Summary

A major difference between the TCP/IP model and the FC model is the manner in which end-to-end delivery mechanisms are implemented. With TCP/IP, the transport layer protocol determines which end-to-end delivery mechanisms are provided. By contrast, FC does not implement distinct transport layer protocols. Instead, the Class of Service determines which end-to-end delivery mechanisms are provided. One feature common to both the TCP/IP and FC models is the ability to negotiate which end-to-end delivery mechanisms will be used between each pair of communicating nodes. For TCP, this is accomplished via the three-way handshake procedure. For UDP, no such negotiation occurs. For FC, this is accomplished via the PLOGI procedure. Whereas the TCP/IP suite offers multiple transport layer protocols, most data is transmitted using TCP and UDP. TCP is connection-oriented and guarantees delivery, while UDP is connectionless and does not guarantee delivery. The nature of the source application determines whether TCP or UDP is appropriate. Similarly, FC offers multiple Classes of Service. However, the vast majority of modern FC-SANs are configured to use only Class 3 service regardless of the nature of the source application. Class 3 service blends the features of TCP and UDP. Like TCP, Class 3 service is connection-oriented. Like UDP, Class 3 service does not guarantee delivery.