Just as RIP enables routers to exchange routing information, SAP enables networked devices, such as network servers and routers, to exchange information about available network services. Servers and routers use SAP to advertise their services and network addresses. SAP enables network devices to constantly correct their information about which network services are available. While servers are running, they use SAP to inform the rest of the network of the services they offer. When a server goes down, it uses SAP to inform the network that its services are no longer available.
Routers gather service information and share it with other routers.
Workstations use the information made available through SAP to obtain the network addresses of servers that offer the services they need. Sequenced Packet Exchange SPX is a transport-layer protocol. Accordingly, SPX provides guaranteed packet delivery and packet sequencing. Like NCP, SPX does not play a direct role in routing. SPX is connected with internetworking only in that it guarantees delivery of all routed packets.