* Extended Super Frame, a line framing standard used in T1 telephony lines

So, why is the T1 Superframe framing format commonly called D4 Framing?

Twelve DS1 frames make up a single T1 Superframe ( T1 SF ).

Each T1 Superframe is composed of two signaling frames.

The ESF T1 framing format allowed for the signaling information to be carried out of band and not as an Inband tone.

In telecommunications, an extended superframe ( ESF ) is a T1 framing standard, sometimes called D5 framing because it was first used in the D5 channel bank, invented in the 1980s.

T1 SF framed circuits yield two independent signaling channels ( A & B ) T1 ESF framed circuits four signaling frames in a twenty four frame extended frame format that yield four independent signaling channels ( A, B, C, and D ).

For example, for E1 trunks the CAS signaling bits are updated once per multiframe of 16 frames ( every 2 milliseconds ) while for T1 ESF trunks the superframe is 24 frames ( 3 milliseconds ).

In North America PRI service is delivered on one or more T1 carriers ( often referred to as 23B + D ) of 1544 kbit / s ( 24 channels ).

A true T1 ( commonly called " Analog T1 " to avoid confusion ) uses 24 channels of 64 kbit / s of in-band signaling.

The T1 line consists of 24 channels, while an E1 has 32.

Originally the T1 format carried 24 pulse-code modulated, time-division multiplexed speech signals each encoded in 64 kbit / s streams, leaving 8 kbit / s of framing information which facilitates the synchronization and demultiplexing at the receiver.

Since each T1 frame contains 1 byte of voice data for each of the 24 channels, that system needs then 8, 000 frames per second to maintain those 24 simultaneous voice channels.

Because each frame of a T1 is 193 bits in length ( 24 channels × 8 bits per channel + 1 framing bit

Newer two wire HDSL ( HDSL-2 ) equipment transports a full 1. 544 Mbit / s T1 over a single copper wire pair up to approximately twelve thousand ( 12, 000 ) feet ( 3. 5 km ), if all 24 gauge cable is used.

A Digital Signal 1 ( DS1 ) circuit carries 24 DS0s on a North American or Japanese T-carrier ( T1 ) line, or 32 DS0s ( 30 for calls plus two for framing and signaling ) on an E-carrier ( E1 ) line used in most other countries.

Higher-speed leased lines are usually presented using FT1 ( Fractional T1 ): a T1 bearer circuit with 1 to 24, 56k or 64k timeslots.

This platform was installed in HSN's new facility and could handle a large number of T1 lines ( each T1 has a capacity of 24 separate callers ).

While an inband T1 seemingly has a slight advantage due to 24 lines being available to make calls ( as opposed to a PRI that has 23 ), each channel in an inband T1 must perform its own setup and tear-down of each call.

Although an inband T1 has 24 channels, the 23 channel PRI can set up more calls faster due to the dedicated 24th signalling channel ( D Channel ).

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 ).

By age 24 he was credited with discovering or co-discovering two comets: comet Grigg-Mellish ( 1907b, 1907 II, C / 1907 G1 ) and comet 1907e ( 1907 V, C / 1907 T1 ) using home built telescopes, and received astronomical medals from both the United States and Mexico as a result.

The T1 circuit is divided into 24 channels, each carrying 8, 000 samples per second, each 8 bits long.

* RBS ( robbed bit signaling )-delivers 24 digital circuits over a four-wire ( T1 ) interface.

A T1 circuit typically carries 24 individual timeslots.

< tr >< td > DS1 </ td >< td > 1. 544 Mbit / s </ td >< td > 24 </ td >< td > T1 </ td ></ tr >

Normally, a PBX is connected via a T1 with robbed bit signaling to indicate on-hook or off-hook conditions and MF and DTMF tones to encode the destination number.

The number of B channels for PRI varies according to the nation: in North America and Japan it is 23B + 1D, with an aggregate bit rate of 1. 544 Mbit / s ( T1 ); in Europe, India and Australia it is 30B + 1D, with an aggregate bit rate of 2. 048 Mbit / s ( E1 ).

Soon after commercial success of T1 in 1962, the T1 engineering team realized the mistake of having only one bit to serve the increasing demand for housekeeping functions.

All T1 DS0 channels that employ in-band signaling will have its eighth bit over written, or " robbed " from the full 64 kbit / s DS0 payload, by either a logical ZERO or ONE bit to signify a circuit signaling state or condition.

Hence robbed bit signaling will restrict a DS0 channel to a rate of only 56 kbit / s during two of the twelve DS1 frames that make up a T1 SF framed circuit.

* Point-to-Point Protocol, a data link protocol that is normally used to provide data link layer services on top of links that do not have built-in data link layer services like modem connections, T-carrier connections like T1 and T3 lines, E-carrier connections like E1 and E3 lines, and SONET and SDH connections like OC-3, STM-1, and higher bit rate optical connections

* A & B, a bit signaling procedure used in SF ( D4 ) framed T1 transmission facilities

DS1 is the logical bit pattern used over a physical T1 line ; however, the terms " DS1 " and " T1 " are often used interchangeably.

In the 1970s it replaced the original T1 / D1 framing scheme of the 1960s in which the framing bit simply alternated.

Unlike unframed TDM for which all bits are available for payload, framed TDM requires dedicating of some number of bits per frame for synchronization and perhaps various other functions ( e. g. 1 bit per T1 frame, 8 bits per E1 frame ).

For data channels, in order to avoid the need of always setting bit 8 to 1, as described above, other T1 encoding schemes ( Modified AMI codes ) ensure regular transitions regardless of the data being carried.

In phones, a framing bit is sent every 24 bits on T1 lines.

StrataCom's first product had T1 ( 1. 544 Mbit / s ) based links which included a 5 bit header CRC, similar to ATM's 8 bit header CRC.

T1 is a time-division multiplexing ( TDM ) protocol with 24 byte payloads carried in a 193 bit frame.

Commonly used in the North American T1 ( Digital Signal 1 ) 1. 544 Mbit / s line code, bipolar with eight-zero substitution ( B8ZS ) replaces each string of 8 consecutive zeros with the special pattern "< tt > 000VB0VB </ tt >".

Instead, the material for the sequel was combined in 1985 with the original T1 storyline and published as an integrated adventure bearing the module code T1-4.

* Verilog source code of the UltraSPARC T1 design ;