AppleTalk is a network system developed by Apple Computer. It is based on the AppleTalk protocol architecture, which is concerned with the way the connectivity of the network system is implemented. AppleTalk Phase 2 supports AppleTalk networks with more than 254 nodes, multiple zones per network, the AppleTalk internet router, and extended Ethernet and token ring support. The features supported by AppleTalk Phase 2 are discussed in more detail later in this chapter.

In Figure 13.1, the AppleTalk protocol architecture is shown as a layered configuration.


Figure 13.1 AppleTalk Protocol Architecture

The protocols shown in each level of Figure 13.1 receive services from the protocols shown in the lower-level layers. In turn, the protocols in each layer provide services to the protocols in the layers above them. These services, listed in Table 13.2, include connectivity, routing, internetworking, reliable end-to-end data transfer, message exchange between two processes or applications, and data value representation.

Table   13.2 AppleTalk Protocols



Datagram Delivery Protocol (DDP)

Provides for data delivery in discrete packets. Neither the order of the data nor its actual delivery is guaranteed.

Routing Table Maintenance Protocol (RTMP)

Used by routers to exchange routing information. Concerned with the establishment and maintenance of routing tables.

AppleTalk Echo Protocol (AEP)

Used to test a system's responsiveness and to establish round-trip transmission times.

AppleTalk Transaction Protocol (ATP)

Provides reliable data transmission.

Name Binding Protocol (NBP)

Provides a name translation service that converts a device name to an AppleTalk network address.

AppleTalk Data Stream Protocol (ADSP)

Provides reliable, full-duplex data transmission between two sockets on an AppleTalk network.

Zone Information Protocol (ZIP)

Maintains the internet-wide mapping of network number ranges to zone names.

AppleTalk Session Protocol (ASP)

Provides for reliable transmission without duplication. Establishes a session between two programs and terminates the session.

Printer Access Protocol

Provides for the reliable transmission of messages. Handles connection setup, maintenance, and termination.

AppleTalk Filing Protocol (AFP)

Provides the interface between an application and a file server. It allows a workstation on an AppleTalk network to access files as an AFP file server.