Back to: FC (Fibre Channel) fundamentals
The Fibre Channel (FC) Frame Structure is the fundamental unit of data transmission in a Fibre Channel network. It consists of several fields that help ensure data integrity, control, and efficient communication between storage devices and hosts. Here’s a breakdown of the FC frame structure:
FC Frame Format
An FC frame is 2148 bytes in total, comprising the following components:
- Start of Frame (SOF) – 4 bytes
- Marks the beginning of the frame.
- Defines the class of service and sequence coordination.
- Helps in synchronization.
- Frame Header – 24 bytes
- Contains control information like:
- Destination ID (D_ID) – Identifies the recipient.
- Source ID (S_ID) – Identifies the sender.
- Type Field – Defines the frame type (data, control, etc.).
- Sequence ID and Exchange ID – Manage data ordering and flow control.
- Contains control information like:
- Payload – Up to 2112 bytes
- Carries actual data being transmitted.
- Maximum size can be 2112 bytes, but it can be smaller.
- Cyclic Redundancy Check (CRC) – 4 bytes
- Ensures data integrity by detecting errors in transmission.
- End of Frame (EOF) – 4 bytes
- Marks the end of the frame.
- Indicates the frame’s validity and helps with flow control.
FC Frame Transmission Process
- The FC frame is encapsulated within an ordered set.
- SOF signals the start, and EOF signals the end of transmission.
- The frame header ensures the correct routing and delivery of the frame.
- CRC ensures data integrity by detecting transmission errors.
Key Features of FC Frames
- Reliable Delivery: Uses acknowledgments and flow control.
- Supports Multiple Classes of Service: Class 1 (Dedicated), Class 2 (Connectionless), and Class 3 (Best-effort).
- High Speed and Low Latency: Optimized for SAN environments.