Traffic Management, Shaping & QoS Provide the Tools to Guarantee Performance
That the capacity of enterprise networks has exploded over the last few years isn’t breaking news, but what’s underappreciated is the increasing diversity of traffic. Convergence is a mantra for many network managers-dedicated voice and data circuits are passé as every form of communication has been packetized for IP transport-and although this strategy makes efficient use of available capacity and is a big money-saver, it exposes limitations of historically data-only networks.
By default, all IP traffic receives equal claim on available capacity, yet divergent network applications such as phone calls and file transfers respond quite differently to bandwidth constraints, delays, or retransmissions. Traditional IP networks behave like a crowded thoroughfare where ambulances and fire engines must wait their turn at a signalized intersection just like everyone else. According to Jim Frey, research director at Enterprise Management Associates, the goal of traffic management is to provide more intelligent handling of network applications. In converged networks, with heterogeneous traffic, that requires a means of prioritizing and managing data flows using QoS priorities and other contention management techniques.
Steven House, director of product marketing at Blue Coat, sees two drivers for traffic management: to protect mission-critical, latency-sensitive applications such as VoIP, video, or remote desktop clients and to control "recreational" network traffic such as YouTube, Facebook, or P2P file-sharing. Frey largely agrees, noting that real-time communication has been the main catalyst behind QoS usage.
Back To Basics
The basics of QoS are quite simple-the ability to differentiate and discriminate between different traffic flows and provide preferred performance or bandwidth guarantees for time-sensitive applications under congested conditions. Unfortunately, the implementation is often mind-numbingly complex. Proper traffic classification is critical, says House; however, with more applications tunnelling through HTTP port 80, it often requires deep packet inspection rather than merely relying on IP and Transport layer data.
Once traffic is classified, Burton Group senior analyst Eric Siegel outlines numerous QoS techniques, including traffic conditioning, policing, and shaping, flow queuing, link fragmentation, and interleaving. Vendors have introduced a number of queuing algorithms with an alphabet soup of acronyms. However, for IT managers who don’t want to become experts in queuing theory, the bottom line, according to Siegel, is that real-time applications such as VoIP or IP teleconferencing require a strict priority queue above all other data, and remaining bandwidth should be allocated among flows managed via a class-based algorithm. Siegel adds that in order to avoid overloading available capacity and in turn violating performance guarantees, admission to the strict priority queue should be controlled using some form of flow conditioning.
Traffic Shaping & Conditioning Technologies
Although queue-based QoS prioritizes traffic, bumping the most critical packets or frames to the head of the line, Siegel says, "Flow [or traffic] conditioning techniques monitor network traffic loads in an effort to anticipate and avoid congestion at common network bottlenecks." These typically follow one of two fundamental strategies: policing, which monitors and discards packet flows that data rate limits, and shaping, which attempts to smooth out flows and avoid traffic bursts by buffering and signalling endpoints to reduce their transmission speed.
Traffic conditioning is often found in WAN accelerators; however, Siegel says several vendors offer special-purpose appliances that orchestrate conditioning across multiple LANs. Not surprisingly, most are high-end appliances designed for large enterprises or ISPs, although Siegel and Frey both note that many telecom providers now offer traffic management services appropriate for SMEs.
SME Traffic Management Basics
Complexity is the biggest problem with traffic management/QoS systems, which Siegel cautions "must be carefully designed and implemented to ensure that all network components work together properly to provide some traffic flows with better service than others"-a requirement, in addition to cost, that makes them infeasible for smaller enterprises. "A major goal for SMBs is to avoid complexity," he says, adding that SMEs should "think about ways to simplify the QoS situation, use it only when necessary, and use the simplest form that works." Yet all isn’t lost, because, Siegel notes, "In many cases, much simpler QoS technology, or no QoS at all, can provide the needed performance without the expense and management headaches of complex QoS systems." These might include an appliance, service provider, or just separate VoIP and data VLANs.
Frey points out that the same technology used to classify and prioritize traffic is needed for security threat detection; thus, many vendors have integrated QoS features into UTM appliances. Some dedicated traffic-shaping products are specifically designed for the SME. In addition to traffic shaping, these often incorporate features such as WAN and VPN load balancing and failover, content acceleration and filtering, and security features (firewall, IDS).
Applications For Traffic Management
Before embarking on a traffic management or QoS initiative, Siegel says it’s important to understand existing network conditions. "People never know what’s on their network," he says, adding that network managers should enable netflow accounting on routers and switches to gather traffic statistics. Yet, as House points out, netflow can’t identify and classify the new generation of network applications that tunnel traffic through port 80, a limitation easily overcome by traffic shaping appliances using deep packet inspection.
Siegel says traffic analysis may reveal that rather than having a QoS problem, the network may just have an "inappropriate use" problem, with employees downloading movies or other bandwidth-hogging content. Instead of a complex QoS solution, he quips, "You may just want to put in some [router] ACLs to blow this stuff away." House adds that packet-shaping appliances offer a less draconian solution because they can automatically identify and classify such uasge and build simple policies-for example, limiting all social networking traffic to 10% of the total bandwidth.
Although traffic management is a powerful tool, particularly on large, complex networks, it’s no panacea. "Quality of service is a useful technology for providing multiple service levels. However, it doesn’t provide additional bandwidth, and it can be expensive and complex to implement," notes Siegel, concluding "It’s always worth careful analysis to see if simpler, less-expensive alternatives can handle the situation instead of a full, complex QoS implementation."
No comments:
Post a Comment