Q

General info about phone lines / connections.

A

The following is a very brief explanation of the relationship between the condition of your telephone lines and the speed with which you connect to the Internet.

* Please note that this information exists only because IBM has posted their research and solutions on their HelpDesk website.

Introduction

This information is provided to assist you in determining if there are line quality issues affecting your connection.

True telephone company related problems should be related to constant disconnections or the lack of a connection. See the section on Connection Speeds if you are getting a lower than expected connection speed. See the section related to your modem and software for information on how to obtain other important troubleshooting information.

Notes about Connection Speeds

The phone network was designed for voice not data communications. Modems are designed to use this network for exchanging data. The latest modem technologies push the upper limits of quality phone lines. Modem connections at 14.4 and higher are unreliable without Error Correction (error correction lowers and increases your baud rate based on current line conditions). A connection speed does not necessarily reflect the current connection speed as this fluctuates. The connection speed is not necessarily a sign of performance. It is an academic issue because the throughput (the speed in which you are downloading data) is what matters the most. See the below paragraphs for V.34 and 56k.

1. V.34 Modems:

   V.34 modems (i.e. 28800 or 33600) enhanced Error Correction protocols and pushed the limits of analog phone lines to their limit (obtain the V.34 guide for more information). 33600 is a theoretical limit and is rarely seen. If you are getting a connection speed of 26400 or higher, consider yourself lucky because one of the most common connection speeds is 24000.

2. 56K Modems:

   56K modems take advantage of the "mostly" upgraded digital phone network. The call route between your home and the ISP must have only ONE Analog to Digital conversion (this is not guaranteed as voice lines do not require this). The highest theoretical connection speed using 56K is 53333 (the FCC regulated limit). The actual connection speed will fluctuate. You may obtain a V.34 (i.e 28800 connection) if there is more than one Analog to Digital conversion. If the call route has only one Analog to Digital conversion you will obtain an x2 connection which may range from 33333 to 53333. This connection speed varies because there is an Analog portion of a 56K connection.

Error Correction and Connection Components

1. Error Correction:

   As mentioned in the connection speed section, error correction was developed to resolve performance problems with modem connections. Without error correction your modem would never connect or frequently disconnect. Error correction allows the modem speed to lower or increase based on current line conditions. It should be performed by the modem itself (hardware error correction). This means the modem has the built in software to perform error correction. Software error correcting modems require your computer to perform the error correction. Since this process is slow these modems do not perform well. Since error correction protocols are changed and updated often most hardware error correcting modems offer Firmware updates (which upgrades the error correction- obtain the modem help guide for more information).