All T1

T1 or PRI Service

>Digital signal 1 (DS1, also known as T1, sometimes “DS-1”) is a T-carrier signaling scheme devised by Bell Labs. Originally, T1 meant “Transmission – Level 1”, and had to do with the media that the signal was passed over. DS-1 meant “Digital Service – Level 1”, and had to do with the service to be sent (originally 24 digitized voice channels over the T1). The terms T1 and DS1 have become synonymous and include a many different services from voice to data to clear-channel pipes. The line speed is always consistent at 1.544 Mbit/s, but the payload can vary greatly.

Metropark will discuss T1 in several different ways:

• Data T1 = 1.544mb of bandwidth
• Voice T1 = 24 channelized digital voice trunks (T-span)
• T1 PRI = 23 channels of digital voice and 1 data channel
• Frac T = less than 24 channelized digital voice trunks
• Integrated T = less than 24 channelized digital voice trunks and remaining channels bonded as data bandwidth
• Dynamic T = Voice and Data working un-channelized together over the 1.544mb
• Point to Point T1 = dedicated 1.544mb of data and voice between two locations

A DS1 circuit is made up of twenty-four 8-bit channels (also known as timeslots and DS0’s), each channel being a 64 kbit/s DS0 multiplexed pseudo-circuit. A DS1 is also a full-duplex circuit, meaning, in theory, the circuit can send 1.544 Mbit/s and receive 1.544 Mbit/s concurrently. A total of 1.536 Mbit/s of bandwidth is achieved by sampling each of the twenty-four 8-bit DS0’s 8000 times per second. This sampling is referred to as 8-kHz sampling. An additional 8 kbit/s is obtained from the placement of a framing bit, for a total of 1.544 Mbit/s, calculated as follows:

The primary rate interface (PRI) is a telecommunications standard for carrying multiple DS0 voice and data transmissions between two physical locations. All data and voice channels are ISDN and operate at 64 kbit/s. North America and Japan use a T1 of 23 B channels and one D channel which corresponds to a T1 line. Fewer active B channels (also called user channels) can be used for a fractional T1. More channels can be used with more T1’s, or with a fractional or full T3.

Higher Ts consists of bonding T1s to make much larger bandwidth options for the customer: