3. Network Access

Network Access

• Physical Layer

  • Type

    • Wired

      • Copper cable

        • Unshielded Twisted-Pair (UTP)

          • Ethernet Straight-through

          • Ethernet Crossover

          • Rollover

        • Shielded Twisted-Pair (STP)

        • Coaxial

      • Fiber-optic cable

        • Single-mode (laser)

        • Multimode (LED)

    • Wireless

  • Connector

    • UTP

      • RJ45

    • Fiber

      • Straight-Tip (ST)

      • Subscriber Connector (SC)

      • Lucent Connector (LC)

  • Function

    • Encoding

    • Signaling

      • Asynchronous

      • Synchronous

    • Modulation

      • Frequency modulation (FM)

      • Amplitude modulation (AM)

      • Pulse-coded modulation (PCM)

• Measurement

  • Bandwidth (Mbps)

  • throughput

  • goodput

• Data Link Layer

  • Logical Link Control (LLC)

  • Media Access Control (MAC)

    • Contention-based access

      • Carrier sense multiple access with collision detection (CSMA/CD)

    • Controlled access

      • Carrier sense multiple access with collision avoidance (CSMA/CA)

  • Frame (have MAC address)

    • Header

    • Data

    • Trailer

  • Ethernet

    • 802.3

    • MAC / Physical Address

      • 48 bits

    • Address Resolution Protocol (ARP) 通过IP地址获取mac地址

      • resolve IPv4 to MAC

      • threat

        • ARP spoofing

  • Mode

    • Half Duplex

    • Full Duplex

  • Auto-MDIX

Data link layer is responsible for the exchange of frames between nodes over a physical network media. It controls media access control and performs error detection. Data link layer also accepts Layer 3 packets and packages them into data units called frames.