Telephony Common Questions, Part 2
  By Todd Ogasawara

The Telephony Forum 56K Modem FAQ/Q&A

These questions are some of the most frequently asked questions (FAQ) found on the MSN Computing Central Telephony Forum's Modem Discussion Newsgroup. Please join the discussion about 56K modems, fax modems, and voice modems in that newsgroup.

What is the 56K modem protocol standard?

The 56K modem protocol standard is named V.90. You may see 56K modems that support the older proprietary K56flex (Lucent/Rockwell) or x2 (3Com/USRobotics) protocols. V.90 replaces both K56flex and x2. You should always look for a modem that supports V.90.

What do the V.32, V.32bis, V.34, and V.90 protocol designations mean?


A family of 2-wire, duplex modems operating at data signaling rates of up to 9,600 bit/s for use on the general switched telephone network and on leased telephone-type circuits

V.32 bis
A duplex modem operating at data signaling rates of up to 14,400 bit/s for use on the general switched telephone network and on leased point-to-point 2-wire telephone-type circuits
A modem operating at data signaling rates of up to 33,600 bit/s for use on the general switched telephone network and on leased point-to-point 2-wire telephone-type circuits
A modem designed for connections which are digital at one end and have only one digital-to-analogue conversion. Download speeds of up to 56,000 bits per second (bit/s) are possible, depending on telephone line conditions, with upload speeds of up to 33,600 bit/s. The International Telecommunication Union Telecommunication Standardization Sector (ITU-T) announced the V.90 56K modem designation in a Feb. 7, 1998, press release, when the technical specification was announced. The V.90 protocol was formally adopted by the ITU-T on September 15, 1998.

I cannot connect to my Internet Service Provider (ISP) 100 percent of the time. Why not?

There are a number of possible reasons. However, the most likely reason is that your ISP is not able to accept the connection some percentage of the time. According to Inverse Network Technology, even the best ISPs have an evening call failure rate of between 1.5 and 3 percent, based on November 1998 measurements. And seven major ISPs had call failure rates greater than 10 percent.

My 56K modem can connect to my ISP but I do not get a 56Kbps modem connection. Why not?

C|Net and PC World have published articles that discuss this in detail. You can find the articles at:

It is important to realize that having a 56K modem does not guarantee a 56Kbps connection. In fact, it is not unusual to consider a connect rate between 36Kbps and 53Kbps as a successful 56K modem connection.

The brief list of possible reasons follow:

  • More than one analog connection. A V.90 56Kbps connection allows for only one analog connection between you and your ISP. This single analog connection is from your modem to your telephone company's Central Office (CO) switch.
  • FCC signal strength limitation. Due to FCC restrictions on signal strength in the U.S., you cannot achieve rates faster than 53Kbps.
  • Excessive line noise. Your telephone line may suffer from excessive line noise that prevents your modem from achieving a 56Kbps connection. Note that this line noise may not be audible when you use your telephone for voice conversations.
  • Too many devices on a line. It is sometimes the case that too many devices on a single line (telephone, fax machine, cordless phone extension, and so on) may limit your modem connect rate.
  • PBX. If you connect your modem to your company's PBX (Private Branch Exchange) switch, the switch's analog-to-digital conversion prevents fast connect rates.
  • Digital Loop Carrier. Your telephone company may use a Digital Loop Carrier (DLC) to allow it to connect up to 96 telephones to its CO switch via a single line. If the DLC uses a universal connection that performs an analog-to-digital conversion, you will not be able to connect at 56Kbps.
  • Analog pad. If your phone company has an analog pad on your line to reduce signal loss, this introduces an analog-to-digital conversion that prevents you from achieving a 56Kbps connection.
  • Load coil. A load-coil amplifier in between your modem and the CO switch can introduce signal distortion that could prevent you from making a 56K connection.

It is also important to distinguish between the reported initial connect rate and the actual throughput you see for the life of a session. Throughput is the average bit per second (bps) rate for some given time period (say, the amount of time it takes to download a 4MB compressed shareware file). Throughput can be affected by all kinds of factors, including the load on the FTP or Web server you are trying to access.

Where can I find the latest firmware or INF file for my 56K modem?

You should always check the modem manufacturer's Web site. In fact, it is a good idea to check a manufacturer's Web site before you buy a modem. You can compare how well different manufacturers support their modems by doing so. Click on the Related Links page to find a list of modem manufacturers.

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