SD-WAN Fundamentals: The Underlay-A Step Deeper

SD-WAN Fundamentals:
The Underlay - A Step Deeper

As a follow-up to SD-WAN Fundamentals – the Underlay Network, here we break down the important components that provide the building blocks of the SD-WAN Underlay: Last Mile, Middle Mile, and Cloud Interconnect.  Any solid SD-WAN Solution comparison will outline and define these elements.  These are differentiators that become more or less significant depending on the origination and destination endpoints of each application traffic path.

The Last Mile refers to the final segment of a telecommunication network leading to and entering into a customer’s service location.  In the U.S., Local Exchange Carriers as well as Cable companies operate these networks today.  Service Level Agreements and Committed Information Rates differ based on local provider offerings, so these differences should be considered.  In some areas there can be limited choices of carriers to provide coverage.  If there are specific locations of importance, they can be analyzed during the initial discovery process to understand the approach of the SD-WAN Service Provider in order to validate the service quality

The Middle Mile is a telecommunications term that describes the network infrastructure that connects each last mile local network to other network service providers, major network carriers, and the greater internet. These segments were traditionally networks of Interexchange/Long Distance Carriers but are now offered by various Network Service Providers. In terms of SD-WAN, this part of the underlay signifies the major segment between geographically dispersed locations. Carriers that provide SD-WAN may connect customer locations into their core network through a variety of methods – secure tunneling over internet, or transport via direct MPLS access or private line commonly. It’s crucial to uncover where these connection points reside, how much redundancy is involved for traffic, how relevant gateways are monitored, and more depth of detail. Site-to-site traffic paths in Hybrid Internet-MPLS solutions should be clearly identified as well. The Middle Mile is a priority discussion point and one of the clearest differentiators between SD-WAN Solutions.

Cloud Interconnect is the generic term for the SD-WAN Solution Provider’s connection to a client’s subscribed cloud services within the provider network – be it at the level of Infrastructure, Platform, or Software.  Outlining a client’s priority applications and where the data flows travel is imperative to delineating and comparing/contrasting the application path between SD-WAN Providers.  From the customer site through the Last Mile, across the Middle Mile, customer users’ application traffic then can connect up to reach a partner network, a customer Data Center, or a hosted application by the SD-WAN vendor.  This Cloud Interconnect can be a game changer for performance, and you will continue to see various SD-WAN Solution Providers offerings bolstered by partnerships that enable direct, secure access to the applications customers demand, in close proximity to the end users.

We hope you found this deeper dive into the Underlay Network components useful.  If nothing more, this discussion reveals that there’s a myriad of factors to consider.  SD-WAN Solutions can include all these elements offered by one Provider or use different Providers for each component – so flexible options should be assessed.  ChoiceTel’s experience across the spectrum of SD-WAN Providers can help you make sure your evaluation weighs the qualities that are most essential! 

To learn more about ChoiceTel and what we can do for your small, medium or enterprise organization, visit our website at Or to schedule a consultation, call us at (248) 922-1150.


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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