System Administration Guide: Network Services

SLP Agents and Processes

The following table describes the SLP agents. For expanded definitions of these terms and other terms that are used in this volume, refer to the Glossary.

Table 7–1 SLP Agents

SLP Agent 



Directory Agent (DA) 

Process that caches SLP advertisements that are registered by Service Agents (SAs). The DA forwards service advertisements to User Agents (UAs) on demand. 


Service Agent (SA) 

SLP agent that acts on behalf of a service to distribute service advertisements and to register the service with Directory Agents (DAs). 


User Agent (UA) 

SLP agent that acts on behalf of a user or application to obtain service advertisement information. 



An administrative or logical grouping of services. 


The following figure shows the basic agents and processes that implement the SLP architecture. The figure represents a default deployment of SLP. No special configuration has been done. Only two agents are required: the UA and SA. The SLP framework allows the UA to multicast requests for services to the SA. The SA unicasts a reply to the UA. For example, when the UA sends a service request message, the SA responds with a service reply message. The service reply contains the location of services that match the client's requirements. Other requests and replies are possible for attributes and service types. For more information, see Chapter 11, SLP (Reference).

Figure 7–1 SLP Basic Agents and Processes

The context describes the graphic.

The following figure shows the basic agents and processes that implement the SLP architecture when a DA is deployed in the framework.

Figure 7–2 SLP Architectural Agents and Processes Implemented With a DA

The context describes the graphic.

When you deploy DAs, fewer messages are sent in the network and UAs can retrieve information much faster. DAs are essential when the size of a network increases or for situations in which there is no support for multicast routing. The DA serves as a cache for registered service advertisements. SAs send register messages (SrvReg) that list all the services they advertise to DAs. SAs then receive acknowledgments (SrvAck) in reply. The service advertisements are refreshed with the DA, or they expire according to the lifetime that is set for the advertisement. After a UA discovers a DA, the UA unicasts a request to the DA rather than multicasting requests to SAs.

For more information about Solaris SLP messages, refer to Chapter 11, SLP (Reference).