1.
Computer data storage
–
Computer data storage, often called storage or memory, is a technology consisting of computer components and recording media used to retain digital data. It is a function and fundamental component of computers. The central processing unit of a computer is what manipulates data by performing computations, in practice, almost all computers use a storage hierarchy, which puts fast but expensive and small storage options close to the CPU and slower but larger and cheaper options farther away. In the Von Neumann architecture, the CPU consists of two parts, The control unit and the arithmetic logic unit. The former controls the flow of data between the CPU and memory, while the latter performs arithmetic and logical operations on data, without a significant amount of memory, a computer would merely be able to perform fixed operations and immediately output the result. It would have to be reconfigured to change its behavior and this is acceptable for devices such as desk calculators, digital signal processors, and other specialized devices. Von Neumann machines differ in having a memory in which they store their operating instructions, most modern computers are von Neumann machines. A modern digital computer represents data using the numeral system. Text, numbers, pictures, audio, and nearly any form of information can be converted into a string of bits, or binary digits. The most common unit of storage is the byte, equal to 8 bits, a piece of information can be handled by any computer or device whose storage space is large enough to accommodate the binary representation of the piece of information, or simply data. For example, the works of Shakespeare, about 1250 pages in print. Data is encoded by assigning a bit pattern to each character, digit, by adding bits to each encoded unit, redundancy allows the computer to both detect errors in coded data and correct them based on mathematical algorithms. A random bit flip is typically corrected upon detection, the cyclic redundancy check method is typically used in communications and storage for error detection. A detected error is then retried, data compression methods allow in many cases to represent a string of bits by a shorter bit string and reconstruct the original string when needed. This utilizes substantially less storage for many types of data at the cost of more computation, analysis of trade-off between storage cost saving and costs of related computations and possible delays in data availability is done before deciding whether to keep certain data compressed or not. For security reasons certain types of data may be encrypted in storage to prevent the possibility of unauthorized information reconstruction from chunks of storage snapshots. Generally, the lower a storage is in the hierarchy, the lesser its bandwidth and this traditional division of storage to primary, secondary, tertiary and off-line storage is also guided by cost per bit. In contemporary usage, memory is usually semiconductor storage read-write random-access memory, typically DRAM or other forms of fast but temporary storage
2.
Server (computing)
–
In computing, a server is a computer program or a device that provides functionality for other programs or devices, called clients. This architecture is called the model, and a single overall computation is distributed across multiple processes or devices. Servers can provide various functionalities, often called services, such as sharing data or resources among multiple clients, a single server can serve multiple clients, and a single client can use multiple servers. A client process may run on the device or may connect over a network to a server on a different device. Typical servers are database servers, file servers, mail servers, print servers, web servers, game servers, designating a computer as server-class hardware implies that it is specialized for running servers on it. The use of the server in computing comes from queueing theory, where it dates to the mid 20th century, being notably used in Kendall. In earlier papers, such as the Erlang, more terms such as operators are used. In computing, server dates at least to RFC5, one of the earliest documents describing ARPANET, the use of serving also dates to early documents, such as RFC4, contrasting serving-host with using-host. The Jargon File defines server in the sense of a process performing service for requests, usually remote, with the 1981 version reading. A kind of DAEMON which performs a service for the requester, strictly speaking, the term server refers to a computer program or process. Through metonymy, it refers to a used to running one or several server programs. On a network, such a device is called a host, in addition to server, the words serve and service are frequently used, though servicer and servant are not. The word service may refer to either the form of functionality. Alternatively, it may refer to a program that turns a computer into a server. Originally used as servers serve users, in the sense of obey, today one says that servers serve data. For instance, web servers serve web pages to users or service their requests, the server is part of the client–server model, in this model, a server serves data for clients. The nature of communication between a client and server is request and response and this is in contrast with peer-to-peer model in which the relationship is on-demand reciprocation. In principle, any computerized process that can be used or called by another process is a server, thus any general purpose computer connected to a network can host servers
3.
Storage area network
–
A storage area network is a network which provides access to consolidated, block level data storage. A SAN typically has its own network of devices that are generally not accessible through the local area network by other devices. The cost and complexity of SANs dropped in the early 2000s to levels allowing wider adoption across both enterprise and small to medium-sized business environments, a SAN does not provide file abstraction, only block-level operations. However, file systems built on top of SANs do provide file-level access, essentially, a SAN consolidates such storage islands together using a high-speed network. Operating systems maintain their own systems on their own dedicated, non-shared LUNs. If multiple systems were simply to attempt to share a LUN, any planned sharing of data on different computers within a LUN requires software, such as SAN file systems or clustered computing. Despite such issues, SANs help to increase capacity utilization. Common uses of a SAN include provision of transactionally accessed data that require high-speed block-level access to the hard drives such as servers, databases. Network-attached storage was designed independently of SAN systems, both NAS and SAN have the potential to reduce the amount of excess storage that must be purchased and provisioned as spare space. In a DAS-only architecture, each computer must be provisioned with enough storage to ensure that the computer does not run out of space at an untimely moment. In a DAS architecture the spare storage on one computer cannot be utilized by another, in a NAS the storage devices are directly connected to a file server that makes the storage available at a file-level to the other computers. In a SAN, the storage is available at a lower block-level. SAN protocols include Fibre Channel, iSCSI, ATA over Ethernet, instead the CPUs use the LAN to communicate, potentially creating bandwidth as well as performance bottlenecks. To understand their differences, a comparison of SAN, DAS and NAS architectures may be helpful, sharing storage usually simplifies storage administration and adds flexibility since cables and storage devices do not have to be physically moved to shift storage from one server to another. Other benefits include the ability to allow servers to boot from the SAN itself and this allows for a quick and easy replacement of faulty servers since the SAN can be reconfigured so that a replacement server can use the LUN of the faulty server. SANs also tend to more effective disaster recovery processes. A SAN could span a distant location containing a secondary storage array and this enables storage replication either implemented by disk array controllers, by server software, or by specialized SAN devices. Since IP WANs are often the least costly method of long-distance transport, the traditional physical SCSI layer could support only a few meters of distance - not nearly enough to ensure business continuance in a disaster
4.
Data center
–
A data center is a facility used to house computer systems and associated components, such as telecommunications and storage systems. It generally includes redundant or backup power supplies, redundant data communications connections, environmental controls, large data centers are industrial scale operations using as much electricity as a small town. Data centers have their roots in the computer rooms of the early ages of the computing industry. Early computer systems, complex to operate and maintain, required an environment in which to operate. Many cables were necessary to all the components, and methods to accommodate and organize these were devised such as standard racks to mount equipment, raised floors. A single mainframe required a deal of power, and had to be cooled to avoid overheating. Security became important – computers were expensive, and were used for military purposes. Basic design-guidelines for controlling access to the room were therefore devised. During the boom of the industry, and especially during the 1980s, users started to deploy computers everywhere. However, as information technology operations started to grow in complexity, the advent of Unix from the early 1970s led to the subsequent proliferation of freely available Linux-compatible PC operating-systems during the 1990s. These were called servers, as timesharing operating systems like Unix rely heavily on the model to facilitate sharing unique resources between multiple users. The use of the data center, as applied to specially designed computer rooms. The boom of data centers came during the bubble of 1997–2000. Companies needed fast Internet connectivity and non-stop operation to deploy systems, installing such equipment was not viable for many smaller companies. Many companies started building very large facilities, called Internet data centers, New technologies and practices were designed to handle the scale and the operational requirements of such large-scale operations. These practices eventually migrated toward the data centers, and were adopted largely because of their practical results. Data centers for cloud computing are called cloud data centers, but nowadays, the division of these terms has almost disappeared and they are being integrated into a term data center. Standards documents from accredited professional groups, such as the Telecommunications Industry Association, well-known operational metrics for data-center availability can serve to evaluate the commercial impact of a disruption
5.
Switched fabric
–
Switched Fabric or switching fabric is a network topology in which network nodes interconnect via one or more network switches. HyperTransport, for example, continues to maintain a processor bus focus even after adopting a higher speed physical layer, similarly, PCI Express is just a serial version of PCI, it adheres to PCI’s host/peripheral load/store DMA-based architecture on top of a serial physical and link layer. In the Fibre Channel Switched Fabric topology, devices are connected to each other one or more Fibre Channel switches. While this topology has the best scalability of the three FC topologies, it is the one requiring switches, which are costly hardware devices. Visibility among devices in a fabric is typically controlled with Fibre Channel zoning, multiple switches in a fabric usually form a mesh network, with devices being on the edges of the mesh. Most Fibre Channel network designs employ two separate fabrics for redundancy, the two fabrics share the edge nodes, but are otherwise unconnected. One of the advantages of such setup is capability of failover, meaning that in case one link breaks or a fabric goes out of order, the fabric topology allows the connection of up to the theoretical maximum of 16 million devices, limited only by the available address space. Clos network Fabric Application Interface Standard Network traffic control RapidIO Shortest Path Bridging VPX What is a Switch Fabric
6.
Optical fiber
–
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
7.
Fibre Channel Protocol
–
Fibre Channel Protocol is the SCSI interface protocol utilizing an underlying Fibre Channel connection. The Fibre Channel standards define a data transfer mechanism that can be used to connect workstations, mainframes, supercomputers, storage devices. Some Fibre Channel characteristics are, Performance from 266 megabits/second to 16 gigabits/second Support both optical and copper media, with distances up to 10 km, fC-3 -- Common Services required for advanced features such as striping, hunt group and multicast. FC-4 -- Application interfaces that can execute over Fibre Channel such as the Fibre Channel protocol for SCSI, unlike a layered network architecture, a Fibre Channel network is largely specified by functional elements and the interfaces between them. These consist, in part, of the following, N_PORTs—The end points for traffic, FC Devices—The devices to which the N_PORTs provide access. Fabric Ports—The interfaces within a network that provide attachment for an N_PORT, the network infrastructure for carrying frame traffic between N_PORTs. Within a switched or mixed fabric, a set of servers, including a name server for device discovery. Fibre Channel network topologies consist of the following, Arbitrated Loop—A series of N_PORTs connected together in daisy-chain fashion, switched Fabric—A network consisting of switching elements. Mixed Fabric—A network consisting of switches and fabric-attached loops, a loop-attached N_PORT is connected to the loop through an L_PORT and accesses the fabric by way of an FL_PORT
8.
SCSI
–
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, electrical and optical interfaces, SCSI is derived from SASI, the Shugart Associates System Interface, developed circa 1978 and publicly disclosed in 1981. A SASI controller provided a bridge between a hard disk drives low-level interface and a host computer, which needed to read blocks of data, SASI controller boards were typically the size of a hard disk drive and were usually physically mounted to the drives chassis. SASI, which was used in mini- and early microcomputers, defined the interface as using a 50-pin flat ribbon connector which was adopted as the first-generation SCSI connector. SASI is a fully compliant subset of SCSI-1 so that many, if not all, larry Boucher is considered to be the father of SASI and SCSI due to his pioneering work first at Shugart Associates and then at Adaptec. A number of such as NCR Corporation, Adaptec and Optimem were early supporters of the SCSI standard. The NCR facility in Wichita, Kansas is widely thought to have developed the industrys first SCSI chip, the small part in SCSI is historical, since the mid-1990s, SCSI has been available on even the largest of computer systems. Since its standardization in 1986, SCSI has been used in the Amiga, Atari, Apple Macintosh and Sun Microsystems computer lines. Apple started using Parallel ATA for its low-end machines with the Macintosh Quadra 630 in 1994, Apple dropped on-board SCSI completely with the Power Mac G3 in 1999, while still offering a PCI controller card as an option on up to the Power Macintosh G4 models. Sun switched its lower-end range to Serial ATA, Commodore included a SCSI interface on the Amiga 3000/3000T systems and it was an add-on to previous Amiga 500/2000 models. Starting with the Amiga 600/1200/4000 systems Commodore switched to the IDE interface, Atari included SCSI interface as standard in its Atari MEGA STE, Atari TT and Atari Falcon computer models. SCSI has never been popular in the low-priced IBM PC world, owing to the lower cost, however, SCSI drives and even SCSI RAIDs became common in PC workstations for video or audio production. Although much of the SCSI documentation talks about the parallel interface, Serial interfaces have a number of advantages over parallel SCSI, including higher data rates, simplified cabling, longer reach, and improved fault isolation. ISCSI preserves the basic SCSI paradigm, especially the command set, almost unchanged, through embedding of SCSI-3 over TCP/IP, SCSI is popular on high-performance workstations, servers, and storage appliances. Almost all RAID subsystems on servers have used some kind of SCSI hard disk drives for decades, moreover, SAS offers compatibility with SATA devices, creating a much broader range of options for RAID subsystems together with the existence of nearline SAS drives. SCSI is available in a variety of interfaces, the first was parallel SCSI, which uses a parallel bus design. Since 2005, SPI was gradually replaced by Serial Attached SCSI, ISCSI, for example, uses TCP/IP as a transport mechanism, which is most often transported over Gigabit Ethernet or faster network links. With the advent of SAS and SATA drives, provision for parallel SCSI on motherboards was discontinued, initially, the SCSI Parallel Interface was the only interface using the SCSI protocol
9.
Mainframe computer
–
The term originally referred to the large cabinets called main frames that housed the central processing unit and main memory of early computers. Later, the term was used to distinguish high-end commercial machines from less powerful units, most large-scale computer system architectures were established in the 1960s, but continue to evolve. Their high stability and reliability enable these machines to run uninterrupted for decades, Mainframes are defined by high availability, one of the main reasons for their longevity, since they are typically used in applications where downtime would be costly or catastrophic. The term reliability, availability and serviceability is a characteristic of mainframe computers. Proper planning and implementation is required to exploit these features, and if improperly implemented, in the late 1950s, most mainframes had no explicitly interactive interface, but only accepted sets of punched cards, paper tape, or magnetic tape to transfer data and programs. In cases where interactive terminals were supported, these were used almost exclusively for applications rather than program development, typewriter and Teletype devices were also common control consoles for system operators through the 1970s, although ultimately supplanted by keyboard/display devices. By the early 1970s, many mainframes acquired interactive user interfaces and operated as timesharing computers, users gained access through specialized terminals or, later, from personal computers equipped with terminal emulation software. By the 1980s, many mainframes supported graphical terminals, and terminal emulation and this format of end-user computing reached mainstream obsolescence in the 1990s due to the advent of personal computers provided with GUIs. After 2000, most modern mainframes have partially or entirely phased out classic green screen terminal access for end-users in favour of Web-style user interfaces, the infrastructure requirements were drastically reduced during the mid-1990s, when CMOS mainframe designs replaced the older bipolar technology. IBM claimed that its newer mainframes could reduce data center energy costs for power and cooling, modern mainframes can run multiple different instances of operating systems at the same time. This technique of virtual machines allows applications to run as if they were on physically distinct computers, in this role, a single mainframe can replace higher-functioning hardware services available to conventional servers. While mainframes pioneered this capability, virtualization is now available on most families of computer systems, Mainframes can add or hot swap system capacity without disrupting system function, with specificity and granularity to a level of sophistication not usually available with most server solutions. Modern mainframes, notably the IBM zSeries, System z9 and System z10 servers, such a two-mainframe installation can support continuous business service, avoiding both planned and unplanned outages. In practice many customers use multiple mainframes linked either by Parallel Sysplex and shared DASD, or with shared, Mainframes are designed to handle very high volume input and output and emphasize throughput computing. Since the late-1950s, mainframe designs have included subsidiary hardware which manage the I/O devices and it is common in mainframe shops to deal with massive databases and files. Gigabyte to terabyte-size record files are not unusual, compared to a typical PC, mainframes commonly have hundreds to thousands of times as much data storage online, and can access it reasonably quickly. Other server families also offload I/O processing and emphasize throughput computing, Mainframes also have execution integrity characteristics for fault tolerant computing. This hardware-level feature, also found in HPs NonStop systems, is known as lock-stepping, not all applications absolutely need the assured integrity that these systems provide, but many do, such as financial transaction processing
10.
Flash memory
–
Flash memory is electronic non-volatile computer storage medium that can be electrically erased and reprogrammed. Toshiba developed flash memory from EEPROM in the early 1980s and introduced it to the market in 1984, the two main types of flash memory are named after the NAND and NOR logic gates. The individual flash memory cells exhibit internal characteristics similar to those of the corresponding gates, where EPROMs had to be completely erased before being rewritten, NAND-type flash memory may be written and read in blocks which are generally much smaller than the entire device. NOR-type flash allows a machine word to be written—to an erased location—or read independently. The NAND type operates primarily in memory cards, USB flash drives, solid-state drives, NAND or NOR flash memory is also often used to store configuration data in numerous digital products, a task previously made possible by EEPROM or battery-powered static RAM. One key disadvantage of flash memory is that it can endure a relatively small number of write cycles in a specific block. In addition to being non-volatile, flash memory offers fast read access times, although flash memory is technically a type of EEPROM, the term EEPROM is generally used to refer specifically to non-flash EEPROM which is erasable in small blocks, typically bytes. Because erase cycles are slow, the block sizes used in flash memory erasing give it a significant speed advantage over non-flash EEPROM when writing large amounts of data. As of 2013, flash memory costs much less than byte-programmable EEPROM and had become the dominant memory type wherever a system required a significant amount of non-volatile solid-state storage, Flash memory was invented by Fujio Masuoka while working for Toshiba circa 1980. According to Toshiba, the flash was suggested by Masuokas colleague, Shōji Ariizumi. Masuoka and colleagues presented the invention at the IEEE1984 International Electron Devices Meeting held in San Francisco, Intel Corporation saw the massive potential of the invention and introduced the first commercial NOR type flash chip in 1988. NOR-based flash has long erase and write times, but provides full address and data buses, allowing random access to any memory location. This makes it a replacement for older read-only memory chips. Its endurance may be from as little as 100 erase cycles for a flash memory, to a more typical 10,000 or 100,000 erase cycles. NOR-based flash was the basis of early flash-based removable media, CompactFlash was originally based on it, however, the I/O interface of NAND flash does not provide a random-access external address bus. Rather, data must be read on a basis, with typical block sizes of hundreds to thousands of bits. This makes NAND flash unsuitable as a replacement for program ROM. In this regard, NAND flash is similar to other data storage devices, such as hard disks and optical media
11.
NVM Express
–
NVM Express or Non-Volatile Memory Host Controller Interface Specification is a logical device interface specification for accessing non-volatile storage media attached via a PCI Express bus. The initialism, NVM, stands for memory, which is commonly flash memory that comes in the form of solid-state drives. By its design, NVM Express allows host hardware and software to fully exploit the levels of parallelism possible in modern SSDs. NVM Express devices exist both in the form of standard-sized PCI Express expansion cards and as 2. 5-inch form-factor devices that provide a four-lane PCI Express interface through the U.2 connector. SATA Express storage devices and the M.2 specification for internally mounted computer expansion cards also support NVM Express as the device interface. Historically, most SSDs used buses such as SATA, SAS or Fibre Channel for interfacing with the rest of a computer system, high-end SSDs had been made using the PCI Express bus before NVMe, but using non-standard specification interfaces. By standardizing the interface of SSDs, operating systems only need one driver to work with all SSDs adhering to the specification and it also means that each SSD manufacturer does not have to use additional resources to design specific interface drivers. This is similar to how USB mass storage devices are built to follow the USB mass-storage device class specification and work with all computers, as of September 2014, a new standard for using NVMe over Fibre Channel is also in development. A NVMHCI working group led by Intel was formed that year, the NVMHCI1.0 specification was completed in April 2008 and released on Intels web site. Technical work on NVMe began in the half of 2009. The NVMe specifications were developed by the NVM Express Workgroup, which consists of more than 90 companies, version 1.0 of the specification was released on 1 March 2011, while version 1.1 of the specification was released on 11 October 2012. Major features added in version 1.1 are multi-path I/O and it is expected that future revisions will significantly enhance namespace management. Because of its focus, NVMe 1.1 was initially called Enterprise NVMHCI. An update for the base NVMe specification, called version 1. 0e, was released in January 2013, in June 2011, a Promoter Group led by seven companies was formed. The first commercially available NVMe chipsets were released by Integrated Device Technology in August 2012, the LSI SandForce SF3700 controller family, released in November 2013, also supports NVMe. Sample engineering boards with the PCI Express 2.0 ×4 model of this controller found 1,800 MB/sec read/write sequential speeds, a Kingston HyperX prosumer product using this controller was showcased at the Consumer Electronics Show 2014 and promised similar performance. As of November 2014, NVMe drives are commercially available, in March 2014, the group incorporated to become NVM Express, Inc. which as of November 2014 consists of more than 65 companies from across the industry. NVM Express specifications are owned and maintained by NVM Express, Inc. which also promotes awareness of NVM Express as an industry-wide standard
12.
Technical Committee T11
–
The InterNational Committee for Information Technology Standards, is an ANSI-accredited standards development organization composed of Information technology developers. It was formerly known as the X3 and NCITS, INCITS is the central U. S. forum dedicated to creating technology standards. INCITS coordinates technical standards activity between ANSI in the USA and joint ISO/IEC committees worldwide and this provides a mechanism to create standards that will be implemented in many nations. As such, INCITS executive board also serves as ANSIs Technical Advisory Group for ISO/IEC Joint Technical Committee 1, JTC1 is responsible for International standardization in the field of information technology. Many times, the U. S. standard that INCITS members develop then will become the standard for the international community. INCITS is guided by its executive board, more than 750 standards have been created and approved through the INCITS process, with another 800 in development. American National Standards are voluntary and serve U. S. interests well because all materially affected stakeholders have the opportunity to together to create them. INCITS-approved standards only become mandatory when, and if, they are adopted or referenced by the government or when market forces make them imperative. INCITS policy is to adopt as Identical American National Standards all ISO/IEC or ISO standards that fall within its program of work, accordingly, INCITS will adopt as Identical American National Standards all ISO/IEC or ISO standards that fall within its program of work. Similarly, INCITS will withdraw any such adopted American National Standard that has been withdrawn as an ISO/IEC or ISO International Standards, the first organizational meeting was in February 1961 with ITI taking Secretariat responsibility. X3 was established under American National Standards Institute procedures, the forum was renamed Accredited Standards Committee NCITS, National Committee for Information Technology Standards in 1997, and the current name was approved in 2001
13.
INCITS
–
The InterNational Committee for Information Technology Standards, is an ANSI-accredited standards development organization composed of Information technology developers. It was formerly known as the X3 and NCITS, INCITS is the central U. S. forum dedicated to creating technology standards. INCITS coordinates technical standards activity between ANSI in the USA and joint ISO/IEC committees worldwide and this provides a mechanism to create standards that will be implemented in many nations. As such, INCITS executive board also serves as ANSIs Technical Advisory Group for ISO/IEC Joint Technical Committee 1, JTC1 is responsible for International standardization in the field of information technology. Many times, the U. S. standard that INCITS members develop then will become the standard for the international community. INCITS is guided by its executive board, more than 750 standards have been created and approved through the INCITS process, with another 800 in development. American National Standards are voluntary and serve U. S. interests well because all materially affected stakeholders have the opportunity to together to create them. INCITS-approved standards only become mandatory when, and if, they are adopted or referenced by the government or when market forces make them imperative. INCITS policy is to adopt as Identical American National Standards all ISO/IEC or ISO standards that fall within its program of work, accordingly, INCITS will adopt as Identical American National Standards all ISO/IEC or ISO standards that fall within its program of work. Similarly, INCITS will withdraw any such adopted American National Standard that has been withdrawn as an ISO/IEC or ISO International Standards, the first organizational meeting was in February 1961 with ITI taking Secretariat responsibility. X3 was established under American National Standards Institute procedures, the forum was renamed Accredited Standards Committee NCITS, National Committee for Information Technology Standards in 1997, and the current name was approved in 2001
14.
American National Standards Institute
–
The organization also coordinates U. S. standards with international standards so that American products can be used worldwide. ANSI accredits standards that are developed by representatives of other organizations, government agencies, consumer groups, companies. These standards ensure that the characteristics and performance of products are consistent, that use the same definitions and terms. ANSI also accredits organizations that carry out product or personnel certification in accordance with requirements defined in international standards, the organizations headquarters are in Washington, DC. ANSIs operations office is located in New York City, the ANSI annual operating budget is funded by the sale of publications, membership dues and fees, accreditation services, fee-based programs, and international standards programs. ANSI was originally formed in 1918, when five engineering societies, in 1928, the AESC became the American Standards Association. In 1966, the ASA was reorganized and became United States of America Standards Institute, the present name was adopted in 1969. At the behest of the AIEE, they invited the U. S. government Departments of War, Navy, according to Adam Stanton, the first permanent secretary and head of staff in 1919, AESC started as an ambitious program and little else. Staff for the first year consisted of one executive, Clifford B, lePage, who was on loan from a founding member, ASME. An annual budget of $7,500 was provided by the founding bodies, aNSIs members are government agencies, organizations, corporations, academic and international bodies, and individuals. In total, the Institute represents the interests of more than 125,000 companies and 3.5 million professionals, though ANSI itself does not develop standards, the Institute oversees the development and use of standards by accrediting the procedures of standards developing organizations. ANSI accreditation signifies that the used by standards developing organizations meet the Institutes requirements for openness, balance, consensus. Voluntary consensus standards quicken the market acceptance of products while making clear how to improve the safety of products for the protection of consumers. There are approximately 9,500 American National Standards that carry the ANSI designation, the Institute is the official U. S. S. ANSI participates in almost the entire program of both the ISO and the IEC, and administers many key committees and subgroups. In many instances, U. S. standards are taken forward to ISO and IEC, through ANSI or the USNC, in 2009, ANSI and the National Institute of Standards and Technology formed the Nuclear Energy Standards Coordination Collaborative. NESCC is a joint initiative to identify and respond to the current need for standards in the nuclear industry. The ASA photographic exposure system, originally defined in ASA Z38.2.1 and ASA PH2.5, together with the DIN system, became the basis for the ISO system, a standard for the set of values used to represent characters in digital computers
15.
SCSI connector
–
A SCSI connector is used to connect computer parts that use a system called SCSI to communicate with each other. Generally, two connectors, designated male and female, plug together to form a connection which allows two components, such as a computer and a drive, to communicate with each other. SCSI connectors can be electrical connectors or optical connectors, there have been a large variety of SCSI connectors in use at one time or another in the computer industry. Serial SCSI added another three transport types, each one or more connector types. Manufacturers have frequently chosen connectors based on factors of size, cost and it is sometimes possible to have cables which have different types of connectors on them, and some cables can have as many as 16 connectors. Some types of connectors are used inside a computer or disk drive case. Many connector designations consist of an abbreviation for the connector family, for example, CN36 would be a 36-pin Centronics-style connector. For some connectors use of the hyphen or space is more common, parallel SCSI allows for attachment of up to 16 devices to the SCSI bus, thus cables may have up to 16 connectors. It is unusual, however, for external cables to have more than 2, early generations of SCSI hard drive assemblies generally had two connectors for 8-bit units, and either two or three connectors for 16-bit units. The power connector was typically the same 4-pin female Molex connector used in other internal computer devices. The communication connectors on the drives were usually a 50 or 68 pin male IDC header which has two rows of pins,0.1 inches apart, thus it is often called an internal SCSI connector. It is worth noting that this type of header was used for most internal connections in a typical desktop PC until recent times, in most cases, the host adapter would have a similar header-style connection. In some cases, though, the host adapter end of the cable would use a different connector, for example, in the Sun 260 series chassis, the connector was the same 3-row 96-pin connector used to attach peripheral cards to the VMEbus backplane. Eventually, there was a desire to power and data signals into a single connector. This allows for quick replacement, more reliable connections, and is more compact. Most parallel SCSI disk-drives now utilize an 80-pin SCA connector and this connector includes a power connection and also has long and short pins which enable hot swapping. Note that this connector is found on disk drive HDAs. Most typically, external drive enclosures will have connectors, while cables will have two male connectors
16.
ESCON
–
ESCON is a data connection created by IBM, and is commonly used to connect their mainframe computers to peripheral devices such as disk storage and tape drives. ESCON is a fiber, half-duplex, serial interface. It originally operated at a rate of 10 Mbyte/s, which was increased to 17Mbyte/s. The current maximum distance is 43 kilometers, ESCON was introduced by IBM in the early 1990s. It replaced the older, slower, copper-based, parallel, Bus & Tag channel technology of 1960-1990 era mainframes, optical fiber is smaller in diameter and weight, and hence could save installation costs. Space and labor could also be reduced when fewer physical links were required - due to ESCONs switching features, ESCON is being supplanted by the substantially faster FICON, which runs over Fibre Channel. ESCON allows the establishment and reconfiguration of channel connections dynamically, without having to take equipment off-line, ESCON supports channel connections using serial transmission over a pair of fibers. The ESCON Director supports dynamic switching and it also allows the distance between units to be extended up to 60 km over a dedicated fiber. “Permanent virtual circuits” are supported through the switch, ESCON switching has advantages over a collection of point-to-point links. A peripheral previously capable of accessing a single mainframe can now be connected simultaneously to up to eight mainframes, the ESCON interface specifications were adopted in 1996 by ANSI X3T1 committee as the SBCON standard, which is now managed by X3T11. Direct access storage device Most important DASD with ESCON interfaces, EMC Symmetrix, DMX, hewlett Packard Enterprise XP Storage family. Hitachi Data Systems Lightning IBM Enterprise Storage Server IBM Storage DS8000 Sun StorageTek SVA
17.
Multi-mode optical fiber
–
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
18.
8b/10b encoding
–
This means that the difference between the counts of ones and zeros in a string of at least 20 bits is no more than two, and that there are not more than five ones or zeros in a row. This helps to reduce the demand for the bandwidth limit of the channel necessary to transfer the signal. An 8b/10b code can be implemented in ways, where the design may focus on specific parameters such as hardware requirements, DC-balance. One implementation was designed by K. Odaka for the DAT digital audio recorder, Kees Schouhamer Immink designed an 8b/10b code for the DCC audio recorder. The IBM implementation was described in 1983 by Al Widmer and Peter Franaszek, as the scheme name suggests, eight bits of data are transmitted as a 10-bit entity called a symbol, or character. The low five bits of data are encoded into a 6-bit group and these code groups are concatenated together to form the 10-bit symbol that is transmitted on the wire. The data symbols are referred to as D. x. y where x ranges over 0–31. Standards using the 8b/10b encoding also define up to 12 special symbols that can be sent in place of a data symbol and they are often used to indicate start-of-frame, end-of-frame, link idle, skip and similar link-level conditions. At least one of them needs to be used to define the alignment of the 10 bit symbols and they are referred to as K. x. y and have different encodings from any of the D. x. y symbols. Some of the 256 possible 8-bit words can be encoded in two different ways, using these alternative encodings, the scheme is able to achieve long-term DC-balance in the serial data stream. Note that in the tables, for each input byte, A is the least significant bit. The output gains two extra bits, i and j. The bits are sent low to high, a, b, c, d, e, i, f, g, h and this ensures the uniqueness of the special bit sequence in the comma codes. The 5b/6b code is a paired disparity code, and so is the 3b/4b code, each 6- or 4-bit code word has either equal numbers of zeros and ones, or comes in a pair of forms, one with two more zeros than ones and one with two less. When a 6- or 4-bit code is used that has a non-zero disparity, in other words, the non zero disparity codes alternate. 8b/10b coding is DC-free, meaning that the ratio of ones. To achieve this, the difference between the number of transmitted and the number of zeros transmitted is always limited to ±2. This difference is known as the running disparity and this scheme needs only two states for running disparity of +1 and −1
19.
Internet Protocol
–
The Internet Protocol is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet, IP has the task of delivering packets from the source host to the destination host solely based on the IP addresses in the packet headers. For this purpose, IP defines packet structures that encapsulate the data to be delivered and it also defines addressing methods that are used to label the datagram with source and destination information. The Internet protocol suite is often referred to as TCP/IP. The first major version of IP, Internet Protocol Version 4, is the dominant protocol of the Internet and its successor is Internet Protocol Version 6. The Internet Protocol is responsible for addressing hosts and for routing datagrams from a source host to a destination host across one or more IP networks. For this purpose, the Internet Protocol defines the format of packets, each datagram has two components, a header and a payload. The IP header is tagged with the source IP address, the destination IP address, the payload is the data that is transported. This method of nesting the data payload in a packet with a header is called encapsulation, IP addressing entails the assignment of IP addresses and associated parameters to host interfaces. The address space is divided into networks and subnetworks, involving the designation of network or routing prefixes, IP routing is performed by all hosts, as well as routers, whose main function is to transport packets across network boundaries. Routers communicate with one another via specially designed routing protocols, either interior gateway protocols or exterior gateway protocols, IP routing is also common in local networks. For example, many Ethernet switches support IP multicast operations and these switches use IP addresses and Internet Group Management Protocol to control multicast routing but use MAC addresses for the actual routing. The versions currently relevant are IPv4 and IPv6, in May 1974, the Institute of Electrical and Electronic Engineers published a paper entitled A Protocol for Packet Network Intercommunication. The papers authors, Vint Cerf and Bob Kahn, described a protocol for sharing resources using packet switching among network nodes. A central control component of this model was the Transmission Control Program that incorporated both connection-oriented links and datagram services between hosts, the model became known as the Department of Defense Internet Model and Internet protocol suite, and informally as TCP/IP. IP versions 0 to 3 were experimental versions, used between 1977 and 1979, IEN26, dated February 1978 describes a version of the IP header that uses a 1-bit version field. IEN28, dated February 1978 describes IPv2, IEN41, dated June 1978 describes the first protocol to be called IPv4. The IP header is different from the modern IPv4 header, IEN44, dated June 1978 describes another version of IPv4, also with a header different from the modern IPv4 header
20.
Computer port (hardware)
–
In computer hardware, a port serves as an interface between the computer and other computers or peripheral devices. In computer terms, a port generally refers to the part of connection. Computer ports have many uses, to connect a monitor, webcam, speakers, on the physical layer, a computer port is a specialized outlet on a piece of equipment to which a plug or cable connects. Electronically, the several conductors where the port and cable contacts connect, Port connectors may be male or female, but female connectors are much more common. Bent pins are easier to replace on a cable than on an attached to a computer. Computer ports in common use cover a variety of shapes such as round, rectangular, square, trapezoidal. There is some standardization to physical properties and function, for instance, most computers have a keyboard port, into which the keyboard is connected. The original IBM PC also had two identical 5 pin DIN connectors, one used for the keyboard, the second for a cassette recorder interface, the two were not interchangeable. Electronically, hardware ports can almost always be divided into two based on the signal transfer, Serial ports send and receive one bit at a time via a single wire pair. Parallel ports send multiple bits at the time over several sets of wires. After ports are connected, they typically require handshaking, where transfer type, transfer rate, hot-swappable ports can be connected while equipment is running. Almost all ports on personal computers are hot-swappable, plug-and-play ports are designed so that the connected devices automatically start handshaking as soon as the hot-swapping is done. USB ports and FireWire ports are plug-and-play, auto-detect or auto-detection ports are usually plug-and-play, but they offer another type of convenience. An auto-detect port may automatically determine what kind of device has been attached, the users response determines the purpose of the port, which is physically a 1/8 tip-ring-sleeve mini jack. Some auto-detect ports can even switch between input and output based on context, as of 2006, manufacturers have nearly standardized colors associated with ports on personal computers, although there are no guarantees. The two extra conductors in the 6-pin connection carry electrical power and this is why a self-powered device such as a camcorder often connects with a cable that is 4-pins on the camera side and 6-pins on the computer side, the two power conductors simply being ignored. This is also why laptop computers usually have only 4-pin FireWire ports, optical fiber, microwave, and other technologies have different kinds of connections, as metal wires are not effective for signal transfers with these technologies. Optical connections are usually a glass or plastic interface, possibly with an oil that lessens refraction between the two interface surfaces
21.
Host adapter
–
In computer hardware, a host controller, host adapter, or host bus adapter connects a computer, which acts as the host system, to other network and storage devices. The terms are used to refer to devices for connecting SCSI, Fibre Channel. However, devices for connecting to IDE, Ethernet, FireWire, USB and these can include TCP offload engines. A SCSI host adapter connects host system to boot from a SCSI device, typically a device driver, linked to the operating system, controls the host adapter itself. In a typical parallel SCSI subsystem, each device has assigned to it a unique numerical ID, as a rule, the host adapter appears as SCSI ID7, which gives it the highest priority on the SCSI bus. The host adapter usually assumes the role of SCSI initiator, in that it issues commands to other SCSI devices, a computer can contain more than one host adapter, which can greatly increase the number of SCSI devices available. Major SCSI adapter manufacturers are HP, ATTO Technology, Promise Technology, Adaptec, LSI, Adaptec, and ATTO offer PCIe SCSI adapters which fit in Apple Mac, on Intel PCs, and low-profile motherboards which lack SCSI support due to the inclusion of SAS and/or SATA connectivity. The term host bus adapter is most often used to refer to a Fibre Channel interface card, Fibre Channel HBAs are available for open systems, computer architectures, and buses, including PCI and SBus. Each HBA has a unique World Wide Name, which is similar to an Ethernet MAC address in that it uses an OUI assigned by the IEEE. There are two types of WWNs on a HBA, a node WWN, which is shared by all ports on a host bus adapter, and a port WWN, which is unique to each port. There are HBA models of different speeds, 1Gbit/s, 2Gbit/s, 4Gbit/s, 8Gbit/s, 10Gbit/s, 16Gbit/s and 20Gbit/s, the major Fibre Channel HBA manufacturers are QLogic and Broadcom. As of mid-2009, these vendors shared approximately 90% of the market, other manufacturers include Agilent, ATTO, Brocade]. HBA is also known to be interpreted as High Bandwidth Adapter in cases of Fibre Channel controllers, the term host channel adapter is usually used to describe InfiniBand interface cards. ATA host adapters are integrated into motherboards of most modern PCs and they are often improperly called disk controllers. The correct term for the component that allows a computer to talk to a bus is host adapter. A proper disk controller only allows a disk to talk to the same bus, SAS or serial-attached SCSI is the current connectivity to replace the previous generation parallel-attached SCSI devices. Ultra320 was the highest level of parallel SCSI available, but SAS has since replaced it as the highest-performing SCSI technology, SATA is a similar technology from the aspect of connection options. HBAs can be created using a connector to connect both SAS and SATA devices
22.
Fibre Channel switch
–
In the computer storage field, a Fibre Channel switch is a network switch compatible with the Fibre Channel protocol. It allows the creation of a Fibre Channel fabric, that is the component of a storage area network. The fabric is a network of Fibre Channel devices which allows many-to-many communication, device name lookup, security, FC switches implement zoning, a mechanism that disables unwanted traffic between certain fabric nodes. A Fibre Channel Director is, by convention, a switch with at least 128 ports and it does not differ from a switch in core FC protocol functionality. The term itself is derived from ESCON Directors such as the IBM 9032-005, Fibre Channel switches may be deployed one at a time or in larger multi-switch configurations. SAN administrators typically add new switches as their server and storage needs grow, some switch vendors offer dedicated high-speed stacking ports to handle inter-switch connections, allowing high-performance multi-switch configurations to be created using fewer switches overall. Major manufacturers of Fibre Channel switches are, Brocade, Cisco Systems, Dell, host Bus Adapter List of Fibre Channel switches Fibre Channel
23.
Fibre Channel point-to-point
–
Fibre Channel point-to-point is a Fibre Channel topology where exactly two ports are directly connected to each other. It is the simplest topology, no network addressing is needed, storage area network Fibre Channel Arbitrated loop Fibre Channel fabric
24.
Arbitrated loop
–
Arbitrated Loop, also known as FC-AL, is a Fibre Channel topology in which devices are connected in a one-way loop fashion in a ring topology. Historically it was a lower-cost alternative to a fabric topology and it allowed connection of many servers and computer storage devices without using then very costly Fibre Channel switches. The cost of the switches dropped considerably, so by 2007 and it is however still common within storage systems. It is an architecture that can be used as the transport layer in a SCSI network. The loop may connect into a fibre channel fabric via one of its ports, the bandwidth on the loop is shared among all ports. Only two ports may communicate at a time on the loop, one port wins arbitration and may open one other port in either half or full duplex mode. A loop with two ports is valid and has the physical topology as point-to-point, but still acts as a loop protocol-wise. Fibre Channel ports capable of arbitrated loop communication are NL_port and FL_port, the ports may attach to each other via a hub, with cables running from the hub to the ports. The physical connectors on the hub are not ports in terms of the protocol, a hub does not contain ports. An arbitrated loop with no fabric port is a private loop, an arbitrated loop connected to a fabric is a public loop. An NL_Port must provide fabric logon and name registration facilities to initiate communication with other node through the fabric, arbitrated loop can be physically cabled in a ring fashion or using a hub. The physical ring ceases to work if one of the devices in the chain fails, the hub on the other hand, while maintaining a logical ring, allows a star topology on the cable level. Each receive port on the hub is simply passed to next active transmit port, Fibre Channel hubs therefore have another function, They provide bypass circuits that prevent the loop from breaking if one device fails or is removed. This gives loops at least a measure of resiliency—failure of one device in a loop doesn’t cause the loop to become inoperable. Storage area network Fibre Channel Switched fabric List of Fibre Channel standards
25.
Token ring
–
Token ring local area network technology is a communications protocol for local area networks. It uses a special three-byte frame called a token that travels around a ring of workstations or servers. This token passing is an access method providing fair access for all stations. Proteon later evolved a 16 Mbit/s version that ran on unshielded twisted pair cable, IBM launched their own proprietary token ring product on October 15,1985. It ran at 4 Mbit/s, and attachment was possible from IBM PCs, midrange computers and it used a convenient star-wired physical topology, and ran over shielded twisted-pair cabling, and shortly thereafter became the basis for the /IEEE standard 802.5. During this time, IBM argued strongly that token ring LANs were superior to Ethernet, especially under load, but these claims were fiercely debated. In 1988 the faster 16 Mbit/s token ring was standardized by the 802.5 working group, Token ring does not inherently support this feature and requires additional software and hardware to operate on a direct cable connection setup. Token ring eliminates collision by the use of a single-use token, Token ring network interface cards contain all of the intelligence required for speed autodetection, routing and can drive themselves on many Multistation Access Units that operate without power. Ethernet network interface cards can operate on a passive hub to a degree, but not as a large LAN. Token ring employs access priority in which certain nodes can have priority over the token, unswitched Ethernet does not have provisioning for an access priority system as all nodes have equal contest for traffic. Multiple identical MAC addresses are supported on token ring, switched Ethernet cannot support duplicate MAC addresses without reprimand. Token Ring was more complex than Ethernet, requiring a specialized processor, by contrast, Ethernet included both the firmware and the lower licensing cost in the MAC chip. The cost of a token ring interface using the Texas Instruments TMS380C16 MAC, even more significant when comparing overall system costs was the much-higher cost of router ports and network cards for token-ring vs Ethernet. The emergence of Ethernet switches may have been the final straw, similar token passing mechanisms are used by ARCNET, token bus, 100VG-AnyLAN and FDDI, and they have theoretical advantages over the CSMA/CD of early Ethernet. A token ring network can be modeled as a system where a single server provides service to queues in a cyclic order. The data transmission process goes as follows, Empty information frames are continuously circulated on the ring, when a computer has a message to send, it seizes the token. The computer will then be able to send the frame, the frame is then examined by each successive workstation. The workstation that identifies itself to be the destination for the copies it from the frame
26.
Ethernet
–
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
27.
OSI model
–
Its goal is the interoperability of diverse communication systems with standard protocols. The model partitions a communication system into abstraction layers, the original version of the model defined seven layers. A layer serves the layer above it and is served by the layer below it, two instances at the same layer are visualized as connected by a horizontal connection in that layer. The model is a product of the Open Systems Interconnection project at the International Organization for Standardization and these two international standards bodies each developed a document that defined similar networking models. In 1983, these two documents were merged to form a standard called The Basic Reference Model for Open Systems Interconnection, the standard is usually referred to as the Open Systems Interconnection Reference Model, the OSI Reference Model, or simply the OSI model. It was published in 1984 by both the ISO, as standard ISO7498, and the renamed CCITT as standard X.200. OSI had two components, an abstract model of networking, called the Basic Reference Model or seven-layer model. The concept of a model was provided by the work of Charles Bachman at Honeywell Information Services. Various aspects of OSI design evolved from experiences with the ARPANET, NPLNET, EIN, CYCLADES network, the new design was documented in ISO7498 and its various addenda. In this model, a system was divided into layers. Within each layer, one or more entities implement its functionality, each entity interacted directly only with the layer immediately beneath it, and provided facilities for use by the layer above it. Protocols enable an entity in one host to interact with an entity at the same layer in another host. Service definitions abstractly described the functionality provided to an -layer by an layer, the OSI standards documents are available from the ITU-T as the X. 200-series of recommendations. Some of the specifications were also available as part of the ITU-T X series. The equivalent ISO and ISO/IEC standards for the OSI model were available from ISO, the recommendation X.200 describes seven layers, labeled 1 to 7. Layer 1 is the lowest layer in this model, at each level N, two entities at the communicating devices exchange protocol data units by means of a layer N protocol. Each PDU contains a payload, called the service data unit, data processing by two communicating OSI-compatible devices is done as such, The data to be transmitted is composed at the topmost layer of the transmitting device into a protocol data unit. The PDU is passed to layer N-1, where it is known as the service data unit, at layer N-1 the SDU is concatenated with a header, a footer, or both, producing a layer N-1 PDU
28.
Encryption
–
In cryptography, encryption is the process of encoding a message or information in such a way that only authorized parties can access it. Encryption does not of itself prevent interference, but denies the intelligible content to a would-be interceptor, in an encryption scheme, the intended information or message, referred to as plaintext, is encrypted using an encryption algorithm, generating ciphertext that can only be read if decrypted. For technical reasons, an encryption scheme usually uses an encryption key generated by an algorithm. It is in possible to decrypt the message without possessing the key. An authorized recipient can decrypt the message with the key provided by the originator to recipients. In symmetric-key schemes, the encryption and decryption keys are the same, communicating parties must have the same key before they can achieve secure communication. In public-key encryption schemes, the key is published for anyone to use. However, only the party has access to the decryption key that enables messages to be read. Public-key encryption was first described in a document in 1973. Encryption has long used by militaries and governments to facilitate secret communication. It is now used in protecting information within many kinds of civilian systems. Encryption can be used to protect data at rest, such as stored on computers. In recent years, there have been reports of confidential data, such as customers personal records. Encrypting such files at rest helps protect them should physical security measures fail, in response to encryption of data at rest, cyber-adversaries have developed new types of attacks. There have been reports of data in transit being intercepted in recent years. Data should also be encrypted when transmitted across networks in order to protect against eavesdropping of network traffic by unauthorized users, standards for cryptographic software and hardware to perform encryption are widely available, but successfully using encryption to ensure security may be a challenging problem. A single error in design or execution can allow successful attacks. Sometimes an adversary can obtain unencrypted information without directly undoing the encryption, see, e. g. traffic analysis, TEMPEST, or Trojan horse
29.
RAID
–
RAID is a data storage virtualization technology that combines multiple physical disk drive components into a single logical unit for the purposes of data redundancy, performance improvement, or both. Data is distributed across the drives in one of several ways, referred to as RAID levels, depending on the level of redundancy. The different schemes, or data distribution layouts, are named by the word RAID followed by a number, each schema, or RAID level, provides a different balance among the key goals, reliability, availability, performance, and capacity. RAID levels greater than RAID0 provide protection against unrecoverable sector read errors, the underlying concept of RAID was first spoken of by the co-founders of Geac Computer Corporation, Gus German and Ted Grunau, who referred to it as MF-100. The term RAID was invented by David Patterson, Garth A. Gibson, although failures would rise in proportion to the number of drives, by configuring for redundancy, the reliability of an array could far exceed that of any large single drive. Around 1983, DEC began shipping subsystem mirrored RA8X disk drives as part of its HSC50 subsystem, in 1986, Clark et al. at IBM filed a patent disclosing what was subsequently named RAID5. Around 1988, the Thinking Machines DataVault used error correction codes in an array of disk drives, a similar approach was used in the early 1960s on the IBM353. Industry RAID manufacturers later tended to interpret the acronym as standing for redundant array of independent disks, many RAID levels employ an error protection scheme called parity, a widely used method in information technology to provide fault tolerance in a given set of data. Most use simple XOR, but RAID6 uses two separate parities based respectively on addition and multiplication in a particular Galois field or Reed–Solomon error correction, RAID can also provide data security with solid-state drives without the expense of an all-SSD system. For example, a fast SSD can be mirrored with a mechanical drive, for this configuration to provide a significant speed advantage an appropriate controller is needed that uses the fast SSD for all read operations. A number of schemes have evolved. Originally, there were five RAID levels, but many variations have evolved, notably several nested levels, the capacity of a RAID0 volume is the sum of the capacities of the disks in the set, the same as with a spanned volume. There is no added redundancy for handling disk failures, just as with a spanned volume, thus, failure of one disk causes the loss of the entire RAID0 volume, with reduced possibilities of data recovery when compared with a broken spanned volume. The concurrent operations make the throughput of most read and write operations equal to the throughput of one multiplied by the number of disks. Increased throughput is the big benefit of RAID0 versus spanned volume, RAID1 RAID1 consists of data mirroring, without parity or striping. Data is written identically to two drives, thereby producing a set of drives. Thus, any read request can be serviced by any drive in the set, if a request is broadcast to every drive in the set, it can be serviced by the drive that accesses the data first, improving performance. Sustained read throughput, if the controller or software is optimized for it, approaches the sum of throughputs of every drive in the set, actual read throughput of most RAID1 implementations is slower than the fastest drive
30.
Line code
–
In telecommunication, a line code is a code chosen for use within a communications system for transmitting a digital signal down a line. Line coding is used for digital data transport. Some line codes are digital baseband modulation or digital baseband transmission methods, Line coding consists of representing the digital signal to be transported, by a waveform that is appropriate for the specific properties of the physical channel. The pattern of voltage, current or photons used to represent the data on a transmission link is called line encoding. The common types of line encoding are unipolar, polar, bipolar, after line coding, the signal is put through a physical channel, either a transmission medium or data storage medium. Sometimes the characteristics of two very different-seeming channels are similar enough that the line code is used for them. The most common physical channels are, the signal can directly be put on a transmission line. The line-coded signal undergoes further pulse shaping and then modulated to create an RF signal that can be sent through free space, the line-coded signal can be used to turn on and off a light source in free-space optical communication, most commonly used in an infrared remote control. The line-coded signal can be printed on paper to create a bar code, the line-coded signal can be converted to magnetized spots on a hard drive or tape drive. The line-coded signal can be converted to pits on an optical disc, some of the more common or binary line codes include, Each line code has advantages and disadvantages. The running disparity is the total of the disparity of all previously transmitted words. Unfortunately, most long-distance communication channels cannot reliably transport a DC component, the DC component is also called the disparity, the bias, or the DC coefficient. The simplest possible line code, unipolar, gives too many errors on such systems, most line codes eliminate the DC component – such codes are called DC-balanced, zero-DC, or DC-free. There are three ways of eliminating the DC component, Use a constant-weight code, for example, Manchester code and Interleaved 2 of 5. In other words, the transmitter has to make sure that every word that averages to a negative level is paired with another code word that averages to a positive level. Therefore, it must keep track of the running DC buildup, the receiver is designed so that either code word of the pair decodes to the same data bits. For example, AMI, 8B10B, 4B3T, etc, for example, the scrambler specified in RFC2615 for 64b/66b encoding. This is important if the signal must pass through a transformer or a transmission line
31.
Fibre Channel electrical interface
–
The Fibre Channel electrical interface is one of two related standards that can be used to physically interconnect computer devices. The other standard is a Fibre Channel optical interface, which is not covered in this article, Fibre channel electrical signals are sent over a duplex differential interface. This usually consists of twisted-pair cables with an impedance of 75 ohms or 150 ohms. This is a genuine differential signalling system so no ground reference is carried through the cable, signalling is AC-coupled, with the series capacitors located at the transmitter end of the link. The definition of the Fibre Channel signalling voltage is complex, eye-diagrams are defined for both the transmitter and receiver. There are many parameters which must all be met to be compliant with the standard. In simple terms, the circuit must output a signal with a minimum of 600 mV peak-to-peak differential. A good signal looks rather like a sine-wave with a frequency of half the data rate. The Bit-Error Rate objective for Fibre Channel systems is 1 in 1012, at 2 Gbit/s this equates to seven errors per hour. Therefore, this is an event and the receiver circuitry must contain error-handling logic. In order to such a low error-rate, jitter budgets are defined for the transmitter. There are various Fibre Channel connectors in use in the computer industry, details of their pinouts are distributed between different official documents. The following sections describe the most common Fibre Channel pinouts with some comments about the purpose of their electrical signals, the most familiar Fibre Channel connectors are cable connectors, used for interconnects between initiators and targets. There are also device connectors that can be found on Fibre Channel disk-drives and backplanes of enclosures, the device connectors include pins for power and for setting disk options. Optional pins 2,3,7, and 8 are intended for use with an external optical converter and this is often called a Media Interface Assembly. Fibre channel DE-9 connectors often have only the 4 required contacts installed, note that they are the four outermost contacts i. e. the same as used for Token Ring, this is an easy way to tell a fibre channel cable from an RS-232 cable. Optional pins 2,4,5, and 7 are intended for use with an external optical converter and this is often called a Media Interface Assembly. Although SCA-2 is the name for this connector, it is often called SCA-40 to distinguish it by its pin count from other similar connectors
32.
64B/66B encoding
–
It was defined by the IEEE802.3 working group as part of the IEEE802. 3ae-2002 amendment which introduced 10 Gbit/s Ethernet. The Protocol overhead of a scheme is the ratio of the number of added coding bits to the number of raw payload bits. The overhead of 64b/66b encoding is 2 overhead bits for every 64 raw bits transmitted or 3. 125% and this is considerably more efficient than the 25% overhead of the previously used 8b/10b encoding scheme which essentially charges every 8 bits of source data with a 2 bit tax. The overhead can be reduced further by doubling the size to produce 128b/130b encoding, as used by PCIe 3.0. As the scheme name suggests,64 bits of data are transmitted as a 66-bit entity, the 66 bit entity is made by prefixing one of two possible two-bit preambles to the 64 bits to be transmitted. If the preamble is 012, the 64 bits are entirely data, if the preamble is 102, an eight-bit type field follows, plus 56 bits of control information and/or data. The preambles 002 and 112 are not used, and generate an error if seen, the use of the 012 and 102 preambles guarantees a bit transition every 66 bits, which means that a continuous stream of 0s or 1s cannot be valid data. It also allows easier clock/timer synchronization, as a transition must be seen every 66 bits, the intention is not to encrypt the data, but to give the transmitted data useful engineering properties. Practical designs will choose system parameters such that a bit-error due to long run-lengths is vanishingly unlikely and this method is different from the codebook based approach of 8b/10b encoding. The encoding and scrambling are normally done entirely in hardware, the using a linear feedback shift register. Upper layers of the stack need not be aware that the link layer is using this code. 64b/66bs design goals are clock recovery, stream alignment, DC balance, transition density, unlike 8b/10b which guarantees strict bounds on DC balance, transition density and run length, 64b/66b provides statistical bounds on these properties. Most clock recovery circuits designed for SONET OC-192 and 64b/66b are specified to tolerate an 80-bit run length, such a run cannot occur in 64b/66b because transitions are guaranteed at 66 bit intervals, and in fact long runs are very unlikely. At 10 Gigabits per second, the event rate of a 66-bit block with a 65 bit run-length, assuming random data, is 66x264/ seconds. The run length statistics may get worse if the data consists of chosen specifically patterns and this vulnerability was kept secret until the scrambler length was increased to 43 bits making it impossible for a malicious attacker to jam the system with a short sequence. This creates 66-bit blocks containing 65-bit runs at a similar to using random data. The DC balance of 64b/66b is not absolutely bounded, however, it can be shown that the scrambler output closely approximates a sequence of random binary bits. Passing such a sequence through an AC-coupled circuit produces a baseline wander noise that follows a Gaussian distribution, to achieve this at normal bit error rates requires at least a four bit hamming distance protection for all packet data
33.
Small form-factor pluggable transceiver
–
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
34.
Single-mode optical fiber
–
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
35.
QSFP
–
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
36.
Optical fiber connector
–
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
37.
Gigabit interface converter
–
A gigabit interface converter is a standard for transceivers, commonly used with Gigabit Ethernet and fibre channel in the 2000s. A variation of the GBIC called the small form-factor pluggable transceiver, also known as mini-GBIC, has the same functionality, announced in 2001, it largely made the GBIC obsolete. The appeal of the GBIC standard in networking equipment, as opposed to fixed physical interface configurations, is its flexibility. Where multiple different optical technologies are in use, an administrator can purchase GBICs as needed, not in advance and this lowers the cost of the base system and gives the administrator far more flexibility. On the other hand, if a switch will mostly have one port type purchasing a switch with that type built in will be cheaper. The GBIC standard is non-proprietary and is defined by the Small Form Factor committee in document number 8053i, the first publication of the proposal was in November 1995. A few corrections and additions were made through September 2000, robert Snively of Brocade Communications was technical editor. Original contributors were AMP Incorporated, Compaq Computers, Sun Microsystems, and Vixel Corporation
Category