| The evolution of the internet has driven a new | | | | data pipe to the internet. This will support a few |
| need for high speed internet connectivity. To | | | | thousand internet users. |
| meet this need the telecommunications industry | | | | There are three major telecommunications |
| has been expanding the availability of dedicated | | | | networks that were originally part of the Bell |
| service connections for business users. The | | | | system. Since the government broke the |
| once-esoteric T1 line is now commonplace and | | | | companies apart they have followed divergent |
| many residential users can use DSL to match the | | | | directions and now have different price structures. |
| rated throughput of a full T1 line. Both DSL and | | | | Each company has its own way of calculating |
| T1 are rated for 1.5Mbps. For some businesses, | | | | mileage charges as well as other pricing |
| the T1 is no longer adequate. Bonded T1 service | | | | differences. These differences mean the actual |
| up to 6 lines can provide a bit over 9Mbps. If | | | | price of a T3 lease can vary greatly. One part of |
| bandwidth requirements exceed that the next | | | | the cost of any dedicated line, including T3, is the |
| step is T3 lines. | | | | local loop charge. This is the charge by the local |
| One full T3 line can support almost 45Mbps | | | | phone company to install and maintain the |
| bandwidth. This is the equivalent of 672 digital | | | | connection between the phone company's T3 |
| voice lines or 28 T1 lines. The jump in lease rates | | | | port and the end user's network interface unit. |
| from T1 to T3 service can be steep. T3 carriers | | | | Some local companies will reduce or eliminate |
| offer fractional T3 service with bandwidth | | | | some of the installations costs if a long term |
| reduced to cut costs. This is a good stepping | | | | contract is signed. |
| stone from bonded T1 service into T3 lines. | | | | The bandwidth is the most obvious benefit of |
| Installation of T3 lines is more complex than lesser | | | | leasing a dedicated line. One less apparent benefit |
| services. A minimum of two 75 ohm coaxial | | | | is reliability. Leased lines typically include a service |
| cables connect the end user's network interface | | | | level agreement that specifies the guaranteed |
| unit to the T3 port at the local phone company | | | | availability of the service. Service interruptions can |
| offices. Depending on the distance involved this | | | | be calculated in seconds with specified latency |
| can be a major undertaking and the cost will be | | | | limits, error rates and 99.9% availability or better. |
| passed on to the user. Increasingly, T3 lines are | | | | Service level agreements also specify charge |
| being connected with optical fiber running SONET | | | | backs or lease payment reductions when service |
| technology. | | | | guarantees are not met. When a carrier may be |
| Many discussions of leased lines use the terms T3 | | | | subjected to reduction in revenue due to |
| and DS3 interchangeably. T3 is the transmission | | | | extended service outages, there is a major |
| system over which DS3 service is delivered - a | | | | incentive to restore service as quickly as possible. |
| minor difference but important when discussions | | | | Such service reliability can be very important to |
| become technical. The DS3 standard is based on | | | | companies that depend on being able to |
| multiplexing 672 digital voice channels or 28 T1 | | | | communicate with millions of customers on a daily |
| equivalent lines and passing the data over the T3 | | | | basis. |
| connection. The two coaxial cables or dual optical | | | | With intense competition among T-carrier |
| fiber cables allow the T3 to run full duplex. | | | | providers comes price volatility. Today's low price |
| Transmitting and receiving occur simultaneously. | | | | may be with one carrier while next week a |
| While DS3 can be carried over optical cable it is | | | | different carrier has a lower price. There are |
| considered the second fasted non-optical | | | | several web services that will help find and lock in |
| connection offered. | | | | low lease rates. Also, fractional T3 connections |
| The T3's 44.7Mbps transmission rate is required | | | | are being seen more and more as a stepping |
| for compatibility with the T1 rate. Setting this rate | | | | stone between T1 and full T3 service. It is worth |
| as a multiple of the T1 rate makes it easier to | | | | spending some time on availability research and |
| design electronics to multiplex several T1 (DS1) | | | | needs evaluation to get the most cost effective |
| signals or 672 digital voice lines (DS0) onto a T3 | | | | arrangement for a particular organization. |
| carrier. Unchannelized T3 provides a 44.7 Mbps | | | | |