T1: Terminology and Definitions

T1 – The Basics

The designation T-1 stands for Trunk Level One, it is a digital transmission link with a total speed of 1.544 Mbps. A T-1 Internet connection is comprised of two parts, the local loop charge, the phone circuit that connects your location to the Internet point of presence (POP) and the actual Internet bandwidth access port charge. DS-O (Digital Signal Level 0) - A non-switched dedicated service that can be provisioned as a private line point-to-point and multi-point service. Designed for full duplex transmission of voice, analog data and digital signals transmitting at speeds of 56 KBPS. The circuit is BI-directional and can move information in both directions. Your home telephone line is a DS-0 line. You can get 56 KBPS of data or voice through your regular phone line. The DS-0 is the "building block" of dedicated products.

DS-1 (Digital Signal Level 1) – The terms "DS-1" and "T1" mean the same thing! Most industry experts are phasing out the use of the term T1 and calling it DS-1. A DS-1 is simply 24 DS-O circuits all bundled together on one T-1 circuit. DS-1 service provides a dedicated connection from your premises to a long distance switch, providing the user with a single high-capacity digital circuit for voice or data applications. With a DS-1, you have the choice of allocating all of the DS-0 channels for data, voice, or any combination of the two. Shop for T1 resource.

A large company needs something more than a T1 line. The following table shows some of the common line designations:

• DS0 - 64 kilobits per second
• ISDN - Two DS0 lines plus signaling (16 kilobits per second), or 128 kilobits per second
• T1 - 1.544 megabits per second (24 DS0 lines)
• T3 - 43.232 megabits per second (28 T1s)
• OC3 - 155 megabits per second (84 T1s)
• OC12 - 622 megabits per second (4 OC3s)
• OC48 - 2.5 gigabits per seconds (4 OC12s)
• OC192 - 9.6 gigabits per second (4 OC48s)

T1 Internet Service

For super high-speed Internet, you can allocate ALL 24 channels to data, giving them a two-way connection to the Internet at 1.544 MBPS! (Typical DSL accounts run between 128KBPS and 728KBPS.) DS-1 Internet connections typically range from $300 to $1000, depending on the geographical distance between your location and the long distance switch.

• DSL Definitions and Terms
• High Speed DSL Broadband Providers

T1 Voice Service

Businesses with 12-24 phone lines can use DS-1 voice service. Since there are 24 DS-O circuits bundled together on one T-1 circuit, you can have 24 phone lines connected to the long distance carrier at the same time. Any number of the total 24 channels (circuits) can be set up as:

• Outbound only
• 800-inbound only
• BI-directional

T1 Voice has two costs associated with it. 1. The Local Loop, and 2. Long Distance Usage. The Local Loop is the flat fee that it costs to connect you to the long distance switch. This is a pass-through fee to the local phone company. The Long Distance Usage (LDU) is a separate charge in addition to the local loop. LDU rates for dedicated accounts are usually 10-40% less than regular switched long distance rates.

T1 PRI Voice Service

T1 PRI Voice Service is exactly the same as T1 "regular" service, with 1 exception: only 23 channels are dedicated to voice or data. The last DS-0 channel is taken off to handle other applications, such as a connection with the local telephone network or routing to a hold queue until 1 of the 23 channels opens up. Call Centers are the most frequent users of PRI Voice Service. Shop for T1 PRI Select PRI instead of "standard" in the drop down box.

Integrated T1 (Voice and Internet) Service

Integrated T1 service is just what the name implies, voice and data traffic on the same T1. Since you have 24 channels (23 with a PRI) to work with, you can divide up the load according to your needs. For example, your company may have 10 phone lines. The PRI (on hold to avert dropped calls) can allocate 10 DS-0 lines for Voice, and 14 DS-0 lines for Internet. In this example, your company could handle 10 simultaneous calls while surfing the web at a speed of 896 KBPS. Just a quick note: If 14 users are online for data, the 896 k "pipe" will slow down per user. Total bandwidth divided by the number of connections will reduce access speed per user. Normally this is not an issue. If the KPS varies per connection, this in not a service issue - the bandwidth adjusts to the number of connections. 

Point to Point Service

If you require constant connectivity to another office location, you should consider Point-to-Point T1 service. This is the same as regular T1 service, except now you have a Local Loop on 2 ends instead of just 1. This increases the cost of the monthly recurring local loop charge, but calls (or data transfer) between these two points is unlimited, with full duplex speed of T1 (1.5 MBPS). Shop for Point to Point resource.

Frame Relay Service

Frame Relay is for offices with 2 or more locations that require constant connectivity. Unlike Point-to-Point, the end-user can select sub-T1 speeds between each satellite location and the main office (or Host). This reduces cost and allows for future upgrades in speed on an as-needed basis. Shop for Frame Relay resource.

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