Inside Macintosh: Networking /

Chapter 8 - AppleTalk Session Protocol (ASP)

This chapter describes the AppleTalk Session Protocol (ASP) that you can use to establish a session between an ASP workstation application or process and an ASP server application. An ASP session is asymmetrical: all communication is initiated by the ASP workstation and responded to by the ASP server.

ASP provides an application programming interface for the workstation side only. ASP is not commonly used by application program developers. The primary use of ASP is to provide services for the AppleTalk Filing Protocol (AFP) that, in turn, provides all of the services necessary to access an AppleTalk AppleShare server. Most developers who want to write an AppleTalk application that establishes a session use the AppleTalk Data Stream Protocol (ADSP) because it provides peer-to-peer services. For these reasons, this chapter includes "About" and "Reference" sections only; it does not include a "Using" section, as do most of the other chapters in this book. This chapter is included to complete the coverage of the AppleTalk protocol stack in this book.

However, if you want to use ASP to write an application that runs on a workstation
and initiates a session with an ASP server, you should read this chapter and the chapter in Inside AppleTalk, second edition, that describes the AppleTalk Session Protocol specification.

You can use ASP to open and close a session with an ASP server; you can also send commands and data across the session to the server and receive replies in response.
The commands that you send to the ASP server must adhere to the syntax of a higher-
level protocol that is built on top of the ASP server. ASP transfers the commands; it
does not interpret or execute them.

This chapter does not describe how to implement an ASP server. If you want to implement an ASP server, you must use the programming interface to the AppleTalk Transaction Protocol (ATP) and follow the AppleTalk Session Protocol specification
as defined in Inside AppleTalk, second edition.

If you want to write an application that supports a peer-to-peer session in which each end of the session can send and receive data at any time, you should use the AppleTalk Data Stream Protocol (ADSP) instead of ASP. The chapter "AppleTalk Data Stream Protocol (ADSP)" in this book describes ADSP.

For an overview of ASP and how it fits within the AppleTalk protocol stack, read the chapter "Introduction to AppleTalk" in this book. "Introduction to AppleTalk" also introduces and defines some of the terminology used in this chapter. Because ASP is built on top of ATP, possessing an understanding of ATP will help you to understand ASP. The chapter "AppleTalk Transaction Protocol (ATP)" in this book describes ATP.

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Chapter Contents

About ASP

ASP Reference

Data Structures

XPP Parameter Block for ASP

Routines

Opening and Closing ASP Sessions

Sending Commands and Writing Data From the Workstation to the Server

Obtaining Information About ASP's Maximum Capacities and the Status of the Server

Canceling an ASP Request to Open a Session

Summary of ASP

Pascal Summary

Constants

Data Types

Address Block Record

XPP Parameter Block for ASP

Routines

Opening and Closing ASP Sessions

Sending Commands and Writing Data From the Workstation to the Server

Obtaining Information About ASP's Maximum Capacities and the Status of the Server

Canceling an ASP Request to Open a Session

C Summary

Constants

Data Types

Address Block Record

XPP Parameter Block for ASP

Routines

Opening and Closing ASP Sessions

Sending Commands and Writing Data From the Workstation to the Server

Obtaining Information About ASP's Maximum Capacities and the Status of the Server

Canceling an ASP Request to Open a Session

Assembly-Language Summary

Constants

Offsets in User Bytes

Offsets in ATP Data Part

Command Codes (csCodes)

ASP Commands

Miscellaneous

Data Structures

XPP Parameter Block Common Fields for ASP Routines

ASPOpenSession Parameter Block

ASPCloseSession Parameter Block

ASPCloseAll Parameter Block

ASPUserCommand Parameter Block

ASPUserWrite Parameter Block

ASPGetParms Parameter Block

ASPGetStatus Parameter Block

ASPAbortOS Parameter Block

Result Codes