Legacy Document

Inside Macintosh: Networking /

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

The LAP Manager

The LAP Manager acts as an interface between the link types and the higher-level AppleTalk protocols. The LAP Manager contains a protocol handler that it attaches directly to the hardware device driver to receive 802.2 Type 1 packets for Ethernet, token ring, and FDDI. If your application handles 802.2 Type 1 packets, you must provide a protocol handler to read the packets and install your protocol handler as a client of the LAP Manager. A protocol handler is a piece of assembly-language code that controls
the reception of a packet of a particular protocol type. When an 802.2 packet for your application arrives, the LAP Manager will call your protocol handler to read the packet.

The LAP Manager also provides and maintains a service called the AppleTalk Transition Queue (ATQ) that you can use to ensure that your application is not adversely affected when an AppleTalk transition occurs.

An example of an AppleTalk transition is an AppleTalk driver being closed or opened
by another routine or the operating system. At any given time, there might be two or more applications running that use AppleTalk. If one of these applications closes the AppleTalk drivers, all AppleTalk applications are affected.

Your application can register itself with the AppleTalk Transition Queue by placing an entry in the queue. The LAP Manager sends a message to each entry in the AppleTalk Transition Queue when a transition occurs. Your application or other routines can also define their own AppleTalk events and call the AppleTalk Transition Queue to inform it that such an event occurred.

The AppleTalk Transition Queue also allows an application that uses the Flagship Naming Service to place an entry in the queue that enables it to stay informed as to changes to the flagship name. A flagship name is a personalized name that users can enter to identify their nodes when they are connected to an AppleTalk network. The flagship name is different from the Chooser name that a node uses for server-connection identification. The LAP Manager uses the transition queue message system to communi-
cate name changes between applications and processes whenever the user resets the flagship name.

The chapter "Link-Access Protocol (LAP) Manager" in this book describes the LAP Manager services and interface. For more information about the LAP Manager, see
the Macintosh AppleTalk Connection Programmer's Guide.

Using AppleTalk's link independence to write portable applications

If you write an application that uses one of the high-level AppleTalk protocols, such as ADSP or ATP, your program will run over any link type. A user running your application can switch between link types, for example, move from one type of network, such as token ring, to another, such as Ethernet, without affecting your program. The LAP Manager handles the interface and connection to the correct link-access protocol based on the link type the user selects.