In earlier topics, we have looked at VOIP and how it works. Is Skype also VOIP?
Well I can make this a short topic by giving the answer immediately: yes, it is, and no, it isn’t. Except that that is not an answer. OK, it has to be the long version then.
The term VOIP in general stands for Voice Over IP. This basically means that voice data is carried over IP networks such as the Internet. Obviously in that sense Skype is VOIP—it allows to you call and speak to other people via the Internet. But on the other hand, VOIP is generally used to refer to implementations of the SIP protocol. And this is exactly what Skype does not do. It does not use the standard VOIP protocols, but relies on their own standards. The Skype software is closed-source, so it is not possible to find out how the voice communication actually takes place.
Is this bad? Well, yes and no, again. Of course any company developing software is free to choose if they do that under an open source or a closed source license. But the closed source heritage of Skype means that it is difficult to understand the protocol and make it work under special circumstances. As you may have guessed, the BGAN network is such a special circumstance…
First of all, the cost of data traffic on BGAN is high. And there is no such thing as a fully unmetered, unlimited BGAN connection, contrary to your ADSL or cable at home. The closed source Skype application has been designed to grab as much bandwidth as it can, with a good goal: to make the call as clear (and the sound quality as high) as possible. But BGAN users generally do not want this as they pay per megabyte. It is almost impossible to tell Skype to use less bandwidth. This is one of the reasons that there are alternatives for use on satellite networks; Sea Secure is such an alternative.
Secondly, the Skype application has been designed to try and find holes in firewalls where it can. Do you want your users to be unable to use Skype? Try to block it in your firewall—it cannot be done. Skype will find a hole and the application will work. Again, a good thing for Skype users in homes and offices worldwide, as they do not have to worry that they may not be reachable on Skype—but a bad thing for our average BGAN customer who wants to limit the traffic. This is the reason why MVS has recently launched and is currently testing with some customers a content-filtering firewall: a firewall that actually looks into the data to find what application it is, and then allows or denies based on the kind of application, instead of on IP address or port number as we are used. The firewalls do this by silently allowing Skype’s “hacking” to find firewall holes and actually offering it such a hole to use—and then, when the Skype application has accepted to use the connection, promptly close it. True magic indeed!
As you see, applications that we depend on in our office or at home, may give us headaches when used in a BGAN environment. Keeps life challenging!
Next time, we will take a deeper look into the technical architecture of Skype. We will see how it communicates between hosts and how the security is arranged. Without telling too much, it is interesting to know that when you happen to connect your computer to a network without NAT (so your computer has a public IP address) and you happen to have a reasonably fast connection, Skype may make your computer a ‘supernode’ and use it to relay calls through it from people you don’t even know!
