STORAGE-AREA NETWORKS
Storing large quantities of data is common in the enterprise, government, and other organizations. RAID (redundant array of independent disks) and JBOD (just a bunch of disks) storage systems are a growing market, and the need to connect them to LANs and the Internet is critical. That’s why special storage-area networks (SANs) were developed.
The most widely used SAN, Fibre Channel (FC), is an optical-fiber network that connects the hard-disk arrays to the servers and the network through host bus adapter (HBA) cards. The medium is fiberoptical cable, and the T11 organization has set standards for data rates of 1, 2, 4, and 8 Gbits/s. Also, a 10-Gbit/s standard has been defined.
Though FC works well and is widely used, it’s expensive to expand and maintain. Nonetheless, most users want to continue it in some way even though lower-cost alternatives like the Internet Small Computer Systems Interface (iSCSI) are out there.
The iSCSI option is a serial version of the widely used older SCSI parallel connections and protocol used with hard drives. It uses Ethernet as the networking medium to tunnel SCSI commands and data. As a result, it costs much less and can run in parallel with existing Ethernet networks. But, except for small and medium businesses, iSCSI’s adoption has been limited.
A forthcoming alternative that combines the best of FC and Ethernet is the Fibre Channel over Ethernet (FCoE) standard being developed by the T11 organization. It packages FC packets and tunnels them over standard Ethernet LANs.
BUT THAT'S NOT ALL...
Many other enhancements, additions, and applications surround Ethernet, such as industrial Ethernet, the LXI instrumentation system, and Ethernet passive optical networks (EPONs).
Industrial Ethernet uses standard Ethernet in place of other special networks developed for the harsh and critical nature of industrial applications. These networks have to operate with high levels of noise and in extreme environments of temperature variations and corrosive atmospheres. Special shielded and protected cables and connectors help in these cases.
In addition, many industrial applications require determinism. That is, they must be able to accurately time data transmissions and related control and measurement actions.
Ethernet is fraught with latencies, delays, and timing inaccuracies common to a best effort service. One solution is to apply the IEEE’s 1588 Precision Time Protocol (PTP). It provides accurate synchronization of nodes on a network by using hardware-generated time stamps. Precision in the nanosecond range is possible. Employing 1588 PTP on Ethernet suits this combination for even the most time-critical industrial applications. The IEEE 1588 PTP is also used in Carrier Ethernet applications.
LXI (LAN eXtensions for Instrumentation) is the relatively new instrumentation communications standard designed to replace the general-purpose instrumentation bus (GPIB) so widely used in test systems over the years. It connects test instruments, PCs, and the Internet for any combination of testing, measuring, recording, storing, and accessing data. Many instruments already incorporate LXI, and more are forthcoming. LXI is based on the use of Ethernet because of its low cost and wide availability.
Finally, work is underway on a 10-Gbit/s version of Ethernet designed for PONs in metro networks that deliver digital TV and Internet access services. PONs use low-cost fiber to distribute video and other services to homes and businesses without the need for costly repeaters or other active intermediary hardware in the field. PONs are widely deployed in cable TV and telecom infrastructures to deliver higher speeds and quality video.
The original PON standards, which were set by the ITU-T, are designated as APON, BPON, and the latest, GPON. There’s also a low-speed Ethernet PON known as EPON or GEPON for gigabit service. Designated 802.3ah, it is widely used in Asia but not in the U.S., where GPON is the dominant standard. The IEEE is currently working on a 10-Gbit/s version designated 802.3av that will utilize different wavelengths of light for 1- and 10-Gbit/s services on a single fiber. A final version of 802.3av is expected later in 2009.