In the 1960s, Bell Labs, an American telecommunications company developed the T1 line. It was capable of carrying the equivalent of 1.544 Mbps. As the need for bandwidth increased, they developed different versions of the T1 by combining multiple T1s into larger bundles.
A T3 line is a bundle of twenty eight T1s which yields an approximate bandwidth of approximately 45 Mbps. A T3 line comes in two different configurations. The first is called channelised. That means the T3 is broken down into channels. It can hold either 672 DS0 (one DS0 is the equivalent of 64kb for a single digital voice channel), or 28 DS1s (DS1 is what a T1 carries). There is some additional equipment required to align and manage the channelised T3 so that all the DS1s are grouped together properly to fit on a T3.
The second type of T3 is the opposite of the above: unchannelised. This means it is the equivalent of a single pipe carrying up to 44.210 Mbps.
Heavy users, usually broadcast corporations and ISPs now require much more bandwidth than a T1 can provide. Telecommunications companies like BT will lease T3 lines to meet the demands of a business. It is possible to lease an entire T3 line, multiple T3s, or even a fraction of a T3 in order to meet the bandwidth requirements of businesses. The benefits of this approach include a dedicated line that isn’t shared with other businesses or residential users. This can be important because it’s often noted that available bandwidth can plummet at certain times of the day when using a shared line (the kids get home from school and start playing games or streaming video).
Prices for a leased T3 line, or the equivalent bandwidth isn’t cheap. It can run from several hundred pounds per month to thousands depending on the packaged and carrier chosen. However for companies looking to stream broadcast quality video in large amounts it is can be worth the cost of a dedicated connection to the Internet.