ip I/O capacity. One solution to such problems is Fibre Channel.
Despite its name, Fib
re Channel is more than a channel and runs on more than just fiber. Channels, such as ESCON and SCSI, are designed for high performance and high reliability, using dedicated, short-distance connections between computers or between computers and peripherals. Traditional networks, on the other hand, offer more flexibility and greater distance capabilities. Fibre Channel integrates features of both: the speed and reliability of channels with the flexibility and connectivity of networks. The result is a high-speed ANSI-standard transport mechanism for data, voice, and video.
Some 80 companies are now members of the Fibre Channel Association, including Hewlett-Packard, IBM, Kodak, Seagate, Silicon Graphics, and Sun Microsystems. Many of these member companies are making and delivering a range of Fibre Channel products, such as network interface cards (NICs), storage devices, routers, and switches.
Under the Hood
Fibre Channel moves data at very high rates. Currently available produ
cts run at 266 or 1062 Mbps--enough to handle even demanding applications, such as uncompressed, full-motion, high-quality video. Fibre Channel can be deployed as a simple point-to-point connection, a loop, or a switched fabric.
A point-to-point configuration is the simplest topology, connecting two Fibre Channel systems directly. Arbitrated loops are Fibre Channel ring connections that provide shared access to bandwidth via arbitration. Switched Fibre Channel networks, called fabrics, yield the highest performance by leveraging the benefits of cross-point switching. For example, when fabric users add ports to their network, they increase the aggregate capacity of the network. The aggregate data rate of a fully configured Fibre Channel network can be in the terabit-per-second range.
The ANSI specification that defines Fibre Channel distributes its functions among five layers that in many ways parallel the Open Systems Interconnection (OSI) model (see the figure
"Pick Your Proto
col"
). FC-0 is the physical layer, which can use single-mode fiber, multimode fiber, or copper. For the fiber interfaces, Fibre Channel uses a low-cost duplex SC connector. Shielded twisted-pair media use a nine-pin connector. And coaxial-cable systems use a TNC receiver and a BNC transmitter.
The next layer, FC-1, specifies byte synchronization and an encoding/decoding scheme, where 8 bits of data are encoded in 10-bit groups. A unique "comma character" ensures proper word and byte alignment; the encoding also handles error correction.
The transport mechanism is defined in Fibre Channel by the FC-2 layer. Each N_port (node port) on a connected device can be an originator of a message, a responder, or both, and each port has a unique address.
FC-3 defines a set of common network functions that span multiple N_ports. One function is striping, in which multiple N_ports use multiple links to transmit data (thereby boosting bandwidth). Another function is hunt groups, which allow sets of
N_ports to be attached to a single node. This lets any of these ports receive data for that node if another port is busy.
The FC-4 layer gives Fibre Channel its ability to handle virtually any payload, including both channel and network traffic. It does this by specifying the way various upper- layer protocols are mapped to Fibre Channel. These specifications ensure interoperability among different implementations. Several channel and network protocols have already been mapped, including SCSI, High Performance Parallel Interface (HIPPI), IP, IPI, AAL5, LE, Single Byte Command Code Set Mapping (bus-and-tag protocol), and IEEE 802. 2 (the data-link-layer standard for Ethernet).
Weaving the Strands Together
Central to Fibre Channel is the use of switching fabrics to connect devices like workstations, PCs, servers, routers, mainframes, and storage devices that have Fibre Channel interfaces. In some ways, the fabric works like the traditional phone system. Each originating port "ca
lls" the fabric by entering the address of the destination port in a frame header. The fabric does all the work of setting up the desired connection. The originator does not have to worry about complex routing algorithms, and there are no complicated Permanent Virtual Circuits (PVCs) to set up.
Because fabrics can handle more than 16 million addresses, Fibre Channel can accommodate very large networks. You can start with a small network and increase the number of ports. As you add ports, Fibre Channel's nonblocking characteristic means that the network increases in capacity. That's because the aggregate bandwidth scales linearly with the number of ports.
Fibre Channel has features that make it useful in large networking environments. For example, Fibre Channel offers you a choice of three networking services. Class 1 provides an acknowledged connection service with guaranteed delivery and end-to-end flow control. It works like a physical channel. Class 2 is a frame-switched service that does not
use a dedicated connection. It provides guaranteed data delivery and buffer-to-buffer flow control. If the receiving node is busy, the sender tries again. Class 3 is a connectionless service that is especially useful for broadcast transmission of datagrams.
Getting into the Action
With its high data rates, Fibre Channel is well suited for use in a number of very different types of applications, including moving large files across building or campus backbones, imaging, multimedia, videoconferencing, and storage.
For example, when serving as a backbone, Fibre Channel provides a big pipe where it's needed the most: the focal points of LAN internetworks. Fibre Channel NICs are available for popular server architectures, and routers are available to link the Fibre Channel backbone desktop LANs, including Ethernet, Switched Ethernet, Token Ring, Fiber Distributed Data Interface (FDDI), and asynchronous transfer mode (ATM). When Fibre Channel is used in this type of application, thr
oughput for the entire enterprise is improved by virtue of off-loading server-to-server or router traffic from desktop LANs (see the figure
"Five Problems Fibre Channel Solves"
).
Basically, Fibre Channel technology offers much more than its name implies. Today's technology goes beyond basic channel connectivity and fits in with the networking needs of many organizations.
illustration_link (33 Kbytes)
The Fibre Channel standard specifies five functional layers that support a range of connectivity speeds as well as interfaces to most of the common networking architectures.
illustration_link (22 Kbytes)
Fibre Channel technology can be used in an enterprise to connect a variety of high-performance devices with existing LANs.
Doug Anderson is a product manager with Ancor Communications (
http://www.ancor.com
). You can reach him at
douga@ancor.com
.
Fibre Channel: Fast and Flexible
