Skype: Hazardous to network health?

While not exactly a low-profile endeavor before its recent acquisition by eBay, Skype is sure to be an even greater presence on the Internet and on home computers - and most likely on your corporate network. But can Skype be hazardous to your network's health?

It might come as no surprise that you could be carrying Skype traffic for your user base, but are you are aware that your LAN and WAN links might be carrying VoIP traffic of complete strangers? That is, traffic of VoIP conversations that neither originate nor terminate on your network. In effect, you are donating what can be scarce and expensive WAN bandwidth to your newly minted multi-millionaire friends at Skype. (I'm sure, however, that they greatly appreciate it!)

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While not exactly a low-profile endeavor before its recent acquisition by eBay, Skype is sure to be an even greater presence on the Internet and on home computers - and most likely on your corporate network. But can Skype be hazardous to your network's health?

It might come as no surprise that you could be carrying Skype traffic for your user base, but are you are aware that your LAN and WAN links might be carrying VoIP traffic of complete strangers? That is, traffic of VoIP conversations that neither originate nor terminate on your network. In effect, you are donating what can be scarce and expensive WAN bandwidth to your newly minted multi-millionaire friends at Skype. (I'm sure, however, that they greatly appreciate it!)

While "free VoIP anywhere" has been too good a deal for many to forgo, little or no attention has been paid to how Skype does what it does. Go to Skype's Web site and it is all about "community," a running tally of the number of downloads (already 168 million) and their pay-for-use adjunct services SkypIn and SkypeOut.

When I first became aware of Skype some time back, there was almost constant flag-waving about being the first and only peer-to-peer phone service. This was often paired with noting the lineage with KaZaa. Somewhere along the line, though, someone at Skype decided to downplay this aspect of the service.

At The Tolly Group, we've taken a closer look at the technical aspects of the service. Because of the dearth of information available to us, we learned most of what we know by studying Skype "in the wild" - that is, running the service, capturing the traffic and analyzing the traces.

The most fundamental information you need to know is that Skype is a peer-to-peer service. Let's quote the Skype Web site on what that means: "A true [peer-to-peer] system, in our opinion, is one where all nodes in a network join together dynamically to participate in traffic routing-, processing- and bandwidth-intensive tasks that would otherwise be handled by central servers."

Your corporate desktops and notebooks are the "peers" that are consigned as Skype pleases to relay traffic and function as mini-servers in the Skype universe. (A Weblog entry on the eBay acquisition envisioned Skype producing an auction conference system that could handle 500 callers at once. Let's hope they don't decide to route that through your network some day.)

According to Skype - and validated by our research - a VoIP call will consume between 24 and 128K bit/sec. When a Skype station is functioning as a relay, the bandwidth is doubled. (We found instances when calls between adjacent stations were relayed to somewhere a continent away.)

When you are functioning as a relay, you have no way of knowing this other than running constant traces on your network interfaces. Read the license agreement and you'll realize that you've given them permission for all this - though the old license was less subtle.

And, lest you think that you can stop all this by exiting Skype, think again. You might not be using Skype - but it might be using you. Skype continues to run in the background unless you uninstall it or kill the process.