Page 9 of 18 March 2001 Fibre Channel: Why another interface? The Fibre Channel approach to data transfer During a Fibre Channel data transfer, hardware in the sending device segments each data block or information unit into a sequence of data structures called “frames.” These frames are analogous to packets in traditional network protocols. Each frame can contain up to 2,112 bytes of information (compared to 1,500 bytes per packet for Ethernet), plus addressing and error correction information. If the information unit fits within a single frame, a single-frame sequence is used to transport the information to the recipient. When the information unit is too large to fit in a single frame, the Fibre Channel hardware combines multiple frames into a sequence. Up to 65,536 frames can be concatenated into a single sequence. The use of sequences reduces the amount of processor overhead during the transfer of very large files by minimizing the time required to process individual frames. The sequenced data is transmitted over a serial cable to the recipient. The recipient breaks each sequence into frames and reassembles the information units in the individual frames to reconstruct the original application data, which is then delivered to the recipient CPU for higher-level processing. The use of sequences makes transferring large blocks of information with minimum processor interruption possible. Hardware in the sending and receiving devices handles the segmentation and reassembly of frames into data blocks Application data block Segmentation Frame Frame Frame FC sequence Sending device Receiving device Fibre Channel transport Application data block Reassembly Frame Frame Frame Frame FC sequence Data Fibre Channel reduces processor overhead by handling the data segmentation and reconstruction, flow control, and error correction in hardware. p1   p2   p3   p4   p5   p6   p7   p8   p9   p10   p11   p12   p13   p14   p15   p16   p17   p18