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Chapter 6. Network Hardware Components (... > 8. Given the name, transceivers pres... - Pg. 216

216 Networking Explained, Second Edition 6. What about a printer cable connector or a modem cable connector? Do they also operate at the physical layer? You are referring to DB (data bus) and DIN (Deutsche Industrie Norm, a German indus- trial standard) connectors. DB connectors serve as an interface between a computer and a peripheral device such as a printer or external modem. Several types of DB connectors exist and are distinguished by the number of "pins" they contain. Common types include DB-9 (a 9-pin serial or video interface), DB-15 (a 15-pin video interface), DB-25 (a 25- pin serial interface--RS-232--or parallel printer interface), and DB-37 (a 37-pin serial interface based on RS-422). (Illustrations of DB-9 and DB-25 connectors are shown in Figure 4.1.) DIN connectors are similar, but they are circular instead of rectangular. DIN connectors are typically used to connect a keyboard to a computer. 7. OK. Enough about connectors. Let's move on to transceivers. What are they? Transceivers are devices used in Ethernet/802.3 networks to connect nodes to the phys- ical medium. They serve as both the physical connection and the electrical interface between a node and the physical medium, enabling the node to communicate with the medium. 8. Given the name, transceivers presumably transmit and receive signals. Right? Precisely. Transceivers transmit and receive signals simultaneously. When a node sends data, the transmitting circuitry of the transceiver places the data bits on the medium. Simultaneously, the transceiver's receiving circuitry listens to the transmission. If what is heard is the same as what was sent, then everything is fine. If not, the transceiver presumes that an error has occurred and notifies the node of this condition. (This error is called a