T3 And Ds3
T3 and DS3 are used interchangeably and mean the same type of service. T3 means trunk line, level 3 and DS3 means digital signal, level 3. They both refer to a 45 Mbps time division multiplexed synchronous digital voice or data service. DS3 actually refers to the digital signal service, which is provided on a T3 coaxial cable or a fiber optic cable.
T3 is part of the T-carrier system and refers to the physical line, which is copper wire. You can get DS3 without the specific T3 wires, but not the other way around. T1 is the other popular T-carrier service. It is a 1.5 Mbps line traditionally provisioned on two pair of copper phone wires. Some providers are now using a single pair to transmit T1 using a more advance modulation scheme than was originally specified. At any rate, the digital signal level for T1 is called DS1.
64 Kbps is just the right size to carry one telephone call or one dial-up modem connection. DS1 is made up by combining 24 DS0 channels. DS3 is made of 28 DS1 channels or 672 DS0 channels. DSL is something else entirely. It stands for Digital Subscriber Line and is a completely different format, although it typically runs at speeds similar to T1 lines.
OC3 is part of the numbering scheme called SONET for Synchronous Optical NETwork. OC3 runs at 156 Mbps. The common theme that runs through all of these digital transmission schemes is the basic design of synchronous time division multiplexing based on the DS0 channel. DS0 carries exactly 1 telephone call and that's the lowest common denominator for the telephone companies who designed the standards.
A T1 or T3 service you order might be delivered on a dedicated copper wire circuit or it might be dropped off from a larger OC3 fiber optic cable. It depends on which hookup is most economical. Remember that T3 and DS3 refer to the same thing. OC3 is much faster, and more expensive.
