Certified Information Systems Security Professional (CISSP) Practice Exam

What does a T1 circuit primarily carry?

1. Digital video signals

2. Voice and video over Internet Protocol (VoIP)

3. Digital data via 24 DS0 channels

4. High-speed fiber-optic transmissions

The correct answer is: Digital data via 24 DS0 channels

A T1 circuit primarily carries digital data through a method known as time-division multiplexing, which allows it to combine multiple channels into a single communication link. Specifically, a T1 line consists of 24 individual DS0 channels, each capable of carrying 64 Kbps of data, totaling a bandwidth of 1.544 Mbps. This setup enables the transmission of a variety of data formats, primarily voice but also including data traffic, thereby making it a versatile option for businesses and telecommunications providers. The ability of a T1 circuit to handle 24 channels effectively makes it a reliable choice for organizations that require stable and robust communication capabilities. It has been historically significant in providing connectivity for both voice services and data transmission before the widespread adoption of higher speed and more modern technologies. Understanding the T1's channel structure helps clarify its limitations in relation to other options presented. For instance, while it can support voice services, it does not specifically cater to video signals or fiber-optic transmissions in the way that other technologies designed for those purposes would. Digital video signals are typically transmitted using different standards that require higher bandwidths and more specialized formats than a T1 can efficiently provide.