T3 and DS Similarity
Although it seems very confusing, it is quite simple when it comes down
to it. 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 refers to the digital signal service that 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.
DS0 is the lowest DS rate specified, which is 64 Kbps or 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 a consolidation 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 optical carrier-numbering scheme called SONET for Synchronous
Optical Network. OC3 runs at 156 Mbps. The unifying thread that runs through
all of these digital transmission schemes is the basic design of synchronous
time division multiplexing based on the DS0 channel.
T1 is a 1.5 Mbps line usually 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.
The 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.
DS0 carries exactly one telephone call and
that's the lowest common denominator for the telephone companies who designed
the standards.
