Session-Based vs Packet-Based SD-WAN

XRoads Networks patented and unique session-based routing technology is more efficent and allows customers to fully utilize two or more broadband connections by splitting traffic based on the session, not the packet. Session-based SD-WAN is superior to packet-based SD-WAN solutions for a number of reasons, the following charts the problems with packet-based SD-WAN.

    Problems with Packet-Based SD-WAN:

  • Splits packets between service providers
  • Doing so creates out-of-order packet delivery
  • Solves out-of-order packet delivery via buffering
  • Buffers fill up causing re-transmissions
  • Re-transmissions are solved by duplicating packets
  • Duplicating packets across both links reduces performance
  • Reduced performance prevents both links from being used
  • Without being able to utilize the speed of both links, true SD-WAN is not achieved.

Session-Based SD-WAN for Dummies

XRoads Networks invented today's session-based broadband link aggregation. XRoads Networks holds multiple patents on session-based SD-WAN developed around our Vector Routing MSA technology. The core of this technology is the ability to distribute traffic across multiple circuits based on the session information, and not on a per packet basis.

Most other SD-WAN solutions, including most cloud-based SD-WAN vendors, implement packet-based SD-WAN. This is essentailly the splitting of the packets using a "dummb" device at the customers site, then routing those packets across two or more circuits within some form of encapsulation back to a central aggregation appliance, and once received by the cloud-based aggregation appliance,re-assembling the packets in the order in which they were sent.

However, since most circuits have differnet performance metrics, these packets are typically assembled out-of-order, i.e. packet #2 will be received prior to packet #1. If this happens often, then memory buffers overflow trying to keep the prior out-of-order packets before they receive the missing packet across the slower link.

In order to solve this problem, packet-based SD-WAN vendors have implemented packet duplication. This was not the original intention, but they had to find a work around to the problem. A problem that we had realized over ten years ago when we first started developing our solutions. By duplicating the packets, the cloud-based SD-wAN vendor and circumvent the out-of-order issue, however they can no longer full utilize each broadband circuit as they are now copying each packet across both circuits, i.e. the same information is being sent over both circuits at the same time, and thus the customers see no added bandwidth by using two circuits with a standard packet-based solution.

XRoads Networks, on the other hand, does not split the traffic based on packet, but instead based on session, thus all of the packets associated with a specific session go across the same circuit. This eliminates any possibility of out-of-order packets, and eliminates the need for packet duplication. Since XRoads Networks does not need to duplicate packets it is free to fully utilize the bandwidth of each circuit, and thus the customer actually gets the advantage of the additional bandwidth that they have purchased. While it is true that session-based routing is a but slower to failover, the difference is a matter of seconds, which does not out weight the lack of additional bandwidth lost during the 90+% of the time the customer is not in a failover condition.

Session-Based SD-WAN Advantages

Most modern networking applications utilize sessions, specifically TCP sessions, to communicate between clients and server applications. XRoads Networks technology leverages this common process in order to route traffic across two or more WAN paths. Over 15 years several technologies existed which performed packet-based bonding across broadband links. XRoads Networks Session-Based SD-WAN was created to overcome the limitations posed by these packet-based bonding techniques.

Session-based routing is more stable as packets are not constantly being switched from one WAN link to the other.

Session-based routing provides better performance as it does not produce heavy retransmission of TCP packets.

Session-based routing enables fast application failover as it re-routes sessions on the fly in the event of a network outage.

Session-based routing is significantly more reliable as it does not require a central aggregation device located at a third party data center. If the data center goes down, the customer is down, as the onsite device is dumb and simply sends the packets to the data center where the actual routing occurs.

Session-based routing are typically less expensive as the customer is not having to essentailly pay of the bandwidth twice as they do with cloud-based SD-WAN (packet-based SD-WAN uses the customer bandwidth to send all traffic to their data center, and then the packets must be sent out to the Internet from there, essentially routing the traffic twice.

Session-based routing provides more scalable bandwidth options as sessions are typically routed directly across the local Internet links. This is the reason why many cloud-based SD-WAN solutions are capped at under 1Gbps performance. XRoads Networks SD-WAN solutions have no bandwidth caps.