How To Internet & Network T1 and T3 Lines for Network Communications These high-speed lines are suitable for business networking uses Share Pin Email Print Yuri_Arcurs / Getty Images Internet & Network Key Concepts Basics Guides & Tutorials Installing & Upgrading Tips & Tricks What Are Bitcoins? The Wireless Connection by Bradley Mitchell An MIT graduate who brings years of technical experience to articles on SEO, computers, and wireless networking. Updated July 17, 2019 38 38 people found this article helpful T1 and T3 are two common types of digital data transmission systems used in telecommunications. Originally developed by AT&T in the 1960s to support telephone service, T1 lines and T3 lines later became a popular option for supporting business-class internet service. T-Carrier and E-Carrier AT&T designed its T-carrier system to allow the grouping of individual channels together into larger units. A T2 line, for example, consists of four aggregated T1 lines. Similarly, a T3 line consists of 28 T1 lines. The system defined five levels — T1 through T5: Name Capacity (maximum data rate) T1 multiples T1 1.544 Mbps 1 T2 6.312 Mbps 4 T3 44.736 Mbps 28 T4 274.176 Mbps 168 T5 400.352 Mbps 250 T-Carrier Signal Levels Some people use the term "DS1" to refer to T1, "DS2" to refer to T2, and so on. The two kinds of terminology can be used interchangeably in most contexts. Technically, DSx refers to the digital signal running over the corresponding physical Tx lines, which can be copper or fiber cabling. "DS0" refers to the signal on one T-carrier user channel, which supports a maximum data rate of 64 Kbps. There is no physical T0 line. While T-carrier communications were deployed throughout North America, Europe adopted a similar standard called E-carrier. An E-carrier system supports the same concept of aggregation but with signal levels called E0 through E5 and different signal levels for each. Leased Line Internet Service Some internet providers offer T-carrier lines for businesses to use as dedicated connections to other geographically separated offices and to the internet. Businesses use leased line internet services to offer T1, T3 or fractional T3 levels of performance because those are the most cost-effective options. More About T1 Lines and T3 Lines Owners of small businesses, apartment buildings, and hotels once relied on T1 lines as their primary method of internet access before business-class DSL became prevalent. T1 and T3 leased lines are high-priced business solutions that are not suitable for residential users, especially now that so many other high-speed options are available to homeowners. A T1 line does not have nearly enough capacity to support significant demand for internet usage nowadays. Besides being used for long-distance internet traffic, T3 lines are often used to build the core of a business network at its headquarters. T3 line costs are proportionately higher than those for T1 lines. So-called "fractional T3" lines allow subscribers to pay for a lesser number of channels than a full T3 line, lowering leasing costs somewhat. Continue Reading Definition of a Leased Line in Networking Most Large Computer Networks Have a Backbone They Can't Live Without What Is a Wide Area Network (WAN) and How Does It Work? Compare and Contrast the Six Fundamental Types of Network Connections Getting a New Internet Connection? Know Your Options Do You Still Use Integrated Services Digital Network (ISDN)? Why Frame Relay Isn't Very Popular Anymore How Power Over Ethernet (PoE) Simplifies Business Networking A Beginner's Guide to Network Cables Using Point-to-Point Protocol and PPPoE for DSL Connections Do Wireless Providers Offer Better Internet Service? What You Need to Know About Business Computer Networks Is DSL the Right Internet Solution For You? Is Fiber Faster Than Traditional Cables? Learn All About Fiber Optics Distinguishing the Different Types of DSL Technology What is Latency in Computer Networking?