Chapter 12 - Datagram Delivery Protocol (DDP)
This chapter describes how Open Transport implements the Datagram Delivery Protocol (DDP). It explains how you can use DDP to send and receive data across an AppleTalk internet. DDP is a connectionless transactionless service that you use to transmit data in discrete packets, each carrying its own addressing information. DDP is well suited to applications that do not require reliable delivery of data and that do not want to incur the additional processing associated with setting up and breaking down a connection. Because DDP is connectionless and does not include reliability services, it offers faster performance than do the higher-level protocols that add these services. Applications such as diagnostic tools that retransmit packets at regular intervals to estimate averages or such as games that can tolerate packet loss are good candidates for the use of DDP.A series of DDP packets transmitted over an AppleTalk internet from one node to another might incur some packet loss, for example, as a result of collisions. If you do not plan on implementing recovery from packet loss in your application, but your application requires it, you can consider using an AppleTalk transport protocol such as the AppleTalk Data Stream Protocol (ADSP) or the AppleTalk Transaction Protocol (ATP). These protocols protect against packet loss and ensure reliability by using positive acknowledgment with mechanisms for retransmitting packets.
This chapter explains how you
This chapter begins with a description of DDP and the services that it provides under Open Transport. The section "Using Open Transport Functions With DDP" then gives detailed information about how DDP client applications use the endpoint functions that Open Transport provides for connectionless transactionless protocols. For a more detailed explanation of endpoints and their functions, read the chapter "Endpoints" in this book.
- open and bind a DDP endpoint
- send and receive data using DDP
- set checksum options to verify that a packet has not been corrupted during transmission
- use echo packets to measure network performance
- use multinodes
For an overview of DDP 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 more information about the AppleTalk address formats, see the chapter "AppleTalk Addressing" in this book. For a complete explanation of the DDP specification, see Inside AppleTalk, second edition.
Chapter Contents
- About DDP
- Using DDP
- Binding a DDP Endpoint
- Using the DDP Type Field to Filter Packet Delivery
- Using the Self-Send and Checksum Options
- Using Echo Packets
- Working With Multinodes
- The DDP Source Address Option
- Using General Open Transport Functions With DDP
- OTBind
- OTSndUData
- OTRcvUData
- DDP Reference
- Options