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100-444: A service set is either a basic service set ( BSS ) or an extended service set ( ESS ). A basic service set is a subgroup, within a service set, of devices that share physical-layer medium access characteristics (e.g. radio frequency, modulation scheme, security settings) such that they are wirelessly networked. The basic service set is defined by a basic service set identifier ( BSSID ) shared by all devices within it. The BSSID

200-529: A shift function (like in ITA2 ), which would allow more than 64 codes to be represented by a six-bit code . In a shifted code, some character codes determine choices between options for the following character codes. It allows compact encoding, but is less reliable for data transmission , as an error in transmitting the shift code typically makes a long part of the transmission unreadable. The standards committee decided against shifting, and so ASCII required at least

300-522: A BS (backspace). Instead, there was a key marked RUB OUT that sent code 127 (DEL). The purpose of this key was to erase mistakes in a manually-input paper tape: the operator had to push a button on the tape punch to back it up, then type the rubout, which punched all holes and replaced the mistake with a character that was intended to be ignored. Teletypes were commonly used with the less-expensive computers from Digital Equipment Corporation (DEC); these systems had to use what keys were available, and thus

400-458: A character count followed by the characters of the line and which used EBCDIC rather than ASCII encoding. The Telnet protocol defined an ASCII "Network Virtual Terminal" (NVT), so that connections between hosts with different line-ending conventions and character sets could be supported by transmitting a standard text format over the network. Telnet used ASCII along with CR-LF line endings, and software using other conventions would translate between

500-481: A flag to express that the SSID is UTF-8 -encoded and could contain any Unicode text. Wireless network stacks must still be prepared to handle all possible values in the SSID field. Since the contents of an SSID field are arbitrary, the 802.11 standard permits devices to advertise the presence of a wireless network with beacon packets in which the SSID field is set to null. A null SSID (the SSID element's length field

600-498: A line terminator. The tty driver would handle the LF to CRLF conversion on output so files can be directly printed to terminal, and NL (newline) is often used to refer to CRLF in UNIX documents. Unix and Unix-like systems, and Amiga systems, adopted this convention from Multics. On the other hand, the original Macintosh OS , Apple DOS , and ProDOS used carriage return (CR) alone as

700-605: A line terminator; however, since Apple later replaced these obsolete operating systems with their Unix-based macOS (formerly named OS X) operating system, they now use line feed (LF) as well. The Radio Shack TRS-80 also used a lone CR to terminate lines. Computers attached to the ARPANET included machines running operating systems such as TOPS-10 and TENEX using CR-LF line endings; machines running operating systems such as Multics using LF line endings; and machines running operating systems such as OS/360 that represented lines as

800-784: A particular wireless MAC address. Randomized MAC addresses can be identified by the "locally administered" bit described above. Using wireless access points in SSID -hidden mode ( network cloaking ), a mobile wireless device may not only disclose its own MAC address when traveling, but even the MAC addresses associated to SSIDs the device has already connected to, if they are configured to send these as part of probe request packets. Alternative modes to prevent this include configuring access points to be either in beacon-broadcasting mode or probe-response with SSID mode. In these modes, probe requests may be unnecessary or sent in broadcast mode without disclosing

900-600: A reserved device control (DC0), synchronous idle (SYNC), and acknowledge (ACK). These were positioned to maximize the Hamming distance between their bit patterns. ASCII-code order is also called ASCIIbetical order. Collation of data is sometimes done in this order rather than "standard" alphabetical order ( collating sequence ). The main deviations in ASCII order are: An intermediate order converts uppercase letters to lowercase before comparing ASCII values. ASCII reserves

1000-541: A reserved meaning. Over time this interpretation has been co-opted and has eventually been changed. In modern usage, an ESC sent to the terminal usually indicates the start of a command sequence, which can be used to address the cursor, scroll a region, set/query various terminal properties, and more. They are usually in the form of a so-called " ANSI escape code " (often starting with a " Control Sequence Introducer ", "CSI", " ESC [ ") from ECMA-48 (1972) and its successors. Some escape sequences do not have introducers, like

1100-639: A service set. Normally it is broadcast in the clear by stations in beacon packets to announce the presence of a network and seen by users as a wireless network name. Unlike basic service set identifiers, SSIDs are usually customizable. These SSIDs can be zero to 32 octets long, and are, for convenience, usually in a natural language , such as English. The 802.11 standards prior to the 2012 edition did not define any particular encoding or representation for SSIDs, which were expected to be treated and handled as an arbitrary sequence of 0–32 octets that are not limited to printable characters . IEEE Std 802.11-2012 defines

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1200-404: A seven-bit code. The committee considered an eight-bit code, since eight bits ( octets ) would allow two four-bit patterns to efficiently encode two digits with binary-coded decimal . However, it would require all data transmission to send eight bits when seven could suffice. The committee voted to use a seven-bit code to minimize costs associated with data transmission. Since perforated tape at

1300-412: A single network to the logical link control layer by using the same SSID. Thus, from the perspective of the logical link control layer, stations within an ESS may communicate with one another, and mobile stations may move transparently from one participating basic service set to another (within the same ESS). Extended service sets make possible distribution services such as centralized authentication. From

1400-616: A system, the BSS created by the access point is distinct from the mesh network, and a wireless client of that BSS is not part of the MBSS. The formation of the mesh BSS, as well as wireless traffic management (including path selection and forwarding) is negotiated between the nodes of the mesh infrastructure. The mesh BSS is distinct from the networks (which may also be wireless) used by a mesh's redistribution points to communicate with one another. The service set identifier ( SSID ) defines or extends

1500-405: A target lifetime of 100 years (until 2080) for applications using EUI-48 space and restricts applications accordingly. The IEEE encourages adoption of the more plentiful EUI-64 for non-Ethernet applications. The distinctions between EUI-48 and MAC-48 identifiers are in name and application only. MAC-48 was used to address hardware interfaces within existing 802-based networking applications; EUI-48

1600-399: A terminal. Some operating systems such as CP/M tracked file length only in units of disk blocks, and used control-Z to mark the end of the actual text in the file. For these reasons, EOF, or end-of-file , was used colloquially and conventionally as a three-letter acronym for control-Z instead of SUBstitute. The end-of-text character ( ETX ), also known as control-C , was inappropriate for

1700-425: A value of all 1s is used to indicate the wildcard BSSID, usable only during probe requests or for communications that take place outside the context of a BSS. An independent BSS ( IBSS ), or ad hoc network , is created by peer devices among themselves without network infrastructure. A temporary network created by a cellular telephone to share its Internet access with other devices is a common example. In contrast to

1800-449: A variety of reasons, while using control-Z as the control character to end a file is analogous to the letter Z's position at the end of the alphabet, and serves as a very convenient mnemonic aid . A historically common and still prevalent convention uses the ETX character convention to interrupt and halt a program via an input data stream, usually from a keyboard. The Unix terminal driver uses

1900-737: Is 0101 in binary). Many of the non-alphanumeric characters were positioned to correspond to their shifted position on typewriters; an important subtlety is that these were based on mechanical typewriters, not electric typewriters. Mechanical typewriters followed the de facto standard set by the Remington No. 2 (1878), the first typewriter with a shift key, and the shifted values of 23456789- were "#$ %_&'()  – early typewriters omitted 0 and 1 , using O (capital letter o ) and l (lowercase letter L ) instead, but 1! and 0) pairs became standard once 0 and 1 became common. Thus, in ASCII !"#$ % were placed in

2000-455: Is 0 (zero), the frame is meant to reach only one receiving network interface . This type of transmission is called unicast . A unicast frame is transmitted to all nodes within the collision domain . In a modern wired setting (i.e. with switches , not simple hubs ) the collision domain usually is the length of the Ethernet cabling between two network interfaces. In a wireless setting,

2100-483: Is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment . This use is common in most IEEE 802 networking technologies, including Ethernet , Wi-Fi , and Bluetooth . Within the Open Systems Interconnection (OSI) network model , MAC addresses are used in the medium access control protocol sublayer of

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2200-440: Is a 48-bit label that conforms to MAC-48 conventions. While a device may have multiple BSSIDs, usually each BSSID is associated with at most one basic service set at a time. A basic service set should not be confused with the coverage area of an access point, known as the basic service area ( BSA ). An infrastructure BSS is created by an infrastructure device called an access point ( AP ) for other devices to join. (Note that

2300-426: Is a wireless network, created by multiple access points, which appears to users as a single, seamless network, such as a network covering a home or office that is too large for reliable coverage by a single access point. It is a set of one or more infrastructure basic service sets on a common logical network segment (i.e. same IP subnet and VLAN). Key to the concept is that the participating basic service sets appear as

2400-443: Is always set to 0 (individual), the universal/local bit of the address is always set to 1 (local), and the remaining 46 bits are randomly generated. A mesh basic service set ( MBSS ) is a self-contained network of mesh stations that share a mesh profile , defined in 802.11s . Each node may also be an access point hosting its own basic service set, for example using the mesh BSS to provide Internet access for local users. In such

2500-698: Is an inactive registry which has been replaced by the MA-S ( MAC address block, small ), previously named OUI-36 , and has no overlaps in addresses with the IAB registry product as of January 1, 2014. The IAB uses an OUI from the MA-L ( MAC address block, large ) registry, previously called the OUI registry. The term OUI is still in use, but the IEEE Registration Authority does not administer them. An OUI

2600-722: Is called multicast addressing. The IEEE has built in several special address types to allow more than one network interface card to be addressed at one time: These are all examples of group addresses , as opposed to individual addresses ; the least significant bit of the first octet of a MAC address distinguishes individual addresses from group addresses. That bit is set to 0 in individual addresses and set to 1 in group addresses. Group addresses, like individual addresses, can be universally administered or locally administered. The U/L and I/G bits are handled independently, and there are instances of all four possibilities. IPv6 multicast uses locally administered, multicast MAC addresses in

2700-408: Is concatenated with 12 additional IEEE-provided bits (for a total of 36 bits), leaving only 12 bits for the organisation owning the IAB to assign to its (up to 4096) individual devices. An IAB is ideal for organizations requiring not more than 4096 unique 48-bit numbers (EUI-48). Unlike an OUI, which allows the assignee to assign values in various different number spaces (for example, EUI-48, EUI-64, and

2800-489: Is now used for 802-based networking and is also used to identify other devices and software, for example Bluetooth . The IEEE now considers MAC-48 to be an obsolete term. EUI-48 is now used in all cases. In addition, the EUI-64 numbering system originally encompassed both MAC-48 and EUI-48 identifiers by a simple translation mechanism. These translations have since been deprecated. The Individual Address Block (IAB)

2900-561: Is optional. The following network technologies use the EUI-48 identifier format: Every device that connects to an IEEE 802 network (such as Ethernet and Wi-Fi) has an EUI-48 address. Common networked consumer devices such as PCs, smartphones and tablet computers use EUI-48 addresses. EUI-64 identifiers are used in: On broadcast networks, such as Ethernet, the MAC address is expected to uniquely identify each node on that segment and allows frames to be marked for specific hosts. It thus forms

3000-611: Is referred to as bit-reversed order , non-canonical form , MSB format , IBM format , or Token Ring format . Printable characters ASCII ( / ˈ æ s k iː / ASS -kee ), an acronym for American Standard Code for Information Interchange , is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment , and other devices. ASCII has just 128 code points , of which only 95 are printable characters , which severely limit its scope. The set of available punctuation had significant impact on

3100-427: Is replaced by a second control-S to resume output. The 33 ASR also could be configured to employ control-R (DC2) and control-T (DC4) to start and stop the tape punch; on some units equipped with this function, the corresponding control character lettering on the keycap above the letter was TAPE and TAPE respectively. The Teletype could not move its typehead backwards, so it did not have a key on its keyboard to send

Service set (802.11 network) - Misplaced Pages Continue

3200-480: Is set to zero) is called a wildcard SSID in IEEE 802.11 standards documents, and as a no broadcast SSID or hidden SSID in the context of beacon announcements, and can be used, for example, in enterprise and mesh networks to steer a client to a particular (e.g. less utilized) access point. A station may also likewise transmit packets in which the SSID field is set to null; this prompts an associated access point to send

3300-473: Is started with a MAC address set by assigning the last three bytes to be unique on the local network. While this is local administration of MAC addresses, it is not an LAA in the IEEE sense. A historical example of this hybrid situation is the DECnet protocol, where the universal MAC address (OUI AA-00-04, Digital Equipment Corporation) is administered locally. The DECnet software assigns the last three bytes for

3400-404: Is the newline problem on various operating systems . Teletype machines required that a line of text be terminated with both "carriage return" (which moves the printhead to the beginning of the line) and "line feed" (which advances the paper one line without moving the printhead). The name "carriage return" comes from the fact that on a manual typewriter the carriage holding the paper moves while

3500-415: Is usually non-configurable, in which case it is either preset during manufacture or mathematically derived from a preset value such as a serial number or a MAC address of another network interface. As with the MAC addresses used for Ethernet devices, an infrastructure BSSID is a combination of a 24-bit organizationally unique identifier (OUI, the manufacturer's identity) and a 24-bit serial number. A BSSID with

3600-442: Is written in transmission order with the least significant bit of each byte transmitted first, and is used in the output of the ifconfig , ip address , and ipconfig commands, for example. However, since IEEE 802.3 (Ethernet) and IEEE 802.4 (Token Bus) send the bytes (octets) over the wire, left-to-right, with the least significant bit in each byte first, while IEEE 802.5 (Token Ring) and IEEE 802.6 (FDDI) send

3700-503: The Comité Consultatif International Téléphonique et Télégraphique (CCITT) International Telegraph Alphabet No. 2 (ITA2) standard of 1932, FIELDATA (1956 ), and early EBCDIC (1963), more than 64 codes were required for ASCII. ITA2 was in turn based on Baudot code , the 5-bit telegraph code Émile Baudot invented in 1870 and patented in 1874. The committee debated the possibility of

3800-636: The Teletype Model 33 , which used the left-shifted layout corresponding to ASCII, differently from traditional mechanical typewriters. Electric typewriters, notably the IBM Selectric (1961), used a somewhat different layout that has become de facto standard on computers – following the IBM PC (1981), especially Model M (1984) – and thus shift values for symbols on modern keyboards do not correspond as closely to

3900-730: The United States Federal Government support ASCII, stating: I have also approved recommendations of the Secretary of Commerce [ Luther H. Hodges ] regarding standards for recording the Standard Code for Information Interchange on magnetic tapes and paper tapes when they are used in computer operations. All computers and related equipment configurations brought into the Federal Government inventory on and after July 1, 1969, must have

4000-667: The carriage return , line feed , and tab codes. For example, lowercase i would be represented in the ASCII encoding by binary 1101001 = hexadecimal 69 ( i is the ninth letter) = decimal 105. Despite being an American standard, ASCII does not have a code point for the cent (¢). It also does not support English terms with diacritical marks such as résumé and jalapeño , or proper nouns with diacritical marks such as Beyoncé (although on certain devices characters could be combined with punctuation such as Tilde (~) and Backtick (`) to approximate such characters.) The American Standard Code for Information Interchange (ASCII)

4100-415: The data link layer . As typically represented, MAC addresses are recognizable as six groups of two hexadecimal digits, separated by hyphens, colons, or without a separator. MAC addresses are primarily assigned by device manufacturers, and are therefore often referred to as the burned-in address , or as an Ethernet hardware address , hardware address , or physical address . Each address can be stored in

Service set (802.11 network) - Misplaced Pages Continue

4200-645: The "Reset to Initial State", "RIS" command " ESC c ". In contrast, an ESC read from the terminal is most often used as an out-of-band character used to terminate an operation or special mode, as in the TECO and vi text editors . In graphical user interface (GUI) and windowing systems, ESC generally causes an application to abort its current operation or to exit (terminate) altogether. The inherent ambiguity of many control characters, combined with their historical usage, created problems when transferring "plain text" files between systems. The best example of this

4300-582: The "help" prefix command in GNU Emacs . Many more of the control characters have been assigned meanings quite different from their original ones. The "escape" character (ESC, code 27), for example, was intended originally to allow sending of other control characters as literals instead of invoking their meaning, an "escape sequence". This is the same meaning of "escape" encountered in URL encodings, C language strings, and other systems where certain characters have

4400-401: The "line feed" function (which causes a printer to advance its paper), and character 8 represents " backspace ". RFC   2822 refers to control characters that do not include carriage return, line feed or white space as non-whitespace control characters. Except for the control characters that prescribe elementary line-oriented formatting, ASCII does not define any mechanism for describing

4500-419: The ASCII chart in this article. Ninety-five of the encoded characters are printable: these include the digits 0 to 9 , lowercase letters a to z , uppercase letters A to Z , and punctuation symbols . In addition, the original ASCII specification included 33 non-printing control codes which originated with Teletype models ; most of these are now obsolete, although a few are still commonly used, such as

4600-679: The ASCII table as earlier keyboards did. The /? pair also dates to the No. 2, and the ,< .> pairs were used on some keyboards (others, including the No. 2, did not shift , (comma) or . (full stop) so they could be used in uppercase without unshifting). However, ASCII split the ;: pair (dating to No. 2), and rearranged mathematical symbols (varied conventions, commonly -* =+ ) to :* ;+ -= . Some then-common typewriter characters were not included, notably ½ ¼ ¢ , while ^ ` ~ were included as diacritics for international use, and < > for mathematical use, together with

4700-470: The DEL character was assigned to erase the previous character. Because of this, DEC video terminals (by default) sent the DEL character for the key marked "Backspace" while the separate key marked "Delete" sent an escape sequence ; many other competing terminals sent a BS character for the backspace key. The early Unix tty drivers, unlike some modern implementations, allowed only one character to be set to erase

4800-399: The MAC address randomization technique vary largely in different devices. Moreover, various flaws and shortcomings in these implementations may allow an attacker to track a device even if its MAC address is changed, for instance its probe requests' other elements, or their timing. If random MAC addresses are not used, researchers have confirmed that it is possible to link a real identity to

4900-469: The Teletype Model 33 machine assignments for codes 17 (control-Q, DC1, also known as XON), 19 (control-S, DC3, also known as XOFF), and 127 ( delete ) became de facto standards. The Model 33 was also notable for taking the description of control-G (code 7, BEL, meaning audibly alert the operator) literally, as the unit contained an actual bell which it rang when it received a BEL character. Because

5000-574: The US National Security Agency has a system that tracks the movements of mobile devices in a city by monitoring MAC addresses. To avert this practice, Apple has started using random MAC addresses in iOS devices while scanning for networks. Other vendors followed quickly. MAC address randomization during scanning was added in Android starting from version 6.0, Windows 10, and Linux kernel 3.18. The actual implementations of

5100-602: The assignment of a MAC address to network interface when scanning for wireless access points to avert tracking systems. In Internet Protocol (IP) networks, the MAC address of an interface corresponding to an IP address may be queried with the Address Resolution Protocol (ARP) for IPv4 and the Neighbor Discovery Protocol (NDP) for IPv6, relating OSI layer 3 addresses with layer 2 addresses. According to Edward Snowden ,

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5200-482: The attached addresses to activate. Hence, various configuration scripts and utilities permit the randomization of the MAC address at the time of booting or before establishing a network connection. Changing MAC addresses is necessary in network virtualization . In MAC spoofing , this is practiced in exploiting security vulnerabilities of a computer system. Some modern operating systems, such as Apple iOS and Android, especially in mobile devices, are designed to randomize

5300-408: The basis of most of the link layer (OSI layer 2 ) networking upon which upper-layer protocols rely to produce complex, functioning networks. Many network interfaces support changing their MAC address. On most Unix -like systems, the command utility ifconfig may be used to remove and add link address aliases. For instance, the active ifconfig directive may be used on NetBSD to specify which of

5400-650: The bytes over the wire with the most significant bit first, confusion may arise when an address in the latter scenario is represented with bits reversed from the canonical representation. For example, an address in canonical form 12-34-56-78-9A-BC would be transmitted over the wire as bits 01001000 00101100 01101010 00011110 01011001 00111101 in the standard transmission order (least significant bit first). But for Token Ring networks, it would be transmitted as bits 00010010 00110100 01010110 01111000 10011010 10111100 in most-significant-bit first order. The latter might be incorrectly displayed as 48-2C-6A-1E-59-3D . This

5500-585: The change into its draft standard. The X3.2.4 task group voted its approval for the change to ASCII at its May 1963 meeting. Locating the lowercase letters in sticks 6 and 7 caused the characters to differ in bit pattern from the upper case by a single bit, which simplified case-insensitive character matching and the construction of keyboards and printers. The X3 committee made other changes, including other new characters (the brace and vertical bar characters), renaming some control characters (SOM became start of header (SOH)) and moving or removing others (RU

5600-421: The collision domain is all receivers that can detect a given wireless signal. If a switch does not know which port leads to a given MAC address, the switch will forward a unicast frame to all of its ports (except the originating port), an action known as unicast flood . Only the node with the matching hardware MAC address will (normally) accept the frame; network interfaces with non-matching MAC-addresses ignore

5700-522: The complete MAC address to be AA-00-04-00-XX-YY where XX-YY reflects the DECnet network address xx.yy of the host. This eliminates the need for DECnet to have an address resolution protocol since the MAC address for any DECnet host can be determined from its DECnet address. The least significant bit of an address's first octet is referred to as the I/G , or Individual/Group , bit. When this bit

5800-493: The concept of "carriage return" was meaningless. IBM's PC DOS (also marketed as MS-DOS by Microsoft) inherited the convention by virtue of being loosely based on CP/M, and Windows in turn inherited it from MS-DOS. Requiring two characters to mark the end of a line introduces unnecessary complexity and ambiguity as to how to interpret each character when encountered by itself. To simplify matters, plain text data streams, including files, on Multics used line feed (LF) alone as

5900-527: The convention was so well established that backward compatibility necessitated continuing to follow it. When Gary Kildall created CP/M , he was inspired by some of the command line interface conventions used in DEC's RT-11 operating system. Until the introduction of PC DOS in 1981, IBM had no influence in this because their 1970s operating systems used EBCDIC encoding instead of ASCII, and they were oriented toward punch-card input and line printer output on which

6000-663: The earlier five-bit ITA2 , which was also used by the competing Telex teleprinter system. Bob Bemer introduced features such as the escape sequence . His British colleague Hugh McGregor Ross helped to popularize this work – according to Bemer, "so much so that the code that was to become ASCII was first called the Bemer–Ross Code in Europe". Because of his extensive work on ASCII, Bemer has been called "the father of ASCII". On March 11, 1968, US President Lyndon B. Johnson mandated that all computers purchased by

6100-576: The earlier teleprinter encoding systems. Like other character encodings , ASCII specifies a correspondence between digital bit patterns and character symbols (i.e. graphemes and control characters ). This allows digital devices to communicate with each other and to process, store, and communicate character-oriented information such as written language. Before ASCII was developed, the encodings in use included 26 alphabetic characters, 10 numerical digits , and from 11 to 25 special graphic symbols. To include all these, and control characters compatible with

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6200-548: The end-of-transmission character ( EOT ), also known as control-D, to indicate the end of a data stream. In the C programming language , and in Unix conventions, the null character is used to terminate text strings ; such null-terminated strings can be known in abbreviation as ASCIZ or ASCIIZ, where here Z stands for "zero". Other representations might be used by specialist equipment, for example ISO 2047 graphics or hexadecimal numbers. Codes 20 hex to 7E hex , known as

6300-501: The first 28 bits being assigned by IEEE. The first 24 bits of the assigned MA-M block are an OUI assigned to IEEE that will not be reassigned, so the MA-M does not include assignment of an OUI. Addresses can either be universally administered addresses (UAA) or locally administered addresses (LAA). A universally administered address is uniquely assigned to a device by its manufacturer. The first three octets (in transmission order) identify

6400-627: The first 32 code points (numbers 0–31 decimal) and the last one (number 127 decimal) for control characters . These are codes intended to control peripheral devices (such as printers ), or to provide meta-information about data streams, such as those stored on magnetic tape. Despite their name, these code points do not represent printable characters (i.e. they are not characters at all, but signals). For debugging purposes, "placeholder" symbols (such as those given in ISO 2047 and its predecessors) are assigned to them. For example, character 0x0A represents

6500-485: The first octet is 06 (hexadecimal), the binary form of which is 000001 1 0, where the second-least-significant bit is 1. Therefore, it is a locally administered address. Even though many hypervisors manage dynamic MAC addresses within their own OUI , often it is useful to create an entire unique MAC within the LAA range. In virtualisation , hypervisors such as QEMU and Xen have their own OUIs. Each new virtual machine

6600-405: The first station in an ad-hoc network. However, that station does not relay traffic between the other stations; instead, the peers communicate directly with one another. Like an infrastructure BSS, an independent BSS also has a 48-bit MAC-address-like identifier. But unlike infrastructure BSS identifiers, independent BSS identifiers are not necessarily unique: the individual/group bit of the address

6700-428: The frame unless they are in promiscuous mode . If the least significant bit of the first octet is set to 1 (i.e. the second hexadecimal digit is odd) the frame will still be sent only once; however, network interface controllers will choose to accept or ignore it based on criteria other than the matching of their individual MAC addresses: for example, based on a configurable list of accepted multicast MAC addresses. This

6800-653: The identity of previously known networks. The standard ( IEEE 802 ) format for printing EUI-48 addresses in human-friendly form is six groups of two hexadecimal digits, separated by hyphens ( - ) in transmission order (e.g. 01-23-45-67-89-AB ). This form is also commonly used for EUI-64 (e.g. 01-23-45-67-89-AB-CD-EF ). Other conventions include six groups of two hexadecimal digits separated by colons (:) (e.g. 01:23:45:67:89:AB ), and three groups of four hexadecimal digits separated by dots (.) (e.g. 0123.4567.89AB ); again in transmission order. The standard notation, also called canonical format, for MAC addresses

6900-525: The interface hardware, such as its read-only memory , or by a firmware mechanism. Many network interfaces, however, support changing their MAC addresses. The address typically includes a manufacturer's organizationally unique identifier (OUI). MAC addresses are formed according to the principles of two numbering spaces based on extended unique identifiers (EUIs) managed by the Institute of Electrical and Electronics Engineers (IEEE): EUI-48 —which replaces

7000-448: The keytop for the O key also showed a left-arrow symbol (from ASCII-1963, which had this character instead of underscore ), a noncompliant use of code 15 (control-O, shift in) interpreted as "delete previous character" was also adopted by many early timesharing systems but eventually became neglected. When a Teletype 33 ASR equipped with the automatic paper tape reader received a control-S (XOFF, an abbreviation for transmit off), it caused

7100-800: The local conventions and the NVT. The File Transfer Protocol adopted the Telnet protocol, including use of the Network Virtual Terminal, for use when transmitting commands and transferring data in the default ASCII mode. This adds complexity to implementations of those protocols, and to other network protocols, such as those used for E-mail and the World Wide Web, on systems not using the NVT's CR-LF line-ending convention. The PDP-6 monitor, and its PDP-10 successor TOPS-10, used control-Z (SUB) as an end-of-file indication for input from

7200-485: The network packets of both independent BSSs and infrastructure BSSs have a logical network service set identifier, and the logical link control does not distinguish between the use of that field to name an ESS network, and the use of that field to name a peer-to-peer ad hoc network. The two are effectively indistinguishable at the logical link control layer level. MAC address A MAC address (short for medium access control address or media access control address )

7300-742: The obsolete term MAC-48 —and EUI-64 . Network nodes with multiple network interfaces, such as routers and multilayer switches , must have a unique MAC address for each network interface in the same network. However, two network interfaces connected to two different networks can share the same MAC address. The IEEE 802 MAC address originally comes from the Xerox Network Systems Ethernet addressing scheme. This 48-bit address space contains potentially 2 (over 281 trillion) possible MAC addresses. The IEEE manages allocation of MAC addresses, originally known as MAC-48 and which it now refers to as EUI-48 identifiers. The IEEE has

7400-555: The organization that issued the identifier and are known as the organizationally unique identifier (OUI). The remainder of the address (three octets for EUI-48 or five for EUI-64) are assigned by that organization in nearly any manner they please, subject to the constraint of uniqueness. A locally administered address is assigned to a device by software or a network administrator, overriding the burned-in address for physical devices. Locally administered addresses are distinguished from universally administered addresses by setting (assigning

7500-432: The perspective of the link layer, all stations within an ESS are all on the same link, and transfer from one BSS to another is transparent to logical link control. The basic service sets formed in wireless ad hoc networks are, by definition, independent from other BSSs, and an independent BSS cannot therefore be part of an extended infrastructure. In that formal sense an independent BSS has no extended service set. However,

7600-452: The previous character in canonical input processing (where a very simple line editor is available); this could be set to BS or DEL, but not both, resulting in recurring situations of ambiguity where users had to decide depending on what terminal they were using ( shells that allow line editing, such as ksh , bash , and zsh , understand both). The assumption that no key sent a BS character allowed Ctrl+H to be used for other purposes, such as

7700-515: The previous section. Code 7F hex corresponds to the non-printable "delete" (DEL) control character and is therefore omitted from this chart; it is covered in the previous section's chart. Earlier versions of ASCII used the up arrow instead of the caret (5E hex ) and the left arrow instead of the underscore (5F hex ). ASCII was first used commercially during 1963 as a seven-bit teleprinter code for American Telephone & Telegraph 's TWX (TeletypeWriter eXchange) network. TWX originally used

7800-413: The printable characters, represent letters, digits, punctuation marks , and a few miscellaneous symbols. There are 95 printable characters in total. Code 20 hex , the "space" character, denotes the space between words, as produced by the space bar of a keyboard. Since the space character is considered an invisible graphic (rather than a control character) it is listed in the table below instead of in

7900-444: The proposed Bell code and ASCII were both ordered for more convenient sorting (i.e., alphabetization) of lists and added features for devices other than teleprinters. The use of ASCII format for Network Interchange was described in 1969. That document was formally elevated to an Internet Standard in 2015. Originally based on the (modern) English alphabet , ASCII encodes 128 specified characters into seven-bit integers as shown by

8000-453: The range 3 3 -33-XX-XX-XX-XX (with both bits set). Given the locations of the U/L and I/G bits, they can be discerned in a single digit in common MAC address notation as shown in the following table: IEEE standard 802c further divides the locally administered MAC address block into four quadrants. This additional partitioning is called Structured Local Address Plan (SLAP) and its usage

8100-522: The same reason, many special signs commonly used as separators were placed before digits. The committee decided it was important to support uppercase 64-character alphabets , and chose to pattern ASCII so it could be reduced easily to a usable 64-character set of graphic codes, as was done in the DEC SIXBIT code (1963). Lowercase letters were therefore not interleaved with uppercase . To keep options available for lowercase letters and other graphics,

8200-494: The second stick, positions 1–5, corresponding to the digits 1–5 in the adjacent stick. The parentheses could not correspond to 9 and 0 , however, because the place corresponding to 0 was taken by the space character. This was accommodated by removing _ (underscore) from 6 and shifting the remaining characters, which corresponded to many European typewriters that placed the parentheses with 8 and 9 . This discrepancy from typewriters led to bit-paired keyboards , notably

8300-538: The simple line characters \ | (in addition to common / ). The @ symbol was not used in continental Europe and the committee expected it would be replaced by an accented À in the French variation, so the @ was placed in position 40 hex , right before the letter A. The control codes felt essential for data transmission were the start of message (SOM), end of address (EOA), end of message (EOM), end of transmission (EOT), "who are you?" (WRU), "are you?" (RU),

8400-402: The special and numeric codes were arranged before the letters, and the letter A was placed in position 41 hex to match the draft of the corresponding British standard. The digits 0–9 are prefixed with 011, but the remaining 4 bits correspond to their respective values in binary, making conversion with binary-coded decimal straightforward (for example, 5 in encoded to 011 0101 , where 5

8500-425: The standard is unclear about the meaning of "delete". Probably the most influential single device affecting the interpretation of these characters was the Teletype Model 33 ASR, which was a printing terminal with an available paper tape reader/punch option. Paper tape was a very popular medium for long-term program storage until the 1980s, less costly and in some ways less fragile than magnetic tape. In particular,

8600-456: The station a list of supported SSIDs. Once a device has associated with a basic service set, for efficiency, the SSID is not sent within packet headers; only BSSIDs are used for addressing. Apple 's location services interpret the SSID of a Wi‑Fi access point ending in _nomap as an opt-out from being included in Apple's crowdsourced location databases. An extended service set ( ESS )

8700-461: The stations in an infrastructure-mode network, the stations in a wireless ad hoc network communicate directly with one another, i.e. without a dependence on a distribution point to relay traffic between them. In this form of peer-to-peer wireless networking, the peers form an independent basic service set ( IBSS ). Some of the responsibilities of a distribution point—such as defining network parameters and other "beaconing" functions—are established by

8800-440: The structure or appearance of text within a document. Other schemes, such as markup languages , address page and document layout and formatting. The original ASCII standard used only short descriptive phrases for each control character. The ambiguity this caused was sometimes intentional, for example where a character would be used slightly differently on a terminal link than on a data stream , and sometimes accidental, for example

8900-515: The syntax of computer languages and text markup. ASCII hugely influenced the design of character sets used by modern computers, including Unicode which has over a million code points, but the first 128 of these are the same as ASCII. The Internet Assigned Numbers Authority (IANA) prefers the name US-ASCII for this character encoding. ASCII is one of the IEEE milestones . ASCII was developed in part from telegraph code . Its first commercial use

9000-441: The tape reader to stop; receiving control-Q (XON, transmit on) caused the tape reader to resume. This so-called flow control technique became adopted by several early computer operating systems as a "handshaking" signal warning a sender to stop transmission because of impending buffer overflow ; it persists to this day in many systems as a manual output control technique. On some systems, control-S retains its meaning, but control-Q

9100-458: The term IBSS is not used for this type of BSS but refers to the independent type discussed below.) The operating parameters of the infrastructure BSS are defined by the AP. The Wi‑Fi segments of common home and business networks are examples of this type. Each basic service set has a unique identifier, a BSSID, which is a 48-bit number that follows MAC address conventions. An infrastructure BSSID

9200-600: The time could record eight bits in one position, it also allowed for a parity bit for error checking if desired. Eight-bit machines (with octets as the native data type) that did not use parity checking typically set the eighth bit to 0. The code itself was patterned so that most control codes were together and all graphic codes were together, for ease of identification. The first two so-called ASCII sticks (32 positions) were reserved for control characters. The "space" character had to come before graphics to make sorting easier, so it became position 20 hex ; for

9300-447: The typebars that strike the ribbon remain stationary. The entire carriage had to be pushed (returned) to the right in order to position the paper for the next line. DEC operating systems ( OS/8 , RT-11 , RSX-11 , RSTS , TOPS-10 , etc.) used both characters to mark the end of a line so that the console device (originally Teletype machines) would work. By the time so-called "glass TTYs" (later called CRTs or "dumb terminals") came along,

9400-522: The value 40:D8:55 was used. The owners of an already assigned IAB may continue to use the assignment. The MA-S registry includes, for each registrant, both a 36-bit unique number used in some standards and a block of EUI-48 and EUI-64 identifiers (while the registrant of an IAB cannot assign an EUI-64). MA-S does not include assignment of an OUI. Additionally, the MA-M ( MAC address block, medium ) provides both 2 EUI-48 identifiers and 2 EUI-64 identifiers,

9500-456: The value of 1 to) the second- least-significant bit of the first octet of the address. This bit is also referred to as the U/L bit, short for Universal/Local , which identifies how the address is administered. If the bit is 0, the address is universally administered, which is why this bit is 0 in all UAAs. If it is 1, the address is locally administered. In the example address 06-00-00-00-00-00

9600-595: The various context-dependent identifier number spaces, like for SNAP or EDID ), the Individual Address Block could only be used to assign EUI-48 identifiers. All other potential uses based on the OUI from which the IABs are allocated are reserved and remain the property of the IEEE Registration Authority. Between 2007 and September 2012, the OUI value 00:50:C2 was used for IAB assignments. After September 2012,

9700-741: Was developed under the auspices of a committee of the American Standards Association (ASA), called the X3 committee, by its X3.2 (later X3L2) subcommittee, and later by that subcommittee's X3.2.4 working group (now INCITS ). The ASA later became the United States of America Standards Institute (USASI) and ultimately became the American National Standards Institute (ANSI). With the other special characters and control codes filled in, ASCII

9800-557: Was in the Teletype Model 33 and the Teletype Model 35 as a seven- bit teleprinter code promoted by Bell data services. Work on the ASCII standard began in May 1961, with the first meeting of the American Standards Association's (ASA) (now the American National Standards Institute or ANSI) X3.2 subcommittee. The first edition of the standard was published in 1963, underwent a major revision during 1967, and experienced its most recent update during 1986. Compared to earlier telegraph codes,

9900-695: Was published as ASA X3.4-1963, leaving 28 code positions without any assigned meaning, reserved for future standardization, and one unassigned control code. There was some debate at the time whether there should be more control characters rather than the lowercase alphabet. The indecision did not last long: during May 1963 the CCITT Working Party on the New Telegraph Alphabet proposed to assign lowercase characters to sticks 6 and 7, and International Organization for Standardization TC 97 SC 2 voted during October to incorporate

10000-450: Was removed). ASCII was subsequently updated as USAS X3.4-1967, then USAS X3.4-1968, ANSI X3.4-1977, and finally, ANSI X3.4-1986. In the X3.15 standard, the X3 committee also addressed how ASCII should be transmitted ( least significant bit first) and recorded on perforated tape. They proposed a 9-track standard for magnetic tape and attempted to deal with some punched card formats. The X3.2 subcommittee designed ASCII based on

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