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Darby Weaver

How SD-WAN Can Provide QoS Over The Internet?

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For as long as organizations have tried to make voice services work over Internet Protocol (IP) network pipes (aka Voice over IP or VoIP), there have been very basic requirements in order to make it operate effectively. The first item needed for IP based voice was a dedicated, business class network line to carry this sensitive traffic. A business class circuit was paramount to reliability and uptime required for a crucial service like voice. This type of network access has low latency characteristics which keeps the amount of time it takes to forward the voice traffic low so that conversations are not made off kilter by long delays. Also absolutely critical to voice over network pipes is an additional layer over these high quality dedicated connections, something called quality of service or QoS. QoS is a suite of bandwidth prioritization and reservation techniques that give select services fast lane access to bypass lesser classifications of traffic and also reserves bandwidth preventing exhaustion of available throughput. Most commonly, QoS is used in tandem with carrier services like an IP VPN or Multi-Protocol Label Switching (MPLS) and have been assumed by many to be the only way to reliably deliver voice services for an organization. I can affirm as a network engineer for the past few decades, this has been the case for most of my career. In order for voice to perform adequately, specific care was required to spec out dedicated pipes with prioritization and if you didn't, you were typically asking for trouble in the way of poor quality, disconnections and general voice issues. That is until a thing called Software Defined Wide Area Networks or SD-WAN came along. This nascent technology space is drastically changing the way we do a lot of things on the wide area network, including managing sensitive real-time protocols that require QoS. Read more on what SD-WAN is in an article here.

Let's take a look at some of the things that make SD-WAN different versus how we've implemented voice over traditional networks up until now. These are items that are truly differentiators from means we used in the past to run network traffic over both tried and true dedicated lines not to mention over the commodity broadband or specifically configured Dedicated Internet pipes.

  1. Multi-Path Steering - SD-WAN can actively forward over multiple lines and is constantly measuring the characteristics and properties of each path available. Because it can very rapidly identify issues like high latency, packet loss and jitter, there are software mechanisms to quickly bypass these issues by utilizing an alternate path on the fly.
  2. Forward Error Correction and/or Packet Duplication - When issues like data loss from dropped packets arise, if there is only one path available or all paths are experiencing loss, that can be a serious issue with traditional networks with little means to remediate. SD-WAN employs features such as Forward Error Correction (FEC) or Packet Duplication which once packet loss is identified on a path, will send duplicates of the same packet to have greater assurance that critical data like voice or video will make it to their destination. At the other side of the SD-WAN connection for that voice or video stream, the first packet received will be sent along and the duplicates will be dropped.
  3. Jitter Buffering - Voice and video quality can suffer from a network condition called "jitter" which is when the information sent over the network is spaced inconsistently leading to a variable tempo for the stream. The result is audio or video that can have gaps, speed up then slow down and generally become impaired. SD-WAN measures the gaps between the packets and can evenly space these packets on the other side providing what is called a "jitter buffer" to realign the timing of these packets to keep the video or audio stream cadence intact.
  4. Prioritization and Queuing over Multiple Paths - Because SD-WAN performs it's queuing and packet forwarding over something called an "overlay", the forwarding decisions for information that has the highest priority and reservation of bandwidth for applications is performed at a layer above the traditional IP interface. With this, a priority "fast pass" can be given to crucial data like voice, video or other business essential apps bi-directionally and this can be done over all paths available.

So as you can see, there are many pieces that come together to make IP based voice over broadband and Dedicated Internet Access (DIA) is now possible. WAN Dynamics has designed many SD-WAN based solutions for customers and has seen it perform in the "real world" so can attest that IT WORKS! For more information, if you would want to discuss further or would like a proof of concept (PoC) please visit http://wandynamics.com, email info@wandynamics.com or give us a call at 877.400.9490. Feel free to connect on LinkedIn and contact me via private message as well!

WAN Dynamics wants to make better performing and more resilient wide area networks for less. It's that simple.

Thanks for reading!


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