In this section, the term “software” refers to drivers and utilities, diagnostics, storage and network management software, and integrated code such as firmware and ASIC state machine integration of software functionality such as CPU and protocol offload engines.

While hardware physically connects the fabric, firmware manages and monitors the fabric. The fabric is divided into logical entities such as ports, nodes, and platforms that have a variety of attributes. When a port logs in to the fabric, it registers various attributes that are stored in the fabric. Management applications can then query the fabric to discover the attributes, capabilities, and topology of the fabric.

Fibre Channel firmware divides the fabric for heterogeneous operation and allows multiple protocols to operate simultaneously across multiple switches. The network administrator creates zones within the fabric that enable simultaneous heterogeneous operation. Fibre Channel efficiently routes traffic between switches to increase scalability and interoperability. Multiple Upper Layer Protocols (ULPs) have been mapped to and utilize the benefits of Fibre Channel. A major benefit of all of the Fibre Channel firmware discussed in this chapter is that it has been standardized by ANSI and operates inband at the high speeds of Fibre Channel.

Logical Entities and Attributes

Fibre Channel ports are the basic entity that connect all Fibre Channel devices. A Fibre Channel address is assigned to each port so that frames can be routed to each end device. Ports are grouped into nodes, and nodes are grouped into platforms, as shown in Figure21. Each entity registers its attributes with the fabric when it logs in. ULPs can also define application specific attributes.

Initializing and Monitoring

When a Fibre Channel fabric initially powers on or when devices are added to the fabric, a series of procedures is followed to inform the fabric of all available resources. Likewise, if a device becomes unavailable, the SAN notifies registered users that the port is no longer available. Fabrics are even smart enough to notify registered ports when there are slight problems with the network, such as a high bit error rate on a link. The fabric is an intelligent network that constantly monitors its own ability and reports trouble.The fabric also provides Management Services such as configuration management and topology discovery.


Since Fibre Channel SANs consolidate data from multiple servers and operating systems, many types of traffic and data are sent through the fabric. To insure security and dedicated resources, an administrator creates zones and zone sets to restrict access to specified areas. A zone divides the fabric into groups of devices as shown in Figure22. Zone sets are groups of zones. Each zone set represents different configurations that optimize the fabric for certain functions.Zoning enables heterogeneous environments and allows the fabric to be dynamically tuned for particular applications.

Interswitch Routing

Fabric Shortest Path First (FSPF) is the accepted routing protocol that allows the cascading of switches from multiple vendors. With FSPF, Fibre Channel frames find the shortest path through multiple switches with a routing protocol similar to the Internet routing protocol. With multiple vendors providing switches that interoperate, IT departments are building Fibre Channel SANs at an unprecedented rate.

Upper Layer Protocol (ULP) Mapping

The Fibre Channel fabric provides the transport layer for ULPs that contain the applications and the user interface. The ULPs are mapped to the Fibre Channel transport via standards developed by ANSI and the Internet Engineering Task Force (IETF). The list of ULPs that have been mapped to Fibre Channel is shown in Table 4.Most storage devices use the SCSI ULP to control the devices. The Fibre Channel Protocol (FCP) maps the SCSI commands to the Fibre Channel transport layer. Fibre Channel can also carry Internet Protocol traffic and this mapping is explained in the IETF document RFC 2625. Fiber Channel – Virtual Interface (FC-VI) defines the mapping of VI messages and VI connections to Fibre Channel. Fibre Channel was designed from the start to allow multiple protocols to operate on the fabric simultaneously. ULPs use Fibre Channel for its increased functionality that enables connections over longer distances in heterogeneous environments.

Virtually any technology can be mapped onto Fibre Channel. The mainframe environments have mapped Enterprise Systems Connection (ESCON) and Fiber Connection (FICON) onto Fibre Channel because of its high integrity and performance. The versatility of Fibre Channel is also shown through the mapping of digital audio and video files in Fibre Channel Audio and Video (FC-AV). The applications that Fibre Channel addresses are increasing every day.

Table 4. Mapping ULPs to Fibre Channel Standards

Upper Level
Fibre Channel Standard Abbreviation
SCSI Fibre Channel Protocol FCP
ESCON Single Byte Command Code Set FC-SB
FICON Single Byte Command Code Set-2 FC-SB-2
Internet Protocol IP and ARP over Fibre Channel None
Virtual Interface Fibre Channel Virtual Interface FC-VI
Audio Visual Fibre Channel Audio Visual FC-AV