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