7-6.1 Rationale

This provision addresses two different problems: 1) how to make information that is normally presented on a display accessible to users who cannot see displays, and 2) how to provide information to TTY users that is usually provided on some landline digital telephone systems. The second problem is an issue when TTY users do not use landline digital telephone systems, due to the potential for the system to corrupt TTY signals.

The kind of information pertinent to this provision is information about telephone functions. Many current office and wireless telephones have displays that provide information such as Caller ID or an indication of new voice mail messages to the user. Caller ID functions display both the name and number of a caller. Someone with a visual disability might not be able to see this information and therefore would not experience “comparable access” to the telephone system, unless that information was provided in another format.

TTY users may have special problems obtaining this telephone function information, which is commonly transmitted and displayed via digital channels on landline telephone systems. TTY users have often been limited to the use of analog lines, which provide a connection point, support ring–signaling assistive technology, and avoid garbling of TTY through the digital telecommunications system (see sections 7-3 and 7-11). However, this approach does not provide some additional information provided through a digital telephone system. Therefore, this problem of TTY user telephone function information access needs to be addressed by design engineers for a telephone system to conform to the 508 standards. Supply Management contract officers should know that this is not a problem with all digital telephone systems.

Products and services that deliver, support, or provide special telephone function information, such as Caller ID, are covered by this provision. Automatic location identification (ALI), which displays a caller's address, is also covered, but is less commonly used.