Modern WAN bonding functionality extends beyond the creation of a ‘fatter pipe’ to improve network performance and strength
There’s something inspiring about reinvention. Whether it’s a new coat of paint on a well-worn cottage or shaving a beard that’s been growing for years, a fresh take on an established icon is a good thing. Enterprise technology is no stranger to reinvention. Take link aggregation, for example. Although this technology has been around for more than 15 years, it embraces reinvention as its functionality expands to new use cases, such as vehicle connectivity, thanks to the intersection of SD-WAN and wireless WAN networks, including cellular and satellite.
Early link bonding with SD-WAN
Since it hit the market over a decade ago, SD-WAN has offered many enterprise benefits, including financial savings from low-cost links, in-depth visibility into end-to-end performance, and the ability to apply granular traffic policies and controls. However, the main draw of SD-WAN technology is its ability to ensure 24/7 business continuity while improving WAN and application quality of experience (QoE). In short, it keeps networks and application data moving without interruption. This is traditionally achieved by manipulating traffic flows across multiple WAN links, ensuring priority for business-critical applications over best-effort traffic.
Regarding link aggregation, early iterations of SD-WAN allowed for creating a “fatter pipe” by combining various wired links to form a single, logical connection. This aggregated link improved the performance of network applications by providing increased bandwidth and speeds.
What is link aggregation in a wireless environment?
Modern SD-WAN solutions are comprised of more than MPLS or Ethernet connections — they now include 5G, LTE, and even satellite links. The wireless-centric attributes of these links, such as bandwidth fluctuations, variations in latency, and the prevalence of data plans, require a unique spin on this mature technology. The same old link bonding applied in the wired world doesn’t work well for Wireless WANs and requires a link bonding solution optimized for the unique demands of wireless.
Using an SD-WAN solution optimized for Wireless WANs, it’s possible to combine wired, cellular, satellite, or Wi-Fi-as-WAN into a single virtual connection. In addition to gaining access to a fatter pipe, improving resiliency and cost-effectiveness is also possible. Modern WAN bonding consists of the following three features:
Flow duplication
This WAN bonding feature duplicates mission-critical traffic across two WAN links for high resilience even during failover events, packet loss, or latency spikes. By sending the same application data across multiple links simultaneously, flow duplication ensures that if there is any congestion on one of the links, there is no impact on the delivery of the application data. For example, suppose a police cruiser using dual modems needs to transmit live data in an emergency. In that case, duplicate traffic can be sent across both the cellular and satellite (or alternate carrier) links from the vehicle.
Flow balancing
Flow balancing, or weighted flow balancing, is mostly used in fixed sites. This feature distributes application traffic across diverse WAN links according to priorities (weights) defined by the network administrator. In the spirit of SD-WAN’s cost-saving roots, flow balancing is most useful when WAN connections have different cost profiles, such as a mix between metered and non-metered links. For example, a business may want to send 70% of their traffic across a wired link and 30% across a cellular link.
Bandwidth aggregation
Bandwidth bonding is most useful for bandwidth-hungry applications such as video streaming or transfers, where a single link might not provide the throughput necessary for a positive QoE. This version of link aggregation most closely resembles the original SD-WAN link bonding experience, where multiple links are combined to aggregate performance.
Creating additional network resiliency through Forward Error Correction
The resiliency benefits of link aggregation in an SD-WAN environment are further enhanced when using Forward Error Correction (FEC). When FEC is turned on, the data transmitter sends redundant data bits across the WAN link to protect against loss. At the other end of the transmission, the receiver extracts the original data and corrects errors using the redundancies as a guide. This process prevents retries when connections are “lossy” and allows enterprises to quickly recover from packet loss — a process that is particularly useful across cellular links experiencing burst loss.
If flow duplication is being leveraged, FEC would not need to be turned on unless simultaneous loss occurs on both WAN connections. Aside from this scenario, FEC would typically be used in tandem with flow balancing or bandwidth aggregation.