The T-Carrier System

The T-Carrier System

The T2 Carrier

The T3 Carrier

• B6ZS (binary six zero substitution): alternate method of ensuring that ample transitions occur in the data
• "+" & "-" = logic 1
• "0" = logic 0
• if violation is detected in the receiver, the original six 0s can be substituted back into the data signal
• substituted patterns produce bipolar violations

A T-3 carrier is an acronym for digital signal level 3 (DS-3) T-carrier, a type of high-bandwidth telecommunications carrier. It corresponds to 28 T1 lines (channels), where each channel runs at a 1.544 Mbps total signaling rate, or 44.736 million bps (approximate upstream/downstream speeds of 43-45 Mbps).

The T2 Carrier

Common Uses for T1

The T-carrier system is entirely digital, using both pulse code modulation (PCM) and time-division multiplexing (TDM). The system uses four wires and provides duplex capability. The four wires were originally a pair of twisted pair copper wires, but can now also include coaxial cables, optical fibers, digital microwave, and other media. A number of variations on the number and use of channels are possible.

• Building dedicated, high-speed WANS
• Providing corporate networks with high-speed access to the internet
• Connecting corporate intra-/extranet web servers to the internet
• Providing high-speed remote access solutions for companies with mobile users
• Providing integrated voice/fax/data services to businesses

• corresponds to DS2 (digital signal two)
• designed for inter-city transmission at distances up to 500 miles
• runs at 6.312 Mbps
• comprises 4 T1s at 1.544 Mbps plus 132kbps of overhead and justification or bit stuffing
• uses BPRZ-AMI
• clock sync is more critical than T1

The T-3 carrier's high-bandwidth capacity facilitates large database transfers through busy wide area networks (WAN). A T-3 carrier is generally installed as a primary networking channel in businesses supporting heavy network traffic and is mostly used by government offices, call centers, and universities as well.

The T-Carrier System

T3 Key Features

A T3 actually begins as four T1s multiplexed into a T2, which then multiplexes seven T2s to yield a signaling rate of 42.924 Mbps. Stuff bits are added to adjust for variations in the clocking rates of the incoming T2s, bringing the signaling rate up to 44.736 Mbps, comprising 672 DS-0 channels at 64kbps. T3 will run over a four-wire twisted-pair circuit, but for no more than 50 feet, due to issues of signal attenuation.

The T-carrier system, introduced by the Bell System in the U.S. in the 1960s, was the first successful system that supported digitized voice transmission.

The original transmission rate at 1.544 Mbps (T1), as well as the 44.736 Mbps (T3) are also commonly used by Internet service providers.

• 44.736 Mbps data rate
• Supports 28 DS-1 level signal transport within its payload
• Widely used by wired and wireless telephony carriers and OC1 optical connections
• Capable of transporting 672 DS-0 level channels within its payload

T1 Key Features

• based on the DS1 signaling standard defined by AT&T
• designed to combine TDM and PCM techniques
• transmission bit rate is 1.544 Mbps incl 8kbps framing bit
• typically range 1 mile to over 50 miles
• transmission medium is generally 19 to 22 gauge twisted-pair metallic tube

The T4 and T5 Carrier

T5 carriers time-division multiplex 8064 64-kbps voice or data channels and transmit the at a 560.16 Mbps rate over a single coaxial cable.

The T1 Carrier

T4M carriers time-division multiplex 4032 64-bit voice or data channels for transmission over a single T4M coaxial cable up to 500 miles. The transmission rate is sufficiently high that substitute patterns are impractical. Instead, T4M carriers transmit scrambled unipolar NRZ digital signals; the scrambling and de-scrambling functions are performed in the subscriber's terminal equipment.

The T1 carrier provides 24 voice channels by TDM and PCM. The system has been designed for low cost and is being widely applied on many trunks interconnecting switching units within Metropolitan areas. WEC manufacture of T1 began in 1962 and about 100,000 channels are now in service throughout the Bell System.