T1 and T3

T1 and T3 lines have some slight differences. T1s are also known as DS1s or "Hi-Caps", for High Capacity facilities, and represent 1.544Mb of bandwidth potential (equivalent to 24 voice circuits). T3s are also known as DS3s, and are even higher speed, representing 45Mb of bandwidth potential (equivalent to 28 T1s or 672 voice circuits). Both can be used for either access from a telecommunications carrier to a customer site, or can be used in a point-to-point arrangement linking two locations together. Either way you look at it, T3/T1 lines are both very fast.

T3s Explained. T3 (more commonly known as a DS3) is a Telecom term for "Digital System 3" which represents a 45MB circuit that is carried by 4 copper wires (or via fiber and converted back to copper at the customer site) and can support a wide range of services to include voice, data, and video. Through multiplexing (explained in detail later), this single DS3 facility can carry a combination of all of these services into a single circuit, reducing monthly access costs.

How and Where DS3s are Used. T3s are high capacity circuits, typically used by Telephone companies and large business users that require more than a DS1 (T1 or 1.544Mb) of connectivity. In terms of capacity, a T3 is equal to 28 DS1s (T1s) of capacity. Due to equipment multiplexing limitations, most business users that need more than a few T1s of capacity opt for the next "level" of service as a T3, because access costs on NxT1 vs. a T3 will typically break-even at about 4 T1s (6mb). Once the T3 facility is leased, adding T1 capacity requires very little lead-time, and no additional monthly cost for the access facility.

Common Names / Muxing Levels:

• DS0 = Digital Service Level 0 (64kb)
• T1 = DS1 = Digital Service Level 1 (1.544mb) = 24 DS0s
• T3 = DS3 = Digital Service Level 3 (45mb) = 28 DS1s or 672 DS0s

Typical Applications:

• DS0s are typically used as voice-level or dial-up data channels.
• T1s are typically used as either private point-to-point circuits between facilities, or more typically, access from a business to either their local or long distance provider.
• T3s are typically used where more than one T1 is needed for capacity. While a T3 might be deployed for capacity reasons, not all T1s must be activated, so if a company needs 6MB of capacity, a typical installation might have a T3 established for "access" and only 4 DS1s "activated" on the T3 facility.

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