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Moving to a unified wireless switch topology

Wireless access is quickly becoming essential in enterprise networks. With the arrival of 802.11n and its capacity of hundreds of megabits per access point, the value of wireless access has increased dramatically and the wireless domain is now able to support not only laptops but VoIP handsets, dual-mode smartphones and even desktop PCs. But how do you distribute this capacity without reducing network efficiency or straining your budget?

Initial enterprise wireless LAN (WLAN) deployments offered, at best, modest bandwidth and poor security. As a result, deployments were limited to a small set of critical applications and typically addressed the shortcomings by using an overlay architecture as a minimally disruptive way to quickly graft WLANs to existing wired networks. With this approach, all WLAN traffic is tunneled to a centralized access controller where it is de-encapsulated and authenticated before entering the wired network.

While 802.11n improves wireless performance, the overlay approach results in a network bottleneck and inefficiencies, and wireless operations are still treated as a special service rather than an essential, inherent network feature.

This leads to inefficiencies that prevent cost-effective scaling as the wireless user base increases. If you're contemplating the migration to 802.11n, you need to ask whether a new architecture will be required to realize all the benefits enabled by wireless access. The answer might be a solution based upon a new building block: the unified wireless/wireline switch.

Making the Case

As WLAN traffic increases, a centralized approach multiplies the amount of loading on the network to the point that functionality is compromised for all traffic. The areas most affected include:

* Scalability: New controllers must be deployed in a linear relationship to the number of access points supported. This centralized approach cannot scale to 802.11n data rates without negatively impacting the network as a whole.

• Performance: Network latency and congestion packet loss increases.

• Security: As access points are added, security requirements become more difficult to meet cost-effectively.

• Resiliency: Centralized control creates a single point of failure.

* Cost: Bandwidth increases in cost the closer it is to the core.

The high bandwidth wireless enterprise demands a new unified wireless/wireline architecture that eliminates the bottlenecks and inefficiencies that arise from centralized control. Instead of handling wireless traffic as an exception, a unified network integrates wireless with traditional wired LAN services to provide a seamless interface between the two.

Want to compare wireless products? View our IT Product Guides now.Specifically, wireless data and management is moved from the core of the network to the edge by terminating secure tunnels at edge switches instead of at the access controllers in the core. Rather than routing wireless traffic to the core and back to the edge, backbone bandwidth is conserved by terminating traffic at the edge and routing traffic directly to its destination. In addition, security processing is moved to the edge, guaranteeing optimal performance that scales to meet user demands while maintaining network resiliency.

New enabling technologies required

The move to a unified wireless switch topology is an expected evolutionary step for wireless, as emerging technologies are commonly introduced in the core and moved to the edge as they mature. To enable the unified wireless switch network, several new silicon and software technologies will be required developments that are expected to be ready well before large-scale 802.11n deployments. The key enabling technologies include:

* Open, hardware-based encapsulation: Rather than continue with the proprietary encapsulation technologies used to backhaul wireless traffic today, the unified network will utilize new open standards such as the Internet Engineering Task Force's control and provisioning wireless access point (CAPWAP) specification that securely communicates between switches and access points. To realize the performance and cost benefits of 802.11n, the encapsulation/de-encapsulation and switching functions should be integrated with the switch silicon.

* Fragmentation and reassembly: Encapsulation headers can increase packet size beyond Ethernet', Ethers 1,518-byte limit. In this instance, CAPWAP support for fragmentation and reassembly of packets solves the problem of buffering fragments without undue latency with an elegant two-fragment limit, therefore facilitating efficient silicon implementations.

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