3Com 2500 manual 2 AppleTalk Protocols and the OSI Reference Model

AppleTalk Protocols 7-5

OSI Reference Model

Application

Presentation

Session

Transport

Network

Link

Physical

AppleTalk®

PostScript®

Filing

Protocol (AFP)

AppleTalk

Zone Information

AppleTalk

Printer Access

Data Stream

Session

Protocol (ZIP)

Protocoo (PAP)

Protocol (ADSP)

Protocol (ASP)

Routing Table

AppleTalk Echo

AppleTalk

Name Binding

Maintenance

Transaction

Protocol (AEP)

Protocol (NBP)

Protocol (RTMP)

Protocol (ATP)

Datagram Delivery Protocol (DDP)

TokenTalk®

EtherTalk®

LocalTalk®

Link Access

Link Access

Link Access

Protocol

Protocol

Protocol

Token Ring

Ethernet

LocalTalk®

Hardware

Hardware

Hardware

Figure 7-2 AppleTalk Protocols and the OSI Reference Model

The AppleTalk six-layer protocol suite is not fully compliant with the OSI seven-layer reference model. However, AppleTalk provides many of the functions and services provided by OSI. Note that AppleTalk has no specific protocols for the application layer, since the lower levels provide printer and file service.

Physical The physical layer of the OSI protocol stack defines the network hardware. Connectivity You can use standard network hardware, such as that defined for Ethernet

and Token Ring networks, with AppleTalk. Apple has also defined its own network hardware, called LocalTalk, which uses a synchronous RS-422A bus for communications.

The data link layer provides the interface between the network hardware and the upper layers of the protocol stack. The AppleTalk data link layer includes three link access protocols (LAPs): TokenTalk LAP (TLAP), Ethernet LAP (ELAP), and LocalTalk Link Access Protocol (LLAP).

The AppleTalk Address Resolution Protocol (AARP), which translates hardware addresses to AppleTalk addresses, also exists at the datalink layer