Legacy Document
Important: The information in this document is obsolete and should not be used for new development.
Important: The information in this document is obsolete and should not be used for new development.
Sending and Receiving Data as Discrete Packets
Your application can use the Datagram Delivery Protocol (DDP) to transmit data in the form of packets across an AppleTalk internet. Because DDP provides best-effort delivery of datagrams with no recovery when packets are lost or discarded because of errors, it involves less overhead and provides for faster performance than do the higher-level protocols that add reliable delivery.For applications, such as some games that don't require reliable delivery of data and can tolerate possible packet loss or diagnostic tools that retransmit at regular intervals to estimate averages, DDP suffices, and it offers the value of good performance. In fact, if you develop a game application that limits players to nodes on a single network, DDP will use short addressing headers on packets, requiring 8 fewer bytes per packet, which are faster to send.
If you are a network software developer who wants to develop a session-oriented protocol, a client-server protocol, or a transaction-based protocol that offers services different from those provided by ADSP, ASP, or ATP, you can design and implement your protocol as a client of DDP. However, this can entail providing your own server implementation in some cases. For a detailed description of DDP and the other AppleTalk protocols, see Inside AppleTalk, second edition.
If you use the DDP interface, you must provide a process called a socket listener to receive datagrams addressed to the socket. The chapter "Datagram Delivery Protocol (DDP)" in this book describes how to write a socket listener.