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BOX C, SNF SYSTEM TYPESSNF systemServes as the root of the entire system hierarchyand provides a minimum set of interfaceswith which each system must comply. Everysystem type must provide the services providedby the SNF system. The SNF system thusserves as a template specification for everysystem in the service network.SNF applicationIs responsible for providing services that areconsumed directly by users.SNF enablerIs responsible for providing services that areconsumed by application systems. The SNFdefines various enablers, such as the commondirectory system (CDS), which serves as acentral directory for user- and service-relateddata that exposes a lightweight directoryaccess protocol (LDAP) interface.SNF gatewayIs responsible for providing services that allowsystems to delegate protocol handling or conversiontasks. The SNF defines various gateways,such as the border gateway (BGW),which supports single sign-on for HTTP traffic.SNF managerIs responsible for providing service networkwideservices. The SNF defines various managers,such as the central provisioning entity(CPE).The IP network is a key aspect of the deploymentenvironment for every system inthe service network.The SNF deployment view provides guidancefor ensuring that the IP network possessesa set of common services and qualitieson which every deployed system can rely.Examples of common services include naming,addressing, routing, load-balancing,firewall and security gateway services. Likewise,common qualities include performance,scalability, flexibility, security, andhigh availability.Figure 8 is a conceptual depiction of howsystems are deployed ro, and make use of,an IP network with various common servicesand qualities.Figure 9 shows an example of how a highlyavailable IP network infrastructure can berealized when systems are deployed onto virtuallocal area networks (VLAN). In rhis example,the application servers have been deployedon VLAN 1, whereas rhe gatewayshave been deployed on VLAN N.Tier viewThe use of N-tier architectures is an acceptedand proven approach toward partitioningor organizing distributed computing architecturesthat require high levels of scalabilityand availability. The SNF recommendsthat N-tier architecture should be employedfor organizing systems into scalable andavailable solutions in a distributed computingenvironment.The various tiers include client, presentation,business, integration, resource, anddata. The client tier is concerned with everydevice that accesses systems or applications.Figure 8SNF deployment view.Ericsson Review No. 1, 2003 23