T-1

T-1 - a multiplexing scheme that enables one circuit to carry 24 voice, video or data conversations at 64 kilobits per channel. T-1 is the most prevalent technology for Internet access and access lines connecting customers to their carriers' POPs (Points of Presence) for LD (Long Distance).

T-1 circuits operate at 1.54 mbps. The letters "DS" stand for digital signal level. DS-1 refers to the entire 1.54 mb T-1 line. The terms DS-1 and T-1 are used interchangeably. The US, Canada and Japan use the 1.54 flavor of T-1. The rest of the world used E-1, which operates at 2.048 mb with 32 channels - 30 channels for voice or data, one channel for signaling, and one channel for framing and remote maintenance. Organizations that run a T-1 from the US to an office in Europe need rate-adaptation equipment so that the carrier the US can connect the domestic T-1 to the European T-1.

DS-0 is the 56 kbps or 64 kbps speed of each of the 24 individual channels of the T-1 or E-1 circuit. The DS-0 speed of 64 kb is the same worldwide.

Fractional T-1
Customers who require more than 64 kbps but less than a full 1.54 mb T-1 or E-1 often opt for lower-priced, fractional T-1/E-1. Fractional T-1/E-1 is sold at speeds of, for example, 4 channels at 256, 8 channels at 512, and 12 channels at 768 kbps. Customers don't purchase fractional DS-1 at higher than 8 or 12 DS-0 channels because the price becomes equivalent to the cost of a full T-1.

Unchannelized T-1
T-1 circuits, or a portion of the T-1 circuit used for data, can be ordered from carriers in an unchannelized format. An unchannelized T-1 is a single pipe with more capacity for data than one broken up into 24 channels using T-1 multiplexing. With unchannelized service, the router performs the multiplexing. Unchannelized T-1 service is used for:

- Access to frame relay, the Internet and VPN service

- Packetized, compressed, digitized voice (i.e. VoIP)

- Dedicated lines between locations

Unlike voice carried in VoIP packets, voice carried on T-1 to the PSTN (Public Switched Telephone Network) must be channelized, put into DS-0 channels compatible with CO (Central Office) switches.