1.
Telephone exchange
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A telephone exchange is a telecommunications system used in the public switched telephone network or in large enterprises. In historical perspective, telecommunication terms have been used with different semantics over time, the term telephone exchange is often used synonymously with central office, a Bell System term. Often, an office is defined as a building used to house the inside plant equipment of potentially several telephone exchanges. Such an area has also referred to as the exchange. Central office locations may also be identified in North America as wire centers, All central offices within a larger region, typically aggregated by state, were assigned a common numbering plan area code. For corporate or enterprise use, a telephone exchange is often referred to as a private branch exchange. Smaller installations might deploy a PBX or key telephone system in the office of a receptionist and this made it possible for subscribers to call each other at homes, businesses, or public spaces. These made telephony an available and comfortable communication tool for everyday use, one of the first to propose a telephone exchange was Hungarian Tivadar Puskás in 1877 while he was working for Thomas Edison. The first experimental telephone exchange was based on the ideas of Puskás, the worlds first commercial telephone exchange opened on November 12,1877 in Friedrichsberg close to Berlin. George W. Coy designed and built the first commercial US telephone exchange opened in New Haven. The switchboard was built from carriage bolts, handles from teapot lids and bustle wire, Charles Glidden is also credited with establishing an exchange in Lowell, MA. with 50 subscribers in 1878. In Europe other early telephone exchanges were based in London and Manchester, Belgium had its first International Bell exchange a year later. In 1887 Puskás introduced the multiplex switchboard, later exchanges consisted of one to several hundred plug boards staffed by switchboard operators. Each operator sat in front of a panel containing banks of ¼-inch tip-ring-sleeve jacks. In front of the jack panel lay a horizontal panel containing two rows of patch cords, each connected to a cord circuit. When a calling party lifted the receiver, the loop current lit a signal lamp near the jack. The operator responded by inserting the rear cord into the jack and switched her headset into the circuit to ask, Number. For a local call, the operator inserted the front cord of the pair into the partys local jack
2.
Optical mesh network
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Optical mesh networks are a type of telecommunications network. The new optical mesh networks support the same fast recovery previously available in ring networks while achieving better capacity efficiency and this was made possible by the emergence of optical network elements that have the intelligence required to automatically control certain network functions, such as fault recovery. The new optical mesh networks support the same fast recovery previously available in ring networks while achieving better capacity efficiency, in addition to switching wavelengths, the equipment is typically also able to multiplex lower speed traffic into wavelengths for transport, and to groom traffic. Finally, these equipment also provide for the recovery of traffic in case of a network failure, optical switches build by companies such as Sycamore and Ciena and Tellium have been deployed in operational mesh networks. Calient has built all-optical switches based on 3D MEMS technology, optical mesh networks support the establishment of circuit-mode connection-oriented services. Multiple recovery mechanisms that provide different levels of protection or restoration against different failure modes are available in mesh networks, channel-, link-, segment- and path- protection are the most common protection schemes. P-cycles is another type of protection that leverages and extends ring-based protection, restorationis another recovery method that can work on its own or complement faster protection schemes in case of multiple failures. In path-protected mesh networks, some connections can be unprotected, others can be protected against single or multiple failures in various ways. A connection can be protected against a failure by defining a backup path. A number of other schemes such as the use of pre-emptible paths, or only partially diverse backup paths. Finally, multiple diverse routes can be designed so that a connection has multiple recovery routes, traditional transport networks are made of optical fiber-based links between telecommunications offices, where multiple wavelengths are multiplexed to increase the capacity of the fiber. The wavelengths are terminated on electronic devices called transponders, undergoing a conversion for signal Reamplification, Reshaping. The act of going through Optical-Electrical-Optical conversion through a telecommunications office causes the network to be considered opaque, hybrid schemes that leverage optical bypasses and provide limited O-E-O conversions at key locations across the network, are referred to as translucent networks. ROADM-based transparent optical mesh networks have been deployed in metropolitan and regional networks since the mid-2000s, routing is a key control and operational aspect of optical mesh networks. In transparent or all-optical networks, routing of connections is tightly linked to the wavelength selection and this is due to the fact that the connection remains on the same wavelength from end-to-end throughout the network. In an opaque network, the problem is one of finding a primary path for a connection and if protection is needed. Wavelengths are used on each link independently of each others, in general, however, the problems of optimal routing for Dedicated Backup Path Protection with arbitrary Shared Risk Link Groups, and for Shared Backup Path Protection are NP-complete. Singh, W. D. Grover, IEEE Communications Surveys and Tutorials, February 2010 Survivable networks, algorithms for diverse routing, by Ramesh Bhandari
3.
Amplitude modulation
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Amplitude modulation is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. In amplitude modulation, the amplitude of the wave is varied in proportion to the waveform being transmitted. That waveform may, for instance, correspond to the sounds to be reproduced by a loudspeaker and this technique contrasts with frequency modulation, in which the frequency of the carrier signal is varied, and phase modulation, in which its phase is varied. AM was the earliest modulation method used to transmit voice by radio and it was developed during the first two decades of the 20th century beginning with Roberto Landell De Moura and Reginald Fessendens radiotelephone experiments in 1900. It remains in use today in many forms of communication, for example it is used in two way radios, VHF aircraft radio, Citizens Band Radio, and in computer modems. AM is often used to refer to mediumwave AM radio broadcasting, when it reaches its destination, the information signal is extracted from the modulated carrier by demodulation. In amplitude modulation, the amplitude or strength of the oscillations is what is varied. For example, in AM radio communication, a continuous wave signal has its amplitude modulated by an audio waveform before transmission. The audio waveform modifies the amplitude of the wave and determines the envelope of the waveform. In the frequency domain, amplitude modulation produces a signal with power concentrated at the carrier frequency, each sideband is equal in bandwidth to that of the modulating signal, and is a mirror image of the other. Standard AM is thus sometimes called double-sideband amplitude modulation to distinguish it more sophisticated modulation methods also based on AM. One disadvantage of all amplitude modulation techniques is that the receiver amplifies and detects noise, increasing the received signal to noise ratio, say, by a factor of 10, thus would require increasing the transmitter power by a factor of 10. For this reason AM broadcast is not favored for music and high fidelity broadcasting, another disadvantage of AM is that it is inefficient in power usage, at least two-thirds of the power is concentrated in the carrier signal. The carrier signal contains none of the information being transmitted. However its presence provides a means of demodulation using envelope detection, providing a frequency. The receiver may regenerate a copy of the frequency from a greatly reduced pilot carrier to use in the demodulation process. Even with the carrier totally eliminated in double-sideband suppressed-carrier transmission, carrier regeneration is possible using a Costas phase-locked loop and this doesnt work however for single-sideband suppressed-carrier transmission, leading to the characteristic Donald Duck sound from such receivers when slightly detuned. Single sideband is used widely in amateur radio and other voice communications both due to its power efficiency and bandwidth efficiency
4.
Wavelength-division multiplexing
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This technique enables bidirectional communications over one strand of fiber, as well as multiplication of capacity. This is purely convention because wavelength and frequency communicate the same information, a WDM system uses a multiplexer at the transmitter to join the several signals together, and a demultiplexer at the receiver to split them apart. With the right type of fiber it is possible to have a device that does both simultaneously, and can function as an optical add-drop multiplexer, the optical filtering devices used have conventionally been etalons. As there are three different WDM types, whereof one is called WDM, we would use the notation xWDM when discussing the technology as such. The concept was first published in 1978, and by 1980 WDM systems were being realized in the laboratory, the first WDM systems combined only two signals. Modern systems can handle 160 signals and can expand a basic 100 Gbit/s system over a single fiber pair to over 16 Tbit/s. A system of 320 channels in also present WDM systems are popular with telecommunications companies because they allow them to expand the capacity of the network without laying more fiber. By using WDM and optical amplifiers, they can accommodate several generations of development in their optical infrastructure without having to overhaul the backbone network. Capacity of a link can be expanded simply by upgrading the multiplexers and demultiplexers at each end. This is often done by use of optical-to-electrical-to-optical translation at the edge of the transport network. Most WDM systems operate on single-mode fiber optical cables, which have a diameter of 9 µm. Certain forms of WDM can also be used in multi-mode fiber cables which have diameters of 50 or 62.5 µm. Early WDM systems were expensive and complicated to run, however, recent standardization and better understanding of the dynamics of WDM systems have made WDM less expensive to deploy. Optical receivers, in contrast to laser sources, tend to be wideband devices, therefore, the demultiplexer must provide the wavelength selectivity of the receiver in the WDM system. WDM systems are divided into three different wavelength patterns, normal, coarse and dense, normal WDM uses the two normal wavelengths 1310 and 1550 on one fiber. Coarse WDM provides up to 16 channels across multiple transmission windows of silica fibers, dense wavelength division multiplexing uses the C-Band transmission window but with denser channel spacing. Channel plans vary, but a typical DWDM system would use 40 channels at 100 GHz spacing or 80 channels with 50 GHz spacing, some technologies are capable of 12.5 GHz spacing. New amplification options enable the extension of the wavelengths to the L-band
5.
Telephone call
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A telephone call is a connection over a telephone network between the called party and the calling party. The first telephone call was made on March 10,1876 by Alexander Graham Bell, Bell demonstrated his ability to talk with electricity by transmitting a call to his assistant, Thomas Watson. The first words transmitted were Mr Watson, come here and this event has been called Bells greatest success, as it demonstrated the first successful use of the telephone. Although it was his greatest success, he refused to have one in his own home because it was something he invented by mistake, the call may use land line, mobile phone, satellite phone or any combination thereof. When a telephone call has more than one called party it is referred to as a conference call, when two or more users of the network are sharing the same physical line, it is called a party line or Rural phone line. If the callers wireline phone is connected directly to the party, when the caller takes their telephone off-hook. This is called a hot line or ringdown, otherwise, the calling party is usually given a tone to indicate they should begin dialing the desired number. In some cases, if the party cannot dial calls directly. Calls may be placed through a public network provided by a telephone company or a private network called a PBX. In most cases a private network is connected to the network in order to allow PBX users to dial the outside world. Most telephone calls through the PSTN are set up using ISUP signalling messages or one of its variants between telephone exchanges to establish the end to end connection, calls through PBX networks are set up using QSIG, DPNSS or variants. Some types of calls are not charged, such as local calls dialed directly by a subscriber in Canada. In most other areas, all calls are charged a fee for the connection. Fees depend on the provider of the service, the type of service being used, in most circumstances, the calling party pays this fee. However, in circumstances such as a reverse charge or collect call. In some circumstances, the caller pays a flat charge for the telephone connection. The caller then rotary dials or presses buttons for the number needed to complete the call. The second phone makes a noise to alert its owner
6.
Frequency modulation
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In telecommunications and signal processing, frequency modulation is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. This contrasts with amplitude modulation, in which the amplitude of the wave varies. This modulation technique is known as frequency-shift keying, FSK is widely used in modems and fax modems, and can also be used to send Morse code. Frequency modulation is used for FM radio broadcasting. For this reason, most music is broadcast over FM radio, frequency modulation has a close relationship with phase modulation, phase modulation is often used as an intermediate step to achieve frequency modulation. Mathematically both of these are considered a case of quadrature amplitude modulation. While most of the energy of the signal is contained within fc ± fΔ, the frequency spectrum of an actual FM signal has components extending infinitely, although their amplitude decreases and higher-order components are often neglected in practical design problems. Mathematically, a baseband modulated signal may be approximated by a continuous wave signal with a frequency fm. This method is also named as Single-tone Modulation. As in other systems, the modulation index indicates by how much the modulated variable varies around its unmodulated level. e. The maximum deviation of the frequency from the carrier frequency. For a sine wave modulation, the index is seen to be the ratio of the peak frequency deviation of the carrier wave to the frequency of the modulating sine wave. If h ≪1, the modulation is called narrowband FM, sometimes modulation index h<0.3 rad is considered as Narrowband FM otherwise Wideband FM. In the case of digital modulation, the carrier f c is never transmitted, rather, one of two frequencies is transmitted, either f c + Δ f or f c − Δ f, depending on the binary state 0 or 1 of the modulation signal. If h ≫1, the modulation is called wideband FM, if the frequency deviation is held constant and the modulation frequency increased, the spacing between spectra increases. The carrier and sideband amplitudes are illustrated for different modulation indices of FM signals, for particular values of the modulation index, the carrier amplitude becomes zero and all the signal power is in the sidebands. Since the sidebands are on sides of the carrier, their count is doubled, and then multiplied by the modulating frequency to find the bandwidth. For example,3 kHz deviation modulated by a 2.2 kHz audio tone produces an index of 1.36. Suppose that we limit ourselves to only those sidebands that have an amplitude of at least 0.01
7.
Spatial multiplexing
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Therefore, the space dimension is reused, or multiplexed, more than one time. If the transmitter is equipped with N t antennas and the receiver has N r antennas and this means that N s streams can be transmitted in parallel, ideally leading to an N s increase of the spectral efficiency. The practical multiplexing gain can be limited by spatial correlation, which means some of the parallel streams may have very weak channel gains. An often encountered problem in open loop spatial multiplexing is to guard against instance of high channel correlation, one such extension which is being considered for DVB-NGH systems is the so-called enhanced Spatial Multiplexing scheme. A closed-loop MIMO system utilizes Channel State Information at the transmitter, in most cases, only partial CSI is available at the transmitter because of the limitations of the feedback channel. A precoding matrix W is used to precode the symbols in the vector to enhance the performance, the column dimension N s of W can be selected smaller than N t which is useful if the system requires N s streams because of several reasons. Examples of the reasons are as follows, either the rank of the MIMO channel or the number of antennas is smaller than the number of transmit antennas. Space–time code Space–time trellis code WiMAX MIMO 3G MIMO
8.
Integrated Services Digital Network
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It was first defined in 1988 in the CCITT red book. Prior to ISDN, the system was viewed as a way to transport voice. The key feature of ISDN is that it integrates speech and data on the same lines, the ISDN standards define several kinds of access interfaces, such as Basic Rate Interface, Primary Rate Interface, Narrowband ISDN, and Broadband ISDN. It offers circuit-switched connections, and packet-switched connections, in increments of 64 kilobit/s, in some countries, ISDN found major market application for Internet access, in which ISDN typically provides a maximum of 128 kbit/s bandwidth in both upstream and downstream directions. Channel bonding can achieve a data rate, typically the ISDN B-channels of three or four BRIs are bonded. ISDN is employed as the network, data-link and physical layers in the context of the OSI model, or could be considered a suite of digital services existing on layers 1,2, and 3 of the OSI model. In a videoconference, ISDN provides simultaneous voice, video, Integrated services refers to ISDNs ability to deliver at minimum two simultaneous connections, in any combination of data, voice, video, and fax, over a single line. Multiple devices can be attached to the line, and used as needed and that means an ISDN line can take care of most peoples complete communications needs at a much higher transmission rate, without forcing the purchase of multiple analog phone lines. It also refers to integrated switching and transmission in that telephone switching, the entry level interface to ISDN is the Basic Rate Interface, a 128 kbit/s service delivered over a pair of standard telephone copper wires. The 144 kbit/s payload rate is broken down into two 64 kbit/s bearer channels and one 16 kbit/s signaling channel and this is sometimes referred to as 2B+D. The T interface is an interface between a computing device and a terminal adapter, which is the digital equivalent of a modem. The S interface is a bus that ISDN consumer devices plug into. The R interface defines the point between a device and a terminal adapter which provides translation to and from such a device. BRI-ISDN is very popular in Europe but is less common in North America. It is also common in Japan — where it is known as INS64, the other ISDN access available is the Primary Rate Interface, which is carried over an E1 in most parts of the world. An E1 is 30 B channels of 64 kbit/s, one D channel of 64 kbit/s and this is often referred to as 30B+2D. In North America PRI service is delivered on one or more T1 carriers of 1544 kbit/s, a PRI has 23 B channels and 1 D channel for signalling. Inter-changeably but incorrectly, a PRI is referred to as T1 because it uses the T1 carrier format, a true T1 uses 24 channels of 64 kbit/s of in-band signaling
9.
Single-sideband modulation
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Amplitude modulation produces an output signal that has twice the bandwidth of the original baseband signal. Single-sideband modulation avoids this bandwidth doubling, and the power wasted on a carrier, at the cost of increased device complexity, radio transmitters work by mixing a radio frequency signal of a specific frequency, the carrier wave, with the signal to be broadcast. That is, the signal has a spectrum with twice the bandwidth of the original input signal. In conventional AM radio, this signal is sent to the radio frequency amplifier. Due to the nature of the process, the quality of the resulting signal can be defined by the difference between the maximum and minimum signal energy. Normally the maximum signal energy will be the carrier itself, perhaps twice as powerful as the mixed signals, SSB takes advantage of the fact that the entire original signal is encoded in either one of these sidebands. It is not necessary to broadcast the entire mixed signal, a receiver can extract the entire signal from either the upper or lower sideband. This means that the amplifier can be used more efficiently. A transmitter can choose to only the upper or lower sideband. By doing so, the amplifier only has to work effectively on one half the bandwidth, as a result, SSB transmissions use the available amplifier energy more efficiently, providing longer-range transmission with little or no additional cost. The first U. S. patent for SSB modulation was applied for on December 1,1915 by John Renshaw Carson, the U. S. Navy experimented with SSB over its radio circuits before World War I. SSB first entered service on January 7,1927 on the longwave transatlantic public radiotelephone circuit between New York and London. The high power SSB transmitters were located at Rocky Point, New York and Rugby, the receivers were in very quiet locations in Houlton, Maine and Cupar Scotland. SSB was also used over long distance lines, as part of a technique known as frequency-division multiplexing. FDM was pioneered by telephone companies in the 1930s and this enabled many voice channels to be sent down a single physical circuit, for example in L-carrier. SSB allowed channels to be spaced just 4,000 Hz apart, amateur radio operators began serious experimentation with SSB after World War II. The Strategic Air Command established SSB as the standard for its aircraft in 1957. It has become a de facto standard for voice radio transmissions since then
10.
GSM
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As of 2014 it has become the de facto global standard for mobile communications – with over 90% market share, operating in over 219 countries and territories. This expanded over time to include communications, first by circuit-switched transport, then by packet data transport via GPRS. Subsequently, the 3GPP developed third-generation UMTS standards followed by fourth-generation LTE Advanced standards, GSM is a trademark owned by the GSM Association. It may also refer to the most common voice codec used, the decision to develop a continental standard eventually resulted in a unified, open, standard-based network which was larger than that in the United States. In February 1987 Europe produced the very first agreed GSM Technical Specification, the MoU drew-in mobile operators from across Europe to pledge to invest in new GSM networks to an ambitious common date. In 1989, the Groupe Spécial Mobile committee was transferred from CEPT to the European Telecommunications Standards Institute, in parallel, France and Germany signed a joint development agreement in 1984 and were joined by Italy and the UK in 1986. In 1986 the European Commission proposed reserving the 900 MHz spectrum band for GSM, the former Finnish prime minister Harri Holkeri made the worlds first GSM call on July 1,1991, calling Kaarina Suonio using a network built by Telenokia and Siemens and operated by Radiolinja. In the following year,1992, saw the sending of the first short messaging service message, work began in 1991 to expand the GSM standard to the 1800 MHz frequency band and the first 1800 MHz network became operational in the UK by 1993 called and DCS1800. Also that year, Telecom Australia became the first network operator to deploy a GSM network outside Europe and the first practical hand-held GSM mobile phone became available. In 1995, fax, data and SMS messaging services were launched commercially, in the same year, the GSM Association formed. Pre-paid GSM SIM cards were launched in 1996 and worldwide GSM subscribers passed 100 million in 1998, in 2000 the first commercial GPRS services were launched and the first GPRS-compatible handsets became available for sale. In 2001 the first UMTS network was launched, a 3G technology that is not part of GSM, worldwide GSM subscribers exceeded 500 million. In 2002 the first Multimedia Messaging Service were introduced and the first GSM network in the 800 MHz frequency band became operational, EDGE services first became operational in a network in 2003 and the number of worldwide GSM subscribers exceeded 1 billion in 2004. By 2005, GSM networks accounted for more than 75% of the cellular network market. In 2005 the first HSDPA-capable network also became operational, the first HSUPA network launched in 2007. Worldwide GSM subscribers exceeded three billion in 2008, GSM is a second-generation standard employing time-division multiple-Access spectrum-sharing, issued by the European Telecommunications Standards Institute. GSM, for the first time, set a standard for Europe for wireless networks. It was also adopted by many countries outside Europe and this allowed subscribers to use other GSM networks that have roaming agreements with each other
11.
Communication channel
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A channel is used to convey an information signal, for example a digital bit stream, from one or several senders to one or several receivers. A channel has a capacity for transmitting information, often measured by its bandwidth in Hz or its data rate in bits per second. Communicating data from one location to another requires some form of pathway or medium and these pathways, called communication channels, use two types of media, cable and broadcast. Cable or wire line media use physical wires of cables to transmit data, twisted-pair wire and coaxial cables are made of copper, and fiber-optic cable is made of glass. In information theory, a channel refers to a theoretical channel model with certain error characteristics, in this more general view, a storage device is also a kind of channel, which can be sent to and received from. Examples of communications include, A connection between initiating and terminating nodes of a circuit. A single path provided by a transmission medium via either physical separation, such as by multipair cable or electrical separation, a path for conveying electrical or electromagnetic signals, usually distinguished from other parallel paths. A storage which can communicate a message over time as well as space The portion of a medium, such as a track or band. A buffer from which messages can be put and got, see Actor model and process calculi for discussion on the use of channels. In a communications system, the physical or logical link that connects a data source to a data sink, a specific radio frequency, pair or band of frequencies, usually named with a letter, number, or codeword, and often allocated by international agreement. Examples, Marine VHF radio uses some 88 channels in the VHF band for two-way FM voice communication, Channel 16, for example, is 156.800 MHz. In the US, seven additional channels, WX1 - WX7, are allocated for weather broadcasts, television channels such as North American TV Channel 2 =55.25 MHz, Channel 13 =211.25 MHz. Each channel is 6 MHz wide, besides these physical channels, television also has virtual channels. Wi-Fi consists of unlicensed channels 1-13 from 2412 MHz to 2484 MHz in 5 MHz steps, the radio channel between an amateur radio repeater and a ham uses two frequencies often 600 kHz apart. For example, a repeater that transmits on 146.94 MHz typically listens for a ham transmitting on 146.34 MHz, all of these communications channels share the property that they transfer information. The information is carried through the channel by a signal, a channel can be modelled physically by trying to calculate the physical processes which modify the transmitted signal. For example, in wireless communications the channel can be modelled by calculating the reflection off every object in the environment, a sequence of random numbers might also be added in to simulate external interference and/or electronic noise in the receiver. Statistical and physical modelling can be combined, for example, in wireless communications the channel is often modelled by a random attenuation of the transmitted signal, followed by additive noise
12.
Packet switching
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Packet switching increases network efficiency and robustness, and enables technological convergence of many applications operating on the same network. Packets are composed of a header and payload, Information in the header is used by networking hardware to direct the packet to its destination where the payload is extracted and used by application software. This concept contrasted and contradicted then-established principles of pre-allocation of network bandwidth, the new concept found little resonance among network implementers until the independent work of British computer scientist Donald Davies at the National Physical Laboratory in the late 1960s. Packet mode communication may be implemented with or without intermediate forwarding nodes, in case of a shared physical medium, the packets may be delivered according to a multiple access scheme. In the late 1950s, the US Air Force established a wide area network for the Semi-Automatic Ground Environment radar defense system and they sought a system that might survive a nuclear attack to enable a response, thus diminishing the attractiveness of the first strike advantage by enemies. Report P-2626 described a general architecture for a large-scale, distributed, Barans work was known to Robert Taylor and J. C. R. Licklider at the Information Processing Technology Office, who advocated wide area networks, starting in 1965, Donald Davies at the National Physical Laboratory, UK, independently developed the same message routing methodology as developed by Baran. He called it packet switching, a more accessible name than Barans and he gave a talk on the proposal in 1966, after which a person from the Ministry of Defence told him about Barans work. A member of Davies team met Lawrence Roberts at the 1967 ACM Symposium on Operating System Principles, Davies had chosen some of the same parameters for his original network design as did Baran, such as a packet size of 1024 bits. In 1966, Davies proposed that a network should be built at the laboratory to serve the needs of NPL, the NPL Data Communications Network entered service in 1970. In 1974, Vint Cerf and Bob Kahn published the specifications for Transmission Control Protocol, Packet switching may be classified into connectionless packet switching, also known as datagram switching, and connection-oriented packet switching, also known as virtual circuit switching. Examples of connectionless protocols are Ethernet, Internet Protocol, and the User Datagram Protocol, connection-oriented protocols include X.25, Frame Relay, Multiprotocol Label Switching, and the Transmission Control Protocol. In connectionless mode each packet includes complete addressing information, the packets are routed individually, sometimes resulting in different paths and out-of-order delivery. Each packet is labeled with an address, source address. It may also be labeled with the number of the packet. At the destination, the original message/data is reassembled in the correct order, connection-oriented transmission requires a setup phase in each involved node before any packet is transferred to establish the parameters of communication. The packets include a connection identifier rather than address information and are negotiated between endpoints so that they are delivered in order and with error checking, the signaling protocols used allow the application to specify its requirements and discover link parameters. Acceptable values for service parameters may be negotiated, routing a packet requires the node to look up the connection id in a table
