Which of the following is NOT a high-speed transmission service?

A fax line is indeed not considered a high-speed transmission service. While it can transmit data, a fax line typically operates at a much lower speed compared to modern high-speed options like ISDN, DSL, and broadband. High-speed transmission services are characterized by their ability to support the rapid transfer of data, which includes internet access and telephone communications that can handle large volumes of information simultaneously.

In contrast, a fax line is primarily designed for transmitting scanned printed material over a telephone line, with typical speeds in the range of 56 kbps or lower, resulting in long transmission times for even simple documents. This distinguishes it from the other options mentioned, which are explicitly designed for handling larger data throughput and providing faster communication for a variety of applications. Thus, the classification of a fax line as not being a high-speed transmission service is accurate.