Internet DS3 Bandwidth T3 Lines

Fundamentals Of A T3 Line

There were many benefits of digitizing the telephony services. Digital signals meant better tolerance to noise and hence better quality of signals over long distances. The digital signals also meant one could use multiplexing. With multiplexing multiple signals would be sent on the same link giving a lot of network build out and cost benefits. T3 line has been one of the most preferred multiplexing link in digital telephony.

To understand the benefits of multiplexing, let us first look at an example. Let us say there are 10 customers in a building, each requiring 1Mbps link. The service provider would have to lay separate cable for each of them from their office to the central office. But each cable can support 10Mbps of line rate without any significant degradation in signal quality.

Rather than having to install and bill the customer for each individual line, the service provider can install a multiplexer at the building. This way all the traffic from 10 users come to the multiplexer which is connected to the central office on one cable. This saves costs for the service provider and hence for the customer.

T3 line uses the same concept and multiplexes twenty eight T1 lines. Each T1 in itself is a multiplex of 24 voice channels. Thus a T3 can carry 672 voice circuits. This makes them perfect for connection between central offices of what is commonly known as core networks.

Given that each T1 line is 1.544Mbps, 28 channels add up to 43.232Mbps. Besides this there is a signaling channel of 1.5Mbps to support important signaling related to calls. So the total T3 line rate is 44.736Mbps. Most times such high capacity links are not used by customers and are reserved for inter office carrier links. Even here the lines are mostly used to carry the voice calls or channelized to carry individual T1 rate data services for the customers.

With growing bandwidth demands though there are some big customers that may require T3 connectivity. A typical coaxial T3 line needs a repeater every 600m for reliable delivery of service. Hence it is generally preferred to transmit them over fibre through SONET.

The DS3 circuits are delivered to customers over fibre rings to the nearest drop points. From here regular copper cables are extended to connect the end customers. By employing this technique the service provider can exploit the higher multiplexing options provided by SONET in the core networks and reduce the copper costs to the customers.