Simplex, Half-Duplex, and Full-Duplex
Those who do not know about duplexing might assume that network transmissions travel in any direction through the media. In fact, specific dialog control modes determine the direction in which data can flow through the network media. The three dialog modes are simplex, half-duplex, and full-duplex.
The simplex mode allows only one-way communication through the media. A good example of simplex is a radio or television signal: There is only one transmitting device, and all other devices are receiving devices. A simplex dialog mode uses the full bandwidth of the media for transmitting the signal. The advantages of the simplex dialog mode can be seen in many applications, but networks are not among them.
EXAM TIP
Simplex Transmission A broadcast messages—that is, one that is sent to all nodes on the network—is a good example of a simplex transmission. Remember this for the exam.
Half-duplex allows each device to both transmit and receive, but only one of these processes can occur at one time. Many networks are configured for and support only half-duplex communication. A good example of half-duplex transmission is a modem that can either transmit or receive but not do both simultaneously. The transmitting device can use the entire bandwidth of the media.
EXAM TIP
Know the Difference Half-duplex allows two-way communication over a single channel. Full-duplex provides two-way communication by using different channels for sending and receiving signals. For the exam, know the difference.
If at all possible, the preferred method of communication on networks is full-duplex mode. Full-duplex allows devices to receive and transmit simultaneously. On a network, network cards that can use full-duplexing can double their transfer rates. For instance, a 100Mbps network card in full-duplex mode can operate at 200Mbps and therefore significantly increases the speed on the network. An example of full-duplex is a telephone conversation, where both parties are able to talk (send) and listen (receive) simultaneously.
IN THE FIELD: NETWORKING TERMINOLOGYThe term segment is used extensively in discussions of network media. However, what segment means appears to be open to some interpretation. Technically speaking, a segment is simply a section of a larger entity. In networking, a segment is a part of the network or a single length of cable. You can just as easily say that one computer is on the same segment as another as you can say that each computer is on its own segment. In this case, the cable type affects the definition of segment. The first statement is correct if you're using coaxial cable; the second is correct if you're using twisted-pair. |