When provisioning WAN circuits from a service provider, it’s important to have an understanding of the various terms used to describe circuit speeds and their groupings. In North America, most digital links are grouped according to what is known as the digital signal standard. The base digital signal standard is known as DS0, and represents a digital channel with 64K of bandwidth, the same amount used for a typical voice call. The North American T, European E, and Japanese Y carrier systems use the DS0 channel as their base multiple in link calculations.
For example, a T1 line is made up of 24 DS0s or channels, for a total aggregate bandwidth of 1.544 Mbps. If you do the multiplication, you’ll notice that 24 channels of 64 Kbps yields only 1.536 Mbps – the “missing” 8 kilobits are used to channelize a T1 line. The list below outlines some of the common speeds associated with carrier lines in North America, Europe, and Japan.
Carrier line designations, DS0s, and speeds for North America, Europe, and Japan:
T1 24 DS0s 1.544 Mbps
T3 672 DS0s 44.736 Mbps
E1 (Europe) 30 DS0s 2.048 Mbps
E3 (Europe) 480 DS0s 34.064 Mbps
Y1 (Japan) 30 DS0s 2.048 Mbps
It is also possible to provision “fractional” service from most service providers. For example, not every company requires (or can afford) a full T1 link between locations. In order to better meet their customer’s need, most providers offer what is known as fractional T1 service. This allows customers to lease only a portion of a T1 line, usually in multiples of 64K. As such, a company could rent 4 channels of a T1 link, providing them with 256 Kbps of bandwidth in total.