0000 = FC-4 Device Data 0010 = Extended Link Data 0011 = FC-4 Link Data 0100 = Video Data 1000 = Basic Link Data 1100 = Link Control Others = Reserved
Information
0000 = Uncategorized information 0001 = Solicited Data 0010 = Unsolicited Control 0011 = Solicited Control 0100 = Unsolicited Data 0101 = Data Descriptor 0111 = Command Status Others = Unspecified
DF_CTL
S_ID D_ID
F_CTL
SEQ_CNT RX_ID
– R_CTL differentiates frames based on function
The R_CTL field differentiates frames based on function or service within an N_Port or F_Port. The R_CTL field consists of two 4-bit subfields that identify the category and function of the frame:
• The Routing Bits identify the category of the frame. For example, link control frames are differentiated from data frames.
• The Information Bits further define the type of data in the frame. For example, SCSI-FCP frames use different codes in this subfield to differentiate data frames from command and status frames.
For example, a Fabric Login (FLOGI) frame has a R_CTL field of 0010 0010, indicating that it is an unsolicited Extended Link Services (ELS) frame. Link Services are used for session management functions, such as login.