SnaBase runs on both client and server computers, but performs slightly different functions on each. SnaBase dynamically maintains a service table of SNA Server computers, links, and invokable transaction programs (TPs) in the subdomain. It supports client-sponsor connections that are used to send the server list to the client. It is also is responsible for initializing SnaDMOD and uses SnaDMOD to send messages to other components in the network by means of sponsor connections.
A sponsor connection is an initial connection between a client and an SNA Server computer. This connection provides the client with the names of all the SNA Server computers in the subdomain. The client uses these names to locate resources, such as LUs, in the network. For example, if a resource is an LU, the server SnaBase provides the client with the name of the server on which the LU resides. If the resource is an LU pool, the server provides the client with a list of servers associated with the pooled LUs. The client tries each server in random order until it finds a server with a free LU.
SnaBase on a server computer also initializes shared memory updates. The information that SnaBase sends depends on whether it is directed to the client or another SNA Server computer in the subdomain.
When the information is sent to the client, SnaBase determines the size and the list of servers available to the client, based on the operating system of the client computer (Windows NT, Windows 95, Windows 3.x, DOS, Macintosh, OS/2, or UNIX). Usually, the information is limited to a list of SNA Server computers in the subdomain.
On a Windows NT Server computer, SnaBase provides the complete service table, including the names of SNA Server computers (also referred to as nodes) in the subdomain, all available services, invokable TPs, and APPC information. All of these are updated frequently using server-to-server broadcasts or directed datagrams depending on the server-to-server communication protocol.