APPLE TALK

Definition::-

AppleTalk is a set of local area network communication PROTOCOLS originally created for Apple computers. An AppleTalk network can support up to 32 devices and data can be exchanged at a speed of 230.4 kilobits per second (Kbps). Devices can be as much as 1,000 feet apart. AppleTalk's Datagram Delivery Protocol corresponds closely to the network layerof the Open Systems Interconnection (OSI) communication model.

NETWORKING MODEL::-

OSI Model	Corresponding AppleTalk layers
Application	Apple Filing Protocol (AFP)
Presentation	Apple Filing Protocol (AFP)
Session	Zone Information Protocol (ZIP) AppleTalk Session Protocol (ASP) AppleTalk Data Stream Protocol (ADSP)
Transport	AppleTalk Transaction Protocol (ATP) AppleTalk Echo Protocol (AEP) Name Binding Protocol (NBP) Routing Table Maintenance Protocol (RTMP)
Network	Datagram Delivery Protocol (DDP)
Data link	EtherTalk Link Access Protocol (ELAP) LocalTalk Link Access Protocol (LLAP) TokenTalk Link Access Protocol (TLAP) Fiber Distributed Data Interface (FDDI)
Physical	LocalTalk driver Ethernet driver Token Ring driver FDDI driver

DESIGN::-

The AppleTalk design rigorously followed the OSI model of protocol layering. Unlike most of the early LAN systems, AppleTalk was not built using the archetypal Xerox XNS system. The intended target was not Ethernet, and it did not have 48-bit addresses to route. Nevertheless, many portions of the AppleTalk system have direct analogs in XNS.

One key differentiation for AppleTalk was it contained three protocols aimed at making the system completely self-configuring. The AppleTalk address resolution protocol (AARP) allowed AppleTalk hosts to automatically generate their own network addresses, and the Name Binding Protocol (NBP) was dynamic system for mapping network addresses to user-readable names. Although systems similar to AARP existed in other systems, Banyan VINES for instance, nothing like NBP has existed until recently.

Both AARP and NBP had defined ways to allow "controller" devices to override the default mechanisms. The concept was to allow routers to provide the information or "hardwire" the system to known addresses and names. On larger networks where AARP could cause problems as new nodes searched for free addresses, the addition of a router could reduce "chattiness." Together AARP and NBP made AppleTalk an easy-to-use networking system. New machines were added to the network by plugging them and optionally giving them a name. The NBP lists were examined and displayed by a program known as the Chooser which would display a list of machines on the local network, divided into classes such as file-servers and printers.