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132-474: Plan 9 from Bell Labs is a distributed operating system which originated from the Computing Science Research Center (CSRC) at Bell Labs in the mid-1980s and built on UNIX concepts first developed there in the late 1960s. Since 2000, Plan 9 has been free and open-source . The final official release was in early 2015. Under Plan 9, UNIX's everything is a file metaphor is extended via

264-450: A captive portal webpage for access. Organizations, enthusiasts, authorities and businesses , such as airports, hotels, and restaurants, often provide free or paid-use hotspots to attract customers, to provide services to promote business in selected areas. Routers often incorporate a digital subscriber line modem or a cable modem and a Wi-Fi access point, are frequently set up in homes and other buildings, to provide Internet access for

396-479: A grid computing platform and as a vehicle for research into ubiquitous computing without middleware . In commerce, Plan 9 underlies Coraid storage systems. However, Plan 9 has never approached Unix in popularity, and has been primarily a research tool: [I]t looks like Plan 9 failed simply because it fell short of being a compelling enough improvement on Unix to displace its ancestor. Compared to Plan 9, Unix creaks and clanks and has obvious rust spots, but it gets

528-508: A Real Operating System Plan 9 is a distributed operating system , designed to make a network of heterogeneous and geographically separated computers function as a single system. In a typical Plan 9 installation, users work at terminals running the window system rio , and they access CPU servers which handle computation-intensive processes. Permanent data storage is provided by additional network hosts acting as file servers and archival storage. Its designers state that, [t]he foundations of

660-626: A Wi-Fi network. Wi-Fi uses a large number of patents held by many different organizations. Australia, the United States and the Netherlands simultaneously claim the invention of Wi-Fi, and a consensus has not been reached globally. In 2009, the Australian CSIRO was awarded $ 200 million after a patent settlement with 14 technology companies, with a further $ 220 million awarded in 2012 after legal proceedings with 23 companies. In 2016,

792-464: A central master element. A distributed system is a collection of autonomous elements with no concept of levels. Centralized systems connect constituents directly to a central master entity in a hub and spoke fashion. A decentralized system (aka network system ) incorporates direct and indirect paths between constituent elements and the central entity. Typically this is configured as a hierarchy with only one shortest path between any two elements. Finally,

924-447: A city-wide campaign to convert old phone booths into digital kiosks in 2014. The project, titled LinkNYC , has created a network of kiosks that serve as public Wi-Fi hotspots, high-definition screens and landlines . Installation of the screens began in late 2015. The city government plans to implement more than seven thousand kiosks over time, eventually making LinkNYC the largest and fastest public, government-operated Wi-Fi network in

1056-456: A common Wi-Fi version. The versions differ between the radio wavebands they operate on, the radio bandwidth they occupy, the maximum data rates they can support and other details. Some versions permit the use of multiple antennas, which permits greater speeds as well as reduced interference. Historically, the equipment listed the versions of Wi-Fi supported using the name of the IEEE standards. In 2018,

1188-443: A common task… Consequently[,] the computer can be used to coordinate the diverse activities of all the external devices into an effective ensemble operation. The specification discussed the architecture of multi-computer systems, preferring peer-to-peer rather than master-slave. Each member of such an interconnected group of separate computers is free at any time to initiate and dispatch special control orders to any of its partners in

1320-581: A complex distributed computing environment by reusing the existing hierarchical name system. As a benefit from the system's design, most tasks in Plan 9 can be accomplished by using ls , cat , grep , cp and rm utilities in combination with the rc shell (the default Plan 9 shell). Factotum is an authentication and key management server for Plan 9. It handles authentication on behalf of other programs such that both secret keys and implementation details need only be known to Factotum. Unlike Unix , Plan 9

1452-407: A computer and an interface controller is called a station . Stations are identified by one or more MAC addresses . Wi-Fi nodes often operate in infrastructure mode in which all communications go through a base station. Ad hoc mode refers to devices communicating directly with each other, without communicating with an access point. A service set is the set of all the devices associated with

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1584-491: A distributed OS. System management components are software processes that define the node's policies . These components are the part of the OS outside the kernel. These components provide higher-level communication, process and resource management, reliability, performance and security. The components match the functions of a single-entity system, adding the transparency required in a distributed environment. The distributed nature of

1716-545: A distributed OS. The intra-node and inter-node communication requirements drive low-level IPC design, which is the typical approach to implementing communication functions that support transparency. In this sense, Interprocess communication is the greatest underlying concept in the low-level design considerations of a distributed operating system. Process management provides policies and mechanisms for effective and efficient sharing of resources between distributed processes. These policies and mechanisms support operations involving

1848-551: A distributed file system   Memory coherence in shared virtual memory systems   Transactions   Sagas   Transactional Memory   Composable memory transactions   Transactional memory: architectural support for lock-free data structures   Software transactional memory for dynamic-sized data structures   Software transactional memory   OceanStore: an architecture for global-scale persistent storage   Weighted voting for replicated data   Consensus in

1980-451: A distributed operating system must realize both individual node and global system goals. Architecture and design must be approached in a manner consistent with separating policy and mechanism. In doing so, a distributed operating system attempts to provide an efficient and reliable distributed computing framework allowing for an absolute minimal user awareness of the underlying command and control efforts. The multi-level collaboration between

2112-431: A distributed operating system. Transparency can impose certain requirements and/or restrictions on other design considerations. Systems can optionally violate transparency to varying degrees to meet specific application requirements. For example, a distributed operating system may present a hard drive on one computer as "C:" and a drive on another computer as "G:". The user does not require any knowledge of device drivers or

2244-539: A founding member of the Wi-Fi Alliance, the term Wi-Fi was chosen from a list of ten names that Interbrand proposed. Interbrand also created the Wi-Fi logo . The yin-yang Wi-Fi logo indicates the certification of a product for interoperability . The name is often written as WiFi , Wifi , or wifi , but these are not approved by the Wi-Fi Alliance. The name Wi-Fi is not short-form for 'Wireless Fidelity', although

2376-418: A global system is referred to as transparency , or single system image ; describing the illusion provided to users of the global system's appearance as a single computational entity. A distributed OS provides the essential services and functionality required of an OS but adds attributes and particular configurations to allow it to support additional requirements such as increased scale and availability. To

2508-641: A greater degree by common building materials than the 2.4 GHz bands and usually give a shorter range. As 802.11 specifications evolved to support higher throughput, the protocols have become much more efficient in their bandwidth use. Additionally, they have gained the ability to aggregate channels together to gain still more throughput where the bandwidth for additional channels is available. 802.11n allows for double radio spectrum bandwidth (40 MHz) per channel compared to 802.11a or 802.11g (20 MHz). 802.11n can be set to limit itself to 20 MHz bandwidth to prevent interference in dense communities. In

2640-422: A kernel and the system management components, and in turn between the distinct nodes in a distributed operating system is the functional challenge of the distributed operating system. This is the point in the system that must maintain a perfect harmony of purpose, and simultaneously maintain a complete disconnect of intent from implementation. This challenge is the distributed operating system's opportunity to produce

2772-399: A new window to run some program in, it first sets up a new namespace in which mouse , cons and bitblt are connected to itself, hiding the actual device files to which it itself has access. The window system thus receives all input and output commands from the program and handles these appropriately, by sending output to the actual screen device and giving the currently focused program

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2904-426: A particular Wi-Fi network. Devices in a service set need not be on the same wavebands or channels. A service set can be local, independent, extended, mesh, or a combination. Each service set has an associated identifier, a 32-byte service set identifier (SSID), which identifies the network. The SSID is configured within the devices that are part of the network. A basic service set (BSS) is a group of stations that share

3036-584: A pervasive network-centric filesystem , and the cursor-addressed , terminal -based I/O at the heart of UNIX-like operating systems is replaced by a windowing system and graphical user interface without cursor addressing, although rc , the Plan 9 shell , is text-based. The name Plan 9 from Bell Labs is a reference to the Ed Wood 1957 cult science fiction Z-movie Plan 9 from Outer Space . The system continues to be used and developed by operating system researchers and hobbyists. Plan 9 from Bell Labs

3168-446: A process' implicit root context is the only way to name a service. Binding a name to an object can only be done by giving an existing name for the object, in the same context as the new name. As such, interface references simply cannot be passed between processes, much less across networks. Instead, communication has to rely on conventions, which are prone to error and do not scale. A later retrospective comparison of Plan 9, Sprite and

3300-685: A resurgence of the distributed OS concept. One of the first efforts was the DYSEAC , a general-purpose synchronous computer. In one of the earliest publications of the Association for Computing Machinery , in April 1954, a researcher at the National Bureau of Standards  – now the National Institute of Standards and Technology ( NIST ) – presented a detailed specification of

3432-582: A set of files—could be successfully implemented in a modern distributed system. Some features from Plan 9, like the UTF-8 character encoding of Unicode, have been implemented in other operating systems. Unix-like operating systems such as Linux have implemented 9P2000, Plan 9's protocol for accessing remote files, and have adopted features of rfork , Plan 9's process creation mechanism. Additionally, in Plan 9 from User Space , several of Plan 9's applications and tools, including

3564-552: A simple master-slave relationship. This is one of the earliest examples of a computer with distributed control. The Dept. of the Army reports certified it reliable and that it passed all acceptance tests in April 1954. It was completed and delivered on time, in May 1954. This was a " portable computer ", housed in a tractor-trailer , with 2 attendant vehicles and 6 tons of refrigeration capacity. Described as an experimental input-output system,

3696-410: A single carrier, whereas 802.11a, Wi-Fi 4, 5 and 6 use orthogonal frequency-division multiplexing . Channels are used half duplex and can be time-shared by multiple networks. Any packet sent by one computer is locally received by stations tuned to that channel, even if that information is intended for just one destination. Stations typically ignore information not addressed to them. The use of

3828-548: A standardized protocol and treat its services as part of the namespace. For example, the original window system, called 8½, exploited these possibilities as follows. Plan 9 represents the user interface on a terminal by means of three pseudo-files: mouse , which can be read by a program to get notification of mouse movements and button clicks, cons , which can be used to perform textual input/output, and bitblt , writing to which enacts graphics operations (see bit blit ). The window system multiplexes these devices: when creating

3960-482: A system's physical arrangement characteristics. Connection covers the communication pathways among nodes. Control manages the operation of the earlier two considerations. A centralized system has one level of structure, where all constituent elements directly depend upon a single control element. A decentralized system is hierarchical. The bottom level unites subsets of a system's entities. These entity subsets in turn combine at higher levels, ultimately culminating at

4092-402: A system, and at any given moment, any of these nodes may have light to idle workloads. Load sharing and load balancing require many policy-oriented decisions, ranging from finding idle CPUs, when to move, and which to move. Many algorithms exist to aid in these decisions; however, this calls for a second level of decision making policy in choosing the algorithm best suited for the scenario, and

Plan 9 from Bell Labs - Misplaced Pages Continue

4224-613: A team of scientists began working on wireless LAN technology. A prototype test bed for a wireless local area network (WLAN) was developed in 1992 by a team of researchers from the Radiophysics Division of the CSIRO (Commonwealth Scientific and Industrial Research Organisation) in Australia, led by John O'Sullivan . A patent for Wi Fi was lodged by the CSIRO in 1992 The first version of

4356-446: A third contemporary distributed research operating system, Amoeba , found that the environments they [Amoeba and Sprite] build are tightly coupled within the OS, making communication with external services difficult. Such systems suffer from the radical departure from the UNIX model, which also discourages portability of already existing software to the platform (...). The lack of developers,

4488-400: A unified protocol, called 9P. Compared to other systems, this reduces the number of custom programming interfaces . 9P is a generic, medium-agnostic, byte-oriented protocol that provides for messages delivered between a server and a client. The protocol is used to refer to and communicate with processes, programs, and data, including both the user interface and the network. With the release of

4620-494: A union directory a /net hierarchy from a remote gateway , using secured 9P over the public Internet. A union directory with the /net hierarchy and filters can be used to sandbox an untrusted application or to implement a firewall . In the same manner, a distributed computing network can be composed with a union directory of /proc hierarchies from remote hosts, which allows interacting with them as if they are local. When used together, these features allow for assembling

4752-413: A user, a distributed OS works in a manner similar to a single-node, monolithic operating system . That is, although it consists of multiple nodes, it appears to users and applications as a single-node. Separating minimal system-level functionality from additional user-level modular services provides a " separation of mechanism and policy ". Mechanism and policy can be simply interpreted as "what something

4884-615: A wider channel for higher throughput. Countries apply their own regulations to the allowable channels, allowed users and maximum power levels within these frequency ranges. 802.11b/g/n can use the 2.4 GHz band, operating in the United States under FCC Part 15 rules and regulations. In this frequency band, equipment may occasionally suffer interference from microwave ovens, cordless telephones , USB 3.0 hubs, Bluetooth and other devices. Spectrum assignments and operational limitations are not consistent worldwide: Australia and Europe allow for an additional two channels (12, 13) beyond

5016-404: A windowing user interface system specific to Plan 9. The bulk of the system is written in a dialect of C ( ANSI C with some extensions and some other features left out). The compilers for this language were custom built with portability in mind; according to their author, they "compile quickly, load slowly, and produce medium quality object code". A concurrent programming language called Alef

5148-562: Is a trademark of the Wi-Fi Alliance , which restricts the use of the term " Wi-Fi Certified " to products that successfully complete interoperability certification testing. Non-compliant hardware is simply referred to as WLAN , and it may or may not work with " Wi-Fi Certified " devices. As of 2017, the Wi-Fi Alliance consisted of more than 800 companies from around the world. As of 2019, over 3.05 billion Wi-Fi-enabled devices are shipped globally each year. Wi-Fi uses multiple parts of

5280-453: Is a wasteful and non-valuable level of indirection . Information was accessed in two ways, direct and cross-retrieval. Direct retrieval accepts a name and returns a parameter set. Cross-retrieval projects through parameter sets and returns a set of names containing the given subset of parameters. This was similar to a modified hash table data structure that allowed multiple values (parameters) for each key (name). This configuration

5412-554: Is about 20 m (66 ft) indoors, while some access points claim up to a 150 m (490 ft) range outdoors. Hotspot coverage can be as small as a single room with walls that block radio waves or as large as many square kilometers using many overlapping access points with roaming permitted between them. Over time, the speed and spectral efficiency of Wi-Fi have increased. As of 2019, some versions of Wi-Fi, running on suitable hardware at close range, can achieve speeds of 9.6 Gbit/s ( gigabit per second). A 1985 ruling by

Plan 9 from Bell Labs - Misplaced Pages Continue

5544-404: Is controlled by a set of conventional locations for common resources. The second idea (a message-oriented filesystem) means that processes can offer their services to other processes by providing virtual files that appear in the other processes' namespace. The client process's input/output on such a file becomes inter-process communication between the two processes. This way, Plan 9 generalizes

5676-432: Is divided into a multitude of channels . In the standards, channels are numbered at 5 MHz spacing within a band (except in the 60 GHz band, where they are 2.16 GHz apart), and the number refers to the centre frequency of the channel. Although channels are numbered at 5 MHz spacing, transmitters generally occupy at least 20 MHz, and standards allow for neighbouring channels to be bonded together to form

5808-456: Is done" versus "how something is done," respectively. This separation increases flexibility and scalability. At each locale (typically a node), the kernel provides a minimally complete set of node-level utilities necessary for operating a node's underlying hardware and resources. These mechanisms include allocation, management, and disposition of a node's resources, processes, communication, and input/output management support functions. Within

5940-427: Is performed, so if top/subdir exists, the files in bottom/subdir are not accessible through the union. A union directory can be created by using a sequence of bind commands: In the example above, /arm/bin is mounted at /bin , the contents of /arm/bin replacing the previous contents of /bin . Acme 's bin directory is then union mounted after /bin , and Alice's personal bin directory

6072-423: Is responsible for shifting activity across nodes when the system is out of balance. One load balancing function is picking a process to move. The kernel may employ several selection mechanisms, including priority-based choice. This mechanism chooses a process based on a policy such as 'newest request'. The system implements the policy Systems resources such as memory, files, devices, etc. are distributed throughout

6204-620: Is submitted for certification. The lack of Wi-Fi certification does not necessarily imply that a device is incompatible with other Wi-Fi devices. The Wi-Fi Alliance may or may not sanction derivative terms, such as Super Wi-Fi , coined by the US Federal Communications Commission (FCC) to describe proposed networking in the UHF TV band in the US. Equipment frequently supports multiple versions of Wi-Fi. To communicate, devices must use

6336-524: Is too big a job". Some Linux binaries can be used with the help of a "linuxemu" (Linux emulator) application; however, it is still a work in progress. Vice versa, the Vx32 virtual machine allows a slightly modified Plan 9 kernel to run as a user process in Linux, supporting unmodified Plan 9 programs. In 1991, Plan 9's designers compared their system to other early nineties operating systems in terms of size, showing that

6468-445: Is union mounted before. When a file is requested from /bin , it is first looked for in /usr/alice/bin , then in /arm/bin , and then finally in /acme/bin/arm . The separate process namespaces thus usually replace the notion of a search path in the shell. A path environment variable ( $ path ) still exists in the rc shell (the shell mainly used in Plan 9); however, rc's path environment variable conventionally only contains

6600-417: Is used in applications such as motion detection and gesture recognition . Wi-Fi stations communicate by sending each other data packets , blocks of data individually sent and delivered over radio on various channels. As with all radio, this is done by the modulation and demodulation of carrier waves . Different versions of Wi-Fi use different techniques, 802.11b uses direct-sequence spread spectrum on

6732-565: The /bin and . directories and modifying the variable is discouraged, instead, adding additional commands should be done by binding several directories together as a single /bin . Unlike in Plan 9, the path environment variable of Unix shells should be set to include the additional directories whose executable files need to be added as commands. Furthermore, the kernel can keep separate mount tables for each process, and can thus provide each process with its own file system namespace . Processes' namespaces can be constructed independently, and

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6864-425: The /proc file system. Each process appears as a directory containing information and control files which can be manipulated by the ordinary file IO system calls. The file system approach allows Plan 9 processes to be managed with simple file management tools such as ls and cat ; however, the processes cannot be copied and moved as files. Plan 9 does not have specialised system calls or ioctls for accessing

6996-528: The Berkeley socket interface through the ANSI/POSIX Environment (APE) that implements an interface close to ANSI C and POSIX , with some common extensions (the native Plan 9 C interfaces conform to neither standard). It also includes a POSIX-compatible shell. APE's authors claim to have used it to port the X Window System (X11) to Plan 9, although they do not ship X11 "because supporting it properly

7128-542: The Eduroam international authentication infrastructure. In the early 2000s, many cities around the world announced plans to construct citywide Wi-Fi networks. There are many successful examples; in 2004, Mysore (Mysuru) became India's first Wi-Fi-enabled city. A company called WiFiyNet has set up hotspots in Mysore, covering the whole city and a few nearby villages. In 2005, St. Cloud, Florida and Sunnyvale, California , became

7260-546: The IEEE 802 protocol family and is designed to work seamlessly with its wired sibling, Ethernet . Compatible devices can network through wireless access points with each other as well as with wired devices and the Internet. Different versions of Wi-Fi are specified by various IEEE 802.11 protocol standards, with different radio technologies determining radio bands, maximum ranges, and speeds that may be achieved. Wi-Fi most commonly uses

7392-597: The Lincoln TX-2 emphasized flexible, simultaneously operational input-output devices, i.e., multiprogramming . The design of the TX-2 was modular, supporting a high degree of modification and expansion. The system employed The Multiple-Sequence Program Technique. This technique allowed multiple program counters to each associate with one of 32 possible sequences of program code. These explicitly prioritized sequences could be interleaved and executed concurrently, affecting not only

7524-853: The Wi-Fi Alliance introduced simplified Wi-Fi generational numbering to indicate equipment that supports Wi-Fi 4 ( 802.11n ), Wi-Fi 5 ( 802.11ac ) and Wi-Fi 6 ( 802.11ax ). These generations have a high degree of backward compatibility with previous versions. The alliance has stated that the generational level 4, 5, or 6 can be indicated in the user interface when connected, along with the signal strength. The most important standards affecting Wi‑Fi are: 802.11a, 802.11b, 802.11g, 802.11n ( Wi-Fi 4 ), 802.11h, 802.11i, 802.11-2007, 802.11–2012, 802.11ac ( Wi-Fi 5 ), 802.11ad, 802.11af, 802.11-2016, 802.11ah, 802.11ai, 802.11aj, 802.11aq , 802.11ax ( Wi-Fi 6 ), 802.11ay . Wi-Fi technology may be used to provide local network and Internet access to devices that are within Wi-Fi range of one or more routers that are connected to

7656-424: The typed interfaces of Sun's object-oriented operating system , Spring : Plan 9 constrains everything to look like a file. In most cases the real interface type comprises the protocol of messages that must be written to, and read from, a file descriptor. This is difficult to specify and document, and prohibits any automatic type checking at all, except for file errors at run time. (...) [A] path name relative to

7788-455: The 11 permitted in the United States for the 2.4 GHz band, while Japan has three more (12–14). 802.11a/h/j/n/ac/ax can use the 5 GHz U-NII band , which, for much of the world, offers at least 23 non-overlapping 20 MHz channels. This is in contrast to the 2.4 GHz frequency band where the channels are only 5 MHz wide. In general, lower frequencies have longer range but have less capacity. The 5 GHz bands are absorbed to

7920-477: The 1970s and continued through the 1990s, with focused interest peaking in the late 1980s. A number of distributed operating systems were introduced during this period; however, very few of these implementations achieved even modest commercial success. Fundamental and pioneering implementations of primitive distributed operating system component concepts date to the early 1950s. Some of these individual steps were not focused directly on distributed computing, and at

8052-608: The 2.4 gigahertz (120 mm) UHF and 5 gigahertz (60 mm) SHF radio bands, with the 6 gigahertz SHF band used in newer generations of the standard; these bands are subdivided into multiple channels. Channels can be shared between networks, but, within range, only one transmitter can transmit on a channel at a time. Wi-Fi's radio bands work best for line-of-sight use. Many common obstructions, such as walls, pillars, home appliances, etc., may greatly reduce range, but this also helps minimize interference between different networks in crowded environments. The range of an access point

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8184-456: The 4th edition, it was modified and renamed 9P2000. Unlike most other operating systems, Plan 9 does not provide special application programming interfaces (such as Berkeley sockets , X resources or ioctl system calls) to access devices. Instead, Plan 9 device drivers implement their control interface as a file system, so that the hardware can be accessed by the ordinary file input/output operations read and write . Consequently, sharing

8316-408: The 5 GHz band, 20 MHz, 40 MHz, 80 MHz, and 160 MHz channels are permitted with some restrictions, giving much faster connections. Wi-Fi is part of the IEEE 802 protocol family. The data is organized into 802.11 frames that are very similar to Ethernet frames at the data link layer, but with extra address fields. MAC addresses are used as network addresses for routing over

8448-427: The 802.11 protocol was released in 1997, and provided up to 2 Mbit/s link speeds. This was updated in 1999 with 802.11b to permit 11 Mbit/s link speeds. In 1999, the Wi-Fi Alliance formed as a trade association to hold the Wi-Fi trademark under which most IEEE 802.11 products are sold. The major commercial breakthrough came with Apple Inc. adopting Wi-Fi for their iBook series of laptops in 1999. It

8580-593: The 9front fork has provided the system Wi-Fi drivers, Audio drivers, USB support and built-in game emulator, along with other features. Other recent Plan 9-inspired operating systems include Harvey OS and Jehanne OS. Plan 9 from Bell Labs is like the Quakers : distinguished by its stress on the 'Inner Light,' noted for simplicity of life, in particular for plainness of speech. Like the Quakers, Plan 9 does not proselytize. —Sape J. Mullender, Pierre G. Jansen. Real Time in

8712-562: The CSIRO's WLAN prototype test bed was chosen as Australia's contribution to the exhibition A History of the World in 100 Objects held in the National Museum of Australia . The name Wi-Fi , commercially used at least as early as August 1999, was coined by the brand-consulting firm Interbrand. The Wi-Fi Alliance had hired Interbrand to create a name that was "a little catchier than 'IEEE 802.11b Direct Sequence'." According to Phil Belanger,

8844-563: The DYSEAC. The introduction focused upon the requirements of the intended applications, including flexible communications, but also mentioned other computers: Finally, the external devices could even include other full-scale computers employing the same digital language as the DYSEAC. For example, the SEAC or other computers similar to it could be harnessed to the DYSEAC and by use of coordinated programs could be made to work together in mutual cooperation on

8976-529: The ISOs, Bell Labs also hosts a repository of externally developed applications and tools. As Bell Labs has moved on to later projects in recent years, development of the official Plan 9 system had stopped. On March 23, 2021, development resumed following the transfer of copyright from Bell Labs to the Plan 9 Foundation. Unofficial development for the system also continues on the 9front fork, where active contributors provide monthly builds and new functionality. So far,

9108-611: The Internet. The coverage of one or more interconnected access points can extend from an area as small as a few rooms to as large as many square kilometres. Coverage in the larger area may require a group of access points with overlapping coverage. For example, public outdoor Wi-Fi technology has been used successfully in wireless mesh networks in London. An international example is Fon . Wi-Fi provides services in private homes, businesses, as well as in public spaces. Wi-Fi hotspots may be set up either free of charge or commercially, often using

9240-477: The Kfs, Paq, Cwfs, FAT , and Fossil file systems. The last was designed at Bell Labs specifically for Plan 9 and provides snapshot storage capability. It can be used directly with a hard drive or backed with Venti , an archival file system and permanent data storage system. The distribution package for Plan 9 includes special compiler variants and programming languages, and provides a tailored set of libraries along with

9372-578: The LAN. Wi-Fi's MAC and physical layer (PHY) specifications are defined by IEEE 802.11 for modulating and receiving one or more carrier waves to transmit the data in the infrared, and 2.4, 3.6 , 5, 6, or 60 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee ( IEEE 802 ). The base version of the standard was released in 1997 and has had many subsequent amendments. The standard and amendments provide

9504-516: The OS requires additional services to support a node's responsibilities to the global system. In addition, the system management components accept the "defensive" responsibilities of reliability, availability, and persistence. These responsibilities can conflict with each other. A consistent approach, balanced perspective, and a deep understanding of the overall system can assist in identifying diminishing returns . Separation of policy and mechanism mitigates such conflicts. The architecture and design of

9636-418: The Plan 9 project had been "put on the back burner" by AT&T in favor of Inferno , intended to be a rival to Sun Microsystems ' Java platform . In the late 1990s, Bell Labs' new owner Lucent Technologies dropped commercial support for the project and in 2000, a third release was distributed under an open-source license . A fourth release under a new free software license occurred in 2002. In early 2015,

9768-542: The SunOS vnode architecture is limited compared to Plan 9's capabilities in that it does not support remote device access and remote inter-process communication cleanly, even though it could have, had the preexisting UNIX domain sockets (which "can essentially be used to name user-level servers") been integrated with the vnode architecture. One critique of the "everything is a file", communication-by-textual-message design of Plan 9 pointed out limitations of this paradigm compared to

9900-554: The U.S. Federal Communications Commission released parts of the ISM bands for unlicensed use for communications. These frequency bands include the same 2.4 GHz bands used by equipment such as microwave ovens , and are thus subject to interference. In 1991 in Nieuwegein , the NCR Corporation and AT&T invented the precursor to 802.11, intended for use in cashier systems, under

10032-452: The Unix notion of the filesystem as the central point of access to computing resources. It carries over Unix's idea of device files to provide access to peripheral devices ( mice , removable media, etc.) and the possibility to mount filesystems residing on physically distinct filesystems into a hierarchical namespace, but adds the possibility to mount a connection to a server program that speaks

10164-543: The Wi-Fi Alliance did use the advertising slogan "The Standard for Wireless Fidelity" for a short time after the brand name was created, and the Wi-Fi Alliance was also called the "Wireless Fidelity Alliance Inc." in some publications. IEEE is a separate, but related, organization and their website has stated "WiFi is a short name for Wireless Fidelity". The name Wi-Fi was partly chosen because it sounds similar to Hi-Fi , which consumers take to mean high fidelity or high quality . Interbrand hoped consumers would find

10296-457: The allocation and de-allocation of processes and ports to processors, as well as mechanisms to run, suspend, migrate, halt, or resume process execution. While these resources and operations can be either local or remote with respect to each other, the distributed OS maintains state and synchronization over all processes in the system. As an example, load balancing is a common process management function. Load balancing monitors node performance and

10428-452: The basic ideas of a distributed logic system with... the macroscopic concept of logical design, away from scanning, from searching, from addressing, and from counting, is equally important. We must, at all cost, free ourselves from the burdens of detailed local problems which only befit a machine low on the evolutionary scale of machines.   Algorithms for scalable synchronization on shared-memory multiprocessors   Measurements of

10560-605: The basis for wireless network products using the Wi-Fi brand. While each amendment is officially revoked when incorporated in the latest version of the standard, the corporate world tends to market to the revisions because they concisely denote capabilities of their products. As a result, in the market place, each revision tends to become its own standard. In addition to 802.11, the IEEE 802 protocol family has specific provisions for Wi-Fi. These are required because Ethernet's cable-based media are not usually shared, whereas with wireless all transmissions are received by all stations within

10692-481: The capability. Some laptops that have a cellular modem card can also act as mobile Internet Wi-Fi access points. Many traditional university campuses in the developed world provide at least partial Wi-Fi coverage. Carnegie Mellon University built the first campus-wide wireless Internet network, called Wireless Andrew , at its Pittsburgh campus in 1993 before Wi-Fi branding existed. Many universities collaborate in providing Wi-Fi access to students and staff through

10824-533: The central entity, while distributed systems communicate along arbitrary paths. This is the pivotal notion of the third consideration. Control involves allocating tasks and data to system elements balancing efficiency, responsiveness, and complexity. Centralized and decentralized systems offer more control, potentially easing administration by limiting options. Distributed systems are more difficult to explicitly control, but scale better horizontally and offer fewer points of system-wide failure. The associations conform to

10956-569: The channel to be idle at the same time and thus begin transmission simultaneously. A collision happens when a station receives signals from multiple stations on a channel at the same time. This corrupts the transmitted data and can require stations to re-transmit. The lost data and re-transmission reduces throughput, in some cases severely. The 802.11 standard provides several distinct radio frequency ranges for use in Wi-Fi communications: 900  MHz , 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz, 6 GHz and 60 GHz bands . Each range

11088-490: The computation in process, but also the control flow of sequences and switching of devices as well. Much discussion related to device sequencing. Similar to DYSEAC the TX-2 separately programmed devices can operate simultaneously, increasing throughput . The full power of the central unit was available to any device. The TX-2 was another example of a system exhibiting distributed control, its central unit not having dedicated control. One early effort at abstracting memory access

11220-552: The conditions surrounding the scenario. Distributed OS can provide the necessary resources and services to achieve high levels of reliability , or the ability to prevent and/or recover from errors. Faults are physical or logical defects that can cause errors in the system. For a system to be reliable, it must somehow overcome the adverse effects of faults. The primary methods for dealing with faults include fault avoidance , fault tolerance , and fault detection and recovery . Fault avoidance covers proactive measures taken to minimize

11352-515: The database. Signal fluctuations can cause errors, which can be reduced with noise-filtering techniques. For low precision, integrating Wi-Fi data with geographical and time information has been proposed. The Wi-Fi RTT capability introduced in IEEE 802.11mc allows for positioning based on round trip time measurement, an improvement over the RSSI method. The IEEE 802.11az standard promises further improvements in geolocation accuracy. Wi-Fi sensing

11484-431: The depth, breadth, and range of design investment and architectural planning required in achieving even the most modest implementation. These design and development considerations are critical and unforgiving. For instance, a deep understanding of a distributed operating system's overall architectural and design detail is required at an exceptionally early point. An exhausting array of design considerations are inherent in

11616-453: The development of a distributed operating system. Each of these design considerations can potentially affect many of the others to a significant degree. This leads to a massive effort in balanced approach, in terms of the individual design considerations, and many of their permutations. As an aid in this effort, most rely on documented experience and research in distributed computing power. Research and experimentation efforts began in earnest in

11748-427: The device across the network can be accomplished by mounting the corresponding directory tree to the target machine. Plan 9 allows the user to collect the files (called names ) from different directory trees in a single location. The resulting union directory behaves as the concatenation of the underlying directories (the order of concatenation can be controlled); if the constituent directories contain files having

11880-508: The distributed operating system requires no pattern; direct and indirect connections are possible between any two elements. Consider the 1970s phenomena of “ string art ” or a spirograph drawing as a fully connected system , and the spider's web or the Interstate Highway System between U.S. cities as examples of a partially connected system . Centralized and decentralized systems have directed flows of connection to and from

12012-410: The drive's location; both devices work the same way, from the application's perspective. A less transparent interface might require the application to know which computer hosts the drive. Transparency domains: Inter-Process Communication (IPC) is the implementation of general communication, process interaction, and dataflow between threads and/or processes both within a node, and between nodes in

12144-411: The final official release of Plan 9 occurred. A user and development community, including current and former Bell Labs personnel, produced minor daily releases in the form of ISO images . Bell Labs hosted the development. The development source tree is accessible over the 9P and HTTP protocols and is used to update existing installations. In addition to the official components of the OS included in

12276-414: The first cities in the United States to offer citywide free Wi-Fi (from MetroFi ). Minneapolis has generated $ 1.2 million in profit annually for its provider . In May 2010, the then London mayor Boris Johnson pledged to have London-wide Wi-Fi by 2012. Several boroughs including Westminster and Islington already had extensive outdoor Wi-Fi coverage at that point. New York City announced

12408-521: The foundation and framework for a reliable, efficient, available, robust, extensible, and scalable system. However, this opportunity comes at a very high cost in complexity. In a distributed operating system, the exceptional degree of inherent complexity could easily render the entire system an anathema to any user. As such, the logical price of realizing a distributed operation system must be calculated in terms of overcoming vast amounts of complexity in many areas, and on many levels. This calculation includes

12540-655: The fraction of time during which the system can respond to requests. Wi-Fi Wi-Fi ( / ˈ w aɪ f aɪ / ) is a family of wireless network protocols based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio waves . These are the most widely used computer networks, used globally in home and small office networks to link devices and to provide Internet access with wireless routers and wireless access points in public places such as coffee shops, hotels, libraries, and airports. Wi-Fi

12672-493: The job done well enough to hold its position. There is a lesson here for ambitious system architects: the most dangerous enemy of a better solution is an existing codebase that is just good enough. Distributed operating system The microkernel and the management components collection work together. They support the system's goal of integrating multiple resources and processing functionality into an efficient and stable system. This seamless integration of individual nodes into

12804-415: The kernel, the communications sub-system is of foremost importance for a distributed OS. In a distributed OS, the kernel often supports a minimal set of functions, including low-level address space management, thread management, and inter-process communication (IPC). A kernel of this design is referred to as a microkernel . Its modular nature enhances reliability and security, essential features for

12936-470: The keyboard and mouse input. The program does not need to know if it is communicating directly with the operating system's device drivers, or with the window system; it only has to assume that its namespace is set up so that these special files provide the kind of input and accept the kind of messages that it expects. Plan 9's distributed operation relies on the per-process namespaces as well, allowing client and server processes to communicate across machines in

13068-530: The name WaveLAN . NCR's Vic Hayes , who held the chair of IEEE 802.11 for ten years, along with Bell Labs engineer Bruce Tuch, approached the Institute of Electrical and Electronics Engineers (IEEE) to create a standard and were involved in designing the initial 802.11b and 802.11a specifications within the IEEE. They have both been subsequently inducted into the Wi-Fi NOW Hall of Fame. In 1989 in Australia,

13200-452: The name catchy, and that they would assume this wireless protocol has high fidelity because of its name. Other technologies intended for fixed points, including Motorola Canopy , are usually called fixed wireless . Alternative wireless technologies include Zigbee , Z-Wave , Bluetooth and mobile phone standards . To connect to a Wi-Fi LAN, a computer must be equipped with a wireless network interface controller . The combination of

13332-413: The need for switching between code sets. Though interesting on their own, the design concepts of Plan 9 were supposed to be most useful when combined. For example, to implement a network address translation (NAT) server, a union directory can be created, overlaying the router 's /net directory tree with its own /net . Similarly, a virtual private network (VPN) can be implemented by overlaying in

13464-508: The needs imposed by its design but not by organizational chaos Transparency or single-system image refers to the ability of an application to treat the system on which it operates without regard to whether it is distributed and without regard to hardware or other implementation details. Many areas of a system can benefit from transparency, including access, location, performance, naming, and migration. The consideration of transparency directly affects decision making in every aspect of design of

13596-433: The networking stack or networking hardware. Instead, the /net file system is used. Network connections are controlled by reading and writing control messages to control files. Sub-directories such as /net/tcp and /net/udp are used as an interface to their respective protocols. To reduce the complexity of managing character encodings , Plan 9 uses Unicode throughout the system. The initial Unicode implementation

13728-399: The occurrence of faults. These proactive measures can be in the form of transactions , replication and backups . Fault tolerance is the ability of a system to continue operation in the presence of a fault. In the event, the system should detect and recover full functionality. In any event, any actions taken should make every effort to preserve the single system image . Availability is

13860-443: The operating system to universities in 1992. Three years later, Plan 9 was made available for commercial parties by AT&T via the book publisher Harcourt Brace . With source licenses costing $ 350, AT&T targeted the embedded systems market rather than the computer market at large. Ritchie commented that the developers did not expect to do "much displacement" given how established other operating systems had become. By early 1996,

13992-575: The operating systems research community, as well as the commercial Unix world, other attempts at achieving distributed computing and remote filesystem access were made concurrently with the Plan 9 design effort. These included the Network File System and the associated vnode architecture developed at Sun Microsystems , and more radical departures from the Unix model such as the Sprite OS from UC Berkeley . Sprite developer Brent Welch points out that

14124-595: The presence of partial synchrony   Sanity checks   The Byzantine Generals Problem   Fail-stop processors: an approach to designing fault-tolerant computing systems   Recoverability   Distributed snapshots: determining global states of distributed systems   Optimistic recovery in distributed systems To better illustrate this point, examine three system architectures ; centralized, decentralized, and distributed. In this examination, consider three structural aspects: organization, connection, and control. Organization describes

14256-566: The project, which was to be completed in 2015. Wi-Fi positioning systems use known positions of Wi-Fi hotspots to identify a device's location. It is used when GPS isn't suitable due to issues like signal interference or slow satellite acquisition. This includes assisted GPS , urban hotspot databases, and indoor positioning systems. Wi-Fi positioning relies on measuring signal strength ( RSSI ) and fingerprinting. Parameters like SSID and MAC address are crucial for identifying access points. The accuracy depends on nearby access points in

14388-542: The range that employ that radio channel. While Ethernet has essentially negligible error rates, wireless communication media are subject to significant interference. Therefore, the accurate transmission is not guaranteed so delivery is, therefore, a best-effort delivery mechanism. Because of this, for Wi-Fi, the Logical Link Control (LLC) specified by IEEE 802.2 employs Wi-Fi's media access control (MAC) protocols to manage retries without relying on higher levels of

14520-504: The receiver uses the destination address to determine whether the transmission is relevant to the station or should be ignored. A scheme known as carrier-sense multiple access with collision avoidance (CSMA/CA) governs the way stations share channels. With CSMA/CA stations attempt to avoid collisions by beginning transmission only after the channel is sensed to be idle, but then transmit their packet data in its entirety. CSMA/CA cannot completely prevent collisions, as two stations may sense

14652-482: The sam and acme editors, have been ported to Unix and Linux systems and have achieved some level of popularity. Several projects seek to replace the GNU operating system programs surrounding the Linux kernel with the Plan 9 operating system programs. The 9wm window manager was inspired by 8½ , the older windowing system of Plan 9; wmii is also heavily influenced by Plan 9. In computer science research, Plan 9 has been used as

14784-400: The same channel also means that the data bandwidth is shared, so for example, available throughput to each device is halved when two stations are actively transmitting. As with other IEEE 802 LANs, stations come programmed with a globally unique 48-bit MAC address. The MAC addresses are used to specify both the destination and the source of each data packet. On the reception of a transmission,

14916-434: The same name, a listing of the union directory ( ls or lc ) will simply report duplicate names. Resolution of a single path name is performed top-down: if the directories top and bottom are unioned into u with top first, then u/name denotes top/name if it exists, bottom/name only if it exists and top/name does not exist , and no file if neither exists. No recursive unioning of subdirectories

15048-511: The same wireless channel, SSID, and other settings that have wirelessly connected, usually to the same access point. Each BSS is identified by a MAC address called the BSSID . The IEEE does not test equipment for compliance with their standards. The Wi-Fi Alliance was formed in 1999 to establish and enforce standards for interoperability and backward compatibility , and to promote wireless local-area-network technology. The Wi-Fi Alliance enforces

15180-485: The source code for a minimal ("working, albeit not very useful") version was less than one-fifth the size of a Mach microkernel without any device drivers (5899 or 4622 lines of code for Plan 9, depending on metric, vs. 25530 lines). The complete kernel comprised 18000 lines of code. (According to a 2006 count, the kernel was then some 150,000 lines, but this was compared against more than 4.8 million in Linux .) Within

15312-445: The structure. Similarly, battery-powered routers may include a mobile broadband modem and a Wi-Fi access point. When subscribed to a cellular data carrier, they allow nearby Wi-Fi stations to access the Internet. Many smartphones have a built-in mobile hotspot capability of this sort, though carriers often disable the feature, or charge a separate fee to enable it. Standalone devices such as MiFi - and WiBro -branded devices provide

15444-462: The system are built on two ideas: a per-process name space and a simple message-oriented file system protocol. The first idea (a per-process name space) means that, unlike on most operating systems, processes (running programs) each have their own view of the namespace , corresponding to what other operating systems call the file system; a single path name may refer to different resources for different processes. The potential complexity of this setup

15576-442: The system. As a consequence, the supervisory control over the common task may initially be loosely distributed throughout the system and then temporarily concentrated in one computer, or even passed rapidly from one machine to the other as the need arises. …the various interruption facilities which have been described are based on mutual cooperation between the computer and the external devices subsidiary to it, and do not reflect merely

15708-483: The time, many may not have realized their important impact. These pioneering efforts laid important groundwork, and inspired continued research in areas related to distributed computing. In the mid-1970s, research produced important advances in distributed computing. These breakthroughs provided a solid, stable foundation for efforts that continued through the 1990s. The accelerating proliferation of multi-processor and multi-core processor systems research led to

15840-756: The use of the Wi-Fi brand to technologies based on the IEEE 802.11 standards from the IEEE. Manufacturers with membership in the Wi-Fi Alliance, whose products pass the certification process, gain the right to mark those products with the Wi-Fi logo. Specifically, the certification process requires conformance to the IEEE 802.11 radio standards, the WPA and WPA2 security standards, and the EAP authentication standard. Certification may optionally include tests of IEEE 802.11 draft standards, interaction with cellular-phone technology in converged devices, and features relating to security set-up, multimedia, and power-saving. Not every Wi-Fi device

15972-586: The user may work simultaneously with programs that have heterogeneous namespaces. Namespaces may be used to create an isolated environment similar to chroot , but in a more secure way. Plan 9's union directory architecture inspired 4.4BSD and Linux union file system implementations, although the developers of the BSD union mounting facility found the non-recursive merging of directories in Plan 9 "too restrictive for general purpose use". Instead of having system calls specifically for process management , Plan 9 provides

16104-460: The very small range of supported hardware and the small, even compared to Plan 9, user base have also significantly slowed the adoption of those systems (...). In retrospect, Plan 9 was the only research distributed OS from that time which managed to attract developers and be used in commercial projects long enough to warrant its survival to this day. Plan 9 demonstrated that an integral concept of Unix—that every system interface could be represented as

16236-493: The way just outlined. For example, the cpu command starts a remote session on a computation server. The command exports part of its local namespace, including the user's terminal's devices ( mouse , cons , bitblt ), to the server, so that remote programs can perform input/output using the terminal's mouse, keyboard and display, combining the effects of remote login and a shared network filesystem. All programs that wish to provide services-as-files to other programs speak

16368-626: The world. The UK has planned a similar project across major cities of the country, with the project's first implementation in the London Borough of Camden . Officials in South Korea's capital Seoul were moving to provide free Internet access at more than 10,000 locations around the city, including outdoor public spaces, major streets, and densely populated residential areas. Seoul was planning to grant leases to KT, LG Telecom, and SK Telecom. The companies were supposed to invest $ 44 million in

16500-479: The years, many notable developers have contributed to the project, including Brian Kernighan , Tom Duff , Doug McIlroy , Bjarne Stroustrup and Bruce Ellis. Plan 9 replaced Unix as Bell Labs's primary platform for operating systems research. It explored several changes to the original Unix model that facilitate the use and programming of the system, notably in distributed multi-user environments. After several years of development and internal use, Bell Labs shipped

16632-468: Was ISO/IEC 10646-1:1993 . Ken Thompson invented UTF-8, which became the native encoding in Plan 9. The entire system was converted to general use in 1992. UTF-8 preserves backwards compatibility with traditional null-terminated strings , enabling more reliable information processing and the chaining of multilingual string data with Unix pipes between multiple processes. Using a single UTF-8 encoding with characters for all cultures and regions eliminates

16764-436: Was Intercommunicating Cells, where a cell was composed of a collection of memory elements. A memory element was basically a binary electronic flip-flop or relay . Within a cell there were two types of elements, symbol and cell . Each cell structure stores data in a string of symbols, consisting of a name and a set of parameters . Information is linked through cell associations. The theory contended that addressing

16896-444: Was available in the first two editions, but was then dropped for maintenance reasons and replaced by a threading library for C. Though Plan 9 was supposed to be a further development of Unix concepts, compatibility with preexisting Unix software was never the goal for the project. Many command-line utilities of Plan 9 share the names of Unix counterparts, but work differently. Plan 9 can support POSIX applications and can emulate

17028-403: Was designed with graphics in mind. After booting, a Plan 9 terminal will run the rio windowing system, in which the user can create new windows displaying rc . Graphical programs invoked from this shell replace it in its window. The plumber provides an inter-process communication mechanism which allows system-wide hyperlinking. Sam and acme are Plan 9's text editors. Plan 9 supports

17160-414: Was ideal for distributed systems. The constant-time projection through memory for storing and retrieval was inherently atomic and exclusive . The cellular memory's intrinsic distributed characteristics would be invaluable. The impact on the user , hardware / device , or Application programming interfaces was indirect. The authors were considering distributed systems, stating: We wanted to present here

17292-484: Was originally developed, starting in the late 1980s, by members of the Computing Science Research Center at Bell Labs, the same group that originally developed Unix and the C programming language . The Plan 9 team was initially led by Rob Pike , Ken Thompson , Dave Presotto and Phil Winterbottom, with support from Dennis Ritchie as head of the Computing Techniques Research Department. Over

17424-429: Was the first mass consumer product to offer Wi-Fi network connectivity, which was then branded by Apple as AirPort . This was in collaboration with the same group that helped create the standard: Vic Hayes , Bruce Tuch, Cees Links , Rich McGinn, and others from Lucent . In the year 2000, Radiata, a group of Australian scientists connected to the CSIRO, were the first to use the 802.11a standard on chips connected to

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