Multi-Tech Systems MT2834BA Series manual Handshaking Details, Call Termination, Abort Timer

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Chapter 4 - Manual Dial and Automatic Answer

4.10 Handshaking Details

This section briefly explains what happens between two modems in a normal call. We are assuming that there are MultiModems at both the originating and at the answering end of the telephone line. (If other brands of modems are used with our modems, they will still communicate, but each manufacturer tends to use slightly different delay timings and sequences, and many of the brands vary in their LED designations.)

When a call is dialed from the originating modem, the called modem responds to the ringing by switching into Answer mode and by turning on its RI (Ring Indicator, RS-232C/V.24 Pin 22) signal as the rings are detected.

Note that in order for the called modem to be able to answer the call, it must have a high DTR (Data Terminal Ready) signal. This signal comes from the computer or terminal to which it is attached, on RS-232C Pin 20.

When the called modem answers the call, its OH (Off Hook) circuit comes on and the ringing stops. Two seconds after the call is answered, the called modem begins transmitting its answerback tone.

The originating modem, which has been off hook and waiting for the answerback tone, turns on its transmitter when it hears the tone. Then after a one second delay, the orignating modem's CD (Carrier Detect) comes on.

The called modem then responds to the originating modem by turning on its CD (Carrier Detect) signal, and the handshaking is completed.

Note: With the modem in Reliable or Auto-Reliable mode, some additional handshaking takes place. This is explained in Section 5.4.8.

4.11 Call Termination

There are a number of ways to terminate a call, or simply stated, hang up. They are:

1)Command Mode Control. To terminate a call by Command Mode, enter +++ATH then RETURN; or, send a BREAK signal followed by ATH and a RETURN.

2)DTR Control. If DTR (Data Terminal Ready) is turned off for 50 milliseconds or more, a disconnect occurs. This is probably the most common method used by computer systems at the automatic answer end of the line to cause the answering modem to disconnect after logging off procedures.

3)Loss of Carrier. After a data connection is established, the modem disconnects if a loss of carrier occurs for 700 milliseconds (0.7 seconds) or more. Note that one cause of carrier loss would be if one of the modems disconnect normally.

4)Abort Timer.

Answer Mode: When OH (Off Hook) comes on, the called modem starts a forty-five-second timer and waits for a carrier signal from the originating modem. If carrier is not detected within this period, the modem disconnects (hangs up) and is ready for another call.

Originate Mode: The abort timer functions the same as in answer mode, except that the timer begins after the modem has completed dialing, instead of when it first goes off hook. It is possible to change this forty-five second wait period to any other value (from 0 seconds up to 255 seconds), or to disable the timer completely by re-configuring S-Register S7 (see Chapter 6).

5)Inactivity Timer. Causes the modem to disconnect if no data is transmitted or received for a specified time. The timer is restored any time a character is passed through the serial port in either a send or receive state. This timer runs in both normal or reliable connections and is controlled by S-Register S30. The Inactivity Timer can be disabled by setting S30 to 0, which is the factory default setting.

Multi-Tech Systems, Inc. MT2834BA/BL Series User Guide

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Contents User Guide Patents User GuideRecord of Revisions Date Description TrademarksContents Registers Index 117Introduction and Description How To Use This Manual IntroductionModem Features 1 MT2834BA/BL Series Features Fax FeaturesTechnical Specifications Power Modem LED Indicators MT2834BA LED DisplayControls on PC Board Installation and Connection Safety Warnings What Is in Your Modem Package?Installation Installation ProcedureMultiModemBA Connections Installing PhoneTools, the Data Communications Software Is Your Modem Ready for Use?Software Configuration and Modem Basics Software Configuration Configuring Your SoftwareConfiguring Software for Your Modem PC Initialization StringsOther Parameters Changing Default ParametersConfiguring Software for Your Computer AT &F S0=0 &F9 &W0 CRSimple Operations Answer/Originate Voice/Data Toggle SwitchModem Basics Manual Dial and Automatic Answer Dialing/On-Line/Answering Manual Dial and Automatic AnswerAutomatic Leased Line Restoral Operation Manual Dial Backup Call TerminationDial Backup and Leased Line Restoral Dial-Up Operation Manual Call OriginationAutomatic Answering Manual AnsweringCall Termination Abort TimerHandshaking Details Command Mode Functional Modes AT Command EditingCommand Mode Summary of AT Commands Functional ModesStore Modem Configure Data Standard AT Result Codes Result CodesMulti-Tech Result Codes Dialing Commands Dialing Action CommandsPulse or Tone Dial P T Dial Modifier CommandsVoice/Data Dialing $VD Set Pulse Dial Ratios &PAutomatic Pauses in Dialing Return to Command Mode After Dial Command ExecutionReverse the Mode of Operation R Long Space Disconnect YCalling Card Detect Tones $ Quiet Answer @Number Linking NN Phone Number Memory CommandsStoring Phone Numbers D...N Listing Numbers Stored in Memory LModem Reset Z Configuration and Default Storage CommandsLoading Factory Defaults &F Synchronous Transmit Clock Select &X Async/Sync Mode Switching &MUnix Uucp Spoofing $SP Result Codes Enable/Disable and No Response Answer Q Command Response Result Code CommandsEcho Command Mode Characters E Result Codes Multi-Tech or Standard AT &QResult Codes Basic and Extended and Call Progress Selection Guard Tones Not Used in BAI/BLI Models &G Phone Line Conditioning CommandsEnable/Disable Trelis Coded Modulation #T Bell/V.21 ToneCleardown at Disconnect &CD Fallback Modes When On-Line #FEnable/Disable Lowspeed Fast Connect $FC Auto Speed Detect #AData Terminal Ready Control &D 7 RS-232C Interface Control CommandsCarrier Detect Control &C CTS Control &RDSR/CD Interaction Control &SF Data Set Ready Control &SCTS/RTS Interaction Control &RF Auto-Reliable Mode &E1 Error Correction CommandsNormal Mode &E0 Reliable Mode &E2Mode Select #L Auto-Reliable Buffering $ARetransmit Count $R Enable/Disable Auto Reliable Fallback Character $FError Correction/300bps $E Xon/Xoff Flow Control &E5 Flow Control CommandsHardware Flow Control &E4 Hewlett-Packard ENQ/ACK Pacing &E9 Xon/Xoff Pass-Through &E7Send Xon/Xoff Characters #X Maximum Block Size &BS Normal Mode Modem Flow Control On &E11Terminal/Computer Initiated Pacing &E13 Parity Selection #PEnq/Ack Pacing Commands Normal/Auto-Reliable/Reliable Mode CommandsXon/Xoff Pass-Through Commands Modem Baud Rate $MB Speed Conversion CommandsSpeed Conversion $BA Serial Port Baud Rate $SB Immediate Action Commands Listing On-Line Diagnostics L8 Off Hook HExiting Command Mode, Going Back On-Line O Line Probe CommandsForce Answer Mode a Registers Escape Code Character Number of Rings Until Modem AnswersRings Which Have Occurred Return CharacterBackspace Character Time for Carrier Abort TimerLine Feed Character Wait Time for Dial ToneCarrier Detect Response Time S10 Carrier Loss Disconnect Delay TimeS13 Remote Configuration Escape Character S11 Tone Dialing Tone Spacing and DurationS16 Callback Attempts S15 Callback Time DelayS19 MT2834BL Only Dial-Back Timer S17 Changing Break TimeS24 PBX/CBX Disconnect Drop Time for DSR/CTS/CD S26 Failed Password AttemptsS29 Local Inactivity Timer S25 DTR Dropout TimeS36 Time Between DTR Inactive and Modem Off-Hook S30 Inactivity TimerS32 Time Elapse for Escape Sequence S37 Time Between DTR Active and Modem On-HookS48 Program V.34bis Connect Speeds Examples of Reading Values Reading and Assigning S-Register ValuesExamples of Assigning Values AT Command and S-Register Summary Callback Security and Remote Configuration Callback Feature Description Callback Security and Remote ConfigurationRemote Configuration Description To change your Remote Configuration feature statusTo set parity of the password/message prompt AT#CBN0xxxxxxxxxxCRCallback Operational Sequence Procedures Remote Configuration Procedures Remote Configuration Operation ProceduresRemote Configuration and Callback Security AT Commands Remote Configuration/Callback Security S-Registers DIP-Switch Settings Dip-Switch Settings MT2834BA PC BoardDIP-Switch Option Settings Switch #4 AS/400 Mode Synchronous Mode/Leased Line/Dial-UP = Down Down Dip-Switch Settings Speaker Volume Control Recording Option Configurations Switch Function Position EffectDIP Switches #15-16 MT2834BL DIP Switches #13-14DIP Switches #15-16 MT2834BA Warranty, Service and Tech Support Multi-Tech Systems, Inc. Warranty & Repairs Policies Warranty, Service, and Technical SupportOnline Warranty Registration Repair Procedures for International DistributorsInternet Sites Replacement PartsTechnical Support Country TelephoneAppendixes Appendix a Upgrading Your Modem’s Firmware Upgrade OverviewAppendix a Upgrading Your Modem’s Firmware Download the Upgrade File Upgrade the Modem’s Firmware Modem Does Not Respond to Commands Appendix B TroubleshootingNone of the LEDs Light When the Modem Is On Appendix B TroubleshootingAppendix B Troubleshooting Modem Dials But Cannot Make a Connection File Transfer Is Slower Than It Should Be Modem Cannot Connect When AnsweringModem Disconnects While On-line Am Losing DataAm Getting Garbage Characters on the Monitor Command Values Description Appendix C AT Command SummaryAppendix C AT Command Summary DsNd Multi-Tech Systems, Inc. MT2834BA/BL Series User Guide 100$FCn MT2834BL Multi-Tech Systems, Inc. MT2834BA/BL Series User Guide 101$MBn Multi-Tech Systems, Inc. MT2834BA/BL Series User Guide 102$SBn Multi-Tech Systems, Inc. MT2834BA/BL Series User Guide 103Dial Tone Multi-Tech Systems, Inc. MT2834BA/BL Series User Guide 104Callback Security/Remote Configuration Command Summary Password Command Summary 25bis Commands25bis Operation Delayed and Forbidden NumbersAppendix D V.25bis Operation Appendix D V.25bis Operation25bis Set-Up and Initialization 25bis Mode AT Commands25bis DIP-Switches Multi-Tech Systems, Inc. MT2834BA/BL Series User Guide 108Change Serial Baud Rate CSP Command 25bis AT CommandsEnable/Disable V.25bis Mode $V Command 25bis Responses Result CodesListing Forbidden Phone Number RLF Command Dial Phone Number Provided CRN CommandListing Delayed Phone Numbers RLD Command Disregard or Connect to Incoming Calls DIC or CIC CommandITU V.25bis Country Specific Information Multi-Tech Systems, Inc. MT2834BA/BL Series User Guide 112 Appendix D V.25bis Operation BelgiumSingapore Appendix E MultiModemBA Cables Appendix E MultiModemBA/BL CablesFCC Part Appendix F Regulatory InformationFCC Part 68 Telecom Canadian Limitations Notice Multi-Tech Systems, Inc. MT2834BA/BL Series User Guide 115South African Notice Multi-Tech Systems, Inc. MT2834BA/BL Series User Guide 116Appendix G Weee Statement Index Multi-Tech Systems, Inc. MT2834BA/BL Series User Guide 11791-116 Multi-Tech Systems, Inc. MT2834BA/BL Series User Guide 118PBX/CBX Disconnect Drop Time for DSR/CTS/CD63 Multi-Tech Systems, Inc. MT2834BA/BL Series User Guide 119