With Gigabit Ethernet coming to a network near you, it is time to think big.
That's the reasoning behind 'jumbo frames', which would increase the maximum Ethernet frame size from about 1,500bytes to 9,000bytes. The technology essentially provides users with a large boost in the packet size for Ethernet, which means unlimited frame size.
Supporting vendors say larger frames would be more efficient and many users like the idea. With the speed and capacity of today's Ethernet pushing the processor limits of most installed servers, users and vendors are recognizing the value of bigger frames.
When Ethernet emerged in the early 1980s, cabling quality wasn't as high as it is today. Lower quality meant frames had to be limited in size, explained Ted Schroeder, an engineer and co-founder of Alteon Networks, one of the most vocal implementors of jumbo frames.
With larger frames, there was a greater chance for errors caused by the copper and an increased chance the error checking mechanism wouldn't catch them. Today, a better grade of copper is used for Fast Ethernet and Gigabit Ethernet runs mainly over fibre optic lines which are cleaner, he added.
At faster speeds, the network cards receive frames more quickly and intensely. The larger the frames, the fewer frames an end device would receive in any given length of time and the less processing it would have to do.
In the past larger frames used to be a concern because they could potentially hold up a shorter packet that needed to go through quickly. This would be a problem for voice or video traffic.
"But the pipes are much larger now," Schroeder said. He added that the competing Lan technologies have used larger frames. For example, FDDI, which runs at 100Mbps, moves data in 4,500byte pieces and Token Ring's limit is 4,000bytes.
Alteon said it has the backing of server suppliers Network Appliances, Silicon Graphics and Sun Microsystems. And the company is working around the standards issues as it implements its version of jumbo frames within its server switches and network interface cards. Each server NIC can "speak" to other end devices using jumbo or standard frames.
While jumbo frames is not a standard, the technology has gained the backing of major players such as Microsoft, Compaq, IBM and Silicon Graphics. Alteon is trying to rally industry support into a de facto standard that will give jumbo frames the leverage necessary to navigate the Institute of Electrical and Electronic Engineers (IEEE) standards process or to present the technology to the Internet Engineering Task Force (IETF).p> Recently Alteon rolled out its ACEswitch 180 which takes server-to-server communications off the client/server backbone. ACEnic server adapters are connected to the ACEswitch on the server side. The switch, which divides servers and end users into separate communities, supports both standard Ethernet frames and 9,000byte jumbo frames.
Alteon said jumbo frames can be used simultaneously with standard Ethernet frames using the same adapter. For example, a server could communicate with another server using jumbo frames while communicating with clients sitting on another VLAN or IP subnet using standard Ethernet frames, all by way of the same physical connection.
"For corporations and ISPs that want to dramatically reduce data back-up times and increase client/server performance by eliminating server-to-server traffic from the mainstream networks, the use of jumbo frames is undeniable," said Schroeder.
Schroeder added that server vendors, such as Sun Microsystems, are excited about the technology because "it makes them look better. But the equipment vendors such as Cisco and 3Com are less enamored with it, probably because they can't support it in their hardware."
According to Alteon, independent tests have verified that the use of jumbo frames can deliver a 50 percent increase in throughput with a simultaneous 50 per cent decrease in CPU usage.
"The debate of frame size has been getting a lot of attention. Frame size is an issue that not only pits token ring vendors against Ethernet vendors, but also Ethernet vendors against one another," said Kevin Tolly, of the strategic consulting and independent testing firm, the Tolly Group.
He added that performance, efficiency and backward compatibility are the main arguing points in the discussion.
Tolly also explained that there is a benefit to upgrading the server and the network. "It's true that upgrading servers with faster buses, more powerful CPUs and faster adapters will almost always improve performance. It's also true that using jumbo frames, with their corresponding lower frame rates, will improve performance. These are complementary not mutually exclusive issues," he said.
Tom Nolle, president of consulting firm, CIMI Corporation, pointed out that Alteon by itself is not in a position to promote the technology as effectively as it might have liked.
"But with IBM, (expected to give its support to jumbo frames anytime), one of the largest providers of server hardware giving it an endorsement, buyers have a much greater probability of adopting jumbo frames."
IBM is expected to support Jumbo Frames by selling relabeled Alteon ACEnic cards for its RS/6000 servers. But the company has no plans to resell Alteon switches. IBM is also expected to deliver Gigabit Ethernet cards with jumbo frames support for its S/390 mainframes and AS/400 mid-range systems, although it does not plan to add support to its Netfinity PC server unit.
The endorsement could promote the extension of jumbo frames within the industry. Alteon's Selina Lo, vice president of product management at the company, explained that the concept of jumbo frames is nothing new, but it is increasingly necessary for an industry that continually requires more bandwidth.
Earlier in the year, Compaq had pledged to OEM a Gigabit speed Alteon network interface card for server systems and Microsoft said it will build a set of software drivers that support Jumbo Frames within the company's Windows NT operating system. The companies also said they plan to push for inclusion of the jumbo frame technology in the Gigabit Ethernet standards.
The Alpha server division of Compaq has called the adapter, which supports jumbo frames, the Etherworks 1000 PCI.
On the other side of the jumbo frame debate, Bernard Daines, president and CEO of Packet Engines, a Gigabit Ethernet equipment vendor, disagrees with the impact.
"Although proponents claim larger packets improve performance on the wire, the impact is relatively insignificant. The increase in efficiency and performance are insignificant compared with other delays and negative factors in the large packet system," he said. "Substantial costs are associated with diverging from the standards on which your network is based."
He pointed out that the greatest potential benefit of larger packets is improving the host computer's efficiency. In the host, the CPU interacts with the network interface card (NIC) to move packets from the wire to the application. Large packets minimize the CPU's workload by decreasing the number of transfers across the bus, the interrupt stack and the protocol stack.
So, the challenge is to make the packet appear large in the system to offload the CPU while remaining standards based on the wire.
But, he added, that it is possible for large-packet networks to coexist with standard Ethernet networks by installing both NICs and switches that can handle multiple packet sizes. However, these features increase the cost, complexity and management charge of the devices.
John Curtis, a senior engineer/analyst at the Tolly Group, pointed out that most of the criticism of jumbo frames is based on flawed arguments.p> Properly deployed, the jumbo frame technology is going to make IS managers' lives easier, says one analyst.
"It may not be for the desktop, but it sure as hell is necessary when you are talking about server farms," said Frank Dzubeck, president of Communications Network Architects, a consultancy in Washington, DC.
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