Everything you ever wanted to know about T1

What is T1

If you have wondered what T1 really is; you will find all of your questions answered in this T1 Tutorial. We will cover:

  • What is T1 and how its name originated
  • What are the protocols and other things you might want to know about T1
  • A short tutorial on how T1 Works

T1 Tutorial - Part 1 - What’s in the name T1

T1 is now an Internet Technology that was developed by Bell Labs. The name T1 however, stuck after one of the pioneers in T1 services at AT&T decided to call it the T-Carrier, since it was the next letter available after the predecessors to the T1 (the L and the N-carriers) that AT&T had also named with letters.




 

  
 
 

T1 however is actually used in North America as a synonym for DS1 or Digital Signal 1, which was what Bell Labs called it when it was invented. In the rest of the world, it is more commonly referred to as E1 or E-Carrier, which was accepted as the standard by The European Conference of Postal and Telecommunications Administrations (CEPT) after making improvements to the original T-Carrier. This was then accepted by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T), which is now followed in all countries except the US, Canada and Japan

T1 Tutorial - Part 2 - How it works

Alright, your T1 line is at the end of the day, an internet connection, so it can carry data, be it packet data that you use to browse the internet, or media in the form of audio and video. In this segment of this T1 Tutorial, we’ll try to understand how T1 transmits data, how it is different from other Internet connections, and the business implications of a T1 line.

For starters, any internet connection has the following properties:

  • Upstream traffic: The data that you upload to the Internet while browsing (your computer sending requests to websites for specific files or pages), attaching files to your email, using a VoIP telephone line or while playing your favorite online game.
  • Downstream traffic: The data that you download from the Internet when you are connected.
  • Upstream and downstream speed: This is the rate at which you can upload and download data. It is good to remember however, that these two are independent of each other and your ISP is more likely to show you “Lightning Fast” Downloads rather than give you an accurate upload speed picture.

Normal dial-up connections that you can connect to through your telephone line have a speed of about 30 Kilobits per second (Kbps) or 30,000 bits per second. This limitation due to the low data carrying capacity of the twisted copper cable you use to access the internet through your phone. Although T1 connections are also available using copper cables, most T1 lines today are fiber optic and are made available either as ‘Fiber To The Curb’ or just outside your premises or right through to your hardware.

The T1 line leverages the enhanced data carriage capacity of fiber optics to provide a symmetric bandwidth of 1.54 Mega bits per second (Mbps). Typically, a T1 line comprises 24 channels, each with a symmetric bandwidth of 64 Kbps. The Symmetric adjective used to describe the bandwidth of a T1 line is due to the fact that a T1 line channel can give you a simultaneous upload and download speed of 64 Kbps, meaning you can upload and download data at the same time, and at the exact same speed. This property is crucial to most of the applications that T1 lines are used today.

Telephony

The biggest significance of a T1 line today is its ability to carry as many as 24 voice channels. This means that you can have 24 telephone lines calling just about anywhere in the world using VoIP, not having to pay the prohibitively expensive rates for long distance calls. Usually businesses that have extensive customer relationship activities, have equally extensive telephone usage making the advent of the T1 line one of the most important events in telephony.

Well, if you think this is it, think again. There are two types of T1 lines that are available: Inband and PRI. While Inband T1 lines are what you normally find in households and businesses, the PRI line provides a little more. While it provides the 23 usable telephony channels also known as B Channels, it provides one extra channel called the D or Delta Channel that carries signaling information of the call, such as Caller Line Identification, Call Handle information, DNIS information, response requests. While Inband T1 can also do the same, PRI, with its dedicated Delta Channel manages to carry the signaling information with the kind of efficiency that a contact center would require.

In addition to all of this, the very fact that T1 bandwidth is symmetric makes it all the more significant for businesses. Since most depend upon their online presence, or their online applications such as CRM systems, email and telephony, there is a significant upstream traffic requirement as well. This is where the equal upload and download speed of the T1 really helps.