Three backbone architecture are available to SD-WAN edge appliances and SD-WAN as a service.
Broadband WAN is the original SD-WAN. The SD-WAN appliance at a location connects to one or more broadband or wireless Internet services, selecting the most appropriate connection based on predefined application policies and real-time conditions. Broadband WANs are more affordable than MPLS but remain subject to the Internet’s unpredictability.
Hybrid WANs augment MPLS with direct Internet access. Companies add broadband or wireless Internet to MPLS-connected locations, and the SD-WAN nodes again select the most appropriate connection (MPLS or Internet) in real time. Hybrid WANs are particularly attractive for migrating from MPLS or reducing MPLS costs. However, given Internet unpredictability and security issues, latency-sensitive or regulated applications often cannot be delivered across the Internet. As such, organizations remains bound to their MPLS providers.
SLA-Backed, Alternative WAN
Favored by cloud network services but unavailable through edge appliance vendors, SLA-backed, alternative WANs replace MPLS with a low-cost, SLA-backed alternative. Instead of relying on the Internet to connect locations, the SLA-backed, alternative WAN relies on the Internet to access a network of PoPs, which are linked by IP transit services across global tier-1 IP backbones.
Unlike Internet peering, transit services avoid the erraticness that comes largely from provider peering. These services generally keep packets on one backbone and are typically backed by guarantees of “five 9s” availability and 0.1 percent loss -- the kind of SLAs you would expect from MPLS services. And transit services cost a fraction of MPLS, allowing cloud network service providers to offer enterprises an affordable alternative to MPLS yet still backed by service guarantees.
With an SLA-backed WAN, companies once again add broadband or wireless Internet to their locations. Like a hybrid WAN, these connections sit alongside the MPLS connection. SD-WAN service endpoints at the location select the most appropriate connection in real-time based on predefined policies. Traffic destined for the SLA-backed WAN travels across the local Internet access link to the nearest PoP and from there onto the SLA-backed, alternative WAN.