Computer Networking

What is AppleTalk?

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12/18/2008

AppleTalk was developed by Apple, Inc. for computer networking. AppleTalk is a set of protocols included in the original version of Macintosh in 1984. Unlike other early LAN systems, AppleTalk was based on the OSI model of protocol layering and was not built on the archetypal Xerox XNS system, although several portions of the AppleTalk system have direct analogs in XNS.

AppleTalk contained two protocols, AppleTalk address resolution protocol (AARP) and name binding protocol (NBP) in order to make the system entirely self-configuring. Through AARP, AppleTalk hosts were able to automatically generate their own network addresses.

NBP mapped network addresses to user-readable names, essentially making it a dynamic Domain Name System (DNS). Routers, however, were able to provide all the information by overriding the default mechanisms. This was beneficial for larger networks, since "chattiness" could occur through AARP as new nodes searched for free addresses.

The two protocols also made AppleTalk the easiest to use among networking systems, making installation of new machines simple, requiring only that they be plugged in and optionally be given a name. A program called the Chooser listed down and classified the machines on a local network through a completely automated procedure.

On larger networks and wide area networks (WAN), the naming services provided by AARP and NBP caused a significant amount of unwanted traffic. This problem was addressed by the introduction of AppleTalk Phase 2.

An AppleTalk address consisted of four bytes: a two-byte network number (obtained from a router), a one-byte node number (chosen by each node), and a one-byte socket number. Names for services were chosen by humans so that they would easily be recognizable by users. They were long enough in order to minimize the chance of conflicts.

Though AppleTalk was originally intended to be part of a project known as Macintosh Office consisting of a host machine that enabled routing, printer sharing and file sharing, development of the Macintosh Office project was halted in 1986. In place of Macintosh Office, the AppleShare File and Print Server was released.

TCP/IP was the default networking model for the Mac; however, AppleTalk is backwards compatible with several products. For TCP/IP-based networks, an Apple implementation called Bonjour provided discovery and configuration services not unlike that of AppleTalk.