Legacy Document

Inside Macintosh: Networking /

Chapter 1 - Introduction to AppleTalk / Deciding Which AppleTalk Protocol to Use

Performing a Transaction

If you want to write an application that performs a transaction, you can use the AppleTalk Transaction Protocol (ATP). A transaction is an interaction between two applications that are clients of ATP in which one application, known as the requester, sends a request to the other application, known as the responder, to perform a task and return a response that reports the outcome of the task. The transaction request must fit in a single packet; however, the response can contain up to eight packets. ATP transactions are an efficient means of transporting small amounts of data across the network. ATP provides a reliable loss-free transport service. ATP's means of ensuring reliable delivery of data is based on the request-response paradigm as opposed to the data stream model that ADSP uses for reliable delivery of data.

You should use ATP

• if you want to send a small amount of data
• if your application requires delivery of all packets
• if your application can tolerate a minor degree of performance degradation
• if you do not want to incur the overhead and more extensive performance degradation involved in maintaining a session

ATP is useful for collecting status information; for example, a network management application might include a responder program on each node to which the central application sends out ATP requests asking for version information, such as the version of AppleTalk that the node is running. The responder program could check the version and send the information back to the main application in response to the request. Games that are based on request-and-response types of dialogs can make efficient use of ATP.