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Moving to a Unified Wireless Switch Topology
Mike Powell, Senior Product Line Manager at Broadcom investigates the advantages of using a single or unified topology for all wireless services.
Wireless access is quickly becoming an essential function of the enterprise network. 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 extend to new applications beyond laptops – such as VoIP handsets, dual-mode smartphones, and desktop PCs – delivering a far more capable network with full mobility. As enterprises become more reliant on the wireless domain for delivery of mission-critical applications, network administrators will need to determine how to distribute this capacity without reducing network efficiency or straining their budgets.
Initial enterprise wireless LAN (WLAN) deployments have offered, at best, modest bandwidth and poor security that has significantly hindered wireless usage in the enterprise. As a result, deployment has been limited to a small set of critical applications. In this scenario, IT professionals were using an overlaid architecture as a minimally-disruptive way to quickly graft WLANs onto their 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.
Traditional wireless access implemented using an overlay approach that tunnels all WLAN traffic to a centralized access controller where it can be de-encapsulated and authenticated before entering the wired network. Increasing activity results in traffic consuming a greater percentage of backbone bandwidth with increased latency and congestion.
While 802.11n improves wireless performance, the overlay approach suffers from a network bottleneck due to inefficiencies, and it also treats wireless operations as a special service running over the network rather than being implemented as an essential, inherent feature. This leads to inefficiencies that prevent cost-effective scaling as the user base for wireless services increases. Network administrators contemplating the migration to 802.11n need to ask whether a new network architecture will be required to realize all the benefits enabled by wireless access. This article outlines the need for a new architecture, and reviews the characteristics and benefits of a solution based upon a new building block: the unified wireless/wireline switch.
Making the Case for a Unified Wireless Switch Topology
As WLAN traffic increases, a centralized approach multiplies the amount of loading on the network to the point that the functionality of the network is compromised for all the traffic it supports. The areas most affected include:
- Cost: Bandwidth increases in cost the closer it is to the core.
- 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.
The pervasive, 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.
Specifically, wireless data and management is moved from the core of the network to the network edge by terminating secure tunnels at the 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.
The unified wireless switch topology eliminates tunneling bottlenecks and the inefficiencies that arise from centralized control by integrating wireless traffic with wired LAN services at the edge.
New Enabling Technologies Required
The move to a unified wireless switch topology is an expected evolutionary step for wireless, as emerging network technologies are commonly introduced in the core and moved to the edge as they mature. To enable the unified wireless switch network, several new technologies will be required. Leaders in the networking industry have already begun development of these technologies, with silicon and software for both switches and wireless access points expected to be ready well before large scale 802.11n deployments. The key enabling technologies include:
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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 (IETF’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.
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Fragmentation and Reassembly: Encapsulation headers can increase packet size beyond Ethernet’s 1518-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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Distributed Access Point Management: With a centralized network, a single controller could manage anywhere between ten and hundreds of access points. In a unified network, each access point may be managed by a different edge switch. Therefore, switch clustering software will be required to form self-organizing, configuration-aware unified switches. Access rights and policy databases also need to be propagated and managed by each unified switch.
Reaping the Benefits of the Unified Wireless Network
The unified wireless network enables many capabilities beyond reducing installation and operational expenses that bring substantial value to the enterprise. Some of the benefits network administrators and users will experience include:
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Significantly improved scalability: Appropriate security capacity is introduced with each increase in bandwidth, for each access point deployed, supporting a more aligned, pay-as-you-grow investment outlay when compared to centralized wireless controllers.
- Simplified network management: Using a homogeneous topology will enable network administrators to view access points and switches from a single management point rather than a series of distinct wired and wireless devices.
- Substantially improved performance: Standardization enables wireless tunneling and other features to be implemented in silicon rather than software.
- Automated management: Features such as auto-configuration and dynamic radio management can be better managed on a per-device basis when compared to centralized implementations.
- Faster authentication: Moving client and policy enforcement to the edge increases responsiveness by reducing turnaround time.
- More efficient bandwidth utilization: Reducing the load over the network backbone will result in increased performance throughout the network.
- Reduced Latency: Users will also experience reduced latency, as well as increased network resiliency, as switching will occur at the edge versus backhauling all wireless traffic to the core and back to the edge again.
Future for Unified Wireless LAN Topology
Wireless services are becoming an every day, critical need for businesses, and as such, high bandwidth wireless access must be an integrated part of the enterprise network. With a unified wireless network, all of the performance, scalability and expense benefits of the traditional network are now available to support wireless traffic. Without this unification, backhauling and scaling limitations will prove cost-prohibitive while restricting the outstanding potential of high bandwidth enterprise WLANs.