FOURTH QUARTER 2002 ARCHIVE ISSUE

TECHNICALLY SPEAKING

Fibre Channel and Ethernet/IP Unite

BY TOM NOSELLA

The primary technology used today for building storage-area networks (SANs) is Fibre Channel. Fibre Channel comprises a set of protocols and standards that define methods for interconnecting storage nodes (hosts, disk arrays, tape arrays, and the like) using a serial communication protocol over copper or optical cable. Development began on the Fibre Channel standards as early as 1988, as the first ANSI standard was approved in 1994 as FC-PH (ANSI X3.230:1994). Fibre Channel as a transport protocol was primarily developed to overcome the shortcomings of the SCSI parallel infrastructure, because Fibre Channel represented a higher-speed, more scalable transport. Although Fibre Channel also can transport other upper-layer protocols including Intelligent Peripheral Interface (IPI), High-Performance Parallel Interface (HIPPI), IP, and IEEE 802.2, it is primarily used to transport SCSI command sets and data.

Fibre Channel provides speeds of 1.0625 Gbps (100 MBps) and 2.125 Gbps (200 MBps), although the ANSI standards also specify a 4.250-Gbps option (400 MBps). The ANSI T11 group is actively working on a 10-Gbps (1200 MBps) standard.

Fibre Channel SANs

A Fibre Channel SAN can consist of multiple different connection topologies including switched fabric, arbitrated loop, and point-to-point. Each topology dictates associated Fibre Channel port modes that must be supported by the participating devices. Point-to-point topology is primarily used to connect a host directly to a disk or tape device. A widely deployed yet older connection topology is the arbitrated loop, a logical loop that consists of up to 126 Fibre Channel devices that arbitrate for permission to transmit data and share the available loop bandwidth. For example, Fibre Channel disk drives are commonly arranged in smaller arbitrated loops within larger disk subsystems.

The preferred Fibre Channel topology today is switched fabric. The switched fabric topology represents a capability similar to that of Ethernet/IP switched networks. Switches are configured in a connected network, known as a fabric, and use a hierarchical three-octet Fibre Channel ID (FC_ID) to route frames around the fabric. A Fibre Channel fabric can consist of a maximum of 239 switches and address up to 15,663,104 devices.

Fibre Channel, Ethernet/IP Common Ground

There are many similarities between Fibre Channel and Ethernet/IP. Fibre Channel uses a routing protocol called Fibre Channel Shortest Path First (FSPF) derived from the same Dykstra algorithm used in the IP world for Open Shortest Path First (OSPF). To scale interswitch bandwidth, Fibre Channel switches support port bundling capabilities commonly referred to as trunking that are similar to IEEE 802.3ad port aggregation in the Ethernet world. For security, Fibre Channel supports a capability called zoning that creates isolated regions of connectivity within a fabric similar to virtual LAN access lists (VACLs) within a Cisco Catalyst® switched Ethernet network. However, one of the main differences between Fibre Channel and Ethernet/IP is the method used for session flow control. In Fibre Channel, flow control is regulated through a credit-granting mechanism used to throttle transmitting devices known simply as buffer-credits. This mechanism allows Fibre Channel to regulate flows without dropping frames as in Ethernet/IP.

Both Fibre Channel and Ethernet/IP allow network administrators to build robust, scalable storage networks used to transport SCSI commands and data between hosts, disk arrays, and tape arrays. In the case of Ethernet/IP, the new Small Computer Systems Interface over IP (iSCSI) protocol can be used to provide servers access to shared resources over an Ethernet/IP network. Fibre Channel is generally used for its high-bandwidth capability for high I/O applications, while iSCSI has been commonly used by those more familiar or comfortable with Ethernet/IP networking and those who want a less expensive option for connecting midrange application servers to a storage network (for example, 100-Mbps Ethernet).

Enterprises can now leverage both of these technologies to build a common, robust, highly resilient storage network. The new Cisco MDS 9000 Family of Multilayer Directors and Fabric Switches integrate high-density Fibre Channel and high-capacity iSCSI into a single platform. To learn more about the features and benefits of these new products, see "The Scalable, Manageable SAN."

TOM NOSELLA, CCIE® No. 1395, is senior manager of technical marketing in Cisco's Storage Technology Group. Nosella and his team are responsible for creating, validating, and promoting Cisco storage networking designs and solutions for enterprise and service provider customers. Before joining Cisco, Nosella served as director of engineering at Bell Canada in residential and commercial Internet services, leading a senior network engineering team. He can be reached at tnosella@cisco.com.

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