Two Network Interface Units. On the left with a single card, the right with two

In telecommunications, T-carrier, sometimes abbreviated as T-CXR, is the generic designator for any of several digitally multiplexed telecommunications carrier systems originally developed by Bell Labs and used in North America, Japan, and Korea. For multiplexing in electronics and signal processing see Multiplexer. In Telecommunication, a carrier system (loosely a synonym with carrier) is a Multichannel telecommunications System in which a number of individual Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) is the Research organization Japan currently possesses one of the most advanced communication networks in the world Communications services improved dramatically in the 1980s with the assistance of foreign partners and as a result of the development of the electronics industry

The basic unit of the T-carrier system is the DS0, which has a transmission rate of 64 kbit/s, and is commonly used for one voice circuit. Digital Signal 0 ( DS0) is a basic Digital signaling rate of 64 Kbit/s, corresponding to the capacity of one Voice-frequency -equivalent In telecommunications Bit rate or Data transfer rate is the average number of Bits characters or blocks per unit time passing between equipment in a data transmission

The E-carrier system, where 'E' stands for European, is incompatible with the T-carrier and is used at most places in the world outside of North America, Japan, and Korea. In digital Telecommunications where a single physical wire pair can be used to carry many simultaneous voice conversations worldwide standards have been created and deployed It typically uses the E1 line rate and the E3 line rate. The line rate of a communications link is the data rate of its raw Bitstream, including all Framing bits and other physical layer overhead The E2 line rate is less commonly used. See the table below for bandwidth comparisons.

T1

Main article: Digital Signal 1

Existing Frequency-division multiplexing carrier systems worked well for connections between distant cities, but required expensive modulators, demodulators and filters for every voice channel. Frequency-division multiplexing ( FDM) is a form of signal Multiplexing where multiple Baseband signals are Modulated on different frequency For connections within metropolitan areas, Bell Labs in the late 1950s sought cheaper terminal equipment. Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) is the Research organization Pulse-code modulation allowed sharing a coder and decoder among several voice trunks, so this method was chosen for the T1 system introduced into local use in 1961. In later decades, the cost of digital electronics declined to the point that an individual codec per voice channel became commonplace, but by then the other advantages of digital transmission had become entrenched. A codec is a device or program capable of encoding and/or decoding a Digital Data stream or signal.

The most common legacy of this system is the line rate speeds. "T1" now seems to mean any data circuit that runs at the original 1. 544 Mbit/s line rate. In telecommunications Bit rate or Data transfer rate is the average number of Bits characters or blocks per unit time passing between equipment in a data transmission 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. Time-Division Multiplexing ( TDM) is a type of Digital or (rarely analog Multiplexing in which two or more signals or bit streams are transferred In telecommunications Bit rate or Data transfer rate is the average number of Bits characters or blocks per unit time passing between equipment in a data transmission While receiving a stream of framed Data, frame synchronization is the process by which incoming frame alignment signals i T2 and T3 circuit channels carry multiple T1 channels multiplexed, resulting in transmission rates of 6. 312 and 44. 736 Mbit/s, respectively.

Supposedly, the 1. 544 Mbit/s rate was chosen because tests done by AT&T Long Lines in Chicago were conducted underground. AT&T Communications Inc is a IXC / Long distance telephone company owned by AT&T. Chicago (ʃɪˈkɑːgoʊ is the largest City by population in the state of Illinois and the American Midwest of the United States. To accommodate loading coils, cable vault manholes were physically 6600 feet apart, and so the optimum bit rate was chosen empirically--the capacity was increased until the failure rate was unacceptable, then reduced to leave a margin. In Electronics, a loading coil or load coil is a Coil ( Inductor) that does not provide coupling to any other circuit, but In Telecommunications and Computing, bitrate (sometimes written bit rate, data rate or as a Variable R or f b In Philosophy, empiricism is a theory of Knowledge which asserts that knowledge arises from Experience. Companding allowed acceptable audio performance with only seven bits per PCM sample in this original T1/D1 system. In Telecommunication, Signal processing, and Thermodynamics, companding (occasionally called compansion) is a method of mitigating the detrimental The later D3 and D4 channel banks had an extended frame format, allowing eight bits per sample, reduced to seven every sixth sample or frame when one bit was "robbed" for signaling the state of the channel. The standard does not allow an all zero sample which would produce a long string of binary zeros and cause the repeaters to lose bit sync. However, when carrying data (Switched 56) there could be long strings of zeroes, so one bit per sample is set to "1" (jam bit 7) leaving 7 bits x 8000 frames per second for data.

A more common understanding of how the rate of 1. 544 Mbit/s was achieved is as follows. (This explanation glosses over T1 voice communications, and deals mainly with the numbers involved. ) Given that the highest voice frequency which the telephone system transmits is 4000 Hz, the required digital sampling rate is 8000 Hz (see Nyquist rate). The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. In Signal processing, the Nyquist rate is two times the bandwidth of a Bandlimited signal or a bandlimited channel Since each T1 frame contains 1 byte of voice data for each of the 24 channels, that system needs then 8000 frames per second to maintain those 24 simultaneous voice channels. Because each frame of a T1 is 193 bits in length (24 channels X 8 bits per channel + 1 framing bit = 193 bits), 8000 frames per second is multiplied by 193 bits to yield a transfer rate of 1. 544 Mbit/s (8000 X 193 = 1544000)

Initially, T1 used Alternate Mark Inversion (AMI) to reduce bandwidth and eliminate the DC component of the signal. In Telecommunication, bipolar encoding is a type of Line code (a method of encoding digital information to make it resistant to certain forms of signal loss during Later B8ZS became common practice. B8ZS is an abbreviation for Bipolar with 8 Zeros Substitution (not Binary Eight Zero Substitution see discussion- which is a method of line coding used in the T-carrier For AMI, each mark pulse had the opposite polarity of the previous one and each space was at a level of zero, resulting in a three level signal which however only carried binary data. Similar British 23 channel systems at 1. 536 Mbaud in the 1970s were equipped with ternary signal repeaters, in anticipation of using a 3B2T or 4B3T code to increase the number of voice channels in future, but in the 1980s the systems were merely replaced with European standard ones. In Telecommunication, a ternary signal is a signal that can assume at any given instant one of three Significant conditions such as power level 4B3T stands for 4 (four Binary 3 (three Ternary, a Line encoding scheme used for ISDN BRI interface American T-carriers could only work in AMI or B8ZS mode.

The AMI or B8ZS signal allowed a simple error rate measurement. The D bank in the central office could detect a bit with the wrong polarity, or "bipolarity violation" and sound an alarm. A Bipolar Violation, Bipolarity Violation, or BPV', is an error in the transmission of a T1 signal where two pulses of Later systems could count the number of violations and reframes and otherwise measure signal quality.

Historical Note on the 193-bit T1 frame

The decision to use a 193-bit frame was made in 1958, during the early stages of T1 system design. To allow for the identification of information bits within a frame, two alternatives were considered. Assign (a) just one extra bit, or (b) additional 8 bits per frame. The 8-bit choice is cleaner, resulting in a 200-bit frame, 25 8-bit channels, of which 24 are traffic and 1 8-bit channel available for operations, administration, and maintenance (OA&M). This article is about the medium access technology The name "TDMA" is also commonly used in the United States to refer to D-AMPS, which is a mobile telephone OA&M (operations administration and maintenance is a general term used to describe the processes activities tools standards etc involved with operating administering and maintaining The single bit per frame was chosen, not because a single bit saves bandwidth (by a trivial amount 1. 544 vs 1. 6 Mbit/s), but from a comment from AT&T Marketing. They claim that "if 8 bits were chosen for OA&M function, someone would then try to sell this as a voice channel and you wind up with nothing. "

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. In Telecommunication, an Extended Super Frame ( ESF) is a T1 framing standard, sometimes called D5 framing invented in the 1980s They petitioned AT&T management to change to 8-bit framing. This was flatly turned down because it would make installed systems obsolete.

Having this hindsight, some ten years later, CEPT chose 8 bits for framing the European E1. The European Conference of Postal and Telecommunications Administrations (CEPT was established on June 26, 1959 as a coordinating body for European state In digital Telecommunications where a single physical wire pair can be used to carry many simultaneous voice conversations worldwide standards have been created and deployed

Higher T

In the late 1960s and early 1970s Bell Labs developed higher rate systems. T-1C with a more sophisticated modulation scheme carried 3 Mbit/s, on those balanced pair cables that could support it. T-2 carried 6. 312 Mbit/s, requiring a special low-capacitance cable with foam insulation. This was standard for Picturephone. A videophone, also known by the trademarked name Picturephone, is a Telephone which is capable of both audio and Video Duplex transmission T-4 and T-5 used coaxial cables, similar to the old L-carriers used by AT&T Long Lines. SystemYearFrequencyCoax per cableDistance between repeatersVoice circuits per coaxL-119413 TD microwave radio relay systems were also fitted with high rate modems to allow them to carry a DS1 signal in a portion of their FM spectrum that had too poor quality for voice service. Microwave radio relay is a technology for transmitting digital and analog signals, such as long-distance Telephone calls and the relay of Later they carried DS3 and DS4 signals. Later optical fiber, typically using SONET transmission scheme, overtook them. An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length Synchronous optical networking (SONET and Synchronous Digital Hierarchy (SDH are two closely related Multiplexing protocols for transferring multiple

Digital signal crossconnect

DS1 signals are interconnected typically at Central Office locations at a common metallic cross-connect point known as a DSX-1. A DS1 signal at a DSX-1 is measured typically at 6 Volts Peak-to-peak (0dBdsx signal level at 772 kHz Nyquist) at plus or minus 1. 2 volts to permit easy interconnection of DS1 equipment NCI Code=04DS9/ /). When a DS1 is transported over metallic outside plant cable, the signal travels over conditioned cable pairs known as a T1 span. In Telecommunication, the term outside plant has the following meanings In civilian Telecommunications, all cables conduits ducts poles A T1 span can have up to -130 Volts of DC power superimposed on the associated four wire cable pairs to line or "Span" power line repeaters, and T1 NIU's (T1 Smartjacks). T1 span repeaters are typically engineered up to 6000 feet apart, depending on cable gauge, and at no more than 36 dB of loss before requiring a repeated span. There can be no cable bridge taps across any pairs. Bridged tap or bridge tap is a long-used method of cabling for telephone lines

T1 copper spans are being replaced by optical transport systems, but if a copper (Metallic) span is used, the T1 is typically carried over an HDSL encoded copper line. High bit rate Digital Subscriber Line ( HDSL) was the first DSL technology to use a higher Frequency spectrum of copper Twisted pair cables Four wire HDSL does not require as many repeaters as conventional T1 spans. Newer two wire HDSL (HDSL-2) equipment transports a full 1. 54400Bp/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. American wire gauge ( AWG) also known as the Brown & Sharpe wire gauge, is a standardized Wire gauge system used since 1857 predominantly HDSL-2 does not employ repeaters as does conventional four wire HDSL, or newer HDSL-4 systems.

One advantage of HDSL is its ability to operate with a limited number of bridge taps, with no tap being closer than 500 feet from any HDSL transceiver. Both two or four wire HDSL equipment transmits and receives over the same cable wire pair, as compared to conventional T1 service that utilizes individual cable pairs for transit or receive.

DS3 signals are rare except within buildings, where they are used for interconnections and as an intermediate step before being muxed onto a SONET circuit. For multiplexing in electronics and signal processing see Multiplexer. Synchronous optical networking (SONET and Synchronous Digital Hierarchy (SDH are two closely related Multiplexing protocols for transferring multiple This is because a T3 circuit can only go about 600 feet between repeaters. A customer who orders a DS3 usually receives a SONET circuit run into the building and a multiplexer mounted in a utility box. For multiplexing in electronics and signal processing see Multiplexer. The DS3 is delivered in its familiar form, two coax cables (1 for send and 1 for receive) with BNC connectors on the ends. Coaxial cable is a cable consisting of an inner conductor surrounded by a tubular insulating layer typically made from a flexible material with a high Dielectric constant, all The BNC ( Bayonet Neill Concelman) connector is a very common type of RF connector used for terminating Coaxial cable.

Reference: ANSI T1. 403//ANSI T1. 231//ANSI T1. 404//ANSI T1. 510.

Bit robbing

Main article: Robbed bit signaling

T1 carrier can utilize out-of-band (Robbed Bit) signalling, as opposed to earlier forms of in-band circuit signaling that utilized in-band audio tones typically at 2600 Hz, and more commonly known as SF signaling. Robbed-bit signaling ( RBS) is a specific type of Channel Associated Signaling in use in North America on T1 trunks and perhaps elsewhere in the world 2600 Hz is the Frequency in Hertz (cycles per second that AT&T formerly put as a steady signal on any Long-distance Telephone In robbed bit signaling, the eight bit, which is the least significant bit in the eight bit PCM sample that comprises the T1 carrier DS0 channel, is used to carry T1 channel signaling information.

Twelve DS1 frames make up a single T1 Superframe (T1 SF). Each T1 Superframe is comprised of two signaling frames. All T1 DS0 channels that employ in-band signaling will have its eighth bit over written, or "robbed", from the full 64Kb/s DS0 payload, and be overwritten by either a logical ZERO or ONE bit to signify a circuit signaling state or condition. Hence robbed bit signaling only will restrict a DS0 channel to a 56KB/s rate during two of the twelve DS1 frames that make up a T1 SF framed circuit. 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,& D).

NOTE: 56KB/s DS0 channels are associated with digital data service (DDS) services typically do not utilize the eighth bit of the DS0 as voice circuits that employ A&B out of band signaling. One exception is Switched 56Kb/s DDS. In DDS, bit eight is used to identify DTE request to send (RTS) condition. Data terminal equipment ( DTE) is an End instrument that converts User information into signals for transmission or reconverts received signals With Switched 56 DDS, bit eight is pulsed (Alternately set to logical Zeros and Ones) to transmit two state dial pulse signaling information between a SW56 DDS CSU/DSU, and a digital end office switch. A CSU/DSU ( Channel Service Unit / Data Service Unit) is a digital-interface device used to connect a Router to a digital circuit such as a T1 or

The incident use of robbed-bit signaling in North America has decreased significantly as a result of Signaling System Seven (SS7) on inter-office dial trunks. With SS7, full the 64KB/s DS0 channel is available for use on a connection, and allows 64KB/s, and 128KB/s ISDN data calls to exist over a switched trunk network connection if the supporting T1 carrier entity is optioned B8ZS (Clear Channel Capable).

REFERENCES: ANSI T1. 403//The Book On ESF, Verilink Corporation, 1986//D4 Digital Channel Bank Family, Bell System Technical Journal, Nov 1982.

Carrier pricing

Carriers price DS1 lines in many different ways. However, most boil down to two simple components; local loop (the cost the local incumbent charges to transport the signal from the end user's central office, otherwise known as a CO, to the point of presence, otherwise known as a POP, of the carrier) and the port (the cost to access the telephone network or the Internet through the carrier's network). In Telephony, the local loop (also referred to as a subscriber line) is the physical link or circuit that connects from the Demarcation point of the In the field of Telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls Typically, the port price is based upon access speed and yearly commitment level while the loop is based on geography. The further the CO and POP, the more the loop cost.

The loop price has several components built into it, including the mileage calculation (performed in V/H coordinates, not standard GPS coordinates) and the telco piece. Each local Bell operating company - namely Verizon, AT&T, and Qwest - charge T-carriers different price per mile rates. "Verizon" redirects here this article is about the corporation see also Verizon Wireless, Verizon Online DSL and Verizon FiOS. Before proposing a merge request please see Talk and see if the merger you propose has recently been made and Qwest Communications International Inc (pronounced like "quest" ˈkwɛst ( is a large Telecommunications carrier Therefore, the price calculation has two distance steps: geomapping and the determination of local price arrangements.

While most carriers utilize a geographic pricing model as described above, some Competitive Local Exchange Carriers (CLECs), such as EarthLink Business Solutions, offer national pricing. A Competitive Local Exchange Carrier ( CLEC) in the United States, is a Telecommunications provider company (sometimes called a " carrier EarthLink ( is an Internet service provider headquartered in Atlanta, Georgia, USA. Under this DS1 pricing model, a provider charges the same price in every geography it services. National pricing is an outgrowth of increased competition in the T-carrier market space and the commoditization of T-carrier products. ^[1] Providers that have adopted a national pricing strategy may experience widely varying margins as their suppliers, the Bell operating companies (e. g. , Verizon, AT&T and Qwest), maintain geographic pricing models, albeit at wholesale prices. "Verizon" redirects here this article is about the corporation see also Verizon Wireless, Verizon Online DSL and Verizon FiOS. Before proposing a merge request please see Talk and see if the merger you propose has recently been made and Qwest Communications International Inc (pronounced like "quest" ˈkwɛst ( is a large Telecommunications carrier

For voice DS1 lines, the calculation is mostly the same, except that the port (required for Internet access) is replaced by LDU (otherwise known as Long Distance Usage). Once the price of the loop is determined, only voice-related charges are added to the total. In short, the total price = loop + LDU x minutes used.

Notes

Note 1: The designators for T-carrier in the North American digital hierarchy correspond to the designators for the digital signal (DS) level hierarchy. A digital system uses discrete (discontinuous values usually but not always Symbolized Numerically (hence called "digital" to represent information for

Note 2: T-carrier systems were originally designed to transmit digitized voice signals. Current applications also include digital data transmission. Data transmission is the transfer of Data from point-to-point often represented as an Electro-magnetic Signal over a physical point-to-point or point-to-multipoint

Note 3: Historically, if an "F" precedes the "T", optical fiber cables are utilized at the same rates. An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length

Note 4: The North American and Japanese hierarchies are based on multiplexing 24 voice-frequency channels and multiples thereof, whereas the European hierarchy is based on multiplexing 32 voice-frequency channels and multiples thereof. For multiplexing in electronics and signal processing see Multiplexer. A voice frequency (VF or voice band is one of the frequencies within part of the audio range that is used for the transmission of speech. See table below.

Note 1: The DS designations are used in connection with the North American hierarchy only. Strictly speaking, a DS1 is the data carried on a T1 circuit, and likewise for a DS3 and a T3, but in practice the terms are used interchangeably.

Note 2: There are other data rates in use, e. Debt AIDS Trade in Africa (or DATA) is a Multinational non-government organization founded in January 2002 in London by U2 's g. , military systems that operate at six and eight times the DS1 rate. At least one manufacturer has a commercial system that operates at 90 Mbit/s, twice the DS3 rate. System (from Latin systēma, in turn from Greek systēma is a set of interacting or interdependent Entities, real or abstract New systems, which take advantage of the high data rates offered by optical communications links, are also deployed or are under development. Higher data rates are now often achieved by using Synchronous optical networking, SONET or Synchronous digital hierarchy, SDH. Synchronous optical networking (SONET and Synchronous Digital Hierarchy (SDH are two closely related Multiplexing protocols for transferring multiple Synchronous optical networking (SONET and Synchronous Digital Hierarchy (SDH are two closely related Multiplexing protocols for transferring multiple

Note 3: A DS3 is delivered native on a copper trunk. DS3 may be converted to a fiber run when needing longer distances between termination points. When a DS3 is delivered over fiber it is still an analog type trunk connection at the termination points. When delivering data over an OC3 or greater SONET is used. SONET is much faster and has a much lower bit error rate.

See also

References

• ANSI T1. Digital Signal 0 ( DS0) is a basic Digital signaling rate of 64 Kbit/s, corresponding to the capacity of one Voice-frequency -equivalent B8ZS is an abbreviation for Bipolar with 8 Zeros Substitution (not Binary Eight Zero Substitution see discussion- which is a method of line coding used in the T-carrier HDB3 ( H igh D ensity B ipolar of order 3 code is a Telecommunications Line code mainly used in Japan In Telecommunication, bipolar encoding is a type of Line code (a method of encoding digital information to make it resistant to certain forms of signal loss during Optical Carrier levels describe a range of digital signals that can be carried on SONET Fiber optic Network. Time-Division Multiplexing ( TDM) is a type of Digital or (rarely analog Multiplexing in which two or more signals or bit streams are transferred For multiplexing in electronics and signal processing see Multiplexer. The Plesiochronous Digital Hierarchy ( PDH) is a technology used in Telecommunications networks to transport large quantities of data over digital transport equipment This is a list of device bandwidths: the Net bit rate (or more informally Digital bandwidth) of some computer devices employing methods of data transport is quantified Modified AMI code is a T-carrier AMI (alternate mark inversion Line code in which Bipolar violations may be deliberately inserted to maintain In digital Telecommunications where a single physical wire pair can be used to carry many simultaneous voice conversations worldwide standards have been created and deployed The STM-1 ( Synchronous Transport Module) is the SDH ITU-T Fiber optic network transmission standard 403-1999 - Network and Customer Installation Interface
• Federal Standard 1037C
• T1: A Survival Guide Chapter 5
• Cisco T1 card documentation
• T1 architecture

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL. The Free On-line Dictionary of Computing ( FOLDOC) is an online searchable encyclopedic Dictionary of Computing subjects The GNU Free Documentation License ( GNU FDL or simply GFDL) is a Copyleft License for free documentation designed by the Free Software

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