CertiGuide to A+ (A+ 4 Real)  9  Chapter 13: Basic Networking Terminology       9  OSI Reference Model and Networking Protocols and Technologies            9  Layer 2 - Data Link Layer

MAC Addressing 1 Duplex

A Network Interface Card (NIC) is the device in the network that is necessary for communication among all computers in the network. It acts as the intermediary between the computers (through parallel connections) and the network medium (through serial connections). The NIC is inserted into the computer usually like a PCI card. Some manufacturers of the equipment integrate a network card in the motherboard.

The Network card requires an IRQ, an I/O address, and upper memory addresses for DOS and Windows 95/98. When selecting a network card, consider the following three factors:

• Type of network (e.g. Ethernet, Token Ring, FDDI, or other)
  
  
• Type of media (e.g. twisted-pair, coaxial, or fiber-optic cable)
  
  
• Type of system bus (e.g. PCI and ISA)

NICs perform important Layer 2 (data link layer) functions, such as the following:

• Logical link control - communicates with upper layers in the computer;
  
  
• Naming - provides a unique MAC address identifier;
  
  
• Framing - part of the encapsulation process, packaging the bits for transport;
  
  
• Media Access Control (MAC) - provides structured access to shared access media;
  
  
• Signaling - creates signals and interface with the media by using built-in transceivers.

The following example illustrates the process of how a NIC uses the MAC address: If one device wants to send data to another device, it can open a communication pathway to the other device by using its MAC address. When a source device sends data out on a network, the data carries the MAC address of its intended destination. The data propagates along the network media, the NIC in each device on the network checks to see if its MAC address matches the physical destination address carried by the data frame. If there is no match, the NIC discards the data frame. When the data passes its destination station, the NIC for that station makes a copy, takes the data out of the envelope and gives it to the computer.

MAC Addressing 1 Duplex