T3 refers to the trunk line level 3, and is sometimes used interchangeably with DS3 (digital signal level 3). In practice, the DS3 signal is transmitted over a T3 physical line, consisting of a fiber optic cable or coaxial cable. The T3 lines, which are symmetrical and duplex, have equal speeds on both upload and download, and therefore allow simultaneous transmissions without clogging the data lines.

A T3 line is an ideal connection for big business, however, small businesses that cannot afford the full 45 Mb or who may not need such a high capacity, have an option of buying a fraction of the full T3 line. The fractional T3 has some of the 28 lines turned off, and has a lower capacity such as 10 or 20 Mbps.

T3 lines are available in different modes and the choice is determined by the organization’s structure, needs and budget.

• T3 for Internet — This is a fractional or full, clear channel for Internet access, available in 10, 20, 30 and 45 Mbps. Fractional T3 can be downgraded or upgraded to meet fluctuating demands.
• Point-to-point or private (VPN) — Provides a secure and private connection for high speed and integrated data, video and voice services between company offices in different locations
• Tiered T3 — A pay-as-you-go option
• Burstable T3 — A flexible option where companies pay for only what they use, and is upgradable at 3 Mbps increments
• Bondable T3 — Combines several T3 lines to provide a massive bandwidth. The lines are configured to use a single line or combined using a router.

Typical applications include:

• High-speed connection between the customer and the ISP, or between two customer locations
• Providing fast data throughput to locations not served with fiber networks
• Virtual private networks with data, video and voice services for research labs, financial institutions, universities, health care providers and other heavy data users