Introduction

The establishment of Class 1 Dedicated Connections for providing guaranteed access and interference-free bandwidth over a multi-N_Port Fabric environment is one of the most distinctive features of the Fibre Channel architecture. It can also be one of the more difficult features for a vendor to support, since it can involve some delicate design problems, it involves close interaction between switch and N_Port elements of the network, and it is an unusual facility for communications networks to provide. It is for these reasons that a good portion of the standards work has been based on assuring that Class 1 Dedicated Connection service can be provided without unduly hurting performance. Class 1 Dedicated Connection management will be covered in somewhat more detail in this chapter than some other parts of the protocol have been.

Utility of Class 1 Dedicated Connections is strongly dependent on the topology used for interconnecting the N_Ports. A Class 1 Dedicated Connection provides a guarantee of service to a pair of communicating N_Ports, ensuring that the full link bandwidth is available to both. In a Point-to-point topology, this is largely guaranteed anyway, since there is no contention for transmission resources with other N_Ports. Similarly, on an Arbitrated Loop topology, provision of full transmission resources is straightforward since the architecture of the Loop arbitration, described in Chapter 16, assures that communication between two N_Ports is essentially identical to point-to-point communications, once Loop access is won. However, on a Fabric topology, establishing a Dedicated Connection requires coordination between switch...