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Network Quality of Service (QoS) is still considered by many IT managers as the savior for application performance. They are right in many respects, but with bandwidth becoming more plentiful and congestion decreasing, some are asking whether network QoS is required.
QoS is much more than a technical feature because the functionality allows us to understand and predict performance. We know of clients that do not believe they will benefit from QoS capability, but welcome the service level agreement (SLA) associated with the feature set. In short, a good SLA for your wide area network (WAN) will allow your business to understand the latency and jitter from point A to B. If the service provider fails to meet the SLA, credits are provided back to the client in the form of a payment.
In the early days of multiprotocol label switching (MPLS) VPN services, the standard capability offered surrounded three main settings.
Platinum -- expedited forwarding
As the naming convention suggests, expedited forwarding (EF) supports applications where the most optimum network QoS performance is key -- voice would be the most common example. EF needs to be considered carefully because traffic over and above the set bandwidth is dropped. As an example, if an organization requires 500 Kbps to support five calls and then they add a sixth, the sixth call will simply not work. The MPLS or virtual private LAN service network will process traffic marked as EF with strict priority. The result? A predictable performance across latency and jitter with prioritization above all other traffic during congestion -- the required capability for voice.
Gold -- assured forwarding
Assured forwarding is where mission-critical applications -- such as virtual desktop services provided by Citrix -- are prioritized to avoid congestion from applications such as email and HTTP Web browsing. Whereas EF is strict in terms of set bandwidth limitations, AF provides more network QoS flexibility. If an organization's design states 500 Kbps as a bandwidth for applications, traffic within that setting will be prioritized against other basic applications but will not be dropped if the limit is exceeded; instead, they are re-marked as basic.
Bronze -- best effort
Bronze is for everything else. Any applications not perceived to be mission-critical in terms of performance are placed here. This does not mean the application itself isn't critical; it means, for example, that if a user has to wait a few seconds for an email to arrive, that delay won't necessarily be detrimental to the business.
The newer 6-QoS approach
As time progressed, the standard for QoS evolved to offer more granularity from service providers. The actual fundamental capability of QoS actually supports many settings for those self-managed clients or private networks where perhaps granularity is key to success. The industry appears to have settled on a 6-QoS approach where each aforementioned level of service -- platinum, gold and bronze -- offers "high" and "low" settings.
So, will QoS benefit my organization?
QoS is an important aspect to any WAN -- even those without congestion. QoS allows businesses to be assured and rely on predictable performance. If the potential for congestion does exist, network QoS ensures user performance is consistent and key delay-sensitive applications will perform well. Above all, QoS extends throughout the provider's core network, meaning your traffic will take optimum routes when traversing from location to location.
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