Skype: putting the hype in VoIP

KaZaA founders target telephony

Reading interviews with the KaZaA founders and looking at their new web site, Skype we think that their second revolution has a chance of being even bigger than their first. Perhaps it's called Skype to rhyme with Hype.

The idea is to use peer-to-peer networks to give free voice over IP telephone calls to the masses, and not just calls to a special instant messenger-like registry of friends, but to virtually anyone.

The KaZaA founders, Janus Friis and Niklas Zennstrom, are the people working on the project.

If you go to their Skype web site you are greeted with the expression "525,000 downloads and counting." In all the articles about Skype this number has mostly been cited as 60,000

The Web never stands still, although Skype has some way to go to reach the 250 million KaZaA downloads. Does this mean that half a million kids have started their own telephone network without asking anyone?

Sounds like it. What if everyone using a P2P network could talk to everyone else on such a network for free? The revenue reduction that has hit music labels will begin to have the same annually deterioratingeffect on telcos.

The first thing you get from Friis and Zennstrom's site is their belief that a true P2P system doesn't need any server software or any central hub. If something is going to scale using peer to peer, then all nodes in a network join together dynamically to participate in traffic routing, processing and any bandwidth intensive tasks that would otherwise be handled by central servers.

They insist that FastTrack (the P2P technology behind KaZaA) was the first truly decentralized P2P application and pioneered the concept of SuperNodes. This approach has since been adopted by numerous file-sharing technologies including recent versions of Gnutella and is behind their programming of Skype.

Voice-over-IP (VoIP) has been around for years but it has not taken off. The KaZaA team feels it understands the reasons, citing lack of sound quality, low call completion rates, the fact that most systems cannot get calls past firewalls and the use of something called Network Address Translation (NAT) which renders over 50 per cent of residential computers unable to communicate with traditional VoIP software).

The Skype team goes further saying that the user interface is bloated and requires substantial configuration and technical skills. So what they have done is design a fully distributed system, which keeps the costs down, which is encrypted end to end with advanced encryption standard (AES), and which they say has better sound clarity than a conventional phone, which can get past firewalls and which doesn't need centralized software to route calls through firewalls or NATs.

Another challenge that the Skype team has had to handle is the fact that all forms of communication need some form of directory to look up people's number. IP numbers in this case. And that's why most VoIP systems have used a central directory. With most ISPs each IP address is dynamically allocated when a client logs on, so any such directory must refresh quickly from current IP addresses, and not derive from a static identity.

The upshot could be a system where most of the people that want to call you won't know if you are currently online or not, as propagating changes to all nodes on a network will take too long. The Skype team has got over this by creating a Global Index as a multi-tiered network where supernodes communicate in such a way that every node in the network has full knowledge of all available users and resources with minimal latency. Seconds after you log on your friends know you are there, rather like instant messaging.

By using every possible network resource, Skype is able to intelligently route encrypted calls through the most effective path possible. Skype even keeps multiple connection paths open and dynamically chooses the one that is best suited at the time. This has the noticeable effect of reducing latency and increasing call quality throughout the network. The Skype interface is said to be intuitive to anyone that can use Windows, and it comes with an instant messenger included, so you can both call and chat at the same time.

At the moment the Skype software is free, but so far it can only communicate with other Skype phones. But the authors are fond of saying "Stay tuned." They say at present to stay tuned for connection to the Plain Old Telephone System, and to mobile phones, for when it will work on operating systems other than Windows 2000 and XP, for when it will support 3 way or better conferencing, for when you can upload a picture and for when it will support proxies and authenticating firewalls or connect to a phone which uses the popular Session Initiation Protocol (they reckon it wasn't good enough for their system). Also stay tuned for logging in from any computer to your phone system, and to porting your friends list from machine to machine. But not yet.

They also say stay tuned to when Skype's IM facilities will connect to Yahoo, ICQ, AOL and MSN Messenger - but also say why bother with complicated, non-intuitive systems anyway. All you need for Skype to work is a reasonably modern PC, the free downloaded software and a computer headset, oh and a connection to the Internet. But it doesn't have to be a broadband line.

You can use Skype when you are connected with a 33.6 Kbps modem or faster. However, when you are using a modem for other types of Internet traffic, such as web surfing, file sharing or email you may experience disruptions in the voice communication.

The minimum requirement is to open up outgoing TCP port 80. In order to achieve the best quality, also open up outgoing UDP for all ports in stateful mode, so that replies to sent UDP packets are let in.

Skype automatically selects the best codec depending on the connection between yourself and the person you are calling. On average, Skype uses between 3-16 Kilobytes/sec - depending on bandwidth available for the other party, network conditions in between, caller's CPUs, etc.

Skype uses 0.5 Kilobytes/sec while idle. This is used mainly for buddy presence updates.

Faultline Opinion

There is a lot of loyalty to messenger programs and phone services, but a sub-culture that doesn't require communication with the rest of the world, just its own sub-culture, could certainly thrive. There are both technical and political difficulties in attaching this network to normal wired telephones, but if this is ever overcome, Skype has the potential to become the world's next phone network, hijacked by the young.

If it makes the leap to respectability (which will be a long way off) in the way that business instant messengers have emerged, then, with layers of PABX function added, Skype could become a serious threat to the future profitability of wireline telcos.

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