Telecommunications & Networking

Telecommunications & Networking Unit Subtitle: Modems

Objectives • Describe the function of a modem • Identify considerations when choosing a modem • Identify different types of modems • Internal modem • External modem • K56 modem • Cable modem

Overview Continued • Describe how a modem works • List the steps to install/replace a modem • Identify testing and troubleshooting techniques for a modem

Modem Functions • A modem is a device that lets computers exchange information through telephone lines • Modem stands for MOdulator/DEModulator

Choosing a Modem • When choosing a modem the following features should be explored before buying: • Fax and Voice Capabilities - Most modem have the capability to send and receive faxes. You can create a document on your computer and fax it to another computer. • Speed – The speed will indicate the amount of information the modem can send and receive.

Choosing a Modem • Communications Program – A communications program is a software that manages the transmission of information between two modems. • Upgrade – Look at the upgrade capabilities of your modem. You may be able to upgrade your current modem, such as faster speed. The upgrade may be a program you install or a chip you add to the modem.

Different types of Modems • Most PCs have modems these days. They can be internal or external. • External modems have LEDs (Light Emitting Diode) that can be useful in seeing whether the modem is transmitting and receiving data • Internal modems don’t have this feature but it is often simulated in software. It is an expansion card that plugs into an expansion slot inside a computer.

Different types of Modems • The K56 Modem will pull more data faster from the Internet. This technology allows a person at a home or office PC to send data at normal analog modem rates but get information back nearly twice as fast. • The cable modem is a device that lets computers access the Internet using television cable.

Different types of Modems • Cable Modems are not really modems because they work with digital signals vs analog signals • DSL (digital subscriber line) and ISDN (integrated services digital network) modems send purely digital signals over telephone lines. They offer extremely fast Internet connections and we can expect them to eventually replace conventional modems.

How a Modem Works 1 2 Communications software sends a voltage along pin 20 of the serial port of which the modem is connected telling it that the PC is turned on. At the same time the PC detects a voltage from the modem on pin 6 telling it the modem is ready to receive data or instructions. A command is sent to the modem over line 2, the Transmit Data line and it tells your modem to go off hook-to open a connection with the phone line. The modem acknowledges the command by replying to the PC on line 3, the Receive Data line. 4 3 When your communications are established, your modem sends your PC a Carrier Detect (CD) on line 8. The signal tells the communications software that the modem is receiving a carrier signal, which is a steady tone of a certain frequency that later will be modulated to transmit data. When the modem on the other end of the phone connection – the remote modem- answers the call, your local modem sends out a hailing tone to let the remote modem know that it’s being called by another modem. The remote modem responds with a higher-pitched tone,

How a Modem Works Cont. 6 5 The two modems exchange information about how they’ll send data to each other, a process called a handshake. If the local and remote systems do not use the same settings during the handshake, either they’ll wind up sending characters that make no sense or they'll refuse to communicate at all. When the communication software wants to send data, it first sends data to line 4 which will ask the modem whether it is free to receive data from your PC. If your PC is busy doing something else, it will send a signal to the modem telling it to stop sending data until the PC finishes its other work. 8 7 At the other end of the phone line, the remote modem hears incoming data as a series of tones with different frequencies. It demodulates these tones back into digital signals and sends them to the receiving computer. When you tell your communications software to end a communications session, the software sends a command to the modem that causes it to break the phone connection.

Installing an External Modem • Before installing a modem, turn off the computer • If desired, connect the cable from your telephone to the back of the modem. This lets your telephone share the telephone line with your computer • Connect the telephone line to the back of the modem. Then connect the telephone line to the telephone jack on the wall.

Installing an External Modem • Connect the serial cable to the back of the modem. Then connect the serial cable to a serial port at the back of the computer. • Connect the power cable to the back of the modem. Then plug the power cable into an electrical outlet.

Installing an Internal Modem • An internal modem is an expansion card that plugs into an expansion slot inside the computer. • Place the expansion card in the slot. Press down firmly and evenly across the top of the card until it is securely inserted in the expansion slot. • Secure the expansion card to the computer case using a small screw.

Installing an Internal Modem • When you install an internal modem, your computer thinks another serial port has been added. Either adjust the jumpers on the modem so it uses the serial port or change the computer’s settings to disable the existing serial port.

Installing an Internal Modem • When you install an external or internal modem the computer may automatically detect and set up the modem, installing the necessary driver for you. If the computer does not automatically set up the modem for you, you will need to install the driver included with the modem.

Test and Troubleshoot • A modem can be tested to make sure it is communicating properly with a computer. Simply use a program which is included with your operating system to test the modem. Try to make a telephone call using the program. You will hear the modem making a dialing noise if it is communicating properly with computer.

Test and Troubleshoot • If your modem is having problems making a connection it may be features on your telephone line such as call waiting or voicemail that cause connection problems. The voicemail features changes the tone of the telephone line to indicate a message is waiting and it may prevent the modem from establishing a connection.

Test and Troubleshoot • The call waiting feature generate a beep to that indicates an incoming call and the beep may cause some modems to lose the connection. You should disable these features before using your modem. • If the modem is operating slowly, the problem may be with the quality of the telephone line. Contact your local telephone company.

Review • What is the definition of a modem? • List the four features that should be explored before buying a modem. • List some different types of modems. • Briefly explain how a modem works. • How is a modem tested? • List some troubleshooting techniques when a modem is interrupted or disconnected by the computer

Telecommunications & Networking