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.
Network interface controller
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A network interface controller is a computer hardware component that connects a computer to a computer network. Early network interface controllers were commonly implemented on expansion cards that plugged into a computer bus, the low cost and ubiquity of the Ethernet standard means that most newer computers have a network interface built into the motherboard. The network controller implements the electronic circuitry required to communicate using a physical layer and data link layer standard such as Ethernet, Fibre Channel. The NIC allows computers to communicate over a network, either by using cables or wirelessly. Although other network technologies exist, IEEE802 networks including the Ethernet variants have achieved near-ubiquity since the mid-1990s, newer server motherboards may even have dual network interfaces built-in. The Ethernet capabilities are integrated into the motherboard chipset or implemented via a low-cost dedicated Ethernet chip. A separate network card is not required unless additional interfaces are needed or some type of network is used. The NIC may use one or more of the techniques to indicate the availability of packets to transfer. Interrupt-driven I/O is where the peripheral alerts the CPU that it is ready to transfer data, also, NICs may use one or more of the following techniques to transfer packet data, Programmed input/output is where the CPU moves the data to or from the NIC to memory. Direct memory access is where some other device other than the CPU assumes control of the bus to move data to or from the NIC to memory. This removes load from the CPU but requires more logic on the card, in addition, a packet buffer on the NIC may not be required and latency can be reduced. There are two types of DMA, third-party DMA in which a DMA controller other than the NIC performs transfers, an Ethernet network controller typically has an 8P8C socket where the network cable is connected. Older NICs also supplied BNC, or AUI connections, a few LEDs inform the user of whether the network is active, and whether or not data transmission occurs. Ethernet network controllers typically support 10 Mbit/s Ethernet,100 Mbit/s Ethernet, such controllers are designated as 10/100/1000, meaning that they can support a notional maximum transfer rate of 10,100 or 1000 Mbit/s. 10 Gigabit Ethernet NICs are also available, and, as of November 2014, are beginning to be available on computer motherboards, multiqueue NICs provide multiple transmit and receive queues, allowing packets received by the NIC to be assigned to one of its receive queues. The hardware-based distribution of the interrupts, described above, is referred to as receive-side scaling, purely software implementations also exist, such as the receive packet steering and receive flow steering. Examples of such implementations are the RFS and Intel Flow Director, with multiqueue NICs, additional performance improvements can be achieved by distributing outgoing traffic among different transmit queues. By assigning different transmit queues to different CPUs/cores, various operating systems internal contentions can be avoided and those NICs support, Accessing local and remote memory without involving the remote CPU
3.
Network switch
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A network switch is a computer networking device that connects devices together on a computer network by using packet switching to receive, process, and forward data to the destination device. Unlike less advanced network hubs, a network switch forwards data only to one or multiple devices that need to receive it, a network switch is a multiport network bridge that uses hardware addresses to process and forward data at the data link layer of the OSI model. Switches for Ethernet are the most common form and the first Ethernet switch was introduced by Kalpana in 1990, Switches also exist for other types of networks including Fibre Channel, Asynchronous Transfer Mode, and InfiniBand. A switch is a device in a network that electrically and logically connects together other devices. Multiple data cables are plugged into a switch to enable communication between different networked devices, Switches manage the flow of data across a network by transmitting a received network packet only to the one or more devices for which the packet is intended. Each networked device connected to a switch can be identified by its network address and this maximizes the security and efficiency of the network. Because broadcasts are still being forwarded to all connected devices, the newly formed network segment continues to be a broadcast domain, an Ethernet switch operates at the data link layer of the OSI model to create a separate collision domain for each switch port. In full duplex mode, each switch port can simultaneously transmit and receive, in the case of using a repeater hub, only a single transmission could take place at a time for all ports combined, so they would all share the bandwidth and run in half duplex. Necessary arbitration would result in collisions, requiring retransmissions. The network switch plays an role in most modern Ethernet local area networks. Mid-to-large sized LANs contain a number of linked managed switches, in most of these cases, the end-user device contains a router and components that interface to the particular physical broadband technology. User devices may include a telephone interface for Voice over IP protocol. Segmentation involves the use of a bridge or a switch to split a larger collision domain into smaller ones in order to reduce collision probability, in the extreme case, each device is located on a dedicated switch port. In contrast to an Ethernet hub, there is a separate collision domain on each of the switch ports and this allows computers to have dedicated bandwidth on point-to-point connections to the network and also to run in full-duplex without collisions. Full-duplex mode has one transmitter and one receiver per collision domain. Switches may operate at one or more layers of the OSI model, including the data link, a device that operates simultaneously at more than one of these layers is known as a multilayer switch. In switches intended for use, built-in or modular interfaces make it possible to connect different types of networks, including Ethernet, Fibre Channel, RapidIO, ATM. This connectivity can be at any of the layers mentioned, while the layer-2 functionality is adequate for bandwidth-shifting within one technology, interconnecting technologies such as Ethernet and token ring is performed easier at layer 3 or via routing
4.
Modular connector
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A modular connector is an electrical connector that was originally designed for use in telephone wiring, but has since been used for many other purposes. Many applications that used a bulkier, more expensive connector have converted to modular connectors. Probably the most well known applications of modular connectors are for telephone jacks and for Ethernet jacks, Modular connectors were originally used in the Registration Interface system, mandated by the Federal Communications Commission in 1976 in which they became known as registered jacks. The registered jack specifications define the wiring patterns of the jacks, instead, these latter aspects are covered by ISO standard 8877, first used in ISDN systems. TIA/EIA-568 is a standard for data circuits wired on modular connectors, other systems exist for assigning signals to modular connectors, physical interchangeability of plugs and jacks does not ensure interoperation, nor protection from electrical damage to circuits. For example, modular cables and connectors have used to supply low-voltage AC or DC power. Modular connectors also go by the names modular phone jack/plug, RJ connector, the term modular connector arose from its original use in a novel system of cabling designed to make telephone equipment more modular. This includes the 4P4C handset connector, a very popular use of 8P8C today is Ethernet over twisted pair, and that may be the most well known context in which the name RJ45 is known, even though it has nothing to do with the RJ45 standard. Likewise, the 4P4C connector is sometimes called RJ9 or RJ22, Modular connectors were originally developed and patented by General Cable Corp in 1974. They replaced the hard-wired connections on most Western Electric telephones around 1976, at the same time, they began to replace screw terminals and larger 3 and 4 pin telephone jacks in buildings. Modular connectors have gender, plugs are considered to be male, while jacks or sockets are considered to be female, plugs are used to terminate loose cables and cords, while jacks are used for fixed locations on surfaces such as walls and panels, and on equipment. Other than telephone extension cables, cables with a plug on one end. Instead, cables are connected using an adapter, which consists of two female jacks wired back-to-back. Modular connectors are designed to latch together, a spring-loaded tab on the plug snaps into a jack so that the plug cannot be pulled out. To remove the plug, the latching tab must be depressed, the standard and most common way to install a jack in a wall or panel is with the tab side down. This usually makes it easier to operate the tab when removing the plug, because the person grabs the plug with thumb on top, the modular connector suffers from a design flaw or weakness however, as the fragile latching tab easily snags on other cables and breaks off. When this happens, the connector is still functional, but the crucial latching feature is lost, some higher quality cables have a flexible sleeve called a boot over the plug, or a special tab design, to prevent this. These cables are marketed as snagless
5.
Optical fiber cable
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An optical fiber cable, also known as fiber optic cable, is a cable containing one or more optical fibers that are used to carry light. The optical fiber elements are typically coated with plastic layers. Different types of cable are used for different applications, for long distance telecommunication. Optical fiber consists of a core and a layer, selected for total internal reflection due to the difference in the refractive index between the two. In practical fibers, the cladding is coated with a layer of acrylate polymer or polyimide. This coating protects the fiber from damage but does not contribute to its optical waveguide properties, individual coated fibers then have a tough resin buffer layer and/or core tube extruded around them to form the cable core. Several layers of protective sheathing, depending on the application, are added to form the cable, rigid fiber assemblies sometimes put light-absorbing glass between the fibers, to prevent light that leaks out of one fiber from entering another. This reduces cross-talk between the fibers, or reduces flare in fiber bundle imaging applications, for indoor applications, the jacketed fiber is generally enclosed, with a bundle of flexible fibrous polymer strength members like aramid, in a lightweight plastic cover to form a simple cable. Each end of the cable may be terminated with an optical fiber connector to allow it to be easily connected and disconnected from transmitting and receiving equipment. For use in more environments, a much more robust cable construction is required. In loose-tube construction the fiber is laid helically into semi-rigid tubes and this protects the fiber from tension during laying and due to temperature changes. Loose-tube fiber may be dry block or gel-filled, dry block offers less protection to the fibers than gel-filled, but costs considerably less. Instead of a tube, the fiber may be embedded in a heavy polymer jacket. Tight buffer cables are offered for a variety of applications, Breakout cables normally contain a ripcord, two non-conductive dielectric strengthening members, an aramid yarn, and 3 mm buffer tubing with an additional layer of Kevlar surrounding each fiber. The ripcord is a cord of strong yarn that is situated under the jacket of the cable for jacket removal. Distribution cables have an overall Kevlar wrapping, a ripcord, and these fiber units are commonly bundled with additional steel strength members, again with a helical twist to allow for stretching. A critical concern in outdoor cabling is to protect the fiber from contamination by water and this is accomplished by use of solid barriers such as copper tubes, and water-repellent jelly or water-absorbing powder surrounding the fiber. Finally, the cable may be armored to protect it from environmental hazards, in September 2012, NTT Japan demonstrated a single fiber cable that was able to transfer 1 petabit per second over a distance of 50 kilometers
6.
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
7.
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
8.
Twisted pair
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It was invented by Alexander Graham Bell. In balanced pair operation, the two wires carry equal and opposite signals, and the destination detects the difference between the two and this is known as differential mode transmission. Noise sources introduce signals into the wires by coupling of electric or magnetic fields, the noise thus produces a common-mode signal which is canceled at the receiver when the difference signal is taken. This problem is especially apparent in telecommunication cables where pairs in the same cable lie next to each other for many miles, one pair can induce crosstalk in another and it is additive along the length of the cable. Twisting the pairs counters this effect as on each half twist the wire nearest to the noise-source is exchanged, providing the interfering source remains uniform, or nearly so, over the distance of a single twist, the induced noise will remain common-mode. Differential signaling also reduces electromagnetic radiation from the cable, along with the associated attenuation allowing for greater distance between exchanges, the twist rate makes up part of the specification for a given type of cable. When nearby pairs have equal twist rates, the conductors of the different pairs may repeatedly lie next to each other. For this reason it is specified that, at least for cables containing small numbers of pairs. In contrast to shielded or foiled twisted pair, UTP cable is not surrounded by any shielding, UTP is the primary wire type for telephone usage and is very common for computer networking, especially as patch cables or temporary network connections due to the high flexibility of the cables. The earliest telephones used telegraph lines, or open-wire single-wire earth return circuits, in the 1880s electric trams were installed in many cities, which induced noise into these circuits. Lawsuits being unavailing, the telephone companies converted to balanced circuits, as electrical power distribution became more commonplace, this measure proved inadequate. Two wires, strung on either side of cross bars on utility poles, within a few years, the growing use of electricity again brought an increase of interference, so engineers devised a method called wire transposition, to cancel out the interference. In wire transposition, the wires exchange position once every several poles, in this way, the two wires would receive similar EMI from power lines. This represented an early implementation of twisting, with a twist rate of about four twists per kilometre, such open-wire balanced lines with periodic transpositions still survive today in some rural areas. Twisted-pair cabling was invented by Alexander Graham Bell in 1881, by 1900, the entire American telephone line network was either twisted pair or open wire with transposition to guard against interference. UTP cables are found in many Ethernet networks and telephone systems, for indoor telephone applications, UTP is often grouped into sets of 25 pairs according to a standard 25-pair color code originally developed by AT&T Corporation. A typical subset of these colors shows up in most UTP cables, for urban outdoor telephone cables containing hundreds or thousands of pairs, the cable is divided into small but identical bundles. Each bundle consists of twisted pairs that have different twist rates, the bundles are in turn twisted together to make up the cable
9.
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
10.
Crossover cable
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A crossover cable connects two devices of the same type, for example DTE-DTE or DCE-DCE, usually connected asymmetrically, by a modified cable called a crosslink. Such distinction of devices was introduced by IBM. e, pCs, linking two or more hubs, switches or routers together, possibly to work as one wider device. Null modem of RS-232 Ethernet crossover cable Rollover cable A loopback is a type of degraded one side crosslinked connection connecting a port to itself, usually for test purposes. A T1 cable uses T568B pairs 1 and 2, so to connect two T1 CSU/DSU devices back-to-back requires a cable that swaps these pairs. Specifically, pins 1,2,4, and 5 are connected to 4,5,1, a 56K DDS cable uses T568B pairs 02 and 04, so a crossover cable for these devices swaps those pairs. Electrical connector wiring Pinout Structured cabling TIA/EIA-568-B
11.
Medium-dependent interface
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A medium dependent interface describes the interface in a computer network from a physical layer implementation to the physical medium used to carry the transmission. Ethernet over twisted pair also defines a medium dependent interface crossover interface, auto MDI-X ports on newer network interfaces detect if the connection would require a crossover, and automatically chooses the MDI or MDI-X configuration to properly match the other end of the link. The popular Ethernet family defines common medium dependent interfaces, for 10BASE5, connection to the coaxial cable was made with either a vampire tap or a pair of N connectors. For 10BASE2 the connection to the cable was typically made with a single BNC connector to which a T-piece was attached. For twisted pair cabling 8P8C modular connectors are used, for fiber a variety of connectors are used depending on manufacturer and physical space availability. With 10BASE-T and 100BASE-TX separate twisted pairs are used for the two directions of communication, since twisted pair cables are conventionally wired pin to pin there are two different pinouts used for the medium dependent interface. These are referred to as MDI and MDI-X, when connecting an MDI port to an MDI-X port a straight through cable is used while to connect two MDI ports or two MDI-X ports a crossover cable must be used. Conventionally MDI is used on end devices while MDI-X is used on hubs, some network hubs or switches have an MDI port to connect to other hubs or switches without a crossover cable. The terminology generally refers to variants of the Ethernet over twisted pair technology that use a female 8P8C port connection on a computer, the X refers to the fact that transmit wires on an MDI device must be connected to receive wires on an MDI-X device. Straight through cables connect pins 1 and 2 on an MDI device to pins 1 and 2 on an MDI-X device, similarly pins 3 and 6 are receive pins on an MDI device and transmit pins on an MDI-X device. The general convention was for network hubs and switches to use the MDI-X configuration, while all other such as personal computers, workstations. Some routers and other devices had a switch to go back. Thus, connecting MDI to MDI-X requires a straight-through cable, connecting MDI to MDI or MDI-X to MDI-X requires a crossover in the cable to get an odd number. When using more complicated setups through multiple patch panels in structured cabling and it is a good idea to have all necessary crossovers on one side, i. e. either on the central hub/switch or on each secondary hub/switch. The confusion of needing two different kinds of cables for anything but hierarchical star network topologies prompted a more automatic solution, as long as it is enabled on either end of a link, either type of cable can be used. For auto MDI-X to operate correctly, the rate on the interface. Auto MDI-X was developed by Hewlett-Packard engineers Daniel Joseph Dove and Bruce W. Melvin, a pseudo-random number generator decides whether or not a network port will attach its transmitter, or its receiver to each of the twisted pairs used to auto-negotiate the link. When two auto MDI-X ports are connected together, which is normal for modern products, the resolution time is typically <500 ms
12.
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
