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Delivering Application Assurance With SD-WAN


When it comes to network performance, the true measure is the user experience, that is, access to the necessary applications, the speed at which the applications perform and the reliability of that access.

The number one factor that will impact the user experience is unpredictability of broadband. As enterprises move away from expensive MPLS and adopt broadband, they risk a bad user experience. 

The answer to this challenge is QoS technologies and more specifically QoS technologies within an SD-WAN implementation.

When the objective of any IT organization is to provide a consistent and high-quality User Experience (UX). The enemy of that UX is the growth in applications and services that are being delivered across the network. At peak times the amount of data that is being attempted exceeds the capacity of the network and this creates congestion – this congestion causes latency, packet loss and affects applications differently depending on how the app consumes network resources. The solution is to smartly slow down certain apps and traffic or move them to other links.

Identify. Classify. Prioritize. The Three Steps to Application Assurance, the SD-WAN Promise

In order to make these decisions, the network needs to Identify, Classify and Prioritize all the competing traffic and then react to congestion based on business rules that describe application needs. This is what we call Application Assurance. The network is adapting intelligently to the situation.

The primary challenge of broadband is that it is a shared medium. This means that even though you have contracted for a specific speed, during a 24-hour period you will have time where you have more than provisioned and times when you have less than provisioned, it is not a steady state situation.

Another challenge of broadband is known as a brownout. This is when the broadband degrades to such a point as to appear “off” and this causes applications to crash and freeze. Our experience has shown us that for a typical enterprise with 500 or more sites, they can expect that on average 20% of their sites will be experiencing brownout conditions every day (a brownout is four seconds of network instability). This is unacceptable, and you need a solution that can adapt to these issues and prevent them from impacting the UX.

Traffic Shaping. Path Control. Forward Error Correction. How SD-WAN is Delivered.

There are three QoS technologies which can help with these issues. Traffic Shaping, which is optimizing a single path; Path Control which is distributing traffic across multiple paths; and Forward Error Correction (FEC) which is sending the same app multiple times on a single link or across multiple links to ensure all packets reach the destination in order and on time.

Based on a definition shown in Tech Target, Traffic Shaping is the regulating of data transfer to assure QoS. It requires delaying the least important traffic in favor of higher priority traffic. This removes the congestion and prevents packet loss.  Traffic shaping is only effective when the system knows exactly how much bandwidth is available, otherwise it doesn’t know “when to slow things down.”

In our experience, the available bandwidth on a broadband circuit can vary by 10 Mbps per day. Instead of traditional QoS that can be configured statically on circuits of fixed sizes, such as T1/MPLS, traffic shaping within an SD-WAN environment must dynamically adjust to the changing available bandwidth in real-time.

For example, if our network is handling voice calls, credit card transactions and Dropbox file sharing, we would put a premium on voice because dropped packets create a terrible UX immediately. We would prioritize Credit Card Transactions above Dropbox sharing and the network would manage traffic accordingly. It’s important to note that lower priority batch traffic has a unique elastic characteristic that fills pipes quickly to move larger amounts of data and this is what causes congestion.  Traffic shaping must slow this traffic down first.

Path control is similar in that it will react to the congestion in a way that ensures voice traffic is highly protected and critical services like credit card processing is also prioritized. Ideally an SD-WAN solution will use path control in a way that it is also aware of the costs of a secondary path that might have a data plan (e.g. LTE) which may impact which services are offloaded to the secondary path, using logic to control business costs. A simple path control solution might move voice traffic to the secondary circuit if it senses congestion, behaving like a simple binary switch.), A more robust solution will use traffic shaping to keep the high priority traffic on the larger/higher quality circuit as much as possible and move the low priority traffic first. Only if traffic shaping is unable to optimize the traffic on the primary link to maintain a desired quality of service, should path control move apps to the secondary circuit. 

FEC is used for those services that simply cannot be down for anytime. Your SD-WAN network will know this and will either use FEC to send multiple copies of the same data on a single circuit or route the identified traffic across multiple circuits ensuring that all of the data arrives at the receiving site in order and on time.

In summary, Application Assurance is your pass to high-quality UX. To get application assurance, you need all three types of QoS service: Traffic Shaping, Path Control and FEC. To be completely successful, you need an SD-WAN implementation to manage and control those layers of QoS. This will give your network the ability to adapt on the fly and will enable you to deliver the high-quality UX across a distributed network that your customers and employees demand.