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As forward-thinking organizations plan their 802.11n high-speed wireless deployments, they would do well to first consider their Ethernet switching infrastructure.
eWeek-working with Strategic Technology Analytics and Michael Fistler, principal at Network Authority, a network consulting and integration company-set out to gauge the costs of a network switch upgrade as companies look to deploy technologies such as VOIP (voice over IP) and 802.11n. The study was conducted by examining the costs associated with upgrading the switching architectures from two of the leaders in this area, Cisco and Extreme Networks.
We used as a scenario an organization that had grown from roughly 2,500 users in 2006 to 3,000 users in 2008. Workgroups were assumed to consist of at least 200 users with a mix of POE (power over Ethernet) and nonpowered ports.
We analyzed nine Cisco architectures and three Extreme architectures, with additional input and modifications from the vendors. Publicly available list pricing was used for all calculations.
What we found was that no one cross-industry application threatens the existing switching infrastructure quite like 802.11n.
The 802.11n standard will generate a whopping 248M bps of raw data-plenty to overwhelm today’s 100M-bps links. Furthermore, 802.11n access points require more than the 15.4W that POE switches can provide to Class 3 POE devices.
To understand how vendors will effectively adapt their switch infrastructure to support 802.11n and POE devices, we looked backward at the way vendors have migrated their constituencies during the past three years.
Cisco Configuration
Our evaluation began with Cisco’s Catalyst 6509-E.
We configured a pair of redundant 6509-E switches. Each was equipped with a Supervisor 720 management module. Connectivity between switches was provided by four 10G-bps Ethernet ports. Downstream connectivity was provided through 48 Gigabit Ethernet ports. All connectors were provided. The software came with the Cat6000 IOS Advanced IP Services load.
Port densities on the 6509-E were insufficient to meet our requirements. When equipped with redundant management modules, the 6509-E provided 16G-bps Ethernet for upstream connectivity and 336 POE ports of 10/100/1000BaseT. Our RFI (request for information) called for 384 ports. Cisco’s 6513 switch provides the necessary scalability-13 slots compared with the 6509-E’s nine-but it is also more expensive than the 6509-E and rarely deployed in the wiring closet.
Cisco officials said a less expensive solution would be to use a stackable switch-namely, the 3750 for 10/100 (data and POE) configurations and the 3750G for 10/100/1000 configurations.
The 3750 does provide a substantially lower price point than alternative Cisco configurations, but it did not meet our requirements for redundancy: The 3750 cannot support redundant supervisor modules, something we feel is very important for a network that’s expected to serve as the basis for VOIP.
Another approach would have been to use the 4500 series switches, but we would then have been unable to take advantage of the application modules available for the 6500 family. This scenario would also require stocking separate blades for the core and access layer switches, complicating sparing.
As for switching fabrics, three options were available in 2006: the near-end-of-life Supervisor 2 modules, the Supervisor 32 that shipped at the end of 2006 and the Supervisor 720.
The Supervisor 32 was the most logical choice for the wiring closet, although we considered what might have happened if the customer had first migrated to the Supervisor 2 in the beginning of 2006. The Supervisor 720 was targeted at core switching.
Compatible with those modules are three types of interface modules. The Classic Interface Modules are the least expensive and take advantage only of 32G-bps backplane. The Cisco Express Forwarding 256 Interface modules work with Supervisor Engine 2 or Supervisor Engine 720. Finally, the Cisco Express Forwarding 720 Interface Modules are the most expensive and fastest of the modules, field-upgradable to the DCEF (Distributed Cisco Express Forwarding) daughter cards. These modules work with Supervisor Engine 2 or Supervisor Engine 720.
Putting that all together, we considered several 6509-E scenarios. The most likely one was the Cisco 6509-E with a Supervisor 2, which went end-of-life at the end of 2006. The solution was based around a mix of classic and fabric-enabled 10/100/1,000M-bps ports.
Extreme Configuration
As a baseline, we selected extreme’s BlackDiamond 8800. The Extreme configuration was less complicated because its range of options is narrower than Cisco’s.
All configurations led with a pair of redundant 8806s in the core. The six-slot chassis were configured with dual 8800 Management Switch Modules for redundancy. There were 48 1000BaseX ports for downstream connectivity providing redundancy to all chassis. There were also four 10GBaseX ports providing for redundant connections to each hub. All connectors were included. Power was provided by three 700W/1,200W power supplies.
Extreme uses the BlackDiamond 8810 in the wiring closet. Each 8810 was equipped with the 8800 Management Switch Module and eight 1G-bps ports (1000BaseX) for upstream connectivity. Downstream, Extreme equipped the 8810 with 336 10/100/1000BaseT POE ports for a total of 4,032 10/100/1000 POE ports across 12 wiring closets. Power was provided by three 700W/1,200W power supplies.
Migration Costs
Overall, the price of the Cisco solution compared favorably with that of the Extreme solution, assuming IT had the foresight to deploy 10/100/1000 POE to the desktop at the outset with a Supervisor 32 module. Cisco’s configuration ($109,000 overall; $325 per port) would have run 11 percent more than Extreme’s configuration ($112,930 overall, $294 per port). Because the 6509-E options are so vast, however, there’s also room for error. Had IT, for example, not deployed 1000BaseT POE to the desktop-but instead had chosen a mixed 10/100/1,000M-bps environment-costs would have been 14 percent higher.
Such a possibility didn’t exist for Extreme because the company only offered 10/100/1000 POE modules. Having said that, organizations that purchased the 8810 in early 2006 would likely have chosen Extreme’s G48P modules, which ran $7,000 more than the non-line-rate module introduced in August of that year.
The second Cisco configuration option in 2006 was the Supervisor 2, which was introduced in the fall of that year.
Companies that chose the Supervisor 2 would likely have done so at least in part to take advantage of its 256G-bps bus. In our scenario, the upshot would have been a $2.1 million overall expenditure in 2006, mainly because of the more expensive interface modules.
By the end of 2006, the Supervisor 2 would have been at end of life. A company that had chosen the Supervisor 2 would have had to migrate to a new switching matrix, most likely the Supervisor 720, in year three. The result would have been an additional $878,282 charge.
Wireless Ready?
The 6509-E’s reliance on a 32-gig backplane means there’s an average of 3.5G bps per slot, or just 72M bps per 1000BaseT port. Even if one assumes that there’s closer to 4.5G bps per slot, then that still leaves only 104M bps per 1000BaseT port. If 802.11n rollouts mirror current wireless deployments, oversubscription numbers like those will likely not pose initial problems.
“I typically see an access point deployed every 75 feet,” said Network Authority’s Fistler. “In a hospital, we might see 20 to 30 of the 200 to 300 ports dedicated per closet for an access point.”
Put another way, that translates into a little more than a gigabyte of traffic per slot, with another 2.5 to 3.5 gigabytes for the remaining 44 ports. In dense 802.11n environments-or in health care, graphic design or CAD/CAM environments-IT may want to carefully assess the capacity of its 6509-E.
Presumably, as organizations deploy 802.11n devices, Cisco will sell them a higher-speed Supervisor module. Ultimately, this means the introduction of a new Supervisor or selling the Supervisor 720 into the wiring closet, which would be a significant upgrade for most organizations.
Extreme officials wouldn’t tell us the capacity of its switching interfaces. We know, though, that Extreme rate-limits its G48Pe modules by 2-to-1.
Extreme offers more expensive modules-for example, modules that the company claims will deliver line-rate performance across all 1000BaseT ports. This suggests that Extreme users will have sufficient capacity in their switch to accommodate 802.11n access points.
Powering Up
Neither vendor today has a solution for the 802.3at (POE Plus) standard in the tested platforms. Cisco offers its Enhanced POE on the 4500 series, and has indicated that it will release Enhanced POE on the 6500 series soon.
When we asked Cisco about supporting 802.3at in the 6500, we were told that customers will need to replace their power supplies to take advantage of their higher-powered Ethernet.
If this is the case, Cisco will need to introduce a new power supply, as the Cisco 8000w-the largest power supply the company currently makes available-won’t be sufficient to power devices across all ports.
Extreme has not announced plans for 802.3at. Today, however, the company runs devices up to about 16.8W. The 8810 is limited to 7,200W.
Given the limitation of both vendors on this score, it seems likely that one or both will introduce a new chassis or new power supplies to accommodate the higher power requirements during the next year.
Complex Configuration
Ultimately, the biggest argument for the 6509-E is also its biggest challenge. There is no switch today on the market that can match the 6509-E’s flexibility–not only in range of wiring options but also in the 6509-E’s ability to accommodate a wide range of application modules. Indeed, in our conversation, Cisco touted the 6509-E as the “all-purpose” switch, not necessarily the one best-suited for a company looking solely for switching capacity. But it’s this flexibility that makes the 6509-E’s configuration so complex.
The Supervisor modules run either the IOS or CAT IOS operating system, depending on their age and the type of module. The problem is the wide array of switch code needed to support the services modules being used: “I’ve had a case when I had a NAM [Cisco Network Analysis Module], Flex WAN, IDSM-2 [Cisco Intrusion Detection Module] and a FWSM [Cisco Firewall Services Module] plugged into a single switch, and spent two weeks with the Technical Assistance Center upgrading code and fixing bugs until we discovered the correct code to use,” said Fistler.
Organizations are thus advised to negotiate contracts with their integrators on project price and not installation time. This is always a good idea, but particularly so when expecting to configure the 6509-E with service modules.
On the other hand, organizations looking for pure switching may want to consider the Extreme solution or the Cisco 4500.
The Extreme switches offer more capacity for a lower price than the 6509-E, while providing the ability to undersubscribe edge ports. Extreme customers can also reduce their recurring costs by settling for less aggressive replacement times on their service contracts.
Conceivably, Cisco customers could do the same, but then they run into the problem of having to spare separate Supervisor and wiring modules for the core and access layers. Extreme’s switches avoid that problem by using the same modules.
Dave Greenfield is a 20-year networking veteran and the principal of Strategic Technology Analytics.