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T1 vs. DS3 vs. OC3


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T1: dedicated connection capable of speeds of up to 1.5Mbps

24 DS-0 channels

A DS-0 service is a single digital channel of 64 Kbps. T lines are popular leased line options for businesses connecting to the Internet and for Internet Service Providers (ISPs) connecting to the Internet backbone. A T-1 line provides DS-1 service and actually consists of 24 DS-0 channels, each channel can be configured to carry voice or data traffic. A T-1 line supports data rates of 1.544Mbits per second. How come? 8000 * 8 bit resolution * 24 = 1.536 Mbps?

DS3: The data rate for this type of signal is 44.736 Mbps

672 DS-0 channels

028 DS-1 channels

DS-3 which stands for Digital Signal Level 3, equates to 28 T-1 lines or 44.736 million bits per second (roughly 43-45 Mbps upstream/downstream speeds). DS-3s have enough bandwidth to allow very large database transferring over busy wide area networks and the capability of handling 672 simultaneous voice conversations. DS-3s typically run long haul over fiber optics and coax in the last mile, however there are many exceptions to this.

In North America, DS-3 translates into T-3, which is the equivalent of 28 T-1 channels, each operating at a total signaling rate of 1.544 Mbps. The 28 T-1s are multiplexed through an M13 (‘Multiplex 1-to-3’ multiplexer), and 188 additional signaling and control bits are added to each T-3 frame. As each frame is transmitted 8,000 times a second, the total T-3 signaling rate is 44.736 Mbps. In a channelized application, T-3 supports 672 channels, each of 64 Kbps. In the European hierarchy, a DS-3 is in the form of a E-3, which runs at a total signaling rate of 34.368 Mbps, supports 480 channels, and is the equivalent of 16 E-1s.


OC-3 is a network line with transmission speeds of up to 155.52 Mbit/s (payload: 148.608 Mbit/s; overhead: 6.912 Mbit/s, including path overhead) using fiber optics. Depending on the system OC-3 is also known as STS-3 (electrical level) and STM-1 (SDH).

When OC-3 is not multiplexed by carrying the data from a single source, the letter c (standing for concatenated) is appended: OC-3c.

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IMA stands for Inverse Multiplexing for ATM. This technology provides a scalable and cost-effective solution for customers seeking to expand WAN bandwidth from T1 speeds, without having to pay for DS3 or OC3 circuits. With IMA, two or more T1 circuits can be "bundled"

for example a 12Meg IMA circuit is 8 T1 circuits (so 1.544Mbps x 8 = 12Mbps)

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