The evolution of telephony networks is quite amazing. While the original telephone in itself was a big thing in the history of mankind, the real revolution came about when the telephone networks got digitized. This ushered a wide range of developments and helped make telecommunication a mass market with wide reach. The founding stone of the digitized telephone network in North America was the T1 line.

The basic principle of digitization is that any analog signal can be digitized and recovered back if it is sampled at twice its highest frequency. This theorem is known as the Nyquist Theorem and this is the foundation for all digital signals in the world. T1s are based on this very principle.

While the range of human voice varies, in most cases it lies within the frequency range of 4kHz. Hence as per Nyquist theorem it is sampled at twice the rate for digitization which gives is 8000 samples per second. Each sample is 125 microseconds long.

As long as the conversation is done in the same tone, digitization is simple. The real challenge comes when It has been observed that with 256 voltage levels most of these variations can be captured well. Hence the samples were mapped on 256 levels and coded with eight bits. The 8000 samples represented at 8 bits per sample gives the basic voice signal rate of 64kbps

One of the biggest advantages of digital signals is multiplexing. With digital signals, the voltage levels would remain constant for the duration of the pulse. So if you can sample this pulse once you know that it would be the same for a fixed duration. This meant that these 64kbps voice signals could be multiplexed.

With a T1 line, 24 such DS0 or 64kbps channels can be multiplexed. So in every T1 you can have 24 voice channels. This really changed the manner in which signals are transmitted over the network. With this concentration the capacity growth in the network was tremendous.

The voice signals are time sensitive and hence the T1 lines required some degree of synchronization. As a result the T1 frame was defined to have 24 voice channels and a synchronizing bit. Now with each of the 24 samples with 8 bits we get 192 bits. So in all the T1 frame sent 193 bits in 125 microseconds which gave the T1 lines the speed of 1.544Mbps. Even today this is a standard and core networks are built to accommodate this line rate.

The digital telephony took a new approach to carrying voice calls. It introduced the concept of multiplexing where multiple circuits could be aggregated into one link. This way multiple people can share the same resource there by distributing the costs among customers. One of the most popular aggregation links was the T3 line.

The benefits of an aggregation can be best understood with an example. Let us say that there is a cable that can support a data rate of 10Mbps. However without multiplexing, 10 users each would need to get this cable and pay for it, even though they need just 1Mbps each. As a service provider, you need in lay 10 cable pairs to connect the customers in the same building.

With multiplexing you can now combine all 10 user traffic on to one single cable and spend on just a single cable. The concentrator of the 10 signals into one is called the multiplexer. With a multiplexer, the customers now pay just a tenth of the cable cost and a tenth of the multiplexer cost which is a lot cheaper than a full cable.

With a T3 line, the multiplexing is done at a T1 level. 28 T1 lines are multiplexed into a single T3. Given that each T1 itself consists of 28 multiplexed voice channels; a T3 can support 672 voice channels at PCM rates. This high capacity made them ideal choices for trunk circuits between central offices.

A T3 or a DS3 (which is its digital component) can support a link rate of 44.736Mbps which comes from 28 T1 rates and a signaling channel. Even today, this link rate is too high for most business needs. So you would rarely find a T3 being pulled right up to a customer location. In most cases they are built to carry voice channels or to support T1 rate data circuits.

However, there are special customer needs that may require T3 level connectivity. In such cases, the service is delivered to them over SONET. SONET is an optic network standard that supports DS3 signals. Being fibre based it can travel much longer than a T3 on copper, which cannot go beyond 600m.

Most commercial DS3 connections are carried over SONET rings to the nearest Add-Drop-Multiplexers and then extended to the customer site on coaxial cable with BNC connections. This ensures maximum reusability of the fibre network for the service provider and minimum copper on the last mile.

T1 service is simply a service delivered directly to the customer, and where the customer needs determine the end use of T1 line bandwidth. The bandwidth capability of a T1 service can be up to 1.54 Mbps. How that capability is directed is determined by what the customer plans to use it for and how much they choose to apply to what service.

T1 service which was intended strictly for voice communications might go directly to the switchboard. This could enable a company to have 23 separate voice lines active at once with a PRI T1 line. Some companies may not have 23 phones in use simultaneously but they need the capability and T1 is the answer.

T1 is not only used for voice but also data and this service can provide the conduit to shunt data from one location to another at 1.54 Mbps. The T1 service is also a full duplex service which means it is able to receive and send data at the same time. While cable and DSL have significant differences between upload speeds and download speed, a T1 service is consistent in speed in both directions.

In today’s connected world some companies require high speed access to the internet to multiple employees and workstations. A T1 service can provide excellent internet service to many computers at one time with excellent speeds as well as reliability. This is an option for businesses with multiple employee work stations that all require internet access in order to do business.

A T1 service might be dedicated to a single application in some companies. Other companies might choose to share the bandwidth or channels among several applications. Phone service might be provided for fewer phones and the excess bandwidth used for internet access or data transfer. In time, when the company needs exceeded the capacity of the single T1 service, a bonded set of lines which act as a single circuit with increased capacity might be chosen.

The service is useful and attractive to large companies as well as smaller enterprises who need the reliability and quality of the service. However smaller businesses may not require as much bandwidth as a full T1 is capable of delivering. When the needs of a business are smaller but reliability and quality are still prime concerns, an option may be a fractional T1. This is a service which allots a fraction of the voice channels or bandwidth to a business, while the remainder might be leased to another company with similar needs.

Large businesses may have bandwidth requirements in excess of what a single T1 can deliver. If that is the case, a bonded line which is simply multiple T1 lines acting as a single line, can increase capabilities without driving up costs in excessively. The next most easily available option is a 45 Mbps T3 line which may be far in excess of many medium sized business bandwidth requirements.

Security, data transfer speeds and reliability of service are critical factors with many companies for selecting service types. T1 service is more reliable than cable or DSL and usually has a service level agreement as well which gives definite service levels and standards for the service providers. Rural businesses are not excluded from these services. While cable and DSL signals degrade over distances, a T1 can be refreshed as often as necessary to provide superior service.

A T1 line has 24 channels and can transmit and receive data at the rate of 1.5 Mbps. It can handle up to 24 telephone lines or provide a broad pipe for data transmission in a network or along the internet. This is a lot of data and lines, but may not serve the needs of every business either. The bonded T1 line steps in to deliver more data and voice lines without upgrading all the way to a T3 line.

The problem is the gap between a T1 and the next size is up is 1.5 Mbps for T1 and 45 Mbps second for the next available widely available size, the T3. That is a large difference in size, which many companies have no need for at first, even when upgrading. The answer is a bonded T1, which can multiply the data transmission capabilities of the regular T1 service without the investment in a service in a T3.

The bonded line has multiple T1 lines being connected in such a way as they act like a single circuit or line. This effectively increases the capacity of the service and instead of delivering approximately 1.5 Mbps the single line delivers, the bonded line with two T1 lines may deliver three Mbps. In some cases, a special router may be used to get the lines to working together.

Every provider has different means of delivering this service but Bonding has certain industry standards to which it is held. Bonding stands for Bandwidth On Demand Interoperability Group. Lines might be bonded and bandwidth increased by two, three, four or even eight times. Bonding more than eight lines may make a T3 service more attractive.

Bonding may be very useful for a call center, which handles a high volume of calls. It could be an exceptional means of transferring audio and video, which is greater than a single T1, may handle. A business, which handles a higher volume of phone calls and transmits large amounts of data, may well bond several lines.

Rural locations are ideal for the T1 service because although high speed DSL or cable may not be available the T1 service was intended to use readily available copper lines such as telephone lines. T1 service or bonded T1 is not usually out of reach no matter how rural the location. While running cable or DSL out that far will often degrade the signal the T1 service can be refreshed every mile or so if necessary.

While some businesses may operate well on a single T1 line other companies in the process of growing and increasing bandwidth usage can use the bonded T1 service to expand their capacities affordably. Location is usually not an issue with this service and the capacity is expandable to almost any size up to the T3 capacity. This makes a bonded line the logical choice for companies experiencing a large amount of growth and the need for increased bandwidth.