What is SD WAN (and what does it mean to me)?

Geoff Tyrrell
Posted by Geoff Tyrrell

SD WAN (Software Defined Wide Area Network) is the hottest topic to hit the Wide Area Networking industry for some time and not without merit. It is set to continue its gain in importance and set the narrative for WAN deployments for the next few years.

What is SD WAN?

SD WAN refers to the use of software to implement and manage the Wide Area Network, including virtualisation of routers and firewalls (NFV) and techniques to orchestrate the network centrally.  The concept is similar to how SDN implements virtualisation within the data centre. There are many SD WAN benefits promised. One aim is to simplify the management of the WAN. Another is to make it more flexible so that, for example, traffic can be off-loaded from MPLS to the internet. This in turn can save cost. 

As with any emerging trend the definition of SD WAN is wide and varied. A multitude of new and existing vendors and carriers are looking to promote a version which fits their own capabilities, both now and in the future.

This has led to confusion as to whether an SD WAN solution includes the underlying connectivity as well as the Customer Premise Equipment (CPE function (router) and over-arching management. Well, depending on who you speak to, it can be both. CPE vendors rely on customers to provide their own connectivity whereas carriers are trying to move the market to an all-encompassing SD WAN solution which includes the connectivity and managed services supplied by themselves.

For clarity, we will make the distinction between an SD WAN CPE solution which should be viewed of in terms of the management and functionality of the Customer Premise Equipment (CPE), and a complete SD WAN solution which encompasses the connectivity and more and is detailed further below.

Download our free guide for SD WAN to help guide you through the myths and jargon you may come across along your journey to implementing your own solution.

Where has SD-WAN come from?

The SD WAN CPE market has been maturing for a couple of years having been founded by new start-ups, such as Viptela and Versa Networks in around 2012.

SD WAN is born out of concerns that were originally seen by forward thinking large enterprises over their static and difficult to manage WAN architectures. With a move to cloud based services and the high cost of international MPLS compared to in-country locally sourced internet there was a desire to be able to deploy and manage the local CPE simply, and to take advantage of internet with its lower costs and shorter route to platforms and applications. Lessons learned from the server virtualisation revolution also showed a future where software based networking and security features could be deployed without the physical hardware with the associated distribution and maintenance logistical support requirement.

Gartner, in their 2017 Competitive Landscape: WAN Edge paper recognised that there would likely be 5 waves of disruption in the SD WAN market starting with the SD WAN start-ups followed by, in 2016, a number of existing providers from adjacent markets such as WAN Optimisation, who would pivot from their current position to refocus and rebrand themselves as SD WAN providers. The 3rd wave of disruption would be the major CPE vendors such as Cisco, Juniper and Huawei either purchasing one of the start-ups (as we’ve seen with Cisco and Viptela) or developing their own capabilities.

The 4th wave is where a complete SD WAN solution starts to emerge. This is where carriers bundle the SD WAN hardware with their carrier circuits to provide a one stop shop. They may even supply a much richer monitoring and alerting experience extending way beyond the WAN CPE and into the LAN, infrastructure and applications. This will satisfy those large enterprises who outsource the management of their network but also paves the way for the carriers to develop a volume solution designed to meet the needs of medium enterprises to who have traditionally bought managed WANs.

The 5th wave, which is likely to take place at the same time as the 4th will be Managed Service Providers (MSP) who have the distinct advantage of not only providing a more cost effective hybrid network (marrying together different carriers, network and access types) but also tend to be able to handle a more hybrid approach to management. MSP’s often allow customers to purchase their own carrier circuits, acting as their own resolver group whilst the MSP maintains overall responsibility for ticket management.

MSP’s are also more likely to bring the extensive monitoring capabilities enjoyed by large enterprise customers of global carriers to customers in the medium enterprise level.

SD WAN definition

What are the characteristics of an SD WAN CPE solution?

If we accept that when we are talking about SD WAN we are talking about the management and the CPE function itself then we would say that an SD WAN Solution has the following five main characteristics;

  • Must support Hybrid Networking and multiple access types at the same time – Internet, MPLS, VPLS, LTE etc
  • Can do Dynamic Path Selection – connectivity must act in an Active/Active state with application specific SLA’s determining which access traffic uses.
  • Simple management interface – supports Zero Touch Deployments where devices call home to obtain their configuration, along with device monitoring, alerting and reporting.
  • Multiple CPE functions – routing, firewall, WAN Optimisation, WiFi, caching etc
  • CPE can be either physical or virtual – vCPE can be deployed as software only, residing on a standard X86 Server.

A more complete SD WAN service

Although the term 'SD WAN' is grabbing all the marketing headlines (with Hybrid Networking also getting some column inches), we at SAS believe they are not the only elements required for an optimal future network.

A complete SD WAN solution will include;

  • SD WAN CPE – whether physical (device and its software) or virtual (just the software);
  • Hybrid Networks – multiple access technologies and network types from multiple carriers;
  • End to End Application Performance Monitoring including End User Experience Monitoring;
  • The digital integration of all of the quoting, provisioning, management, fault ticketing and billing systems to support the above;
  • Professional Services to advise, set-up and optimise the solution;
  • Flexible In-life Managed Services to dovetail into existing suppliers and resolver groups.

The SD WAN CPE solutions have created the market and now carriers are looking at how they bundle the connectivity and enhanced performance together to create a more complete solution. This second major evolution is still in its early stages with solutions likely to be separate components until digital integration of multiple systems from multiple vendors can be achieved.

SD-WAN is an overlay - you still need an underlay!

When you ask "What is SD WAN?" it’s really important to understand exactly which definition of SD WAN is being described to you. Since most SD WAN vendors are WAN edge device companies they will not be offering the connectivity within their solution. That will be left to the customer or their Managed Service Provider (who may or not be a carrier) to provide and manage, or at least to monitor. The WAN edge devices (otherwise known as CPE), their functionality and management are known as the Overlay, since they overlay the Wide Area Network. Similarly, the connectivity is known as the Underlay.  This could be public (internet) or private (MPLS, VPLS, Ethernet P2P etc.)  or semi-private network (Optimised IP).  SD WAN makes it easier to mix connectivity types within your underlay to create Hybrid Networking which is a topic in its own right, with its own hype cycle.

To complement your SD WAN CPE solution you must carefully choose your Underlay, since this is where the likely cost savings will arise. And this isn’t just true for customers with international sites. To maximise your application performance and budget and minimise your management overhead, you need an in-depth understanding of the carrier market place.  You need to understand access options and associated SLA’s, private and public networks, and details of your users and applications (and where they both reside). Take a look at our Guide to Reducing WAN Costs for further information. 

Where is SD-WAN going?

The utopian vision for a complete SD WAN solution would be a single interface that combined your SD WAN CPE with the various underlay providers and networks, that also integrates into all of the Operational Support System (OSS) and Business Support System (BSS) platforms. You would be able to monitor and control not only your SD WAN CPE but further into the network to be able to measure application performance and diagnose any issues. You’d be able to place an order at the start of the process and see it accurately reflected on you bill at the end.

We may be some way off this dream. At present the SD WAN management function is fairly simple; the central controller just needs to be able to communicate with the SD WAN CPE and as every SD WAN CPE company has their own controller this is a given. When we expand the requirements to other components and systems we can see that there is a major piece of work to combine this eco-system.

SD WAN makes promises that you can change your bandwidth in an instant. Well if your central controller doesn’t control the underlay and the overlay then this isn’t possible.

In the future there may also need to be a different commercial model from the carriers and their third party tail providers. At present with most carriers the commercial model is based around fixed monthly pricing for an agreed speed on a standard access bearer, for example 20Mbps on a 100Mbps bearer. If you want to change the port speed, then there is a change in the commercials so a quote needs to be supplied and an order placed. Further complications come with international MPLS as they tend to use tiered long line access circuits from third parties. To make a change to the port speed the carrier will often have to ask their third party to change their tiered access circuit before they can also make the changes to their own network.

If one of the advantages of Hybrid Networking is that you can provide your own locally sourced internet connectivity, then this makes controlling the underlay with the overlay very difficult indeed.

However, there are moves afoot to address this interoperability. The Metro Ethernet Forum (MEF) is a non-profit industry association made up of over 200 members. MEF members include Tier 1, 2 and 3 service providers, hardware and OSS/orchestration software providers, as well as test labs, test equipment and test software providers. MEF are maybe best known for creating standards for Metro Ethernet that international carriers could all sign up to and are now looking at SD WAN orchestration with MEF 3.0. MEF 3.0 introductory video . Having an industry standard may give rise to separate SD WAN Orchestration vendors but in the meantime companies will need to develop their own solutions with each of their chosen overlay and underlay providers. 

Introduction to SD WAN

If you have a question, or would like some help, let us know!