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Introduction to Computer Networks The Network Interface Card Network interface cards (NICs) provide the interface between cables and computers. This lesson explores the many different types of cards and how their performance affects a network. The Role of the NIC • NICs, act as the physical interface or connection between the computer and the network cable. • The NIC contains the hardware and firmware (software routines stored in read-only memory, ROM) programming that implements the Logical Link Control and Media Access Control functions. The Role of the NIC • Prepare data from the computer for the network cable. • Send the data to another computer. • Control the flow of data between the computer and the cabling system. • Receive incoming data from the cable and translate it into bytes that can be understood by the computer's central processing unit (CPU). Network Address (MAC Address) • NIC also has to advertise its own location, or address, to the rest of the network to distinguish it from all the other cards on the network. • A committee of the Institute of Electrical and Electronics Engineers (IEEE) assigns blocks of addresses to each NIC manufacturer. The manufacturers hardwire these addresses into chips on the card by a process known as "burning" the address into the card. • Each NIC— and therefore each computer — has an unique address (MAC address) on a network. Configuration Options and Settings • Network interface cards often have configurable options that must be set in order for the card to function properly. • The following are examples of configurable options: • Interrupt (IRQ) • Base input/output (I/O) port address • Base memory address • Transceiver Configuration Options and Settings • Network interface cards often have configurable options that must be set in order for the card to function properly. • The following are examples of configurable options: • Interrupt (IRQ) • Base input/output (I/O) port address • Base memory address • Transceiver Selecting the Transceiver • 2(9) 3 4 5 6 7 8 10 11 12 13 14 15 EGA/VGA Adapter Available (Serial port [COM2, COM4] or bus mouse) COM1, COM3 Available (parallel port [LPT2] or sound card) Floppy-disk controller Parallel port (LPT1) Real-time clock Available Available Mouse (PS/2) Math coprocessor Hard-disk controller Available (secondary hard-disk controller) NIC, Bus, and Cable Compatibility • To ensure compatibility between the computer and the network, the NIC must: • Fit with the computer's internal structure (data bus architecture). • Have the right type of cable connector for the cabling. • Data Bus Architecture: • Industry Standard Architecture (ISA) • Extended Industry Standard Architecture (EISA) • Micro Channel Architecture • Peripheral Component Interconnect (PCI) NIC, Bus, and Cable Compatibility Network Cabling and Connectors • To select the appropriate NIC for your network, you first need to determine the type of cabling and cabling connectors it will have. • Some NICs have more than one interface connector. Network Performance (1) • You can speed up the movement of data through the card by adding the following enhancements: • Direct memory access (DMA): With this method, the computer moves data directly from the NIC's buffer to the computer's memory, without using the computer's microprocessor. • Shared adapter memory: In this method, the NIC contains RAM that it shares with the computer. The computer identifies this RAM as if it is actually installed in the computer. • Shared system memory: In this system, the NIC's processor selects a section of the computer's memory an Network Performance (2) • Bus mastering: the NIC takes temporary control of the computer's bus, bypasses the computer's CPU, and moves data directly to the computer's system memory. This speeds up operations by freeing the computer's processor to deal with other tasks. Bus mastering can improve network performance by 20 to 70 percent. • RAM buffering: Network traffic often travels too fast for most NICs to handle. RAM chips on the NIC serve as a buffer. When the card receives more data than it can process immediately, the RAM buffer holds some of the data until the NIC can process it. This speeds up the card's performance and helps keep the card from becoming a bottleneck. Network Performance (3) • On-board microprocessor With a microprocessor, the NIC does not need the computer to help process data. Most cards feature their own processors that speed network operations. Specialized NICs • Wireless NICs: These NICs can be used to create an allwireless LAN or to add wireless stations to a cabled LAN. • Usually, these NICs are used to communicate with a component called a wireless concentrator that acts as a transceiver to send and receive signals. • Fiber-Optic NICs: fiber-optic network cards allow direct connections to high-speed fiber-optic networks. • Remote-Boot PROMs: With remote-boot PROMs, diskless workstations can join the network when they start.