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    Network Interface Cards (NICs)

    The physical interface between the computer and the media.
      One side of the NIC offers a port for the network media, while another side plugs into the computer system's bus.

    NIC Function Media Control
    Link and Flow Control

    Media Control

      Places data on and accepts data from the cable.
      Controls access to the communication medium.

    Link and Flow Control
    Controls the flow of data between the computer and the media.

    Links to other systems.

    With an internal transceiver, takes internal parallel data from the computer bus and converts it to serial data for the wire.

    Compatibility
    To ensure compatibility between the computer and the network, the NIC must:

    • Fit into the computer's bus architecture
    • Accommodate connection with the network medium
    PC System Bus Architecture

    ISA (Industry Standard Architecture)

    PC, XT, and AT.
    Began in '81, in '84 expanded width from 8 to 16 bits.
    Runs at 8.33 MHz.
    PCI 32 bit local bus. Developed by Compaq/Intel et al.
    Supports plug and play.
    Runs at 33 Mhz
    Future versions may be faster (64,66)
    EISA (Extended Industry Standard Architecture). Consortium backed 32 bit bus that runs at speeds up to 8.33 MHz.
    Backwards compatible with ISA.
    MicroChannel (MCA) Introduced in '87, electrically and physically incompatible with the ISA.
    Can be either 16 or 32 bit.
    Intelligent and proprietary.
    NIC Features
    • NICs may support multiple cable types.
    • Thicknet compatible boards use an external transceiver that plugs into an AUI port.
    • TWP and thin net compatible boards have internal transceivers.
    • 32 bit interfaces are faster than 16 bit interfaces.
    MAC (Media Access Control) Address
      Each NIC card contains a unique address.
    • This address is called a Media Access Control (MAC) address.
    • This level's functionality is defined by the IEEE's 802.3 standard.
    Three NIC Configuration Issues
    1. How does the NIC get the CPU's attention?
    2. How does a NIC communicate with the CPU?
    3. Where does the NIC store the information moving to and from the cable and computer?
    NIC Configuration Process May be accomplished with hardware or software.
    The process specifies: IRQs
    Base I/O port addresses
    Base memory address         Plug and Play attempts to automate this process.

    Interrupts (IRQs)

    Signals that let the CPU know that a device needs attention.
    IRQs are part of a system architecture. Consequently, their number is fixed. (15)
    IRQs have priorities Each device, that requires CPU attention, must be assigned a unique IRQ
    Diagnostic software, such as MSD.EXE can help determine which IRQs are available.
    Common IRQ Assignments 3 COM 2/COM 4
    4 COM 1/COM 3
    5 SoundBlaster or LPT2
    7 Parallel Port LPT 1     Depending on the system, IRQs 10,11, and 15 may be available (Sometimes other IRQs may also be available)

    Base I/O Port

    The memory address where the CPU and the NIC can leave messages for each other.
    Identified by a three digit hexadecimal number often expressed as a 16-bit range.
    For example, 200h or 210h.
    Base Memory Address Identifies a location in a computer's memory (RAM) that is used by the NIC as a buffer to store incoming and outgoing data frames.
    D8000 is conventional.
    Not required by all devices.
    Performance Features Shared memory. NICs buffers map directly to computer's memory.
    Direct Memory Access (DMA). NIC transfers data directly from its on-board buffers into the computers memory with requiring CPU attention.
    Bus Mastering. NIC can take control of the computer's memory independent of the CPU.
    Diskless Network Stations Remote boot PROMs
    Availability varies
    Requires open socket on the NIC.
    NIC Device Drivers Enables O/S to work with a particular device.
    Ensure communication between the O/S and the network adapter.

    Two standards apply to NIC Drivers:

    Both ODI and NDIS allows multiple protocols to be used simultaneously by a NIC.
    NIC Device Driver Standards ODI - - Open Data Link Interface
    NDIS -- Network Device Interface Specification
    Both standards allow multiple upper level protocols to be used simultaneously by a NIC