1. Chapter 10 Supporting Modems

2. You Will Learn… How modems work and how to install them About communications software that modems use to communicate with the OS Guidelines for troubleshooting modems

3. All About Modems 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

4. External Modem

5. Modem Card

6. Modem Manufacturers

7. All About Modems 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)

8. AMR Slot

9. Modulation/Demodulation

10. RJ-11 Connection

11. How Modems Are Rated Modem properties affect performance and compatibility with other modems  Speed  Protocols  Data compression  Error correction Getting started: handshaking or training

12. Modem Speeds Measured in bits per second (bps) 56.6 Kbps most common

13. Viewing Modem Ratings

14. The Ceiling on Modem Speeds 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)

15. Modem Standards 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

16. Modem Transmission Standards continued…

17. Modem Transmission Standards continued…

18. Modem Transmission Standards

19. Data Compression on a Modem Performed by firmware housed on the modem Follows one of three protocols, all of which also perform error correction  MNP-5  CCITTV.42  V.42bis

20. Error Correction on a Modem 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

21. Key Points about the Handshaking Process 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

22. Serial Port Settings 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

24. Port Settings and Modem Settings 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

25. Port Settings and Modem Settings

28. Modem Features Caller ID Display readout Flash ROM Plug and Play for Windows Voice/data capability Auto-answer

29. Installing an Internal Modem 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

30. Setting Jumpers

31. Installing an External Modem 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

32. Configuring a Modem 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

34. The AT Command Set 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

35. Core AT Commands CommandDescription ATGets modem’s attention *70Disable call waiting +++Escape sequence OnGo Online A/Repeat last command InIdentification Zn &F Reset Factory default continued…

36. Core AT Commands CommandDescription AAnswer the phone DnDial HnHang up MnSpeaker control LnLoudness XnResponse

37. HyperTerminal Controlling a Modem Using AT Command

38. Interchange Between a Modem and a User

39. Other Examples of AT Commands

40. Using AT Commands to Help Diagnose Modem Problems

41. Troubleshooting Guidelines for Modems 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?

42. Potential Modem Problems 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 continued…

43. Potential Modem Problems 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 continued…

44. Potential Modem Problems 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

45. Troubleshooting Modems

46. Chapter Summary How modems work Installing and troubleshooting modems