The FC architecture represents true channel/network integration with standard interconnecting devices. Channel technologies provide high levels of performance with low protocol overheads. Such performance is due to the static nature of channels and the high level of hardware and software integration provided by the channel technologies. However, these technologies suffer from inherent limitations in terms of the number of devices that can be connected and the distance between these devices.
Fibre Channel Protocol (FCP) is the implementation of serial SCSI-3 over anFC network. In the FCP architecture, all external and remote storage devices attached to the SAN appear as local devices to the host operating system. The key advantages of FCP are as follows:
- Sustained transmission bandwidth over long distances.
- Support for a larger number of addressable devices over a network. Theoretically, FC can support over 15 million device addresses on a network.
- Exhibits the characteristics of channel transport and provides speeds up to 8.5 Gb/s (8 GFC).
The FC standard enables mapping several existing Upper Layer Protocols (ULPs) to FC frames for transmission, including SCSI, IP, High Performance Parallel Interface (HIPPI), Enterprise System Connection (ESCON), and Asynchronous Transfer Mode (ATM).
Fibre Channel Protocol Stack:
FCP defines the communication protocol in five layers: FC-0 through FC-4 (except FC-3 layer, which is not implemented). In a layered communication model, the peer layers on each node talk to each other through defined protocols. Following figure illustrates the fibre channel protocol stack.
- Fibre Channel Addressing:
FC Address is assigned during Fabric Login. It is used to communicate between nodes within SAN. It is Similar in functionality to an IP address on NICs.
World Wide Names
Each device in the FC environment is assigned a 64-bit unique identifier called the World Wide Name (WWN). The Fibre Channel environment uses two types of WWNs: World Wide Node Name (WWNN) and World Wide Port Name (WWPN). Unlike an FC address, which is assigned dynamically, a WWN is a static name for each device on an FC network.WWNs are burned into the hardware or assigned through software.
- FC Frame
Frame is fundamental unit of data transfer.Each frame can contain up to 2112 bytes of payload.An FC frame consists of five parts: start of frame (SOF), frame header, data field, cyclic redundancy check (CRC), and end of frame (EOF).The SOF and EOF act as delimiters. In addition to this role, the SOF is a flag that indicates whether the frame is the first frame in a sequence of frames.The frame header is 24 bytes long and contains addressing information for the frame.