TABLE OF CONTENTS In addition to normal data transmission procedures, any communications protocol requires procedures for performing link level and setup operations such as controlling link status, polling other Ports for verification of the status of various operations, and for aborting operations already begun, in case of errors. Under Fibre Channel, these operations are provided for under the heading Link Services.
There are three types of Link Services:
Basic Link Services, which are distinguished by being single Frame commands that can either be sent inside an existing Sequence or inside a newly initiated one;
Extended Link Services, which are transmitted within their own Exchange, as independent operations separate from any ongoing communication; and
FC-4 Link Services, which follow the same procedures used for Basic and Extended Link Services in performing FC-4 level operations.
The Link Service Frames and Sequences are composed of Link Data Frames and operate according to the normal R_RDY Primitive Signal and the Link Control Frame (ACK, RJT, and BSY) response rules used for Data Frames. Basic Link Service Frames cannot contain optional headers, so the DF_CTL Frame Header field is meaningless on these Frames. The Extended Link Service and FC-4 Link Data Frames may contain only the Expiration/Security optional header. Link Service Frames can be sent in any supported Class of service.
The Basic Link Service commands are shown in Figure 11.1. All Basic Link Service commands must be supported by all N_Ports. Five Basic Link Service commands are defined: three...
