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Many devices are used to create networks. Every network except the simplest, single-segment coaxial networks uses one or more of these devices. Knowledge of the purpose of the devices discussed in this chapter is vital for the Network+ exam, as well as for the real world.
Hubs and switches provide a mechanism to connect devices to a network that is created with twisted-pair cabling. Switches offer a speed advantage over hubs because they can use full-duplex communications. They also create dedicated paths between devices, reducing the number of collisions that occur. Both hubs and switches are available in managed and nonmanaged varieties.
Bridges allow network traffic to be confined to certain network segments, thereby reducing the amount of network traffic. On Ethernet networks, an additional benefit is reduced collisions.
Routers are devices that connect networks and thereby create internetworks. Because routers use software-configured network addresses instead of hardware-defined MAC addresses, they can provide more functionality than bridges. Routers can be either dedicated hardware devices or implemented through software on server systems.
A gateway is a device that translates from one data format to another; it can be a hardware device or a software application. A CSU/DSU is an example of a gateway: CSUs/DSUs translate from the data format used on LANs to that used on WANs. A modem, which translates a signal from digital to analog so that it can be transmitted across a conventional phone line, is another example of a gateway.
WAPs are a relative newcomer to the networking equipment field. Wireless network clients use WAPs to connect to the network. WAPs also generally have a connection point that lets them connect to a wired network infrastructure.
NICs are the point of connectivity between devices and the network. NICs can be add-in expansion cards, PCMCIA devices for laptops, or devices that are built into the system board. When you install NICs, you must observe ESD best practices and also pay attention to hardware compatibility and bus compatibility issues.
In addition to NICs used to connect to a LAN, ISDN terminal adapters are sometimes used for remote connectivity.
When you're using clustering, a special system-area NIC is applied to network interfaces used to communicate clustering information between servers.
On a network, each NIC is identified by a unique MAC address. MAC addresses are assigned by the manufacturers that produce the devices, although the high-level assignment of addresses is managed and carried out by the IEEE.
If you get a chance to use all the hardware devices discussed in this chapter, count yourself lucky. Almost every environment will use some of them, but very few use them all.