High-Speed Connectivity: A Tangled Web of Cables and Speed

• 05/05/1999

As a network guy, until recently I only paid cursory attention to Fibre Channel and devoted most of my time to dealing with Ethernet. I didn’t view Storage Area Networks (SANs) running over Fibre Channel as "real" networks, but rather as a way to tie a bunch of high-speed disks together.

After reading the many claims that Fibre Channel would be the only transport ever needed and that every computer device sold would need a power receptacle and one universal I/O connector, I began to proactively look at how Fibre Channel and Ethernet technologies compare. What follows will shed some light on how these technologies stack up and where they are headed. Then maybe we can determine if the world of connectivity will remain diversified or become a one-medium show.

Ethernet is everywhere. According to an International Data Corp. (www.idc.com) study, at the end of 1997 Ethernet was used in 85 percent of installed network connections. Ethernet has managed to remain the network media mogul for nearly two decades, successfully fending off Token Ring and ATM.

Only during the past few years have we been able to break through the shared 10 Mbps barrier. First, Fast Ethernet came on the scene around 1995. A short time later, Gigabit Ethernet emerged. Gigabit Ethernet is now finding its way into the corporate campus backbone.

The saving grace with Fast and Gigabit Ethernet is that, despite higher speeds, they both are still Ethernet. The 802.3 standard on which Ethernet is based is the same standard on which the 802.3z Gigabit Ethernet standard relies. Frames are built the same way and are the same lengths; switches work the same way; and management objects are the same. All the popular protocols that run over "slow" Ethernet run over Gigabit Ethernet. There is even a 1000Base-T Task Force assigned with finishing work on the 802.3ab standard to make Gigabit Ethernet run over CAT5 cabling using the same 100 meter lengths over which Fast and traditional Ethernet run now.

What we love about Gigabit Ethernet is its familiarity. Performance is not an issue. Primarily deployed as a switched, full-duplex technology, sustained throughput said to be greater than 98 percent of wire speed. Gigabit Ethernet can also be run in half-duplex mode, where it uses the same collision detection methods as its slower kin. Who could ask for anything more?

Fibre Channel is a different ballgame. But it is not necessarily a new ballgame. Fibre Channel traces its roots to the channel I/O employed in mainframes. The American National Standards Institute (ANSI) began work on an official Fibre Channel standard in 1988. An approved ANSI standard (ANSI X3.232-1994) appeared in 1995. Some companies, such as Emulex Corp. (www.emulex.com), have been producing Fibre Channel products since that time. Only recently has Fibre Channel exploded onto the PC server scene, with the introduction of SANs as a way to overcome the constraints of SCSI.

Despite what its name implies, Fibre Channel is designed to handle traditional connectionless mode LAN traffic as well as channelized I/O, and it does not have to run over optical fiber cabling. Currently, four classes of service accommodate various types of traffic, from dedicated connection-oriented service to connectionless and datagram service. The segregated approach allows Fibre Channel to carry disk-oriented protocols like SCSI, while simultaneously carrying LAN-type traffic using protocols such as IP.

Like Gigabit Ethernet, Fibre Channel attains speeds of 200 MBps full duplex. Cable distances are long -- now extending up to 30 meters over copper, 500 meters for short-wave laser and 10 kilometers for long wave laser over singlemode fiber. Some companies are beginning to experiment with inter-SAN campus backbones running SCSI over Fibre Channel rather than traditional communications protocols.

Fibre Channel nodes can be connected via three primary topologies: in a switched fabric, in a ring environment dubbed "arbitrated loop" or in a hubless point-to-point scheme. Many vendors already produce Fibre Channel switches and other gear, including ATTO Technology Inc. (www.attotech.com), Ancor Communications Inc. (www.ancor.com), EMC Corp. (www.emc.com), Emulex Corp., Gadzoox Networks Inc. (www.gadzoox.com), Inrange Technologies Corp., (www.inrange.com), JNI (www.jni.com), Storage Technology Corp. (www.storagetek.com) and Vixel Corp. (www.vixel.com).

One of the things we like about Fibre Channel technology is its ability to run standard disk protocols such as SCSI, making even far away devices appear to be directly attached and providing a simple way to increase storage capacity and speed.

When developing a long-term network infrastructure plan, it is helpful to know if Fibre Channel is a serious contender for the generalized LAN space, or if it will be relegated to SAN applications.

According to Kirby Lambert, technical director at MGI Studio (www.ackmart.com), a graphics prepress company, there is room for both Fibre Channel and Ethernet. Lambert is more than an end user. He was instrumental in the development of FibreFlex, a complete SAN solution offered by MicroNet Technology Inc. (www.micronet.com). Despite its adoption, Lambert predicts that Fibre Channel, "probably will never replace Ethernet in areas that do not need its bandwidth."

Lambert believes Fibre Channel’s real value is its ability to bring storage directly to the client desktop. "What Fibre Channel can bring to the table that legacy technologies cannot, is a pure serverless, shared-storage architecture," he says.

Brian Reed, vice president of marketing at Vixel Corp., agrees. "Ninety-nine percent of our installed base is using Fibre Channel in a SAN environment for server to storage connections," he says. "Gigabit Ethernet will remain dominant on the LAN side, with Fibre Channel remaining the primary technology on the SAN side. In the immediate future, Fibre Channel will be applied to high-speed, low-latency applications, such as server-to-server connections and clustering. Much of this will still be based on the SCSI protocol over Fibre Channel."

Reed believes some applications currently supported by Fast Ethernet or Gigabit Ethernet will convert to Fibre Channel, but this will be a small percentage of applications in the Ethernet LAN space. He also notes that certain niche markets, such as prepress and video processing, could benefit from an end-to-end Fibre Channel solution. These applications typically need access to large files served at high speeds.

MGI Studio’s Lambert adds that applications, such as prepress, can derive incremental benefit from Fibre Channel. For example, prepress houses that typically send material outside for rendering would no longer need to do so. He believes it is possible that high-speed rendering devices could be leased or rented when needed and connected and disconnected from the Fibre Channel fabric.

"What folks really want is a storage connect solution that is scalable, manageable and reliable," Reed adds. "Fibre Channel solutions provide levels of these features that Gigabit Ethernet currently cannot." In this case, Reed draws attention to Fibre Channel’s classes of service and flow control capabilities.

Both Lambert and Reed see no reason why either technology must become the only media choice. The effort required to transform a primarily Ethernet-based world into something else ensures Ethernet’s longevity. ATM, for example, failed to replace Ethernet. The cost of change is too high, and Ethernet got fast enough quickly enough to make the matter a non-issue.

Lambert says, "Fibre Channel does not require a complete replacement of current technologies. Only in the areas where the current LAN is incapable of delivering the needed bandwidth will changes be necessary. By using some new storage and by migrating existing storage, the benefits of a SAN can be realized without a wholesale makeover."

What about the other side of the equation? Is it possible that Fibre Channel will be a short-lived technology? Can Gigabit Ethernet be used in SAN applications as well as Fibre Channel? If so, could it obviate the need for Fibre Channel technology?

Lambert cites Fibre Channel’s ability to provide directly connected storage as a feature that will ultimately make it successful. "Ethernet cannot bring to SANs what Fibre Channel offers. All workstations or servers connected to the network share the same storage in common at the maximum speed each type of storage is capable of providing. This centralized storage model allows economy of scale and improved management of data resources."

Vixel’s Reed notes that getting Gigabit Ethernet to run traditional disk protocols would require a monumental driver development effort. He adds, "IP is simply not a good protocol to use for disk storage applications."

In the short term, it appears Gigabit Ethernet and Fibre Channel will both find a place in the enterprise network. Furthermore, it’s unlikely that either technology will enter a development stall anytime soon. On the Ethernet side, advances such as dense wave division multiplexing will make Terabit Ethernet possible. Conversely, Fibre Channel’s full-duplex bandwidth of 2 Gbps is expected to quadruple within two years.

Lambert doesn’t expect limiting factors for either technology to come from media types, framing protocols or signaling methods. "The drawback to Ethernet of any type is going to be the continued reliance on traditional servers, he notes. "It does not matter if the fabric of the network can support Gigabit and up speeds if the bandwidth of the server is limited. Fibre Channel can take the server out of the equation except in areas where the increased bandwidth is not an issue."

A final reason Gigabit Ethernet is not threatened by Fibre Channel is that it will take years for users to exploit Fibre Channel’s capabilities. "Most current implementations of Fibre Channel and SANs are of the simple variety," Reed remarks. "Currently, customers’ concerns are for bigger and faster storage. However, many users have yet to realize what they can do with Fibre Channel." Reed says intelligent users will look ahead and start considering Fibre Channel in LAN-free backup and clustering applications as well as deployment of Fibre Channel over ATM or SONET for wide-area storage connectivity.

So my beloved Ethernet is safe for now. Fibre Channel appears to be a complementary partner rather than a competitor. Savvy managers will enjoy the opportunity to increase both network and server performance by using each technology for its strengths.