Fibre Channel Data Constructs Ordered Sets and Primitives
Ordered Sets
• An Ordered Set is a command that:
–Is a single word – Is not part of a frame (except when it’s a delimiter) – Is not addressable – Has K28.5 as the first character
Frames
Ordered Set
K28.5
Data
Data
Data
When a node transmits data to another node, FC packages that data into frames. Frames are used to transport both data and FC control signals. However, there are a few simple command signals that ports must use frequently to perform basic link synchronization and flow control functions. Wrapping an entire frame around each one of these command signals would waste bandwidth and increase latency.
In FC, the smallest unit of data is the word, which is a 4-byte unit of data. All of the data that flows across an FC network—frame headers, control signals, and even the application data that is being sent from node to node—consists of a series of 4-byte words. FC designates special words to be used as simple command signals. These signals are called Ordered Sets.