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Advertising and Advertising Services
Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.
Advertising is a technique used by a server to announce the services it has available. Advertising was traditionally used in the NetWare environment, although that has changed recently. The NetWare operating system used SAP (Service Advertising Protocol) to broadcast information about available services on the network that other network devices can listen to. A server sends out SAP messages every 60 seconds. A server also sends out SAP messages to inform other devices that it is closing down. Workstations use SAP to find services they need on the network. For example, a workstation can send a SAP message to a local router to obtain the address of a node on another network.
SAP is a legacy protocol that has been used in almost all versions of NetWare. However, excessive SAP messages can sap network throughput. In NetWare 4, NDS (Novell Directory Services) helps reduce the need for SAP because the NDS database can be consulted for service locations. However, SAP is still used on NetWare 4.x networks because many network devices require it.
While SAP and similar protocols provide a way to advertise services on local networks, services on the Web are found using search services, word of mouth, or paid advertisements that catch the eye of readers and viewers. Recently, several methods have been proposed to help users locate services in domains on the Internet. The Service Location Protocol described in RFC 2165 eliminates the need for a user to know the DNS name of a host that provides a particular service. Instead, users can find services by specifying the type of service they need along with attributes of that service. Refer to "SLP (Service Location Protocol)" for more information.
Another scheme is the Dublin Core Metadata Initiative, which is working to develop conventions for resource discovery on the Web. Metadata refers to data structure that describes some other data, just like a library card describes a book. The Dublin Core is designed to provide a flexible way to represent resources and relationships among resources in both traditional and digital formats that simplify resource discovery. Refer to "Dublin Core" for more information.
Still another protocol, PIP (Presence Information Protocol), provides a way to alert users when another user logs on, thus allowing those users to exchange instant messages.
Emerging service advertising techniques are discussed under "Service Advertising and Discovery."
Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.