Why Use DS3? Comparing T1, T3, OC3 &
DS3 bandwidth, plus Carrier Ethernet
By: John Shepler
If your business class DSL or T1 broadband
service no longer has enough speed to meet your bandwidth needs
for video or data transfer, you may be considering a move up
to DS3 or T3 service. Here's when that makes sense... and when
What's the difference between DS3 and
Ah, what's in a name? Both of these terms have their origination
in the T-carrier system, originally developed to provide high
speed "trunk" lines between telephone company offices.
Everything is based on DS0 or "digital signal level zero"
which is a 64K bit per second channel. Group 24 DS0 channels
together and you have a DS1. When the DS1 is connected to a wire
circuit, it is called a T1. T1 runs at 1.544 Mbps (megabits per
Not fast enough? OK, group 28 DS1 channels
together (equivalent to 28 T1 lines) and you have a DS3 or digital
signal level 3 running at 44.736 Mbps, or 45 Mbps for short.
Connect that to a wire circuit and its called a T3. By the way,
that T3 line is equivalent to 672 voice channels. DS3 and T3
terms are often used interchangeably.
So, are T3 and OC-3 equivalent?
No, not really. T3 is the "big daddy" of the T-carrier
system. T3 is copper wire based, although using coaxial cable
rather than pairs of phone wires to support the higher speed.
OC-3 is another animal entirely. It is
part of the Optical Carrier (OC) levels defined for a fiber optic
transmission system called SONET (Synchronous Optical Network).
OC-3 runs at 155 Mbps verses T3 at 45 Mbps. That's a big difference
in speed and, as you might imagine, cost.
OC-1 service is the equivalent of DS3 or
T3. It provides 672 voice channels (or 64K data channels) and
runs at 52 Mbps to include the extra bits needed for the optical
service. The highest OC level you can get at present is OC-768
which runs at 39,512 Mbps or about 40 Gbps (Gigabits per second).
When does DS3 or T3 service make sense?
If all you require is 2 or 3 times the speed of a T1 line, then
you are better off with multiple T1 lines or connecting them
together in what is called "bonded T1" service. Once
you get past 6 or 8 T1 lines, the price of a T3 line is often
competitive. Remember, with T3 you get the equivalent of 28 T1
lines, which is a LOT more capability.
DS3 Bandwidth generally
makes sense for corporations that have a need for high speed
electronic data transfer between plant sites or offices. Very
large call centers, enterprise wide VoIP and IP PBX systems,
Internet service providers, universities, research labs, video
conference centers and software development companies are also
good candidates for T3 lines with DS3 level service.
DS3 transport may be a cost effective substitute
for point to point microwave for MPEG
Broadcast Video Transmission. It is also applicable for Surveillance
Systems, and VLAN
If a full DS3 line is more bandwidth that
you really need, it is also possible to get Fractional
DS3, which gives you a portion of full ds3 bandwidth at a
lower cost. Of course, DS3 is also available in multiples to
increase bandwidth, similar to bonded T1 service.
Competition from Carrier Ethernet
In recent years, a newer technology called Carrier Ethernet has started replacing both T1 lines, DS3 and SONET OCx fiber. Ethernet over Copper (EoC) uses the same twisted pair wiring at T1 and is available from 2 to 45 Mbps. Ethernet over Fiber (EoF) is highly scalable in the range from 10 Mbps to 10 Gbps, with 100 Mbps and Gigabit Ethernet being very popular service levels. Ethernet is far more scalable than earlier technologies and enjoys a cost advantage as well.
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