Fibre Channel, or FC, is a high-speed network technology primarily used to connect computer
data storage.
Fibre Channel is standardized in the T11 Technical Committee of the International Committee for
Information Technology Standards, an American National Standards Institute-accredited standards
committee.
Fibre Channel was primarily used in supercomputers, but has become a common connection type for
storage area networks in enterprise storage.
Despite its name, Fibre Channel signaling can run on an electrical interface in addition
to fiber-optic cables.
Fibre Channel Protocol is a transport protocol that predominantly transports SCSI commands
over Fibre Channel networks.
The origin of the name When the technology was developed, it supported
only optical cabling.
At some point support for copper cables was added, so the development committee decided
to keep the same name but switch to the British English spelling fibre for the standard.
The American English spelling fiber refers only to optical cabling.
Thus, a network using fibre can be implemented either with copper or optical fiber.
History Fibre Channel was developed in a committee
through industry cooperation, while SCSI was developed by a single vendor and later submitted
for standardization.
Fibre Channel started in 1988, with ANSI standard approval in 1994, as a way to simplify the
HIPPI system then in use for similar roles.
HIPPI used a massive 50-pair cable with bulky connectors, and had limited cable lengths.
When fibre channel started to compete for the mass storage market its primary competitor
was IBM's proprietary Serial Storage Architecture interface.
Eventually the market chose fibre channel over SSA, depriving IBM of control over the
next generation of mid- to high-end storage technology.
Fibre Channel was primarily concerned with simplifying the connections and increasing
distances, as opposed to increasing speeds.
Later, designers added the goals of connecting SCSI disk storage, providing higher speeds
and far greater numbers of connected devices.
It also added support for any number of "upper layer" protocols, including ATM, IP and FICON,
with SCSI being the predominant usage.
The fibre channel protocol has a rich roadmap of speeds on a variety of underlying transport
media.
For example, the following table shows native fibre channel speed variants:
* – Throughput for duplex connections Fibre Channel topologies
There are three major fibre channel topologies, describing how a number of ports are connected
together.
A port in fibre channel terminology is any entity that actively communicates over the
network, not necessarily a hardware port.
This port is usually implemented in a device such as disk storage, an HBA on a server or
a fibre channel switch.
Point-to-point.
Two devices are connected directly to each other.
This is the simplest topology, with limited connectivity.
Arbitrated loop.
In this design, all devices are in a loop or ring, similar to token ring networking.
Adding or removing a device from the loop causes all activity on the loop to be interrupted.
The failure of one device causes a break in the ring.
Fibre Channel hubs exist to connect multiple devices together and may bypass failed ports.
A loop may also be made by cabling each port to the next in a ring.
A minimal loop containing only two ports, while appearing to be similar to FC-P2P, differs
considerably in terms of the protocol.
Only one pair of ports can communicate concurrently on a loop.
Maximum speed of 8GFC.
switched fabric.
All devices or loops of devices are connected to fibre channel switches, similar conceptually
to modern ethernet implementations.
Advantages of this topology over FC-P2P or FC-AL include:
The switches manage the state of the fabric, providing optimized interconnections.
The traffic between two ports flows through the switches only, it is not transmitted to
any other port.
Failure of a port is isolated and should not affect operation of other ports.
Multiple pairs of ports may communicate simultaneously in a fabric.
Layers Fibre Channel does not follow the OSI model
layering, but is split similarly into five layers:
FC4 – Protocol-mapping layer, in which application protocols, such as SCSI or IP, are encapsulated
into a PDU for delivery to FC2.
FC3 – Common services layer, a thin layer that could eventually implement functions
like encryption or RAID redundancy algorithms; FC2 – Network layer, defined by the FC-PI-2
standard, consists of the core of fibre channel, and defines the main protocols;
FC1 – Data link layer, which implements line coding of signals;
FC0 – PHY, includes cabling, connectors etc.;
Layers FC0 through FC2 are also known as FC-PH, the physical layers of fibre channel.
Fibre Channel routers operate up to FC4 level, switches up to FC2 and hubs on FC0 only.
Fibre Channel products are available at 1, 2, 4, 8, 10, 16 and 20 Gbit/s; these protocol
flavors are called accordingly 1GFC, 2GFC, 4GFC, 8GFC, 10GFC, 16GFC or 20GFC.
The 16GFC standard was approved by the INCITS T11 committee in 2010, and those products
became available in 2011.
Products based on the 1GFC, 2GFC, 4GFC, 8GFC and 16GFC standards should be interoperable
and backward compatible.
The 1GFC, 2GFC, 4GFC, 8GFC designs all use 8b/10b encoding, while the 16GFC standard
uses 64b/66b encoding.
Unlike the 10GFC and 20GFC standards, 16GFC provides backward compatibility with 4GFC
and 8GFC.
The 10 Gbit/s standard and its 20 Gbit/s derivative, however, are not backward-compatible with
any of the slower-speed devices, as they differ considerably on FC1 level in using 64b/66b
encoding instead of 8b/10b encoding and are primarily used as inter-switch links.
Ports
The following types of ports are defined by Fibre Channel:
node ports N_port is a port on the node used with both
FC-P2P or FC-SW topologies.
Also known as node port.
NL_port is a port on the node used with an FC-AL topology.
Also known as Node Loop port.
F_port is a port on the switch that connects to a node point-to-point.
Also known as fabric port.
An F_port is not loop capable.
FL_port is a port on the switch that connects to a FC-AL loop.
Also known as fabric loop port.
E_port is the connection between two fibre channel switches.
Also known as an Expansion port.
When E_ports between two switches form a link, that link is referred to as an inter-switch
link.
B_port A Bridge Port is a Fabric inter-element port used to connect Bridge devices with E_Ports
on a Switch.
The B_Port provides a subset of the E_port functionality
D_port is a diagnostic port, used solely for the purpose of running link-level diagnostics
between two switches and to isolate link level fault on the port, in the SFP, or in the cable.
EX_port is the connection between a fibre channel router and a fibre channel switch.
On the side of the switch it looks like a normal E_port, but on the side of the router
it is an EX_port.
TE_port * Is an extended ISL or EISL.
The TE_port provides not only standard E_port functions but allows for routing of multiple
VSANs.
This is accomplished by modifying the standard Fibre Channel frame upon ingress/egress of
the VSAN environment.
Also known as Trunking E_port.
VE_Port an INCITS T11 addition, FCIP interconnected E-Port/ISL, i.e. fabrics will merge.
VEX_Port an INCITS T11 addition, is a FCIP interconnected EX-Port, routing needed via
lsan zoning to connect initiator to a target.
general types Auto or auto-sensing port can automatically
become an E_, TE_, F_, or FL_port as needed.
Fx_port a generic port that can become a F_port or a FL_port.
GL_port on a switch can operate as an E_port, FL_port, or F_port.
Found on QLogic switches.
G_port or generic port on a switch can operate as an E_port or F_port.
Found on Brocade, McData, and QLogic switches.
L_port is the loose term used for any arbitrated loop port, NL_port or FL_port.
Also known as Loop port.
U_port is the loose term used for any arbitrated port.
Also known as Universal port.
Found only on Brocade switches.
(*Note: The term "trunking" is not a standard Fibre Channel term and is used by vendors
interchangeably.
For example: A trunk in a Brocade device is referred to as a Port Channel by Cisco.
Whereas Cisco refers to trunking as an EISL.)
Optical carrier medium variants
Modern Fibre Channel devices support SFP transceiver, mainly with LC fiber connector.
Older 1GFC devices used GBIC transceiver, mainly with SC fiber connector.
Fibre Channel infrastructure
Fibre Channel switches can be divided into two classes.
These classes are not part of the standard, and the classification of every switch is
a marketing decision of the manufacturer: Directors offer a high port-count in a modular
chassis with no single point of failure.
Switches are typically smaller, fixed-configuration, less redundant devices.
A fabric consisting entirely of one vendor is considered to be homogeneous.
This is often referred to as operating in its "native mode" and allows the vendor to
add proprietary features which may not be compliant with the Fibre Channel standard.
If multiple switch vendors are used within the same fabric it is heterogeneous, the switches
may only achieve adjacency if all switches are placed into their interoperability modes.
This is called the "open fabric" mode as each vendor's switch may have to disable its proprietary
features to comply with the Fibre Channel standard.
Some switch manufacturers offer a variety of interoperability modes above and beyond
the "native" and "open fabric" states.
These "native interoperability" modes allow switches to operate in the native mode of
another vendor and still maintain some of the proprietary behaviors of both.
However, running in native interoperability mode may still disable some proprietary features
and can produce fabrics of questionable stability.
Fibre Channel host bus adapters Fibre Channel HBAs are available for all major
open systems, computer architectures, and buses, including PCI and SBus.
Some are OS dependent.
Each HBA has a unique World Wide Name, which is similar to an Ethernet MAC address in that
it uses an Organizationally Unique Identifier assigned by the IEEE.
However, WWNs are longer.
There are two types of WWNs on a HBA; a node WWN, which can be shared by some or all ports
of a device, and a port WWN, which is necessarily unique to each port.
Development tools When developing and/or troubleshooting the
Fibre Channel bus, examination of hardware signals can be very important to find problems.
Logic analyzers and bus analyzers are tools which collect, analyze, decode, store signals
so people can view the high-speed waveforms at their leisure.
See also
References
INCITS Fibre Channel standards
Sources Clark, T. Designing Storage Area Networks,
Addison-Wesley, 1999.
ISBN 0-201-61584-3 Further reading
RFC 2625 – IP and ARP over Fibre Channel RFC 2837 – Definitions of Managed Objects
for the Fabric Element in Fibre Channel Standard RFC 3723 – Securing Block Storage Protocols
over IP RFC 4044 – Fibre Channel Management MIB
RFC 4625 – Fibre Channel Routing Information MIB
RFC 4626 – MIB for Fibre Channel's Fabric Shortest Path First Protocol
External links Fibre Channel Industry Association
INCITS technical committee responsible for FC standards(T11)
IBM SAN Survival Guide Introduction to Storage Area Networks
Fibre Channel overview Fibre Channel tutorial
Storage Networking Industry Association Virtual fibre Channel in Hyper V