| dbpprop:abstract
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- LocalTalk is a particular implementation of the physical layer of the AppleTalk networking system from Apple Computer. LocalTalk specifies a system of shielded twisted pair cabling, plugged into self-terminating transceivers, running at a rate of 230.4 kbit/s. Networking was envisioned in the Macintosh during planning, so the Mac was given expensive RS-422 capable serial ports. The ports were driven by the Zilog SCC which could serve as either a standard UART or handle the much more complicated HDLC protocol which was a packet oriented protocol which incorporated addressing, bit-stuffing, and packet checksumming in hardware. Coupled together with the RS422 electrical connections, this provided a reasonably high-speed data connection. The 230.4 kbit/s bit rate is the highest in the series of standard serial bit rates (110, 150, 300, 600, 1200, 2400, 4800, 9600, 14400, 19200, 28800, 38400, 57600, 115200, 230400) derived from the 3.6864MHz clock after the customary divide-by-16. This clock frequency, 3.6864 MHz, was chosen (in part) to support the common asynchronous baud rates up to 38.4 kbit/s using the SCC's internal baud-rate generator. When the SCC's internal PLL was used to lock to the clock embedded in the LocalTalk serial data stream (using its FM0 encoding method) a divide-by-16 setting on the PLL yielded the fastest rate available, namely 230.4 kbit/s. There is a rumor that Steve Jobs was initially opposed to including any sort of networking on the Mac, and that the RS-422 port and its associated software support was developed largely in secret. Originally released as "AppleTalk Personal Network", LocalTalk used shielded twisted-pair cable with 3-pin Mini-DIN connectors. Cables were daisy-chained from transceiver to transceiver. Each transceiver had two 3-pin Mini-DIN ports, and a cable to connect to the Mac's DE-9 serial connector. Later, when the Mac Plus introduced the 8-pin Mini-DIN serial connector, transceivers were updated as well. A variation of LocalTalk, called PhoneNet, was introduced by Farallon Computing. It used standard unshielded twisted pair telephone wire with 6 position modular connectors (same as used in the popular RJ11 telephone connectors) connected to a PhoneNet transceiver, instead of the expensive shielded twisted-pair cable. In addition to being lower cost, PhoneNet-wired networks were more reliable due to the connections being more difficult to accidentally disconnect. In addition, because it used the "outer" pair of the modular connector, it could travel on many pre-existing phone cables and jacks where just the inner pair was in use for RJ11 telephone service. PhoneNet was also able to use an office's existing phone wire, allowing for entire floors of computers to be easily networked. Farallon introduced a 12 port hub which made constructing star topology networks of up to 48 devices as easy as adding jacks at the workstations and some jumpers in the phone closet. These factors led to PhoneNet largely supplanting LocalTalk wiring in low cost networking. The useful life of PhoneNet was extended with the introduction of LocalTalk switching technology by Tribe Computer Works. Introduced in 1990, the Tribe LocalSwitch was a 16 port packet switch designed to speed up overloaded PhoneNet networks. The widespread introduction of Ethernet-based networking in the early 1990s led to the swift disappearance of both LocalTalk and PhoneNet. They remained in use for some time in low-cost applications, but as Ethernet became universal on the PC most offices were installing it anyway. Early models of Power Macintosh and the Macintosh Quadra supported 10BASE-T via the Apple Attachment Unit Interface while still supporting LocalTalk-based networking. For older Macintosh computers that did not have built-in Ethernet expansion options, a high speed SCSI-to-Ethernet adapter was popular, particularly on PowerBooks. This enabled all but the earliest models to access a high speed Ethernet network. With the release of the iMac in 1998 the traditional Mac serial port disappeared — and thus, the ability to use both LocalTalk and PhoneNet — from new models of Macintosh. LocalTalk-to-Ethernet bridges were introduced to allow legacy devices to function on newer networks. For very old Macintosh computers, LocalTalk remains the only option.
- LocalTalk ist ein Begriff aus der Informatik und bezeichnet ein veraltetes, proprietäres Netzwerksystem von Apple.
- LocalTalk es una implementación particular de la capa física del sistema de redes AppleTalk de los ordenadores de la empresa Apple Inc.. LocalTalk se basa en un sistema de cable de par trenzado y un transceptor funcionando todo ello a una velocidad de 230'4 kbit/s.
- LocalTalk est la technique de réseau local d'Apple, basée sur des paire torsadées de 300 mètres de long maximum, et transmettant 230 kbps en utilisant le protocole AppleTalk. Il s'agit essentiellement d'un RS485 à liaison par transformateur. La connectique garantit une terminaison correcte, tant qu'on ne réalise pas de boucle, ce qui autorise un câblage correct par un néophyte total. La topologie est celle d'une chaîne pouvant contenir jusqu'à 32 éléments. Ce réseau, lent mais gratuit (moins coûteux qu'une boîte à partager une imprimante), a été le plus répandu au monde jusqu'au début des années 1990, pour être supplanté progressivement par Ethernet, y compris sur Macintosh. Depuis 1994, toutes les cartes mères de Macintosh comportent une interface Ethernet (en 2006, principalement 1000baseT, les machines grand public en restant à l'antique 100baseTx). L'iMac de 1998 est la première machine d'Apple à ne plus comporter d'interface LocalTalk depuis le Macintosh original. Le protocole AppleTalk de 1984 est toujours utilisé sur Ethernet, en parallèle avec IP, la convivialité de ce dernier, bien qu'en progrès, ayant encore quelques progrès à faire.
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| rdfs:comment
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- LocalTalk is a particular implementation of the physical layer of the AppleTalk networking system from Apple Computer. LocalTalk specifies a system of shielded twisted pair cabling, plugged into self-terminating transceivers, running at a rate of 230.4 kbit/s. Networking was envisioned in the Macintosh during planning, so the Mac was given expensive RS-422 capable serial ports.
- LocalTalk ist ein Begriff aus der Informatik und bezeichnet ein veraltetes, proprietäres Netzwerksystem von Apple.
- LocalTalk es una implementación particular de la capa física del sistema de redes AppleTalk de los ordenadores de la empresa Apple Inc.. LocalTalk se basa en un sistema de cable de par trenzado y un transceptor funcionando todo ello a una velocidad de 230'4 kbit/s.
- LocalTalk est la technique de réseau local d'Apple, basée sur des paire torsadées de 300 mètres de long maximum, et transmettant 230 kbps en utilisant le protocole AppleTalk. Il s'agit essentiellement d'un RS485 à liaison par transformateur. La connectique garantit une terminaison correcte, tant qu'on ne réalise pas de boucle, ce qui autorise un câblage correct par un néophyte total. La topologie est celle d'une chaîne pouvant contenir jusqu'à 32 éléments.
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