1.
Ethernet
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Ethernet /ˈiːθərnɛt/ is a family of computer networking technologies commonly used in local area networks, metropolitan area networks and wide area networks. It was commercially introduced in 1980 and first standardized in 1983 as IEEE802.3, over time, Ethernet has largely replaced competing wired LAN technologies such as token ring, FDDI and ARCNET. The original 10BASE5 Ethernet uses coaxial cable as a medium, while the newer Ethernet variants use twisted pair. Over the course of its history, Ethernet data transfer rates have increased from the original 2.94 megabits per second to the latest 100 gigabits per second. The Ethernet standards comprise several wiring and signaling variants of the OSI physical layer in use with Ethernet, systems communicating over Ethernet divide a stream of data into shorter pieces called frames. As per the OSI model, Ethernet provides services up to, since its commercial release, Ethernet has retained a good degree of backward compatibility. Features such as the 48-bit MAC address and Ethernet frame format have influenced other networking protocols, the primary alternative for some uses of contemporary LANs is Wi-Fi, a wireless protocol standardized as IEEE802.11. Ethernet was developed at Xerox PARC between 1973 and 1974 and it was inspired by ALOHAnet, which Robert Metcalfe had studied as part of his PhD dissertation. In 1975, Xerox filed a patent application listing Metcalfe, David Boggs, Chuck Thacker, in 1976, after the system was deployed at PARC, Metcalfe and Boggs published a seminal paper. Metcalfe left Xerox in June 1979 to form 3Com and he convinced Digital Equipment Corporation, Intel, and Xerox to work together to promote Ethernet as a standard. The so-called DIX standard, for Digital/Intel/Xerox, specified 10 Mbit/s Ethernet, with 48-bit destination and source addresses and it was published on September 30,1980 as The Ethernet, A Local Area Network. Data Link Layer and Physical Layer Specifications, version 2 was published in November,1982 and defines what has become known as Ethernet II. Formal standardization efforts proceeded at the time and resulted in the publication of IEEE802.3 on June 23,1983. Ethernet initially competed with two largely proprietary systems, Token Ring and Token Bus, in the process, 3Com became a major company. 3Com shipped its first 10 Mbit/s Ethernet 3C100 NIC in March 1981, an Ethernet adapter card for the IBM PC was released in 1982, and, by 1985, 3Com had sold 100,000. Parallel port based Ethernet adapters were produced for a time, with drivers for DOS, by the early 1990s, Ethernet became so prevalent that it was a must-have feature for modern computers, and Ethernet ports began to appear on some PCs and most workstations. This process was sped up with the introduction of 10BASE-T and its relatively small modular connector. Since then, Ethernet technology has evolved to meet new bandwidth, in addition to computers, Ethernet is now used to interconnect appliances and other personal devices
2.
Coaxial cable
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Coaxial cable, or coax, is a type of cable that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield. Many coaxial cables also have an outer sheath or jacket. The term coaxial comes from the conductor and the outer shield sharing a geometric axis. Coaxial cable was invented by English engineer and mathematician Oliver Heaviside, Coaxial cable is used as a transmission line for radio frequency signals. Its applications include feedlines connecting radio transmitters and receivers with their antennas, computer network connections, digital audio and this allows coaxial cable runs to be installed next to metal objects such as gutters without the power losses that occur in other types of transmission lines. Coaxial cable also provides protection of the signal from external electromagnetic interference, the cable is protected by an outer insulating jacket. Normally, the shield is kept at ground potential and a signal carrying voltage is applied to the center conductor, the advantage of coaxial design is that electric and magnetic fields are restricted to the dielectric with little leakage outside the shield. Conversely, electric and magnetic fields outside the cable are largely kept from interfering with signals inside the cable, larger diameter cables and cables with multiple shields have less leakage. Common applications of coaxial cable include video and CATV distribution, RF and microwave transmission, the characteristic impedance of the cable is determined by the dielectric constant of the inner insulator and the radii of the inner and outer conductors. A controlled cable characteristic impedance is important because the source and load impedance should be matched to ensure maximum power transfer, other important properties of coaxial cable include attenuation as a function of frequency, voltage handling capability, and shield quality. Coaxial cable design choices affect physical size, frequency performance, attenuation, power handling capabilities, flexibility, strength, the inner conductor might be solid or stranded, stranded is more flexible. To get better performance, the inner conductor may be silver-plated. Copper-plated steel wire is used as an inner conductor for cable used in the cable TV industry. The insulator surrounding the conductor may be solid plastic, a foam plastic. The properties of control some electrical properties of the cable. A common choice is a solid polyethylene insulator, used in lower-loss cables, solid Teflon is also used as an insulator. Some coaxial lines use air and have spacers to keep the conductor from touching the shield. Many conventional coaxial cables use braided copper wire forming the shield and this allows the cable to be flexible, but it also means there are gaps in the shield layer, and the inner dimension of the shield varies slightly because the braid cannot be flat
3.
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
4.
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
5.
N connector
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The N connector is a threaded, weatherproof, medium-size RF connector used to join coaxial cables. It was one of the first connectors capable of carrying microwave-frequency signals, originally, the connector was designed to carry signals at frequencies up to 1 GHz in military applications, but todays common Type N easily handles frequencies up to 11 GHz. More recent precision enhancements to the design by Julius Botka at Hewlett Packard have pushed this to 18 GHz, the male connector is hand-tightened and has an air gap between the center and outer conductors. The coupling has a 5/8-24 thread, the center coaxial contacts are identical to TNC and BNC connectors. Amphenol suggests tightening to a torque of 15 inch-pounds, while Andrew Corporation suggest 20 inch-pounds for their hex nut variant, the peak power rating of an N connector is determined by voltage breakdown/ionisation of the air near the center pin. The average power rating is determined by overheating of the contact due to resistive insertion loss. Typical makers curves for a new clean connector with a perfect load give limits of ≈5000 W at 20 MHz and this square root frequency derating law is expected from the skin depth decreasing with frequency. At lower frequencies the same maker recommends an upper bound of ≈1000 V RMS, the N connector follows the MIL-STD-348 standard, defined by the US military, and comes in 50 and 75 ohm versions. The 50 ohm version is used in the infrastructure of land mobile, wireless data, paging. The 75 ohm version is used in the infrastructure of cable television systems. Connecting these two different types of connectors to each other can lead to damage, and/or intermittent operation due to the difference in diameter of the center pin. Unfortunately, many type N connectors are not labeled, and it can be difficult to prevent this situation in a mixed impedance environment. The 50 ohm type N connector is favored by enthusiasts who create their own Wireless LAN antenna systems, the Cantenna is one such design. The enthusiasts have settled on using the N connector as a connection for homebrew antennas. By using a cable with an N connector one can easily interchange homebrew antennas,50 Ω N connectors are also commonly used on amateur radio devices operating in UHF bands. A male N-connector can plug into an female SnapN, the HN connector is slightly larger and is designed for high-voltage applications. RF connector SMA connector, SMB connector, SMC connector UHF connector Optical fiber connector ^ N type connectors from Cmpter Electronics
6.
10BASE2
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As of 2011, IEEE802.3 has deprecated this standard for new installations. The name 10BASE2 is derived from several characteristics of the physical medium, the 10 comes from the transmission speed of 10 Mbit/s. The BASE stands for baseband signalling, and the 2 for a maximum segment length approaching 200 m.10 Mbit/s Ethernet uses Manchester coding. A binary zero is indicated by a low to high transition in the middle of the bit period and this allows the clock to be recovered from the signal. However, the additional transitions double the signal bandwidth, 10BASE2 coax cables have a maximum length of 185 metres. The maximum practical number of nodes that can be connected to a 10BASE2 segment is limited to 30 with a distance of 50 cm. In a 10BASE2 network, each stretch of cable is connected to the using a BNC T-connector. The T-connector must be plugged directly into the network adaptor with no cable in between, as is the case with most other high-speed buses, Ethernet segments have to be terminated with a resistor at each end. Each end of the cable has a 50 ohm resistor attached, typically this resistor is built into a male BNC and attached to the last device on the bus. This is most commonly connected directly to the T-connector on a workstation though it not technically have to be. A few devices such as Digitals DEMPR and DESPR have a built-in terminator, if termination is missing, or if there is a break in the cable, the AC signal on the bus is reflected, rather than dissipated, when it reaches the end. This reflected signal is indistinguishable from a collision, so no communication can take place, when wiring a 10BASE2 network, special care has to be taken to ensure that cables are properly connected to all T-connectors, and appropriate terminators are installed. One, and only one, terminator must be connected to ground via a ground wire, bad contacts or shorts are especially difficult to diagnose, though a time-domain reflectometer will find most problems quickly. A failure at any point of the network cabling tends to prevent all communications, for this reason, 10BASE2 networks can be difficult to maintain and were often replaced by 10BASE-T networks, which also provided a good upgrade path to 100BASE-TX. An alternative, more reliable connection was established by the introduction of EAD sockets, there were proprietary wallport/cable systems that claimed to avoid these problems but these never became widespread, possibly due to a lack of standardization. 10BASE2 systems do have a number of advantages over 10BASE-T, no hub is required as with 10BASE-T, so the hardware cost is minimal, and wiring can be particularly easy since only a single wire run is needed, which can be sourced from the nearest computer. These characteristics mean that 10BASE2 is ideal for a network of two or three machines, perhaps in a home where easily concealed wiring may be an advantage. For a larger complex office network, the difficulties of tracing poor connections make it impractical, unfortunately for 10BASE2, by the time multiple home computer networks became common, the format had already been practically superseded
7.
Electrical termination
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Electrical termination is an electrical industry term used to describe the specific point at which a conductive device, such as wire or cable, ends or starts. The conductive device may or may not pass the carried electricity or signal onto another conductive device at this point, a common point of electrical termination is at a terminal block. A wire typically ends, or terminates, at the terminal block, ordinary electrical cables suffice to carry low frequency alternating current, such as mains power, which reverses direction 100 to 120 times per second, and audio signals. However, they cannot be used to carry currents in the frequency range, above about 30 kHz, because the energy tends to radiate off the cable as radio waves. The higher the frequency of waves moving through a given cable or medium. Transmission lines become necessary when the length of the cable is longer than a significant fraction of the transmitted frequencys wavelength, types of transmission line cables include parallel line, and coaxial cable. and these require high frequency signal termination. The terminator is usually placed at the end of a line or daisy chain bus, and is designed to match the AC impedance of the cable and hence minimize signal reflections. Less commonly, a terminator is also placed at the end of the wire or cable. Radio frequency currents tend to reflect from discontinuities in the such as connectors and joints. Secondary reflections can also occur at the start, allowing interference to persist as repeated echoes of old data. These reflections also act as bottlenecks, preventing the signal power from reaching the destination, transmission line cables require impedance matching to carry electromagnetic signals with minimal reflections and power losses. Signal terminators are designed to match the characteristic impedances at both cable ends. Types of transmission line cables include balanced line such as line, and twisted pairs. Passive terminators often consist of a resistor, however significantly reactive loads may require other passive components such as inductors, capacitors. Active terminators consist of a regulator that keeps the voltage used for the terminating resistor at a constant level. Forced Perfect Termination Forced Perfect Termination can be used on single ended buses where diodes remove over, the signal is locked between two actively regulated voltage levels, which results in superior performance over a standard active terminator. All parallel SCSI units use terminators, SCSI is primarily used for storage and backup. Controller area network, commonly known as CAN Bus, uses terminators consisting of a 120 ohm resistor, dummy loads are commonly used in HF to EHF frequency circuits
8.
Transceiver
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A transceiver is a device comprising both a transmitter and a receiver that are combined and share common circuitry or a single housing. When no circuitry is common between transmit and receive functions, the device is a transmitter-receiver, the term originated in the early 1920s. Similar devices include transponders, transverters, and repeaters, in radio terminology, a transceiver means a unit which contains both a receiver and a transmitter. From the beginning days of radio the receiver and transmitter were separate units, amateur radio or ham radio operators can build their own equipment and it is now easier to design and build a simple unit containing both of the functions, transmitting and receiving. Almost all modern radio equipment is now a transceiver but there is an active market for pure radio receivers. An example of a transceiver would be a walkie-talkie or a CB radio, on a wired telephone, the handset contains the transmitter and receiver for the audio and in the 20th century was usually wired to the base unit by tinsel wire. The whole unit is referred to as a receiver. On a mobile telephone or other radiotelephone, the unit is a transceiver. A cordless telephone uses an audio and radio transceiver for the handset, if a speakerphone is included in a wired telephone base or in a cordless base station, the base also becomes an audio transceiver in addition to the handset. A modem is similar to a transceiver, in that it sends and receives a signal and it modulates a signal being transmitted and demodulates a signal being received. Transceivers are called Medium Attachment Units in IEEE802.3 documents and were used in 10BASE2. Fiber-optic gigabit,10 Gigabit Ethernet,40 Gigabit Ethernet, and 100 Gigabit Ethernet utilize transceivers known as GBIC, SFP, SFP+, QSFP, XFP, XAUI, CXP, and CFP. 4P4C, de facto standard connector for telephone handsets Duplex, two-Way communications capability Transponder#Optical communications U. S, patent 0,716,136, John Stone Stone, Apparatus for simultaneously transmitting and receiving space telegraph signals 7 MHz SSB transceiver Homebrew HF transceivers
9.
Fast Ethernet
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In computer networking, Fast Ethernet is a collective term for a number of Ethernet standards that carry traffic at the nominal rate of 100 Mbit/s. Of the Fast Ethernet standards, 100BASE-TX is by far the most common, Fast Ethernet was introduced in 1995 as the IEEE802. 3u standard and remained the fastest version of Ethernet for three years before the introduction of Gigabit Ethernet. The acronym GE/FE is sometimes used for supporting both standards. Fast Ethernet is an extension of the 10-megabit Ethernet standard and it runs on UTP data or optical fiber cable in a star wired bus topology, similar to 10BASE-T where all cables are attached to a hub. Fast Ethernet devices are backward compatible with existing 10BASE-T systems. Fast Ethernet is sometimes referred to as 100BASE-X, where X is a placeholder for the FX, the standard specifies the use of CSMA/CD for media access control. A full-duplex mode is also specified and in all modern networks use Ethernet switches. The 100 in the type designation refers to the transmission speed of 100 Mbit/s. The letter following the dash refers to the medium that carries the signal. A Fast Ethernet adapter can be divided into a media access controller, which deals with the higher-level issues of medium availability. The MAC may be linked to the PHY by a four-bit 25 MHz synchronous parallel interface known as a media-independent interface, in rare cases the MII may be an external connection but is usually a connection between ICs in a network adapter or even within a single IC. The specs are based on the assumption that the interface between MAC and PHY will be a MII but they do not require it. Repeaters may use the MII to connect to multiple PHYs for their different interfaces, the MII fixes the theoretical maximum data bit rate for all versions of Fast Ethernet to 100 Mbit/s. 100BASE-T is any of several Fast Ethernet standards for twisted pair cables, including, 100BASE-TX, 100BASE-T4, the segment length for a 100BASE-T cable is limited to 100 metres. All are or were standards under IEEE802.3, almost all 100BASE-T installations are 100BASE-TX. In the early days of Fast Ethernet, much vendor advertising centered on claims by competing standards that said vendors standards will work better with existing cables than other standards. Thus most networks had to be rewired for 100 Megabit speed whether or not there had supposedly been CAT3 or CAT5 cable runs, 100BASE-TX is the predominant form of Fast Ethernet, and runs over two wire-pairs inside a category 5 or above cable. Like 10BASE-T, the pairs in a standard connection are terminated on pins 1,2,3 and 6
10.
Vampire tap
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A vampire tap is a device for physically connecting a station, typically a computer, to a network that uses 10BASE5 cabling. The vampire tap usually has an integrated AUI, from this a short multicore cable connects to the card in the station. Vampire taps allow new connections to be made on a physical cable while the cable is in use. This allows administrators to expand bus-topology network sections without interrupting communications, without a vampire tap, the cable has to be cut and connectors have to be attached to both ends. Network tap Insulation-displacement connector, another insulation-piercing system Image of a Vampire Tap
11.
Ohm
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The ohm is the SI derived unit of electrical resistance, named after German physicist Georg Simon Ohm. The definition of the ohm was revised several times, today the definition of the ohm is expressed from the quantum Hall effect. In many cases the resistance of a conductor in ohms is approximately constant within a range of voltages, temperatures. In alternating current circuits, electrical impedance is also measured in ohms, the siemens is the SI derived unit of electric conductance and admittance, also known as the mho, it is the reciprocal of resistance in ohms. The power dissipated by a resistor may be calculated from its resistance, non-linear resistors have a value that may vary depending on the applied voltage. The rapid rise of electrotechnology in the last half of the 19th century created a demand for a rational, coherent, consistent, telegraphers and other early users of electricity in the 19th century needed a practical standard unit of measurement for resistance. Two different methods of establishing a system of units can be chosen. Various artifacts, such as a length of wire or a standard cell, could be specified as producing defined quantities for resistance, voltage. This latter method ensures coherence with the units of energy, defining a unit for resistance that is coherent with units of energy and time in effect also requires defining units for potential and current. Some early definitions of a unit of resistance, for example, the absolute-units system related magnetic and electrostatic quantities to metric base units of mass, time, and length. These units had the advantage of simplifying the equations used in the solution of electromagnetic problems. However, the CGS units turned out to have impractical sizes for practical measurements, various artifact standards were proposed as the definition of the unit of resistance. In 1860 Werner Siemens published a suggestion for a reproducible resistance standard in Poggendorffs Annalen der Physik und Chemie and he proposed a column of pure mercury, of one square millimetre cross section, one metre long, Siemens mercury unit. However, this unit was not coherent with other units, one proposal was to devise a unit based on a mercury column that would be coherent – in effect, adjusting the length to make the resistance one ohm. Not all users of units had the resources to carry out experiments to the required precision. The BAAS in 1861 appointed a committee including Maxwell and Thomson to report upon Standards of Electrical Resistance, in the third report of the committee,1864, the resistance unit is referred to as B. A. unit, or Ohmad. By 1867 the unit is referred to as simply Ohm, the B. A. ohm was intended to be 109 CGS units but owing to an error in calculations the definition was 1. 3% too small. The error was significant for preparation of working standards, on September 21,1881 the Congrès internationale délectriciens defined a practical unit of Ohm for the resistance, based on CGS units, using a mercury column at zero deg
12.
Attachment Unit Interface
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The Attachment Unit Interface is a physical and logical interface defined in the original IEEE802.3 standard for 10BASE5 Ethernet. In the OSI Model, this serves as the demarcation point between the Physical and Data-Link layers. The physical interface consists 15 pin connection that provides a path between an Ethernet nodes Physical Signalling and the Medium Attachment Unit, sometimes known as a transceiver. An AUI cable may be up to 50 meters long, although frequently the cable is omitted altogether, the electrical AUI connection was still present inside the equipment. By the mid-1990s AUI had all but disappeared as Fast Ethernet became more common, Gigabit Ethernet and 10 Gigabit Ethernet have respectively the GMII and XGMII standards which are equivalent to AUI. A modified form using a connector called the AAUI was introduced on Apple Macintosh computers in 1991. An AUI connector is a DA-15 and it has a sliding clip in place of the thumbscrews normally found on a D-connector to hold two connectors together. This clip permits the MAU and MAC to be attached to one another even when their size. This clip is however found to be awkward and/or unreliable.3 or later
