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Aptiva - Limitations on K56Flex protocol modem speeds
Applicable to: World-Wide
The public switched telephone network (PSTN) imposes limitations on the speeds actually achieved by K56flex protocol modems. The communication protocol used by your Internet service provider's equipment can also have an impact on your modem's communication speed. This document provides information for those who are interested in some of the technical details associated with these limitations.
This information is provided in part by Lucent Technologies. K56flex is a trademark of Lucent Technologies.
If your Aptiva PC has a K56flex protocol modem:
Aptiva PCs with K56flex protocol modems are capable of downstream speeds approaching 56 kilobits per second (kbps). However, actual data transfer speeds may vary and may often be slower because of equipment compatibility issues and telephone network line conditions.
Speeds approaching 56 kbps are for data transfer only (not fax) and specifically for the downstream path from an Internet service provider (ISP) to your computer. On the upstream path from your computer to the ISP, data transfer is limited to V.34 speeds. If two modems are unable to connect at K56flex protocol rates, they will automatically drop down to a mutually acceptable data rate, such as 28.8 kbps or 33.6 kbps.
Compatibility issues:
The K56flex technology is compatible with previous communication standards like ITU V.34, which means that whenever high-speed communication is not possible, the connection can be established using V.34.
If the K56flex protocol modem in your computer is to communicate at speeds higher than those permitted by V.34, then these speeds can be achieved only during communication with Internet service providers (ISPs) that also use K56flex protocol modems. ISPs using X2 protocol modems cannot achieve these higher rates with a K56flex protocol modem in your computer.
Network-imposed limitations:
The public switched telephone network (PSTN) is designed to carry data at speeds no faster than approximately 53 kbps. Several components of the PSTN contribute to speed limitations.
Loading coils connected to phone lines will not allow high speed modem connections. Loading coils are placed on phone lines to decrease noise and make voice calls quieter. Approximately 9% of the homes in the United States have loading coils on their phone lines.
Frequently, in newer neighborhoods, Subscriber Line Interface Circuits (SLICs) and Universal Digital Loop Carriers (UDLCs) are used to multiplex many residential copper lines to a central point whereby the voice traffic is sent back to the central office digitally. It is not possible to achieve high speed modem connections when connected to a UDLC. A SLIC does have some impediments to high speed connections, but if call signalling is set up properly (one or more bits may be "stolen" for the purposes of call signalling), high speed connections may be possible. Your phone company can determine if you are connected to a SLIC or a Digital Loop Carrier. SLICs appear as a small green box in your neighborhood.
Additional information:
For additional information on K56flex protocol modems, including a list of frequently asked questions (FAQs), see the following site:
This site is maintained by third parties and may therefore be subject to updates and deletions without notice to IBM.
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Hint Category |
Communications Software, Modems | |
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Date Created |
30-04-98 | |
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Last Updated |
10-03-99 | |
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Revision Date |
10-03-2000 | |
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IBM Aptiva | |
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Product Family |
Aptiva | |
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Machine Type |
2137, 2138, 2139, 2140, 2142, 2153, 2161, 2162 | |
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