Inside Macintosh: Networking With Open Transport / Part 1 - Open Transport Essentials

Chapter 1 - Introduction to Open Transport

Introduction to Open Transport

Open Transport is the networking architecture used by Apple Computer, Inc. for Mac OS computers. Whereas AppleTalk provided a proprietary networking system for Macintosh computers, the current Macintosh OS with Open Transport provides not only AppleTalk but also the industry-standard TCP/IP protocols and serial connections. In addition, the Open Transport architecture allows developers to add other networking systems to the Macintosh Operating System without altering the user experience or the application programming interface (API).

The independence of the APIs from the underlying networking or transport technology is called transport independence and is one of the cardinal features of Open Transport. This feature is described in more detail in "Transport Independence".

Other important features of Open Transport are its support of multihoming and multinodes.

• Multihoming allows multiple Ethernet, token ring, FDDI, and other network interface controller (NIC) cards to be active on a single computer at the same time. This feature is currently available only for AppleTalk protocols. Single link multihoming, introduced with Open Transport version 1.3, supports multiple IP addresses on the same hardware interface. This feature is available only to TCP/IP protocols.

• Multinode support is an AppleTalk feature that allows an application to acquire node IDs in addition to the standard node ID that is assigned to the system when the node joins an AppleTalk network. The prime example of a multinode application is Apple Remote Access (ARA). The chapters "AppleTalk Addressing" and "Datagram Delivery Protocol (DDP)" in this book describe the use of multinodes.