7-10 CHAPTER 7: ROUTING IN AN APPLETALK® ENVIRONMENT

AppleTalk Data Stream Protocol (ADSP). The ADSP works with the ATP to ensure reliable data transmission. Unlike ATP, however, ADSP provides full-duplex byte-stream delivery. This means that two nodes can communicate simultaneously. ASDP also includes flow control, so that a fast sender does not overwhelm a slow receiver.

AppleTalk Session Protocol (ASP). The ASP passes commands between a workstation and a server once a connection is made between the two. ASP ensures that the commands are delivered in the same order as they were sent and returns the results of these commands to the workstation.

Printer Access Protocol (PAP). The PAP maintains communications between a workstation and a printer or print service. The PAP functions include setting up and maintaining a connection, transferring the data, and tearing down the connection on completion of the job. Like other protocols at the session layer, PAP relies on NBP to find the addresses of named entities. PAP also depends on ATP for sending data.

Presentation Layer The presentation layer maintains information about files, formats, and

 

translations between formats. An AppleTalk internet has two protocols at

 

the presentation layer: the AppleTalk Filing Protocol (AFP) and PostScript®.

 

AFP provides remote access to files on the network. PostScript is a paged

 

description language used by many printers.

 

 

About AARP

The AppleTalk Address Resolution Protocol (AARP) maps the hardware

 

address of an AppleTalk node to an AppleTalk protocol address. It does this

 

mapping for both extended and nonextended networks.

 

When a node on the network initializes, it randomly selects an AppleTalk

 

address for itself. At the same time, it sends out ten AARP probe packets.

 

The probe packets determine whether any other nodes on the network are

 

using the address it has chosen. If a node on the network is already using

 

that address, the node randomly selects another address and sends out

 

another probe packet.

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3Com 2500 manual About Aarp, Description language used by many printers, Mapping for both extended and nonextended networks