The speed at which data may be transferred to and from a NIC is determined by many factors: the computer's I/O bus bandwidth and processor speed, design and quality of the NIC itself, computer's OS software, and type of network in use.

Different Networks, Different NICs

Each type of NIC is designed for a particular type of transmission medium (wire, radio signals, or optical fiber) and network transmission method. (We will discuss all of these a little later in this course.) Thus, a computer would need one type of NIC to send electrical signals over a copper-wired network, and a different NIC to send light pulses over a fiber optic system.

On a copper-wired network, a NIC varies the voltage level on the line in a precise pattern that represents data bits. On a fiber optic network, a NIC converts outgoing bits to flashes of light. On a wireless network, a NIC transmits bits by changing the pattern of a radio wave. In each case, the NIC also receives incoming signals as changing voltages, light flashes, or radio waves, and converts those signals into electrical bit patterns a computer can use.

Regardless of what physical medium a network uses, a NIC's job is to both generate and receive the signals that represent binary 1s and 0s. These signals must be precisely timed, thus the timing circuitry in sending and receiving NICs must be coordinated. The resulting sequence of bits is called a bit stream.

Each NIC is Unique

Each NIC contains a unique ID number which is built in at the factory. A central organization of computer manufacturers coordinates the assignment of these numbers to ensure that each ID is used by only one NIC anywhere in the world. Thus, in addition to physically transmitting and receiving signals, a NIC also uniquely identifies the device that contains it.

Each network node (computer, printer, or other device) must have a NIC to directly communicate with other nodes. However, if a resource, such as a printer, does not have a NIC, it can be indirectly connected to the network through a computer that does have a NIC. That computer can then be set to "share" its resource with other network nodes. All traffic to that printer would then pass through the computer, and not go to the printer directly.

In this way, a NIC is like a telephone. To "talk" directly with other nodes, a device must have its own communication equipment. However, if a device lacks that equipment, it can sometimes borrow it from another device, just as a person with a telephone may share it with a friend who does not have one.

   Activities

See the Activities and Extended Activities section in Unit 1 Lesson 2 in your textbook Introduction to Networking to test what you have learned so far.

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