| FC Layers Fibre Channel is a standards-based, layered architecture. FC-0 defines the physical interface, which may be optical or copper. FC-1 provides low-level link controls and data encoding for gigabit transport. FC-2 defines segmentation and reassembly of data via frames, flow control, and classes of service. FC-3 is being developed for common services. FC-4 is the Upper layer protocol interface between Fibre Channel and IP, SCSI-3, and other protocols. Gigabit and 2Gbps Transport Fibre Channel supports 1Gbps and 2Gbps transmission rates. Fibre Channel standards enforce a 10 12 bit error rate. Timing deviation is referred to as jitter. Fibre Channel network components are assigned a jitter budget; if the budget is exceeded, excessive errors may occur. 10Gbps Fibre Channel will be based on 10Gbps Ethernet transport standards. Physical Layer Options Fibre Channel supports both optical and copper media. The maximum distance for intracabinet copper is 13 meters. The maximum distance for intercabinet copper is 30 meters. Shortwave laser supports up to 500 meters on 50mm/125mm multimode cable. Longwave laser supports up to 10 kilometers on 9mm/125mm single-mode cable. The most commonly used transceivers are GBICs and small form factor transceivers. Data Encoding For reliable transport at gigabit speeds, data must be encoded. 8b/10b encoding converts 8-bit bytes into 10-bit characters. The special K28.5 character is used to indicate Fibre Channel commands. Running disparity is used to maintain balanced signaling. Ordered Sets A Fibre Channel word is four 10-bit characters. Words with K28.5 in the first character position are ordered sets. Ordered sets are used as frame delimiters, primitive signals, and primitive sequences for low-level transport protocol. Framing Protocol Data is segmented into frames for transport. The maximum frame size is 2,148 bytes, with 2,112 bytes of payload. Frames are transmitted as sequences of related frames. An exchange can include multiple sequences. Class of Service Class 1 service is a dedicated connection between two communicators with acknowledgment of frame delivery. Class 2 service is connectionless but provides acknowledgment. Class 3 service is connectionless and provides no notification of delivery. Class 4 allows fractional bandwidth for virtual circuits. Class 6 provides multicast with acknowledgment. Class F is used for switch-to-switch communications in a fabric. Flow Control Flow control is maintained by a credit scheme between communicators and prevents a target from being overwhelmed with frames. End-to-end credit is monitored by the communicating nodes and is replenished by acknowledgments. Buffer-to-buffer credit is replenished by receiver-ready (R_RDY) primitives. An alternative buffer-to-buffer credit is used by arbitrated loop. Naming and Addressing Conventions A node is a communicating device. A node is identified by a unique 8-byte node name, or World-Wide Name. A node may contain multiple ports, or N_Ports, each of which has a unique 8-byte port name. Each N_Port has a 24-bit port address, or N_Port ID, used for frame routing. A Fibre Channel fabric switch port is an F_Port for attachment to N_Ports, or an FL_Port when attached to arbitrated loop FL_Ports. An E_Port is a fabric switch expansion port used to connect fabrics. A G_Port can support either node or expansion port attachment. A GL_Port can support node, loop, or expansion port attachment. A B_Port is a bridge port used to connect fabrics to non-Fibre Channel interconnects or networks. |
