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- How modems work and how to install them
- About communications software that modems use to communicate with the OS
- Guidelines for troubleshooting modems
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- Devices used by PCs to communicate over phone lines
- Can be an external device connected to a USB or serial port
- Can be a modem card, which can use either an ISA or PCI slot
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- Some motherboards have a small expansion slot called an audio/modem
riser (AMR) or a communication and networking riser (CNR) slot
- Are both hardware and firmware
- MOdulation/DEModulation
- Convert digital data to analog, then back to digital
- Provide an RJ-11 connection
- Must be able to both receive and transmit data (full-duplex)
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- Modem properties affect performance and compatibility with other modems
- Speed
- Protocols
- Data compression
- Error correction
- Getting started: handshaking or training
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- Measured in bits per second (bps)
- 56.6 Kbps most common
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- Analog phone lines were designed for transmission of human voice;
affects ability to attain high transmission speeds for data
- Method used when an analog signal is converted to a digital signal
- Noise (line disturbance)
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- Written by the CCITT, now called the ITU (International
Telecommunication Union)
- The more standards a modem supports, the better it can communicate with
a variety of other modems
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- Performed by firmware housed on the modem
- Follows one of three protocols, all of which also perform error
correction
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- Performed by firmware housed on the modem
- Works by breaking data up into small packets (frames)
- Sending modem performs calculations on a frame, then sums calculations
into a checksum
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- Answering modem sends a guard tone so connection is not broken
- Carrier is established
- Equalization stage
- Modem speed (line speed) is set between modems
- Modem speakers turn off
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- Serial ports that modems use are controlled by UART logic
- UART-to-UART communication is controlled by port settings
- Five protocols control these port settings
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- Communication between DTE and DCE (computer and modem) is controlled by
port settings
- Communication between two DCE devices (two modems) is controlled by
modem settings
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- Caller ID
- Display readout
- Flash ROM
- Plug and Play for Windows
- Voice/data capability
- Auto-answer
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- Read documentation
- Determine available serial port
- Set jumpers or DIP switches on modem card
- Turn off computer; remove cover; mount the card
- Replace cover
- Plug phone line from house into line jack on modem
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- Connect high-quality cable to modem and to the serial or USB port
- Plug electrical cord from modem into an 110V AC outlet
- Plug phone line from house into line jack on modem
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- Start-Settings-Control Panel-Modem-Properties in Windows 98
- Set modem speed at highest value in drop-down list
- Set port protocol at “8, No, and 1” (represents 8 bits, no parity, 1
stop bit)
- Use hardware flow control
- Create a Dial-Up Networking connection if desired
- Test the modem with HyperTerminal
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- Hayes language for modem control
- Each command line is prefaced with AT for ATtention
- A modem that uses this language stays in command mode any time that it
is not connected to another modem
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- What works and what doesn’t work?
- What has worked in the past that doesn’t work now?
- What has changed since things last worked?
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- Modem does not respond
- Modem says there is no dial tone, but you can hear it
- Modem dials, then says other end is busy, even when you know it is not
- Sending modem and receiving modem take a long time to negotiate the
connection
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- During connection, it sounds as if handshaking starts all over again
- File transfers are slow
- Modem loses connection at odd times or is slow
- Modem drops connection and gives NO CARRIER message
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- Whenever weather is bad, disconnects often
- Whenever large files are downloaded, some data is lost
- Connection fails whenever large files are uploaded or downloaded
- Nothing but garbage across the connection
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- How modems work
- Installing and troubleshooting modems
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