CertiGuide to Network+  9  Chapter 0011:  Network Hardware       9  III  Layer 1 – Physical Layer

III  Layer 1 – Physical Layer 1 Hub

As briefly noted earlier, the NIC is the interface between the PC and the network cable that connects the PC to the rest of the network. Data is sent from the PC’s CPU and memory, through the PC’s bus, to the NIC. From the NIC, the data is sent out to the network cable. Like most PC expansion cards, the NIC plugs into the PC’s bus, and includes connectors that are exposed on the back of the PC, where the network cable is attached. Depending on the network cable topology, the NIC may have connectors to attach twisted pair, fiber optic, or coax cable. A NIC has different interfaces at the expansion card side and the network connector input/output on the back of the card.

To successfully complete the NETWORK+ test, you must demonstrate understanding of the different PC bus types to which a NIC might be connected, such as ISA (Industry Standard Architecture), EISA (Extended Industry Standard Architecture) and PCI (Peripheral Connect Interface) for typical desktop computers. For notebook computers, the NIC may be connected via PCMCIA or USB (Universal Serial Bus).

Note that the network connector input/output might not be a physical connector in the case of wireless networking – it may merely be an antenna or other sort of sensor.

Troubleshooting questions may include your ability to successfully demonstrate knowledge of IRQ and memory addresses, as well as why sometimes Plug ‘n Play becomes Plug ‘n Pray. (To review an A+ topic, Plug ‘n Play is the hardware standard that allows for devices to identify themselves to the OS, and auto-configure their IRQ, DMA and memory address settings without user input. When it works, it greatly simplifies life.

When it fails, you could be playing a game of trial-and-error with different configuration settings, as in the old PC days, for hours.)

When describing the OSI model, we explained that devices are identified via unique physical addresses associated with each piece of hardware, called the MAC address. In almost all cases, the manufacturer pre-determines the unique ID that each card will have. If every manufacturer is assigning serial numbers to the NIC’s they manufacture, how can we be sure that no two NIC’s have the same serial numbers?

The first numbers in the ID comprise the manufacturer’s ID. These numbers are followed by a unique set of number for that particular card. The combination creates a unique ID that is used at the 2^nd layer in the OSI model, called the Data Link layer.

Above is a picture of a typical PC NIC. The back of the card includes jacks, which network cables connect to. You can tell by looking at the jack, the approximate media required connecting the NIC to the network, but you cannot always tell precisely. For example, in the above illustration, we see a 10xBaseTx RJ-45 connector, but we do not know which category of cable is required. To determine the precise capabilities of the card, see its documentation. There are different types of NICs for different networking technologies (Token Ring, Ethernet, etc.) and different media types (10Base2, fiber, 10nBaseTx, etc.).

III  Layer 1 – Physical Layer 1 Hub