Passing around the signals

Passing around the signals

Here are descriptions of the networking terms you may encounter on the A+ exams. These devices play a key role in the performance of the network. You don't need to memorize them, but understand how they're used.

l Repeater: An electronic echo machine that has no other function other than to retransmit whatever it hears, literally in one ear and out the other. A repeater is used to extend the signal distance of the cable by regenerating the signal.

l Hub: Used to connect workstations and peripheral devices to the network. Each workstation or device is plugged in to one of the hub's ports. A hub receives a signal from one port and passes it on to all of its other ports and therefore to the device or workstation attached to the port. For example, if an eight-port hub receives a signal on port 4, it immediately passes the signal to ports 1, 2, 3, 5, 6, 7, and 8. Hubs are common to Ethernet networks.

l Bridge: Used to connect two different LANs or two similar network segments to make them operate as though they were one network. The bridge builds a bridging table of physical device addresses that is used to determine the correct bridging or MAC (Media Access Control) destination for a message. Because a bridge sends messages only to the part of the network on which the destination node exists, the overall effect of a bridge on a network is reduced network traffic and a reduction of message bottlenecks.

l Router: Routes data across networks using the logical or network address of a message to determine the path it should take to arrive at its destination.

Remember Too many workstations broadcasting too many messages to the whole network causes a broadcast storm. A router helps prevent broadcast storms by routing messages only to certain segments of the network.

l Switch: A switch is a device that segments a network. The primary difference between a hub and a switch is that a switch does not broadcast incoming messages to all ports, but instead sends it out only to the port on which the addressee workstation exists based o a MAC table created by listening to the nodes on the network.

l Gateway: A combination of hardware and software that enables two networks with different protocols to communicate with one another. A gateway is usually a dedicated server on a network because it typically requires large amounts of system resources.

Three different types of gateways exist:

¡ Address gateway: Connects networks with different directory structures and file management techniques.

¡ Protocol gateway: Connects networks that use different protocols. This is the most common type of gateway.

¡ Format gateway: Connects networks using different data format schemes, for example, one using the American Standard Code for Information Interchange (ASCII) and another using Extended Binary-Coded Decimal Interchange Code (EBCDIC).