Network+ (N10-009) Objective 1.0: Networking Fundamentals

Network Models Overview
Conceptual frameworks for understanding network communications

OSI Model: 7 Layers

The Open Systems Interconnection model is a conceptual framework that standardizes the functions of a communication system into seven abstraction layers. It's primarily used for understanding network operations and troubleshooting.

Mnemonic: Please Do Not Throw Sausage Pizza Away (Physical, Data Link, Network, Transport, Session, Presentation, Application)
Layer 1: PhysicalEthernet (IEEE 802.3), USB...

Responsible for the physical connection between devices and the transmission of raw bit streams.

Key Responsibilities:

  • Physical topology and connections
  • Bit-level transmission
  • Cable and connector specifications
  • Signaling and data encoding
  • Hardware specifications

Examples:

  • Cables (CAT5e, CAT6, fiber optic)
  • Hubs
  • Repeaters
  • Transceivers
  • NIC adapters
Exam Tip: Know the common cable types, connectors, and hardware associated with this layer. Understand the difference between digital and analog signals.
Layer 2: Data LinkEthernet (IEEE 802.3), PPP...

Provides node-to-node data transfer and handles error correction from the physical layer.

Key Responsibilities:

  • MAC addressing
  • Framing
  • Error detection and correction
  • Flow control
  • Media access control

Examples:

  • Switches
  • Bridges
  • NICs
  • MAC addresses
  • Ethernet frames
Exam Tip: Focus on MAC addressing, framing concepts, and the difference between switches and bridges. Understand the IEEE 802 standards, especially 802.3 (Ethernet) and 802.11 (Wi-Fi).
Layer 3: NetworkIP, ICMP...

Handles packet routing and logical addressing for data transmission between networks.

Key Responsibilities:

  • Logical addressing (IP)
  • Routing
  • Path determination
  • Packet switching
  • Subnet traffic handling

Examples:

  • Routers
  • Layer 3 switches
  • IP addresses
  • Routing tables
  • Routing protocols
Exam Tip: Understand IP addressing, subnetting, and the difference between routing protocols like RIP, OSPF, and BGP. Know how ARP works to resolve IP addresses to MAC addresses.
Layer 4: TransportTCP, UDP...

Provides reliable data transfer, segmentation, flow control, and error recovery.

Key Responsibilities:

  • End-to-end connections
  • Segmentation and reassembly
  • Connection management
  • Flow control
  • Error detection and recovery

Examples:

  • TCP segments
  • UDP datagrams
  • Ports
  • Sockets
  • Windowing and buffering
Exam Tip: Compare TCP and UDP thoroughly. Understand port numbers, the three-way handshake, windowing, and connection-oriented vs connectionless communication.
Layer 5: SessionNetBIOS, RPC...

Establishes, manages, and terminates sessions between applications.

Key Responsibilities:

  • Session establishment, maintenance, and termination
  • Session synchronization
  • Dialogue control
  • Checkpointing

Examples:

  • Session management in remote access
  • Authentication mechanisms
  • Dialog control (simplex, half-duplex, full-duplex)
  • SQL database connections
Exam Tip: This layer is often minimized in exam coverage, but understand its role in establishing and managing communication sessions between applications.
Layer 6: PresentationSSL/TLS, MIME...

Formats data for the application layer and handles encryption, compression, and translation.

Key Responsibilities:

  • Data translation
  • Encryption/decryption
  • Compression/decompression
  • Character encoding
  • Data format conversion

Examples:

  • Data encryption
  • File format conversion
  • Character set translation
  • MIME encoding
  • Media formatting
Exam Tip: Understand the role of encryption protocols like SSL/TLS. Focus on data formatting and translation functions.
Layer 7: ApplicationHTTP/HTTPS, FTP...

Provides network services directly to end-user applications.

Key Responsibilities:

  • Network applications
  • Service advertisement
  • API for application access to network
  • Resource sharing
  • Remote file access

Examples:

  • Web browsers
  • Email clients
  • File transfer applications
  • Remote login services
  • Network management tools
Exam Tip: Know the common application protocols, their functions, and default port numbers. Understand client-server and peer-to-peer models.
OSI vs TCP/IP Model Comparison
Understanding how the two models relate to each other

OSI Model

  • 7. Application - User interfaces, data presentation
  • 6. Presentation - Data formatting, encryption
  • 5. Session - Session establishment, management
  • 4. Transport - End-to-end connections, reliability
  • 3. Network - Logical addressing, routing
  • 2. Data Link - Physical addressing, access control
  • 1. Physical - Binary transmission, hardware

TCP/IP Model

  • 4. Application - Network applications, services
    Combines OSI Layers 5-7
  • 3. Transport - End-to-end connections (TCP/UDP)
  • 2. Internet - Logical addressing, routing (IP)
  • 1. Network Interface - Hardware addressing, media access
    Combines OSI Layers 1-2

Key Differences

  • OSI model is conceptual; TCP/IP is the implemented standard
  • OSI has 7 layers; TCP/IP has 4 layers
  • TCP/IP combines the top 3 OSI layers into one Application layer
  • TCP/IP combines the bottom 2 OSI layers into Network Interface
  • OSI separates network functions more distinctly
  • TCP/IP is more protocol-specific; OSI is more general

Practical Applications

  • Troubleshooting: OSI model helps identify where an issue might be occurring
  • Network Design: Both models guide implementation decisions
  • Protocol Development: Ensures protocols fulfill specific layer functions
  • Security: Helps implement security at appropriate layers
  • Communication: Provides common terminology for network professionals