The popular vernacular for WAN links conjures up an image of data bits jostling for space as they rapidly flow through the WAN "pipes" on their way to the impatient end user. It's a romantic image of application packets, but it's not exactly accurate. In fact, WAN links are a serial process, and some bits must travel the wire before other bits. By setting QoS (Quality of Service) policies, you establish the rules that put the packets of your organization's key applications in line before the packets of less important applications. Nothing can improve network performance as simply and effectively as QoS settings, which prioritize the traffic in your enterprise and manage traffic congestion.
An indispensable aspect of network-performance management, QoS is implemented in network devices, primarily routers, across the enterprise. Cisco Systems Inc. defines QoS as a "collection of technologies which allows applications/users to request and receive predictable service levels in terms of data throughput capacity, latency variations and delay."
Mark Urban, Packeteer Inc.'s director of product marketing, laid out the three QoS best practices recommended by the WAN optimization vendor. "First, discover the applications on the network. Second, contain recreational traffic. Those two steps are the simplest approaches that can be very powerful. Third, identify the mission-critical applications that are key communication vehicles or drive revenue, and that really depends on what the business mission is."
When QoS rules are appropriately set and managed, business-critical applications get the bandwidth necessary for top performance — ultimately, QoS becomes an essential tool in aligning IT with the business. But first, you must determine which applications deserve to be at the front of the packet queue.
"Understand the traffic composition on each WAN link, [including] which users of which apps are consuming the most bandwidth and when during business cycles. That way, you'll know what applications you need to consider prioritizing," advised Steve Harriman, vice president of marketing at NetQoS Inc., a network-performance-management vendor.
With QoS, you assign application data to different traffic classifications, and the applications are delivered accordingly. Cisco Systems describes four traffic classes: Platinum with low latency (voice); Gold with guaranteed latency and delivery (email, perhaps); Silver with guaranteed delivery (most application traffic); and Bronze, which is best-effort delivery (everything else). In this way, QoS helps you maximize your existing network bandwidth, protect mission-critical applications and ensure the quality of delay-sensitive traffic such as VoIP.
"The world operates over Port 80, from SAP Financials to YouTube. So the challenge becomes sorting through the hundreds of applications and effectively [moving] to the right service classes," Urban said. Also, "Being able to break down compound business applications is very important. SAP is a group of processes — SAP Order Operations could be highest priority and very different from SAP Data Synchronization."
QoS settings can be configured and managed directly on the routers through ACLs (access-control lists), but the device's configuration tools are difficult to use. And that's where QoS management software — such as Packeteer's PacketShaper, NetScout Systems Inc.'s nGenius, or NetQos's ReporterAnalyzer and SuperAgent — comes in, offering an overlay of intelligence to make better decisions about traffic shaping with a higher level of information than a router can provide.
Software is vital for discovery and measuring what's on your network, but even that baseline of network performance won't give you the full picture you need to accurately prioritize applications. To use QoS to better align IT functions with business, you must meet with the business managers across your organization and ask what applications they deem critical to achieve their business goals.
In March 2007, industry analyst Jim Metzler of Ashton, Metzler & Associates, conducted a survey of 300 members of the NetScout community to find out where they stood with QoS. Nearly 62 percent of the respondents had already deployed QoS, and more than 35 percent of them had done so to support VoIP applications. Clearly, everyone agrees that voice applications require preferential treatment, but which applications stand second in line? And which applications should be relegated to the best-effort class of service? In this same survey, almost 44 percent of respondents discussed the decision with business managers.
"It helps if you have a good understanding of the business priorities. Do you prioritize your ERP [Enterprise Resource Planning] app over your email? [It's useful to have] some sort of business policy that the IT group can use as their backdrop," Harriman said.
Optimizing your network performance only begins with QoS. The natural next step is to add acceleration technologies — protocol, caching and compression acceleration — which provide different types of WAN optimization on top of QoS.
"QoS helps contain disruptive traffic," Urban explained. "Protocol acceleration provides more bandwidth to applications by taking off natural bandwidth protocols underneath it. If you want to shove a big file through a narrow WAN pipe, more bandwidth makes that happen a lot faster." For instance, an engineering firm may apply protocol acceleration to an enormous CAD (computer-aided design) file. But the same technologies that allow a CAD file to speed through the link can also be used by recreational bandwidth hogs such as iTunes.
"But the same technologies can force the consumption of the entire link, so it pushes out your voice, financials, etc. It can be very disruptive if you don't have the [software] intelligence to use it properly," Urban warned. "QoS makes sure it doesn't disrupt key business applications."
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