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51-628: An E1 link operates over two separate sets of wires, usually unshielded twisted pair (balanced cable) or using coaxial (unbalanced cable). A nominal 3 volt peak signal is encoded with pulses using a method avoiding long periods without polarity changes. The line data rate is 2.048  Mbit/s ( full duplex , i.e. 2.048 Mbit/s downstream and 2.048 Mbit/s upstream) which is split into 32 timeslots, each being allocated 8  bits in turn. Thus each timeslot sends and receives an 8-bit PCM sample, usually encoded according to A-law algorithm , 8,000 times per second (8 × 8,000 × 32 = 2,048,000). This

102-476: A balanced circuit is electronic circuitry for use with a balanced line , or the balanced line itself. Balanced lines are a common method of transmitting many types of electrical signals between two points on two wires. In a balanced line, the two signal lines are of a matched impedance to help ensure that interference , induced in the line, is common-mode and can be removed at the receiving end by circuitry with good common-mode rejection . To maintain

153-407: A balanced line , which as part of a balanced circuit can greatly reduce the effect of noise currents induced on the line by coupling of electric or magnetic fields. The idea is that the currents induced in each of the two wires are very nearly equal. The twisting ensures that the two wires are on average the same distance from the interfering source and are affected equally. The noise thus produces

204-435: A common-mode signal which can be cancelled at the receiver by detecting the difference signal only, the latter being the wanted signal. Common-mode rejection starts to fail on untwisted wires when the noise source is close to the signal wires; the closer wire will couple with the noise more strongly and the receiver will be unable to eliminate it. This problem is especially apparent in telecommunication cables where pairs in

255-493: A single conductor or an untwisted balanced pair , a twisted pair reduces electromagnetic radiation from the pair and crosstalk between neighbouring pairs and improves rejection of external electromagnetic interference . It was invented by Alexander Graham Bell . For additional noise immunity, twisted-pair cabling may be shielded . Cable with shielding is known as shielded twisted pair ( STP ) and without as unshielded twisted pair ( UTP ). A twisted pair can be used as

306-482: A balanced line is through transformers at each end shown in figure 5. Transformers were the original method of making such connections in telephony, and before the advent of active circuitry were the only way. In the telephony application they are known as repeating coils . Transformers have the additional advantage of completely isolating (or "floating") the line from earth and earth loop currents , which are an undesirable possibility with other methods. The side of

357-432: A differential input. On the other hand, the line signal is not symmetrical. The voltages at the input to the two legs, V + and V − are given by; Where Z in is the input impedance of the line. These are clearly not symmetrical since V − is much smaller than V + . They are not even opposite polarities. In audio applications V − is usually so small it can be taken as zero. A circuit that has

408-402: A four-pair cable, there would be a total of eight solid wires. Stranded cable uses multiple wires wrapped around each other in each conductor and in a four-pair with seven strands per conductor cable, there would be a total of 56 wires (2 per pair × 4 pairs × 7 strands). Solid core cable is intended for permanently installed runs ( permanent link ). It is less flexible than stranded cable and

459-490: A freely chosen set of timeslots or on a different physical channel. When using E1 frames for data communication, some systems use those timeslots slightly differently, either The PDH based on the E0 signal rate is designed so that each higher level can multiplex a set of lower level signals. Framed E1 is designed to carry 30 or 31 E0 data channels plus 1 or 2 special channels, all other levels are designed to carry 4 signals from

510-401: A more complex circuit than figure 6, but still avoiding the expense of a transformer. A floating op-amp output can only float within the limits of the op-amp's supply rails. An isolated output can be achieved without transformers with the addition of opto-isolators . As noted above, it is possible to drive a balanced line with a single-ended signal and still maintain the line balance. This

561-405: A resin to prevent the ingress of moisture which would seriously degrade the insulating properties of the paper insulation. However, such seals made future maintenance and changes more difficult. These cables are no longer made but are still occasionally encountered in old buildings and in various external areas, commonly rural villages. A loaded twisted pair has intentionally added inductance and

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612-430: A set of bits is used to replicate opening and closing the circuit (as if picking up the telephone receiver and pulsing digits on a rotary phone), or using tone signalling which is passed through on the voice circuits themselves. More recent systems use common-channel signaling (CCS) such Signalling System 7 (SS7) where no particular timeslot is reserved for signalling purposes, the signalling protocol being transmitted on

663-410: A symmetrical circuit, which is a circuit showing symmetry of its components about a vertical line at its midpoint. An example of a symmetrical circuit is shown in figure 2. Circuits designed for use with balanced lines will often be designed to be both balanced and symmetrical as shown in figure 4. The advantages of symmetry are that the same impedance is presented at both ports and that the circuit has

714-438: A twist rate of about four twists per kilometre , or six per mile . Such open-wire balanced lines with periodic transpositions still survive today in some rural areas. Twisted-pair cabling was invented by Alexander Graham Bell in 1881. By 1900, the entire American telephone network was either twisted pair or open wire with transposition to guard against interference. Today, most of the millions of kilometres of twisted pairs in

765-402: Is a variant of standard ribbon cable in which adjacent pairs of conductors are bonded and twisted together. The twisted pairs are then lightly bonded to each other in a ribbon format. Periodically along the ribbon, there are short sections with no twisting where connectors may be attached using the usual ribbon cable IDC techniques. A solid-core cable uses one solid wire per conductor and in

816-484: Is ideal for voice telephone calls where the voice is sampled at that data rate and reconstructed at the other end. The timeslots are numbered from 0 to 31. One timeslot (TS0) is reserved for framing purposes, and alternately transmits a fixed pattern. This allows the receiver to lock onto the start of each frame and match up each channel in turn. The standards allow for a full cyclic redundancy check to be performed across all bits transmitted in each frame, to detect if

867-636: Is more prone to failure if repeatedly flexed due to work hardening . Stranded cable is used at patch panels and for connections from wall ports to end devices ( patch cord or drop cable), as it resists cracking of the conductors. Connectors are designed differently for solid core than for stranded. Use of a connector with the wrong cable type can lead to unreliable cabling. Plugs designed for solid and stranded cores are readily available, and some vendors even offer plugs designed for use with both types. The punch-down blocks on patch-panel and wall-port jacks are designed for use with solid core cable. These work via

918-502: Is not surrounded by any shielding. UTP is the primary wire type for telephone usage and is very common for computer networking . The earliest telephones used telegraph lines which were single-wire earth return circuits. In the 1880s electric trams were installed in many cities, which induced noise into these circuits. In some countries, the tram companies were held responsible for disruption to existing telegraph lines and had to pay for remedial work. For new installations, however, it

969-514: Is one where the voltages on each wire are symmetrical with respect to ground (or some other reference). That is, the signals are inverted with respect to each other. A balanced circuit is a circuit where the two sides have identical transmission characteristics in all respects. A balanced line is a line in which the two wires will carry balanced currents (that is, equal and opposite currents) when balanced (symmetrical) voltages are applied. The condition for balance of lines and circuits will be met, in

1020-406: Is possible to create a floating output. This is important if one leg of the line might become grounded or connected to some other voltage reference. Grounding one leg of the line in the circuit of figure 6 will result in the line voltage being halved since only one op-amp is now providing signal. To achieve a floating output additional feedback paths are required between the two op-amps resulting in

1071-420: Is represented in outline in figure 7. The amplifier driving one leg of the line through a resistor is assumed to be an ideal (that is, zero output impedance) single-ended output amp. The other leg is connected from ground through another resistor of the same value. The impedance to ground of both legs is the same and the line remains balanced. The receiving amplifier still rejects any common-mode noise as it has

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1122-421: Is used, it is very difficult to demultiplex low level tributaries directly, requiring equipment to individually demultiplex every single level down to the one that is required. Unshielded twisted pair Twisted pair cabling is a type of communications cable in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility . Compared to

1173-492: The baseband of television signals, UTP is now used in some video applications, primarily in security cameras . As UTP is a balanced transmission line, a balun is needed to connect to unbalanced equipment, for example any using BNC connectors and designed for coaxial cable. Twisted pair cables may incorporate shielding in an attempt to prevent electromagnetic interference. Shielding provides an electrically conductive barrier to attenuate electromagnetic waves external to

1224-476: The insulation-displacement method , whereby the device pierces the sides of the insulation and "bites" into the copper conductor to form a connection. Punchdown blocks are used as patch panels or as break-out boxes, for twisted pair cable. Twisted pair has the following useful attributes: Twisted pair has the following limitations: [REDACTED] Media related to Twisted-pair cables at Wikimedia Commons Balanced circuit In electrical engineering ,

1275-402: The balance, circuit blocks which interface to the line or are connected in the line must also be balanced. Balanced lines work because the interfering noise from the surrounding environment induces equal noise voltages into both wires. By measuring the voltage difference between the two wires at the receiving end, the original signal is recovered while the noise is rejected. Any inequality in

1326-520: The cable. UTP is also the most common cable used in computer networking . Modern Ethernet , the most common data networking standard, can use UTP cables, with increasing data rates requiring higher specification variants of the UTP cable. Twisted-pair cabling is often used in data networks for short and medium-length connections because of its relatively lower costs compared to optical fibre and coaxial cable . As UTP cable bandwidth has improved to match

1377-407: The case of passive circuitry, if the impedances are balanced. The line and circuit remain balanced, and the benefits of common-mode noise rejection continue to apply, whether or not the applied signal is itself balanced (symmetrical), always provided that the generator producing that signal maintains the impedance balance of the line. There are a number of ways that a balanced line can be driven and

1428-404: The circuit is losing bits (information), but this is not always used. An alarm signal may also be transmitted using timeslot TS0. Finally, some bits are reserved for national use. One timeslot (TS16) is often reserved for signalling purposes, to control call setup and teardown according to one of several standard telecommunications protocols. This includes channel-associated signaling (CAS) where

1479-504: The coloured insulation typically made from an insulator such as polyethylene or FEP and the total package covered in a polyethylene jacket. For urban outdoor telephone cables containing hundreds or thousands of pairs, the cable is divided into small but identical bundles. Each bundle consists of twisted pairs that have different twist rates, as pairs having the same twist rate within the cable can still experience some degree of crosstalk . The bundles are in turn twisted together to make up

1530-416: The common use of polyethylene and other plastics for insulation, telephone twisted pair cable was insulated with waxed paper or cotton with a wax coating applied to the copper. The overall sheath of this type of cable was usually lead. This style of cable came into use in the late 19th century shortly after the invention of the telephone. The cable termination in termination boxes were sealed with molten wax or

1581-417: The difference detector) is the same for both conductors at all points along the length of the line. If one wire has a higher impedance to ground it will tend to have a higher noise induced, destroying the balance. A balanced circuit will normally show a symmetry of its components about a horizontal line midway between the two conductors (example in figure 3). This is different from what is normally meant by

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1632-425: The length of the cable. Pioneered by Belden , it is intended to help assure configuration consistency during and after installation. One key benefit is that the noise immunity performance of the cable can be protected despite potentially rough handling. The enhanced performance may be unnecessary and bonding reduces the flexibility of the cable and makes it prone to failure where it is flexed. A twisted ribbon cable

1683-471: The level below. Because of the necessity for overhead bits, and justification bits to account for rate differences between sections of the network, each subsequent level has a capacity greater than would be expected from simply multiplying the lower level signal rate (so for example E2 is 8.448 Mbit/s and not 8.192 Mbit/s as one might expect when multiplying the E1 rate by 4). Note, because bit interleaving

1734-403: The line as shown in figure 5. With transformers the sending and receiving circuitry can be entirely unbalanced with the transformer providing the balancing. Active balance is achieved using differential amplifiers at each end of the line. An op-amp implementation of this is shown in figure 6, other circuitry is possible. Unlike transformer balance, there is no isolation of the circuitry from

1785-436: The line. Each of the two wires is driven by an op amp circuit which are identical except that one is inverting and one is non-inverting. Each one produces an asymmetrical signal individually but together they drive the line with a symmetrical signal. The output impedance of each amp is equal so the impedance balance of the line is maintained. While it is not possible to create an isolated drive with op-amp circuitry alone, it

1836-404: The noise induced in each wire is an imbalance and will result in the noise not being fully rejected. One requirement for balance is that both wires are an equal distance from the noise source. This is often achieved by placing the wires as close together as possible and twisting them together. Another requirement is that the impedance to ground (or to whichever reference point is being used by

1887-436: The route with electrical power lines . Within a few years, the growing use of electricity again brought an increase of interference, so engineers devised a method called wire transposition , to cancel out the interference. In wire transposition, the wires exchange position once every several poles. In this way, the two wires would receive similar EMI from power lines. This represented an early implementation of twisting, with

1938-417: The same cable lie next to each other for many miles. Twisting the pairs counters this effect as on each half twist the wire nearest to the noise source is exchanged. Provided the interfering source remains uniform, or nearly so, over the distance of a single twist, the induced noise will remain common-mode. The twist rate (also called pitch of the twist, usually defined in twists per metre ) makes up part of

1989-517: The same effect on signals travelling in both directions on the line. Balance and symmetry are usually associated with reflected horizontal and vertical physical symmetry respectively as shown in figures 1 to 4. However, physical symmetry is not a necessary requirement for these conditions. It is only necessary that the electrical impedances are symmetrical. It is possible to design circuits that are not physically symmetrical but which have equivalent impedances which are symmetrical. A balanced signal

2040-404: The secondary, but at the receiving end the line side winding is the primary. When discussing a two-wire circuit primary and secondary cease to have any meaning at all, since signals are flowing in both directions at once. The equipment side winding of the transformer does not need to be so carefully balanced. In fact, one leg of the equipment side can be earthed without effecting the balance on

2091-600: The shield. The shield also provides a conduction path by which induced currents can be circulated and returned to the source via a ground reference connection. Such shielding can be applied to individual pairs or to a collection of pairs. Shielding may be foil or braided wire. When shielding is applied to a collection of pairs, it is usually referred to as screening, but usage among vendors and authors in applying such words as screening , shielding , and STP (shielded twisted pair) can be subject to variability. ISO/IEC 11801 :2002 (Annex E) attempts to internationally standardize

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2142-436: The shielding is conductive, it may also serve as a path to ground. A foil-shielded, twisted pair cable may have an integrally incorporated grounding wire called a drain wire which makes electrical contact with the shield. The purpose of the drain wire is for easy connection to terminals which are usually designed for connection of round wires. Common shield construction types include: An early example of shielded twisted-pair

2193-477: The signal detected. In all methods, for the continued benefit of good noise immunity, it is essential that the driving and receiving circuit maintain the impedance balance of the line. It is also essential that the receiving circuit detects only differential signals and rejects common-mode signals. It is not essential (although it is often the case) that the transmitted signal is balanced, that is, symmetrical about ground. The conceptually simplest way to connect to

2244-450: The specification for a given type of cable. When nearby pairs have equal twist rates, the same conductors of the different pairs may repeatedly lie next to each other, partially undoing the benefits of twisting. For this reason, it is commonly specified that, at least for cables containing small numbers of pairs, the twist rates must differ. In contrast to shielded or foiled twisted pair (typically S/FTP or F/UTP cable shielding ), UTP cable

2295-399: The transformer facing the line, in a good quality design, will have the winding laid in two parts (often with a centre tap provided) which are carefully balanced to maintain the line balance. Line side and equipment side windings are more useful concepts than the more usual primary and secondary windings when discussing these kinds of transformers. At the sending end the line side winding is

2346-465: The various shielding designations for twisted pair (TP) cables using an explicit two-part abbreviation in the form of x/xTP , where the first x indicates the shielding for the overall cable and the second x indicates the shielding for individual pairs or quads, where each x can be: Shielded Cat 5e , Cat 6/6A , and Cat 8/8.1 cables typically have F/UTP construction, while shielded Cat 7/7 A and Cat 8.2 cables use S/FTP construction. Because

2397-621: The world are outdoor landlines, owned and maintained by telephone companies, used for voice service. Unshielded twisted pair (UTP) cables are found in many Ethernet networks and telephone systems. For indoor telephone applications, UTP is often grouped into sets of 25 pairs according to a standard 25-pair colour code originally developed by AT&T Corporation . A typical subset of these colours (white/blue, blue/white, white/orange, orange/white) shows up in most UTP cables. The cables are typically made with copper wires measured at 22 or 24 American Wire Gauge (AWG) (0.644 or 0.511 mm²), with

2448-605: Was IBM STP-A, which is a two-pair 150 ohm S/FTP cable defined in 1985 by the IBM Cabling System specifications, and used with Token Ring or FDDI networks . Before digital communication and Ethernet became widespread there was no international standard for telephone cable. Standards were set at a national level. For instance, in the UK the General Post Office specified CW1293 and CW1308 cables. CW1308

2499-464: Was a similar specification to the earlier CW1293 but with an improved colour code. CW1293 used mostly solid colours on the cores making it difficult to identify the pair it was twisted with without stripping back a large amount of sheath. To solve this problem. CW1308 has narrow rings of the paired colour printed over the base colour. Both cables are a similar standard to category 3 cable. Cables with categories 3 through 7 have 4 twisted pairs. Prior to

2550-443: Was formerly common practice on telecommunication lines. The added inductors are known as load coils and reduce attenuation for voiceband frequencies but increase it on higher frequencies. Load coils reduce distortion in voiceband on very long lines. In this context a line without load coils is referred to as an unloaded line. A bonded twisted pair is a construction variant in which the two wires of each pair are bonded together for

2601-455: Was necessary to protect against existing trams from the outset. Interference on telephone lines is even more disruptive than it is on telegraph lines. Telephone companies converted to balanced circuits , which had the incidental benefit of reducing attenuation , hence increasing range. As electrical power distribution became more commonplace, this measure proved inadequate. Two wires, strung on either side of cross bars on utility poles , shared

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