Inside Macintosh: Networking /

Chapter 6 - AppleTalk Transaction Protocol (ATP)

This chapter describes the AppleTalk Transaction Protocol (ATP) that you use to send
a request from one application or process to another that can satisfy the request and respond to it. Because ATP is transaction-based--that is, the response data is bound to the request data and the exchange of information is limited to the transaction--you do not incur the overhead entailed in establishing, maintaining, and breaking a connection that is associated with connection-oriented protocols, such as ADSP. However, you can transfer only a limited amount of data using ATP.

You should read this chapter if you want to write an application that requires reliable delivery of data while allowing one side of the communication to ask the other side to perform a service and return a small amount of data.

For an overview of ATP and how it fits within the AppleTalk protocol stack, read the chapter "Introduction to AppleTalk" in this book, which also introduces and defines some of the terminology used in this chapter. For complete explanation of the ATP specification, see Inside AppleTalk, second edition.

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Chapter Contents

About ATP

The ATP Packet Format

The Control Information Byte

The Bitmap/Sequence Number

The Transaction ID

User Bytes

At-Least-Once and Exactly-Once Transactions

The Buffer Data Structure

ATP Flags

Using ATP

Writing a Requester ATP Application

Creating a Buffer Data Structure

Specifying the Parameters for the Send Request Function

Setting the Timeout and Retry Count Parameters

Setting the Release Timer Value

Writing a Responder ATP Application

Opening and Setting Up a Socket to Receive Requests

Responding to Requests

Canceling an ATP Function

ATP Reference

Data Structures

The Buffer Data Structure

The ATP Parameter Block

The Address Block Record

Routines

Sending an ATP Request

Opening and Closing an ATP Socket

Setting Up a Socket to Listen for Requests

Responding to Requests

Canceling Pending ATP Functions

Building a Buffer Data Structure

Summary of ATP

Pascal Summary

Constants

Data Types

The Buffer Data Structure

The Address Block Record

The ATP Parameter Block

Routines

Sending an ATP Request

Opening and Closing an ATP Socket

Setting Up a Socket to Listen for Requests

Responding to Requests

Canceling Pending ATP Functions

Building a Buffer Data Structure

C Summary

Constants

Data Types

The Buffer Data Structure

The Address Block Record

The ATP Parameter Block

Routines

Sending an ATP Request

Opening and Closing an ATP Socket

Setting Up a Socket to Listen for Requests

Responding to Requests

Canceling Pending ATP Functions

Building a Buffer Data Structure

Assembly-Language Summary

Constants

ATP Header

ATP Control Field

ATP Type Code

ATP Limits

ATP Command Codes

ATPQueue Element Standard Structure

ATP Bits

Data Structures

Buffer Data Structure (BDS)

ATP Parameter Block Common Fields

SendRequest Parameter Variant

NSendRequest Parameter Variant

OpenATPSkt Parameter Variant

CloseATPSkt Parameter Variant

GetRequest Parameter Variant

SendResponse Parameter Variant

AddResponse Parameter Variant

KillSendReq Parameter Variant

RelTCB Parameter Variant

KillGetReq Parameter Variant

KillAllGetReq Parameter Variant

RelRspCB Parameter Variant

Result Codes