The High Price of Wireless on Network Switches

 
 
By Dave Greenfield  |  Posted 2008-08-18 Print this article Print
 
 
 
 
 
 
 

Organizations planning to implement 802.11n should consider the impact on their Ethernet switching architecture.

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.



 
 
 
 
 
 
 
 
 
 
 

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