In the last newsletter I wrote about Talari Networks, a San Jose start-up whose technology lets enterprises take advantage of lower-priced broadband services, such as DSL or cable, to supplement (or even replace) expensive private WAN links.

The company’s appliances allow enterprises to use DSL, cable or Wi-Fi networks in parallel with dedicated T-1s or private MPLS links, for example. The disparate network services then act as backup for one another. In addition, Talari’s route-optimization technology steers traffic over the various network paths, depending on real-time conditions and application priorities.

“We encapsulate each packet, and put a time-stamp and a sequence number on it,” explains CEO Andy Gottlieb. “Based on that, we know continuously, in real time and packet-by-packet, what the loss, latency and jitter is on each of the various paths between two locations,”

To mitigate latency or packet loss, the appliances can buffer or retransmit TCP traffic, as appropriate. If there’s excessive latency or high loss on a path, the Talari appliances stop using it. “Because we’re continuously measuring this stuff, we can do this sub-second. It takes us about two-and-a-half round-trip times -- so about 200 milliseconds on a link across the United States -- to stop using a link that’s acting flakey,” Gottlieb says.

For voice and video traffic, Talari’s gear will select the best path with the lowest loss and jitter. For the highest quality voice and video, Talari relies on duplication to offset packet loss: “We can take a packet, replicate it, and send it on two different paths, as unrelated to each other as possible, then get rid of the duplicate on the other end,” Gottlieb says.

The ability to monitor and respond to real-time network conditions is what separates Talari’s technology from basic network bonding, Gottlieb says.

“Bonding has been around for a long time. If you have TDM circuits, like ISDNs or point-to-point T-1s, you can definitely do bonding. If you have Ethernet in your LAN, you can do it,” he says. But simple bonding is only effective on links with low loss and low jitter -- which isn’t the case for shared IP networks. “If you did the simple bonding schemes in an environment with high loss or high jitter, then you will frequently get performance that’s worse than not doing anything at all,” Gottlieb says. “The fact that we’re continuously monitoring loss, latency and jitter, and communicating that information back and forth, is the key.”

Ann Bednarz is associate news editor at Network World.