T-1 Defined
T-1, T-3: The T-carrier system, introduced by the Bell System in the U.S. in the 1960s, was the first successful system that supported digitized voice transmission. The original data transmission rate (1.544 Mbps) in the T-1 line is still in common use today in Internet service provider (ISP) connections to the Internet. A T-1 line could transfer a megabyte in less than 10 seconds if at maximum theoretical capacity. A T-1 line contains 24 individual channels, each of which can transfer data at 64 Kbps. Each of these 24 channels can transfer voice or data traffic. T-1 is the aggregation of 24 voice circuits (eg, "phone calls"). DS1 is one big data "pipe" also known as a “Fat” pipe.
Many telephone companies will allow you to buy a portion of these individual channels, called "fractional T-1 access". T-1 lines are also called DS1 lines, which is the rental of some portion of the 24 channels in a T-1 line, with the other channels going unused.
T-3 Defined
Another level, the T-3 line, providing 44.736 Mbps or at 34.368-Mbps in both directions on an E3 facility, is also commonly used by Internet service providers.
T-3 - A leased-line connection to the Internet which can transfer data at 28 times the speed of a T-1. It is used mainly by ISPs (Internet Service Providers) connecting to the Internet backbone. A T-3 line contains 672 individual channels, each of which can transfer data at 64 Kbps. T-3 lines are also called DS3 lines.
DS3 Defined
DS3 - Digital Signal Level 3 Physical Layer Convergence Protocol equates to 28 T-1 lines or 44.736 million bits per second (roughly 43-45 Mbps upstream/downstream speeds).
DS-3s have enough bandwidth to allow very large database transferring over busy wide area networks and the capability of handling as many as 672 simultaneous voice conversations. DS-3s typically run long haul over fiber optics and coax in the last mile, however there are many exceptions to this. Also, because fiber is only available in limited parts of the US (vs. copper), expensive build-outs are sometimes required for full DS-3 access.
In North America, DS-3 translates into T-3, which is the equivalent of 28 T-1 channels, each operating at a total signaling rate of 1.544 Mbps. The 28 T-1s are multiplexed through an M13 (‘Multiplex 1-to-3’ multiplexer), and 188 additional signaling and control bits are added to each T-3 frame. As each frame is transmitted 8,000 times a second, the total T-3 signaling rate is 44.736 Mbps. In a channelized application, T-3 supports 672 channels, each of 64 Kbps. In the European hierarchy, a DS-3 is in the form of a E-3, which runs at a total signaling rate of 34.368 Mbps, supports 480 channels, and is the equivalent of 16 E-1s.
If you’re moving a DS-3 (or any other DS signal) across continents, the standards of the target country rule. Channels get muxed and demuxed, with signaling conventions translated as well. For example: On the US side T-1s are in multiples of 24 x 64 Kbps circuits (total 1.5 Mbps) and in the UK, it’s 30 x 64 Kbps (total 2 Mbps). If you were to interconnect to the US at a DS-3 level, you would not receive 28 T-1s with 6 spare channels- You would get multiples of 30 E/T-1s. As they arrived in the UK, they would be muxed and demuxed, along with translated signaling conventions.
Who uses DS-3s? Companies who host high traffic web sites, support web hosting, and need high capacity bandwidth on an as-needed basis. Also universities, colleges, government offices, and high volume call centers. A full DS3 can accommodate many simultaneous users depending on the requirements of the business.
Generally a DS3 line is installed as a major networking channel for large corporations or universities with high volume network traffic. This is an always-on, high-speed connection that provides a dedicated, stable and reliable link to the Internet, and can support up to 500 or more computer users. Newer applications like large scale HD Video conferencing with 50 or more simultaneous participants require more bandwidth like DS3 lines.
If a full 45 Mbps DS-3 isn't a requirement, then 'tiered' and 'burstable' speeds are an option. Tiered is more suitable for clients who expect their bandwidth requirements to increase steadily and will continually rise in the near future. Companies with other access such as T1 lines can rapidly and easily switch their bandwidth to a faster single Fractional-DS3.
Burstable is defined as the ability to increase the throughput of your broadband connection for determined times should you require an increase in speed without paying for a larger pipe. For example, if you are downloading a large file or a ton of Internet connections (Live Event, your Infomercial is on TV) or other data blast requirements that may happen at 1 point during the week.
Burstable is a dedicated point-to-point circuit from a customer's premises to the telecommunication carrier's network operation center (NOC). This service is sometimes priced in billing tiers of 3mbps increments from 3mbps to 45mbps. As a burstable DS3 user, you always have the full bandwidth available over an unshared, non-fractional 45mbps digital leased line when needed.
Although anyone can purchase a burstable DS-3, this type of connection can be expensive, sometimes costing as much as a full 45 Mbps connection. Burstable lines can often be found at their lowest price within a collocation facility.
OC-3 Defined
At a collocation facility (or simply referred to as a "colo") many users share a large OC-3 or OC-12 pipe. As a customer, you will not have to pay for the fixed cost of such a large pipe, but will have the benefit of being able to burst up to very high bandwidths if necessary. If you need the reliability of a large pipe fur bursty traffic but don't have the capital, consider a Colo. If you have a steady volume and are consistent, you may consider keeping services in house and going with a T-3/DS-3 connection. Whether you're considering a collocation facility or a T3 to the door, make sure you use a telecommunications broker to help guide you through the many providers and plans available.
Optical Carrier 3 (155 Mbps) specification used in ATM/SONET. OC-3 Refers to a circuit that transmits 155,000,000 bits per second. This is the size of the largest Internet backbone providers’ networks.
Verizon operates the world's most expansive* Internet Protocol (IP) network, which provides connectivity in over 100 countries and operates at speeds up to OC-192.
The general rule for calculating the speed of Optical Carrier lines is when a specification is given as OC-n, that the speed will equal n × 51.8 Mbit/s.
What's Next...
Above and beyond the call of duty, unless you’re in the fortune 100 or have the Gross national output of some third world country.
OC-192 / STM-64x / 10G Sonet
OC-192 is a network line with transmission speeds of up to 9953.28 Mbit/s (payload: 9621.504 Mbit/s; overhead: 331.776 Mbit/s). This along with 10 gigabit Ethernet is the fastest connection commonly available on the Internet.
A standardized variant of 10 gigabit Ethernet (10GbE), called WAN-PHY, is designed to inter-operate with OC-192 transport equipment while the common version of 10GbE is called LAN-PHY (which is not compatible with OC-192 transport equipment in its native form). The naming is somewhat misleading, because both variants are suitable for use on a wide area network.
As of 2005, OC-192 connections are the most common for use on the backbones of large ISPs.
OC-768 / STM-256x
OC-768 is a network line with transmission speeds of up to 39,813.12 Mbit/s (payload: 38,486.016 Mbit/s; overhead: 1327.104 Mbit/s).
OC-768 SONET interfaces have been available with short-reach optical interfaces from Cisco since as early as 2006. As of September 2007, Cisco will use OC-768 DWDM line cards from a third party. These line cards will plug into the Cisco chassis. These same line cards will also be made available to Siemens. These cards will use four Xilinx FPGA, a Power PC, a TI c6200 DSP, Four AMCC FEC, two DeMux and two Mux.
Infinera made a field trial demonstration data transmission using optical lines on a live production network involving the service transmission of a 40Gb/s OC-768/STM-256 service over a 1,969 km terrestrial network spanning Europe and the U.S designed to carry data from the world's largest particle accelerator.
