Introduction

A significant problem in designing data communications systems, especially systems that are targeted toward transmitting many types of data or message traffic, is that different types of traffic patterns require different kinds of network performance. For example, some kinds of traffic require long-term data transfer between pairs of Nodes, while others require a single Port to send small pieces of data to multiple destination Nodes in turn. A network architecture which is optimized for one kind of traffic pattern may not perform well at all on a different traffic pattern, since efficient flow control and routing control algorithms depend on the traffic patterns of the data transmission.

To address these issues, the Fibre Channel architecture allows the N_Port sending data to give the network help in determining what kind of performance is needed. This is done by specifying that the data is to be sent in one of three Classes of service. The Class of service used for transmission determines what type of flow control will be used for the Sequence and what resources are required to handle transmission.

Following are the general characteristics of the various Classes of service:

Class 1: provides Dedicated Connections, where a Sequence Initiator requests that all the links and related resources on the route to the Sequence Recipient are guaranteed for the duration of a communication period, possibly including multiple Sequences and Exchanges, until either the Initiator or Recipient requests that the Connection be removed.

Class 2: provides a...