1.
Computer network
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A computer network or data network is a telecommunications network which allows nodes to share resources. In computer networks, networked computing devices exchange data with other using a data link. The connections between nodes are established using either cable media or wireless media, the best-known computer network is the Internet. Network computer devices that originate, route and terminate the data are called network nodes, nodes can include hosts such as personal computers, phones, servers as well as networking hardware. Two such devices can be said to be networked together when one device is able to exchange information with the other device, Computer networks differ in the transmission medium used to carry their signals, communications protocols to organize network traffic, the networks size, topology and organizational intent. In most cases, application-specific communications protocols are layered over other more general communications protocols and this formidable collection of information technology requires skilled network management to keep it all running reliably. The chronology of significant computer-network developments includes, In the late 1950s, in 1960, the commercial airline reservation system semi-automatic business research environment went online with two connected mainframes. Licklider developed a group he called the Intergalactic Computer Network. In 1964, researchers at Dartmouth College developed the Dartmouth Time Sharing System for distributed users of computer systems. The same year, at Massachusetts Institute of Technology, a group supported by General Electric and Bell Labs used a computer to route. Throughout the 1960s, Leonard Kleinrock, Paul Baran, and Donald Davies independently developed network systems that used packets to transfer information between computers over a network, in 1965, Thomas Marill and Lawrence G. Roberts created the first wide area network. This was an precursor to the ARPANET, of which Roberts became program manager. Also in 1965, Western Electric introduced the first widely used telephone switch that implemented true computer control, in 1972, commercial services using X.25 were deployed, and later used as an underlying infrastructure for expanding TCP/IP networks. In July 1976, Robert Metcalfe and David Boggs published their paper Ethernet, Distributed Packet Switching for Local Computer Networks, in 1979, Robert Metcalfe pursued making Ethernet an open standard. In 1976, John Murphy of Datapoint Corporation created ARCNET, a network first used to share storage devices. In 1995, the transmission speed capacity for Ethernet increased from 10 Mbit/s to 100 Mbit/s, by 1998, Ethernet supported transmission speeds of a Gigabit. Subsequently, higher speeds of up to 100 Gbit/s were added, the ability of Ethernet to scale easily is a contributing factor to its continued use. Providing access to information on shared storage devices is an important feature of many networks, a network allows sharing of files, data, and other types of information giving authorized users the ability to access information stored on other computers on the network
2.
Ethernet frame
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A data packet on an Ethernet link is called an Ethernet packet, which transports an Ethernet frame as its payload. An Ethernet frame is preceded by a preamble and start frame delimiter, each Ethernet frame starts with an Ethernet header, which contains destination and source MAC addresses as its first two fields. The middle section of the frame is payload data including any headers for other protocols carried in the frame, the frame ends with a frame check sequence, which is a 32-bit cyclic redundancy check used to detect any in-transit corruption of data. A data packet on the wire and the frame as its payload consist of binary data, Ethernet transmits data with the most-significant octet first, within each octet, however, the least-significant bit is transmitted first. The internal structure of an Ethernet frame is specified in IEEE802.3, the table below shows the complete Ethernet packet and the frame inside, as transmitted, for the payload size up to the MTU of 1500 octets. Some implementations of Gigabit Ethernet and other higher-speed variants of Ethernet support larger frames, the optional 802. 1Q tag consumes additional space in the frame. Field sizes for this option are indicated parenthetically in the table above, IEEE802. 1ad allows for multiple tags in each frame. This option is not illustrated here, an Ethernet packet starts with a seven-octet preamble and one-octet start frame delimiter. The preamble consists of a 56-bit pattern of alternating 1 and 0 bits, allowing devices on the network to easily synchronize their receiver clocks and it is followed by the SFD to provide byte-level synchronization and to mark a new incoming frame. The SFD is the value that marks the end of the preamble, which is the first field of an Ethernet packet. The SFD is designed to break the bit pattern of the preamble, the SFD is immediately followed by the destination MAC address, which is the first field in an Ethernet frame. SFD has the value of 171, which is transmitted with least-significant bit first as 213, physical layer transceiver circuitry is required to connect the Ethernet MAC to the physical medium. The connection between a PHY and MAC is independent of the medium and uses a bus from the media independent interface family. Fast Ethernet transceiver chips utilize the MII bus, which is a wide bus, therefore the preamble is represented as 14 instances of 0x5. Gigabit Ethernet transceiver chips use the GMII bus, which is a wide interface. The header features destination and source MAC addresses, the EtherType field and, optionally, the EtherType field is two octets long and it can be used for two different purposes. When used as EtherType, the length of the frame is determined by the location of the interpacket gap, the IEEE802. 1Q tag, if present, is a four-octet field that indicates virtual LAN membership and IEEE802. 1p priority. The minimum payload is 42 octets when an 802. 1Q tag is present and 46 octets when absent, the maximum payload is 1500 octets
3.
Optical fiber
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An optical fiber or optical fibre is a flexible, transparent fiber made by drawing glass or plastic to a diameter slightly thicker than that of a human hair. Fibers are also used for illumination, and are wrapped in bundles so that they may be used to carry images, thus allowing viewing in confined spaces, as in the case of a fiberscope. Specially designed fibers are used for a variety of other applications, some of them being fiber optic sensors. Optical fibers typically include a transparent core surrounded by a transparent cladding material with an index of refraction. Light is kept in the core by the phenomenon of internal reflection which causes the fiber to act as a waveguide. Fibers that support many propagation paths or transverse modes are called multi-mode fibers, multi-mode fibers generally have a wider core diameter and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibers are used for most communication links longer than 1,000 meters, being able to join optical fibers with low loss is important in fiber optic communication. This is more complex than joining electrical wire or cable and involves careful cleaving of the fibers, precise alignment of the cores. For applications that demand a permanent connection a fusion splice is common, in this technique, an electric arc is used to melt the ends of the fibers together. Another common technique is a splice, where the ends of the fibers are held in contact by mechanical force. Temporary or semi-permanent connections are made by means of specialized optical fiber connectors, the field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics. The term was coined by Indian physicist Narinder Singh Kapany who is acknowledged as the father of fiber optics. Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon, John Tyndall included a demonstration of it in his public lectures in London,12 years later. When the ray passes from water to air it is bent from the perpendicular. If the angle which the ray in water encloses with the perpendicular to the surface be greater than 48 degrees, the angle which marks the limit where total reflection begins is called the limiting angle of the medium. For water this angle is 48°27′, for flint glass it is 38°41′, unpigmented human hairs have also been shown to act as an optical fiber. Practical applications, such as close internal illumination during dentistry, appeared early in the twentieth century, image transmission through tubes was demonstrated independently by the radio experimenter Clarence Hansell and the television pioneer John Logie Baird in the 1920s. The principle was first used for medical examinations by Heinrich Lamm in the following decade
4.
Twinaxial cabling
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Twinaxial cabling, or Twinax, is a type of cable similar to coaxial cable, but with two inner conductors instead of one. Due to cost efficiency it is becoming common in modern very-short-range high-speed differential signaling applications, the data transmission is half-duplex, balanced transmission, at 1 Mbit/s, on a single shielded,110 Ω twisted pair. With Twinax seven devices can be addressed, from workstation address 0 to 6, the devices do not have to be sequential. Twinax is a bus topology that requires termination to function properly, most Twinax T-connectors have an automatic termination feature. For use in buildings wired with Category 3 or higher twisted pair there are baluns that convert Twinax to twisted pair and its main advantages were high speed and multiple addressable devices per connection. The main disadvantage was the requirement for proprietary Twinax cabling with bulky screw-shell connectors, signals are sent differentially over the wires at 1 Mbit/s, Manchester coded, with preemphasis. The signal coding is only approximately differential and not completely differentially balanced, however, to provide preemphasis, for the first 250 ns after a signal is driven low, the negative signal line is driven to −1.6 V. During this time, the voltage is −0.8 V. This signal is designed to provide a minimum of ±100 mV at the end of 152 m of cable, the two wires are denoted A and B. To encode a 0 bit, A>B for the first half of the bit time, thus, each signal line is driven low for either 500 or 1000 ns at a time, of which the first 250 ns is emphasized. A message begins with five normal 1 bits for bit synchronization, followed by a frame sync pattern. A is driven low for 1500 ns, then B is driven low for 1500 ns and this is like a 1 bit sent at 1/3 normal speed. This pattern is followed by up to 256 16-bit data frames, each data frame consists of a start bit of 1, an 8-bit data field, a 3-bit station address, and an even parity bit. This is then followed by three or more bits of 0. Unusually for an IBM protocol, the bits within each frame are sent lsbit-first, all messages are sent between the controller and one slave device. The first frame in a message from the controller contains the devices address, the address field of following frames can be any value from 0 to 6, although is usually set to the devices address as well. The final frame in a message includes an address of 7 as an end-of-message indicator, a single-frame message does not have an EOM indicator. When a command calls for a response, the device is expected to respond in 30 to 80 μs, a devices response also consists of up to 256 frames, and includes its address in all frames but the last
5.
Gigabit Ethernet
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In computer networking, Gigabit Ethernet is a term describing various technologies for transmitting Ethernet frames at a rate of a gigabit per second, as defined by the IEEE802. 3-2008 standard. It came into use beginning in 1999, gradually supplanting Fast Ethernet in wired local networks, the cables and equipment are very similar to previous standards and have been very common and economical since 2010. Ethernet was the result of the research done at Xerox PARC in the early 1970s, Ethernet later evolved into a widely implemented physical and link layer protocol. Fast Ethernet increased speed from 10 to 100 megabits per second, Gigabit Ethernet was the next iteration, increasing the speed to 1000 Mbit/s. The initial standard for Gigabit Ethernet was produced by the IEEE in June 1998 as IEEE802. 3z,802. 3z is commonly referred to as 1000BASE-X, where -X refers to either -CX, -SX, -LX, or -ZX. For the history behind the X see Fast Ethernet, IEEE802. 3ab, ratified in 1999, defines Gigabit Ethernet transmission over unshielded twisted pair category 5, 5e or 6 cabling, and became known as 1000BASE-T. With the ratification of 802. 3ab, Gigabit Ethernet became a desktop technology as organizations could use their existing copper cabling infrastructure, IEEE802. 3ah, ratified in 2004 added two more gigabit fiber standards, 1000BASE-LX10 and 1000BASE-BX10. This was part of a group of protocols known as Ethernet in the First Mile. Initially, Gigabit Ethernet was deployed in high-capacity backbone network links, in 2000, Apples Power Mac G4 and PowerBook G4 were the first mass-produced personal computers featuring the 1000BASE-T connection. It quickly became a feature in many other computers. There are five physical layer standards for Gigabit Ethernet using optical fiber, twisted pair cable and these standards use 8b/10b encoding, which inflates the line rate by 25%, from 1000 Mbit/s to 1250 Mbit/s, to ensure a DC balanced signal. The symbols are sent using NRZ. Optical fiber transceivers are most often implemented as modules in SFP form or GBIC on older devices. IEEE802. 3ab, which defines the widely used 1000BASE-T interface type, uses a different encoding scheme in order to keep the rate as low as possible. IEEE802. 3ap defines Ethernet Operation over Electrical Backplanes at different speeds, Ethernet in the First Mile later added 1000BASE-LX10 and -BX10. 1000BASE-CX is a standard for Gigabit Ethernet connections with maximum distances of 25 meters using balanced shielded twisted pair. The short segment length is due to high signal transmission rate. 1000BASE-KX is part of the IEEE802. 3ap standard for Ethernet Operation over Electrical Backplanes and this standard defines one to four lanes of backplane links, one RX and one TX differential pair per lane, at link bandwidth ranging from 100Mbit to 10Gbit per second
6.
QSFP
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The Quad Small Form-factor Pluggable is a compact, hot-pluggable transceiver used for data communications applications. The form factor and electrical interface are specified by an agreement under the auspices of the Small Form Factor Committee. It interfaces networking hardware to a fiber cable or active or passive electrical copper connection. It is an industry format jointly developed and supported by many network component vendors, the format specification is evolving to enable higher data rates, as of May 2013, highest possible rate is 4x28 Gbit/s. QSFP modules are available in several different categories, The original QSFP document specified four channels carrying Gigabit Ethernet, 4GFC. QSFP+ is an evolution of QSFP to support four 10 Gbit/sec channels carrying 10 Gigabit Ethernet, 10GFC FiberChannel, the 4 channels can also be combined into a single 40 Gigabit Ethernet link. The QSFP14 standard is designed to carry FDR InfiniBand and SAS-3, the QSFP28 standard is designed to carry 100 Gigabit Ethernet or EDR InfiniBand. This transceiver type is used with direct-attach breakout cables to adapt a single 100GbE port to four independent 25 gigabit ethernet ports. Sometimes this transceiver type is referred to as QSFP100 or 100G QSFP for sake of simplicity. QSFP has 38 pins with 4 high-speed TX pairs and 4 high-speed RX pairs, C Form-factor Pluggable CXP OSFP transceiver slightly larger 400GbE transceiver standard Small form-factor pluggable transceiver SFF Committee
7.
Ethernet physical layer
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The Ethernet physical layer evolved over a considerable time span and encompasses quite a few physical media interfaces and several magnitudes of speed. The speed ranges from 1 Mbit/s to 100 Gbit/s, while the medium can range from bulky coaxial cable to twisted pair. In general, network protocol stack software will work similarly on all physical layers,10 Gigabit Ethernet was already used in both enterprise and carrier networks by 2007, with 40 Gbit/s and 100 Gigabit Ethernet ratified. Robert Metcalfe, one of the co-inventors of Ethernet, in 2008 said he believed commercial applications using Terabit Ethernet may occur by 2015, though it might require new Ethernet standards. Many Ethernet adapters and switch ports support multiple speeds, using autonegotiation to set the speed, while this can practically be taken for granted for ports supporting twisted-pair cabling, only few optical-fiber ports support multiple speeds. If auto-negotiation fails, some multiple-speed devices sense the speed used by their partner, a 10/100 Ethernet port supports 10BASE-T and 100BASE-TX. A 10/100/1000 Ethernet port supports 10BASE-T, 100BASE-TX, and 1000BASE-T, generally, layers are named by their specifications,10,100,1000, 10G. – the nominal, usable speed for the MAC layer, encoded PHY sublayers usually run higher bitrates BASE, BROAD, PASS – indicates baseband, broadband, or passband signaling -T, -S, -L, -C, -K. g. X for 8b/10b block encoding, R for large blocks 1,2,4,10 – number of lanes used per link or reach for WAN PHYs For 10 Mbit/s, most twisted pair layers use unique encoding, so most often just -T is used. The following sections provide a summary of official Ethernet media types. In addition to official standards, many vendors have implemented proprietary media types for various reasons—often to support longer distances over fiber optic cabling. Early Ethernet standards used Manchester coding so that the signal was self-clocking, all Fast Ethernet variants use a star topology. All Gigabit Ethernet variants use a star topology, initially, half-duplex mode was included in the standard but has been abandoned since. Very few devices support gigabit speed in half-duplex,2. 5GBASE-T and 5GBASE-T are scaled-down variants of 10GBASE-T. These physical layers support twisted pair copper cabling only,10 Gigabit Ethernet defines a version of Ethernet with a nominal data rate of 10 Gbit/s, ten times as fast as Gigabit Ethernet. In 2002, the first 10 Gigabit Ethernet standard was published as IEEE Std 802. 3ae-2002, subsequent standards encompass media types for single-mode fibre, multi-mode fibre, copper backplane and copper twisted pair. All 10-gigabit standards were consolidated into IEEE Std 802. 3-2008, as of 2009,10 Gigabit Ethernet is predominantly deployed in carrier networks, where 10GBASE-LR and 10GBASE-ER enjoy significant market shares. Single-lane 25-gigabit Ethernet is based on one 25.78125 GBd lane of the four from the 100 Gigabit Ethernet standard developed by task force P802. 3by, 25GBASE-T over twisted pair was approved alongside 40GBASE-T within IEEE802. 3bq
8.
Duplex (telecommunications)
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A duplex communication system requires a pair of channels/frequencies hence the term duplex meaning two parts. The two channels are defined as uplink/downlink or reverse/forward, in a full-duplex system simultaneous transmission/reception is available, i. e. One can transmit and receive simultaneously, in a half-duplex system, each party can communicate with the other but not simultaneously, the communication is one direction at a time. Half duplex systems utilize separate channels for uplink and downlink, i. e. a transmit, in a half duplex communications system one user is allowed to transmit on the uplink channel at a time. The transmitted uplink signal is frequency translated via a radio/repeater to the downlink receive frequency which is received by all other radios tuned to the downlink/receive frequency. A half-duplex system is defined as system which operates two, hence duplex, dedicated uplink/downlink channels/frequencies. In a half duplex system a single path is provided for uplink, all uplink messages are broadcast via the downlink channel to all users simultaneously via a repeater which performs uplink to downlink channel/frequency translation. All cellular and land line PSTNs and PDSNs are full duplex systems, all full duplex systems require a channel/frequency translator via a radio/repeater. This is required in order to translate the uplink/transmit transmission from one to the downlink/receive channel/frequency of user two. Full duplex systems are one to one private systems unlike half duplex systems which broadcast to all users and this effectively makes the cable itself a collision-free environment and doubles the maximum total transmission capacity supported by each Ethernet connection. Time-division duplexing is commonly referred to as simplex communications, a single channel/frequency is employed for bidirectional communications. The term simplex communication as applied to TDM single channel systems predates the term TDD by at least 80 years, frequency-division duplexing as with any other duplex system is defined by two channel/frequency simultaneous communication. A channel/frequency pair are assigned to individual user on the system. An FDD system requires frequency translation from user 1 uplink/reverse frequency to user 2 downlink/forward frequency, full-duplex audio systems like telephones can create echo, which needs to be removed. Echo occurs when the coming out of the speaker, originating from the far end. The sound then reappears at the source end, but delayed. This feedback path may be acoustic, through the air, or it may be mechanically coupled, echo cancellation is a signal-processing operation that subtracts the far-end signal from the microphone signal before it is sent back over the network. Echo cancellation is important to the V.32, V.34, V.56, echo cancelers are available as both software and hardware implementations
9.
Bit error rate
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The bit error rate is the number of bit errors per unit time. The bit error ratio is the number of bit errors divided by the number of transferred bits during a studied time interval. Bit error ratio is a performance measure, often expressed as a percentage. The bit error probability pe is the value of the bit error ratio. The bit error ratio can be considered as an estimate of the bit error probability. This estimate is accurate for a time interval and a high number of bit errors. The BER is 3 incorrect bits divided by 10 transferred bits, the packet error ratio is the number of incorrectly received data packets divided by the total number of received packets. A packet is declared incorrect if at least one bit is erroneous, for small bit error probabilities, this is approximately p p ≈ p e N. Similar measurements can be carried out for the transmission of frames, blocks, in a communication system, the receiver side BER may be affected by transmission channel noise, interference, distortion, bit synchronization problems, attenuation, wireless multipath fading, etc. The transmission BER is the number of detected bits that are incorrect before error correction, normally the transmission BER is larger than the information BER. The information BER is affected by the strength of the error correction code. The BER may be evaluated using stochastic computer simulations, if a simple transmission channel model and data source model is assumed, the BER may also be calculated analytically. An example of such a source model is the Bernoulli source. Examples of simple channel models used in theory are, Binary symmetric channel Additive white gaussian noise channel without fading. A worst-case scenario is a random channel, where noise totally dominates over the useful signal. This results in a transmission BER of 50%, in a noisy channel, the BER is often expressed as a function of the normalized carrier-to-noise ratio measure denoted Eb/N0, or Es/N0. For example, in the case of QPSK modulation and AWGN channel, people usually plot the BER curves to describe the performance of a digital communication system. In optical communication, BER vs. Received Power is usually used, while in wireless communication, measuring the bit error ratio helps people choose the appropriate forward error correction codes
10.
Media Access Control
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In the IEEE802 reference model of computer networking, the medium access control or media access control layer is the lower sublayer of the data link layer of the seven-layer OSI model. g. The hardware that implements the MAC is referred to as a media access controller, the MAC sublayer acts as an interface between the logical link control sublayer and the networks physical layer. The MAC layer emulates a full-duplex logical communication channel in a multi-point network and this channel may provide unicast, multicast or broadcast communication service. According to IEEE Std 802-2001 section 6.2. 3-2002 section 4.1, a MAC address is intended as a unique serial number. MAC addresses are assigned to network interface hardware at the time of manufacture. The most significant part of the address identifies the manufacturer, who assigns the remainder of the address, thus provide a potentially unique address. This makes it possible for frames to be delivered on a link that interconnects hosts by some combination of repeaters, hubs, bridges and switches. Examples of physical networks are Ethernet networks and Wi-Fi networks, both of which are IEEE802 networks and use IEEE802 48-bit MAC addresses, a MAC layer is not required in full-duplex point-to-point communication, but address fields are included in some point-to-point protocols for compatibility reasons. The channel access control mechanisms provided by the MAC layer are known as a multiple access protocol. This makes it possible for several stations connected to the physical medium to share it. Examples of shared physical media are bus networks, ring networks, hub networks, wireless networks, the channel access control mechanism relies on a physical layer multiplex scheme. The most widespread multiple access protocol is the contention based CSMA/CD protocol used in Ethernet networks and this mechanism is only utilized within a network collision domain, for example an Ethernet bus network or a hub-based star topology network. An Ethernet network may be divided into several domains, interconnected by bridges and switches. A multiple access protocol is not required in a switched network, such as todays switched Ethernet networks. The MAC protocol in cellular networks is designed to maximize the utilization of the expensive licensed spectrum, the air interface of a cellular network is at layers 1 and 2 of the OSI model, at layer 2, it is divided into multiple protocol layers. In UMTS and LTE, those protocols are the Packet Data Convergence Protocol, the Radio Link Control protocol, the base station has the absolute control over the air interface and schedules the downlink access as well as the uplink access of all devices. The MAC protocol is specified by 3GPP in TS25.321 for UMTS and TS36.321 for LTE.3 or later
11.
Single-mode optical fiber
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In fiber-optic communication, a single-mode optical fiber is an optical fiber designed to carry light only directly down the fiber - the transverse mode. Modes are the solutions of the Helmholtz equation for waves, which is obtained by combining Maxwells equations. These modes define the way the wave travels through space, i. e. how the wave is distributed in space, waves can have the same mode but have different frequencies. Although the ray travels parallel to the length of the fiber, the 2009 Nobel Prize in Physics was awarded to Charles K. Kao for his theoretical work on the single-mode optical fiber. In September 1970, they announced they had made single-mode fibers with attenuation at the 633-nanometer helium-neon line below 20 dB/km, professor Huang Hongjia of the Chinese Academy of Sciences, developed coupling wave theory in the field of microwave theory. He led a team that successfully developed Single-mode optical fiber in 1980. Like multi-mode optical fibers, single mode fibers do exhibit modal dispersion resulting from multiple spatial modes, Single mode fibers are therefore better at retaining the fidelity of each light pulse over longer distances than multi-mode fibers. For these reasons, single-mode fibers can have a higher bandwidth than multi-mode fibers, equipment for single mode fiber is more expensive than equipment for multi-mode optical fiber, but the single mode fiber itself is usually cheaper in bulk. A typical single mode optical fiber has a diameter between 8 and 10.5 µm and a cladding diameter of 125 µm. Data rates are limited by polarization mode dispersion and chromatic dispersion, as of 2005, data rates of up to 10 gigabits per second were possible at distances of over 80 km with commercially available transceivers. By using optical amplifiers and dispersion-compensating devices, state-of-the-art DWDM optical systems can span thousands of kilometers at 10 Gbit/s, and several hundred kilometers at 40 Gbit/s. The solution of Maxwells equations for the lowest order bound mode will permit a pair of orthogonally polarized fields in the fiber, in step-index guides, single-mode operation occurs when the normalized frequency, V, is less than or equal to 2.405. For power-law profiles, single-mode operation occurs for a frequency, V, less than approximately 2.405 g +2 g. In practice, the orthogonal polarizations may not be associated with degenerate modes, oS1 and OS2 are standard single-mode optical fiber used with wavelengths 1310 nm and 1550 nm with a maximum attenuation of 1 dB/km and 0.4 dB/km. OS1 is defined in ISO/IEC11801, and OS2 is defined in ISO/IEC24702, Optical fiber connectors are used to join optical fibers where a connect/disconnect capability is required. The basic connector unit is a connector assembly, a connector assembly consists of an adapter and two connector plugs. However, the assembly and polishing operations involved can be performed in the field, Optical fiber connectors are used in telephone company central offices, at installations on customer premises, and in outside plant applications. Outside plant applications may involve locating connectors underground in subsurface enclosures that may be subject to flooding, on outdoor walls, or on utility poles
12.
Laser
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A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term laser originated as an acronym for light amplification by stimulated emission of radiation, the first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories, based on theoretical work by Charles Hard Townes and Arthur Leonard Schawlow. A laser differs from other sources of light in that it emits light coherently, spatial coherence allows a laser to be focused to a tight spot, enabling applications such as laser cutting and lithography. Spatial coherence also allows a laser beam to stay narrow over great distances, Lasers can also have high temporal coherence, which allows them to emit light with a very narrow spectrum, i. e. they can emit a single color of light. Temporal coherence can be used to produce pulses of light as short as a femtosecond, Lasers are distinguished from other light sources by their coherence. Spatial coherence is typically expressed through the output being a narrow beam, Laser beams can be focused to very tiny spots, achieving a very high irradiance, or they can have very low divergence in order to concentrate their power at a great distance. Temporal coherence implies a polarized wave at a single frequency whose phase is correlated over a great distance along the beam. A beam produced by a thermal or other incoherent light source has an amplitude and phase that vary randomly with respect to time and position. Lasers are characterized according to their wavelength in a vacuum, most single wavelength lasers actually produce radiation in several modes having slightly differing frequencies, often not in a single polarization. Although temporal coherence implies monochromaticity, there are lasers that emit a broad spectrum of light or emit different wavelengths of light simultaneously, there are some lasers that are not single spatial mode and consequently have light beams that diverge more than is required by the diffraction limit. However, all devices are classified as lasers based on their method of producing light. Lasers are employed in applications where light of the spatial or temporal coherence could not be produced using simpler technologies. The word laser started as an acronym for light amplification by stimulated emission of radiation, in the early technical literature, especially at Bell Telephone Laboratories, the laser was called an optical maser, this term is now obsolete. A laser that produces light by itself is technically an optical rather than an optical amplifier as suggested by the acronym. It has been noted that the acronym LOSER, for light oscillation by stimulated emission of radiation. With the widespread use of the acronym as a common noun, optical amplifiers have come to be referred to as laser amplifiers. The back-formed verb to lase is frequently used in the field, meaning to produce light, especially in reference to the gain medium of a laser. Further use of the laser and maser in an extended sense, not referring to laser technology or devices, can be seen in usages such as astrophysical maser
13.
Multi-mode optical fiber
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Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Typical multi-mode links have data rates of 10 Mbit/s to 10 Gbit/s over link lengths of up to 600 meters, Multi-mode fiber has a fairly large core diameter that enables multiple light modes to be propagated and limits the maximum length of a transmission link due to modal dispersion. The equipment used for communications over multi-mode optical fiber is less expensive than that for optical fiber. Typical transmission speed and distance limits are 100 Mbit/s for distances up to 2 km,1 Gbit/s up to 1000 m, because of its high capacity and reliability, multi-mode optical fiber generally is used for backbone applications in buildings. An increasing number of users are taking the benefits of closer to the user by running fiber to the desktop or to the zone. Because of the core and also the possibility of large numerical aperture. However, compared to single-mode fibers, the multi-mode fiber bandwidth–distance product limit is lower, because multi-mode fiber has a larger core-size than single-mode fiber, it supports more than one propagation mode, hence it is limited by modal dispersion, while single mode is not. The LED light sources sometimes used with multi-mode fiber produce a range of wavelengths and this chromatic dispersion is another limit to the useful length for multi-mode fiber optic cable. In contrast, the used to drive single-mode fibers produce coherent light of a single wavelength. Due to the dispersion, multi-mode fiber has higher pulse spreading rates than single mode fiber. Single-mode fibers are used in high-precision scientific research because restricting the light to only one propagation mode allows it to be focused to an intense. Jacket color is used to distinguish multi-mode cables from single-mode ones. The standard TIA-598C recommends, for applications, the use of a yellow jacket for single-mode fiber. Some vendors use violet to distinguish higher performance OM4 communications fiber from other types, Multi-mode fibers are described by their core and cladding diameters. Thus,62. 5/125 µm multi-mode fiber has a size of 62.5 micrometres. The transition between the core and cladding can be sharp, which is called a profile, or a gradual transition. The two types have different dispersion characteristics and thus different effective propagation distance, Multi-mode fibers may be constructed with either graded or step-index profile. In addition, multi-mode fibers are described using a system of classification determined by the ISO11801 standard — OM1, OM2, OM4 was finalized in August 2009, and was published by the end of 2009 by the TIA
14.
Backplane
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A backplane is a group of electrical connectors in parallel with each other, so that each pin of each connector is linked to the same relative pin of all the other connectors, forming a computer bus. It is used as a backbone to connect several printed circuit boards together to make up a computer system. Backplanes commonly use a circuit board, but wire-wrapped backplanes have also been used in minicomputers. Early microcomputer systems like the Altair 8800 used a backplane for the processor, a backplane is generally differentiated from a motherboard by the lack of on-board processing and storage elements. A backplane uses plug-in cards for storage and processing, backplanes are normally used in preference to cables because of their greater reliability. In a cabled system, the cables need to be flexed every time that a card is added or removed from the system, a backplane does not suffer from this problem, so its service life is limited only by the longevity of its connectors. For example, the DIN41612 connectors used in the VMEbus system can withstand 50 to 500 insertions and removals, to transmit information, Serial Back-Plane technology uses a low voltage differential signaling transmission method for sending information. These cable sets have a board located in the computer, an expansion board in the remote backplane. Backplanes have grown in complexity from the simple Industry Standard Architecture or S-100 style where all the connectors were connected to a common bus, due to limitations inherent in the Peripheral Component Interconnect specification for driving slots, backplanes are now offered as passive and active. True passive backplanes offer no active bus driving circuitry, any desired arbitration logic is placed on the daughter cards. Active backplanes include chips which buffer the various signals to the slots, the distinction between the two isnt always clear, but may become an important issue if a whole system is expected to not have a single point of failure. A passive backplane, even if it is single, is not usually considered a SPOF, active backplanes are more complicated and thus have a non-zero risk of malfunction. While there are a few motherboards that offer more than 8 slots, in addition, as technology progresses, the availability and number of a particular slot type may be limited in terms of what is currently offered by motherboard manufacturers. However, backplane architecture is somewhat unrelated to the SBC technology plugged into it, there are some limitations to what can be constructed, in that the SBC chip set and processor have to provide the capability of supporting the slot types. In addition, virtually an unlimited number of slots can be provided with 20, including the SBC slot, as a practical though not an absolute limit. Thus, a PICMG backplane can provide any number and any mix of ISA, PCI, PCI-X, for example, an SBC with the latest i7 processor could interface with a backplane providing up to 19 ISA slots to drive legacy I/O cards. Some backplanes are constructed with slots for connecting to devices on both sides, and are referred to as midplanes and this ability to plug cards into either side of a midplane is often useful in larger systems made up primarily of modules attached to the midplane. Midplanes are often used in computers, mostly in blade servers, where server blades reside on one side, orthogonal midplanes connect vertical cards on one side to horizontal boards on the other side
15.
ISO/IEC 11801
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It covers both balanced copper cabling and optical fibre cabling. The standard was designed for use within commercial premises that may consist of either a building or of multiple buildings on a campus. It was optimized for premises that span up to 3 km, up to 1 km2 office space, Class F features even stricter specifications for crosstalk and system noise than Class E. To achieve this, shielding has been added for individual wire pairs, besides the shield, the twisting of the pairs and number of turns per unit length increases RF shielding and protects from crosstalk. The Category 7 cable standard has been created to allow 10 Gigabit Ethernet over 100 m of copper cabling, the cable contains four twisted copper wire pairs, just like the earlier standards. Category 7 cable can be terminated either with 8P8C compatible GG45 electrical connectors which incorporate the 8P8C standard or with TERA connectors, when combined with GG-45 or TERA connectors, Category 7 cable is rated for transmission frequencies of up to 600 MHz. Category 7 is not recognized by the TIA/EIA, Class FA channels and Category 7A cables, introduced by ISO11801 Edition 2 Amendment 2, are defined at frequencies up to 1000 MHz, suitable for multiple applications including CATV. Each pair offers 1200 MHz of bandwidth, simulation results have shown that 40 Gigabit Ethernet may be possible at 50 meters and 100 Gigabit Ethernet at 15 meters. In 2007, researchers at Pennsylvania State University predicted that either 32 nm or 22 nm circuits would allow for 100 Gigabit Ethernet at 100 meters. Category 8 should be fully compatible with Category 6A and below. As of January 2014, draft versions of ISO/IEC TR 11801-99-1, the final specifications will depend on transceiver requirements to be defined by IEEE802. 3bq workforce. Annex E, Acronyms for balanced cables, provides a system to specify the exact construction for both unshielded and shielded balanced twisted pair cables, european standard EN50173, Information technology — Generic cabling systems
16.
Google
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Google is an American multinational technology company specializing in Internet-related services and products. These include online advertising technologies, search, cloud computing, software, Google was founded in 1996 by Larry Page and Sergey Brin while they were Ph. D. students at Stanford University, in California. Together, they own about 14 percent of its shares, and they incorporated Google as a privately held company on September 4,1998. An initial public offering took place on August 19,2004, in August 2015, Google announced plans to reorganize its various interests as a conglomerate called Alphabet Inc. Google, Alphabets leading subsidiary, will continue to be the company for Alphabets Internet interests. Upon completion of the restructure, Sundar Pichai became CEO of Google, replacing Larry Page, rapid growth since incorporation has triggered a chain of products, acquisitions, and partnerships beyond Googles core search engine. The company leads the development of the Android mobile operating system, the Google Chrome web browser, and Chrome OS, the new hardware chief, Rick Osterloh, stated, a lot of the innovation that we want to do now ends up requiring controlling the end-to-end user experience. Google has also experimented with becoming an Internet carrier, alexa, a company that monitors commercial web traffic, lists Google. com as the most visited website in the world. Several other Google services also figure in the top 100 most visited websites, including YouTube, Googles mission statement, from the outset, was to organize the worlds information and make it universally accessible and useful, and its unofficial slogan was Dont be evil. In October 2015, the motto was replaced in the Alphabet corporate code of conduct by the phrase Do the right thing, Google began in January 1996 as a research project by Larry Page and Sergey Brin when they were both PhD students at Stanford University in Stanford, California. They called this new technology PageRank, it determined a websites relevance by the number of pages, and the importance of those pages, Page and Brin originally nicknamed their new search engine BackRub, because the system checked backlinks to estimate the importance of a site. Originally, Google ran under Stanford Universitys website, with the domains google. stanford. edu, the domain name for Google was registered on September 15,1997, and the company was incorporated on September 4,1998. It was based in the garage of a friend in Menlo Park, craig Silverstein, a fellow PhD student at Stanford, was hired as the first employee. The first funding for Google was an August 1998 contribution of $100,000 from Andy Bechtolsheim, co-founder of Sun Microsystems, given before Google was incorporated. At least three other investors invested in 1998, Amazon. com founder Jeff Bezos, Stanford University computer science professor David Cheriton. Author Ken Auletta claims that each invested $250,000, early in 1999, Brin and Page decided they wanted to sell Google to Excite. They went to Excite CEO George Bell and offered to sell it to him for $1 million, vinod Khosla, one of Excites venture capitalists, talked the duo down to $750,000, but Bell still rejected it. Googles initial public offering took place five years later, on August 19,2004, at that time Larry Page, Sergey Brin, and Eric Schmidt agreed to work together at Google for 20 years, until the year 2024
17.
Brocade Communications Systems
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Brocade Communications Systems, Inc. is an American technology company specializing in data and storage networking products. Originally known for its Fibre Channel storage networks, the company expanded include a range of products marketed as third platform technologies. On November 2,2016, Singapore-based chip maker Broadcom announced they were buying Brocade for about $5.5 billion, Brocade was founded in August 1995, by Seth Neiman, Kumar Malavalli and Paul R. Bonderson. Neiman became the first CEO of the company, Brocade was incorporated on May 14,1998, in Delaware. The companys first product, SilkWorm, which was a Fibre Channel switch, was released in early 1997, on May 25,1999, the company went public at a split-adjusted price of $4.75. On initial public offering, the company offered 3,250,000 shares, the top three underwriters for Brocades IPO were, in order, Morgan Stanley Dean Witter, BT Alex. Brown, and Dain Rauscher Wessels. Brocade stock traded in the National Market System of the NASDAQ GS stock market under the ticker symbol BRCD, a second generation of switches was announced in 1999. On January 14,2013, Brocade named Lloyd Carney as new chief executive, on November 2,2016, Singapore-based chip maker Broadcom announced they were buying Brocade for $5.5 billion. As part of the announcement, Broadcom said they would sell Brocades networking business to avoid competing with its top customers such as Cisco Systems. Other hardware solutions from Brocade support common protocols including iSCSI, FCIP, GigE, FICON, FCoE, DCB/CEE, Brocades first Fibre Channel switch SilkWorm 1000 was based on the Stitch ASIC and their own VxWorks-based firmware. Bruce Bergman was the CEO during most of this period, Product names were generally puns on various kinds of woven fabric, since a switched Fibre Channel network is also called a fabric. In 1998, Gregory Reyes joined the company as CEO, in 2001, Brocade released the SilkWorm 6400, which was designated a director similarly to IBM ESCON directors already well-established in the mainframe computer market. The term director became universally used for more expensive FC switches, from 2001 to 2003, Brocade released switches based on its third generation ASIC, BLOOM. BLOOM introduced increased throughput of 2 Gbit/s instead of 1 Gbit/s, Brocade integrated BLOOM into its first pure director, the SilkWorm 12000, in April 2002. The director offered up to 128 ports in two 64-port pseudo-switches, the Bloom ASIC also introduced a notable capability of frame-level Fibre Channel trunking, which provided high throughput with load balancing across multiple cables. It needed to be implemented in the ASIC hardware to ensure delivery of frames. Also hot firmware upgrade was introduced with FOS v4.1 in October 2003, at the time, Brocades main rival, McDATA, held over 90% market share in director segment, owing to a strong position first in the ESCON market, and then in the FICON market. The SilkWorm 12000 director gained over one-third of the market share after its release in 2002, Brocade added mainframe customers with FICON and FICON CUP support on the SilkWorm 12000
18.
JDSU
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It was headquartered in Milpitas, California. It was formerly known as JDS Uniphase, prior to a rebranding of its image on September 14,2005. The legal entity was called JDS Uniphase Corporation, but more commonly called JDSU, on August 2015, JDSU split into two different companies, Viavi Solutions and Lumentum Holdings. Uniphase was started in 1979 in a San Jose, California garage, in 1981, JDS Optics was founded in Canada by Jozef Straus, Philip Garel-Jones, Gary Duck, and Bill Sinclair. The JDS is short for Jones, Duck and Straus/Sinclair, the company became JDS Fitel when it formed a partnership with Fitel, a fiber optic and optical connector company. In 1999, JDSU was formed by the merger between JDS Fitel and Uniphase, and became known as JDS Uniphase subsequent to the merger, in 2003, CEO Straus retired and the company moved its headquarters to San Jose, California, to consolidate its business. In August 3,2005, the company acquired test and measurement equipment company Acterna for $760 million, Acterna had been formed by the May 2000 merger of network test solutions developer Wavetek Wandel Goltermann and hand-held test equipment developer TTC. In 2006, the company moved its headquarters to Milpitas, California, in December 2013, the company announced it was acquiring fellow network performance management company Network Instruments, for $200 million. On August 1,2015 JDSU split into Viavi Solutions and Lumentum Holdings Inc, during the 1990s, JDS Uniphase stock was a high-flyer tech stock investor favorite. After the telecom downturn, JDS Uniphase announced in late July 2001 the largest write-down of goodwill, on September 23,2005, JDSU announced a reverse stock split one-to-eight. Unlike most similar lawsuits, which are dismissed or settled before trial, JDSU was acquitted of all charges in November,2007. JDS Uniphase Scores a Win in Securities Case, Law. com, USA Today article about best and worst stocks of the George W. Bush presidency
19.
Oplink Communications
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Oplink Communications LLC is a US-based business manufacturing and selling optical components. Oplink headquarter is located in Fremont, California and has R/D center and manufacture facility in China, the company was founded in San Jose, California in 1995. Oplink moved its facility from San Jose, California to Free-trade-zone in Zhuhai. The company went public in 2000 with initial public offering of 13,700,000 shares of its stock at a price of $18.00 per share. Oplink moved its headquarter to Fremont, California in 2004, Koch Industries acquired Oplink for 445 million in December 2014. The legal entity changes to Oplink Communications LLC, Oplink is currently owned by Molex, a global electronics components company and Koch Industries subsidiary. Oplink acquired Optical Communication Products, Inc. for 85. 3M in 2007, Oplink was acquired by Koch Industries for $445M in 2014
20.
Huawei
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Huawei Technologies Co. Ltd. is a Chinese multinational networking and telecommunications equipment and services company headquartered in Shenzhen, Guangdong. It is the largest telecommunications equipment manufacturer in the world, having overtaken Ericsson in 2012, Huawei was founded in 1987 by Ren Zhengfei, a former engineer in the Peoples Liberation Army. Huawei has over 170,000 employees as of September 2015, around 76,000 of whom are engaged in research and development.4 billion USD in R&D, in 2014, Huawei recorded a profit of 34.2 billion CNY. Its products and services have been deployed in more than 140 countries, Huawei is the official translation of the firms Chinese name. The etymology of the character 华 is derived from 花 which means flower and this is hinted at in Huaweis logo. The character can also mean splendid or magnificent, but nowadays mostly refers to China or Chinese and it is common for Chinese companies to use this word, another example being the Taiwanese company Asus that was founded back in 1989. The second character of Huaweis name, 为, means action or achievement and it is pronounced Wah-Way according to a Gizmodo video that claims to provide the official pronunciation, as well as many other internet sources. However, Wah-Way is incorrect, and is a perpetuation of a mistaken combination of the Cantonese and Mandarin pronunciations for the first and second characters. The Cantonese pronunciation is Wah-Waii, while the Mandarin pronunciation is Hwa-Way, although the company is based in the Cantonese-speaking area of Guangdong, the use of Huawei as the spelling for its name reflects the Mandarin pronunciation the two characters. During the 1980s, Chinas government tried to modernize the countrys underdeveloped telecommunications infrastructure, Ren Zhengfei, a former deputy director of the Peoples Liberation Army engineering corp, founded Huawei in 1987 in Shenzhen. At a time all of Chinas telecommunications technology was imported from abroad. The company reports that it had RMB21,000 in registered capital at the time of its founding, the Far Eastern Economic Review also reported that it received an $8.5 million loan from a state-owned bank, though the company has denied the existence of the loan. During its first several years the business model consisted mainly of reselling private branch exchange switches imported from Hong Kong. Meanwhile, it was reverse-engineering imported switches and investing heavily in research, by 1990 the company had approximately 600 R&D staff, and began its own independent commercialization of PBX switches targeting hotels and small enterprises. The companys first major breakthrough came in 1993, when it launched its C&C08 program controlled telephone switch and it was by far the most powerful switch available in China at the time. By initially deploying in small cities and rural areas and placing emphasis on service and customizability, ahrens writes that these methods were unorthodox, bordering on corrupt, but not illegal. Jiang reportedly agreed with this assessment, Huawei was promoted by both the government and the military as a national champion, and established new research and development offices. In 1997, Huawei won its first overseas contract, providing fixed-line network products to Hong Kong company Hutchison Whampoa, later that year, Huawei launched its wireless GSM-based products and eventually expanded to offer CDMA and UMTS
21.
Pulse-amplitude modulation
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Pulse-amplitude modulation, is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulse. It is an analog pulse modulation scheme in which the amplitudes of a train of pulses are varied according to the sample value of the message signal. Demodulation is performed by detecting the level of the carrier at every single period. There are two types of pulse amplitude modulation, Single polarity PAM, In this a suitable fixed DC bias is added to the signal to ensure all the pulses are positive. Double polarity PAM, In this the pulses are positive and negative. In particular, all telephone modems faster than 300 bit/s use quadrature amplitude modulation, the number of possible pulse amplitudes in analog PAM is theoretically infinite. Digital PAM reduces the number of pulse amplitudes to some power of two, some versions of the Ethernet communication standard are an example of PAM usage. Pulse-amplitude modulation has also developed for the control of light-emitting diodes. Pulse-amplitude modulation LED drivers are able to synchronize pulses across multiple LED channels to enable perfect colour matching. Due to the inherent nature of PAM in conjunction with the switching speed of LEDs it is possible to use LED lighting as a means of wireless data transmission at high speed. The North American Advanced Television Systems Committee standards for digital television uses a form of PAM to broadcast the data that makes up the television signal. This system, known as 8VSB, is based on a three-level PAM like 100BASE-TX, using a single 6 MHz channel allocation, as defined in the previous NTSC analog standard, 8VSB is capable of transmitting 32 Mbit/s. After accounting for error correcting codes and other overhead, the rate in the signal is 19.39 Mbit/s
22.
10 Gigabit Ethernet
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10 Gigabit Ethernet is a group of computer networking technologies for transmitting Ethernet frames at a rate of 10 gigabits per second. It was first defined by the IEEE802. 3ae-2002 standard, half duplex operation and repeater hubs do not exist in 10GbE. Like previous versions of Ethernet, 10GbE can use either copper or fiber cabling, however, because of its bandwidth requirements, higher-grade copper cables are required, category 6a or Class F/Category 7 cables for lengths up to 100 meters. The 10 Gigabit Ethernet standard encompasses a number of different physical layer standards, a networking device, such as a switch or a network interface controller may have different PHY types through pluggable PHY modules, such as those based on SFP+. At the time that the 10 Gigabit Ethernet standard was developed, the WAN PHY encapsulates Ethernet packets in SONET OC-192c frames and operates at a slightly slower data-rate than the local area network PHY. Over the years the Institute of Electrical and Electronics Engineers 802.3 working group has published several standards relating to 10GbE, to implement different 10GbE physical layer standards, many interfaces consist of a standard socket into which different PHY modules may be plugged. Physical layer modules are not specified in a standards body. Relevant MSAs for 10GbE include XENPAK, XFP and SFP+, when choosing a PHY module, a designer considers cost, reach, media type, power consumption, and size. A single point-to-point link can have different MSA pluggable formats on either end as long as the 10GbE optical or copper port type inside the pluggable is identical, XENPAK was the first MSA for 10GE and had the largest form factor. X2 and XPAK were later competing standards with smaller form factors, X2 and XPAK have not been as successful in the market as XENPAK. XFP came after X2 and XPAK and it is also smaller, the newest module standard is the enhanced small form-factor pluggable transceiver, generally called SFP+. Based on the small form-factor pluggable transceiver and developed by the ANSI T11 fibre channel group, it is smaller still, SFP+ has become the most popular socket on 10GE systems. SFP+ modules do only optical to electrical conversion, no clock and data recovery, SFP+ modules share a common physical form factor with legacy SFP modules, allowing higher port density than XFP and the re-use of existing designs for 24 or 48 ports in a 19 rack width blade. Optical modules are connected to a host by either a XAUI, XENPAK, X2, and XPAK modules use XAUI to connect to their hosts. XAUI uses a data channel and is specified in IEEE802.3 Clause 48. XFP modules use a XFI interface and SFP+ modules use an SFI interface, XFI and SFI use a single lane data channel and the 64b/66b encoding specified in IEEE802.3 Clause 49. SFP+ modules can further be grouped into two types of host interfaces, linear or limiting, limiting modules are preferred except when using old fiber infrastructure which requires the use of the linear interface provided by 10GBASE-LRM modules. There are two classifications for optical fiber, single-mode and multi-mode, in SMF light follows a single path through the fiber while in MMF it takes multiple paths resulting in differential mode delay
23.
Small form-factor pluggable transceiver
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The small form-factor pluggable is a compact, hot-pluggable transceiver used for both telecommunication and data communications applications. The form factor and electrical interface are specified by an agreement under the auspices of the SFF Committee. It is an industry format jointly developed and supported by many network component vendors. The SFP interfaces a network device motherboard to a fiber optic or copper networking cable, SFP transceivers are designed to support SONET, gigabit Ethernet, Fibre Channel, and other communications standards. Due to its size, SFP obsolesces the formerly ubiquitous gigabit interface converter. In fact, no device with this name has ever been defined in the MSAs, transceivers are most often designated by the standard transmission speed on the medium, but sometimes they are labeled with their nominal Ethernet speed or a higher speed the manufacturer specifies. Not compatible with SX or 100BASE-FX, based on LX but engineered to work with a multi-mode fiber using a standard multi-mode patch cable rather than a mode-conditioning cable commonly used to adapt LX to multi-mode. Coupled with CWDM, these double the density of fiber links. They are not compatible with Fiber channel or SONET, unlike non-SFP, copper 1000BASE-T ports integrated into most routers and switches, 1000BASE-T SFPs usually cannot operate at 100BASE-TX speeds. 100 Mbit/s copper and optical - some vendors have shipped 100 Mbit/s limited SFPs for fiber to the home applications and these are relatively uncommon and can be easily confused with 1 Gbit/s SFPs. The enhanced small form-factor pluggable is a version of the SFP that supports data rates up to 16 Gbit/s. The SFP+ specification was first published on May 9,2006, SFP+ supports 8 Gbit/s Fibre Channel,10 Gigabit Ethernet and Optical Transport Network standard OTU2. It is an industry format supported by many network component vendors. 10 Gbit/s SFP+ modules are exactly the same dimensions as regular SFPs, allowing the equipment manufacturer to re-use existing physical designs for 24 and 48-port switches, although the SFP+ standard does not include mention of 16G Fibre Channel it can be used at this speed. Besides the data rate, the big difference between 8G Fibre Channel and 16G Fibre Channel is the encoding method, 64b/66b encoding used for 16G is a more efficient encoding mechanism than 8b/10b used for 8G, and allows for the data rate to double without doubling the line rate. The result is the 14.025 Gbit/s line rate for 16G Fibre Channel, in comparison to earlier XENPAK or XFP modules, SFP+ modules leave more circuitry to be implemented on the host board instead of inside the module. Through the use of an active adapter, SFP+ modules may be used in older equipment with XENPAK ports. SFP+ modules can be described as limiting or linear types, this describes the functionality of the inbuilt electronics, limiting SFP+ modules include a signal amplifier to re-shape the received signal whereas linear ones do not
24.
Cisco Systems
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Through its numerous acquired subsidiaries, such as OpenDNS, WebEx, and Jasper, Cisco specializes into specific tech markets, such as Internet of Things, domain security, and energy management. Cisco is the largest networking company in the world, the stock was added to the Dow Jones Industrial Average on June 8,2009, and is also included in the S&P500 Index, the Russell 1000 Index, NASDAQ-100 Index and the Russell 1000 Growth Stock Index. By the time the company went public in 1990, when it was listed on the NASDAQ, Cisco was the most valuable company in the world by 2000, with a more than $500 billion market capitalization. Despite founding Cisco in 1984, Bosack, along with Kirk Lougheed, continued to work at Stanford on Ciscos first product and it consisted of exact replicas of Stanfords Blue Box router and a stolen copy of the Universitys multiple-protocol router software. The software was written some years earlier at Stanford medical school by research engineer William Yeager. Bosack and Lougheed adapted it into what became the foundation for Cisco IOS, in 1987, Stanford licensed the router software and two computer boards to Cisco. In addition to Bosack, Lerner and Lougheed, Greg Satz, a programmer, and Richard Troiano, the companys first CEO was Bill Graves, who held the position from 1987 to 1988. In 1988, John Morgridge was appointed CEO, the name Cisco was derived from the city name San Francisco, which is why the companys engineers insisted on using the lower case cisco in its early years. The logo is intended to depict the two towers of the Golden Gate Bridge, on February 16,1990, Cisco Systems went public and was listed on the NASDAQ stock exchange. On August 28,1990, Lerner was fired, upon hearing the news, her husband Bosack resigned in protest. The couple walked away from Cisco with $170 million, 70% of which was committed to their own charity, although Cisco was not the first company to develop and sell dedicated network nodes, it was one of the first to sell commercially successful routers supporting multiple network protocols. Classical, CPU-based architecture of early Cisco devices coupled with flexibility of operating system IOS allowed for keeping up with evolving technology needs by means of frequent software upgrades, some popular models of that time managed to stay in production for almost a decade virtually unchanged—a rarity in high-tech industry. This philosophy dominated the companys product lines throughout the 1990s, in 1995, John Morgridge was succeeded by John Chambers. The phenomenal growth of the Internet in mid-to-late 1990s quickly changed the telecom landspe, as the Internet Protocol became widely adopted, the importance of multi-protocol routing declined. In late March 2000, at the height of the bubble, Cisco became the most valuable company in the world. In July 2014, with a cap of about US$129 billion. One of them, Juniper Networks, shipped their first product in 1999, Cisco answered the challenge with homegrown ASICs and fast processing cards for GSR routers and Catalyst 6500 switches. In 2004, Cisco also started migration to new high-end hardware CRS-1, as part of a massive rebranding campaign in 2006, Cisco Systems adopted the shortened name Cisco and created The Human Network advertising campaign
25.
Optical fiber connector
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An optical fiber connector terminates the end of an optical fiber, and enables quicker connection and disconnection than splicing. The connectors mechanically couple and align the cores of fibers so light can pass, better connectors lose very little light due to reflection or misalignment of the fibers. In all, about 100 fiber optic connectors have been introduced to the market, optical fiber connectors are used to join optical fibers where a connect/disconnect capability is required. Due to the polishing and tuning procedures that may be incorporated into optical connector manufacturing, however, the assembly and polishing operations involved can be performed in the field, for example, to make cross-connect jumpers to size. Most optical fiber connectors are spring-loaded, so the fiber faces are pressed together when the connectors are mated, the resulting glass-to-glass or plastic-to-plastic contact eliminates signal losses that would be caused by an air gap between the joined fibers. Every fiber connection has two values, Attenuation or insertion loss Reflection or return loss, measurements of these parameters are now defined in IEC standard 61753-1. The standard gives five grades for insertion loss from A to D, the other parameter is return loss, with grades from 1 to 5. A variety of optical fiber connectors are available, but SC, typical connectors are rated for 500–1,000 mating cycles. The main differences among types of connectors are dimensions and methods of mechanical coupling, generally, organizations will standardize on one kind of connector, depending on what equipment they commonly use. Different connectors are required for multimode, and for single-mode fibers, in many data center applications, small and multi-fiber connectors are replacing larger, older styles, allowing more fiber ports per unit of rack space. In such settings, protective enclosures are used, and fall into two broad categories, hermetic and free-breathing. Hermetic cases prevent entry of moisture and air but, lacking ventilation, free-breathing enclosures, on the other hand, allow ventilation, but can also admit moisture, insects and airborne contaminants. Selection of the correct housing depends on the cable and connector type, the location, careful assembly is required to ensure good protection against the elements. To ensure the integrity of optical fiber connections and housing seals, many types of optical connector have been developed at different times, and for different purposes. Many of them are summarized in the tables below, modern connectors typically use a physical contact polish on the fiber and ferrule end. This is a convex surface with the apex of the curve accurately centered on the fiber. Higher grades of polish give less insertion loss and lower back reflection, many connectors are available with the fiber end face polished at an angle to prevent light that reflects from the interface from traveling back up the fiber. Because of the angle, the light does not stay in the fiber core
26.
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
27.
Mellanox Technologies
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Mellanox Technologies is an Israeli supplier of end-to-end InfiniBand and Ethernet interconnect solutions and services for servers and storage. Mellanox Technologies provides InfiniBand and Ethernet switches for servers and storage used in data centers. The company is listed on NASDAQ under the symbol MLNX, in 2016, Mellanox Technologies began to employ programmers in the Gaza Strip in addition to its team of Israeli Arab programmers and programmers in Ramallah and Nablus. Initially founded as a integrated circuit manufacturer, it evolved into a producer of complete end-to-end systems by 2009, the company raised over $89 million in 3 financing rounds of venture capital. Strategic investors included Dell, IBM, JNI, Quanta Computer, Vitesse Semiconductor, the company went public in 2007, with an initial public offering on NASDAQ that raised $102 million, and valued the company at over half a billion dollars. Since 2010, Oracle Corporation has been an investor in the company. Oracle stated it has no plans to acquire Mellanox, but uses its InfiniBand technology in its Exadata, in February 2016, Mellanox acquired publicly held EZchip, a leading provider of Networking Processor Units and advanced multi-core processors. The addition of network and multi-core processor technology enables Mellanox to provide end to end intelligent interconnect solutions, in July 2013, Mellanox acquired privately held Kotura, Inc. a leading innovator and developer of advanced silicon photonics optical interconnect technology for high-speed networking applications. Silicon photonics is expected to play a significant role in high-speed networks, Kotura technology enables Mellanoxs interconnect products to scale to bandwidths of 100Gbit/s and beyond, and have longer reach optical connectivity at a lower cost. Mellanox believes that the Kotura acquisition enhances its ability to provide technologies for high speed, scalable, in July 2013, Mellanox acquired privately held IPtronics A/S, a leader in optical interconnect component design for digital communications. Mellanox 100Gbit/s silicon photonics interconnect solutions will incorporate the high-speed opto-electronic technology from Kotura, in February 2011, Mellanox acquired Voltaire Ltd. a leading provider of scale-out data center fabrics. Mellanoxs acquisition of Voltaire addresses this need by strengthening Mellanoxs market leadership position as the provider of end-to-end connectivity systems. Mellanox is a semiconductor company. The current generation of its chips are produced by Taiwan Semiconductor Manufacturing Corp, in 2010, a press release from Oracle described Mellanox as the premier switched fabric provider for enterprise data centers and high performance computing. According to the press release, Mellanoxs InfiniBand technology is faster, more scalable. Larry Ellison, CEO of Oracle, described Mellanox’s main technology, InfiniBand, switchX is a multi-protocol ASIC that handles both InfinBand and Ethernet traffic. It builds on the older 90 nanometer architecture of ConnectX technology, switchX is the fifth generation, using a 40 nanometer process with 1.4 billion transistors on a 45mm by 45mm chip. ConnectX-4 and ConnectX-5 adapters have enhanced capabilities, the ConnectX architecture has been described as novel, with excellent performance that is very well suited for modern multi-core platforms
28.
Sumitomo Electric Industries
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Sumitomo Electric Industries, Ltd. is a manufacturer of electric wire and optical fiber cables. Its headquarters are in Chūō-ku, Osaka, Japan, the companys shares are listed in the first section of the Tokyo, Nagoya Stock Exchanges, and the Fukuoka Stock Exchange. In the period ending March 2013, the company reported consolidated sales of US$23 billion, the company was founded in 1897 to produce copper wire for electrical uses. It has more than 350 subsidiaries and over 200,000 employees in more than 30 countries, Sumitomo Electric has traditionally had an intensive focus on R&D to develop new products. Sumitomo Electrics electrical wiring harness systems, which are used to send information and energy to automobiles, Sumitomo Electric also continues to be the leading manufacturer of composite semiconductors, which are widely used in semiconductor lasers, LEDs, and mobile telecommunications devices. The company is one of the top three manufacturers in the world of optical fiber, started operation 2001 - J-Power Systems Corporation started operational 2002 - Sumitomo Electric Networks, Inc. Sumitomo Steel Wire Corp. and Sumitomo Electric Wintec, Inc, started operation 2003 - Sumiden Hitachi Cable Ltd. and Sumitomo Electric Hardmetal Corp. started operation 2004 - A. L. M. T. The automotive segment accounts for 50% of Sumitomo Electrics annual sales, the automotive wiring harness business commenced in 1949 with supplies to the Occupation Forces for their jeeps. In 1961, for the first time, the company supplied wiring harnesses for four-wheel-drive vehicles, as a result, Sumitomo Electrics electrical wiring harness systems, which are used to send information and energy to automobiles, have garnered the second largest market share in the world. The division also provides products for supporting the Information and Communication Technology society such as traffic control systems. In 1986, Sumitomo Electric developed Z-fiber, pure silica core fiber with the worlds lowest transmission loss and this has supported the construction of optical communication networks, such as its wide use in many submarine cables. Sumitomo Electrics optical fibers ranks among the best in optical transmission networks, the Sumitomo Electric Groups electronics division supplies various products to manufacturers of smartphones, flat-screen televisions, and other highly advanced electronic goods. Sumitomo Electric also continues to be the manufacturer of composite semiconductors, which are widely used in semiconductor lasers, LEDs. This division provides electric wire and cable products that underpin stable energy supply, hard metal products, such as cutting tools, are essential for high-speed, high-performance, and high-precision mechanical processing. This division also makes sintered parts that are used as components in automobiles and home electric appliances. Starting in 2013, Sumitomo Electric will expand into two divisions, “Life Sciences” and “Resources” by making full use of the Groups wide-ranging technological capabilities
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100 Gigabit Ethernet
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40 Gigabit Ethernet and 100 Gigabit Ethernet are groups of computer networking technologies for transmitting Ethernet frames at rates of 40 and 100 gigabits per second, respectively. The technology was first defined by the IEEE802. 3ba-2010 standard and later by the 802. 3bg-2011,802. 3bj-2014, the standards define numerous port types with different optical and electrical interfaces and different numbers of optical fiber strands per port. Short distances over twinaxial cable are supported, 40GBASE-T uses twisted pair cabling for 40 Gbit/s over up to 30 m. On July 18,2006, a call for interest for a High Speed Study Group to investigate new standards for high speed Ethernet was held at the IEEE802.3 plenary meeting in San Diego. The first 802.3 HSSG study group meeting was held in September 2006, in June 2007, a trade group called Road to 100G was formed after the NXTcomm trade show in Chicago. The project is to provide for the interconnection of equipment satisfying the requirements of the intended applications. The 802. 3ba task force met for the first time in January 2008 and this standard was approved at the June 2010 IEEE Standards Board meeting under the name IEEE Std 802. 3ba-2010. On June 17,2010, the IEEE802. 3ba standard was approved In March 2011 the IEEE802. 3bg standard was approved, on September 10,2011, the P802. 3bj 100 Gbit/s Backplane and Copper Cable task force was approved. The scope of project is to specify additions to and appropriate modifications of IEEE Std 802. On May 10,2013, the P802. 3bm 40 Gbit/s and 100 Gbit/s Fiber Optic Task Force was approved and this project is to specify additions to and appropriate modifications of IEEE Std 802. In addition, to add 40 Gb/s Physical Layer specifications and management parameters for operation on extended reach single-mode fiber optic cables, also on May 10,2013, the P802. 3bq 40GBASE-T Task Force was approved. On June 12,2014, the IEEE802. 3bj standard was approved, on February 16,2015, the IEEE802. 3bm standard was approved. On May 12,2016, the IEEE P802. 3cd Task Force started working to define next generation two-lane 100 Gbit/s PHY, the IEEE802.3 working group is concerned with the maintenance and extension of the Ethernet data communications standard. Additions to the 802.3 standard are performed by forces which are designated by one or two letters. For example, the 802. 3z task force drafted the original Gigabit Ethernet standard,802. 3ba is the designation given to the higher speed Ethernet task force which completed its work to modify the 802.3 standard to support speeds higher than 10 Gbit/s in 2010. The speeds chosen by 802. 3ba were 40 and 100 Gbit/s to support both end-point and link aggregation needs and this was the first time two different Ethernet speeds were specified in a single standard. The decision to include both speeds came from pressure to support the 40 Gbit/s rate for local applications and the 100 Gbit/s rate for internet backbones. The standard was announced in July 2007 and was ratified on June 17,2010, the 40/100 Gigabit Ethernet standards encompass a number of different Ethernet physical layer specifications
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Coarse WDM
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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
31.
Ixia (company)
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Ixia is a public company operating in around 25 countries. Ixia is headquartered in Calabasas, California and has approximately 1750 employees, ixias key customers include manufacturers of network equipment such as Cisco and Alcatel-Lucent, service providers such as Verizon, NTT and Deutsche Telekom, and enterprises and government agencies. Ixia was founded by Errol Ginsberg and Joel Weissberger in 1997, atul Bhatnagar succeeded Ginsberg as President and CEO in 2007. On March 19,2012 Ixia announced Victor Alston as president and chief executive, on October 2013, Ixia announced Victor Alstons resignation as chief executive, and he was replaced by Ginsberg as acting CEO. On August 21,2014, the board named Bethany Mayer president, Mayer was also named to the board of directors. Historically an IP/Ethernet testing house, the acquisition of Catapult Communications in June 2009 established Ixia as a player in the wireless market, Ixia made a second acquisition in 2009, buying Agilent Technologies N2X Data Networks Product Line for $44 million. Ixia further expanded its capabilities by acquiring Wi-Fi testing company VeriWave. On 4 June 2012 Ixia announced the completion of the acquisition of Anue Systems, Inc. a developer of network visibility/tap aggregation products founded by Kevin Przybocki, Hemi Thaker, and Chip Webb. On August 24,2012, the company announced another acquisition, BreakingPoint Systems, Ixia continued its acquisitions by announcing the purchase of Net Optics on October 29,2013. On January 30,2017, Keysight Technologies Inc. agreed to buy Ixia for about $1.6 billion in all-cash, official site TMCnet Testing Wireless Networks Resource Center
32.
Spirent
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Spirent Communications plc is a multinational telecommunications testing company headquartered in Crawley, West Sussex, in the United Kingdom. It is listed on the London Stock Exchange, the company was founded by Jack Bowthorpe in 1936 as Goodliffe Electric Supplies. In 1949 it changed its name to Bowthorpe and it acquired Optima Electronics in 1987 and disposed of its defence businesses in 1990. In 2000 it also bought Hekimian, a major Operations Support Systems business, Zarak Systems, another communications software business and Net-Hopper, in 2000 it changed its name to Spirent. The name is derived from the words inspired innovation, in July 2014, Spirent acquired Radvisions Technology Business Unit from Avaya. Radvision a company based in Tel Aviv, Israel, offers development and test suites for voice, Spirent Communications PLC is a communications and network testing company
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EXFO
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EXFO is a company that designs and manufactures test instruments and service assurance products for fixed and mobile telecom networks. EXFO is headquartered in Quebec City, Canada, and has over 1200 employees worldwide, EXFO was founded in 1985 in Quebec City by Germain Lamonde and Robert Tremblay. Its original products were portable testing products for optical networks, in 1996, EXFO started designing products for optical component and optical system research and development and manufacturing. The company has since added 3G, LTE, protocol, copper/xDSL, IMS, and VoIP test and service assurance products, mainly through acquisitions
34.
Technical University of Denmark
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The Technical University of Denmark, often simply referred to as DTU, is a university in Kongens Lyngby, just north of Copenhagen, Denmark. It was founded in 1829 at the initiative of Hans Christian Ørsted as Denmarks first polytechnic, DTU, along with École Polytechnique Fédérale de Lausanne, Eindhoven University of Technology and Technical University of Munich, is a member of EuroTech Universities Alliance. DTU was founded in 1829 as the College of Advanced Technology with the physicist Hans Christian Ørsted, then a professor at the University of Copenhagen, the inspiration was the École Polytechnique in Paris, France which Ørsted had visited as a young scientist. The new institution was inaugurated on 5 November 1829 with Ørsted as its principal, the new colleges first home was two buildings in Studiestræde and St- Pederstræde in central Copenhagen. Although expanded several times, they remained inadequate and in 1890 a new building complex was inaugurated in Sølvgade in 1890, the new buildings were designed by the architect Johan Daniel Herholdt. In the 1920s space had once again become insufficient and in 1929 the foundation stone was laid for a new school at Østervold, completion of the building was delayed by World War II and it was not completed until 1954. From 1933 the institution was known as Danmarks tekniske Højskole. The formal name, Den Polytekniske Læreanstalt, Danmarks Tekniske Universitet, in 1960 a decision was made to move the College of Advanced Technology to new and larger facilities in Lyngby north of Copenhagen. They were inaugurated on 17 May 1974, on 23 and 24 November 1967 the University Computing Center hosted the NATO Science Committees Study Group first meeting discussing the newly coined term Software Engineering. The President of DTU is appointed by the university board, the president in turn appoints deans, and deans appoint heads of departments. Since DTU has no faculty senate, and since the faculty is not involved in the appointment of president, deans, or department heads, the area was previously home to the airfield Lundtofte Flyveplads. DTU was the subject of controversy in 2009 because the former director of the Department of Chemistry was a high-ranking member of Scientology. In relation to this, the university was accused of violating the principles of free speech by threatening to fire employees who voice their criticism of the institute director. On 7 April 2010, his successor was announced, at a department meeting, as Erling Stenby, shortly thereafter, the university management threatened Rolf W. Berg with dismissal for publicly criticizing the university. In November 2007 the Times Higher Education Supplement put the university as number 130 in their ranking of the universities of the world, in the The Worlds Most Innovative Universities 2015 ranking by Thomson Reuters, DTU is ranked, No. A student union at DTU is the student association Nul-kryds formed in 1947. Barrett, former CEO of Intel Jørgen Lindegaard, former CEO of the SAS Group Henrik O
35.
Synchronous Ethernet
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Synchronous Ethernet, also referred as SyncE, is an ITU-T standard for computer networking that facilitates the transference of clock signals over the Ethernet physical layer. This signal can then be traceable to an external clock. The aim of Synchronous Ethernet is to provide a signal to those network resources that may eventually require such a type of signal. The Synchronous Ethernet signal transmitted over the Ethernet physical layer should be traceable to a clock, ideally a master. Applications include cellular networks, access technologies such as Ethernet passive optical network, unlike time-division multiplexing networks, the Ethernet family of computer networks do not carry clock synchronization information. Several means are defined to address this issue, iETF’s Network Time Protocol, IEEEs 1588-2008 Precision Time Protocol are some of them. SyncE was standardized by the ITU-T, in cooperation with IEEE, G.8261 that defines aspects about the architecture and the wander performance of SyncE networks ITU-T Rec. G.8262 that specifies Synchronous Ethernet clocks for SyncE ITU-T Rec, G. Extension of the synchronization network to consider Ethernet as a building block. This enables Synchronous Ethernet network equipment to be connected to the synchronization network as Synchronous Digital Hierarchy. Synchronization for SDH can be transported over Ethernet and vice versa, ITU-T G.8262 defines Synchronous Ethernet clocks compatible with SDH clocks. Synchronous Ethernet clocks, based on ITU-T G.813 clocks, are defined in terms of accuracy, noise transfer, holdover performance, noise tolerance and these clocks are referred as Ethernet Equipment Slave clocks. While the IEEE802.3 standard specifies Ethernet clocks to be within ±100 ppm, eECs accuracy must be within ±4.6 ppm. In addition, by timing the Ethernet clock, it is possible to achieve Primary Reference Clock traceability at the interfaces, G. 8262/Y.1362 is an ITU-T recommendation for Synchronous Ethernet that defines timing characteristics of synchronous Ethernet equipment slave clock. It was first published in August 2007, amended in 2008 and 2010, in SDH, the SSM message is carried in fixed locations within the SDH frame. However, in Ethernet there is no equivalent of a fixed frame, the mechanisms needed to transport the SSM over Synchronous Ethernet are defined by the ITU-T in G.8264 in cooperation with IEEE. More specifically, the ESMC, defined by the ITU-T is based on the Organization Specific Slow Protocol, the ITU-T G.8264 defines a background or heart-beat message to provide a continuous indication of the clock quality level. However, event type messages with a new SSM quality level are generated immediately, the ESMC protocol is composed of the standard Ethernet header for a slow protocol, an ITU-T specific header, a flag field and a type length value structure. The SSM encoded within the TLV is a field whose meaning is described in ITU-T G.781
36.
Internet
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The Internet is the global system of interconnected computer networks that use the Internet protocol suite to link devices worldwide. The origins of the Internet date back to research commissioned by the United States federal government in the 1960s to build robust, the primary precursor network, the ARPANET, initially served as a backbone for interconnection of regional academic and military networks in the 1980s. Although the Internet was widely used by academia since the 1980s, Internet use grew rapidly in the West from the mid-1990s and from the late 1990s in the developing world. In the two decades since then, Internet use has grown 100-times, measured for the period of one year, newspaper, book, and other print publishing are adapting to website technology, or are reshaped into blogging, web feeds and online news aggregators. The entertainment industry was initially the fastest growing segment on the Internet, the Internet has enabled and accelerated new forms of personal interactions through instant messaging, Internet forums, and social networking. Business-to-business and financial services on the Internet affect supply chains across entire industries, the Internet has no centralized governance in either technological implementation or policies for access and usage, each constituent network sets its own policies. The term Internet, when used to refer to the global system of interconnected Internet Protocol networks, is a proper noun. In common use and the media, it is not capitalized. Some guides specify that the word should be capitalized when used as a noun, the Internet is also often referred to as the Net, as a short form of network. Historically, as early as 1849, the word internetted was used uncapitalized as an adjective, the designers of early computer networks used internet both as a noun and as a verb in shorthand form of internetwork or internetworking, meaning interconnecting computer networks. The terms Internet and World Wide Web are often used interchangeably in everyday speech, however, the World Wide Web or the Web is only one of a large number of Internet services. The Web is a collection of interconnected documents and other web resources, linked by hyperlinks, the term Interweb is a portmanteau of Internet and World Wide Web typically used sarcastically to parody a technically unsavvy user. The ARPANET project led to the development of protocols for internetworking, the third site was the Culler-Fried Interactive Mathematics Center at the University of California, Santa Barbara, followed by the University of Utah Graphics Department. In an early sign of growth, fifteen sites were connected to the young ARPANET by the end of 1971. These early years were documented in the 1972 film Computer Networks, early international collaborations on the ARPANET were rare. European developers were concerned with developing the X.25 networks, in December 1974, RFC675, by Vinton Cerf, Yogen Dalal, and Carl Sunshine, used the term internet as a shorthand for internetworking and later RFCs repeated this use. Access to the ARPANET was expanded in 1981 when the National Science Foundation funded the Computer Science Network, in 1982, the Internet Protocol Suite was standardized, which permitted worldwide proliferation of interconnected networks.5 Mbit/s and 45 Mbit/s. Commercial Internet service providers emerged in the late 1980s and early 1990s, the ARPANET was decommissioned in 1990
