| A | B |
|---|
| Serial lines that are established over serial cabling connect to | one of the standard RS-232 communication (COM) ports of the computer. |
| Serial transmission sends data | one bit at a time. |
| Analog or digital signals depend on changes in the | state (modulations) to represent the actual binary data. |
| Timing is very important in a network because the | receiving network device must know precisely when to measure the signal |
| The two techniques used to provide proper timing for serial transfers | Synchronous serial transmission, and Asynchronous serial transmission |
| a built-in timing mechanism coordinates the clocks of the sending and receiving devices | guaranteed state change synchronization |
| Guaranteed state change synchronization is the most commonly used | type of synchronous transmission method. |
| During Synchronous serial transmission data bits are | sent together with a synchronizing clock pulse |
| During Asynchronous serial transmission data bits are | sent without a synchronizing clock pulse. |
| Asynchronous serial transmission method uses a | start bit at the beginning of each message |
| During Asynchronous serial transmission method when the receiving device gets the start bit, it | can synchronize its internal clock with the sender clock |
| PC serial ports and most analog modems use the | asynchronous communication method |
| digital modems (also called Terminal Adapters) and LAN adapters use the | synchronous communication method |
| The industry standard for the serial line interface is the | Electronic Industries Association (EIA) RS-232C. |
| single-chip devices that perform all the functions that are necessary for serial transfers to occur | Universal Asynchronous Receiver/Transmitters (UART) |
| The synchronous devices are known as Universal Synchronous/Asynchronous Receiver/Transmitters (USART) and can handle | both synchronous and asynchronous transmissions. |
| The modem is an electronic device that is used for computer communications through | telephone lines. |
| The UARTs convert byte-oriented data to | serial bit streams. |
| Internal modems combine | a UART and a modem on board |
| The modems convert digital data to analog signals and | analog signals back to digital data |
| There are four main types of modems | Expansion cards, PCMCIA, External, & Built-in |
| the most common type of moden | Expansion cards |
| External modems plug into a | serial port (COM1 or COM2) on the back of the computer. |
| PCMCIA modems are a variation of modems that are designed for | easy installation in notebook computers. |
| An external modem uses the | IRQ and I/O address assigned to the serial port |
| To configure non plug-and-play internal modems, | jumpers may have to be set in order to select the IRQ and I/O addresses. |
| In most current modem types, a phone line is | plugged into a standard RJ-11 telephone jack. |
| Function of modem (AT) control command AT | Attention code that precedes all modern action commands |
| Function of modem (AT) control command ATDPxxxxxxx | Dial the phone number,xxxxxxx, using pulse dialing |
| Function of modem (AT) control command ATDTxxxxxxx | Dial the phone number,xxxxxxx, using tone dialing |
| Function of modem (AT) control command ATA | Answer the phone immediately |
| Function of modem (AT) control command ATHO | Hang up the phone immediately |
| Function of modem (AT) control command ATZ | Reset the modem to its power up setting |
| Function of modem (AT) control command ATF | Reset modem parameters and settings to the factory defaults |
| Function of modem (AT) control command AT+++ | Break signa., change from data mode to command mode |
| When computers use the public telephone system or network to communicate, it is called | Dial-Up Networking (DUN). |
| Modems communicate with each other using audio tone signals, which means | that they are able to duplicate the dialing characteristics of a telephone. |
| DUN creates a Protocol (PPP) connection between the two computers over a phone line which causes | the modem to act like a network interface card. |
| The two states the modem must operate in, in order to enable DUN: | Local command state, Online state |
| The modem is off –line, it receives commands and provides status information to the host computer to which the modem is installed. | Local command state |
| In this state, the modem is transferring data between the host machine and a remote computer via the telephone system | Online state |
| The three activities that occur during the Local command and Online states | Dialing, Data exchange, and Answering |
| a flurry of short events that take place between the two systems to establish the readiness of the two modems and their computers to engage in data exchange | handshaking sequence |
| The type of UART chip determines the | top speed at which devices can communicate using the port. |
