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Communication Software can be defined as the programs that supportcommunication protocols, control (drive) communication hardware, and theinterface with the operating system and the user that enable the exchangeof data and information. In order for this to take place, there must besome sort of a computer network. At each station of the network there mustbe:
A modem, modulator-demodulator,is a communications device that converts computer digital signals to phoneline analog signals and vice-versa. The speed at which this is done iscalled the baud rate. The two most popular modem rates are 28,800 and 56,600bits per second.
oversee the fast movement of data in and out of your PCthrough one of the COM ports. When the software is doing its job well,you aren’t even aware that you are using some particular software. Thisallows you to pay attention to the messages that magically appear on yourscreen from far-off places and people that you have never even met.
Often, you only become conscious of this software when it fails andthe messages turn into electronic garbage. This happens because the translationof the digital data of 0s and 1s in your computer to analog signals ofthe phone system is fragile.
The communications software must act as a translator between differentcommunication systems. There are many combinations of rules for groupingdata, communicating about when data is ready to be sent, and doing therequired checking. Your communication software must:
The good news is that once you have communication software set upproperly, you rarely have to be concerned with this setup again. Then,the barriers of distance are broken and the world is at your fingertips.
| When you select a communication host from your software menu, the softwaresends a set of initialization commands. These commands make sure that themodem is set properly. Your communication software sends a voltage to apin of the serial port and so along a wire in the cable connected to yourmodem. This voltage on this pin is called the Data Terminal Ready signal.It tells the modem the PC is turned on and ready to transmit data. The modem responds by sending a voltage back along a wire to a differentpin in the PC: this is the Data Set Ready signal. Now the PC knows thatthe modem is ready to receive data or instructions. Both these signalsmust be present before anything else can happen. |
So what happens...?
| You launch your communications software. The OS is responsiblefor handling your request to do this. |  |
| You select a communication host from your software menu.This involves the part of the software that interfaces with the OS andwith application software. |  |
| The device driver software sends a set of initializationcommands. The driver can then communicate with the modem using a standardset of commands that the modem is designed to recognize, sent through theTransmitted Data wire. |  |
| The device driver software then sends a command to the modemto open a connection with the phone line (go off hook). This is the sameas if you picked up the handset from your telephone. The modem hardwareand firmware is designed to detect standard dial tones, and will signalthe driver when a dial tone is heard. |  |
| Then the driver sends another command to tell the modemto issue tones (or pulses) to dial the specific phone number. The modemacknowledges the command by replying to the PC on the Receive Data line. |  |
| When the modem on the other end of the phone connection(remote modem) answers, your modem sends out a hailing tone to let theremote modem know that it is being contacted by another modem. The remotemodem responds with a higher-pitched tone. (If your modem has a speaker,you may be able to hear these tones.) A program in the modem itself (usuallyfirmware - that is, "burned" into a ROM chip) controls the hardware thatsends and receives tones. When communications are established, your modem sends your PC a CarrierDetect signal on a specific line. This signal tells the driver in the PCthat the modem is receiving a carrier signal. This carrier signal is asteady tone of a certain frequency, which is later changed. The tones arechanged to represent digital data according to the protocol in useby the modems. |  |
| The two modems exchange information about how they willsend the data to each other. This is called the handshake. The two modems,under control of the modems' firmware, must agree on several items, includingthe transfer speed; the number of bits contained in a data packet and howmany bits signal the beginning and the end of a packet. If any of your software’s settings do not work with the settings ofthe remote system, they may not communicate at all. If the two modems donot use the same protocol, they can wind up sending characters that makeno sense. |  |
| If the two modems complete the handshaking correctly, thedriver software sends a voltage along a line to the serial port. This isthe Request to Send, which asks if the modem is ready to receive data fromyour PC. At the other end of the phone line, the remote modem hears the incomingdata as a series of tones in varying frequencies. Using its firmware andspecialized hardware, it changes these tones back into digital signalsand sends them on to the receiving computer. In actuality, both computerscan send signals back and forth at the same time because the protocolsspecify standard tones, allowing the modems to distinguish between incomingand outgoing signals by their relative frequency (pitch). Modem protocols include error detection and recovery measures. If, atany time during the session, your modem does not receive a type of signalit recognizes, it asks the other modem to re-send the signal. If the errordiscovery protocols don't work, your modem notifies your driver software.The driver, then, uses its interface with the OS to display an error messageon your screen. |  |
| Most remote systems will require you to log on. This meansto identify yourself with a name and a password. Your password is not displayedon the screen so other people won't see and possibly steal your password.You can tell your OS interface software to store the phone, computer name,and password in a file so it can be used in future sessions to log on tothe same system automatically. |  |
| If the modem is receiving data that it wants to send toyour PC and the PC is busy, the PC will stop the Request to Send signal.This tells the modem to stop sending data until the PC finishes what itis doing and restarts the Request to Send signal. |  |
| If your modem is free to receive new data from your PC,it sends a Clear to Send signal to your modem driver. Your applicationsoftware (browser, email program, etc.) responds by sending the data tothe OS interface, which passes it to the device driver, and finally tothe modem. If the modem can not send data as fast as the PC sends it, the modemdrops the Clear to Send signal. This tells your modem driver software towait with any further data until the modem catches up. At this time, themodem renews the Clear to Send signal. The modem sends data received from the remote modem to your PC alongthe Receive Data line. Modem driver software converts the voltages to ASCIIcharacters, which it send to the Communications Interface software, andso to the application (browser, email, etc.) that you use. |  |
| When you tell your application or communications interfacesoftware to end a session, the interface sends another command to the driver,which passes it along the Transmitted Data line to the modem. This tellsthe modem to break the phone connection. |  |
| If the phone connection is broken by the remote modem, yourmodem will drop the Carrier Detect signal. This tells your driver to tellthe interface software that communications are broken. Your OS or applicationsoftware will then notify you that the carrier has been lost. |  |
Computers communicate with other computers through networks to exchangedata and share software and hardware resources. A local area network (LAN)is a group of computers that are linked or connected together in a line,star or ring network. A network allows user-to-user communication and transferof data files from one machine to any other on the network. It is madeup of several PCs physically connected to each other or to a server. Thislinking is accomplished by a variety of materials. Some of these materialsare twisted-pair cables, fiber optics, phone lines, TV cables, infraredlight and radio signals. The LAN relays information from one PC to another.The server stores and manages programs and data. The network can also includeprint servers that everyone on the LAN can use for printing.
A modem is not necessary for a local area network, but an operatingsystem interface software is. So, also, is the network protocol software,network connection circuits, device drivers, wires to hub for multi-connectorsand hub to hub or servers.
Wide area networks (WANs) span large areas. Computers can connect tothese networks to use facilities in another city or country. The largestWAN is the Internet. It is a global system of networked computers. TheInternet can be described as a group of local area networks connected togetheras a wide area network. A local area network or a standalone computer canconnect to the Internet via its communication software, modem and an Internetservice provider. The World Wide Web (WWW) is an information system thatcan be connected to through the Internet.
PPP - Point to Point Protocol –This protocol connectstwo TCP/IP computers over a phone line and modem. Point-to-Point Protocolis a newer way of connecting that allows your computer to have its own(temporary) Internet address. That way, it can send and receive packetsdirectly. Packets are a way of bundling data into a specificformat. To use PPP, your computer needs to have the correct communicationsoftware.
SLIP - Serial Line Internet Protocol – This older protocolconnects two TCP/IP computers over a phone line and modem in a similarfashion as PPP.
Direct Connection – This protocol allows you to connect toa remote computer directly without going through the Internet. Thisprotocol is commonly used in connecting to bulletin boards. A bulletinboard is a computer that accepts outside calls; hold messages and/or filesand then delivers them to appropriate users.
To set up a data communications link within Windows 95/98, thereare two phases –
Once your modem is installed, you will need to connect the telephonecord in the jack on the back of your modem labeled Line and the other endinto phone jack. Plug in your computer and turn it on. Your modem willturn on automatically when the computer is turned on.
At this point, Windows will detect the modem and display a New HardwareFound dialog box. Follow the instructions on your screen.
You will also set up Dial-Up Networking. This starts on the ControlPanel. The Control Panel is used for installing or changing settings forhardware and software. You can also set up or change settings for a networkhere. If you need to add any Windows components, click on the Control Paneland then double-click on Add/Remove Programs. Follow the instructions onyour screen.
Note: It is not necessary to use HyperTerminal for accessto the Internet. HyperTerminal enables you to connect to bulletin boards,host systems or text-based online services.
