DS3 Line | T3 Internet

Understanding The Fundamentals Of T3 Line

One of the biggest boons of digital telephony has been the network growth and spread. With digital signals, multiplexing became a possibility. This reduced the need for building new networks and thus helps customers share existing resources optimally. T3 line was and has been over the years one of the most standard multiplexed lines used to transfer traffic between central offices.

How does multiplexing translate into savings? It can be well appreciated with this example. Let us say that there are 10 users who need a 1Mbps connection. Without multiplexing, each would order a separate cable to be installed to their house, even if they are in the same building. So each customer pays for a dedicated cable which may in fact be capable of carrying 10Mbps traffic.

Now if the service provider opts for multiplexing, the dedicated cable may go only up to the building base. From there onwards the multiplexer will send traffic on a single cable. This brings down the cost of the service to just about one tenth of individual dedicated lines.

The digital telephony hierarchy uses the same concept. In this case the T1 lines multiplex 24 voice channels and T3 multiplexes 28 such T1 lines. This hierarchical multiplexing allows for orderly expansion of the network. Near the customer homes we have T1 with just 24 voice channel capacity and towards the core we have T3s with 672 voice channels.

From a link rate perspective, T3 can support 44.736Mbps rates which are sufficient to carry 672 voice channels and some signaling. These are ideal for core networks where there are huge bandwidth demands for carrying aggregated traffic. At customer location, these are rarer. Typically today you would find T3 links connecting central offices to carry voice traffic or individual T1 lines with data traffic.

Times are changing though and demand for bandwidth is increasing. There are some customers that may opt to go for T3 connectivity too. However a T3 copper line cannot go beyond 600m without repeaters. To reduce cost of network deployment, service providers leverage their fibre networks to carry T3 link as close to customer location as possible and use copper for the last mile.

The standard fibre standard used in the core networks is SONET. SONET can carry DS3 signals and being fibre it is more cost effective than copper. Of course, given that fibre has not reached individual customer locations, the last mile is delivered in traditional coaxial cable connection.