:**
- **Internet**: Global network of interconnected computers using TCP/IP protocols
- **Network Edge**: End systems (hosts) that connect to the Internet
- **Network Core**: Routers and switches that forward data
- **ISP Hierarchy**: Tier-1, Regional, and Local ISPs

**Components:**
- **Hosts/End Systems**: Computers, smartphones, IoT devices
- **Communication Links**: Fiber, copper, radio, satellite
- **Packet Switches**: Routers and link-layer switches
- **Protocols**: Rules for communication (TCP, IP, HTTP, etc.)

### 1.2 Network Edge

**Access Technologies:**
- **DSL**: Digital Subscriber Line over telephone lines
- **Cable Internet**: Over cable TV infrastructure
- **FTTH**: Fiber to the Home
- **Ethernet**: Wired LAN connections
- **Wi-Fi**: Wireless LAN (802.11)
- **Cellular**: 3G, 4G/LTE, 5G mobile networks

**Physical Media:**
- **Guided Media**: Twisted pair, coaxial cable, fiber optic
- **Unguided Media**: Terrestrial radio, satellite, microwave

### 1.3 Network Core

**Switching Techniques:**

| Aspect | Circuit Switching | Packet Switching |
|--------|------------------|------------------|
| **Connection** | Dedicated path | Store-and-forward |
| **Resources** | Reserved for entire call | Shared dynamically |
| **Efficiency** | Poor for bursty data | Good for bursty data |
| **Delay** | Consistent | Variable |
| **Examples** | Traditional telephony | Internet |

**Packet Switching Concepts:**
- **Store-and-Forward**: Entire packet received before forwarding
- **Queuing Delay**: Waiting in output buffer
- **Packet Loss**: Buffer overflow causes dropped packets

### 1.4 Delay, Loss, and Throughput

**Types of Delay:**

1. **Processing Delay (d_proc)**: Router processing time
2. **Queuing Delay (d_queue)**: Waiting in output queue
3. **Transmission Delay (d_trans)**: Time to push packet onto link
   - Formula: d_trans = L/R (L = packet length, R = transmission rate)
4. **Propagation Delay (d_prop)**: Time for signal to travel
   - Formula: d_prop = d/s (d = distance, s = propagation speed)

**Total Nodal Delay:**
```
d_nodal = d_proc + d_queue + d_trans + d_prop
```

**Throughput:**
- **Instantaneous**: Rate at a given instant
- **Average**: Long-term average rate
- **Bottleneck Link**: Link with minimum transmission rate

**Traffic Intensity:**
- Formula: La/R (L = avg packet length, a = avg arrival rate, R = transmission rate)
- If La/R > 1: Queues grow without bound
- If La/R ≈ 1: Large delays
- If La/R << 1: Small delays

---

## Unit 2: Application Layer

### 2.1 Principles of Network Applications

**Application Architectures:**

1. **Client-Server Model**:
   - Server: Always-on, permanent IP address
   - Clients: Communicate with server, may be intermittently connected

2. **Peer-to-Peer (P2P)**:
   - Minimal/no dedicated servers
   - End systems communicate directly
   - Self-scalability

**Transport Services:**
- **Reliable Data Transfer**: TCP provides, UDP does not
- **Throughput**: Minimum guaranteed vs best-effort
- **Timing**: Low-delay guarantees
- **Security**: Encryption, authentication

### 2.2 Web and HTTP

**HTTP (HyperText Transfer Protocol):**
- **Stateless**: Server maintains no client state
- **TCP-based**: Uses reliable transport
- **Methods**: GET, POST, HEAD, PUT, DELETE

**HTTP Connections:**
- **Non-persistent**: Separate TCP connection for each object
- **Persistent**: Multiple objects over single TCP connection
  - Without pipelining: Wait for response before next request
  - With pipelining: Send requests back-to-back

**Response Codes:**
- 200 OK: Request succeeded
- 301 Moved Permanently: Object moved
- 400 Bad Request: Request not understood
- 404 Not Found: Requested document not found
- 505 HTTP Version Not Supported

**Web Caching:**
- **Proxy Server**: Acts as intermediary
- **Benefits**: Reduced response time, reduced traffic
- **Conditional GET**: If-Modified-Since header

### 2.3 Electronic Mail

**Email System Components:**
- **User Agents**: Mail readers (Outlook, Gmail)
- **Mail Servers**: Store and forward messages
- **SMTP**: Simple Mail Transfer Protocol

**Email Protocols:**

| Protocol | Purpose | Port | Characteristics |
|----------|---------|------|-----------------|
| **SMTP** | Sending mail | 25 | Push protocol, ASCII-based |
| **POP3** | Retrieving mail | 110 | Download-and-delete |
| **IMAP** | Retrieving mail | 143 | Server-side storage |

**SMTP Process:**
1. Client establishes TCP connection to server port 25
2. Client sends commands, server responds with status codes
3. Transfer message using DATA command
4. Close connection

### 2.4 Domain Name System (DNS)

**DNS Functions:**
- **Hostname-to-IP translation**
- **Host aliasing** (canonical vs alias names)
- **Mail server aliasing**
- **Load distribution** (replicated web servers)

**DNS Hierarchy:**
- **Root DNS Servers**: Top level (13 logical servers worldwide)
- **TLD DNS Servers**: .com, .org, .net, country codes
- **Authoritative DNS Servers**: Organization's own servers
- **Local DNS Server**: ISP's default name server

**DNS Record Types:**
- **A**: Hostname to IPv4 address
- **AAAA**: Hostname to IPv6 address
- **CNAME**: Alias to canonical hostname
- **MX**: Mail exchange server
- **NS**: Authoritative name server

**DNS Queries:**
- **Recursive**: DNS server queries on behalf of client
- **Iterative**: DNS server returns next server to query

### 2.5 P2P File Distribution

**Scalability Comparison:**

**Client-Server File Distribution:**
- Distribution time: D_cs ≥ max{NF/u_s, F/d_min}
- Grows linearly with N (number of clients)

**P2P File Distribution:**
- Distribution time: D_P2P ≥ max{F/u_s, F/d_min, NF/(u_s + Σu_i)}
- Self-scaling: upload capacity increases with peers

**BitTorrent Protocol:**
- **Torrent**: Group of peers sharing same file
- **Tracker**: Infrastructure node tracking participating peers
- **Chunks**: File divided into 256KB pieces
- **Tit-for-tat**: Trade pieces with neighbors

---

## Unit 3: Transport Layer

### 3.1 Transport Layer Principles

**Transport vs Network Layer:**
- **Network Layer**: Logical communication between hosts
- **Transport Layer**: Logical communication between processes

**Multiplexing/Demultiplexing:**
- **Multiplexing**: Gathering data from multiple sockets
- **Demultiplexing**: Delivering received segments to correct socket
- **Socket Identification**: (source IP, source port, dest IP, dest port)

### 3.2 UDP (User Datagram Protocol)

**UDP Characteristics:**
- **Connectionless**: No handshaking
- **Unreliable**: No delivery guarantee
- **No congestion control**: Sends at desired rate
- **Small header**: 8 bytes only

**UDP Header:**
- Source port (16 bits)
- Destination port (16 bits)
- Length (16 bits)
- Checksum (16 bits)

**UDP Checksum:**
- **Purpose**: Error detection
- **Calculation**: 1's complement of 1's complement sum
- **Receiver**: Adds all 16-bit words including checksum
  - No errors: Result = 1111111111111111
  - Errors detected: Result ≠ 1111111111111111

### 3.3 TCP (Transmission Control Protocol)

**TCP Characteristics:**
- **Connection-oriented**: Three-way handshake
- **Reliable**: Guarantees delivery
- **Flow control**: Receiver controls sender rate
- **Congestion control**: Network-aware rate control
- **Full-duplex**: Bidirectional data flow

**TCP Segment Structure:**
- **Header Length**: 20-60 bytes (options)
- **Sequence Number**: Byte stream number
- **Acknowledgment Number**: Next expected sequence number
- **Window Size**: Flow control (bytes)
- **Flags**: SYN, FIN, RST, PSH, URG, ACK

**TCP Reliable Data Transfer:**

1. **Sequence Numbers**: Byte-stream numbers
2. **Acknowledgments**: Cumulative ACKs
3. **Retransmission Timer**: Single timer for oldest unACKed segment
4. **Fast Retransmit**: 3 duplicate ACKs trigger immediate retransmission

**TCP Connection Management:**

**Three-Way Handshake (Connection Establishment):**
1. Client sends SYN segment
2. Server responds with SYN-ACK
3. Client sends ACK

**Connection Termination:**
1. Client sends FIN
2. Server sends ACK and FIN
3. Client sends ACK
4. Connection closed

### 3.4 TCP Congestion Control

**Congestion Control Principles:**
- **End-to-end**: TCP infers congestion from loss/delay
- **Network-assisted**: Routers provide feedback

**TCP Congestion Control Algorithm:**

**Slow Start:**
- cwnd starts at 1 MSS
- cwnd doubles each RTT until loss or threshold
- Exponential growth

**Congestion Avoidance:**
- cwnd increases by 1 MSS per RTT
- Linear growth (additive increase)

**Fast Recovery:**
- On 3 duplicate ACKs: cwnd = ssthresh + 3
- Multiplicative decrease on timeout

**TCP Tahoe vs Reno:**
- **Tahoe**: Always goes to slow start on loss
- **Reno**: Fast recovery on 3 duplicate ACKs

**Congestion Window Evolution:**
- **Sawtooth Pattern**: Linear increase, multiplicative decrease
- **Average Throughput**: ~0.75 × W/RTT (W = max window size)

---

## Unit 4: Network Layer - Data Plane

### 4.1 Network Layer Overview

**Network Layer Functions:**
- **Forwarding**: Move packets from input to output port
- **Routing**: Determine path from source to destination

**Data Plane vs Control Plane:**
- **Data Plane**: Per-router forwarding function
- **Control Plane**: Network-wide routing logic

### 4.2 Router Architecture

**Router Components:**
- **Input Ports**: Physical layer, link layer, lookup/forwarding
- **Switching Fabric**: Transfer packets from input to output
- **Output Ports**: Store and forward packets
- **Routing Processor**: Control plane functions

**Input Port Processing:**
- **Line Termination**: Physical layer
- **Link Layer Protocol**: Data link layer
- **Lookup/Forwarding**: Destination-based forwarding

**Switching Fabric Types:**
- **Memory**: Via system bus (slowest)
- **Bus**: Via shared bus
- **Crossbar**: Interconnection network (fastest)

**Output Port Processing:**
- **Queuing**: When arrival rate > transmission rate
- **Packet Scheduler**: FIFO, priority, weighted fair queuing

### 4.3 Internet Protocol (IP)

**IPv4 Header Format:**
- **Version** (4 bits): IP version
- **Header Length** (4 bits): 32-bit words
- **Type of Service** (8 bits): Priority, delay, throughput
- **Total Length** (16 bits): Header + data
- **Identification** (16 bits): Fragmentation
- **Flags** (3 bits): Don't fragment, more fragments
- **Fragment Offset** (13 bits): Fragment position
- **Time to Live** (8 bits): Max hops
- **Protocol** (8 bits): Upper layer protocol
- **Header Checksum** (16 bits): Error detection
- **Source Address** (32 bits): Sender IP
- **Destination Address** (32 bits): Receiver IP

**IPv4 Addressing:**

**Classful Addressing (Historical):**
- **Class A**: 1.0.0.0 to 126.0.0.0 (/8)
- **Class B**: 128.0.0.0 to 191.255.0.0 (/16)  
- **Class C**: 192.0.0.0 to 223.255.255.0 (/24)

**CIDR (Classless Inter-Domain Routing):**
- **Format**: a.b.c.d/x (x = number of network bits)
- **Subnet Mask**: Network portion identification
- **Longest Prefix Matching**: Most specific route wins

**Subnetting Example:**
- Network: 192.168.1.0/24
- Subnet 1: 192.168.1.0/26 (hosts .1-.62)
- Subnet 2: 192.168.1.64/26 (hosts .65-.126)
- Subnet 3: 192.168.1.128/26 (hosts .129-.190)
- Subnet 4: 192.168.1.192/26 (hosts .193-.254)

**Special IP Addresses:**
- **Loopback**: 127.0.0.0/8
- **Private**: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16
- **Link-Local**: 169.254.0.0/16
- **Multicast**: 224.0.0.0/4
- **Broadcast**: 255.255.255.255

**NAT (Network Address Translation):**
- **Purpose**: Share single IP among multiple hosts
- **NAT Table**: (internal IP, port) ↔ (external IP, port)
- **Problems**: Violates end-to-end principle, complicates P2P

### 4.4 IPv6

**IPv6 Motivation:**
- **Address Space**: 128-bit addresses (vs 32-bit IPv4)
- **Header Simplification**: Fixed 40-byte header
- **Flow Labeling**: Quality of service
- **Built-in Security**: IPSec integration

**IPv6 Header:**
- **Version** (4 bits): IP version (6)
- **Traffic Class** (8 bits): QoS
- **Flow Label** (20 bits): Flow identification
- **Payload Length** (16 bits): Data length
- **Next Header** (8 bits): Protocol type
- **Hop Limit** (8 bits): TTL equivalent
- **Source Address** (128 bits)
- **Destination Address** (128 bits)

**IPv6 Address Types:**
- **Unicast**: Single interface
- **Multicast**: Group of interfaces
- **Anycast**: Nearest of group

**IPv4 to IPv6 Transition:**
- **Dual Stack**: Run both protocols
- **Tunneling**: Encapsulate IPv6 in IPv4
- **Translation**: Convert between protocols

### 4.5 Generalized Forwarding (SDN)

**Traditional Forwarding:**
- **Destination-based**: Forward based on destination IP
- **Fixed Function**: Hardware-based lookup

**Generalized Forwarding:**
- **Flow-based**: Forward based on header fields
- **Programmable**: Software-defined rules

**OpenFlow Protocol:**
- **Flow Table**: Match + Action + Stats
- **Match Fields**: 12-tuple (IPs, ports, protocol, etc.)
- **Actions**: Forward, drop, modify, send to controller
- **Controller**: Centralized control plane

**SDN Benefits:**
- **Centralized Control**: Global network view
- **Programmability**: Custom forwarding logic
- **Separation**: Control plane from data plane
- **Innovation**: Rapid protocol development

---

## Unit 5: Network Layer - Control Plane

### 5.1 Routing Algorithms

**Graph Abstraction:**
- **Nodes**: Routers
- **Edges**: Physical links
- **Edge Costs**: Delay, congestion, monetary cost

**Routing Algorithm Classification:**
- **Global vs Decentralized**: Complete topology knowledge
- **Static vs Dynamic**: Route changes over time
- **Load-sensitive vs Load-insensitive**: Cost reflects traffic load

### 5.2 Link State Routing (Dijkstra's Algorithm)

**Algorithm Steps:**
1. **Initialization**: Distance to source = 0, others = ∞
2. **Find minimum**: Select unvisited node with minimum distance
3. **Update neighbors**: Relax edge weights
4. **Repeat**: Until all nodes visited

**Dijkstra's Complexity:**
- **Time**: O(n²) with simple implementation, O(n log n) with heap
- **Space**: O(n) for distance and predecessor arrays

**Link State Protocol Features:**
- **Flooding**: Broadcast link state to all routers
- **LSDB**: Link State Database at each router
- **SPF**: Shortest Path First calculation
- **Convergence**: Fast when topology changes

### 5.3 Distance Vector Routing

**Bellman-Ford Equation:**
- d_x(y) = min_v{c(x,v) + d_v(y)}
- Distance from x to y = minimum over neighbors v

**Distance Vector Algorithm:**
1. **Initialize**: Distance vector at each node
2. **Periodic Updates**: Send DV to neighbors
3. **Update**: Recalculate using Bellman-Ford
4. **Notify**: Send updates if changes occur

**Problems:**
- **Count-to-Infinity**: Bad news travels slowly
- **Routing Loops**: Temporary loops during convergence
- **Solution**: Split horizon, poison reverse

### 5.4 OSPF (Open Shortest Path First)

**OSPF Characteristics:**
- **Link State Protocol**: Uses Dijkstra's algorithm
- **Area Concept**: Hierarchical routing
- **Authentication**: Secure routing updates
- **Load Balancing**: Multiple equal-cost paths

**OSPF Areas:**
- **Backbone Area**: Area 0, connects all other areas
- **Regular Areas**: Connected to backbone
- **Stub Areas**: No external routes
- **NSSA**: Not-So-Stubby Areas

**LSA Types:**
- **Type 1**: Router LSA
- **Type 2**: Network LSA
- **Type 3**: Summary LSA
- **Type 4**: ASBR Summary LSA
- **Type 5**: External LSA

### 5.5 BGP (Border Gateway Protocol)

**BGP Purpose:**
- **Inter-domain Routing**: Between autonomous systems
- **Policy-based**: Economic and political considerations
- **Path Vector Protocol**: Maintains entire AS path

**BGP Attributes:**
- **AS-PATH**: Sequence of ASs through which route passed
- **NEXT-HOP**: IP address of next-hop router
- **LOCAL-PREF**: Degree of preference (higher = better)
- **MED**: Multi-Exit Discriminator (lower = better)

**BGP Route Selection:**
1. **Highest LOCAL-PREF**
2. **Shortest AS-PATH**
3. **Closest NEXT-HOP** (hot potato routing)
4. **Additional tie-breakers**

**BGP Loop Prevention:**
- **AS-PATH Attribute**: Contains list of ASs
- **Loop Detection**: Reject routes containing own AS number

**BGP Policy Examples:**
- **Customer-Provider**: Provider advertises customer routes
- **Peer-Peer**: Peers exchange customer routes
- **Valley-Free**: No provider pays another provider

### 5.6 SDN Control Plane

**SDN Architecture:**
- **Data Plane**: Network switches
- **Control Plane**: SDN controller
- **Management Plane**: Network operating system

**OpenFlow Protocol:**
- **Southbound API**: Controller to switch
- **Flow Tables**: Match-action rules
- **Reactive vs Proactive**: On-demand vs pre-installed rules

**SDN Controller Functions:**
- **Topology Discovery**: Learn network topology
- **Routing Calculations**: Compute paths
- **Flow Installation**: Program switch flow tables
- **Load Balancing**: Distribute traffic

**Benefits:**
- **Centralized Control**: Global optimization
- **Programmability**: Custom applications
- **Vendor Independence**: Open standards

### 5.7 Network Management

**SNMP (Simple Network Management Protocol):**
- **Manager**: Monitoring system
- **Agent**: Managed device
- **MIB**: Management Information Base
- **Operations**: GET, SET, TRAP

**SNMP Messages:**
- **GetRequest**: Retrieve variable value
- **SetRequest**: Set variable value
- **GetResponse**: Response to Get/Set
- **Trap**: Asynchronous notification

**Why UDP for SNMP:**
- **Simplicity**: Minimal overhead
- **Reliability**: Application-level retransmission
- **Efficiency**: Small message sizes
- **Availability**: Works during network problems

---

## Unit 6: Link Layer and LANs

### 6.1 Link Layer Introduction

**Link Layer Services:**
- **Framing**: Encapsulate network layer packets
- **Link Access**: Coordinate access to shared medium
- **Reliable Delivery**: Error detection and correction
- **Flow Control**: Pace between sender and receiver
- **Error Detection**: Detect bit errors in frames
- **Error Correction**: Correct bit errors
- **Half-duplex/Full-duplex**: Bidirectional communication

**Where is Link Layer Implemented:**
- **Network Interface Card (NIC)**: Hardware + software
- **Network Adapter**: Ethernet card, Wi-Fi card

### 6.2 Error Detection and Correction

**Error Types:**
- **Single Bit Error**: One bit flipped
- **Burst Error**: Multiple consecutive bits flipped

**Detection vs Correction:**
- **Detection**: Identify presence of errors
- **Correction**: Fix errors without retransmission

### Parity Checking

**Single Bit Parity:**
- **Even Parity**: Even number of 1s (including parity bit)
- **Odd Parity**: Odd number of 1s (including parity bit)
- **Detection**: Single bit errors only

**Two-Dimensional Parity:**
- **Row and Column Parity**: Arrange bits in matrix
- **Detection**: Single bit errors
- **Correction**: Single bit errors (locate intersection)

### Checksums

**1's Complement Checksum:**
1. **Sum**: Add all 16-bit words
2. **Wraparound**: Add carry to result
3. **Complement**: Flip all bits
4. **Check**: Add all words + checksum = all 1s

**Internet Checksum Algorithm:**
- Used in IP, TCP, UDP headers
- Relatively weak error detection
- Fast computation in software

### Cyclic Redundancy Check (CRC)

**CRC Process:**
1. **Generator**: Agreed upon r+1 bit pattern G
2. **Remainder**: R = remainder of (D×2^r) ÷ G
3. **Transmitted**: D concatenated with R
4. **Check**: (D||R) divisible by G

**CRC Properties:**
- **Detection**: All single bit errors
- **Detection**: All double bit errors  
- **Detection**: Odd number of bit errors (if G has factor (x+1))
- **Detection**: All burst errors of length ≤ r

**Common CRC Standards:**
- **CRC-8**: 8-bit remainder
- **CRC-16**: 16-bit remainder  
- **CRC-32**: 32-bit remainder (Ethernet, Wi-Fi)

### 6.3 Multiple Access Protocols

**Multiple Access Problem:**
- **Shared Medium**: Single broadcast channel
- **Collision**: Two or more simultaneous transmissions
- **Goal**: Coordinate access to avoid/handle collisions

**Protocol Categories:**
1. **Channel Partitioning**: Divide channel
2. **Random Access**: Allow collisions, recover
3. **Taking Turns**: Pass token or poll

### Channel Partitioning Protocols

**TDMA (Time Division Multiple Access):**
- **Time Slots**: Each node gets fixed time slot
- **Advantages**: No collisions, fair
- **Disadvantages**: Unused slots wasted

**FDMA (Frequency Division Multiple Access):**
- **Frequency Bands**: Each node gets frequency band
- **Advantages**: No collisions
- **Disadvantages**: Limited frequency spectrum

**CDMA (Code Division Multiple Access):**
- **Unique Codes**: Each sender assigned unique code
- **Advantages**: Simultaneous transmission
- **Applications**: Cellular networks

### Random Access Protocols

**ALOHA:**
- **Pure ALOHA**: Transmit immediately
  - **Efficiency**: 18.4% maximum
- **Slotted ALOHA**: Synchronize to time slots
  - **Efficiency**: 36.8% maximum

**CSMA (Carrier Sense Multiple Access):**
- **Listen Before Talk**: Sense channel before transmit
- **Collisions Still Possible**: Propagation delay
- **1-Persistent**: Always transmit when idle
- **p-Persistent**: Transmit with probability p

**CSMA/CD (Collision Detection):**
- **Listen While Talk**: Detect collisions during transmission
- **Jam Signal**: Alert other stations of collision
- **Binary Exponential Backoff**: Exponentially increase backoff time
- **Minimum Frame Size**: Ensure collision detection

**CSMA/CD Algorithm:**
1. **Sense**: Is channel idle?
2. **Transmit**: If idle, start transmission
3. **Collision Detection**: Monitor for collisions
4. **Jam**: If collision, send jam signal
5. **Backoff**: Wait random time, go to step 1

**CSMA/CA (Collision Avoidance):**
- **Used in Wi-Fi**: Can't detect collisions reliably
- **RTS/CTS**: Request to Send / Clear to Send
- **ACK**: Explicit acknowledgments
- **Backoff**: Random backoff before each transmission

### 6.4 Ethernet

**Ethernet Evolution:**

| Standard | Year | Speed | Cable | Max Distance |
|----------|------|-------|-------|--------------|
| **10BASE-T** | 1990 | 10 Mbps | UTP Cat3 | 100m |
| **100BASE-TX** | 1995 | 100 Mbps | UTP Cat5 | 100m |
| **1000BASE-T** | 1999 | 1 Gbps | UTP Cat5e | 100m |
| **10GBASE-T** | 2006 | 10 Gbps | UTP Cat6a | 100m |

**Ethernet Frame Format:**
- **Preamble** (8 bytes): Synchronization (10101010...)
- **Destination Address** (6 bytes): MAC address
- **Source Address** (6 bytes): MAC address  
- **Type** (2 bytes): Higher layer protocol
- **Data** (46-1500 bytes): Payload
- **CRC** (4 bytes): Error detection

**MAC Addresses:**
- **48-bit**: Unique identifier (e.g., 1A-2F-BB-76-09-AD)
- **OUI**: Organizationally Unique Identifier (first 24 bits)
- **NIC**: Network Interface Card specific (last 24 bits)
- **Broadcast**: FF-FF-FF-FF-FF-FF
- **Multicast**: First bit = 1

### 6.5 Link Layer Switches

**Switch Functions:**
- **Learning**: Build MAC address table
- **Flooding**: Forward to all ports if unknown destination
- **Filtering**: Drop frames destined for same segment
- **Forwarding**: Send to specific port

**Switch Learning Algorithm:**
1. **Record**: Source MAC and input port
2. **Age**: Remove old entries
3. **Lookup**: Check destination in table
4. **Forward**: Send to appropriate port or flood

**Spanning Tree Protocol (STP):**
- **Purpose**: Prevent loops in switched networks
- **Root Bridge**: Elected based on lowest bridge ID
- **Port States**: Blocking, listening, learning, forwarding
- **BPDU**: Bridge Protocol Data Units

**VLANs (Virtual LANs):**
- **Purpose**: Logically separate broadcast domains
- **Trunk Links**: Carry multiple VLAN traffic
- **802.1Q**: VLAN tagging standard
- **Benefits**: Security, traffic management, flexibility

---

## Unit 7: Wireless and Mobile Networks

### 7.1 Wireless Networking Fundamentals

**Wireless Challenges:**
- **Signal Strength**: Decreases with distance
- **Interference**: Other sources in same frequency
- **Multipath Propagation**: Signal reflection/scattering
- **Hidden Terminal**: Can't detect all collisions

**Wireless Network Elements:**
- **Wireless Hosts**: Laptops, smartphones
- **Base Station**: Access point, cell tower
- **Wireless Link**: Radio spectrum connection

### 7.2 Wi-Fi (802.11 Wireless LANs)

**802.11 Architecture:**
- **BSS (Basic Service Set)**: Wireless hosts + AP
- **ESS (Extended Service Set)**: Multiple interconnected BSSs
- **Ad Hoc Network**: No access point

**802.11 Standards:**

| Standard | Year | Frequency | Max Speed | Range |
|----------|------|-----------|-----------|-------|
| **802.11a** | 1999 | 5 GHz | 54 Mbps | ~35m |
| **802.11b** | 1999 | 2.4 GHz | 11 Mbps | ~100m |
| **802.11g** | 2003 | 2.4 GHz | 54 Mbps | ~100m |
| **802.11n** | 2009 | 2.4/5 GHz | 600 Mbps | ~70m |
| **802.11ac** | 2013 | 5 GHz | 6.93 Gbps | ~35m |
| **802.11ax** | 2019 | 2.4/5/6 GHz | 9.6 Gbps | ~35m |

**802.11 Frame Structure:**
- **Frame Control** (2 bytes): Frame type, flags
- **Duration** (2 bytes): Time to transmit frame
- **Address Fields**: Up to 4 MAC addresses
- **Sequence Control** (2 bytes): Fragment/sequence numbers
- **Data**: Payload (0-2312 bytes)
- **CRC** (4 bytes): Error detection

**802.11 MAC Protocol (CSMA/CA):**
1. **DIFS**: Distributed Inter-Frame Space wait
2. **Random Backoff**: If channel busy
3. **Transmission**: Send frame
4. **SIFS**: Short Inter-Frame Space
5. **ACK**: Acknowledgment frame

**RTS/CTS Protocol:**
- **Purpose**: Solve hidden terminal problem
- **RTS**: Request to Send (small frame)
- **CTS**: Clear to Send (broadcast response)
- **Collision Avoidance**: Reserves channel

**802.11 Power Management:**
- **Sleep Mode**: Node can sleep
- **Beacon Frames**: AP announces sleeping nodes
- **TIM**: Traffic Indication Map

### 7.3 Cellular Networks

**Cellular Concept:**
- **Cell**: Geographic area served by base station
- **Frequency Reuse**: Same frequencies in distant cells
- **Handoff**: Transfer between cells
- **Roaming**: Service outside home network

**1G Networks:**
- **Technology**: Analog, FDMA
- **Service**: Voice only
- **Example**: AMPS (Advanced Mobile Phone System)

**2G Networks:**
- **Technology**: Digital, TDMA/CDMA
- **Services**: Voice, SMS, low-speed data
- **Examples**: GSM, IS-95 CDMA

**3G Networks:**
- **Technology**: CDMA-based
- **Services**: Voice, data up to 2 Mbps
- **Examples**: UMTS/WCDMA, CDMA2000

**4G/LTE Networks:**
- **Technology**: OFDMA, all-IP
- **Services**: High-speed data (100+ Mbps)
- **Architecture**: Evolved Packet Core (EPC)

**5G Networks:**
- **Technology**: Massive MIMO, mmWave
- **Services**: Ultra-low latency, IoT, enhanced mobile broadband
- **Speeds**: Up to 20 Gbps

### 7.4 Mobility Management

**Mobility Challenges:**
- **Addressing**: How to find mobile user?
- **Routing**: How to route to mobile user?
- **Handoff**: Seamless connectivity during movement

**Mobile IP (IPv4):**
- **Home Network**: Permanent network
- **Foreign Network**: Visited network  
- **Home Agent**: Router in home network
- **Foreign Agent**: Router in foreign network
- **Care-of-Address**: Temporary address in foreign network

**Mobile IP Process:**
1. **Registration**: Mobile node registers with foreign agent
2. **Tunneling**: Home agent tunnels packets to care-of-address
3. **Delivery**: Foreign agent delivers to mobile node
4. **Reverse**: Direct routing or via home agent

**GSM Mobility Management:**
- **HLR (Home Location Register)**: User's home database
- **VLR (Visitor Location Register)**: Current location database
- **MSC (Mobile Switching Center)**: Call switching
- **Authentication**: Challenge-response with shared secret

---

## Key Formulas and Calculations

### Delay Calculations

**Transmission Delay:**
```
d_trans = L / R
where: L = packet length (bits), R = transmission rate (bps)
```

**Propagation Delay:**
```
d_prop = d / s  
where: d = distance (m), s = propagation speed (m/s)
```

**Total Delay:**
```
d_total = d_proc + d_queue + d_trans + d_prop
```

**Round-Trip Time (RTT):**
```
RTT = 2 × d_prop (assuming negligible other delays)
```

### Throughput Calculations

**Throughput:**
```
Throughput = min(R1, R2, ..., Rn) for bottleneck link
```

**File Transfer Time:**
```
Transfer Time = File Size / Throughput
```

### Queuing Theory

**Traffic Intensity:**
```
ρ = λa / μ = La / R
where: λ = arrival rate, a = avg packet size, μ = service rate, R = link capacity
```

**Average Queue Length (M/M/1):**
```
L = ρ / (1 - ρ)
```

**Average Waiting Time (M/M/1):**
```
W = ρ / (μ(1 - ρ))
```

### TCP Congestion Control

**TCP Throughput Approximation:**
```
Throughput ≈ (3/4) × (MSS / RTT) × (1 / √p)
where: MSS = maximum segment size, p = loss probability
```

**TCP Sawtooth Average:**
```
Average Window = (3/4) × W_max
where: W_max = maximum window size before loss
```

### Subnet Calculations

**Number of Subnets:**
```
Number of Subnets = 2^n
where: n = number of borrowed bits
```

**Number of Hosts per Subnet:**
```
Hosts per Subnet = 2^h - 2
where: h = number of host bits, -2 for network and broadcast
```

**Subnet Address Range:**
```
Network Address = IP & Subnet Mask
Broadcast Address = Network Address | (~Subnet Mask)
First Host = Network Address + 1
Last Host = Broadcast Address - 1
```

### Error Detection

**1's Complement Checksum:**
1. Sum all 16-bit words
2. Add carry to result
3. Take 1's complement
4. Append to data

**CRC Polynomial Division:**
```
Transmitted = Data || CRC
where: CRC = remainder of (Data × 2^r) ÷ Generator
```

### Wireless Calculations

**Path Loss (Free Space):**
```
Path Loss (dB) = 20 log10(d) + 20 log10(f) + 32.44
where: d = distance (km), f = frequency (MHz)
```

**Signal-to-Noise Ratio:**
```
SNR (dB) = 10 log10(Signal Power / Noise Power)
```

**Shannon Capacity:**
```
C = B log2(1 + SNR)
where: C = capacity (bps), B = bandwidth (Hz)
```

---

## Protocol Comparison Tables

### Transport Protocols

| Feature | TCP | UDP |
|---------|-----|-----|
| **Connection** | Connection-oriented | Connectionless |
| **Reliability** | Reliable, ordered delivery | Unreliable, no ordering |
| **Flow Control** | Yes (sliding window) | No |
| **Congestion Control** | Yes | No |
| **Header Size** | 20-60 bytes | 8 bytes |
| **Speed** | Slower (overhead) | Faster (minimal overhead) |
| **Applications** | HTTP, FTP, SMTP, SSH | DNS, DHCP, streaming, games |

### Routing Protocols

| Aspect | Link State (OSPF) | Distance Vector (RIP) | Path Vector (BGP) |
|--------|-------------------|----------------------|------------------|
| **Algorithm** | Dijkstra's | Bellman-Ford | Path vector |
| **Convergence** | Fast | Slow | Slow |
| **Scalability** | Good (areas) | Poor | Excellent |
| **Loop Prevention** | SPF tree | Split horizon | AS-PATH |
| **Metric** | Cost | Hop count | Policy-based |
| **Updates** | Event-triggered | Periodic | Incremental |

### Ethernet Standards

| Standard | Speed | Cable | Distance | Collision Domain |
|----------|-------|-------|-----------|-----------------|
| **10BASE-T** | 10 Mbps | Cat3 UTP | 100m | Per segment |
| **100BASE-TX** | 100 Mbps | Cat5 UTP | 100m | Per segment |
| **1000BASE-T** | 1 Gbps | Cat5e UTP | 100m | Per link |
| **10GBASE-T** | 10 Gbps | Cat6a UTP | 100m | Per link |

### Wi-Fi Standards

| Standard | Frequency | Max Speed | Range | MIMO |
|----------|-----------|-----------|-------|------|
| **802.11n** | 2.4/5 GHz | 600 Mbps | 70m | 4×4 |
| **802.11ac** | 5 GHz | 6.93 Gbps | 35m | 8×8 |
| **802.11ax** | 2.4/5/6 GHz | 9.6 Gbps | 35m | 8×8 |

### Multiple Access Protocols

| Protocol | Efficiency | Delay | Complexity | Use Case |
|----------|------------|-------|------------|----------|
| **TDMA** | High | Low | Medium | Cellular |
| **FDMA** | High | Low | Medium | Radio |
| **CSMA/CD** | Medium | Variable | Low | Ethernet |
| **CSMA/CA** | Low | High | Medium | Wi-Fi |

---

## Common Exam Topics

### Calculation Problems

1. **Delay and Throughput**
   - Calculate transmission, propagation, and total delay
   - Determine bottleneck links and end-to-end throughput
   - File transfer time calculations

2. **Subnet Design**
   - CIDR notation and subnet masks
   - Number of subnets and hosts
   - IP address ranges and broadcast addresses

3. **TCP Performance**
   - Congestion window evolution
   - Throughput estimation
   - Connection establishment time

4. **Checksum Calculations**
   - 1's complement arithmetic
   - Error detection probability
   - Two-dimensional parity

5. **Routing Algorithm Execution**
   - Dijkstra's shortest path
   - Distance vector updates
   - BGP path selection

### Conceptual Questions

1. **Protocol Comparison**
   - TCP vs UDP characteristics
   - Circuit vs packet switching
   - Link state vs distance vector routing

2. **Network Architecture**
   - OSI vs Internet protocol stack
   - Client-server vs P2P applications
   - SDN vs traditional networking

3. **Error Control**
   - Detection vs correction
   - ARQ protocols (Stop-and-wait, Go-back-N, Selective Repeat)
   - Forward error correction

4. **Multiple Access**
   - Hidden and exposed terminal problems
   - CSMA/CD vs CSMA/CA
   - Random access vs controlled access

5. **Wireless Networking**
   - Wi-Fi architecture and protocols
   - Cellular network evolution
   - Mobility management

### Design Problems

1. **Network Topology Design**
   - Subnet planning and addressing
   - Router placement and configuration
   - QoS and traffic engineering

2. **Protocol Selection**
   - Application requirements analysis
   - Transport protocol choice
   - Routing protocol selection

3. **Performance Optimization**
   - Bottleneck identification
   - Capacity planning
   - Load balancing strategies

### Security Considerations

1. **Network Attacks**
   - DoS and DDoS attacks
   - Man-in-the-middle attacks
   - Packet sniffing and spoofing

2. **Security Mechanisms**
   - Encryption and authentication
   - Firewalls and intrusion detection
   - VPNs and secure tunneling

---

## Final Exam Preparation Tips

### Study Strategy

1. **Review assignments** - Your completed assignments cover key exam topics
2. **Practice calculations** - Master delay, throughput, and subnetting problems
3. **Understand protocols** - Know when and why different protocols are used
4. **Create comparison tables** - Organize similar technologies and protocols
5. **Draw diagrams** - Visualize network architectures and protocol operations

### Key Areas to Focus

1. **Fundamentals** (Unit 1): Delay calculations, throughput, switching
2. **Application Layer** (Unit 2): HTTP, DNS, P2P file sharing
3. **Transport Layer** (Unit 3): TCP reliability and congestion control
4. **Network Layer** (Units 4-5): IP addressing, routing algorithms
5. **Link Layer** (Unit 6): Error detection, Ethernet, switching
6. **Wireless** (Unit 7): Wi-Fi protocols, cellular networks

### Problem-Solving Approach

1. **Read carefully** - Identify what's given and what's asked
2. **Draw diagrams** - Visualize the network or protocol operation
3. **Show work** - Step-by-step calculations with units
4. **Check answers** - Verify reasonableness and units
5. **Explain reasoning** - Justify protocol choices and design decisions

**Good luck with your final exam!**