FICON protocol. Brief educational program

In this article, I will briefly talk about the basics of FICON, a protocol inextricably linked to the world of mainframes. This is a small introduction article describing the FICON concept and therefore I will refrain from deep technical details. If necessary, this will be done in the following articles.

A bit of history

FICON (FIber CONnection) is a proprietary protocol and industry standard I / O used to connect mainframes to storage systems and peripherals. It appeared in 1998 as a replacement for the outdated ESCON (Enterprise Server CONnection) protocol and greatly surpasses it in all main characteristics. As you might have guessed, this standard was invented within the walls of the company, which is the main producer of mainframes on our planet - IBM.

Currently, IBM-compatible mainframes are also manufactured by Fujitsu, NEC, Hitachi, although they practically do not compete with IBM and are mainly sold in the Japanese market. Their products also use FICON. And storage systems and tape libraries with FICON support are produced by all the largest players in the storage systems market (EMC, Hewlett-Packard, IBM, Hitachi). In fact, the support of the FICON protocol data storage system is almost one of the signs that this Hi-End class system.

The FICON switch market is not so full of manufacturers. In fact, this market is divided by two manufacturers: the majority of it is occupied by Brocade (according to various estimates, about 70-80%), and the rest is controlled by the well-known Cisco Systems.

The need to develop this protocol appeared due to the fact that mainframes were always built on a closed architecture and, in particular, everyone did not support their beloved SCSI. And in our century, SCSI is used on almost every first server: SAS disks on servers (Serial Attached SCSI), virtual volumes from external storage systems using the FCP protocol (SCSI over FC), virtual volumes from external storage systems using the iSCSI protocol. In a historical interface speed race, one day there was such a situation that ESCON speeds did not suit anyone anymore, and replacements from open systems (in particular SCSI) for mainframes could not be used, because such migration led to the need for a large number of architectural changes to mainframe software. So the cunning minds of IBM decided to develop a protocol, similar in ESCON format but on an open and dynamically developing infrastructure. Such infrastructure turned out to be Fiber Channel. Developed by IBM in 1998, FICON is nothing more than an adaptation and some modification of ESCON to use it as a top-level protocol in the Fiber Channel stack.


Existing FICON devices support speeds of 2, 4, 8, 16 Gbit / s. True, it is worth noting that at the moment the speed is 16 Gb / s. can be obtained exclusively on Brocade equipment, as Cisco does not yet have such solutions. The maximum distance depends on the speed of the interfaces, equipment used and other factors, but usually does not exceed 100 kilometers (without using FCIP routers). At distances of more than 500 meters, it will be necessary to use special optical modules (long-wave SFP) and single-mode optical fiber (dark fiber).


There are three main ways to connect mainframes to peripheral equipment through FICON:
  1. Using direct connections (point-to-point). This is the easiest way. In this case, the FICON mainframe port is connected directly to the peripheral device port.
  2. Switched point-to-point In this case, the mainframe port and the peripheral port are connected to the same FC switch.
  3. Cascading FICON. In this case, the mainframe port is connected to one switch, and the peripheral device port is connected to another switch connected to the first through inter-switch communication (ISL, Inter-Switch Link).
    These three methods differ not only in the physical aspect of the connection, but also directly affect the way the FICON switches and the mainframe are configured. They even use different types of addressing. In particular, when using direct connections, the point-to-point address consists of only one byte, which is used to address the device. When using cascaded FICON topology, the address consists of two bytes. The first byte is used to identify the FC switch into which the peripheral device (domain ID of the switch) is connected, the second - to identify the physical address of the device port on the switch.

Similarities and differences with Fiber Channel Protocol (FCP)

FICON uses the Fiber Channel hardware infrastructure. That is, the same switches are used, the same fiber-optic cables with an LC-LC connector, the same transceivers that are used to connect open system servers (not mainframes) to storage systems. FICON is just one of the upper level protocols that is encapsulated on the Fiber Channel stack at the upper level (FC-4). It is encapsulated on the FC stack, just like SCSI in the most popular FCP. FICON and FCP can be used simultaneously on the same hardware infrastructure (share the same switches and storage network directors). Administration of FICON factories is very similar to the administration of ordinary factories for open systems, but has its own very funny features, primarily related to the addressing of devices in mainframes.

That's all! Thank you for reading to the end! If suddenly someone is interested in a technical extension, then it will not be long in coming.

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