SD-WAN Fundamentals: The Underlay

SD-WAN Fundamentals:
The Underlay

In this edition of our SD-WAN Fundamentals, we define and examine the actual foundation of Software Defined Wide Area Networks – the Underlay Network.

The Underlay consists of the combination of physical media for signal propagation (Fiber/Copper/Radio Frequency, etc.), Data Link Layer Communication modalities (Switching), and Network Layer Communications Protocols (IPv4/v6 Routing).  The Underlay is the basic full communication channel that will need to exist between Business sites before any SD-WAN can be built to engage in site-to-site transmission.  Many new SD-WAN solutions are built with Public Internet as the underlay, but other private/virtual private network connection types can be used, such as MPLS or Ethernet Virtual Private Line.

When using Public Internet circuits specifically, it is recommended to look at some key elements when planning the foundation for your service:

  • What is your required uptime for your Business locations’ WAN communication?  Does the Internet Service Provider offer Service Level Agreements to match those requirements?
  • Is the Service Provider offering Dedicated and Symmetrical (Download/Upload) Bandwidth?
  • If connecting multiple Business sites across geography, is there a possibility of using the same Tier 1 Internet Provider?
  • If two circuits make up the connection at one or multiple sites, what amount of diversity is included between the physical circuit paths?

Answering these questions about the Underlay Network really represents the beginning of identifying core qualities you will want to include in this fundamental building block of any SD-WAN solution.  Not every Service Provider will present a solution focused on the underlay – particularly if they do not provide the network.  Work with a trusted partner who is laser-focused on your needs, and who has worked with all the major carriers and vendors before.  ChoiceTel will be there every step of the way, assisting to gather the essential details required to design and plan your successful SD-WAN journey.


Choice Telecommunications, Inc

7640 Dixie Highway, Suite 150

Clarkston, MI 48346

Phone: 248-922-1150

Email: [email protected]

U.S. Offices

7000 Central Pkwy.

Suite 1600

Atlanta, GA 30328

(800) 815-3320

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