SD-WAN
SD-WAN is software at each office that chooses which internet connection an application should use, so cloud systems and calls take a suitable path and can switch if a link fails.
SD-WAN stands for software-defined wide area network. It is a control layer over the internet connections that serve your offices. A device at each site watches each link and sends traffic according to the job. A phone call and a large backup have different needs, so they should not share the same path.
In a multi-site firm, staff expect email, cloud files and phones to behave the same in every office. SD-WAN gives each location more than one way out. A leased line can carry live work while broadband or a mobile link sits ready if that circuit slows or drops. The switch happens at the equipment, so a branch doesn't wait for someone to log a ticket. You apply the same rules across every office from one place.
It fails when the overlay is sold as a cheaper MPLS swap and the circuits underneath are consumer broadband with no second path. A single link at a site gives SD-WAN nothing to fail over to. Voice still suffers if nobody has told the software which traffic to protect. Firewalls and identity checks still have to wrap the WAN; the overlay doesn't do that job. A project that ends at go-live also fails: path quality has to be watched, or failover happens and nobody hears until users do.
When it matters
- →You have more than one office and staff work in Microsoft 365.
- →A circuit fault at one branch currently stops that site working.
- →Phone calls drop or cloud systems slow when the office is busy.
- →You're paying for MPLS at sites that mainly use the cloud.
Related terms
SD-WAN: common questions
What is SD-WAN?
SD-WAN means software-defined wide area network. For a business, it is the system that treats several internet connections as one pool and sends each application down a path that fits the job. The physical circuits stay as they are: leased lines, broadband or a mobile backup. The software's job is choosing and switching, not replacing those circuits. When a path degrades, traffic can move without a visit to that office.
How does SD-WAN work?
Each site has a device that can see every internet connection serving that office. It measures delay and loss on those paths. You write rules for which applications matter most. Live calls get the cleaner path; bulk transfers use leftover capacity. If the preferred link degrades, traffic moves onto the next healthy path. You manage policies in one place rather than configuring each office separately. The circuits still need an SLA, because the software cannot invent capacity that isn't there.
What's the difference between SD-WAN and a leased line?
A leased line is the physical circuit into a site, with a committed speed and an uptime SLA. SD-WAN is software on top of the circuits you have. It decides which path each application should use. You can run it over a leased line, broadband and a mobile backup together. SD-WAN without a reliable primary circuit has little to work with. A leased line without SD-WAN still leaves you with one path unless you add failover another way.
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