Why "Session Keep-Alive" Makes a Huge Difference in Multi-WAN Networks
With the availability of a wide variety of Internet connections, from layer 2 MPLS to broadband connections such as DSL and Cable, taking advantage of multi-WAN network designs is a no-brainer. However, simply having multiple WAN connections in your office and a multi-WAN router with 2 or more WAN ports is not by itself the perfect solution. There are various multi-WAN routers available on the market, however, broadband bonding enabled routers that support SD-WAN architectures are more rare. One of the main features of a multi-WAN router is its ability to be able to keep an ongoing session alive, even during WAN network problems. This can be achieved through Broadband Bonding, whereby the router can create an overlay bonding tunnel on top of the two or more WAN links.
Once the overlay tunnel is setup, the IP traffic going through this tunnel is protected against any network problems, as long as at least one of the WAN links is still functioning correctly. The ability to shield these network problems from the IP sessions is called “session keep-alive” and will enable a fail-safe design of your network so that problems are handled pro-actively. This means no more emergency calls or support tickets due to network outages. With session keep-alive, applications and services will be kept alive and therefore the users of those services will not suffer from the network problem that would have otherwise brought down the office network.
Session keep-alive, even though simple in concept, requires careful implementation by the multi-WAN vendor, as there are application and flow specific aspects that can impact the performance of the session keep-alive feature. As an example, VOIP traffic relies on different metrics, compared to say, data transfer. Therefore the overlay bonding tunnel should implement the session keep-alive accordingly so that the metrics that matter for the application are preserved. In the case of VOIP traffic packet loss, latency and jitter are metrics that are very important to keep the user experience undisturbed. A bonding strategy that can work perfectly fine for file transfers, that relies on retroactively retransmitting lost packets, will not perform well for VOIP / SIP traffic. VOIP traffic should instead take advantage of network-coding schemes that can pro-actively add a protective layer to the VOIP packets and therefore can recover from lost packets without requiring retransmissions.
Multi-WAN network designs should target a seamless Internet connectivity experience to the end users, both in terms of up-time, as well as application performance. Especially in hybrid cloud environments where applications and services might be provided through in-house data centers or public cloud infrastructure, being able to provide a seamless experience requires “session keep-alive“.
Cahit Akin, CEO, Mushroom Networks, Inc.
Mushroom Networks is the provider of Software Defined WAN and load balancing solutions capable of Broadband Bonding that enables self-healing WAN networks that route around network problems such as latency, jitter and packet loss.