LocalTalk is a term used in computer science and refers to an outdated, proprietary network system from Apple.
More specifically, it is a specific implementation of the physical layer ( according to the OSI model at level 1) for the AppleTalk protocol family.
LocalTalk specifies a two-wire line that uses the RS -422 port on the older Apple Macintosh, which works with 230.4 kbit / s and permits a maximum packet size of 603 bytes; without data preamble and without Trailer. The transmit and receive lines of the RS -422 interface are bridged in the LocalTalk operation, so it is electrically like Ethernet to a bus system, access control CSMA / CD is inserted.
To wire a splitter box is used, it includes the one galvanic separation elements to avoid equalization currents between the individual stations in spatially broader networks; and secondly to provide two plug connections to available way to connect multiple workstations to a computer network. The ends of the network segment thus formed were automatically terminated.
A single LocalTalk network segment can be up to 300 meters in length. It is recommended the operation of a maximum of 32 devices per segment.
Originally called LocalTalk AppleTalk Personal Network and worked with a shielded twisted-pair cable and a three-pin mini- DIN connector. The devices were connected similarly Thin Ethernet in a chain ( daisy chain ).
The printer of Apple were at least optionally equipped with a Mac -compatible, intended only for LocalTalk RS- 422 interface. To be in this market segment can also be successful, other manufacturers have equipped their printers with matching interfaces.
For file transfers via AFP gives a transfer rate of about 22 KBytes / s
By the time LocalTalk was not least because
- The low speed and
- With increasing the number of nodes per branch increases processor load ( also uninvolved stations )
Surpassed by other techniques, such as Ethernet or token ring in relation to speed, and thus comfort.
With the introduction of the iMac in 1998 to support LocalTalk from Apple was set.
A modification of LocalTalk was introduced by the company under the name of Farallon Computing PhoneNet. Here, a simple RJ- 11 connector is used instead of the elaborate mini- DIN connector and easy telephone cable instead of expensive twisted- pair cable. The lower cost of cable connections procured PhoneNet in a better position than LocalTalk and displaced it entirely even in smaller networks.
PhoneNET allows for simple daisy chains lengths of 600 meters per strand, in particular constellations up to 1200 meters.
Another point for the dissemination of PhoneNet is the fact that existing telephone installations use in the U.S., the same connectors and thus a multi-room networks can be formed without cable laying work - hence the name " PhoneNet ". In the period following products have been published on RJ11 base of other manufacturers to save costs partly manually to install RJ11 terminators instead of the user-friendly automatic termination.
LocalTalk and IP
With the increasing importance of TCP / IP in computer networks Apple offered a software called MacIP gateway embeds the IP packets in AppleTalk packets. MacTCP or Open Transport on the client side in their own settings one mode to dekapsulieren these packages again, and so to use IP also use the really suitable only for AppleTalk LocalTalk. Also, Cisco has built into IOS respective functions, even if LocalTalk is not supported by the routers themselves.
Due to the low maximum size of LocalTalk packets MTU thus tailed computer is only 576 bytes.
Integration of LocalTalk to Ethernet networks
With the increasing proliferation of Ethernet networks in the 1990s there was a need to integrate components such as LocalTalk printer or computer without an Ethernet interface (investment protection ).
Apple offered this to the software LocalTalk Bridge, with the functions a Macintosh with two interfaces as a software bridge. This function can also be mapped with the Apple Internet Router, this mapping software a full AppleTalk router for many types of interfaces.
Different manufacturers have offered hardware-based Ethernet LocalTalk bridges whose benefits among other
- Lower power consumption than a complete computer software solution,
- Regardless of the location as a complete computer
- No unnecessary load on the computer by Softwarebridging,
- Less network failures due to incorrect operation ( accidentally turning off the bridge computer)
Some manufacturers also provided bridges Token Ring after LocalTalk.
The AppleTalk protocol stack
The AppleTalk protocols can be divided into several layers that form a protocol stack ( protocol stack ). The protocols can be classified as follows in the ISO - OSI reference model: