When A Modem Does Not Answer

 
DATE: August 20,1999 

SUMMARY: 

This document gives information on what to do when an analog modem rings but does not answer the telephone line. 

The Lucent PortMaster (TM) must provide a Data Terminal Ready (DTR) signal to the modem on pin 20 over  the straight through serial cable. DTR allows the modem to detect that  the PortMaster is connected to the modem . If the modem does not detect the PortMaster connected to it, the modem will not answer the incoming call. 

All PortMaster products keep DTR high all the time except when resetting the port.  DTR is dropped momentarily when the port resets. 

BEFORE YOU START: 

  1. Have a telephone available. Maintain a list of all the telephone numbers, ports they connect to on your PortMaster and the order that they roll over. It is recommended to keep list updated. 
  2. Have copy of the modem manual provided by your modem manufacturer. 
  3. Be familiar with the modem manufacturer website.
  4. Have an RS-232 analyzer (optional but useful, can be found at Radio Shack). 
  5. Spare serial cables, spare modems (different brands) if you have them. 

TROUBLESHOOTING: 

  1. Verify that  the modem is turned "ON".
  2. Verify that  the modem is firmly connected to the PortMaster with a straight through serial cable and that the cable.
  3. Verify that  the modem is connected to a telephone line.

    4. Verify this by plugging a telephone into the second telephone socket (RJ-11) on the modem. The telephone should ring when you call the modem. If it does not ring you may have the wrong telephone number. 

  4. Verify that the modem is receiving DTR from the PortMaster.

    5. How to verify DTR is being asserted. 

    • Most modems will illuminate a led labeled "TR" (Terminal Ready) when receiving DTR from the PortMaster. 
    • Get an RS-232 line analyzer which is a DB25 to DB25 connector with lights for various signal types. (Radio Shack carries them). This will allow you to see whether or not DTR is being sent over the serial cable to the modem. 

    If the DTR signal is not being sent to the modem: 

    • Verify that the port on the PortMaster has DTR "ON".

      • Command> set [port] dtr on | off   

      Example: Command> set s0 dtr on
DTR Idle for port S0 changed from on to on

      You may see the DTR changes from "OFF" to "ON" . 

    • Swapping ports.

      • Swap the serial cable, modem, telephone wire, telephone line assembly attached to the port that is not working with the serial cable, modem, telephone wire, telephone line assembly attached to a known good port. 
      - If the problem follows the modem there is a problem with either the serial cable, modem, telephone wire or telephone line. 
      - If the problem follows the port contact Lucent Technical Support @1800-458-9966.  The PortMaster may have a defective port.

     

  5. Make sure the modem is programmed to answer on the first ring. 

    6. Most modems will answer on the first ring when programmed with the  AT command shown in the example below. 

    The S0 register designates how many rings the modem will wait before the modem answers the telephone line. S0=0 tells the modem to "never"  answer the telephone. You can automatically program your modem to do this with a modem table. 
    Syntax: n= How many rings to wait before answering the telephone.  

    ATS0=n

    Example:  

    Command> ats0=1
OK

    Displaying the Modem configuration 

    Most modems  have AT commands that display the current configuration as well as pre-programmed factory settings. These commands are usually AT&V.  USRobotics modems use ATI4. 

    Example:  

    AT&V
ACTIVE PROFILE:            DTE:115200 8N1        DCE:
B16 B2 E1 L2 M1 N1 P Q0 V1 W0 X4 Y0 &A0 &B1 &C1
&D3 &G0 &K3 &Q5 &R0 &S0 &U0 &Y0
S00:001 S01:000 S02:043 S03:013 S04:010 S05:008
S06:002 S07:050 S08:002 S09:006 S10:014 S11:095 S12:050
S25:005 S26:001 S30:000 S36:007 S37:000 S38:020 S43:000
S46:002 S48:007 S63:000 S82:128 S86:000 S95:000
S101:000 S108:001 S109:4095 S110:006          
STORED PROFILE 0:
B16 B2 E1 L2 M1 N1 P Q0 V1 W0 X4 Y0 &A0 &B1 &C1
&D3 &G0 &K3 &Q5 &R0 &S0 &U0
S00:000 S02:043 S06:002 S07:050 S08:002 S09:006 S10:014
S11:095 S12:050 S25:005 S26:001 S30:000 S36:007 S37:000
S38:020 S46:002 S48:007 S63:000 S82:128 S95:000
S101:000 S108:001 S109:4095 S110:006
STORED PROFILE 1:
B16 B2 E1 L2 M1 N1 P Q0 V1 W0 X4 Y0 &A0 &B1 &C1
&D2 &G0 &K3 &Q5 &R0 &S0 &U0 S00:000
S02:043 S06:002 S07:050 S08:002 S09:006 S10:014 S11:095
S12:050 S25:005 S26:001 S30:000 S36:007 S37:000 S38:020
S46:002 S48:007 S63:000 S82:128 S95:000 S101:000
S108:001 S109:4095 S110:006
TELEPHONE NUMBERS:
&Z0=                                   &Z1=
&Z2=                                   &Z3=
OK
  6. Some modems have dip switches that can override the Auto Answer settings on a modem. Refer to the modem manual provided by the modem manufacturer for details on your modem.

    7. For example:  On many USRobotics modems dip switch five will override the programmable Auto Answer setting. 

  7. If you have active telephone lines in your 1 or 1 that are not attached to anything you will get ring-no-answer.

    8. An active telephone line with nothing attached will cause a line to ring continuously without answering.. 

    Most telephone line roll-overs and 1 used in modem pools will pass over a line that rings busy. If you have a telephone line, but no modem to plug into it 

    Information on how to busy a modem: 

    • Attach any telephone to the line and leave it off hook. 
    •  An adapter can be made to busy out a line with an RJ-11 jack and a LED. The LED provides  enough resistance to busy out the line. (Everything you need can be found at Radio Shack).
    • Assuming your modem is working you can use the ATH1 command to take your modem "Off Hook" which will cause the line to return a busy signal. You can automate this with the modem table.

     

  8. If the telephone block or telephone jack is found to reversed or incorrectly wired on the customer premises this will cause a ring-no-answer condition on the line.
  9. The line is not '0'
  10. If the telephone company does not have the line number properly wired and translated in their central office this will cause a ring-no-answer condition.  Always verify that you are dialing the correct number.
  11. Defective modems

    12. Modems may be defective or the modem code in the modem may have a bug that could result in the modem failing to answer the telephone line. 
     

  12. When you dial into a USRobotics external 28.8 or 33.3 Sportster modem, the modem generates tone, but  fails to give the telephone line an off hook condition

    13. The RJ11 cable from the wall jack may be  plugged into the wrong modem jack. Verify that it is plugged into the OUTER jack. The INNER jack is only for an optional telephone. The only label is on the bottom of the case. No visible label on the back may lead to the assumption that the two RJ11 jacks are equivalent, they are not. 
     

  13. On some modems if you have the telephone line plugged into the jack (RJ-11) on the modem meant for a telephone you will get ring-no-answers.