LocalTalk
Encyclopedia
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 transceiver
s, running at a rate of 230.4 kbit/s. CSMA/CA was implemented as a random multiple access method.
Networking was envisioned in the Macintosh during planning, so the Mac was given expensive RS-422 capable serial port
s. 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 3.6864 MHz 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 side-by-side telephone wire with 6 position modular connector
s (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 availability 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 and applications where Ethernet was not available, 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 available, and was particularly popular on PowerBook
s. This enabled all but the earliest Macintosh models to access a high speed Ethernet network.
With the release of the iMac
in 1998 the traditional Mac serial port — and thus, the ability to use both LocalTalk and PhoneNet — disappeared from new models of Macintosh. LocalTalk-to-Ethernet bridge
s were introduced to allow legacy devices
(especially printers) to function on newer networks. For very old Macintosh computers, LocalTalk remains the only option.
printer initially with the Macintosh
family of computers as an integral part of the newly announced Macintosh Office
. However, well past the move to Ethernet, the connector's design continued to be used on all of Apple's peripherals and cable connectors as well as influencing the connectors used throughout the industry as a whole.
Physical layer
The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY....
of the AppleTalk
AppleTalk
AppleTalk is a proprietary suite of protocols developed by Apple Inc. for networking computers. It was included in the original Macintosh released in 1984, but is now unsupported as of the release of Mac OS X v10.6 in 2009 in favor of TCP/IP networking...
networking
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
system from Apple Computer
Apple Computer
Apple Inc. is an American multinational corporation that designs and markets consumer electronics, computer software, and personal computers. The company's best-known hardware products include the Macintosh line of computers, the iPod, the iPhone and the iPad...
. LocalTalk specifies a system of shielded twisted pair cabling, plugged into self-terminating transceiver
Transceiver
A transceiver is a device comprising both a transmitter and a receiver which are combined and share common circuitry or a single housing. When no circuitry is common between transmit and receive functions, the device is a transmitter-receiver. The term originated in the early 1920s...
s, running at a rate of 230.4 kbit/s. CSMA/CA was implemented as a random multiple access method.
Serial port
In computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time...
s. The ports were driven by the Zilog SCC
Zilog SCC
The Zilog Z16C01 SCC was introduced in the early 1980s and provided the ability to do both standard UART style serial communications along with the HDLC protocol for a reasonable price. It was a descendant of the earlier Zilog SIO, and its main enhancement was the inclusion of a built-in baud rate...
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 3.6864 MHz 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
Steve Jobs
Steven Paul Jobs was an American businessman and inventor widely recognized as a charismatic pioneer of the personal computer revolution. He was co-founder, chairman, and chief executive officer of Apple Inc...
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
Twisted pair
Twisted pair cabling is a type of wiring in which two conductors are twisted together for the purposes of canceling out electromagnetic interference from external sources; for instance, electromagnetic radiation from unshielded twisted pair cables, and crosstalk between neighboring pairs...
cable with 3-pin Mini-DIN
Mini-DIN connector
The mini-DIN connectors are a family of multi-pin electrical connectors used in a variety of applications. Mini-DIN is similar to the larger, older DIN connector...
connectors. Cables were daisy-chained
Daisy chain
Daisy chain may refer to a daisy garland created from daisy flowers, the original meaning and the one from which the following derive by analogy:*Daisy chain *Daisy chain *Daisy chain...
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
PhoneNet
PhoneNet was an implementation of the AppleTalk networking physical layer created by Farallon Computing . Instead of using expensive shielded twisted pair wiring as in Apple's LocalTalk implementation, PhoneNet uses standard four-conductor telephone patch cords and modular connectors, and is...
, was introduced by Farallon Computing. It used standard unshielded side-by-side telephone wire with 6 position modular connector
Modular connector
Modular connector is the name given to a family of electrical connectors originally used in telephone wiring and now used for many other purposes. Many applications that originally used a bulkier, more expensive connector have now migrated to modular connectors...
s (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 availability of Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
-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 and applications where Ethernet was not available, but as Ethernet became universal on the PC most offices were installing it anyway. Early models of Power Macintosh
Power Macintosh
Power Macintosh, later Power Mac, was a line of Apple Macintosh workstation-class personal computers based on various models of PowerPC microprocessors that were developed, marketed, and supported by Apple Inc. from March 1994 until August 2006. The first models were the Power Macintosh 6100,...
and the Macintosh Quadra
Macintosh Quadra
The Macintosh Quadra series was Apple Computer's product family of professional high-end Apple Macintosh personal computers built using the Motorola 68040 CPU. The first two models in the Quadra line were introduced in 1991, and the name was used until the Power Mac was introduced in 1994...
supported 10BASE-T via the Apple Attachment Unit Interface
Apple Attachment Unit Interface
Apple Attachment Unit Interface is a mechanical re-design by Apple of the standard Attachment Unit Interface used to connect Ethernet transceivers to computer equipment...
while still supporting LocalTalk-based networking. For older Macintosh computers that did not have built-in Ethernet expansion options, a high speed SCSI
SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
-to-Ethernet adapter was available, and was particularly popular on PowerBook
PowerBook
The PowerBook was a line of Macintosh laptop computers that was designed, manufactured and sold by Apple Computer, Inc. from 1991 to 2006. During its lifetime, the PowerBook went through several major revisions and redesigns, often being the first to incorporate features that would later become...
s. This enabled all but the earliest Macintosh models to access a high speed Ethernet network.
With the release of the iMac
IMac
The iMac is a range of all-in-one Macintosh desktop computers built by Apple. It has been the primary part of Apple's consumer desktop offerings since its introduction in 1998, and has evolved through five distinct forms....
in 1998 the traditional Mac serial port — and thus, the ability to use both LocalTalk and PhoneNet — disappeared from new models of Macintosh. LocalTalk-to-Ethernet bridge
LocalTalk-to-Ethernet bridge
A LocalTalk-to-Ethernet Bridge is a network bridge that joins the physical layer of the AppleTalk networking used by previous generations of Apple Computer products to an Ethernet network....
s were introduced to allow legacy devices
Legacy system
A legacy system is an old method, technology, computer system, or application program that continues to be used, typically because it still functions for the users' needs, even though newer technology or more efficient methods of performing a task are now available...
(especially printers) to function on newer networks. For very old Macintosh computers, LocalTalk remains the only option.
Design legacy
The LocalTalk connector had the distinction of being the first to use Apple's unified AppleTalk Connector Family design, created by Brad Bissell of Frogdesign using Rick Meadows' Apple Icon Family designs. LocalTalk connectors were first released in January 1985 to connect the LaserwriterLaserWriter
The LaserWriter was a laser printer with built-in PostScript interpreter introduced by Apple in 1985. It was one of the first laser printers available to the mass market...
printer initially with the Macintosh
Macintosh
The Macintosh , or Mac, is a series of several lines of personal computers designed, developed, and marketed by Apple Inc. The first Macintosh was introduced by Apple's then-chairman Steve Jobs on January 24, 1984; it was the first commercially successful personal computer to feature a mouse and a...
family of computers as an integral part of the newly announced Macintosh Office
Macintosh Office
The Macintosh Office was Apple's third failed attempt to enter into the business environment as a serious competitor to IBM. Consisting of three key parts, a network file server, local area network and a network Laser printer, Apple announced Macintosh Office in January 1985 with an ill-fated,...
. However, well past the move to Ethernet, the connector's design continued to be used on all of Apple's peripherals and cable connectors as well as influencing the connectors used throughout the industry as a whole.
See also
- AppleTalkAppleTalkAppleTalk is a proprietary suite of protocols developed by Apple Inc. for networking computers. It was included in the original Macintosh released in 1984, but is now unsupported as of the release of Mac OS X v10.6 in 2009 in favor of TCP/IP networking...
- List of device bandwidths