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A Mini faq on Modem Optimization

by Hari Nair

There is no reason for one to resign onself to a poor line connection, and the consequent reduction in modem throughput. Though in many places in India, the line quality leaves much to be desired, one can configure the modem and the software used, to gain the best under the existing circumstances.
We can look into this in a series of questions and answers. These mostly refer to the Windows environment.

The Mini faq

  • Q 1 : My modem does not detect the dial tone, hence does not dial.

    A : Many modems do not recognise the dial tone in India. To get around this, go to

    Control Panel -->Modems -->Properties --Connections and uncheck "Wait for Dial Tone before dialling". If this does not work, go to Control Panel > Modems -->Properties -->Connections -->Advanced and add atx3 in the extra settings box. If it still does not work, try atx1 instead of atx3

    Note: Modem commands begin AT or at, followed by the command strings. Make sure all entries are either in UPPER or lower case, not mixed.
  • Q 2 : My modem does not respond to AT commands. (Communication software does not recognise the modem)

    A : Ensure that the Com port assigned for the modem is the same as for the software. This problem is more common for the older non PNP modems. Also see the next question
  • Q 3 : My internal modem is on Com 3 and locks up when I try to dial.

    A : Com 3 and Com 1 (Where the mouse is commonly used) usually shares the same IRQ. Try changing the mouse to Com 2. Similarly, Com 2 and Com 4 share the same IRQ
  • Q 4: I can hear my modem dialling, but it does not connect. The dial tone continues after dialling.

    A : Try changing from Tone to Pulse dial

    Go to Control Panel -->Modems -->Dialling Properties. Perhaps your telephone exchange does not support Tone dialling.
  • Q 5 : My modem connects and works well, but sometimes I get disconnected unexpectedly or the modem stalls for a while.

    A : Someone may have picked up an extension handset on the same line. Another possibility is that you have call waiting enabled and someone has just dialled your number.
    Disable call waiting. (Ask your telephone exchange for details)
  • Q 6 : My modem seems to take a long time to connect to the Net.

    A : Give the following procedure a try.... Go to My Computer> Dial Up Networking, ( Right click on your connection, ) > Properties > Server Types. Ensure that only <Enable Software Compression> and <TCP/IP) are checked and other boxes are blank.
  • Q 7 : My modem hangs up frequently.

    A : Probably a line problem. Add the following string to the Extra Settings box (see Q 1) <s10=250>. This changes the settings of the s10 register in the modem which determines the time between carrier loss and modem hangup in 100milliseconds units. So a setting of 250 gives you 25 seconds after carrier loss before the modem hangs up. If you have added the string as mentioned in Q 1, your extra settings box will look like : atx3s10=250


After you are comfortable using the modem and can get a reasonably good connection, you can try optimising the Windows Registry for better modem performance. There are some free software on the Net which does the job, one of them being iSpeed by High Mountain Software.  Please bear in mind that tweaking the Windows Registry can be detrimental to performance unless you know what you are doing. Passage from the documentation of iSpeed:

iSpeed is a utility that will help to optimize your networking connections - both ethernet and modem (dialup networking). It does this by manipulating the Maximum Transmission Unit (MTU), Maximum Segment Size (MSS), Receive Window (RWIN), Time To Live (TTL), MTU Auto Discovert, and Black Hole detection. These items are relatively undocumented by Microsoft, and fine tuning them can have a dramatic effect on your throughput (both positive and negative).

Tips on installation of modems and lines:

  1. Generally, underground telephone cables from the exchange have less noise than overhead lines.
  2. If you can lay your hands on one, fit a spike suppressor onto the telephone cable. This can improve the signal quality and also protect your modem in case of lightening and heavy spikes.
  3. Avoid routing the telephone cable through areas of high electrical noise. (Close to domestic wiring, microwave ovens, induction heaters, electric motor driven appliances like Mixi etc. Avoid routing telephone lines along with cable TV lines.
  4. Avoid operation of appliances which can cause spikes and surges in the electrical line at the time of using the modem. Eg. Pumpsets, mixi, power tools etc.
  5. Digital telephone exchanges give superior data throughput with reduced line noise. If you have a choice, connect to a digital exchange. If your telephone connection gives you a clear connection with no line noises while carrying out a conversation, in all probability, it is also capable of transmitting data well.
  6. It is imperative you buy a high quality modem, as a poor modem will cost you much more in terms of phone bills. Buy a model which gives you good lineholding and data transfer from your area. Some modems work well from one telephone exchange, but poorly from another. If you live in an area where 56 kbps connections are not available, it is better to invest in a high quality 33.6 kbps modem, rather than a cheap 56 kbps modem. Remember, even where available, good connections on 56 kbps is subject to a many factors. Distance from the exchange, the number of D/A and A/D conversions, line noise etc. play a crucial role in the data throughput. If your ISP gives you only 33.6 kbps, a 56 kbps modem will not improve the data transfer. Also remember that you obtain 56 kbps only on downloads. Uploads still is limited to 33.6 kbps

Copyright 1999 Dr. Raj Mehta. All rights reserved.