Internet connections have become faster and faster over the last few years with the advent of high bandwidth connections.

In the times when the internet first emerged, only dial-up access was available, and anyone that survived that period can remember how many hassles there were in order to be able to surf the net. There was, for example, the 33 kbps access speed, which was exceedingly s-l-o-w. Connections often crashed due to line problems or requests to websites just timed out if we were trying to access it. Even so, the internet became more and more popular until we finally reached cable and DSL speeds that we know today.

In order to connect to the internet with a high bandwidth connection, ISP’s establish your access speed according to what you choose. Connection speeds are categorized according to what is known as the digital hierarchy.

Values are commonly organized within this hierarchy according to slots in a base T-1 connection. A T-1 is essentially a cable that runs from your house, or company, to the ISP’s central office, for either cable or DSL connections. T-1 cables are subdivided mainly into 24 slots of 56/64 kbps each. According to the speed requested, a certain amount of slots are used. For example, for a 128 kbps connection, two slots will be used, for 256 kbps – four slots, for 512 kbps – eight slots, and so on. These connections are known as fractional T-1 connections, as they do not use the full T-1 pipe.

A full T-1 connection adds up to 1.544 Mbps, which means that we will be using all 24 slots of 64 kbps each, even though 64 kbps x 24 slots is not exactly 1,544 Mbps. This is because the remaining bits are used for framing, in order to organize the transmission of data in packets.

Of course, internet access speeds do not stop at the T-1 level. For higher speeds, we can use multiple T-1’s to reach 3 Mbps (two T-1’s), 6 Mbps (four T-1’s), etc. These type of connections are known as N x T-1’s.

The next jump in the digital hierarchy is to the T-3 level. T-3 connections are trunks divided into 28 T-1 slots, where each slot transmits 1.544 Mbps. These connection speeds are quite expensive and are normally used by large corporations that have a very high volume of data transfer. A full T-3 connection runs at 44.736 Mbps.

In order to transmit these large volumes of information, the ISP sends it from their T-1’s or T-3’s to the carrier that will be in charge of the long distance haul such as UUNET or AT&T, to access the host server. At this level, the T-3’s data is converted to optical data in order to transmit it over fibre, which can handle very large volumes of information at very high speeds. Fibre data transmission works at what is called the OC level (Optical Carrier), where OC-1 is equivalent to one T-3. Thus, OC-3 means that it can carry information that corresponds to three T-3’s, that is, at about 134 Mbps.

OC levels can go as high up as OC-768, which can transmit at 39.812 Gbps.