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In digital telecommunications, where a single physical wire can be used to carry many simultaneous voice conversations, worldwide standards have been created and deployed. The European Conference of Postal and Telecommunications Administrations (CEPT) originally standardized the E-carrier system, which revised and improved the earlier American T-carrier technology, and this has now been adopted by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T). The European Conference of Postal and Telecommunications Administrations (CEPT was established on June 26, 1959 as a coordinating body for European state In Telecommunications T-carrier, sometimes abbreviated as T-CXR, is the generic designator for any of several digitally multiplexed telecommunications The ITU Telecommunication Standardization Sector ( ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication This is now widely used in almost all countries outside USA, Canada and Japan.

The E-carrier standards form part of the Plesiochronous Digital Hierarchy (PDH) where groups of E1 circuits may be bundled onto higher capacity E3 links between telephone exchanges or countries. The Plesiochronous Digital Hierarchy ( PDH) is a technology used in Telecommunications networks to transport large quantities of data over digital transport equipment This allows a network operator to provide a private end-to-end E1 circuit between customers in different countries that share single high capacity links in between. A telephone company (or telco) provides Telecommunications services such as Telephony and Data communications Most of the largest telcos whatever

In practice, only E1 (30 circuit) and E3 (480 circuit) versions are used. Physically E1 is transmitted as 32 timeslots and E3 512 timeslots, but one is used for framing and typically one allocated for signalling call setup and tear down. 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 In Computer networking, a frame is a Data packet of fixed or variable length which has been encoded by a Data link layer communications protocol for digital Unlike Internet data services, E-carrier systems permanently allocate capacity for a voice call for its entire duration. This ensures high call quality because the transmission arrives with the same short delay (Latency) and capacity at all times. Latency is a time delay between the moment something is initiated and the moment one of its effects begins or becomes detectable

E1 circuits are very common in most telephone exchanges and are used to connect to medium and large companies, to remote exchanges and in many cases between exchanges. In the field of Telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls E3 lines are used between exchanges, operators and/or countries, and have a transmission speed of 34. 368 Mbit/s.

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E1

An E1 link operates over two separate sets of wires, usually twisted pair cable. Twisted pair Cabling is a form of wiring in which two conductors (two halves of a single circuit) are wound together for the purposes of canceling out A nominal 2. 4 Volt signal is encoded with pulses using a method that avoids long periods without polarity changes. The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. The line data rate is 2. 048 Mbit/s (full duplex, i. 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 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. A bit is a binary digit, taking a value of either 0 or 1 Binary digits are a basic unit of Information storage and communication Thus each timeslot sends and receives an 8-bit sample 8000 times per second (8 x 8000 x 32 = 2,048,000). This is ideal for voice telephone calls where the voice is sampled into an 8 bit number at that data rate and reconstructed at the other end. In Signal processing, sampling is the reduction of a Continuous signal to a Discrete signal.

One timeslot (TS1) is reserved for framing purposes, and alternately transmits a fixed pattern. While receiving a stream of framed Data, frame synchronization is the process by which incoming frame alignment signals i 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 the circuit is losing bits (information), but this is not always used. A cyclic redundancy check (CRC is a type of function that takes as input a data stream of any length and produces as output a value of a certain space commonly a 32-bit integer

One timeslot (TS17) 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 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. See also Signalling (telecommunications Channel Associated Signaling (CAS also known as Per-Trunk Signaling (PTS is a form of digital communication signaling More recent systems used Common Channel Signaling (CCS) such as ISDN or Signalling System 7 (SS7) which send short encoded messages with more information about the call including caller ID, type of transmission required etc. See also Signaling (telecommunications In telephony Common Channel Signaling (CCS or in the US Common Channel Interoffice Signaling (CCIS is the transmission Signaling System #7 (SS7 is a set of Telephony signaling protocols which are used to set up most of the world's Public switched telephone network telephone ISDN is often used between the local telephone exchange and business premises, whilst SS7 is almost exclusively used between exchanges and operators. SS7 can handle up to 4096 circuits per signalling channel, thus allowing slightly more efficient use of the overall transmission bandwidth (for example: uses 31 voice channels on an E1).

Unlike the earlier T-carrier systems developed in North America, all 8 bits of each sample are available for each call. In Telecommunications T-carrier, sometimes abbreviated as T-CXR, is the generic designator for any of several digitally multiplexed telecommunications This allows the E1 systems to be used equally well for circuit switch data calls, without risking the loss of any information.

While the original CEPT standard G.703 specifies several options for the physical transmission, almost exclusively HDB3 format is used. G703 is a ITU-T standard for transmitting voice or data over digital carriers such as T1 and E1. HDB3 ( H igh D ensity B ipolar of order 3 code is a Telecommunications Line code mainly used in Japan

Hierarchy levels

The PDH based on the E0 signal rate is designed so that each higher level can multiplex a set of lower level signals. The Plesiochronous Digital Hierarchy ( PDH) is a technology used in Telecommunications networks to transport large quantities of data over digital transport equipment For multiplexing in electronics and signal processing see Multiplexer. E1 is designed to carry 30 E0 signals, all other levels are designed to carry 4 signals from 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 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. Interleaving in Computer science is a way to arrange Data in a non- Contiguous way in order to increase performance

Signal Rate
E0 64 kbit/s
E1 2. 048 Mbit/s
E2 8. 448 Mbit/s
E3 34. 368 Mbit/s
E4 139. 264 Mbit/s

See also

References

External links

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