Fiber Connectivity (FICON) Part 1
RAID Recovery - Fiber Connectivity (FICON)
FICON (Fiber Connectivity) is a high-speed I/O interface developed by IBM to connect mainframes to storage devices such as disk storage and tape drives. Mainframes are computers based on IBM z/Architecture. FICON uses a mapping technology developed for Fiber Channel (FC) protocol. It has a fabric topology that utilizes FC switches or directors.
FICON can connect devices at much higher speeds and greater distances – up to eight times compared to its predecessor fiber optic channel standard Enterprise Systems Connection (ESCON). FICON can support speeds of 1, 2, and 4 gigabit data rates at distances up to 100 km. It also supports full-duplex data transfers; thus it can read and write data over the same link at the same time.
FICON uses FC’s multiplexing capabilities to enable multiple concurrent small data exchanges (a maximum of 32) on the link alongside larger transfers. Thus, they do not have to wait till the larger transfer is completed.
Advantages
- Flexible in terms of network layout.
- Compatibility with different channel types on S/390 G5 servers
- Support for existing ESCON control units
- Full duplex data transfer enables simultaneous reading and writing of data over a single link.
- Multiplexing enables transfer of small data alongside larger ones
There are fiber channel sequences in which information for active exchanges is transferred. These are mapped as FICON Information Units (IUs) and consist of one to four Fibre Channel frames. Among these, only the first frame carries 32 bytes of FICON (FC-SB-3) mapping protocol. Each FICON exchange may transfer one or many such IUs.
CRC
FICON contains a 32-bit cyclic redundancy check (CRC) to ensure integrity of data. CRC is contained in the last frame of an information unit (IU), which is called as an ending IU within each data transfer. Additionally, there is a standard Fiber Channel CRC running to verify the integrity of each individual FC frame.
