graph TB
    subgraph "Before OSI Model"
        A[IBM Computer] --> B[IBM Computer]
        C[DEC Computer] --> D[DEC Computer]
        E[HP Computer] --> F[HP Computer]
        A -.-> Incompatible1[Incompatible]
        C -.-> Incompatible2[Incompatible]
    end

    subgraph "After OSI Model"
        G[Any Computer] --> H[OSI Standard]
        J[Any Computer] --> H
        K[Any Computer] --> H
        H --> I[Any Computer]
    end

graph TD
    subgraph "OSI Model Stack"
        L7[Layer 7: ApplicationHTTP, FTP, SMTP, DNS]
        L6[Layer 6: PresentationEncryption, Compression, Translation]
        L5[Layer 5: SessionSession Management, Dialog Control]
        L4[Layer 4: TransportTCP, UDP, Ports]
        L3[Layer 3: NetworkIP, Routing, ICMP]
        L2[Layer 2: Data LinkEthernet, MAC Addresses, Switches]
        L1[Layer 1: PhysicalCables, Signals, Hubs]
    end

    L7 --> L6 --> L5 --> L4 --> L3 --> L2 --> L1

sequenceDiagram
    participant You as You (Application)
    participant Language as Language Service (Presentation)
    participant PostOffice as Post Office (Session)
    participant Delivery as Delivery Service (Transport)
    participant GPS as GPS/Routing (Network)
    participant Truck as Mail Truck (Data Link)
    participant Road as Physical Road (Physical)

    You->>Language: Write letter in English
    Language->>PostOffice: Translate if needed
    PostOffice->>Delivery: Start delivery session
    Delivery->>GPS: Plan route
    GPS->>Truck: Load in mail truck
    Truck->>Road: Drive on physical roads

    Note over Road: Letter travels through physical infrastructure

    Road->>Truck: Arrives at destination
    Truck->>GPS: Route completed
    GPS->>Delivery: Delivery confirmed
    Delivery->>PostOffice: Session ended
    PostOffice->>Language: Process for recipient
    Language->>You: Letter delivered

graph LR
    subgraph "Sender Side - Encapsulation"
        Data[Original Data]
        AppData[App Header + Data]
        PresData[Pres Header + App Header + Data]
        SessData[Sess Header + Pres Header + App Header + Data]
        TransData[Trans Header + Sess Header + Pres Header + App Header + Data]
        NetData[Net Header + Trans Header + Sess Header + Pres Header + App Header + Data]
        DataData[Data Header + Net Header + Trans Header + Sess Header + Pres Header + App Header + Data]
        PhysData[Physical Signals]
    end

    Data --> AppData --> PresData --> SessData --> TransData --> NetData --> DataData --> PhysData

sequenceDiagram
    participant S7 as Sender App (L7)
    participant S6 as Sender Pres (L6)
    participant S5 as Sender Sess (L5)
    participant S4 as Sender Trans (L4)
    participant S3 as Sender Net (L3)
    participant S2 as Sender Data (L2)
    participant S1 as Sender Phys (L1)
    participant Medium as Physical Medium
    participant R1 as Receiver Phys (L1)
    participant R2 as Receiver Data (L2)
    participant R3 as Receiver Net (L3)
    participant R4 as Receiver Trans (L4)
    participant R5 as Receiver Sess (L5)
    participant R6 as Receiver Pres (L6)
    participant R7 as Receiver App (L7)

    Note over S7, R7: Logical peer-to-peer communication
    S7-->>R7: Application data
    S6-->>R6: Presentation formatting
    S5-->>R5: Session management
    S4-->>R4: Transport reliability
    S3-->>R3: Network routing
    S2-->>R2: Data link framing

    Note over S1, R1: Physical transmission
    S7->>S6: Data
    S6->>S5: Formatted data
    S5->>S4: Session data
    S4->>S3: Segments
    S3->>S2: Packets
    S2->>S1: Frames
    S1->>Medium: Bits
    Medium->>R1: Bits
    R1->>R2: Frames
    R2->>R3: Packets
    R3->>R4: Segments
    R4->>R5: Session data
    R5->>R6: Formatted data
    R6->>R7: Data

graph TB
    subgraph "Application Examples"
        Email[Email Client]
        Web[Web Browser]
        FTP[FTP Client]
    end

    subgraph "OSI Layers"
        subgraph "Upper Layers (Host-to-Host)"
            L7[Layer 7: Application<br/>Network processes to applications]
            L6[Layer 6: Presentation<br/>Data representation & encryption]
            L5[Layer 5: Session<br/>Host-to-host communication]
        end

        subgraph "Transport Layer"
            L4[Layer 4: Transport<br/>End-to-end connections & reliability]
        end

        subgraph "Lower Layers (Point-to-Point)"
            L3[Layer 3: Network<br/>Path determination & logical addressing]
            L2[Layer 2: Data Link<br/>Physical addressing & error detection]
            L1[Layer 1: Physical<br/>Media, signal & binary transmission]
        end
    end

    subgraph "Physical Media"
        Cable[Ethernet Cable]
        WiFi[WiFi Radio]
        Fiber[Fiber Optic]
    end

    Email --> L7
    Web --> L7
    FTP --> L7
    L7 --> L6 --> L5 --> L4 --> L3 --> L2 --> L1
    L1 --> Cable
    L1 --> WiFi
    L1 --> Fiber

sequenceDiagram
    autonumber
    participant User
    participant L7 as Layer 7<br/>Application
    participant L6 as Layer 6<br/>Presentation
    participant L5 as Layer 5<br/>Session
    participant L4 as Layer 4<br/>Transport
    participant L3 as Layer 3<br/>Network
    participant L2 as Layer 2<br/>Data Link
    participant L1 as Layer 1<br/>Physical
    participant Network

    User->>L7: Compose email
    Note over L7: SMTP protocol
    L7->>L6: Email message
    Note over L6: ASCII encoding, TLS encryption
    L6->>L5: Encrypted message
    Note over L5: Establish session with mail server
    L5->>L4: Session data
    Note over L4: TCP segment with port 587
    L4->>L3: TCP segment
    Note over L3: IP packet with destination address
    L3->>L2: IP packet
    Note over L2: Ethernet frame with MAC addresses
    L2->>L1: Ethernet frame
    Note over L1: Electrical signals on cable
    L1->>Network: Digital bits

    Network-->>L1: Response bits
    L1-->>L2: Electrical signals converted
    L2-->>L3: Frame processed, packet extracted
    L3-->>L4: Packet processed, segment extracted
    L4-->>L5: Segment processed, acknowledgment
    L5-->>L6: Session confirmed
    L6-->>L7: Decrypted confirmation
    L7-->>User: Email sent successfully

mindmap
  root)OSI Model(
    Physical
      ::icon(fa fa-plug)
      Cables
      Signals
      Voltage
      Connectors
    DataLink
      ::icon(fa fa-link)
      MAC Addresses
      Frames
      Switches
      Error Detection
    Network
      ::icon(fa fa-globe)
      IP Addresses
      Routing
      Routers
      Path Selection
    Transport
      ::icon(fa fa-truck)
      TCP/UDP
      Ports
      Reliability
      Flow Control
    Session
      ::icon(fa fa-handshake)
      Dialog Control
      Checkpoints
      Recovery
      Session Management
    Presentation
      ::icon(fa fa-eye)
      Encryption
      Compression
      Translation
      Data Format
    Application
      ::icon(fa fa-desktop)
      HTTP
      FTP
      SMTP
      User Interface

graph TB
    subgraph "Protocol Stack"
        subgraph "Layer 7 - Application"
            HTTP[HTTP/HTTPS]
            FTP[FTP/SFTP]
            SMTP[SMTP]
            DNS[DNS]
            DHCP[DHCP]
            SSH[SSH]
        end

        subgraph "Layer 6 - Presentation"
            TLS[TLS/SSL]
            JPEG[JPEG]
            GIF[GIF]
            ASCII[ASCII]
            EBCDIC[EBCDIC]
        end

        subgraph "Layer 5 - Session"
            NetBIOS[NetBIOS]
            RPC[RPC]
            SQL[SQL Sessions]
            PPTP[PPTP]
        end

        subgraph "Layer 4 - Transport"
            TCP[TCP]
            UDP[UDP]
            SCTP[SCTP]
        end

        subgraph "Layer 3 - Network"
            IP[IPv4/IPv6]
            ICMP[ICMP]
            OSPF[OSPF]
            BGP[BGP]
            ARP[ARP]
        end

        subgraph "Layer 2 - Data Link"
            Ethernet[Ethernet]
            WiFi[802.11 WiFi]
            PPP[PPP]
            Frame[Frame Relay]
        end

        subgraph "Layer 1 - Physical"
            Cat5[Cat5/6 Cable]
            Fiber[Fiber Optic]
            Radio[Radio Waves]
            Bluetooth[Bluetooth]
        end
    end

graph LR
    subgraph "Layer 1 - Physical"
        Hub[Hub]
        Repeater[Repeater]
        Cable[Cables]
        Connector[Connectors]
    end

    subgraph "Layer 2 - Data Link"
        Switch[Switch]
        Bridge[Bridge]
        NIC[Network Card]
        AP[Access Point]
    end

    subgraph "Layer 3 - Network"
        Router[Router]
        L3Switch[Layer 3 Switch]
        Gateway[Gateway]
    end

    subgraph "Layer 4 - Transport"
        Firewall[Firewall]
        LoadBalancer[Load Balancer]
    end

    subgraph "Layer 7 - Application"
        Proxy[Proxy Server]
        WebServer[Web Server]
        MailServer[Mail Server]
    end

graph TB
    subgraph "Transportation System"
        Highway[Highway System]
        Road[Local Roads]
        Bridge[Bridges]
        Tunnel[Tunnels]
    end

    subgraph "Physical Layer"
        Ethernet[Ethernet Cables]
        Fiber[Fiber Optic Cables]
        WiFi[Wireless Signals]
        Bluetooth[Bluetooth Radio]
    end

    Highway -.-> Ethernet
    Road -.-> WiFi
    Bridge -.-> Fiber
    Tunnel -.-> Bluetooth

graph LR
    subgraph "Twisted Pair Cable Structure"
        subgraph "UTP Cable"
            Wire1[Pair 1: Orange/White-Orange]
            Wire2[Pair 2: Green/White-Green]
            Wire3[Pair 3: Blue/White-Blue]
            Wire4[Pair 4: Brown/White-Brown]
        end

        subgraph "Categories"
            Cat5[Cat 5: 100 Mbps]
            Cat5e[Cat 5e: 1 Gbps]
            Cat6[Cat 6: 1 Gbps / 10 Gbps short]
            Cat6a[Cat 6a: 10 Gbps]
            Cat7[Cat 7: 10 Gbps+ Shielded]
        end
    end

graph LR
    subgraph "Coaxial Cable Structure"
        Core[Copper Core]
        Insulator[Dielectric Insulator]
        Shield[Metallic Shield]
        Jacket[Outer Jacket]

        Core --> Insulator --> Shield --> Jacket
    end

    subgraph "Types"
        RG58[RG-58: Thin Ethernet]
        RG8[RG-8: Thick Ethernet]
        RG6[RG-6: Cable TV/Internet]
    end

graph TB
    subgraph "Fiber Optic Cable"
        subgraph "Single Mode Fiber"
            SMCore[9μm Core]
            SMCladding[125μm Cladding]
            SMCoating[Primary Coating]
            SMJacket[Outer Jacket]
        end

        subgraph "Multi Mode Fiber"
            MMCore[50μm or 62.5μm Core]
            MMCladding[125μm Cladding]
            MMCoating[Primary Coating]
            MMJacket[Outer Jacket]
        end
    end

    subgraph "Light Propagation"
        LED[LED Light Source] --> MM[Multi Mode]
        Laser[Laser Light Source] --> SM[Single Mode]

        MM --> ShortDist[Short Distance2km]
        SM --> LongDist[Long Distance100km+]
    end

graph LR
    subgraph "Radio Frequency Spectrum"
        subgraph "ISM Bands"
            Band24[2.4 GHz<br/>WiFi 802.11b/g/n]
            Band5[5 GHz<br/>WiFi 802.11a/n/ac/ax]
            Band6[6 GHz<br/>WiFi 6E/7]
        end

        subgraph "Licensed Bands"
            Cellular[700-2600 MHz<br/>4G/5G]
            Microwave[6-40 GHz<br/>Point-to-point]
        end
    end

    subgraph "Propagation"
        LOS[Line of Sight]
        NLOS[Non-Line of Sight]
        Reflection[Signal Reflection]
        Absorption[Signal Absorption]
    end

graph LR
    subgraph "Infrared Communication"
        IR_LED[IR LED] --> IR_Signal[Infrared Light] --> IR_Detector[IR Photodiode]

        subgraph "Characteristics"
            Range[Range: 1-10 meters]
            LOS_Required[Requires Line of Sight]
            No_Interference[No RF Interference]
            Security[Good Security]
        end
    end

graph TB
    subgraph "Signal Types"
        subgraph "Digital Signal"
            DigitalWave[Square Wave<br/>Discrete Values<br/>0s and 1s]
        end

        subgraph "Analog Signal"
            AnalogWave[Sine Wave<br/>Continuous Values<br/>Infinite Range]
        end
    end

    subgraph "Digital Encoding Schemes"
        NRZ[Non-Return-to-Zero<br/>0 = Low, 1 = High]
        Manchester[Manchester<br/>Mid-bit transitions]
        Differential[Differential<br/>Change = 1, No change = 0]
    end

gantt
    title Digital Encoding Schemes for Binary: 10110100
    dateFormat X
    axisFormat %s

    section NRZ-L
    Bit 1    :0, 1
    Bit 0    :1, 2
    Bit 1    :2, 3
    Bit 1    :3, 4
    Bit 0    :4, 5
    Bit 1    :5, 6
    Bit 0    :6, 7
    Bit 0    :7, 8

    section Manchester
    1 High-Low   :0, 1
    0 Low-High   :1, 2
    1 High-Low   :2, 3
    1 High-Low   :3, 4
    0 Low-High   :4, 5
    1 High-Low   :5, 6
    0 Low-High   :6, 7
    0 Low-High   :7, 8

graph TB
    subgraph "Physical Topologies"
        subgraph "Bus Topology"
            B1[Computer 1] --- BusLine[Main Bus Cable]
            B2[Computer 2] --- BusLine
            B3[Computer 3] --- BusLine
            B4[Computer 4] --- BusLine
        end

        subgraph "Star Topology"
            SHub[Hub/Switch] --- S1[Computer 1]
            SHub --- S2[Computer 2]
            SHub --- S3[Computer 3]
            SHub --- S4[Computer 4]
        end

        subgraph "Ring Topology"
            R1[Computer 1] --- R2[Computer 2]
            R2 --- R3[Computer 3]
            R3 --- R4[Computer 4]
            R4 --- R1
        end

        subgraph "Mesh Topology"
            M1[Computer 1] --- M2[Computer 2]
            M1 --- M3[Computer 3]
            M1 --- M4[Computer 4]
            M2 --- M3
            M2 --- M4
            M3 --- M4
        end
    end

graph LR
    subgraph "Repeater Function"
        WeakSignal[Weak Signal] --> Repeater["Repeater</br>Amplifies & Regenerates"] --> StrongSignal[Strong Signal]

        subgraph "Signal Regeneration"
            Original["Original Digital Signal"]
            Degraded["Degraded Signal</br>After 90m cable"]
            Regenerated["Regenerated Signal</br>After repeater"]
        end
    end

    subgraph "Hub Operation"
        H1[Port 1] --> Hub["Hub</br>Collision Domain"]
        H2[Port 2] --> Hub
        H3[Port 3] --> Hub
        H4[Port 4] --> Hub

        Note["All ports share</br>same collision domain"]
    end

graph TB
    subgraph "Network Interface Card (NIC)"
        subgraph "NIC Components"
            Controller[Network Controller]
            Buffer[Buffer Memory]
            Connector[Physical Connector]
            LED[Status LEDs]
        end

        subgraph "Transceiver Functions"
            Transmit[Transmit Data]
            Receive[Receive Data]
            Collision[Collision Detection]
            Carrier[Carrier Sense]
        end
    end

    subgraph "Media Converters"
        Ethernet[Ethernet] --> Converter[Media Converter] --> Fiber[Fiber Optic]
        Copper[Copper Wire] --> Converter2[Media Converter] --> Wireless[Wireless]
    end

sequenceDiagram
    participant Sender
    participant Clock as Clock Signal
    participant Receiver

    Note over Sender, Receiver: Synchronous Communication
    Sender->>Clock: Data ready
    Clock->>Receiver: Clock pulse
    Sender->>Receiver: Bit 1
    Clock->>Receiver: Clock pulse
    Sender->>Receiver: Bit 0
    Clock->>Receiver: Clock pulse
    Sender->>Receiver: Bit 1

    Note over Sender, Receiver: Self-Synchronizing (Manchester)
    Sender->>Receiver: High-to-Low (Bit 1)
    Note over Receiver: Clock extracted from transition
    Sender->>Receiver: Low-to-High (Bit 0)
    Note over Receiver: Clock extracted from transition

graph LR
    subgraph "Transmission Modes"
        subgraph "Simplex"
            S_A[Device A] -->|One Direction Only| S_B[Device B]
            S_Example[Example: Radio, TV]
        end

        subgraph "Half-Duplex"
            H_A[Device A] <-->|One Direction at a Time| H_B[Device B]
            H_Example[Example: Walkie-talkie, Old Ethernet Hub]
        end

        subgraph "Full-Duplex"
            F_A[Device A] <-->|Both Directions Simultaneously| F_B[Device B]
            F_A2[Separate Channels] -.-> F_B2[Separate Channels]
            F_Example[Example: Modern Ethernet, Telephone]
        end
    end

graph TB
    subgraph "Signal Problems"
        subgraph "Attenuation"
            StrongSig[Strong Signal] --> Distance[Long Distance] --> WeakSig[Weak Signal]
        end

        subgraph "Noise"
            CleanSig[Clean Signal] --> EMI[EMI/RFI] --> NoisySig[Noisy Signal]
        end

        subgraph "Distortion"
            SquareWave[Square Wave] --> Capacitance[Cable Capacitance] --> RoundedWave[Rounded Wave]
        end
    end

    subgraph "Solutions"
        Repeater[Repeaters]
        Shielding[Shielded Cables]
        Amplifier[Amplifiers]
        Filter[Filters]
    end

timeline
    title Ethernet Physical Layer Evolution

    1980s : 10BASE5 (Thick Ethernet)
          : Coaxial cable
          : 10 Mbps
          : 500m segments

    1985 : 10BASE2 (Thin Ethernet)
         : Thinner coaxial
         : 10 Mbps
         : 185m segments

    1990 : 10BASE-T
         : Twisted pair
         : 10 Mbps
         : 100m distance

    1995 : 100BASE-TX (Fast Ethernet)
         : Cat 5 UTP
         : 100 Mbps
         : Full duplex

    1999 : 1000BASE-T (Gigabit)
         : Cat 5e/6 UTP
         : 1 Gbps
         : 4 pairs used

    2006 : 10GBASE-T
         : Cat 6a UTP
         : 10 Gbps
         : 100m distance

    2017 : 25G/40G/100G
         : Fiber optic
         : Data center focus
         : Multiple lanes

graph LR
    subgraph "WiFi Standards Evolution"
        subgraph "Early Standards"
            WiFi1["802.11 (1997)2 Mbps"]
            WiFi2["802.11b (1999)11 Mbps, 2.4GHz"]
            WiFi3["802.11a (1999)54 Mbps, 5GHz"]
        end

        subgraph "Modern Standards"
            WiFi4["802.11g (2003)54 Mbps, 2.4GHz"]
            WiFi5["802.11n (2009)600 Mbps, MIMO"]
            WiFi6["802.11ac (2013)6.8 Gbps, 5GHz"]
            WiFi7["802.11ax (2019)9.6 Gbps, WiFi 6"]
        end
    end

graph TB
    subgraph "Cable Testing Process"
        subgraph "Continuity Testing"
            Pin1[Pin 1] --> Wire1[Wire] --> Pin1_End[Pin 1 End]
            Pin2[Pin 2] --> Wire2[Wire] --> Pin2_End[Pin 2 End]
        end

        subgraph "Common Issues"
            Open[Open CircuitBroken wire]
            Short[Short CircuitWires touching]
            Cross[Cross-overWrong pin mapping]
            Length[Length IssuesToo long/short]
        end

        subgraph "Testing Tools"
            Multimeter[Digital Multimeter]
            CableTester[Cable Tester]
            TDR[Time Domain Reflectometer]
            CertTester[Certification Tester]
        end
    end

graph LR
    subgraph "Signal Quality Metrics"
        subgraph "Digital Signals"
            BitRate[Bit Ratebits per second]
            ErrorRate[Bit Error RateBER]
            Jitter[Timing JitterClock variation]
            EyeDiagram[Eye DiagramSignal integrity]
        end

        subgraph "Analog Signals"
            Amplitude[Signal AmplitudeVoltage level]
            Frequency[FrequencyHz]
            SNR[Signal-to-Noise RatiodB]
            Bandwidth[BandwidthFrequency range]
        end
    end

graph TB
    subgraph "PoE Implementation"
        subgraph "PSE (Power Sourcing Equipment)"
            Switch[PoE Switch/Injector]
            Detection[Device Detection]
            Classification[Power Classification]
            PowerDelivery[Power Delivery]
        end

        subgraph "PD (Powered Device)"
            APCamera[IP Camera]
            Phone[VoIP Phone]
            AccessPoint[WiFi Access Point]
            Light[LED Light]
        end

        subgraph "Cable Pairs"
            DataPairs[Pairs 1,2 & 3,6Data + Power]
            SparePairs[Pairs 4,5 & 7,8Additional Power]
        end
    end

    Switch --> APCamera
    Switch --> Phone
    Switch --> AccessPoint
    Switch --> Light

graph TB
    subgraph "Physical Layer Threats"
        subgraph "Cable Threats"
            Cutting[Cable Cutting]
            Tapping[Wire Tapping]
            Splicing[Cable Splicing]
            EMI[EMI Interference]
        end

        subgraph "Wireless Threats"
            Jamming[Signal Jamming]
            Eavesdropping[Signal Interception]
            Spoofing[Signal Spoofing]
            Injection[Signal Injection]
        end

        subgraph "Physical Access"
            Equipment[Equipment Theft]
            Ports[Unauthorized Port Access]
            Facility[Facility Breach]
            Social[Social Engineering]
        end
    end

    subgraph "Countermeasures"
        Encryption[Signal Encryption]
        Shielding[Cable Shielding]
        Monitoring[Physical Monitoring]
        Access[Access Control]
    end

graph TB
    subgraph "Data Link Layer Functions"
        subgraph "LLC Sublayer"
            LLC[Logical Link ControlError & Flow ControlMultiplexing]
        end

        subgraph "MAC Sublayer"
            MAC[Media Access ControlFrame formattingPhysical addressingMedia access]
        end

        subgraph "Physical Interface"
            PHY[Physical Layer InterfaceBit transmissionSignal encoding]
        end
    end

    NetworkLayer[Network Layer] --> LLC
    LLC --> MAC
    MAC --> PHY
    PHY --> Medium[Physical Medium]

packet-beta
title LLC Frame Format
0-7: "DSAP"
8-15: "SSAP"
16-23: "Control"
24-31: "Data"

graph LR
    subgraph "MAC Address Format"
        subgraph "48-bit Address"
            OUI[24-bit OUIOrganizationally Unique IdentifierVendor Assignment]
            NIC[24-bit NICNetwork Interface ControllerDevice Specific]
        end

        subgraph "Example: 00:1B:44:11:3A:B7"
            Vendor[00:1B:44Intel Corporation]
            Device[11:3A:B7Specific Device]
        end
    end

    subgraph "Address Types"
        Unicast[UnicastSingle destinationBit 0 = 0]
        Multicast[MulticastGroup destinationBit 0 = 1]
        Broadcast[BroadcastAll devicesFF:FF:FF:FF:FF:FF]
    end

graph TB
    subgraph "Special MAC Address Types"
        subgraph "Broadcast"
            BroadcastAddr[FF:FF:FF:FF:FF:FFSent to all devices on LAN]
        end

        subgraph "Multicast Examples"
            AllSystems[01:00:5E:00:00:01All Systems Multicast]
            AllRouters[01:00:5E:00:00:02All Routers Multicast]
            STP[01:80:C2:00:00:00Spanning Tree Protocol]
        end

        subgraph "Local Administration"
            LocalBit[Bit 1 = 1Locally AdministeredOverride manufacturer]
        end
    end

packet-beta
title Generic Frame Format
0-63: "Preamble & SFD"
64-111: "Destination MAC"
112-159: "Source MAC"
160-175: "Type/Length"
176-1535: "Data & Padding"
1536-1567: "Frame Check Sequence"

sequenceDiagram
    participant Sender
    participant Medium as Physical Medium
    participant Receiver

    Note over Sender, Receiver: Frame Transmission Process

    Sender->>Medium: Preamble (Clock sync)
    Note over Medium: 10101010... pattern

    Sender->>Medium: Start Frame Delimiter
    Note over Medium: 10101011 pattern

    Sender->>Medium: Destination MAC Address
    Receiver->>Receiver: Check if address matches

    Sender->>Medium: Source MAC Address
    Sender->>Medium: Type/Length Field
    Sender->>Medium: Data Payload
    Sender->>Medium: Frame Check Sequence

    Receiver->>Receiver: Verify FCS
    Receiver->>Sender: ACK (if required)

packet-beta
title Ethernet II Frame
0-55: "Preamble"
56-63: "SFD"
64-111: "Dest MAC"
112-159: "Src MAC"
160-175: "EtherType"
176-1535: "Data"
1536-1567: "FCS"

packet-beta
title IEEE 802.3 Frame
0-55: "Preamble"
56-63: "SFD"
64-111: "Dest MAC"
112-159: "Src MAC"
160-175: "Length"
176-191: "LLC Header"
192-1535: "Data"
1536-1567: "FCS"

graph TB
    subgraph "Switch Architecture"
        subgraph "MAC Address Table"
            Entry1[Port 1: 00:1A:2B:3C:4D:5E]
            Entry2[Port 2: 00:1B:3C:4D:5E:6F]
            Entry3[Port 3: 00:1C:4D:5E:6F:7A]
            Entry4[Port 4: 00:1D:5E:6F:7A:8B]
        end

        subgraph "Switch Fabric"
            Port1[Port 1] --> Fabric[Switching Matrix]
            Port2[Port 2] --> Fabric
            Port3[Port 3] --> Fabric
            Port4[Port 4] --> Fabric
        end

        subgraph "Frame Processing"
            Learning[MAC Learning]
            Forwarding[Frame Forwarding]
            Filtering[Frame Filtering]
            Flooding[Frame Flooding]
        end
    end

sequenceDiagram
    participant A as Device AMAC: AA:AA:AA:AA:AA:AA
    participant SW as Switch
    participant B as Device BMAC: BB:BB:BB:BB:BB:BB
    participant C as Device CMAC: CC:CC:CC:CC:CC:CC

    Note over SW: MAC Address Table Initially Empty

    A->>SW: Frame: Src=AA:AA, Dst=BB:BB
    Note over SW: Learn: Port 1 = AA:AADestination unknown - FLOOD
    SW->>B: Forward to all ports except source
    SW->>C: Forward to all ports except source

    B->>SW: Frame: Src=BB:BB, Dst=AA:AA
    Note over SW: Learn: Port 2 = BB:BBDestination known - FORWARD
    SW->>A: Forward only to Port 1

    Note over SW: MAC Table now contains:Port 1: AA:AAPort 2: BB:BB

graph TB
    subgraph "VLAN Configuration"
        subgraph "Physical Switch"
            Port1[Port 1VLAN 10]
            Port2[Port 2VLAN 20]
            Port3[Port 3VLAN 10]
            Port4[Port 4VLAN 20]
            Trunk[Trunk PortAll VLANs]
        end

        subgraph "Logical VLANs"
            VLAN10[VLAN 10: Sales192.168.10.0/24]
            VLAN20[VLAN 20: Engineering192.168.20.0/24]
        end

        Port1 -.-> VLAN10
        Port3 -.-> VLAN10
        Port2 -.-> VLAN20
        Port4 -.-> VLAN20
    end

packet-beta
title 802.1Q VLAN Tagged Frame
0-111: "Standard Ethernet Header"
112-127: "TPID (0x8100)"
128-130: "PCP"
131: "DEI"
132-143: "VID"
144-159: "EtherType"
160-1535: "Data"
1536-1567: "FCS"

graph LR
    subgraph "CRC Process"
        subgraph "Sender"
            Data[Data Bits] --> CRC_Gen[CRC GeneratorPolynomial Division] --> Frame[Frame + CRC]
        end

        subgraph "Receiver"
            RecFrame[Received Frame] --> CRC_Check[CRC CheckerPolynomial Division] --> Result{Error?}
            Result -->|No Error| Accept[Accept Frame]
            Result -->|Error| Discard[Discard Frame]
        end
    end

    Frame -.->|Network| RecFrame

graph TB
    subgraph "Error Types"
        subgraph "Single Bit Error"
            Original1[01010101]
            Error1[01011101]
            Arrow1[Bit 3 flipped]
        end

        subgraph "Burst Error"
            Original2[01010101]
            Error2[01111001]
            Arrow2[Multiple consecutive bits]
        end

        subgraph "Random Errors"
            Original3[01010101]
            Error3[11010001]
            Arrow3[Multiple random bits]
        end
    end

    subgraph "Detection Methods"
        Parity[Parity CheckSimple, Limited]
        Checksum[ChecksumBetter coverage]
        CRC[CRCBest coverage]
    end

sequenceDiagram
    participant Sender
    participant Receiver

    Note over Sender, Receiver: Stop-and-Wait Flow Control

    Sender->>Receiver: Frame 1
    Note over Receiver: Process Frame 1
    Receiver->>Sender: ACK 1

    Sender->>Receiver: Frame 2
    Note over Receiver: Process Frame 2
    Receiver->>Sender: ACK 2

    Sender->>Receiver: Frame 3
    Note over Receiver: Buffer Full!
    Receiver->>Sender: NAK 3 (or no ACK)

    Note over Sender: Timeout - Retransmit
    Sender->>Receiver: Frame 3 (Retransmitted)
    Note over Receiver: Buffer available
    Receiver->>Sender: ACK 3

sequenceDiagram
    participant Sender
    participant Receiver

    Note over Sender, Receiver: Sliding Window (Window Size = 3)

    par Send multiple frames
        Sender->>Receiver: Frame 1
        Sender->>Receiver: Frame 2
        Sender->>Receiver: Frame 3
    end

    Note over Receiver: Process frames

    par Acknowledge multiple frames
        Receiver->>Sender: ACK 1
        Receiver->>Sender: ACK 2
        Receiver->>Sender: ACK 3
    end

    Note over Sender: Window slides, send next frames

    par Send next window
        Sender->>Receiver: Frame 4
        Sender->>Receiver: Frame 5
        Sender->>Receiver: Frame 6
    end

sequenceDiagram
    participant A as Station A
    participant Medium as Shared Medium
    participant B as Station B
    participant C as Station C

    Note over A, C: CSMA/CD Process

    A->>Medium: Listen for carrier
    Note over Medium: Medium idle
    A->>Medium: Start transmission

    B->>Medium: Listen for carrier
    Note over Medium: Medium busy
    Note over B: Wait for idle

    C->>Medium: Start transmission
    Note over Medium: COLLISION DETECTED!

    A->>Medium: Send jam signal
    C->>Medium: Send jam signal

    Note over A: Random backoff
    Note over C: Random backoff

    A->>Medium: Listen again
    Note over Medium: Medium idle
    A->>Medium: Retransmit successfully

sequenceDiagram
    participant Station
    participant AP as Access Point
    participant Medium as Wireless Medium

    Note over Station, Medium: CSMA/CA Process (WiFi)

    Station->>Medium: Listen for carrier
    Note over Medium: Medium idle
    Station->>Medium: Wait random backoff
    Station->>Medium: Listen again
    Note over Medium: Still idle

    Station->>AP: RTS (Request to Send)
    AP->>Station: CTS (Clear to Send)

    Station->>AP: Data frame
    AP->>Station: ACK

    Note over Station, AP: Successful transmission

graph TB
    subgraph "Network with Loops"
        SW1[Switch 1] --- SW2[Switch 2]
        SW2 --- SW3[Switch 3]
        SW3 --- SW1
        SW1 --- PC1[PC 1]
        SW3 --- PC2[PC 2]
    end

    subgraph "Problems"
        Storm[Broadcast Storm]
        Duplicate[Duplicate Frames]
        Instability[MAC Table Instability]
    end

graph TB
    subgraph "STP Enabled Network"
        SW1[Switch 1Root Bridge] --- SW2[Switch 2]
        SW2 --- SW3[Switch 3]
        SW3 -.->|Blocked Port| SW1
        SW1 --- PC1[PC 1]
        SW3 --- PC2[PC 2]
    end

    subgraph "Port States"
        Blocking[BlockingNo data forwarding]
        Listening[ListeningBuilding topology]
        Learning[LearningBuilding MAC table]
        Forwarding[ForwardingNormal operation]
    end

packet-beta
title STP BPDU Format
0-15: "Protocol ID"
16-23: "Version"
24-31: "BPDU Type"
32-39: "Flags"
40-103: "Root Bridge ID"
104-135: "Root Path Cost"
136-199: "Bridge ID"
200-215: "Port ID"
216-231: "Message Age"
232-247: "Max Age"
248-263: "Hello Time"
264-279: "Forward Delay"

graph LR
    subgraph "Link Aggregation"
        subgraph "Switch A"
            A_Port1[Port 1]
            A_Port2[Port 2]
            A_Port3[Port 3]
            A_Port4[Port 4]
        end

        subgraph "Logical Channel"
            LAG[LAG GroupIncreased BandwidthRedundancy]
        end

        subgraph "Switch B"
            B_Port1[Port 1]
            B_Port2[Port 2]
            B_Port3[Port 3]
            B_Port4[Port 4]
        end

        A_Port1 --- LAG --- B_Port1
        A_Port2 --- LAG --- B_Port2
        A_Port3 --- LAG --- B_Port3
        A_Port4 --- LAG --- B_Port4
    end

graph TB
    subgraph "LAG Load Balancing"
        subgraph "Hash-based Distribution"
            SrcMAC[Source MAC]
            DstMAC[Destination MAC]
            SrcIP[Source IP]
            DstIP[Destination IP]
            Port[Port Numbers]
        end

        subgraph "Hash Function"
            Hash[Hash Algorithm] --> Link1[Link 1]
            Hash --> Link2[Link 2]
            Hash --> Link3[Link 3]
            Hash --> Link4[Link 4]
        end

        SrcMAC --> Hash
        DstMAC --> Hash
        SrcIP --> Hash
        DstIP --> Hash
        Port --> Hash
    end

packet-beta
title 802.11 MAC Frame
0-15: "Frame Control"
16-31: "Duration/ID"
32-79: "Address 1"
80-127: "Address 2"
128-175: "Address 3"
176-191: "Sequence Control"
192-239: "Address 4"
240-2287: "Data"
2288-2319: "FCS"

graph TB
    subgraph "802.11 Frame Types"
        subgraph "Management Frames"
            Beacon[Beacon]
            ProbeReq[Probe Request]
            ProbeResp[Probe Response]
            Auth[Authentication]
            Assoc[Association]
        end

        subgraph "Control Frames"
            RTS[RTS]
            CTS[CTS]
            ACK[ACK]
            PS[Power Save Poll]
        end

        subgraph "Data Frames"
            Data[Data]
            Null[Null Data]
            QoS[QoS Data]
        end
    end

graph LR
    subgraph "802.1p QoS Priority"
        subgraph "Priority Levels"
            P0[0: Best Effort]
            P1[1: Background]
            P2[2: Spare]
            P3[3: Excellent Effort]
            P4[4: Controlled Load]
            P5[5: Video]
            P6[6: Voice]
            P7[7: Network Control]
        end

        subgraph "Traffic Types"
            Background[Background Data]
            Web[Web Browsing]
            Video[Video Streaming]
            Voice[Voice Calls]
            Critical[Network Management]
        end

        Background -.-> P1
        Web -.-> P0
        Video -.-> P5
        Voice -.-> P6
        Critical -.-> P7
    end

graph LR
    subgraph "Frame Size Comparison"
        subgraph "Standard Ethernet"
            Std[1500 byte MTUMore overheadMore processing]
        end

        subgraph "Jumbo Frames"
            Jumbo[9000 byte MTULess overheadBetter efficiency]
        end

        subgraph "Benefits"
            Throughput[Higher Throughput]
            CPU[Lower CPU Usage]
            Latency[Reduced Latency]
        end

        Jumbo --> Throughput
        Jumbo --> CPU
        Jumbo --> Latency
    end

graph TB
    subgraph "Layer 2 Troubleshooting"
        subgraph "Physical Issues"
            BadCable[Bad Cable] --> ReplaceCable[Replace Cable]
            BadPort[Bad Port] --> TestPort[Test Different Port]
            Duplex[Duplex Mismatch] --> FixDuplex[Configure Duplex]
        end

        subgraph "Configuration Issues"
            WrongVLAN[Wrong VLAN] --> ConfigVLAN[Configure VLAN]
            STPLoop[STP Loop] --> CheckSTP[Verify STP Config]
            MACLimit[MAC Limit] --> IncreaseMACLimit[Increase MAC Table]
        end

        subgraph "Performance Issues"
            Collisions[Excessive Collisions] --> UpgradeSwitch[Upgrade to Switch]
            Broadcast[Broadcast Storm] --> SegmentNetwork[Segment Network]
            Errors[Frame Errors] --> CheckCabling[Check Cabling]
        end
    end

graph LR
    subgraph "Troubleshooting Tools"
        subgraph "Command Line"
            ShowMAC[show mac address-table]
            ShowInt[show interface]
            ShowSTP[show spanning-tree]
            ShowVLAN[show vlan]
        end

        subgraph "Network Tools"
            Wireshark[WiresharkPacket Capture]
            PingTest[Ping TestConnectivity]
            SwitchLED[Switch LEDsStatus Indicators]
        end

        subgraph "Metrics"
            Utilization[Link Utilization]
            ErrorRate[Error Rates]
            Collisions[Collision Count]
            Drops[Packet Drops]
        end
    end

graph TB
    subgraph "Network Layer Functions"
        subgraph "Addressing"
            IPv4[IPv4 Addressing</br>32-bit addresses]
            IPv6[IPv6 Addressing</br>128-bit addresses]
            Subnetting[Subnetting</br>Network segmentation]
        end

        subgraph "Routing"
            StaticRouting[Static Routing</br>Manual configuration]
            DynamicRouting[Dynamic Routing</br>Automatic discovery]
            RouteTable[Routing Table</br>Path information]
        end

        subgraph "Protocols"
            IP[Internet ProtocolPacket delivery]
            ICMP[ICMP</br>Error reporting]
            ARP[ARP</br>Address resolution]
        end
    end

packet-beta
title IPv4 Header Format
0-3: "Version"
4-7: "IHL"
8-15: "Type of Service"
16-31: "Total Length"
32-47: "Identification"
48-50: "Flags"
51-63: "Fragment Offset"
64-71: "TTL"
72-79: "Protocol"
80-95: "Header Checksum"
96-127: "Source IP Address"
128-159: "Destination IP Address"
160-191: "Options (if IHL > 5)"
192-223: "Data"

graph LR
    subgraph "Key IPv4 Header Fields"
        subgraph "Version & Length"
            Version["Version: 4</br>IP version"]
            IHL["IHL: 5-15</br>Header length in 32-bit words"]
        end

        subgraph "Service & Length"
            ToS["Type of Service</br>QoS marking"]
            TotalLen["Total Length</br>Entire packet size"]
        end

        subgraph "Fragmentation"
            ID["Identification</br>Fragment grouping"]
            Flags["Flags</br>DF, MF bits"]
            FragOffset["Fragment Offset</br>Position in original"]
        end

        subgraph "Routing & Protocol"
            TTL["TTL</br>Hop limit"]
            Protocol["Protocol</br>Next layer (TCP=6, UDP=17)"]
            Checksum["Header Checksum</br>Error detection"]
        end
    end

graph TB
    subgraph "IPv4 Address Classes"
        subgraph "Class A"
            ClassA[0.0.0.0 to 127.255.255.255</br>First bit: 0</br>Network: /8</br>Hosts: 16,777,214]
        end

        subgraph "Class B"
            ClassB[128.0.0.0 to 191.255.255.255</br>First bits: 10</br>Network: /16</br>Hosts: 65,534]
        end

        subgraph "Class C"
            ClassC[192.0.0.0 to 223.255.255.255</br>First bits: 110</br>Network: /24</br>Hosts: 254]
        end

        subgraph "Special Ranges"
            Private[Private Ranges:</br>10.0.0.0/8</br>172.16.0.0/12</br>192.168.0.0/16]
            Loopback[Loopback:</br>127.0.0.0/8]
            Multicast[Multicast:</br>224.0.0.0/4]
        end
    end

graph LR
    subgraph "Subnetting Example: 192.168.1.0/24"
        subgraph "Original Network"
            Original[192.168.1.0/24256 addresses254 hosts]
        end

        subgraph "Subnet into /26"
            Sub1[192.168.1.0/26Hosts: 1-62]
            Sub2[192.168.1.64/26Hosts: 65-126]
            Sub3[192.168.1.128/26Hosts: 129-190]
            Sub4[192.168.1.192/26Hosts: 193-254]
        end

        Original --> Sub1
        Original --> Sub2
        Original --> Sub3
        Original --> Sub4
    end

graph TB
    subgraph "CIDR Notation"
        subgraph "Network Examples"
            CIDR24["192.168.1.0/24Subnet Mask: 255.255.255.0Network: 192.168.1.0Broadcast: 192.168.1.255"]
            CIDR26["192.168.1.0/26Subnet Mask: 255.255.255.192Network: 192.168.1.0Broadcast: 192.168.1.63"]
            CIDR30["192.168.1.0/30Subnet Mask: 255.255.255.252Network: 192.168.1.0Broadcast: 192.168.1.3"]
        end

        subgraph "Host Calculation"
            Formula["Hosts = 2^(32-prefix) - 2-2 for network and broadcast"]
        end
    end

graph LR
    subgraph "IPv6 Address Format"
        subgraph "128-bit Address"
            Format[2001:0db8:85a3:0000:0000:8a2e:0370:73348 groups of 4 hexadecimal digits]
        end

        subgraph "Compression Rules"
            LeadingZero[Leading zeros can be omitted</br>2001:db8:85a3:0:0:8a2e:370:7334]
            Consecutive[Consecutive zeros can be ::2001:db8:85a3::8a2e:370:7334]
        end

        subgraph "Address Types"
            Unicast[Unicast: Single interface]
            Multicast[Multicast: Multiple interfaces]
            Anycast[Anycast: Nearest interface]
        end
    end

packet-beta
title IPv6 Header Format
0-3: "Version"
4-11: "Traffic Class"
12-31: "Flow Label"
32-47: "Payload Length"
48-55: "Next Header"
56-63: "Hop Limit"
64-191: "Source Address (128 bits)"
192-319: "Destination Address (128 bits)"

graph TB
    subgraph "IPv6 Address Categories"
        subgraph "Unicast Addresses"
            Global[Global Unicast</br>2000::/3</br>Internet routable]
            LinkLocal[Link-Local</br>fe80::/10</br>Local segment only]
            Unique[Unique Local</br>fc00::/7</br>Private addressing]
            Loopback[Loopback</br>::1</br>Local host]
        end

        subgraph "Multicast Addresses"
            AllNodes[All Nodes</br>ff02::1]
            AllRouters[All Routers</br>ff02::2]
            Solicited[Solicited Node</br>ff02::1:ffxx:xxxx]
        end

        subgraph "Special Addresses"
            Unspecified[Unspecified::</br>No address assigned]
            Documentation[Documentation</br>2001:db8::/32</br>Example/testing]
        end
    end

graph TB
    subgraph "Routing Table Components"
        subgraph "Route Entry"
            Destination[Destination Network</br>192.168.1.0/24]
            NextHop[Next Hop</br>10.0.0.1]
            Interface[Exit Interface</br>eth0]
            Metric[Metric/Cost</br>Administrative Distance]
            Protocol[Source Protocol</br>Static, OSPF, RIP]
        end

        subgraph "Route Types"
            Connected[Connected Routes</br>Directly attached networks]
            Static[Static Routes</br>Manually configured]
            Dynamic[Dynamic Routes</br>Learned via protocols]
            Default[Default Route</br>0.0.0.0/0 or ::/0]
        end
    end

sequenceDiagram
    participant Packet as Incoming Packet
    participant Router as Router
    participant Table as Routing Table
    participant Interface as Exit Interface

    Note over Packet, Interface: Route Selection Process

    Packet->>Router: Packet arrives
    Router->>Table: Look up destination

    alt Exact match found
        Table-->>Router: Return exact match
    else Subnet match found
        Table-->>Router: Return longest prefix match
    else No match found
        Table-->>Router: Return default route
    end

    Router->>Interface: Forward to next hop
    Interface->>Packet: Packet forwarded

    Note over Router: If no route exists, send ICMP unreachable

graph LR
    subgraph "Longest Prefix Match Example"
        subgraph "Routing Table"
            Route1[192.168.0.0/16 → Router A]
            Route2[192.168.1.0/24 → Router B]
            Route3[192.168.1.128/25 → Router C]
            Default[0.0.0.0/0 → Router D]
        end

        subgraph "Destination: 192.168.1.150"
            Match1[Matches /16 ✓]
            Match2[Matches /24 ✓]
            Match3[Matches /25 ✓ - Most Specific]
            Selected[Selected: Router C]
        end

        Route3 --> Selected
    end

graph TB
    subgraph "Routing Types Comparison"
        subgraph "Static Routing"
            StaticPros[Advantages:</br>• Predictable</br>• Secure</br>• No bandwidth overhead</br>• Simple configuration]
            StaticCons[Disadvantages:</br>• No fault tolerance</br>• Manual configuration</br>• Not scalable</br>• No load balancing]
        end

        subgraph "Dynamic Routing"
            DynamicPros[Advantages:</br>• Automatic convergence</br>• Fault tolerance</br>• Scalable</br>• Load balancing]
            DynamicCons[Disadvantages:</br>• Complex configuration</br>• Bandwidth overhead</br>• CPU intensive</br>• Convergence time]
        end
    end

sequenceDiagram
    participant R1 as Router 1
    participant R2 as Router 2
    participant R3 as Router 3

    Note over R1, R3: RIP Route Advertisement (Every 30 seconds)

    R1->>R2: Network 10.1.0.0/24, Metric: 1
    R1->>R2: Network 10.2.0.0/24, Metric: 2

    R2->>R1: Network 10.3.0.0/24, Metric: 1
    R2->>R3: Network 10.1.0.0/24, Metric: 2
    R2->>R3: Network 10.2.0.0/24, Metric: 3

    R3->>R2: Network 10.4.0.0/24, Metric: 1

    Note over R1, R3: Metric = Hop Count (Max 15)

graph TB
    subgraph "OSPF Operation"
        subgraph "LSA Flooding"
            LSA1[Router LSA</br>Router's interfaces]
            LSA2[Network LSA</br>Multi-access networks]
            LSA3[Summary LSA</br>Inter-area routes]
            LSA5[External LSA</br>External routes]
        end

        subgraph "SPF Calculation"
            Topology[Link State Database]
            SPF[Dijkstra Algorithm]
            Tree[Shortest Path Tree]
            Routes[Routing Table]
        end

        subgraph "OSPF Areas"
            Area0[Area 0Backbone Area]
            Area1[Area 1Regular Area]
            Area2[Area 2Stub Area]
            ABR[Area Border Router]
        end

        Topology --> SPF --> Tree --> Routes
    end

graph LR
    subgraph "EIGRP Metric Calculation"
        subgraph "Composite Metric"
            Bandwidth[Bandwidth</br>Slowest link in path]
            Delay[Delay</br>Cumulative delay]
            Reliability[Reliability</br>Path reliability]
            Load[Load</br>Path utilization]
            MTU[MTU</br>Maximum Transmission Unit]
        end

        subgraph "DUAL Algorithm"
            FeasibleDistance[Feasible Distance</br>Best metric to destination]
            ReportedDistance[Reported Distance</br>Neighbor's metric]
            FeasibilityCondition[Feasibility Condition</br>Loop prevention]
        end
    end

graph TB
    subgraph "BGP Operation"
        subgraph "BGP Session Types"
            EBGP["External BGP</br>Between different ASes"]
            IBGP["Internal BGP</br>Within same AS"]
        end

        subgraph "Path Attributes"
            ASPath["AS_PATHList of ASes"]
            NextHop["NEXT_HOP</br>Next hop IP"]
            LocalPref["LOCAL_PREF</br>Path preference"]
            MED["MED</br>Multi-Exit Discriminator"]
        end

        subgraph "Route Selection"
            Weight["1. Weight (Cisco)"]
            LocalPreference["2. Local Preference"]
            Originate["3. Locally Originated"]
            ShortestAS["4. Shortest AS Path"]
            Origin["5. Origin Code"]
            LowestMED["6. Lowest MED"]
        end
    end

sequenceDiagram
    participant PC as Private PC192.168.1.10
    participant Router as NAT Router
    participant Server as Web Server203.0.113.10

    Note over PC, Server: NAT Translation Process

    PC->>Router: SRC: 192.168.1.10:1024</br>DST: 203.0.113.10:80
    Note over Router: Create NAT entry:192.168.1.10:1024 ↔ 203.0.113.5:2048
    Router->>Server: SRC: 203.0.113.5:2048</br>DST: 203.0.113.10:80

    Server->>Router: SRC: 203.0.113.10:80</br>DST: 203.0.113.5:2048
    Note over Router: Lookup NAT entry
    Router->>PC: SRC: 203.0.113.10:80</br>DST: 192.168.1.10:1024

graph TB
    subgraph "NAT Types"
        Static["Static:<br/>One-to-One Mapping<br/>192.168.1.10 ↔ 203.0.113.10<br/>Permanent translation"]
        Dynamic["Dynamic:<br/>Many-to-Many Mapping<br/>Pool of public addresses<br/>Temporary assignments"]
        PAT["PAT:<br/>Many-to-One Mapping<br/>Multiple private IPs<br/>Single public IP<br/>Different ports"]
        NAT64["NAT64:<br/>IPv6 to IPv4 Translation<br/>Enable IPv6-only hosts<br/>Access IPv4 resources"]
    end

graph TB
    subgraph "ICMP Message Categories"
        subgraph "Error Messages"
            Unreachable["Destination Unreachable<br/>Type 3"]
            Redirect["Redirect<br/>Type 5"]
            TimeExceeded["Time Exceeded<br/>Type 11"]
            ParameterProblem["Parameter Problem<br/>Type 12"]
        end

        subgraph "Informational Messages"
            EchoRequest["Echo Request<br/>Type 8 (Ping)"]
            EchoReply["Echo Reply<br/>Type 0 (Ping Reply)"]
            Timestamp["Timestamp Request/Reply<br/>Type 13/14"]
        end

        subgraph "Router Messages"
            RouterSolicitation["Router Solicitation<br/>Type 10"]
            RouterAdvertisement["Router Advertisement<br/>Type 9"]
        end
    end

sequenceDiagram
    participant Source
    participant R1 as Router 1
    participant R2 as Router 2
    participant R3 as Router 3
    participant Dest as Destination

    Note over Source, Dest: Traceroute Operation

    Source->>R1: ICMP Echo, TTL=1
    R1->>Source: ICMP Time Exceeded
    Note over Source: Hop 1: Router 1

    Source->>R2: ICMP Echo, TTL=2
    R2->>Source: ICMP Time Exceeded
    Note over Source: Hop 2: Router 2

    Source->>R3: ICMP Echo, TTL=3
    R3->>Source: ICMP Time Exceeded
    Note over Source: Hop 3: Router 3

    Source->>Dest: ICMP Echo, TTL=4
    Dest->>Source: ICMP Echo Reply
    Note over Source: Hop 4: Destination reached

graph LR
    subgraph "IP ToS/DSCP Field"
        subgraph "IPv4 ToS Field"
            DSCP["DSCP (6 bits)"]
            ECN["ECN (2 bits)"]
        end

        subgraph "Common DSCP Values"
            EF["EF (46)Expedited Forwarding</br>Voice traffic"]
            AF41["AF41 (34)Assured Forwarding</br>Video traffic"]
            AF31["AF31 (26)Assured Forwarding</br>Critical data"]
            BE["BE (0)Best Effort</br>Default traffic"]
        end

        subgraph "PHB (Per-Hop Behavior)"
            Expedited["Expedited Forwarding</br>Low latency, low jitter"]
            Assured["Assured Forwarding</br>Guaranteed bandwidth"]
            BestEffort["Best Effort</br>No guarantees"]
        end
    end

graph TB
    subgraph "QoS Mechanisms"
        subgraph "Traffic Shaping"
            Buffer[Buffer excess traffic</br>Smooth traffic bursts</br>Delay packets if needed]
        end

        subgraph "Traffic Policing"
            Drop[Drop excess traffic</br>Enforce rate limits</br>Mark non-conforming traffic]
        end

        subgraph "Queue Management"
            FIFO[FIFOFirst In, First Out]
            Priority[Priority Queuing</br>High priority first]
            WFQ[Weighted Fair Queuing</br>Bandwidth allocation]
            CBWFQ[Class-Based WFQ</br>Traffic classification]
        end
    end

graph LR
    subgraph "MPLS Operation"
        subgraph "Label Structure"
            Label["Label (20 bits)"]
            EXP["EXP (3 bits)QoS marking"]
            BoS["BoS (1 bit)Bottom of Stack"]
            TTL["TTL (8 bits)"]
        end

        subgraph "LSR Operations"
            Push["Label Push</br>Add label at ingress"]
            Swap["Label Swap</br>Forward through network"]
            Pop["Label Pop</br>Remove at egress"]
        end

        subgraph "MPLS Benefits"
            Performance["Improved Performance</br>Label lookup vs IP lookup"]
            TE["Traffic Engineering</br>Explicit path control"]
            VPN["VPN Services</br>Layer 3 VPNs"]
        end
    end

graph TB
    subgraph "SD-WAN Architecture"
        subgraph "Control Plane"
            Orchestrator[SD-WAN Orchestrator</br>Centralized management]
            Controller[SD-WAN Controller</br>Policy distribution]
        end

        subgraph "Data Plane"
            CPE1[SD-WAN CPE</br>Branch Office 1]
            CPE2[SD-WAN CPE</br>Branch Office 2]
            Gateway[SD-WAN Gateway</br>Data Center]
        end

        subgraph "Underlay Networks"
            MPLS[MPLS Network]
            Internet[Internet]
            LTE[4G/5G LTE]
        end

        Orchestrator --> Controller
        Controller --> CPE1
        Controller --> CPE2
        Controller --> Gateway

        CPE1 --> MPLS
        CPE1 --> Internet
        CPE2 --> LTE
        CPE2 --> Internet
    end

graph TB
    subgraph "IPv6 Transition Strategies"
        subgraph "Dual Stack"
            DualStack[Run IPv4 and IPv6</br>simultaneouslyGradual migration]
        end

        subgraph "Tunneling"
            Manual[Manual Tunnels</br>6in4 tunnels]
            Auto[Automatic Tunnels</br>6to4, Teredo]
            ISATAP[ISATAP</br>Intra-Site Automatic</br>Tunnel Addressing]
        end

        subgraph "Translation"
            NAT64[NAT64</br>IPv6 to IPv4 translation]
            DNS64[DNS64</br>AAAA to A record synthesis]
            XLAT[464XLAT</br>Mobile network translation]
        end
    end

sequenceDiagram
    participant IPv6 Host as IPv6 Host
    participant Tunnel 1 as Tunnel Endpoint 1
    participant IPv4 Net as IPv4 Network
    participant Tunnel 2 as Tunnel Endpoint 2
    participant IPv6 Net as IPv6 Network

    Note over IPv6Host, IPv6Net: 6in4 Tunnel Communication

    IPv6Host->>Tunnel1: IPv6 packet
    Note over Tunnel1: Encapsulate IPv6 in IPv4
    Tunnel1->>IPv4Net: IPv4 packet (Protocol 41)
    IPv4Net->>Tunnel2: Forward IPv4 packet
    Note over Tunnel2: Decapsulate IPv6 from IPv4
    Tunnel2->>IPv6Net: IPv6 packet

sequenceDiagram
    participant IPv6 Host as IPv6 Host
    participant Tunnel 1 as Tunnel Endpoint 1
    participant IPv4 Net as IPv4 Network
    participant Tunnel 2 as Tunnel Endpoint 2
    participant IPv6 Net as IPv6 Network

    Note over IPv6Host, IPv6Net: 6in4 Tunnel Communication

    IPv6Host->>Tunnel1: IPv6 packet
    Note over Tunnel1: Encapsulate IPv6 in IPv4
    Tunnel1->>IPv4Net: IPv4 packet (Protocol 41)
    IPv4Net->>Tunnel2: Forward IPv4 packet
    Note over Tunnel2: Decapsulate IPv6 from IPv4
    Tunnel2->>IPv6Net: IPv6 packet

sequenceDiagram
    participant Client as VPN Client
    participant Gateway as VPN Gateway
    participant Internal as Internal Server

    Note over Client, Internal: Site-to-Site VPN Setup

    Client->>Gateway: IKE Phase 1 (Main Mode)
    Note over Client, Gateway: Establish secure channelAuthenticate peers

    Client->>Gateway: IKE Phase 2 (Quick Mode)
    Note over Client, Gateway: Negotiate IPSec SAsExchange keys

    Client->>Gateway: ESP encrypted data
    Note over Gateway: Decrypt and forward
    Gateway->>Internal: Plain IP packet

    Internal->>Gateway: Response packet
    Note over Gateway: Encrypt response
    Gateway->>Client: ESP encrypted response

graph TB
    subgraph "Layer 3 Troubleshooting"
        subgraph "Connectivity Issues"
            NoRoute[No Route to Destination]
            WrongRoute[Incorrect Routing]
            RouteLoop[Routing Loop]
            MTUProblem[MTU Issues]
        end

        subgraph "Address Issues"
            IPConflict[IP Address Conflict]
            WrongSubnet[Wrong Subnet Mask]
            NATIssue[NAT Translation Problems]
            DHCPProblem[DHCP Assignment Issues]
        end

        subgraph "Performance Issues"
            Fragmentation[Excessive Fragmentation]
            QoSMisconfig[QoS Misconfiguration]
            Congestion[Network Congestion]
            SuboptimalRoute[Suboptimal Routing]
        end
    end

graph LR
    subgraph "Network Troubleshooting Tools"
        subgraph "Basic Tools"
            Ping[ping</br>Test connectivity]
            Tracert[traceroute</br>Path discovery]
            NSLookup[nslookup</br>DNS queries]
            ARP[arp</br>Address resolution]
        end

        subgraph "Advanced Tools"
            MTR[mtr</br>Continuous traceroute]
            Wireshark[Wireshark</br>Packet analysis]
            SNMP[SNMP</br>Network monitoring]
            NetStat[netstat</br>Connection status]
        end

        subgraph "Router Commands"
            ShowRoute[show ip route]
            ShowARP[show arp]
            ShowInterface[show interface]
            Debug[debug ip packet]
        end
    end

graph TB
    subgraph "Transport Layer Services"
        subgraph "Connection Management"
            Establish[Connection Establishment</br>Three-way handshake]
            Maintain[Connection Maintenance</br>Keep-alive mechanisms]
            Terminate[Connection Termination</br>Graceful close]
        end

        subgraph "Data Transfer"
            Segmentation[Data Segmentation</br>Breaking data into segments]
            Sequencing[Sequence Control</br>Ordered delivery]
            Acknowledgment[Acknowledgments</br>Confirm receipt]
        end

        subgraph "Error & Flow Control"
            ErrorDetection[Error Detection</br>Checksums]
            Retransmission[Retransmission</br>Lost segment recovery]
            FlowControl[Flow Control</br>Rate matching]
            CongestionControl[Congestion Control</br>Network load management]
        end
    end

packet-beta
title TCP Header Format
0-15: "Source Port"
16-31: "Destination Port"
32-63: "Sequence Number"
64-95: "Acknowledgment Number"
96-99: "Data Offset"
100-105: "Reserved"
106-111: "Flags"
112-127: "Window Size"
128-143: "Checksum"
144-159: "Urgent Pointer"
160-191: "Options"
192-223: "Data"

packet-beta
title UDP Header Format
0-15: "Source Port"
16-31: "Destination Port"
32-47: "Length"
48-63: "Checksum"
64-95: "Data"

graph LR
    subgraph "Transport Protocol Comparison"
        subgraph "TCP Characteristics"
            TCPReliable["Connection-oriented</br>Reliable delivery</br>Ordered data</br>Flow control</br>Congestion control</br>Large header (20+ bytes)"]
        end

        subgraph "UDP Characteristics"
            UDPSimple["Connectionless</br>Best-effort delivery</br>No ordering</br>No flow control</br>No congestion control</br>Small header (8 bytes)"]
        end

        subgraph "TCP Applications"
            WebTraffic[HTTP/HTTPS]
            Email[SMTP/POP3/IMAP]
            FileTransfer[FTP/SFTP]
            RemoteAccess[SSH/Telnet]
        end

        subgraph "UDP Applications"
            DNS[DNS Queries]
            DHCP[DHCP]
            Streaming[Video/Audio Streaming]
            Gaming[Online Gaming]
            SNMP[Network Management]
        end
    end

graph TB
    subgraph "Port Number Classification"
        subgraph "Well-Known Ports (0-1023)"
            System[System/Privileged Ports</br>Assigned by IANA</br>Require administrative privileges]
            Examples1[HTTP: 80</br>HTTPS: 443</br>FTP: 21</br>SSH: 22</br>Telnet: 23</br>SMTP: 25</br>DNS: 53]
        end

        subgraph "Registered Ports (1024-49151)"
            Registered[Registered by IANA</br>User applications</br>Can be used by any user]
            Examples2[MySQL: 3306</br>PostgreSQL: 5432</br>HTTP Alt: 8080</br>HTTPS Alt: 8443]
        end

        subgraph "Dynamic/Private Ports (49152-65535)"
            Dynamic[Ephemeral Ports</br>Temporary client ports</br>Automatically assigned]
            Examples3[Client connections</br>Temporary services</br>Outbound connections]
        end
    end

graph LR
    subgraph "Socket Identification"
        subgraph "Socket Components"
            Protocol[Protocol</br>TCP or UDP]
            SrcIP[Source IP Address</br>192.168.1.10]
            SrcPort[Source Port12345]
            DstIP[Destination IP</br>203.0.113.10]
            DstPort[Destination Port</br>80]
        end

        subgraph "Socket Examples"
            Socket1[TCP:192.168.1.10:12345↔203.0.113.10:80]
            Socket2[UDP:192.168.1.10:5353↔8.8.8.8:53]
        end

        subgraph "Multiplexing"
            Multiple[Multiple application</br>scan use same IP</br>with different ports]
        end
    end

sequenceDiagram
    participant Client
    participant Server

    Note over Client, Server: TCP Three-Way Handshake

    Client->>Server: SYN (seq=x)
    Note over Client: State: SYN_SENT
    Note over Server: State: SYN_RCVD

    Server->>Client: SYN-ACK (seq=y, ack=x+1)
    Note over Client: State: ESTABLISHED

    Client->>Server: ACK (seq=x+1, ack=y+1)
    Note over Server: State: ESTABLISHED

    Note over Client, Server: Connection establishedData transfer can begin

stateDiagram-v2
    [*] --> CLOSED
    CLOSED --> LISTEN : passive open
    CLOSED --> SYN_SENT : active open/SYN

    LISTEN --> SYN_RCVD : SYN/SYN+ACK
    SYN_SENT --> SYN_RCVD : SYN/SYN+ACK
    SYN_SENT --> ESTABLISHED : SYN+ACK/ACK
    SYN_RCVD --> ESTABLISHED : ACK

    ESTABLISHED --> FIN_WAIT_1 : close/FIN
    ESTABLISHED --> CLOSE_WAIT : FIN/ACK

    FIN_WAIT_1 --> FIN_WAIT_2 : ACK
    FIN_WAIT_1 --> CLOSING : FIN/ACK
    FIN_WAIT_2 --> TIME_WAIT : FIN/ACK

    CLOSE_WAIT --> LAST_ACK : close/FIN
    CLOSING --> TIME_WAIT : ACK
    LAST_ACK --> CLOSED : ACK
    TIME_WAIT --> CLOSED : timeout

sequenceDiagram
    participant Client
    participant Server

    Note over Client, Server: TCP Four-Way Handshake (Connection Termination)

    Client->>Server: FIN (seq=x)
    Note over Client: State: FIN_WAIT_1

    Server->>Client: ACK (ack=x+1)
    Note over Client: State: FIN_WAIT_2
    Note over Server: State: CLOSE_WAIT

    Note over Server: Application closes connection
    Server->>Client: FIN (seq=y)
    Note over Server: State: LAST_ACK

    Client->>Server: ACK (ack=y+1)
    Note over Client: State: TIME_WAIT
    Note over Server: State: CLOSED

    Note over Client: Wait 2MSL, then CLOSED

sequenceDiagram
    participant Sender
    participant Receiver

    Note over Sender, Receiver: TCP Reliable Data Transfer

    Sender->>Receiver: Seq=100, Len=500, Data
    Note over Receiver: Expecting seq=100</br>Received correctly
    Receiver->>Sender: ACK=600

    Sender->>Receiver: Seq=600, Len=300, Data
    Note over Receiver: Expecting seq=600</br>Received correctly
    Receiver->>Sender: ACK=900

    Sender->>Receiver: Seq=900, Len=400, Data
    Note over Receiver: Packet lost!

    Note over Sender: Timeout waiting for ACK
    Sender->>Receiver: Seq=900, Len=400, Data (Retransmission)
    Receiver->>Sender: ACK=1300

sequenceDiagram
    participant Sender
    participant Receiver

    Note over Sender, Receiver: TCP SACK Operation

    Sender->>Receiver: Seg 1 (100-199)
    Sender->>Receiver: Seg 2 (200-299) - LOST
    Sender->>Receiver: Seg 3 (300-399)
    Sender->>Receiver: Seg 4 (400-499)

    Note over Receiver: </br>Received: 100-199, 300-399, 400-499</br>Missing: 200-299

    Receiver->>Sender: ACK=200, SACK: 300-399, 400-499
    Note over Sender: Only retransmit missing segment

    Sender->>Receiver: Seg 2 (200-299) - Retransmission
    Receiver->>Sender: ACK=500

graph TB
    subgraph "TCP Timer Types"
        subgraph "Retransmission Timer"
            RTO[Retransmission Timeout</br>Wait for ACK</br>Exponential backoff]
        end

        subgraph "Persist Timer"
            Persist[Persist Timer</br>Zero window probing</br>Prevent deadlock]
        end

        subgraph "Keepalive Timer"
            Keepalive[Keepalive Timer</br>Detect broken connections</br>2 hours default]
        end

        subgraph "TIME_WAIT Timer"
            TimeWait[TIME_WAIT Timer</br>2 * MSL</br>Ensure connection cleanup]
        end
    end

sequenceDiagram
    participant Sender
    participant Receiver

    Note over Sender, Receiver: TCP Sliding Window (Window = 3 segments)

    Note over Receiver: Advertise window size = 3000 bytes
    Receiver->>Sender: Window = 3000

    par Send within window
        Sender->>Receiver: Seq=1000, Len=1000
        Sender->>Receiver: Seq=2000, Len=1000
        Sender->>Receiver: Seq=3000, Len=1000
    end

    Note over Sender: Window full, stop sending

    Receiver->>Sender: ACK=2000, Window=2000
    Note over Sender: Window slides, can send more

    Sender->>Receiver: Seq=4000, Len=1000
    Receiver->>Sender: ACK=5000, Window=3000

graph LR
    subgraph "TCP Window Scaling"
        subgraph "Problem"
            Original[Original TCP Window16-bit field</br>Max 65,535 bytes</br>Inadequate for high-speed links]
        end

        subgraph "Solution"
            Scaling[Window Scale Option</br>Multiply by 2^scale</br>Scale factor 0-14</br>Max window: 1GB]
        end

        subgraph "Example"
            Calculation[Window = 65,535</br>Scale = 3</br>Effective = 65,535 × 2³= 524,280 bytes]
        end
    end

graph TB
    subgraph "TCP Congestion Control"
        subgraph "Congestion Window States"
            SlowStart[Slow Start</br>Exponential growth</br>cwnd doubles each RTT]
            CongestionAvoidance[Congestion Avoidance</br>Linear growthcwnd += 1/cwnd each RTT]
            FastRecovery[Fast Recovery</br>Half cwnd</br>Retransmit lost segment]
        end

        subgraph "Congestion Detection"
            Timeout[Timeout</br>Severe congestioncwnd = 1]
            DuplicateACK[3 Duplicate ACKs</br>Mild congestion</br>Fast retransmit]
        end

        subgraph "Modern Algorithms"
            Reno[TCP Reno</br>Fast retransmit/recovery]
            NewReno[TCP New Reno</br>Improved recovery]
            CUBIC[TCP CUBIC</br>Cubic function growth]
            BBR[TCP BBR</br>Bandwidth-delay product]
        end
    end

gantt
    title TCP Congestion Window Evolution
    dateFormat X
    axisFormat %s

    section Slow Start
    cwnd=1    :0, 1
    cwnd=2    :1, 2
    cwnd=4    :2, 3
    cwnd=8    :3, 4

    section Congestion Avoidance
    cwnd=9    :4, 5
    cwnd=10   :5, 6
    cwnd=11   :6, 7
    cwnd=12   :7, 8

    section Congestion Event
    Timeout   :8, 9
    cwnd=1    :9, 10

    section Recovery
    cwnd=2    :10, 11
    cwnd=4    :11, 12
    cwnd=8    :12, 13

graph LR
    subgraph "Bandwidth-Delay Product Calculation"
        subgraph "Components"
            Bandwidth[Bandwidth</br>100 Mbps]
            Delay[Round-Trip Time</br>50 ms]
        end

        subgraph "Calculation"
            BDP[BDP = Bandwidth × RTT= 100 Mbps × 50 ms= 625,000 bytes= 610 KB]
        end

        subgraph "Meaning"
            Pipeline[Maximum data in flight</br>Optimal window size</br>Network pipe capacity]
        end
    end

graph TB
    subgraph "UDP Features"
        subgraph "Advantages"
            Low_Overhead[Low Overhead</br>8-byte header only]
            Fast[Fast Transmission</br>No connection setup]
            Broadcast[Broadcast Support</br>One-to-many communication]
            Realtime[Real-time Applications</br>No retransmission delays]
        end

        subgraph "Disadvantages"
            No_Reliability[No Reliability</br>Packets may be lost]
            No_Ordering[No Ordering</br>Packets may arrive out of order]
            No_Flow_Control[No Flow Control</br>Can overwhelm receiver]
            No_Congestion_Control[No Congestion Control</br>Can cause network congestion]
        end
    end

graph LR
    subgraph "UDP Applications"
        subgraph "Request-Response"
            DNS[DNS Queries</br>Single request/response</br>Timeout and retry at application]
            DHCP[DHCPNetwork configuration</br>Broadcast messages]
            SNMP[SNMPNetwork management</br>Simple operations]
        end

        subgraph "Real-time Applications"
            VoIP[VoIP/Video Calls</br>Low latency required</br>Some loss acceptable]
            Gaming[Online Gaming</br>Fast updates needed</br>Old data irrelevant]
            Streaming[Live Streaming</br>Real-time delivery</br>Buffering handles loss]
        end

        subgraph "Multicast Applications"
            IPTV[IPTV Broadcasting</br>One-to-many delivery]
            Discovery[Service Discovery</br>Network announcements]
            Updates[Software Updates</br>Efficient distribution]
        end
    end

sequenceDiagram
    participant Client
    participant Server

    Note over Client, Server: TCP Fast Open (TFO)

    Note over Client, Server: First Connection (Cookie Exchange)
    Client->>Server: SYN + TFO Cookie Request
    Server->>Client: SYN-ACK + TFO Cookie
    Client->>Server: ACK

    Note over Client, Server: Subsequent Connections
    Client->>Server: SYN + TFO Cookie + HTTP Request
    Note over Server: Validate cookie and process request
    Server->>Client: SYN-ACK + HTTP Response
    Client->>Server: ACK

    Note over Client, Server: Saves 1 RTT for application data

graph TB
    subgraph "Multipath TCP Architecture"
        subgraph "Application Layer"
            App[Single TCP Socket</br>Application sees normal TCP]
        end

        subgraph "MPTCP Layer"
            MPTCP[MPTCP Scheduler</br>Path management</br>Sequence mapping]
        end

        subgraph "Subflows"
            Path1[Subflow 1</br>WiFi Interface</br>192.168.1.0/24]
            Path2[Subflow 2</br>Cellular Interface</br>10.0.0.0/8]
            Path3[Subflow 3</br>Ethernet Interface</br>172.16.0.0/16]
        end

        App --> MPTCP
        MPTCP --> Path1
        MPTCP --> Path2
        MPTCP --> Path3
    end

graph LR
    subgraph "QUIC Protocol Stack"
        subgraph "Traditional Stack"
            HTTP2[HTTP/2]
            TLS[TLS 1.3]
            TCP[TCP]
            IP[IP]
        end

        subgraph "QUIC Stack"
            HTTP3[HTTP/3]
            QUIC[QUICTransport + TLS + HTTP/2 features]
            UDP[UDP]
            IP2[IP]
        end

        subgraph "QUIC Benefits"
            Faster[Faster Connection Setup</br>0-RTT resumption]
            Multiplexing[True Multiplexing</br>No head-of-line blocking]
            Migration[Connection Migration</br>IP address changes]
            Encryption[Built-in Encryption</br>Always secure]
        end
    end

sequenceDiagram
    participant Client
    participant Server

    Note over Client, Server: TLS 1.3 Handshake

    Client->>Server: ClientHello (cipher suites, random)
    Server->>Client: ServerHello (selected cipher, random)
    Server->>Client: Certificate, CertificateVerify
    Server->>Client: Finished

    Note over Client: Verify certificate
    Client->>Server: Certificate (if requested)
    Client->>Server: CertificateVerify (if cert sent)
    Client->>Server: Finished

    Note over Client, Server: Secure communication established
    Client->>Server: Application Data (encrypted)
    Server->>Client: Application Data (encrypted)

graph LR
    subgraph "DTLS for UDP"
        subgraph "Problem"
            UDPInsecure[UDP is connectionless</br>No built-in security</br>Packets can be lost/reordered]
        end

        subgraph "Solution"
            DTLS[DTLS ProtocolTLS over UDP</br>Handles packet loss</br>Preserves datagram semantics]
        end

        subgraph "Applications"
            VPN[VPN Protocols</br>OpenVPN, WireGuard]
            VoIP[Secure VoIPSRTP key exchange]
            IoT[IoT SecurityCoAP over DTLS]
        end
    end

graph TB
    subgraph "TCP Performance Tuning"
        subgraph "Buffer Sizes"
            SendBuffer[Send Buffer Size</br>net.core.wmem_max</br>Amount of data to buffer]
            RecvBuffer[Receive Buffer Size</br>net.core.rmem_max</br>Prevent packet drops]
            AutoTuning[Auto-tuning</br>Dynamic buffer sizing</br>Adapts to network conditions]
        end

        subgraph "Congestion Control"
            Algorithm[Congestion Algorithm</br>net.ipv4.tcp_congestion_control</br>bbr, cubic, reno]
            InitCwnd[Initial cwnd</br>net.ipv4.tcp_init_cwnd</br>Start with larger window]
        end

        subgraph "Connection Management"
            MaxConn[Max Connections</br>net.core.somaxconn</br>Listen queue size]
            KeepAlive[Keep-alive Settings</br>Detect dead connections]
            TimeWait[TIME_WAIT tuning</br>Faster port reuse]
        end
    end

graph TB
    subgraph "Transport Layer Load Balancing"
        subgraph "Layer 4 Load Balancing"
            L4LB[Layer 4 Load Balancer</br>IP + Port based</br>Fast forwarding</br>Connection persistence]
        end

        subgraph "Load Balancing Algorithms"
            RoundRobin[Round Robin</br>Equal distribution]
            WeightedRR[Weighted Round Robin</br>Capacity-based distribution]
            LeastConn[Least Connections</br>Load-based selection]
            IPHash[IP Hash</br>Session persistence]
        end

        subgraph "Health Checking"
            TCPCheck[TCP Connect Check</br>Port accessibility]
            HTTPCheck[HTTP Health Check</br>Application availability]
            CustomCheck[Custom Health Check</br>Application-specific]
        end
    end

graph TB
    subgraph "TCP Troubleshooting"
        subgraph "Connection Issues"
            ConnRefused[Connection Refused</br>Port not listening</br>Firewall blocking]
            ConnTimeout[Connection Timeout</br>Network unreachable</br>Long RTT]
            ConnReset[Connection Reset</br>Application error</br>Firewall RST]
        end

        subgraph "Performance Issues"
            SlowTransfer[Slow Data Transfer</br>Small window size</br>Network congestion</br>High RTT]
            HighRetrans[High Retransmissions</br>Packet loss</br>Network errors</br>Buffer overruns]
            WindowProbe[Window Probes</br>Receiver overwhelmed</br>Application not reading]
        end

        subgraph "Configuration Issues"
            MSS[MSS ProblemsPath MTU issues</br>Fragmentation]
            Scaling[Window Scaling</br>Disabled scaling</br>Scale factor mismatch]
            Congestion[Congestion Control</br>Inappropriate algorithm</br>Tuning needed]
        end
    end

graph LR
    subgraph "Transport Layer Diagnostics"
        subgraph "Basic Tools"
            Netstat[netstat</br>Connection states</br>Listening ports]
            SS[ss</br>Socket statistics</br>Modern netstat]
            TCPDump[tcp</br>dumpPacket capture</br>Protocol analysis]
        end

        subgraph "Performance Tools"
            Iperf[iperf3</br>Bandwidth testing</br>Throughput measurement]
            TCPTrace[tcptrace</br>TCP flow analysis</br>Performance metrics]
            Wireshark[Wireshark</br>Detailed protocol analysis</br>TCP stream following]
        end

        subgraph "System Monitoring"
            SysStats["/proc/net/tcp</br>Kernel TCP statistics"]
            SNMPStats[SNMP MIB</br>Network device counters]
            AppLogs[Application Logs</br>Error messages</br>Performance data]
        end
    end

graph TB
    A[Application Layer] --> B[Presentation Layer]
    B --> C[Session Layer]
    C --> D[Transport Layer]
    D --> E[Network Layer]
    E --> F[Data Link Layer]
    F --> G[Physical Layer]

    style C fill:#e1f5fe,stroke:#01579b,stroke-width:3px

    classDef highlight fill:#e8f5e8,stroke:#2e7d32,stroke-width:2px
    class C highlight

sequenceDiagram
    participant App1 as Application 1
    participant S1 as Session Layer 1
    participant S2 as Session Layer 2
    participant App2 as Application 2

    App1->>S1: Request Session
    S1->>S2: Session Request
    S2->>App2: Session Request
    App2->>S2: Accept Session
    S2->>S1: Session Accepted
    S1->>App1: Session Established

    Note over S1,S2: Session Active

    App1->>S1: Data
    S1->>S2: Data Transfer
    S2->>App2: Data

    App1->>S1: End Session
    S1->>S2: Session Termination
    S2->>App2: Session Ended

graph LR
    subgraph "Simplex Communication"
        A1[Sender] -->|One Direction| B1[Receiver]
    end

    subgraph "Half-Duplex Communication"
        A2[Device A] <-->|Takes Turns| B2[Device B]
    end

    subgraph "Full-Duplex Communication"
        A3[Device A] <-->|Simultaneous| B3[Device B]
        A3 -->|Send & Receive| B3
    end

timeline
    title Session Synchronization Example

    section Session Start
        Authentication : Session establishment
        Authorization  : Permission verification

    section Data Transfer
        Checkpoint 1   : Minor sync point
        Data Block 1   : File transfer begins
        Checkpoint 2   : Major sync point
        Data Block 2   : Continue transfer

    section Error Recovery
        Error Detected : Connection lost
        Rollback       : Return to Checkpoint 2
        Resume         : Continue from sync point

    section Session End
        Completion     : Transfer finished
        Termination    : Session closed

sequenceDiagram
    participant Client
    participant SMB as SMB Session
    participant Server

    Client->>SMB: Negotiate Protocol
    SMB->>Server: Protocol Negotiation
    Server->>SMB: Protocol Response
    SMB->>Client: Negotiation Complete

    Client->>SMB: Session Setup
    SMB->>Server: Authentication
    Server->>SMB: Auth Response
    SMB->>Client: Session Established

    Client->>SMB: Tree Connect
    SMB->>Server: Connect to Share
    Server->>SMB: Tree Connected
    SMB->>Client: Share Available

    loop File Operations
        Client->>SMB: File Request
        SMB->>Server: Process Request
        Server->>SMB: File Data
        SMB->>Client: File Response
    end

    Client->>SMB: Session Logoff
    SMB->>Server: Close Session
    Server->>SMB: Session Closed
    SMB->>Client: Logout Complete

graph TB
    subgraph "Authentication Methods"
        A[Password-based]
        B[Certificate-based]
        C[Token-based]
        D[Biometric]
        E[Multi-factor]
    end

    subgraph "Session Security"
        F[Session Tokens]
        G[Session Encryption]
        H[Session Timeout]
        I[Session Monitoring]
    end

    A --> F
    B --> G
    C --> H
    D --> I
    E --> F
    E --> G
    E --> H
    E --> I

graph TB
    A[Application Layer] --> B[Presentation Layer]
    B --> C[Session Layer]
    C --> D[Transport Layer]
    D --> E[Network Layer]
    E --> F[Data Link Layer]
    F --> G[Physical Layer]

    style B fill:#e8f5e8,stroke:#2e7d32,stroke-width:3px

    classDef highlight fill:#e8f5e8,stroke:#2e7d32,stroke-width:2px
    class B highlight

graph LR
    subgraph "Sender System"
        A1[Application Data] --> B1[ASCII Encoding]
        B1 --> C1[Little Endian]
    end

    subgraph "Presentation Layer"
        C1 --> D[Format Conversion]
        D --> E[Standard Format]
        E --> F[Target Format]
    end

    subgraph "Receiver System"
        F --> G1[Big Endian]
        G1 --> H1[EBCDIC Encoding]
        H1 --> I1[Application Data]
    end