Resilient Multipath Connectivity

Resilient Multipath Connectivity technology is how Adaptive Private Networking delivers end-to-end network reliability and protected application performance for both TCP-based applications and real-time applications like VoIP and videoconferencing. Powered by the rich information delivered by the Multipath Network Spectrometry technology, it is what allows enterprises to reliably leverage “reasonable quality” networks—such as public Internet connections—even when such connections by themselves don’t deliver the 99.95% to 99.99% reliability and packet delivery that a business expects from its WAN.

Resilient Multipath Connectivity provides multi-path multiplexing for both aggregating bandwidth and delivering end-to-end reliability, dynamically engineering around network trouble—not just outright link failure, but high packet loss or excess latency— as it occurs. It does stateful traffic steering via proprietary adaptive path selection algorithms, choosing the best path for each traffic type on a per packet basis. It can deliver greater individual flow performance by enabling packets, even from a single flow, to be striped across multiple network paths covering multiple WAN connections. It adapts to loss, latency and jitter “network events” within ~250 milliseconds for domestic connections, or ~500-600 milliseconds even for longer-distance international connections. This sub-second response is more than fast enough to handle any IP application that can run on an IP WAN, and so must be able to tolerate some amount of congestion-based jitter.

The intelligent actions and reaction in the face of packet loss by Resilient Multipath Connectivity provide predictable, protected application performance for any TCP-based application. It uses a NACK-based retransmission scheme combined with flow reordering and intelligent buffering. Given transient loss, it quickly retransmits lost packets to avoid TCP’s Slow Start and Fast Retransmit algorithms. When faced with more than transient loss on a given path, it quickly redirects all traffic off that path to other good paths until the network event is resolved and normal network performance returns.

Resilient Multipath Connectivity makes the WAN look to each TCP application as if it were a zero-packet-loss WAN with the occasional bout of jitter—something TCP and TCP-based applications are designed to expect and accommodate without incident. In so doing, it delivers much higher link utilization without hurting flow “goodput”.

For real-time applications like VoIP and videoconferencing, Resilient Multipath Connectivity uniquely delivers ultra-reliable, cost-effective support. It routinely chooses network paths with the least packet loss and lowest jitter for such high-priority real-time traffic. Just as for TCP-based applications, it rapidly recovers from any network loss, latency, jitter, or connection-failure event, switching the traffic with sub-second response to a better path.

Even further protection is provided in cases where the additional bandwidth APN enables allows the replication of real-time traffic flows along a second path. The receiving APN node suppressed duplicates, and effectively turns loss or excessive jitter on the “primary” path into nothing more than a small amount of jitter and microscopically low packet loss. This unique protection is far stronger than Forward Error Correction (FEC). FEC is designed to handle bit errors that are relatively uniformly distributed and fairly low in loss rate. Such episodes occur occasionally on public IP networks, but in reality, packet loss on shared-IP networks such as the Internet is rarely uniformly distributed, instead occurring in bursts of unpredictable duration, rendering single-path FEC all but useless.

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